DESCRIPTION
RADIO COMMUNICATION SYSTEM
Technical Field
The embodiments discussed herein are related to
radio communication systems including a mobile
telecommunication system, a radio LAN (Local Area Network)
and the like.
Background Art
In recent years a new high-speed communication
service referred to as LTE (Long Term Evolution) has been
expected as a standard for communication by a mobile
station such as a portable telephone. In addition, a LTE-
advanced system which is a further developed version of
LTE is discussed in 3GPP (3rd Generation Partnershio
Project).
Furthermore, the LTE-advanced system is to be
proposed as an IMT-advanced system which is a further
developed version of an IMT (International Mobile
Telecommunication)-2000 system which ITU-R (International
Telecommunication Union Radio communications sector)
determines to discuss.
W-CDMA (Wideband-Code Division Multiple Access),
CDMA one, and WiMax (Worldwide Interoperability for
Microwave Access) are typical IMT-2000 systems.
With a LTE-advanced system introducing a MBSFN
(Multimedia Broadcast multicast service Single Frequency
Network) in which MBMS (Multimedia Broadcast Multicast
Service) data is transmitted and a relay apparatus (relay
node) for performing radio relay with a LTE system as a
base is discussed (expansion of uplink/downlink bandwidth,
introduction of uplink MIMO (Multiple Input Multiple
Output), and the like are also discussed). Description
will now be given with a LTE-advanced system as an example
(1) MBMS and MBSFN
A MBMS is a service for broadcasting data to
unspecified or specific users. To be concrete,
broadcasting information such as news or multicasting
information to specific users is possible.
Furthermore, A MBSFN in which a plurality of base
stations transmit MBMS data in synchronization with one
another by the use of the same resource is discussed as a
method for transmitting broadcast data (MBMS data) by the
use of a MBMS.
"SFN" (Single Frequency Network) of "MBSFN" means
using the same radio frequency. That is to say, usually a
transmission area (MBSFN are) is set in a MBSFN and the
same radio frequency is used in that area (see
TS36.300V8.6.0 15 MBMS).
Moreover, with a MBSFN a plurality of base stations
transmit the same data at the same frequency at the same
timing. As a result, a mobile station can receive MBMS
data transmitted from the plurality of base stations.
The reason for this is as follows. If delay time
is shorter than or equal to the length of a CP (Cyclic
Prefix) in, for example, OFDM (Orthogonal Frequency
Division Multiplexing) receiving, then plural pieces of
data can be received and synthesized. By receiving and
synthesizing plural pieces of data, the effect of the
improvement of a receiving characteristic can be obtained.
A CP is a redundant portion added at data
transmission time to prevent a data overlap, and
corresponds to a GI (Guard Interval) in terrestrial
digital broadcasting. The length of a CP used in a MBSFN
is longer than that of a CP added to unicast data in
normal communication.
FIG. 20 illustrates the format of radio data.
Radio data includes a CP and data. A CP used at unicast
transmission time is referred to as a normal CP and a CP
used in a MBSFN is referred to as an extended CP. The
length of a normal CP is 4.69 )jsec and the length of a CP
used in a MBSFN (length of a CP included in MBMS data) is
16.67 usee.
FIG. 21 illustrates data receiving and combining.
It is assumed that a mobile station 120 receives MBMS data
(data b) transmitted from a base station B and that the
mobile station 120 receives MBMS data (data a) transmitted
from a base station A time t after receiving the data b
(data a and b are broadcast data and are equal in service
contents).
If the delay time t falls within the range of the
length of a CP from the time when the mobile station 120
begins to receive the data b, then the mobile station 120
can receive not only the data b but also the data a and
combine the data a and b. As described above, a CP is long
in a MBSFN. Therefore, a mobile station can also receive
MBMS data transmitted from a remote base station
(corresponding to the base station A in this example) and
can perform combining.
(2) Relay apparatus (relay node)
With a LTE-advanced system a relay node is
installed between a base station and a mobile station, for
example, for cell extension or as countermeasures for dead
spots.
FIG. 22 illustrates cell extension. A mobile
station 120 is outside a cell 100a of a base station 100.
A relay node 110 is installed within the cell 100a. The
mobile station 120 is within a relay area 110a in which
the relay node 110 can perform relay.
If a relay node such as the relay node 110 does not
exist, the mobile station 120 is outside the cell 100a and
cannot communicate with the base station 100. However, if
the relay node 110 is installed, the mobile station 120 is
within the relay area 110a of the relay node 110. Even if
the mobile station 120 is outside the cell 100a, radio
relay is performed via the relay node 110 and
communication can be performed between the base station
100 and the mobile station 120.
