DESCRIPTION
Title of Invention
RADIO COMMUNICATION SYSTEM, BASE STATION, RELAY
STATION, AND RADIO COMMUNICATION METHOD
Technical Field
The embodiments discussed herein are related to a
radio communication system, a base station, a relay station,
and a radio communication method.
Background Art
At present, radio communication systems such as a
cell-phone system and a radio MAN (Metropolitan Area
Network) are widely used. For attaining a further speeding
up and large capacity of radio communication, lively
discussion is continuously performed about a next
generation radio communication technology. For example,
the 3GPP (3rd Generation Partnership Project), which is one
of international standardization organizations, proposes a
standard referred to as LTE (Long Term Evolution) , and a
standard referred to as LTE-A (Long Term Evolution-
Advanced) that is an evolution of LTE (see, for example,
Non-Patent Literature 1).
In a radio communication system including a base
station and a mobile station, a relay station which relays
radio communication may be provided between the base

station and the mobile station. By providing a relay
station, an area (dead spot) in which radio communication
is difficult due to radio propagation blocking caused by
buildings is covered, a range of a cell covered by a base
station is expanded, and communication throughput is
improved.
However, in a relay station, interference (which
may be referred to as self-interference) may occur between
a transmission signal of its own station and a reception
signal. Suppose, for example, that a frequency band used
between a base station and a relay station and a frequency
band used between the relay station and a mobile station
are overlapped with each other. In this case, a radio
signal transmitted to the mobile station comes into a
receiver of the relay station, and as a result a radio
signal may not correctly be received from the base station-
To cope with the problem, the relay station is proposed to
be controlled in such a manner that reception of a radio
signal from the base station and transmission of a radio
signal to the mobile station are not performed at the same
time (see, for example, section 9. 3 of Non-Patent
Literature 2).
Another radio communication system including a
base station and a mobile station may provide a
configuration in which a procedure of random access from
the mobile station to the base station is specified. In
the random access, the mobile station accesses the base

station without being dedicatedly allocated a radio
resource by the base station (see, for example, section 10.
1. 5 of Non-Patent Literature 3).
As a random access preamble (which may be referred
to as Msg 1), for example, the mobile station transmits to
the base station a signal sequence selected from among a
plurality of candidates through a predetermined random
access channel. The base station, having received the Msg
1, transmits as a response a random access response (which
may be referred to as Msg 2). Note that at this time, the
base station does not recognize the transmission source
device of the Msg 1. The mobile station, having received
the Msg 2, transmits to the base station a message (which
may be referred to as Msg 3) including the identifier of
its own station. The base station, having received the Msg
3, transmits to the mobile station a message (which may be
referred to as Msg 4) as a response.
Here, an interval until the base station sends
back the Msg 2 from reception of the Msg 1 and an interval
until the base station sends back the Msg 4 from reception
of the Msg 3 are not fixed, and preferably stay within a
predetermined allowable range. Based on this flexibility,
the base station may perform scheduling and efficiently
transmit the Msg 2 and Msg 4. While the base station may
transmit the Msg 2 or Msg 4, the mobile station monitors a
radio signal from the base station and detects the Msg 2 or
Msg 4 (see, for example, section 5. 1 of Non-Patent

Literature 6).
Citation List
Non-Patent Literature
NPTL1: 3rd Generation Partnership Project,
"Requirements for further advancements for Evolved
Universal Terrestrial Radio Access (E-UTRA)", 3GPP TR
36.913 V8.0.1, 2009-03.
NPTL2: 3rd Generation Partnership Project,
"Feasibility study for Further advancements for E-UTRA",
3GPP TR 36.912 V9.0.0, 2009-09.
NPTL3: 3rd Generation Partnership Project,
"Evolved Universal Terrestrial Radio Access (E-UTRA) and
Evolved Universal Terrestrial Radio Access Network (E-
UTRAN); Overall description", 3GPP TS 36.300 V9.3.0, 2010-
03.
NPTL4: 3rd Generation Partnership Project,
"Evolved Universal Terrestrial Radio Access (E-UTRA); Radio
Resource Control (RRC); Protocol specification", 3GPP TS
36.331 V9.2.0, 2010-03.
NPTL5: 3rd Generation Partnership Project,
"Evolved Universal Terrestrial Radio Access (E-UTRA);
Physical Channels and Modulation", 3GPP TS 36.211 V9.1.0,
2010-03.
NPTL6: 3rd Generation Partnership Project,
"Evolved Universal Terrestrial Radio Access (E-UTRA);
Medium Access Control (MAC) protocol specification", 3GPP

TS 36.321 V9.3.0, 2010-06.
NPTL7: 3rd Generation Partnership Project,
"Evolved Universal Terrestrial Radio Access (E-UTRA); Radio
Link Control (RLC) protocol specification", 3GPP TS 36.322
V9.2.0, 2010-06.
Summary of Invention
Technical Problem
Think of a radio communication system which
includes a base station, a relay station, and a mobile
station, and in which the relay station performs random
access to the base station. At this time, there arises a
problem that how the base station and the relay station
preferably perform a random access procedure. Specifically,
in the conventional random access, timing at which a base
station may send back a message varies. If the message is
sent back at timing at which the relay station transmits a
radio signal to the mobile station, the relay station may
not correctly receive the message due to self-interference.
In view of the foregoing, it is an object of the
present invention to provide a radio communication system
in which random access through a relay station is smoothly
performed, a base station, a relay station, and a radio
communication method.
Solution to Problem
To solve the above-described problem, there is

provided a radio communication system which includes a base
station; a relay station which performs wireless
communications with the base station; and a mobile station
which performs wireless communications with the base
station or relay station, wherein: the relay station
includes: a first radio communication unit which transmits
a first message about random access to the base station and
which receives from the base station a radio signal
including a second message about the random access; and a
first controller which limits reception of a radio signal
from the base station at timing at which a radio signal is
transmitted to the mobile station; and the base station
includes: a second radio communication unit which receives
the first message and transmits the second message; and a
second controller which controls transmission timing of the
second message based on whether a transmission source of
the received first message is the relay station.
Further, to solve the above-described problem,
there is provided a radio communication system which
includes a base station; a mobile station; and a relay
station which performs wireless communications with the
base station and mobile station, wherein: the base station
includes a first radio communication unit which receives a
first message about random access and which transmits a
second message about the random access within a period with
a predetermined length after receiving the first message;
and the relay station includes: a second radio

communication unit which transmits the first message to the
base station and receives the second message from the base
station; and a controller which limits transmission of a
radio signal to the mobile station at least during a period
from a start of the period with a predetermined length
after transmission of the first message up to reception of
the second message.
Further, to solve the above-described problem,
there is provided a radio communication method used in a
system which includes a base station, a relay station, and
a mobile station and in which the relay station performs
wireless communications with the base station, and in which
the mobile station performs wireless communications with
the base station or relay station, the radio communication
method comprising: allowing the relay station to limit
reception of a radio signal from the base station at timing
at which a radio signal is transmitted to the mobile
station; allowing the relay station to transmit a first
message about random access to the base station; allowing
the base station to transmit a second message about random
access at timing which is determined based on whether a
transmission source of the first message is the relay
station; and allowing the relay station to receive the
second message from the base station.
Advantageous Effects of Invention
According to the above-described radio

communication system, base station, relay station, and
radio communication method, random access through the relay
station is smoothly performed.
The above-mentioned and other objects, features
and advantages of this invention will become apparent from
the following detailed description of the presently
preferred embodiment of the invention, taken in conjunction
with the accompanying drawings.
Brief Description of Drawings
[FIG. 1] FIG. 1 illustrates a radio communication
system according to a first embodiment.
[FIG. 2] FIG. 2 illustrates a radio communication
system according to a second embodiment.
[FIG. 3] FIG. 3 illustrates a structure example of
a radio frame.
[FIG. 4] FIG. 4 illustrates a use example of a
radio resource.
[FIG. 5] FIG. 5 is a sequence diagram illustrating
a procedure example of random access.
[FIG. 6] FIG. 6 is a block diagram illustrating a
base station.
[FIG. 7] FIG. 7 is a block diagram illustrating a
relay station.
[FIG. 8] FIG. 8 is a block diagram illustrating a
mobile station.
[FIG. 9] FIG. 9 is a flowchart illustrating a

process of a base station according to a second embodiment.
[FIG. 10] FIG. 10 is a flowchart illustrating a
process of a relay station according to a second embodiment.
[FIG. 11] FIG. 11 is a flowchart illustrating a
process of a mobile station according to a second
embodiment.
[FIG. 12] FIG. 12 illustrates a random access
example according to a second embodiment.
[FIG. 13] FIG. 13 is a flowchart illustrating a
process of a base station according to a third embodiment.
[FIG. 14] FIG. 14 is a flowchart illustrating a
process of a relay station according to a third embodiment.
[FIG. 15] FIG. 15 is a flowchart illustrating a
process of a mobile station according to a third embodiment.
[FIG. 16] FIG. 16 illustrates a random access
example according to a third embodiment.
[FIG. 17] FIG. 17 illustrates another random
access example according to a third embodiment.
[FIG. 18] FIG. 18 is a flowchart illustrating a
process of a base station according to a fourth embodiment.
[FIG. 19] FIG. 19 is a flowchart illustrating a
process of a relay station according to a fourth embodiment.
[FIG. 20] FIG. 20 illustrates a random access
example according to a fourth embodiment.
[FIG. 21] FIG. 21 illustrates another random
access example according to a fourth embodiment.
[FIG. 22] FIG. 22 is a flowchart illustrating a