FIG. 23 illustrates countermeasures for a dead spot.
A relay node 110 is installed within a cell 100a of a base
station 100. There is a dead spot 110b within the cell
100a. A mobile station 120 is in the dead spot 110b. It
is assumed that a relay area 110a of the relay node 110
covers the dead spot 110b.
If a relay node such as the relay node 110 does not
exist and the mobile station 120 is in the dead spot 110b,
it is difficult for the mobile station 120 to communicate
with the base station 100. However, if the relay node 110
is installed and the relay area 110a of the relay node 110
covers the dead spot 110b, then radio relay is performed
via the relay node 110 and communication can be performed
between the base station 100 and the mobile station 120 in
the dead spot 110b.
The following technique is proposed in patent
document 1 as a conventional technique regarding a MBMS. A
mobile station estimates cell quality on the basis of the
difference in transmission power between a common pilot
channel and a common control channel and receives data
from an adjacent cell in which cell quality is the highest.
In addition, the following technique is proposed in
patent document 2 as a conventional radio relay technique.
A transmission apparatus hierarchizes and transmits a
relay apparatus signal which a relay apparatus retransmits
and a receiving apparatus signal transmitted directly to a
receiving apparatus. The relay apparatus demodulates the
relay apparatus signal, modulates it again, and
retransmits it.
Patent Document 1: Japanese Laid-open Patent
Publication No. 2008-503130 (Paragraphs [0015]-[ 0020], FIG.
1)
Patent Document 2: Japanese Laid-open Patent
Publication No. 10-032557 (Paragraphs [0019]-[ 0021], FIG.
1)
Disclosure of the Invention
Problem to be Solved by the Invention
With a MBMS radio network, as described above, a
relay node can be installed for performing cell extension
or taking countermeasures for a dead spot. In addition,
with a MBSFN a radio signal is transmitted by the use of
an extended CP which is longer than a normal CP used for
normal unicast transmission. Accordingly, a radio signal
transmitted from a base station distant from a mobile
station can be received via a relay node. As a result, the
possibility of receiving and combining more pieces of data
can be enhanced.
With a conventional MBMS radio network, however,
the problem of being unable to distinguish between unicast
data and MBMS data transmitted in a MBSFN exists.
FIG. 24 illustrates the problem of being unable to
distinguish between unicast data and MBMS data. There are
base stations 101 through 103, mobile stations 121 through
123, and a relay node 110. The base station 101 transmits
unicast data rl to the mobile station 121. The base
station 103 transmits unicast data r3 to the mobile
station 123. In addition, the base station 102 transmits
MBMS data r2 to the relay node 110 and the relay node 110
relay-transmits the MBMS data r2 to the mobile station 122.
With unicast data transmission the base station
scrambles unicast data so that the unicast data can be
distinguished from another piece of unicast data
transmitted by the use of the same radio resource. That is
to say, by using scrambling codes which differ in initial
value, the unicast data can be distinguished from another
piece of unicast data transmitted by the use of the same
radio resource. Accordingly, the unicast data rl and r3
indicated in FIG. 24 can be distinguished. In addition,
with MBSFN transmission plural pieces of MBMS data are
transmitted so that they can be distinguished. Therefore,
pieces of MBMS data can be distinguished. That is to say,
if the same communication format is used, pieces of data
can be distinguished.
However, unicast data and MBMS data differ in
communication format. In addition, there is no express
provision that unicast data and MBMS data differ in
scrambling code initial value. Accordingly, there is no
guarantee that unicast data and MBMS data can be
distinguished by scrambling codes. Furthermore, unicast
data and MBMS data may be transmitted at the same time by
the use of the same radio resource. As a result, in an
environment in which unicast data and MBMS data mingle, it
may be impossible to distinguish between them.
To be concrete, there is no guarantee that a
scrambling code for a PDSCH (Physical Downlink Shared
Channel), which is a radio channel used for transmitting
user data in unicast communication, and a scrambling code
for a PMCH (Physical Multicast Channel), which is a radio
channel used for transmitting user data in MBSFN
transmission can be distinguished. As a result, it may be
impossible to distinguish between a PDSCH and a PMCH. This
may cause interference.
In the case of FIG. 24, it is assumed that the
mobile station 121 is at a position where the mobile
station 121 can receive both the unicast data rl and the
MBMS data r2 and that the mobile station 123 is at a
position where the mobile station 123 can receive both the
unicast data r3 and the MBMS data r2.
In this environment, the mobile station 121 or 123
which originally wants to receive unicast data is unable
to distinguish MBMS data r2 transmitted from the relay
node 110, so that the MBMS data r2 becomes an interference
wave.
On the other hand, even if unicast data and MBMS
data can be distinguished for a certain period of time,
base stations or a base station and a relay node are not
necessarily synchronized. Accordingly, timing at which
scrambling begins, for example, in one base station
gradually deviates from timing at which scrambling begins
in the other base station. This degrades code
identification capability. As a result, it is impossible
to distinguish a PDSCH and a PMCH, and interference occurs.
FIG. 25 illustrates the occurrence of interference
caused by a timing deviation. A black slot indicates MBMS
data in MBSFN transmission and a white slot indicates
unicast data. In a state in which transmission sequences
Al and Bl can be distinguished, two pieces of MBMS data
are in the same timing, for example, at a timing Tl.
Accordingly, the two pieces of MBMS data can be
distinguished and interference does not occur. Two pieces
of unicast data are in the same timing at a timing T2.
Accordingly, the two pieces of unicast data can be
distinguished and interference does not occur.
On the other hand, it is assumed that the
transmission sequence Al changes to a transmission
sequence Ala due to a timing deviation. In this case, MBMS
data and unicast data are in the same timing in the
transmission sequences Ala and Bl at each of timings T3
through T6. Accordingly, the MBMS data and the unicast
data cannot be distinguished and interference occurs. This
degrades the transmission characteristics of one or both
of the MBMS data and the unicast data, resulting in
degradation in transmission quality.
The present invention was made to solve the above
problem. An object of the present invention is to provide
a radio communication system which can distinguish MBMS
data and unicast data, prevent interference, and improve a
radio transmission characteristic.
Means for Solving the Problem
In order to solve the above problem, there is
provided a radio communication system. This radio
communication system includes a first radio station which
performs communication by the use of a first radio signal,
a second radio station, and a third radio station which is
in an area common to a radio communication area of the
first radio station and a radio communication area of the
second radio station.
The second radio station includes a communication
format conversion unit which converts, at the time of
receiving a second radio signal on which scrambling which
cannot be distinguished from the first radio signal is
performed, a communication format of the second radio
signal. The communication format conversion unit generates
a third radio signal by performing scrambling which can be
distinguished from the first radio signal on the second
radio signal so as to convert a communication format, and
communicates with the third radio station by the use of
the third radio signal.
Advantageous Effects of the Invention
Radio transmission quality is improved.
The above and other objects, features and
advantages of the present invention will become apparent
from the following description when taken in conjunction
with the accompanying drawings which illustrate preferred
embodiments of the present invention by way of example.
Brief Description of the Drawings
FIG. 1 illustrates an example of the structure of a
radio communication system;
FIG. 2 illustrates an example of the structure of a
radio communication system;
FIG. 3 illustrates an example of the structure of a
radio communication system;
FIG. 4 illustrates a MBSFN network;
FIG. 5 is a sequence diagram of operation in the
MBSFN network;
FIG. 6 illustrates a radio communication system in
a MBSFN network;
FIG. 7 illustrates the replacement of a CP;
FIG. 8 illustrates the structure of a radio
communication system;
FIG. 9 illustrates the structure of a relay node;
FIG. 10 illustrates the structure of the relay
node;
FIG. 11 illustrates the structure of a mobile
station;
FIG. 12 illustrates the structure of a radio
communication system;
FIG. 13 is a sequence diagram of operation;
FIG. 14 illustrates the structure of a radio
communication system;
FIG. 15 illustrates the structure of a radio
communication system;
FIG. 16 is a sequence diagram of operation;
FIG. 17 illustrates the structure of a radio
communication system;
FIG. 18 is a sequence diagram of transmission of
MBMS data before normal MBSFN transmission timing;
FIG. 19 illustrates the structure of a radio
communication system;
FIG. 20 illustrates the format of radio data;
FIG. 21 illustrates data receiving and combining;
FIG. 22 illustrates cell extension;
FIG. 23 illustrates countermeasures for a dead
spot;
FIG. 24 illustrates the problem of being unable to
distinguish between unicast data and MBMS data; and
FIG. 25 illustrates the occurrence of interference
caused by a timing deviation.
Best Mode for Carrying out the Invention
Embodiments will now be described with reference to
the accompanying drawings. FIG. 1 illustrates an example
of the structure of a radio communication system. A radio
communication system 1 includes a radio station (first
radio station) lr, a radio station (second radio station)
2r, and a radio station (third radio station) 3r.
The radio station lr performs communication by the
use of a radio signal (first radio signal) dl. The radio
station 2r receives a radio signal (second radio signal)
d2 on which scrambling that cannot be distinguished from
the radio signal dl is performed. The radio station 2r
includes a communication format conversion unit 21. The
radio station 3r is in a radio communication area (cell)
of the radio station lr and a cell of the radio station 2r.