process of a base station according to a fifth embodiment.
[FIG. 23] FIG. 23 is a flowchart illustrating a
process of a relay station according to a fifth embodiment.
[FIG. 24] FIG. 24 illustrates a random access
example according to a fifth embodiment.
[FIG. 25] FIG. 25 is a flowchart illustrating a
process of a base station according to a sixth embodiment.
[FIG. 2 6] FIG. 2 6 is a flowchart illustrating a
process of a relay station according to a sixth embodiment.
[FIG. 27] FIG. 27 illustrates a random access
example according to a sixth embodiment.
[FIG. 28] FIG. 28 is a flowchart illustrating a
process of a base station according to a seventh embodiment.
[FIG. 29] FIG. 29 is a flowchart illustrating a
process of a relay station according to a seventh
embodiment.
[FIG. 30] FIG. 30 illustrates a random access
example according to a seventh embodiment.
Description of Embodiments
Preferred embodiments of the present invention
will now be described in detail below with reference to the
accompanying drawings, wherein like reference numerals
refer to like elements throughout.
(First Embodiment)
FIG. 1 illustrates a radio communication system
according to a first embodiment. The radio communication

system according to the first embodiment includes a base
station 10, a relay station 20, and a mobile station 30.
Examples of the mobile station 30 include a cellular phone
and a personal digital assistant device. The relay station
20 may be a mobile radio relay station or a fixed radio
relay station. The mobile station 30 performs wireless
communications with the base station 10 or relay station 20.
The relay station 20 performs random access (RA) to the
base station 10 and establishes a connection, thus relaying
data communication between the base station 10 and the
mobile station 30.
The base station 10 includes a radio communication
unit 11 and a controller 12. The radio communication unit
11 receives a first message (message #1) about random
access and transmits a second message {message #2) about
the random access. Examples of the message #1 include a
Msg 1 and a Msg 3, and examples of the message #2 include a
Msg 2 and a Msg 4. The controller 12 determines whether a
transmission source of the message #1 received by the radio
communication unit 11 is the relay station 20. Based on
whether the transmission source is the relay station 20,
the controller 12 then controls timing at which the radio
communication unit 11 transmits the message #2.
The relay station 20 includes a radio
communication unit 21 and a controller 22. The radio
communication unit 21 performs wireless communications with
the base station 10. During the random access, the radio

communication unit 21 transmits the message #1 to the base
station 10, and receives the message #2 from the base
station 10. The controller 22 controls timing of radio
communication so that self-interference will not occur
between a radio signal received from the base station 10
and a radio signal transmitted to the mobile station 30.
Concretely, at timing at which a radio signal is
transmitted to the mobile station 30, the radio
communication unit 21 limits reception of a radio signal
from the base station 10 (e.g., stops a receiving circuit).
In the radio signal transmitted to the mobile station 30 by
the relay station 20, an RS {Reference Signal) used for a
measurement of communication quality through the mobile
station 30 is included.
Here, in the case where the message #1 is the Msg
1, examples of the method for determining a transmission
source of the message #1 through the controller 12 include
a method based on a signal sequence included in the message
#1 and a method based on timing at which the message #1 is
received. In the former method, a signal sequence for the
relay station and a signal sequence for the mobile station
are prepared and the radio communication unit 21 generates
the message #1 by using the signal sequence for the relay
station. In the case where another relay station is
present in the radio communication system, the relay
station 20 may use the signal sequence for the relay
station shared with the another relay station. In the

latter method, a RACH (random access channel) for the relay
station and a RACH for the mobile station are configured
separately and the radio communication unit 21 transmits
the message #1 through the RACH for the relay station.
In the case where a transmission source of the
message #1 is the relay station 20 (or another relay
station) or the mobile station 30 (or another mobile
station), the controller 12 then changes an algorithm for
determining transmission timing of the message #2. In the
former case, the controller 12 selects timing at which the
relay station 20 does not limit reception of a radio signal.
About the timing at which data is capable of being
transmitted from the base station 10 to the relay station
20, for example, when some agreements have been reached
between both the stations, the controller 12 selects the
timing according to the agreements. On the other hand, in
the latter case, the controller 12 performs scheduling and
selects arbitrary timing within an allowable period.
According to the proposed radio communication
system of the first embodiment, the relay station 20 limits
reception of a radio signal from the base station 10 at the
timing at which a radio signal is transmitted to the mobile
station 30. The relay station 20 further transmits the
message #1 to the base station 10. The base station 10
determines whether a transmission source of the message #1
is the relay station 20, and transmits the message #2 at
timing determined according to determination results. The

relay station 20 receives the message #2 from the base
station 10.
As a result, the radio communication system
smoothly performs random access from the relay station 20
to the base station 10. Specifically, the relay station 20
limits the reception so that self-interference will not
occur between a radio signal received from the base station
10 and a radio signal transmitted to the mobile station 30.
When a transmission source of the message #1 is not the
mobile station 30 but the relay station 20, the base
station 10 determines transmission timing of the message #2
in consideration of the limitation of the reception timing
of the relay station 20. Therefore, the radio
communication system suppresses the possibility that the
relay station 20 cannot receive the message #2 in a normal
way.
In second to seventh embodiments described below,
there is included an example of a radio communication
system including a base station, a relay station, and a
mobile station in conformity to the LTE or LTE-A.
(Second Embodiment)
FIG. 2 illustrates a radio communication system
according to a second embodiment. The radio communication
system according to the second embodiment includes a base
station 100, relay stations 200 and 200a, and mobile
stations 300 and 300a. In the following description,
suppose mainly that the mobile station 300 performs data

communication with the base station 100 via the relay
station 200 and the mobile station 300a directly performs
data communication with the base station 100.
The base station 100 is a radio communication
apparatus which performs wireless communications with the
relay stations 200 and 200a, and the mobile station 300a.
The base station 100 is connected to a host station {not
illustrated) via a wired line. The base station 100
receives data from the host station, and transfers it to
the relay stations 200 and 200a, and the mobile station
300a through a downlink (DL). On the other hand, through
an uplink (UL), the base station 100 receives data from the
relay stations 200 and 200a, and the mobile station 300a,
and transfers it to the host station.
The relay station 200 is a radio communication
apparatus which relays data communication between the base
station 100 and the mobile station 300. Through the DL,
the relay station 200 receives data from the base station
100 and transfers it to the mobile station 300. On the
other hand, through the UL, the relay station 200 receives
data from the mobile station 300 and transfers it to the
base station 100. In a similar fashion, the relay station
200a also relays data communication. The relay stations
200 and 200a may be mobile radio relay stations or fixed
radio relay stations.
Here, the relay stations 200 and 200a correspond
to a so-called Type 1 of relay station. Specifically, the

relay stations 200 and 200a perform protocol processing up
to a layer 3, and behave to the mobile stations 300 and
300a in the same manner as in the base station 100. From
the mobile stations 300 and 300a, a cell apart from that
provided by the base station 100 is viewed to be provided
by the relay stations 200 and 200a. A frequency band used
for radio communication between the base station and the
relay station is at least partially overlapped with a
frequency band used for radio communication between the
relay station and the mobile station.
The mobile stations 300 and 300a are radio
terminal apparatus which communicate with the base station
100. The mobile stations 300 and 300a communicate with the
base station 100 via the relay stations 200 and 200a.
Examples of the mobile stations 300 and 300a include a
cellular phone and a personal digital assistant device.
Through the DL, the mobile station 300 receives data from
the relay station 200. Through the UL, on the other hand,
the mobile station 300 transmits data to the relay station
200.
For radio communication through the DL, an OFDMA
(Orthogonal Frequency Division Multiple Access) is used,
and for radio communication through the UL, an SC-FDMA
{Single Carrier Frequency Division Multiple Access) is used.
Further, a base station may be called a BS (Base Station),
a relay station may be called an RN (Relay Node) or an RS
(Relay Station), and a mobile station may be called an MS

(Mobile Station) or a UE (User Equipment).
FIG. 3 illustrates a structure example of a radio
frame. Through each of the DL and UL, the radio frame as
illustrated in FIG. 3 is transmitted and received between a
base station and a relay station as well as between a relay
station and a mobile station. In the second embodiment, an
FDD (Frequency Division Duplex) is used as a duplex system.
Note that a TDD (Time Division Duplex) may be used.
A radio frame with a width of 10 msec includes ten
subf rames (sub frames #0 to #9) with a width of 1 msec.
Each subframe includes two slots (a first-half slot and a
second-half slot) with a width of 0.5 msec. Scheduling of
data or control signals is performed in units of subframes.
A radio resource of the subframe is segmentalized in the
frequency direction or in the time direction for management.
A minimum unit in the frequency direction is a sub-carrier
and a minimum unit in the time direction is a symbol. The
number of symbols included in the subframe may be different
depending on a type of subframes.
FIG. 4 illustrates an example of radio resource
usage. A communication channel is provided on a DL
subframe and an UL subframe transmitted and received by the
relay stations 200 and 200a.
In the DL subframe, several symbols {one to three
symbols) of the head are an area for control and remaining
symbols are an area for data. On the area for control, a
PDCCH (Physical Downlink Control Channel) for transmitting

a physical control signal is provided. On the area for
data, a PBCH (Physical Broadcast Channel) for transmitting
broadcast information and an R-PDCCH (Relay Physical
Downlink Control Channel) for transmitting control data on
a relay are provided. On the UL subframe, a PRACH
(Physical Random Access Channel) for transmitting a random
access preamble is provided.
On the DL subframe, a reference signal being a
pilot signal is transmitted in both of the areas for
control and data. While DL data communication is not
performed, a reference signal is transmitted. The mobile
station 300 measures a reception power level or radio
quality by using a reference signal.
Here, the relay stations 200 and 200a receive data
from the base station 100 and configure a subframe (DL
backhaul) which does not carry data to a subordinate mobile
station. In signals in which transmission is stopped, a
reference signal is also included. Note that in the area
for control, the relay stations 200 and 200a are allowed to
receive data from the base station 100 and transmit data to
the subordinate mobile station at the same time. In other
words, the relay stations 200 and 200a may stop
transmitting data in both of the areas for control and data,
or only in the area for data.
For example, the DL backhaul is configured so that
the DL subframe of the relay stations 200 and 200a may be
an MBSFN (Multimedia Broadcast multicast service Single

Frequency Network) subframe. The MBSFN subframe is a
subframe in which the base station 100 normally performs
MBSFN transmission. The MBSFN transmission is used in the
case where a plurality of transmitting stations concertedly
transmit data of the same content at the same timing by
using the same frequency and modulation scheme. In the
second embodiment, in the radio communication system
including the relay stations 200 and 200a, the MBSFN
subframe is used for configuring a DL backhaul subframe of
the relay stations 200 and 200a. Through the process, as
illustrated in FIG. 4, for example, since the relay
stations 200 and 200a do not transmit a reference signal in
the area for data of the MBSFN subframe, self-interference
does not occur even if the relay stations 200 and 200a
receive data in the area.
The relay stations 200 and 200a further transmit
data to the base station 100 and configure a subframe (UL
backhaul) in which data is not received from a subordinate
mobile station. Timing for the DL backhaul and timing for
the UL backhaul may be the same or different from each
other.
The relay stations 200 and 200a configured with
the UL backhaul do not give data transmission permissions
(UL grant) before a predetermined time (e.g., four
subframes) from the UL backhaul. As a result, the
subordinate mobile stations do not transmit data in the UL
backhaul. Further, the relay stations 200 and 200a do not

transmit data to the subordinate mobile stations before a
predetermined time from the UL backhaul. As a result, the
subordinate mobile stations do not transmit an ACK
(Acknowledgement)/NACK (Negative Acknowledgement) in the UL
backhaul.
Note that the relay stations 200 and 200a control
timing at which the subordinate mobile stations transmit
data as described above. Therefore, even in every subframe
except the predetermined UL backhaul, the relay stations
200 and 200a can stop receiving data from the subordinate
mobile station and transmit data to the base station 100
through scheduling.
In addition, timing for the backhaul has been
agreed between the base station 100 and the relay stations
200 and 200a. The relay stations 200 and 200a may
determine the timing and notify the base station 100 of the
timing. Or, alternatively, the base station 100 may
determine the timing and notify the relay stations 200 and
200a of the timing. The timing for the backhaul may be
different between the relay stations 200 and 2 00a. The
relay stations 200 and 200a broadcast information
indicating the timing for the backhaul. The mobile station
300 recognizes the timing based on the broadcast
information received from the relay station 200.
FIG. 5 is a sequence diagram illustrating a
procedure example of the random access. Here, the mobile
station 300a performs random access to the base station 100.

The procedure of the random access illustrated in FIG. 5
includes the following steps:
{Step SI) The mobile station 300a selects one
signal sequence from among candidates of a plurality of
signal sequences and transmits it as a random access
preamble (Msg 1) through the PRACH. Hereinafter, the
random access preamble may be referred to simply as a
preamble.
(Step S2) After detecting Msg 1, the base station
100 transmits a random access response (Msg 2). The Msg 2
is transmitted within a predetermined period. More
specifically, the base station 100 transmits the Msg 2
within a period of A pieces of subframes counted after
three subframes from the subframe in which the Msg 1 is
received. A value of A is previously set to any of 2, 3, 4,
5, 6, 7, 8, and 10.
(Step S3) Within the period in which the Msg 2 may
be transmitted, the mobile station 300a monitors a received
signal from the base station 100. After detecting the Msg
2, the mobile station 300a transmits a message (Msg 3)
called a scheduled transmission to the base station 100.
In the Msg 3, an identifier of the mobile station 300a is
included.
(Step S4) The base station 100 receives the Msg 3
from the mobile station 300a and transmits a message (Msg
4) called Contention Resolution to the mhotlle station 300^.*
The Msg 4 is transmitted within a predetermined period.

More specifically, the base station 100 transmits the Msg 4
within B pieces of subframes counted from the subframe in
which the Msg 3 is received. A value of B is previously
set to any of 8, 16, 24, 32, 40, 48, 56, and 64. Within
the period in which the Msg 4 may be transmitted, the
mobile station 300a monitors a received signal from the
base signal 100.
Incidentally, a clue (RA trigger) in which random
access is performed includes the following.
(1) Abnormality is detected in a connection
between the base station 100 and the mobile station 300a.
The abnormality in the connection includes a case where a
timer T310 is time out as described in the foregoing Non-
Patent Literature 4 and a case of failing in retransmission
control of data in an RLC (Radio Link Control) layer.
(2) The mobile station 300a receives an
instruction of starting a handover from a base station as a
handover source, and accesses a base station as a handover
destination.
(3) The mobile station 300a fails in access to the
base station 100 by using a scheduling request scheme. The
scheduling request scheme is an access scheme in which the
mobile station 300a transmits a scheduling request to the
base station 100 by using a radio resource for control data
and receives an allocation of a radio resource for data
transmission.
(4) The mobile station 300a fails in data

transmission to the base station 100 by using a contention
based uplink transmission method. The contention based
uplink transmission method is a method in which the mobile
station 300a transmits data to the base station 100 by
using a radio resource shared by a plurality of mobile
stations. Failure in the data transmission may be caused
by the contention. The contention based uplink
transmission method is described, for example, in a
collection of writing about 3GPP (R2-093812, "Contention
based uplink transmission").
(5) The mobile station 300a fails in security
authentication.
(6) The mobile station 300a fails in
reconfiguration of a radio resource, namely,
reconfiguration of RRC (Radio Resource Control) connection.
Reconfiguration of the RRC connection is described, for
example, in a section 5. 3. 5. 5 of the foregoing Non-
Patent Literature 4.
Even at the time of the random access from the
relay stations 2 00 and 200a to the base station 100, the
Msg 1 to Msg 4 are transmitted in the same manner as in the
random access from the mobile station 300a to the base
station 100. Note that in the case of the relay stations
200 and 200a, transmission timing of the Msg 2 and Msg 4 is
different from that of the mobile station 300a.
FIG. 6 is a block diagram illustrating the base
station. The base station 100 includes a radio

communication unit 110, a wired communication unit 120, a
data processing unit 130, and a controller 140.
The radio communication unit 110 is a radio
interface which performs wireless communications with the
relay stations 200 and 200a, and the mobile station 300a.
The radio communication unit 110 performs signal processing
including demodulation and decoding to the received radio
signal, and extracts data and a control signal. The radio
communication unit 110 further detects a preamble
transmitted through the PRACH. The radio communication
unit 110 supplies data to be transferred to a host station
to the data processing unit 130. On the other hand, the
radio communication unit 110 obtains data from the data
processing unit 130 and generates a control signal based on
an instruction from the controller 140. The radio
communication unit 110 then performs signal processing
including coding and modulation to data and a control
signal, and outputs a radio signal.
The wired communication unit 120 is a
communication interface which performs wired communication
with the host station. The wired communication unit 120
receives data addressed to the mobile stations 300 and 300a
from the host station, and supplies it to the data
processing unit 130. On the other hand, the wired
communication unit 120 converts the data obtained from the
data processing unit 130 into a packet form of a wired
network and transmits it to the host station.

The data processing unit 130 obtains data to be
transferred to the host station from the radio
communication unit 110 and supplies it to the wired
communication unit 120. On the other hand, the data
processing unit 130 obtains data addressed to the mobile
stations 300 and 300a from the wired communication unit 120
and maps data to a radio frame under the control of the
controller 140, thus supplying it to the radio
communication unit 110.
The controller 140 controls processes of the radio
communication unit 110, wired communication unit 120, and
data processing unit 130. The controller 140 has a data
plane unit 150 and a control plane unit 160. The data
plane unit 150 controls transmission and reception of data
between its own station and any of the relay stations 200
and 200a and the mobile station 300a. The control plane
unit 160 controls transmission and reception of a control
signal between its own station and any of the relay
stations 200 and 200a and the mobile station 300a.
Namely, the control plane unit 160 obtains the
control signal extracted by the radio communication unit
110 and performs communication control according to the
control signal. The control plane unit 160 further
notifies the radio communication unit 110 of the
transmitted control signal. The control plane unit 160 has
a preamble management unit 161, an RA slot management unit
162, and a backhaul controller 163.

The preamble management unit 161 manages
candidates of the preambles used for random access. When a
preamble for the relay station and a preamble for the
mobile station are distinguished, the preamble management
unit 161 determines whether the preamble detected by the
radio communication unit 110 is one for the relay station
or one for the mobile station.
The RA slot management unit 162 manages a slot (RA
slot) in which the PRACH is configured. When an RA slot
for the relay station and an RA slot for the mobile station
are distinguished, the RA slot management unit 162
determines whether a slot in which a preamble is detected
by the radio communication unit 110 is one for the relay
station or one for the mobile station. Further, the RA
slot management unit 162 may dynamically configure an RA
slot according to occurrence conditions of an RA trigger or
configuration status of a DL backhaul of the relay stations
200 and 200a.
The backhaul controller 163 manages backhauls of
the relay stations 200 and 200a, and controls timing of
transmission and reception of a radio signal. When a
random access source is the relay station, the backhaul
controller 163 refers to configuration status of the DL
backhaul of the relay stations 200 and 200a, and determines
timing for transmitting the Msg 2 or Msg 4.
FIG. 7 is a block diagram illustrating the relay
station. The relay station 200 includes radio

communication units 210 and 220, a scheduler 230, and a
controller 24 0. The relay station 200a is also deployed
through the same block structure as that of the relay
station 200.
The radio communication unit 210 is a radio
interface which performs wireless communications with the
base station 100. The radio communication unit 210
performs signal processing including demodulation and
decoding to the received radio signal, and extracts data or
a control signal. The radio communication unit 210
supplies data addressed to the mobile station 300 to the
scheduler 230. On the other hand, the radio communication
unit 210 obtains data from the scheduler 230 and generates
a control signal or a preamble based on the instruction
from the controller 240. The radio communication unit 210
then performs signal processing including coding and
modulation and outputs a radio signal.
The radio communication unit 220 is a radio
interface which performs wireless communications with the
mobile station 300. The radio communication unit 220
performs signal processing including demodulation and
decoding to the received radio signal and extracts data or
a control signal. The radio communication unit 220
supplies data to be transferred to the base station 100 to
the scheduler 230. On the other hand, the radio
communication unit 220 obtains data from the scheduler 230,
and generates a control signal or a reference signal based