Being unable to distinguish the radio signal dl and
the radio signal d2 means being unable to distinguish a
code for scrambling which is performed on the radio signal
dl and a code for scrambling which is performed on the
radio signal d2.
When the communication format conversion unit 21
included in the radio station 2r receives the radio signal
d2, the communication format conversion unit 21 converts a
communication format of the radio signal d2 by performing
scrambling which can be distinguished from the radio
signal dl on the radio signal d2. By doing so, the
communication format conversion unit 21 generates a radio
signal d2a (third radio signal). The communication format
conversion unit 21 communicates with the radio station 3r
by the use of the radio signal d2a.
The contents themselves of a service signal in the
radio signal d2a are the same as those of a service signal
in the radio signal d2. However, the communication format
of the radio signal d2 is converted so that the radio
signals dl and d2a can be distinguished.
As has been described, even if the radio signals dl
and d2 cannot be distinguished, the communication format
conversion unit 21 converts the communication format of
the radio signal d2 to be distinguished from the radio
signal dl. The communication format conversion unit 21
communicates with the radio station 3r by the use of the
generated distinguishable radio signal d2a.
In order to make it possible to distinguish the
radio signals dl and d2, it is desirable that frames (or
slots included in frames) transmitted from the first and
second radio stations should be synchronized. In addition,
different radio resources may be used for the radio
signals dl and d2.
The radio signals dl and d2a can be distinguished,
so they do not interfere with each other. Therefore,
receiving quality at the radio station 3r and radio
transmission quality in the entire system can be improved.
FIG. 2 illustrates an example of the structure of a
radio communication system. A radio communication system
1A includes a base station (first base station) 10-1, a
base station (second base station) 10-2, a relay node 20,
and a mobile station 30.
The base station 10-1 performs communication by the
use of a radio signal (first radio signal) dl. The base
station 10-2 transmits a radio signal (second radio
signal) d2 which cannot be distinguished from the radio
signal dl. The relay node 20 includes a communication
format conversion unit 21 and relays the radio signal d2
transmitted from the base station 10-2.
The communication format conversion unit 21
converts a communication format of the radio signal d2 to
a communication format which can be distinguished from the
radio signal dl. That is to say, the communication format
conversion unit 21 generates a radio signal d2a in the
communication format after the conversion and communicates
with the mobile station 30 by the use of the radio signal
d2a.
If the relay node 20 relays the radio signal d2
received from the base station 10-2 to the mobile station
30 without changing its communication format, the radio
signals dl and d2 cannot be distinguished. Accordingly,
interference occurs.
With the radio communication system 1A, on the
other hand, the relay node 20 performs relay communication
by converting the communication format of the radio signal
d2 to a communication format which can be distinguished
from the radio signal dl and by generating the radio
signal d2a. As a result, the radio signals dl and d2a do
not interfere with each other. Therefore, receiving
quality at the mobile station 30 and radio transmission
quality in the entire system can be improved.
FIG. 3 illustrates an example of the structure of a
radio communication system. In a radio communication
system 1-1 a radio signal dl is a normal communication
signal dl and a radio signal d2 is a broadcast signal d2.
The structure of the radio communication system 1-1 is the
same as that of the radio communication system 1A
illustrated in FIG. 2.
When a communication format conversion unit 21
receives the broadcast signal d2, the communication format
conversion unit 21 converts a broadcast format which is a
communication format of the broadcast signal d2 to a
normal communication format which is a communication
format of the normal communication signal dl, and relay-
transmits the broadcast signal d2 in the normal
communication format.
A broadcast signal d2a the communication format of
which has been converted to the normal communication
format is transmitted to a mobile station 30. Even when
the mobile station 30 is in an environment in which the
mobile station 30 can receive both the normal
communication signal dl and the broadcast signal d2a, the
communication format (normal communication format) of the
normal communication signal dl is the same as that of the
broadcast signal d2a (that is to say, there is a guarantee
that radio signals in the same communication format can be
distinguished) and interference does not occur. Therefore,
receiving quality at the mobile station 30 and radio
transmission quality in the entire system can be improved.
In an example in which the radio communication
system 1-1 is applied to MBMS, the structure of a system
and operation will now be described. First the structure
of an entire MBSFN network to which the radio
communication system 1-1 is applied will be described.
FIG. 4 illustrates a MBSFN network. A MBSFN
network 40 includes a MBMS controller or MBMS control unit
(hereinafter generically named "MBMS controller") 41 which
is a MCE (Multi-Cell/Multicast Coordination Entity), a
MBMS GW (Gate Way) 42, BTSs (Base Transceiver Stations)
43a and 43b, and mobile stations 30-1 through 30-4.
A MBMS radio signal includes MBMS data and a
control signal (hereinafter referred to as a "MBMS control
signal") for receiving a MBMS. The MBMS controller 41
controls MBMS transmission for transmitting the MBMS
control signal to the MBMS GW 42 and the base transceiver
stations 43a and 43b. The MBMS GW 42 transmits the MBMS
data to the base transceiver stations 43a and 43b. The
MBMS GW 42 stores and manages the MBMS data and may be
referred to as a MBMS data storage unit.
FIG. 5 is a sequence diagram of operation in the
MBSFN network. The MBMS controller 41 performs scheduling
to determine MBMS data to be transmitted and its
transmission method (such as a modulation scheme, a coding
scheme, transmission timing, and a radio frequency to be
used) . The MBMS controller 41 then gives the MBMS GW 42
notice of information regarding the modulation scheme, the
coding scheme, and the like determined and a control
signal generated on the basis of the information.
In addition, the MBMS controller 41 requests the
MBMS GW 42 to transmit the MBMS data to base transceiver
stations. The MBMS GW 42 which receives the notice
transmits the control signal (MCCH: Multicast Control
Channel) and the MBMS data (MTCH: MBMS Traffic Channel) to
the base transceiver station. In addition, the MBMS GW 42
gives the base transceiver station notice of control
information, such as the transmission timing and the radio
frequency to be used, for MBSFN transmission.
The base transceiver station which receives the
notice of the control information, the MBMS data, and the
control signal performs MBSFN transmission in accordance
with the control information. A DF (Decode and Forward)
relay node (which performs processes such as demodulation,
error correction decoding, and re-coding and re-modulation
on a received radio signal and relays the resultant) which
receives the MBSFN transmission performs demodulation and
decoding, error correction, and recoding and remodulation
and transmits MBMS data obtained to a mobile station.
The MBMS data forms a MTCH which is a logical
channel, is mapped to a MCH (Multicast Channel) which is a
transport channel, and is radio-transmitted via a PMCH
which is a radio channel. When the MBMS data is
transmitted, scrambling is performed on the basis of an ID
(identifier) according to MBSFN area (see TS36.211).
The MBMS control signal is included in a MCCH which
is a logical channel, is mapped to a MCH which is a
transport channel, and is radio-transmitted via a PMCH
which is a radio channel.
The MBMS controller 41 performs scheduling, such as
resource assignment and determination of a MCS (Modulation
and Coding Scheme) and MBMS data transmission timing,
superimposes a scheduling result on the MBMS control
signal, and transmits it. The base transceiver stations
43a and 43b perform radio transmission on the basis of the
scheduling result.
The above MCS (which may also be referred to as AMC
(Adaptive Modulation and Coding)) means a modulation and
coding scheme. With the MCS a modulation scheme or a
coding rate is adaptively changed according to radio
channel quality and is used. The MCS includes attributes
such as a modulation scheme, a coding rate, and a
transmission rate.
With MCS1, for example, a modulation scheme is QPSK
(Quadrature Phase Shift Keying), a coding rate is 1/8, and
a transmission rate is 1.891 Mb/s. With MCS5 a modulation
scheme is 16QAM (Quadrature Amplitude Modulation) , a
coding rate is 1/2, and a transmission rate is 15.221 Mb/s
Usually an optimum MCS is selected according to the
receiving state of a mobile station.
The MBMS controller 41 selects one of a plurality
of MCSs. One method for selecting a MCS is to select a MCS
with a cell in which a propagation characteristic
(propagation environment) is most undesirable as reference
and to apply the same MCS selected in the whole of a MBSFN
area.
For example, if the determination that
communication is performed on the basis of MCS1 in a cell
in which a propagation characteristic is most undesirable
is made, then MCS1 is applied in all the other cells in a
MBSFN area (MCS1 is also applied in a cell in which a
propagation characteristic is good) . It is also possible
to set a certain MCS regardless of a propagation
environment.
The operation of a radio communication system in a
MBSFN network will now be described concretely.
Hereinafter description will be given with unicast data as
an example of a normal communication signal, a unicast
communication format as an example of a normal
communication format, MBMS data as an example of a
broadcast signal, and a MBSFN communication format as an
example of a broadcast format.
FIG. 6 illustrates a radio communication system in
a MBSFN network. A radio communication system la includes
a MBMS controller 41, a MBMS GW 42, base transceiver
stations 43a through 43c, a relay node 20, and mobile
stations 30-1 through 30-4. The relay node 20 includes a
communication format conversion unit 21.