on the instruction from the controller 240. The radio
communication unit 220 then performs signal processing
including coding and modulation, and outputs a radio signal.
The scheduler 230 schedules transfer of data from
the base station 100 to the mobile station 300 and transfer
of data from the mobile station 300 to the base station 100.
Namely, the scheduler 230 maps data addressed to the mobile
station 300 obtained from the radio communication unit 210
to a DL radio frame, and supplies it to the radio
communication unit 220. On the other hand, the scheduler
230 maps data addressed to the base station 100 obtained
from the radio communication unit 220 to an UL radio frame,
and supplies it to the radio communication unit 210.
The controller 240 controls processes of the radio
communication units 210 and 220 and the scheduler 230. The
controller 240 has a data plane unit 250 and a control
plane unit 260.
The data plane unit 250 controls transmission and
reception of data between its own station and any of the
base station 100 and the mobile station 300. The data
plane unit 2 50 has a scheduler controller 251. The
scheduler controller 251 manages a method for scheduling
the scheduler 230.
The control plane unit 2 60 controls transmission
and reception of a control signal between its own station
and any of the base station 100 and the mobile station 300.
Specifically, the control plane unit 2 60 obtains the

control signal extracted by the radio communication units
210 and 220, and performs communication control according
to the control signal. The control plane unit 2 60 further
notifies the radio communication units 210 and 220 of the
transmitted control signal. The control plane unit 260 has
a preamble management unit 261, an RA transmission
management unit 262, and a backhaul controller 263.
The preamble management unit 2 61 manages
candidates of the preambles used in the random access, and
selects a preamble used in the Msg 1 during the random
access to the base station 100. When the preamble for the
relay station and the preamble for the mobile station are
distinguished, the preamble management unit 261 selects the
preamble for the relay station.
The RA transmission management unit 262 grasps an
RA slot and selects an RA slot used to transmit the Msg 1
during the random access to the base station 100. When the
RA slot for the relay station and the RA slot for the
mobile station are distinguished, the RA transmission
management unit 262 selects the RA slot for the relay
station.
The backhaul controller 263 manages a backhaul of
its own station and controls timing of transmission and
reception of a radio signal. Particularly, at least in the
area for data of the DL backhaul, the backhaul controller
2 63 does not transmit data or a reference signal to the
mobile station 300. In addition to the backhaul used in

normal data communication, the backhaul controller 2 63 may
configure a temporary backhaul during the random access.
FIG. 8 is a block diagram illustrating the mobile
station. The mobile station 300 includes a radio
communication unit 310, a data processing unit 320, and a
controller 330. The mobile station 300a is also deployed
by using the same block structure as that of the mobile
station 300.
The radio communication unit 310 is a radio
interface which performs wireless communications with the
relay station 200 or base station 100. The radio
communication unit 310 performs signal processing including
demodulation and decoding to the received radio signal, and
extracts data or a control signal. The radio communication
unit 310 supplies the extracted data to the data processing
unit 320. On the other hand, the radio communication unit
310 obtains data from the data processing unit 320 and
generates a control signal based on the instruction from
the controller 330. The radio communication unit 310 then
performs signal processing including coding and modulation,
and outputs a radio signal.
The data processing unit 320 generates data to be
transmitted to the relay station 200 or base station 100
and supplies it to the radio communication unit 310. On
the other hand, the data processing unit 320 obtains data
addressed to its own station from the radio communication
unit 310 and performs a process according to a type of data.

The controller 330 controls processes of the radio
communication unit 310 and the data processing unit 320.
The controller 330 has a data plane unit 340 and a control
plane unit 350. The data plane unit 34 0 controls
transmission and reception of radio data. The control
plane unit 350 controls transmission and reception of a
radio control signal. The control plane unit 350 has a
preamble management unit 351 and an RA slot management unit
352.
The preamble management unit 351 manages
candidates of the preambles used in the random access, and
selects the preamble used in the Msg 1 during the random
access to the relay station 200 or base station 100. When
the preamble for the relay station and the preamble for the
mobile station are distinguished, the preamble management
unit 351 selects the preamble for the mobile station.
The RA slot management unit 352 grasps an RA slot,
and selects an RA slot used to transmit the Msg 1 during
the random access to the relay station 200 or base station
100. When the RA slot for the relay station and the RA
slot for the mobile station are distinguished, the RA slot
management unit 352 selects the RA slot for the mobile
station.
With regard to the random access, processes
performed by the base station 100, relay station 200 and
mobile station 300 (or mobile station 300a) will be
described below. In the second embodiment, the base

station 100 determines based on the used preamble whether a
transmission source of the Msg 1 is the relay station or
mobile station.
FIG. 9 is a flowchart illustrating a process of
the base station according to the second embodiment. The
process illustrated in FIG. 9 includes the following steps:
(Step Sill) The radio communication unit 110
receives the preamble (Msg 1) through the PRACH. At this
time, a transmission source of the Msg 1 is not concretely
identified.
(Step S112) The preamble management unit 161
determines whether the received preamble is a preamble for
the relay station. If so, the process advances to step
S113. If not, the process proceeds to step S114.
(Step S113) The backhaul controller 163 selects a
DL backhaul of each of the relay stations 200 and 200a
within the period in which the Msg 2 is transmitted {namely,
the period within A pieces of subframes after three
subframes from the subframe in which the Msg 1 is received).
The process then proceeds to step S115.
(Step S114) The control plane unit 160 performs
scheduling and selects an arbitrary subframe within the
period in which the Msg 2 is transmitted.
(Step S115) The radio communication unit 110
transmits the Msg 2 through the PDCCH or R-PDCCH of the
subframe selected at step S113 or S114. In the case where
a plurality of subframes are selected at step S113 when

timing of the DL backhauls is different between the relay
stations 200 and 200a, the radio communication unit 110
transmits the Msg 2 in each subframe. The reason is that
whether at the time of receiving the Msg 1, any of the
relay stations 200 and 200a transmit the Msg 1 is not
identified.
{Step S116) The radio communication unit 110
receives the Msg 3.
(Step S117) The control plane unit 160 determines
a transmission source of the Msg 3. The transmission
source of the Msg 3 is determined by using an identifier
included in the Msg 3. If the transmission source is the
relay station, the process advances to step S118. If the
transmission source is not the relay station, the process
proceeds to step SI19. Here, the transmission source is
supposed to be the relay station 200.
(Step S118) The backhaul controller 163 selects a
DL backhaul of the relay station 200 within the period
(namely, the period within B pieces of subframes counted
from the subframe in which the Msg 3 is received) in which
the Msg 4 is transmitted. The process then proceeds to
step S120. Since the transmission source of the Msg 3 is
concretely . identified at the time of receiving the Msg 3,
the backhaul controller 163 need not select a DL backhaul
of the relay station 200a.
(Step S119) The control plane unit 160 performs
scheduling and selects an arbitrary subframe within the

period in which the Msg 4 is transmitted.
(Step S120) The radio communication unit 110
transmits the Msg 4 through the PDCCH or R-PDCCH of the
subframe selected at step S118 or S119.
FIG. 10 is a flowchart illustrating a process of
the relay station according to the second embodiment. The
process illustrated in FIG. 10 includes the following
steps:
(Step S121) The radio communication unit 210
receives broadcast information through the PBCH from the
base station 100. In the broadcast information,
information on timing of the RA slot is included. The RA
slot may be shared by the relay station and the mobile
station. The RA transmission management unit 262 selects
the RA slot of the UL backhaul. Note that when reception
of radio signals from the mobile station 300 may be stopped,
the RA transmission management unit 262 may select RA slot
except RA slot in the UL backhaul.
(Step S122) From among candidates of the preambles,
the preamble management unit 261 selects a preamble for the
relay station. The preamble for the relay station may be
shared by the relay stations 200 and 200a. The radio
communication unit 210 transmits the selected preamble by
using the RA slot selected at step S121.
(Step S123) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 through the DL backhaul.

When the Msg 2 is transmitted through the PDCCH, the
backhaul controller 263 stops transmitting a signal in both
of the areas for control and data. When the Msg 2 is
transmitted through the R-PDCCH, the backhaul controller
263 stops transmitting a signal at least in the area for
data.
(Step S124) The radio communication unit 210
receives the Msg 2 from the base station 100 through the
PDCCH or R-PDCCH of the DL backhaul.
(Step S125) The radio communication unit 210
transmits the Msg 3 to the base station 100. Preferably,
the radio communication unit 210 transmits the Msg 3 to the
base station 100 through the UL backhaul.
(Step S126) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 through the DL backhaul.
When the Msg 4 is transmitted through the PDCCH, the
backhaul controller 263 stops transmitting a signal in both
of the areas for control and data. When the Msg 4 is
transmitted through the R-PDCCH, the backhaul controller
263 stops transmitting a signal at least in the area for
data.
(Step S127) The radio communication unit 210
receives the Msg 4 from the base station 100 through the
PDCCH or R-PDCCH of the DL backhaul. Through the above
steps, the radio communication unit 210 completes a
procedure of random access from the relay station 200 to