The base transceiver station 43a transmits MBMS
data in the MBSFN communication format to the mobile
station 30-1 and the relay node 20. The base transceiver
station 43b transmits unicast data in the unicast
communication format to the mobile station 30-3. The base
transceiver station 43c transmits unicast data in the
unicast communication format to the mobile station 30-4.
When the communication format conversion unit 21
included in the relay node 20 receives the MBMS data in
the MBSFN communication format, the communication format
conversion unit 21 converts the MBSFN communication format
to the unicast communication format and transmits the MBMS
data in the unicast communication format.
It is assumed that the mobile station 30-2 receives
data relayed by the relay node 20 and that the mobile
station 30-2 is in an area where the mobile station 30-2
can also receive unicast data transmitted from the base
transceiver station 43b.
If the relay node 20 relay-transmits the MBMS data
in the MBSFN communication format to the mobile station
30-2 under these conditions, then the mobile station 30-2
receives both the MBMS data in the MBSFN communication
format and the unicast data in the unicast communication
format.
With the MBSFN communication format the MBMS data
is transmitted via a radio channel PMCH. With the unicast
communication format the unicast data is transmitted via a
radio channel PDSCH. However, there is no guarantee that a
code for scrambling performed on a PMCH and a code for
scrambling performed on a PDSCH can be distinguished.
Accordingly, it may be impossible to distinguish these
codes. As a result, the MBMS data interferes with the
unicast data at the mobile station 30-2.
On the other hand, it is assumed that the relay
node 20 includes the communication format conversion unit
21. When the communication format conversion unit 21
receives the MBMS data in the MBSFN communication format,
the communication format conversion unit 21 changes the
communication format of the MBMS data from the MBSFN
communication format to the unicast communication format
and relay-transmits the MBMS data in the unicast
communication format.
That is to say, the MBSFN communication format is
converted to the unicast communication format (radio data
format using an extended CP is converted to a radio data
format using a normal CP), so the MBMS data can be
transmitted not via a radio channel PMCH but via a radio
channel PDSCH.
As a result, the MBMS data in the unicast
communication format transmitted from the relay node 20
does not interfere with the unicast data in the unicast
communication format transmitted from the base transceiver
station 43b.
That is to say, the MBMS data and the unicast data
are transmitted via. radio channels PDSCH, so there is a
guarantee that the MBMS data and the unicast data can be
distinguished. This can prevent interference. Accordingly,
the mobile station 30-2 can sensitively receive the MBMS
data which is transmitted from the relay node 20 and which
the mobile station 30-2 originally wants to receive.
In the above description the communication format
conversion unit 21 changes the communication format of the
MBMS data from the MBSFN communication format to the
unicast communication format and relay-transmits the MBMS
data. By changing the communication format of the MBMS
data from the MBSFN communication format to a single cell
MBMS communication format and relay-transmitting the MBMS
data, however, the occurrence of interference can also be
prevented. A single cell MBMS will now be described.
With a LTE system not only MBSFN transmission but
also single cell MBMS transmission (term "single cell
transmission" is used in TS36.300, but in this
specification the term "single cell MBMS transmission" is
used for differentiating it from unicast transmission) by
which MBMS data is transmitted only to a specific cell is
discussed.
With the MBSFN transmission MBMS data is
transmitted to the whole of an area which is a group of
cells. With the single cell MBMS transmission, unlike the
MBSFN transmission, MBMS data is transmitted only to a
specific cell. Accordingly, there is no need for a
plurality of base transceiver stations to transmit the
same data at the same frequency at the same timing. As a
result, each base transceiver station performs scheduling.
Moreover, MBMS data is transmitted to one cell, so
propagation distance is short compared with the MBSFN
transmission. As a result, CP length can be made shorter.
In other words, a normal CP used in the unicast
communication can be used. This means that the unicast
transmission can be performed. That is to say,
transmission can be performed by the use of a PDSCH which
is a radio channel used in the unicast communication.
Therefore, when the communication format conversion
unit 21 receives the MBMS data in the MBSFN communication
format, the communication format conversion unit 21 may
convert the MBSFN communication format to the unicast
communication format or a single cell MBMS communication
format. By relay-transmitting the MBMS data in the unicast
communication format or the single cell MBMS communication
format, the occurrence of interference at the mobile
station can be prevented.
Format conversion (replacement of a redundant
portion (CP)) will now be described. FIG. 7 illustrates
the replacement of a CP. When the communication format
conversion unit 21 converts the MBSFN communication format
to the unicast communication format or the single cell
MBMS communication format, the communication format
conversion unit 21 performs data format conversion by
replacing an extended CP with a normal CP.
By adding a short normal CP to received data, the
amount of information which can be transmitted can be
increased by the use of an empty field (because (length of
normal CP) < (length of extended CP) or transmission can
be performed with a coding rate decreased and the number
of parity bits increased. As a result, a transmission
characteristic can be improved (transmission may be
performed with a coding rate unchanged and 0' s or 1' s
inserted into unused bits as padding characters).
The case where the unicast communication format is
converted to the MBSFN communication format will now be
described. FIG. 8 illustrates the structure of a radio
communication system. The structure of a radio
communication system la-0 is the same as that of the radio
communication system la illustrated in FIG. 6. In the case
of FIG. 8, however, the unicast communication format is
converted to the MBSFN communication format.
A base transceiver station 43a transmits unicast
data in the unicast communication format to a mobile
station 30-1 and a relay node 20. A base transceiver
station 43b transmits MBMS 'data in the MBSFN communication
format to a mobile station 30-3. A base transceiver
station 43c transmits MBMS data in the MBSFN communication
format to a mobile station 30-4.
When a communication format conversion unit 21
included in the relay node 20 receives the unicast data in
the unicast communication format, the communication format
conversion unit 21 converts the unicast communication
format to the MBSFN communication format and transmits the
unicast data in the MBSFN communication format (radio data
format using a normal CP is converted to a radio data
format using an extended CP).
As a result, the unicast data in the MBSFN
communication format transmitted from the relay node 20
does not interfere with the MBMS data in the MBSFN
communication format transmitted from the base transceiver
station 43b. A communication format conversion reverse to
that described in FIG. 6 can also be made in this way.
The structure of the relay node 20 will now be
described. Methods of relay by the relay node 20 are
broadly divided into an AF (Amplify and Forward) method
and the DF method. With the AF method a relay node
receives a radio signal transmitted from a base
transceiver station or a mobile station, amplifies the
received radio signal, and transmits a radio signal
obtained to a mobile station or a base transceiver station.
With the DF method, as described above, a relay
node receives a radio signal transmitted from a base
transceiver station or a mobile station, performs an error
correction process by demodulation and decoding, performs
coding and modulation again, and transmits a signal
obtained to a mobile station or a base transceiver station.
The structure of the relay node 20 having the DF function
will now be described.
FIGS. 9 and 10 illustrate the structure of the
relay node 20. The relay node 20 includes an antenna al, a
receiving unit 22a-l, a demodulation and decoding unit
22a-2, a radio channel quality information acquisition
unit 23a, a scheduler 24a, a channel setting unit 25a, an
uplink connection request signal extraction unit 26a-l, an
uplink connection request signal generation unit 26a-2, an
uplink transmission control signal generation unit 26a-3,
a channel quality measurement unit 27a-l, a channel
quality information generation unit 27a-2, a coding and
modulation unit 28a-l, and a transmission unit 28a-2.
In addition, the relay node 20 includes an antenna
a2, a receiving unit 22b-l, a demodulation and decoding
unit 22b-2, a downlink transmission control signal
extraction unit 23b-l, a MBMS control signal extraction
unit 23b-2, a downlink control signal generation unit 23b-
3, a MBSFN transmission control unit 23b-4, a transmitted
data buffer 24b, a communication format conversion.unit 21,
a coding and modulation unit 25b-l, and a transmission
unit 25b-2.
On the basis of a scheduling result, the receiving
unit 22a-l and the demodulation and decoding unit 22a-2
receive an uplink radio signal transmitted from a mobile
station via the antenna al, down-convert it, and
demodulate and decode an uplink signal after the down-
conversion.
The radio channel guality information collection
unit 23a collects radio channel quality information
(indicator of the quality of a radio channel between the
relay node and the mobile station) from the uplink signal
after the demodulation and decoding and transmits the
radio channel quality information to the scheduler 24a.
The uplink connection request signal extraction
unit 26a-l extracts an uplink connection request signal
from the uplink signal after the demodulation and decoding
and transmits the uplink connection request signal to the
channel setting unit 25a. When the channel setting unit
25a receives the uplink connection request signal, the
channel setting unit 25a transmits uplink connection
request signal generation instructions on the basis of the
scheduling result.
When the uplink connection request signal
generation unit 26a-2 receives the uplink connection
request signal generation instructions, the uplink
connection request signal generation unit 26a-2 generates
an uplink connection request signal. The uplink
transmission control signal generation unit 26a-3
generates an uplink transmission control signal on the
basis of the scheduling result.
The channel quality measurement unit 27a-l measures
the quality of a channel between a base transceiver
station and the relay node 20 and transmits a measurement
result to the channel quality information generation unit
27a-2. The channel quality information generation unit
27a-2 generates channel quality information on the basis
of the measurement result.