the base station 100.
FIG. 11 is a flowchart illustrating a process of
the mobile station according to the second embodiment.
Suppose here that the mobile station 300 performs the
random access to the relay station 200 or base station 100.
The process illustrated in FIG. 11 includes the following
steps:
{Step S131) The radio communication unit 310
receives broadcast information through the PBCH from the
relay station 200 or base station 100. In the broadcast
information, information on the timing of the RA slot is
included. The RA slot management unit 352 selects one RA
slot.
(Step S132) The preamble management unit 351
selects one preamble for the mobile station from among
candidates of the preambles. The radio communication unit
310 transmits the selected preamble through the RA slot
selected at step S131.
(Step S133) The radio communication unit 310
monitors the PDCCH within the period (namely, the period of
A pieces of subframes after three subframes from the
subframe in which the Msg 1 is transmitted) in which the
Msg 2 is transmitted, and receives the Msg 2 from the relay
station 200 or base station 100. Note that the radio
communication unit 310 receives the Msg 2 in subframe
except the subframe in DL backhaul.
(Step S134) The radio communication unit 310

transmits the Msg 3 to the relay station 200 or base
station 100. The radio communication unit 310 transmits
the Msg 3 to the relay station 200 in subframe except the
subframe in UL backhaul.
(Step S135) The radio communication unit 310
monitors the PDCCH within the period (namely, the period of
B pieces of subframes counted from the subframe in which
the Msg 3 is transmitted) in which the Msg 4 is transmitted,
and receives the Msg 4 from the relay station 200 or base
stationlOO. Note that the radio communication unit 310
receives the Msg 4 from the relay station 200 in subframe
except the subframe in DL backhaul.
(Step S136) Through the process up to step S135,
the radio communication unit 310 completes a procedure of
the random access from its own station to the relay station
200 or base station 100. Subsequently, the radio
communication unit 310 performs data communication between
its own station and any of the relay station 200 and the
base station 100. Note that when connected to the relay
station 200, the mobile station 300 performs data
communication in subframe except the subframe in backhaul.
FIG. 12 illustrates a random access example
according to the second embodiment. The message flow
illustrated in FIG. 12 includes the following steps:
(Step Sll) The relay station 200 transmits the Msg
1 to the base station 100 through the UL backhaul. The
preamble to be transmitted as the Msg 1 is a preamble for

the relay station. Based on the preamble, the base station
100 recognizes that a transmission source of the Msg 1 is
the relay station 200.
(Step S12) The base station 100 transmits the Msg
2 through the R-PDCCH of the DL backhaul of the relay
station 200 within the period in which the Msg 2 is
transmitted. When a signal such as a reference signal is
not transmitted in the area for data, the relay station 200
receives the Msg 2.
(Step S13) The base station 100 transmits the Msg
2 through the DL backhaul of the relay station 200a within
the period in which the Msg 2 is transmitted. Note that
since the relay station 200a did not transmit Msg 1, it
ignores the Msg 2 received from the base station 100.
(Step S14) The relay station 200 transmits the Msg
3 to the base station 100 through the UL backhaul. Based
on an identifier included in the Msg 3, the base station
100 recognizes that a transmission source of the Msg 3 is
the relay station 200.
(Step S15) The base station 100 transmits the Msg
4 through the R-PDCCH of the DL backhaul of the relay
station 200 within the period in which the Msg 4 is
transmitted. When a signal such as a reference signal is
not transmitted in the area for data, the relay station 200
receives the Msg 4.
In the proposed radio communication system of the
second embodiment, the base station 100 is configured to

determine based on the preamble received as the Msg 1
whether a transmission source of the Msg 1 is the relay
station or mobile station. In the case where the
transmission source is the relay station, the base station
100 then controls transmission timing so that the
transmission source may receive the Msg 2 through an
existing DL backhaul. In the case where a transmission
source of the Msg 3 is the relay station 200, the base
station 100 further controls transmission timing so that
the relay station 200 may receive the Msg 4 through an
existing DL backhaul. According to the second embodiment,
the radio communication system suppresses self-interference
of the relay station 200 and smoothly performs random
access from the relay station 200 to the base station 100.
(Third Embodiment)
A third embodiment will be described below. Since
the third embodiment shares some elements with the
foregoing second embodiment, the following discussion will
focus on their distinctive points, omitting explanations of
similar elements. The third embodiment differs from the
second embodiment in a method for determining whether a
transmission source of the Msg 1 is the relay station or
mobile station.
A radio communication system according to the
third embodiment is deployed by using the same apparatus
configuration as that of the second embodiment illustrated
in FIG. 2. Further, a base station, a relay station, and a

mobile station according to the third embodiment are
deployed by using the same block configurations as those of
the second embodiment illustrated in FIGS. 6 to 8.
Hereinafter, the third embodiment will be described with
reference to the same reference numerals as those
illustrated in FIGS. 6 to 8.
FIG. 13 is a flowchart illustrating a process of
the base station according to the third embodiment. The
process illustrated in FIG. 13 includes the following
steps:
{Step S211) The RA slot management unit 162
configures separate RA slots for the relay station and the
mobile station. Through the PBCH, the radio communication
unit 110 transmits information indicating timing of the RA
slots for the mobile station and the relay station as
broadcast information. Note that the radio communication
unit 110 may transmit information indicating timing of the
RA slot for the relay station as individual control data to
the relay stations 200 and 200a.
As described in the foregoing Non-Patent
Literature 5, normal information indicating timing of the
RA slot is transmitted as a parameter (PRACH Configuration
Index) in the broadcast information. Suppose, for example,
that the information indicating timing of the RA slot for
the relay station is inserted as a new parameter into the
broadcast information for transmission. The RA slot for
the relay station may be set to a low frequency such as one

time per 40 msec.
(Step S212) The radio communication unit 110
receives a preamble through the PRACH.
(Step S213) The RA slot management unit 162
determines whether the preamble is received through the RA
slot for the relay station or the mobile station. If the
preamble is received through the RA slot for the relay
station, the process advances to step S214. If the
preamble is received through the RA slot for the mobile
station, the process proceeds to step S215.
(Step S214) The backhaul controller 163 selects
each DL backhaul of the relay stations 200 and 200a within
the period in which the Msg 2 is transmitted. The process
then proceeds to step S216.
(Step S215) The control plane unit 160 performs
scheduling and selects an arbitrary subframe within the
period in which the Msg 2 is transmitted.
(Step S216) The radio communication unit 110
transmits the Msg 2 through the PDCCH or R-PDCCH of the
subframe selected at step S214 or S215. When the timing of
the DL backhauls is different between the relay stations
200 and 200a, the radio communication unit 110 transmits
the Msg 2 through each DL backhaul.
(Step S217) The radio communication unit 110
receives the Msg 3.
(Step S218) The control plane unit 160 determines
a transmission source of the Msg 3. If the transmission

source is the relay station, the process advances to step
S219. If the transmission source is not the relay station,
the process proceeds to step S220. Here, the transmission
source is supposed to be the relay station 200.
(Step S219) The backhaul controller 163 selects
the DL backhaul of the relay station 200 within the period
in which the Msg 4 is transmitted. The process then
proceeds to step S221. The backhaul controller 163 need
not select the DL backhaul of the relay station 200a.
(Step S220) The control plane unit 160 performs
scheduling and selects an arbitrary subframe within the
period in which the Msg 4 is transmitted.
(Step S221) The radio communication unit 110
transmits the Msg 4 through the PDCCH or R-PDCCH of the
subframe selected at step S219 or S220.
FIG. 14 is a flowchart illustrating a process of
the relay station according to the third embodiment. The
process illustrated in FIG. 14 includes the following
steps:
(Step S231) Through the PBCH, the radio
communication unit 210 receives broadcast information from
the base station 100, In the broadcast information,
information indicating timing of the RA slot for the relay
station is included.
(Step S232) The RA transmission management unit
262 selects the RA slot for the relay station. The RA
transmission management unit 262 preferably selects the RA

slot for the relay station provided on the UL backhaul.
(Step S233) The preamble management unit 2 61
selects one preamble from among the candidates of the
preambles. The candidates of the preambles are shared by
the relay stations 200 and 200a, or by the mobile stations
300 and 300a. The radio communication unit 210 transmits
the selected preamble through the RA slot selected at step
S232.
(Step S234) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 through the DL backhaul.
(Step S235) The radio communication unit 210
receives the Msg 2 from the base station 100 through the
PDCCH or R-PDCCH of the subframe in DL backhaul.
(Step S236) The radio communication unit 210
transmits the Msg 3 to the base station 100. Preferably,
the radio communication unit 210 transmits the Msg 3 to the
base station 100 through the UL backhaul.
(Step S237) The backhaul controller 2 63 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 through the DL backhaul.
(Step S238) The radio communication unit 210
receives the Msg 4 from the base station 100 through the
PDCCH or R-PDCCH of the subframe in DL backhaul.
FIG. 15 is a flowchart illustrating a process of
the mobile station according to the third embodiment. Here,
the mobile station 300 is supposed to perform random access

to the relay station 200 or base station 100. The process
illustrated in FIG. 15 includes the following steps:
(Step S241) The radio communication unit 310
receives broadcast information from the relay station 200
or base station 100 through the PBCH. In the broadcast
information, information indicating timing of the RA slot
for the mobile station is included. The RA slot management
unit 352 selects the RA slot for the mobile station.
(Step S242) The preamble management unit 351
selects one preamble from among the candidates of the
preambles. The candidates of the preambles are shared by
the relay stations 200 and 200a or by the mobile stations
300 and 300a. The radio communication unit 310 transmits
the selected preamble through the RA slot selected at step
S241.
(Step S243) The radio communication unit 310
monitors the PDCCH within the period in which the Msg 2 is
transmitted, and receives the Msg 2 from the relay station
200 or base station 100. Note that the radio communication
unit 310 receives the Msg 2 from the relay station 200
through subframe except the subframe in DL backhaul.
(Step S244) The radio communication unit 310
transmits the Msg 3 to the relay station 200 or base
station 100. The radio communication unit 310 transmits
the Msg 3 to the relay station 200 through subframe except
the subframe in UL backhaul.
(Step S245) The radio communication unit 310

monitors the PDCCH within the period in which the Msg 4 is
transmitted, and receives the Msg 4 from the relay station
200 or base station 100. Note that the radio communication
unit 310 receives the Msg 4 from the relay station 200
through subframe except the subframe in DL backhaul.
(Step S246) The radio communication unit 310
performs data communication between its own station and any
of the relay station 200 and the base station 100. Note
that when connected to the relay station 200, the radio
communication unit 310 performs data communication through
subframe except subframe in the backhaul.
FIG. 16 illustrates a random access example
according to the third embodiment. The message flow
illustrated in FIG. 16 includes the following steps:
(Step S21) The relay station 200 transmits the Msg
1 to the base station 100 through the RA slot for the relay
station of the UL backhaul subframe. The preamble
transmitted as the Msg 1 may be shared by the relay station
and the mobile station. Based on the reception timing of
the preamble, the base station 100 recognizes that a
transmission source of the Msg 1 is the relay station 200.
(Step S22) The base station 100 transmits the Msg
2 through the R-PDCCH of the DL backhaul of the relay
station 200 within the period in which the Msg 2 is
transmitted. When a signal such as a reference signal is
not transmitted in the area for data, the relay station 200
receives the Msg 2.

(Step S23) The base station 100 transmits the Msg
2 through the DL backhaul of the relay station 200a within
the period in which the Msg 2 is transmitted.
{Step S24) The relay station 200 transmits the Msg
3 to the base station 100 through the UL backhaul. Based
on the identifier included in the Msg 3, the base station
100 recognizes that a transmission source of the Msg 3 is
the relay station 200.
(Step S25) The base station 100 transmits the Msg
4 through the R-PDCCH of the DL backhaul of the relay
station 200 within the period in which the Msg 4 is
transmitted. When a signal such as a reference signal is
not transmitted in the area for data, the relay station 200
receives the Msg 4.
Incidentally, the base station 100 need not always
configure the RA slot for the relay station. Specifically,
the base station 100 may configure the RA slot after
detecting the RA trigger about the relay stations 200 and
200a.
FIG. 17 illustrates another random access example
according to the third embodiment. The base station 100
does not allocate a radio resource to the PRACH for the
relay station in normal situation. On the other hand, when
detecting an RA trigger and determining that any of the
relay stations 200 and 200a may perform random access, the
base station 100 allocates a radio resource to the PRACH
for the relay station. At this time, by using a timer, the

base station 100 may limit a period in which a radio
resource is allocated. The relay stations 200 and 200a
transmit the Msg 1 within the period. As can be seen from
the above discussion, when the relay stations 200 and 200a
do not perform random access, the base station 100
allocates a radio resource of the RA slot used for the
relay station to arbitrary channel except the PRACH, thus
making use of a radio resource efficient.
According to the third embodiment, the proposed
radio communication system permits the base station 100 to
determine, based on the timing at which the Msg 1 is
received, whether a transmission source of the Msg 1 is the
relay station or mobile station. When the transmission
source is the relay station, the base station 100 then
controls transmission timing so that the relay station may
receive the Msg 2 through an existing DL backhaul. When
the transmission source of the Msg 3 is the relay station
200, the base station 100 further controls transmission
timing so that the relay station 200 may receive the Msg 4
through an existing DL backhaul. According to the third
embodiment, the radio communication system suppresses self-
interference of the relay station 200 and smoothly performs
random access from the relay station 200 to the base
station 100.
(Fourth Embodiment)
A fourth embodiment will be described below. Since
the fourth embodiment shares some elements with the

foregoing second and third embodiments, the following
discussion will focus on their distinctive points, omitting
explanations of similar elements. The fourth embodiment
differs from the second and third embodiments in timing at
which the Msg 2 or A is transmitted.
A radio communication system according to the
fourth embodiment is deployed by using the same apparatus
configuration as that of the second embodiment illustrated
in FIG. 2. Further, a base station, a relay station, and a
mobile station according to the fourth embodiment are
deployed by using the same block configurations as those of
the second embodiment illustrated in FIGS. 6 to 8.
Hereinafter, the fourth embodiment will be described with
reference to the same reference numerals as those
illustrated in FIGS. 6 to 8.
FIG. 18 is a flowchart illustrating a process of
the base station according to the fourth embodiment. Since
processes of steps S311, S312, S314 to S317, S319, and S320
illustrated in FIG. 18 are the same as those of steps Sill,
S112, S114 to S117, S119, and S120 illustrated in FIG. 9, a
description will not be repeated.
(Step S313) The backhaul controller 163 selects
the DL default backhaul within the period in which the Msg
2 is transmitted. The default backhaul is a backhaul which
is not effective in normal situation but automatically
becomes effective at the time of the random access. The
timing of the default backhaul is, for example, mutually

configured between the relay stations 200 and 200a. The
timing of the default backhaul of the relay stations 200
and 200a is previously configured between their own
stations and the base station 100, and is configured, for
example, by a telecommunications operator at the time of
deploying the relay stations 200 and 200a.
(Step S318) The backhaul controller 163 selects
the DL default backhaul within the period in which the Msg
4 is transmitted.
FIG. 19 is a flowchart illustrating a process of
the relay station according to the fourth embodiment. The
process illustrated in FIG. 19 includes the following
steps:
(Step S321) The control plane unit 2 60 determines
whether to detect the RA trigger. If so, the process
proceeds to step S322. If not, the control plane unit 260
repeats a process of step S321.
(Step S322) In addition to an existing backhaul,
the backhaul controller 263 makes the default backhaul with
predetermined timing effective.
(Step S323) The RA transmission management unit
262 selects an RA slot of the UL default backhaul subframe.
Note that when stopping receiving a radio signal from the
mobile station 300, the RA transmission management unit 262
may select RA slot except that of the UL default backhaul.
(Step S324) From among the candidates of the
preambles, the preamble management unit 261 selects the

preamble for the relay station. The radio communication
unit 210 transmits the selected preamble through the RA
slot selected at step S323.
(Step S325) In addition to the DL backhaul, the
backhaul controller 263 limits transmission of a radio
signal to the mobile station 300 through the DL default
backhaul.
(Step S326) The radio communication unit 210
receives the Msg 2 from the base station 100 through the
PDCCH or R-PDCCH of the DL default backhaul.
(Step S327) The radio communication unit 210
transmits the Msg 3 to the base station 100. Preferably,
the radio communication unit 210 transmits the Msg 3 to the
base station 100 through the UL default backhaul.
(Step S328) In addition to the DL backhaul, the
backhaul controller 263 limits transmission of a radio
signal to the mobile station 300 through the DL default
backhaul.
(Step S329) The radio communication unit 210
receives the Msg 4 from the base station 100 through the
PDCCH or R-PDCCH of the DL default backhaul.
FIG. 20 illustrates a random access example
according to the fourth embodiment. The message flow
illustrated in FIG. 20 includes the following steps:
(Step S31) The relay station 200 transmits the Msg
1 to the base station 100 through the UL default backhaul.
The preamble to be transmitted is a preamble for the relay

station. Based on the preamble, the base station 100
recognizes that a transmission source of the Msg 1 is the
relay station.
(Step S32) The base station 100 transmits the Msg
2 through the R-PDCCH of the DL default backhaul within the
period in which the Msg 2 is transmitted. The base station
100 need not transmit the Msg 2 through each DL backhaul of
the relay stations 200 and 200a. When a signal such as a
reference signal is not transmitted in the area for data,
the relay station 200 receives the Msg 2. When the default
backhaul is validated, the relay station 200a receives the
Msg 2, whereas when the default backhaul is not validated,
the relay station 200a does not receive the Msg 2.
(Step S33) The relay station 200 transmits the Msg
3 to the base station 100 through the UL default backhaul.
Based on the identifier included in the Msg 3, the base
station 100 recognizes that a transmission source of the
Msg 3 is the relay station 200.
(Step S34) The base station 100 transmits the Msg
4 through the R-PDCCH of the DL default backhaul within the
period in which the Msg 4 is transmitted. When a signal
such as a reference signal is not transmitted in the area
for data, the relay station 200 receives the Msg 4.
In the foregoing description, whether a
transmission source of the Msg 1 is the relay station is
determined by using a method according to the second
embodiment. Further, determination may be performed by

using a method according to the third embodiment.
FIG. 21 illustrates another random access example
according to the fourth embodiment. The message flow
illustrated in FIG. 21 includes the following steps:
(Step S35) The relay station 200 transmits the Msg
1 to the base station 100 through the RA slot for the relay
station of the UL default backhaul subframe. Based on the
reception timing of the preamble, the base station 100
recognizes that a transmission source of the Msg 1 is the
relay station. After detecting the RA trigger, the base
station 100 may make the RA slot for the relay station
validated.
(Step S36) The base station 100 transmits the Msg
2 through the R-PDCCH of the DL default backhaul within the
period in which the Msg 2 is transmitted. When a signal
such as a reference signal is not transmitted in the area
for data, the relay station 200 receives the Msg 2.
(Step S37) The relay station 200 transmits the Msg
3 to the base station 100 through the UL default backhaul.
Based on an identifier included in the Msg 3, the base
station 100 recognizes that a transmission source of the
Msg 3 is the relay station 200.
(Step S38) The base station 100 transmits the Msg
4 through the R-PDCCH of the DL default backhaul within the
period in which the Msg 4 is transmitted. When a signal
such as a reference signal is not transmitted in the area
for data, the relay station 200 receives the Msg 4.

In the fourth embodiment, in the same manner as in
the second and third embodiments, the proposed radio
communication system smoothly performs random access from
the relay station 200 to the base station 100. Further, in
the fourth embodiment, the radio communication system makes
common transmission timing of the Msg 2 and Msg 4, and
simplifies control of random access. A point that the
transmission timing is made to be common is particularly
validated in the case of random access involved in a
handover.
(Fifth Embodiment)
A fifth embodiment will be described below. Since
the fifth embodiment shares some elements with the
foregoing second and third embodiments, the following
discussion will focus on their distinctive points, omitting
explanations of similar elements. The fifth embodiment
differs from the second and third embodiments in a subframe
in which an RA slot is configured.
A radio communication system according to the
fifth embodiment is deployed by using the same apparatus
configuration as that of the second embodiment illustrated
in FIG. 2. Further, a base station, a relay station, and a
mobile station according to the fifth embodiment are
deployed by using the same block configurations as those of
the second embodiment illustrated in FIGS. 6 to 8.
Hereinafter, the fifth embodiment will be described with
reference to the same reference numerals as those

illustrated in FIGS. 6 to 8.
FIG. 22 is a flowchart illustrating a process of
the base station according to the fifth embodiment. Since
processes of steps S412, S413, and S415 to S421 illustrated
in FIG. 22 are the same as those of steps S212, S213, and
S215 to S221 illustrated in FIG. 13, a description will not
be repeated.
(Step S411) The RA slot management unit 162
configures an RA slot for the relay station in a subframe
before k pieces of subframes (e.g., three subframes) from
the DL backhaul of the relay stations 200 and 200a. When
timing of the DL backhauls is different between the relay
stations 200 and 200a, the RA slot management unit 162
configures the RA slot for the relay station before k
pieces of subframes from each DL backhaul.
(Step S414) The backhaul controller 163 selects a
DL backhaul after k pieces of subframes from the subframe
in which the Msg 1 is received. Note that when there are
circumstances that the Msg 2 cannot be transmitted from a
subframe after k pieces of subframes from the above
subframe, the backhaul controller 163 may select another DL
backhaul after k pieces of subframes or later from the
above subframe within the period in which the Msg 2 is
transmitted.
FIG. 23 is a flowchart illustrating a process of
the relay station according to the fifth embodiment. Since
processes of steps S432, S433, and S435 to S437 illustrated

in FIG. 23 are the same as those of steps S233, S234, and
S236 to S238 illustrated in FIG. 14, a description will not
be repeated.
{Step S4 31) The RA transmission management unit
262 selects an RA slot of a subframe before k pieces of
subframes {e.g., three subframes) from the DL backhaul as
the RA slot for the relay station. When a;sufc^rrarfie cfefhe s^AA
- Rh <$lol is not an UL backhaul subframe, the backhaul
controller 263 controls that data not to be received from
the mobile station 300 through the subframe.
(Step S434) The radio communication unit 210
starts monitoring the PDCCH or R-PDCCH from the DL backhaul
subframe after k pieces of subframes from the subframe in
which the Msg 1 is transmitted. The Msg 2 is expected to
be received through the DL backhaul. Note that when the
Msg 2 is not received through the DL backhaul, the radio
communication unit 210 monitors the PDCCH or R-PDCCH from
the DL backhaul subframe after the above subframes or later.
FIG. 24 illustrates a random access example
according to the fifth embodiment. The message flow
illustrated in FIG. 24 includes the following steps:
(Step S41) The relay station 200 transmits the Msg
1 to the base station 100 through the RA slot of a subframe
before three subframes from the DL backhaul subframe.
Based on the reception timing of the preamble, the base
station 100 recognizes that a transmission source of the
Msg 1 is the relay station.

(Step S42) The base station 100 transmits the Msg
2 through the R-PDCCH of the DL backhaul subframe after
three subframes from the subframe in which the Msg 1 is
received. When a signal such as a reference signal is not
transmitted in the area for data, the relay station 200
receives the Msg 2.
(Step S43) The relay station 200 transmits the Msg
3 to the base station 100 through the UL backhaul. Based
on the identifier included in the Msg 3, the base station
100 recognizes that a transmission source of the Msg 3 is
the relay station 200.
(Step S44) The base station 100 transmits the Msg
4 through the R-PDCCH of the DL backhaul of the relay
station 200 within the period in which the Msg 4 is
transmitted. When a signal such as a reference signal is
not transmitted in the area for data, the relay station 200
receives the Msg 4.
In the foregoing description, whether a
transmission source of the Msg 1 is the relay station is
determined by using a method according to the third
embodiment; further, may be determined by using a method
according to the second embodiment.
In the fifth embodiment, in the same manner as in
the second and third embodiments, the proposed radio
communication system smoothly performs random access from
the relay station 200 to the base station 100, Further, in
the fifth embodiment, the relay station 200 smoothly starts

random access even if an RA slot is not provided on the UL
backhaul. In addition, the relay station 200 preferably
monitors a reception signal after predetermined time after
transmitting the Msg 1, thus simplifying control.
(Sixth Embodiment)
A sixth embodiment will be described below. Since
the sixth embodiment shares some elements with the
foregoing second and third embodiments, the following
discussion will focus on their distinctive points, omitting
explanations of similar elements. In the sixth embodiment,
the Msg 2 and Msg 4 are transmitted also through subframe
except the subframe in DL backhaul of the relay station.
A radio communication system according to the
sixth embodiment is deployed by using the same apparatus
configuration as that of the second embodiment illustrated
in FIG. 2. Further, a base station, a relay station, and a
mobile station according to the sixth embodiment are
deployed by using the same block configurations as those of
the second embodiment illustrated in FIGS. 6 to 8.
Hereinafter, the sixth embodiment will be described with
reference to the same reference numerals as those
illustrated in FIGS. 6 to 8.
FIG. 25 is a flowchart illustrating a process of
the base station according to the sixth embodiment. Since
processes of steps S511, S512, S514 to S517, S519, and S520
illustrated in FIG. 25 are the same as those of steps Sill,
S112, S114 to S117, S119, and S120 illustrated in FIG. 9, a

description will not be repeated.
{Step S513) The backhaul controller 163 selects a
subframe after m pieces of subframes from the subframe in
which the Msg 1 is received. A character m indicates a
predetermined value of the base station 100 and the relay
stations 200 and 200a, and is set, for example, to be equal
to three.
(Step S518) The backhaul controller 163 selects a
subframe after n pieces of subframes from the subframe in
which the Msg 3 is received. A character n indicates a
predetermined value of the base station 100 and the relay
stations 200 and 200a, and is set, for example, to be equal
to eight.
FIG. 26 is a flowchart illustrating a process of
the relay station according to the sixth embodiment. Since
processes of steps S521, S522, and S525 illustrated in FIG.
26 are the same as those of steps S121, S122, and S125
illustrated in FIG. 10, a description will not be repeated.
(Step S523) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 through a subframe after
m pieces of subframes from the subframe in which the Msg 1
is transmitted. When the Msg 2 is transmitted through the
PDCCH, the backhaul controller 263 stops transmitting a
signal in both of the areas for control and data. When the
Msg 2 is transmitted through the R-PDCCH, the backhaul
controller 263 stops transmitting a signal at least in the

area for data.
(Step S524) The radio communication unit 210
receives the Msg 2 from the base station 100 through the
PDCCH or R-PDCCH of a subframe after the m pieces of
subframes from the above subframe.
(Step S52 6) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 through a subframe after
n pieces of subframes from the subframe in which the Msg 3
is transmitted. When the Msg 4 is transmitted through the
PDCCH, the backhaul controller 263 stops transmitting a
signal in both of the areas for control and data. When the
Msg 4 is transmitted through the R-PDCCH, the backhaul
controller 263 stops transmitting a signal at least in the
area for data.
(Step S527) The radio communication unit 210
receives the Msg 4 from the base station 100 through the
PDCCH or R-PDCCH of a subframe after the n pieces of
subframes from the above subframe.
FIG. 27 illustrates a random access example
according to the sixth embodiment. The message flow
illustrated in FIG. 27 includes the following steps:
(Step S51) The relay station 200 transmits the Msg
1 to the base station 100 by using a preamble for the relay
station. Based on the preamble, the base station 100
recognizes that a transmission source of the Msg 1 is the
relay station.

(Step S52) The base station 100 transmits the Msg
2 through the R-PDCCH of a subframe after three subframes
from the subframe in which the Msg 1 is received. Through
a subframe after three subframes of the subframe in which
the Msg 1 is transmitted, the relay station 200 controls a
signal such as a reference signal not to be transmitted in
the area for data, thus receiving the Msg 2.
(Step S53) The relay station 200 transmits the Msg
3 to the base station 100. Based on the identifier
included in the Msg 3, the base station 100 recognizes that
a transmission source of the Msg 3 is the relay station 200.
(Step S54) Through the R-PDCCH of a subframe after
eight subframes from the subframe in which the Msg 3 is
received, the base station 100 transmits the Msg 4.
Through a subframe after eight subframes from the subframe
in which the Msg 3 is transmitted, the relay station 200
controls a signal such as a reference signal not to be
transmitted in the area for data, thus receiving the Msg 4.
In the foregoing description, whether a
transmission source of the Msg 1 is the relay station is
determined by using a method according to the second
embodiment; further, may be determined by using a method
according to the third embodiment.
In the sixth embodiment, in the same manner as in
the second and third embodiments, the proposed radio
communication system smoothly performs random access from
the relay station 200 to the base station 100. In the

sixth embodiment, since an interval between the Msg 1 and
Msg 2 as well as the interval between the Msg 3 and Msg 4
is fixed, the radio communication system simplifies control
of random access in the relay station 200. On the other
hand, about the random access from the mobile station 300a
to the base station 100, since the intervals are not fixed,
the radio communication system secures flexibility of
scheduling.
(Seventh Embodiment)
A seventh embodiment will be described below.
Since the seventh embodiment shares some elements with the
foregoing second embodiment, the following discussion will
focus on their distinctive points, omitting explanations of
similar elements. In the foregoing second to sixth
embodiments, transmission timing of the Msg 2 or Msg 4 is
changed based on the fact that a transmission source of the
Msg 1 or Msg 3 is the relay station or mobile station. As
compared with the above, in the seventh embodiment, even if
the base station does not distinguish that a transmission
source is the relay station or the mobile station, the
radio communication system performs random access.
A radio communication system according to the
seventh embodiment is deployed by using the same apparatus
configuration as that of the second embodiment illustrated
in FIG. 2. Further, a base station, a relay station, and a
mobile station according to the seventh embodiment are
deployed by using the same block configurations as those of

the second embodiment illustrated in FIGS. 6 to 8.
Hereinafter, the seventh embodiment will be described with
reference to the same reference numerals as those
illustrated in FIGS. 6 to 8.
FIG. 28 is a flowchart illustrating a process of
the base station according to the seventh embodiment. The
process illustrated in FIG. 28 includes the following
steps:
(Step S611) The radio communication unit 110
receives a preamble (Msg 1) through the PRACH. At this
time, a transmission source of the Msg 1 is not concretely
identified.
(Step S612) The control plane unit 160 performs
scheduling, and selects an arbitrary subframe within the
period in which the Msg 2 is transmitted.
(Step S613) The radio communication unit 110
transmits the Msg 2 through the PDCCH or R-PDCCH of the
subframe selected at step S612.
(Step S614) The radio communication unit 110
receives the Msg 3, Here, the transmission source is
supposed to be the relay station 200.
(Step S615) The control plane unit 160 performs
scheduling and selects an arbitrary subframe within the
period in which the Msg 4 is transmitted.
(Step S616) The radio communication unit 110
transmits the Msg 4 through the PDCCH or R-PDCCH of the
subframe selected at step S615.

FIG. 29 is a flowchart illustrating a process of
the relay station according to the seventh embodiment. The
process illustrated in FIG. 29 includes the following
steps:
(Step S621) The radio communication unit 210
receives broadcast information from the base station 100
through the PBCH. In the broadcast information,
information on the timing of the RA slot is included. The
RA transmission management unit 262 selects one RA slot.
The backhaul controller 2 63 controls data not to be
received from the mobile station 300 through the subframe
on which the RA slot is provided.
(Step S622) The preamble management unit 261 ,
selects one preamble from among candidates of the preambles.
The radio communication unit 210 transmits the selected
preamble through the RA slot selected at step S621.
(Step S623) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 until receiving the Msg 2
from a head of the period in which the Msg 2 may be
received. When the Msg 2 is transmitted through the PDCCH,
the backhaul controller 263 stops transmitting a signal in
both of the areas for control and data. When the Msg 2 is
transmitted through the R-PDCCH, the backhaul controller
263 stops transmitting a signal at least in the area for
data.
(Step S624) The radio communication unit 210

receives the Msg 2 from the base station 100 through the
PDCCH or R-PDCCH.
(Step S625) The backhaul controller 263 restarts
transmission of a radio signal {including a reference
signal) to the mobile station 300.
(Step S626) The radio communication unit 210
transmits the Msg 3 to the base station 100.
(Step S627) The backhaul controller 263 limits
transmission of a radio signal (including a reference
signal) to the mobile station 300 until receiving the Msg 4
from a head of the period in which the Msg 4 may be
received. When the Msg 2 is transmitted through the PDCCH,
the backhaul controller 263 stops transmitting a signal in
both of the areas for control and data. When the Msg 2 is
transmitted through the R-PDCCH, the backhaul controller
263 stops transmitting a signal at least in the area for
data.
{Step S628) The radio communication unit 210
receives the Msg 2 from the base station 100 through the
PDCCH or R-PDCCH.
(Step S629) The backhaul controller 263 restarts
transmission of a radio signal (including a reference
signal) to the mobile station 300.
FIG. 30 illustrates a random access example
according to the seventh embodiment. The message flow
illustrated in FIG. 30 includes the following steps:
(Step S61) The relay station 200 transmits the Msg

1 to the base station 100.
(Step S62) The base station 100 performs
scheduling, and transmits the Msg 2 through the R-PDCCH of
any subframe within the period in which the Msg 2 is
transmitted. Through a subframe after three subframes or
later from the subframe in which the Msg 1 is transmitted,
the relay station 200 controls a signal such as a reference
signal not to be transmitted in the area for data, thus
receiving the Msg 2.
(Step S63) The relay station 200 transmits the Msg
3 to the base station 100. Based on the identifier
included in the Msg 3, the base station 100 recognizes that
a transmission source of the Msg 3 is the relay station 200.
(Step S64) The base station 100 performs
scheduling, and transmits the Msg 4 through the R-PDCCH of
any subframe within the period in which the Msg 4 is
transmitted. Through the subframe or later in which the
Msg 3 is transmitted, the relay station 200 controls a
signal such as a reference signal not to be transmitted in
the area for data, thus receiving the Msg 4.
In the seventh embodiment, the proposed radio
communication system suppresses self-interference of the
relay station 200 and smoothly performs random access from
the relay station 200 to the base station 100. Further,
the base station 100 does not distinguish random access
through the relay station 200 and random access through the
mobile station 300a, and therefore preferably performs a

common procedure. As a result, the radio communication
system simplifies control of the random access.
The foregoing is considered as illustrative only
of the principles of the present invention. Further, since
numerous modifications and changes will readily occur to
those skilled in the art, it is not desired to limit the
invention to the exact construction and applications shown
and described, and accordingly, all suitable modifications
and equivalents may be regarded as falling within the scope
of the invention in the appended claims and their
equivalents.
Reference Signs List
10 Base station
20 Relay station
11, 21 Radio communication unit
12, 22 Controller
30 Mobile station

We Claim:
[Claim 1]
A radio communication system comprising:
a base station;
a relay station which performs wireless
communications with the base station; and
a mobile station which performs wireless
communications with the base station or relay station,
wherein:
the relay station includes:
a first radio communication unit which transmits a
first message about random access to the base station and
which receives from the base station a radio signal
including a second message about the random access; and
a first controller which limits reception of a
radio signal from the base station at timing at which a
radio signal is transmitted to the mobile station; and
the base station includes:
a second radio communication unit which receives
the first message and transmits the second message; and
a second controller which controls transmission
timing of the second message based on whether a
transmission source of the received first message is the
relay station.
[Claim 2]

The radio communication system according to claim
1, wherein the second controller determines, based on a
signal sequence included in the first message, whether the
transmission source of the first message is the relay
station.
[Claim 3]
The radio communication system according to claim
1, wherein the second controller determines, based on
timing at which the first message is received, whether the
transmission source of the first message is the relay
station.
[Claim 4]
The radio communication system according to claim
3, wherein after detecting that there is a possibility that
random access is performed by considering a situation of
radio communication, the second controller allocates a
radio resource used for transmission of the first message
through the relay station.
[Claim 5]
The radio communication system according to claim
1, wherein:
the first controller switches a first period in
which transmission of a radio signal to the mobile station
is limited and a second period in which reception of a

radio signal from the base station is limited to control
radio communication; and
when the transmission source of the first message
is the relay station, the second radio communication unit
transmits the second message in the first period.
[Claim 6]
The radio communication system according to claim
5, wherein the second controller allocates a radio resource
before a predetermined time of the first period, as a radio
resource used for transmission of the first message.
[Claim 7]
The radio communication system according to claim
5, further comprising another relay station which switches
a third period in which transmission of a radio signal to
the mobile station is limited and a fourth period in which
reception of a radio signal from the base station is
limited to perform radio communication,
wherein the second radio communication unit
transmits the second message within the third period in
addition to the first period.
[Claim 8]
The radio communication system according to claim
1, wherein:
when random access is performed, the first

controller limits transmission of a radio signal to the
mobile station within a predetermined period; and
when the transmission source of the first message
is the relay station, the second radio communication unit
transmits the second message within the predetermined
period.
[Claim 9]
The radio communication system according to claim
1, wherein:
the first controller limits transmission of a
radio signal to the mobile station after a predetermined
time after the first radio communication unit transmits the
first message; and
the second radio communication unit transmits the
second message after a predetermined time after receiving
the first message.
[Claim 10]
A radio communication system comprising:
a base station;
a mobile station; and
a relay station which performs wireless
communications with the base station and mobile station,
wherein:
the base station includes a first radio
communication unit which receives a first message about

random access and which transmits a second message about
the random access within a period of a predetermined length
after receiving the first message; and
the relay station includes:
a second radio communication unit which transmits
the first message to the base station and receives the
second message from the base station; and
a controller which limits transmission of a radio
signal to the mobile station at least during a period from
a start of the period of a predetermined length after
transmission of the first message up to reception of the
second message.
[Claim 11]
A base station used in a system including a mobile
station and a relay station which limits reception of a
radio signal within a partial period, and for receiving
random access from the relay station or mobile station, the
base station comprising:
a radio communication unit which receives a first
message about random access and transmits a second message
about the random access; and
a controller which controls transmission timing of
the second message based on whether a transmission source
of the received first message is the relay station.
[Claim 12]

A relay station used in a system including a base
station and a mobile station, the relay station comprising:
a controller which switches a first period in
which transmission of a radio signal to the mobile station
is limited and a second period in which reception of a
radio signal from the base station is limited to control
radio communication; and
a radio communication unit which transmits a first
message about random access to the base station and
receives a second message about the random access from the
base station,
wherein when the first message is transmitted by
using a signal sequence indicating that a transmission
source is the relay station or at timing indicating that a
transmission source is the relay station, the radio
communication unit receives the second message from the
base station within the first period.
[Claim 13]
A radio communication method used in a system
which includes a base station, a relay station, and a
mobile station and in which the relay station performs
wireless communications with the base station, and in which
the mobile station performs wireless communications with
the base station or relay station, the radio communication
method comprising:
limiting, by the relay station, reception of a

radio signal from the base station at timing at which a
radio signal is transmitted to the mobile station;
transmitting, by the relay station, a first
message about random access to the base station;
transmitting, by the base station, a second
message about random access at timing which is determined
based on whether a transmission source of the first message
is the relay station; and
receiving, by the relay station, the second
message from the base station.