On the basis of the scheduling result, the coding
and modulation unit 28a-l and the transmission unit 28a-2
code and modulate the uplink connection request signal,
the uplink transmission control signal, and the channel
quality information, superimpose these signals on one
another, up-convert a signal obtained, and transmit the
signal to the base transceiver station via the antenna a2.
On the basis of information regarding coding and
modulation included in a downlink transmission control
signal, the receiving unit 22b-l and the demodulation and
decoding unit 22b-2 receive via the antenna a2 a downlink
radio signal transmitted from the base transceiver station,
down-convert it, and demodulate and decode a downlink
signal after the down-conversion. The downlink
transmission control signal extraction unit 23b-l extracts
the downlink transmission control signal from the downlink
signal and transmits it to the receiving unit 22b-l and
the demodulation and decoding unit 22b-2.
The MBMS control signal extraction unit 23b-2
extracts a MBMS control signal from the downlink signal
and transmits it to the MBSFN transmission control unit
23b-4. The MBSFN transmission control unit 23b-4 sets
MBSFN control in the scheduler 24a.
The transmitted data buffer 24b buffers the
downlink signal and outputs data on the basis of a
scheduling result. The communication format conversion
unit 21 converts the communication format of the downlink
signal after the buffering (MBSFN -> unicast, for example).
The downlink control signal generation unit 23b-3
generates a downlink control signal on the basis of the
scheduling result.
On the basis of the scheduling result, the coding
and modulation unit 25b-l and the transmission unit 25b-2
code and modulate the downlink control signal and the
downlink signal after the communication format conversion,
up-convert them, and transmit them to the mobile station
via the antenna al.
The structure of a mobile station will now be
described. FIG. 11 illustrates the structure of a mobile
station. A mobile station 30 includes an antenna a3 and a
receiving unit 31. It is assumed that the mobile station
30 is in an area where the mobile station 30 can receive a
radio signal (first radio signal) dl and a radio signal
(second radio signal) d2 which cannot be distinguished
from the radio signal dl.
When the receiving unit 31 receives the radio
signal dl, the receiving unit 31 performs a process for
receiving the radio signal dl. Alternatively, a
communication format of the radio signal d2 is converted
on the mobile station 30 side to a communication format
which can be distinguished from the radio signal dl, and
the receiving unit 31 performs a process for receiving a
radio signal d2a in the communication format after the
conversion.
Detailed operation in a radio communication system
will now be described. In a first embodiment operation
performed at the time of converting the MBSFN
communication format to the unicast communication format
and performing relay transmission will be described. A
relay node included in a radio communication system has a
MBMS scheduling function.
FIG. 12 illustrates the structure of a radio
communication system. A radio communication system la-1
includes a MBMS controller 41, a MBMS GW 42, base
transceiver stations 43a and 43b, a relay node 20a, and
mobile stations 30-1 through 30-3. The relay node 20a
includes a communication format conversion unit 21 and a
scheduler 2a.
The relay node 20a originally includes a scheduler
for unicast communication. However, the scheduler 2a has
not only a unicast communication scheduling function but
also a MBMS scheduling function.
The base transceiver station 43a transmits MBMS
data in the MBSFN communication format to the mobile
station 30-1 and the relay node 20a. The base transceiver
station 43b transmits unicast data in the unicast
communication format to the mobile station 30-3.
When the communication format conversion unit 21
included in the relay node 20a receives the MBMS data in
the MBSFN communication format, the communication format
conversion unit 21 converts the MBSFN communication format
to the unicast communication format and transmits the MBMS
data in the unicast communication format to the mobile
station 30-2.
The mobile station 30-2 requests the MBMS
controller 41 via the relay node 20a and the base
transceiver station 43a to relay MBSFN transmission. The
relay node 20a which receives the request requests the
MBMS controller 41 via the base transceiver station 43a to
relay MBSFN transmission and transmit MBMS control
information managed by the MBMS controller 41 to the relay
node 2 0a.
FIG. 13 is a sequence diagram of operation. In FIG.
13, it is assumed that a relay request from a mobile
station is transmitted to at least a DF relay node, that
the relay request is transmitted to a base transceiver
station via the DF relay node, and that the relay request
is transmitted to a MBMS controller via the base
transceiver station.
The MBMS controller which receives the relay
request transmits MBSFN transmission information
(information indicative of the type of transmitted MBMS
data, the MBMS data which has already been transmitted,
and the like) held by the MBMS controller to the DF relay
node so that the DF relay node will change the
communication format of received MBMS data from the MBSFN
communication format to the unicast communication format
and so that the DF relay node will transmit the MBMS data
to the mobile station. In FIG. 13, the MBMS controller
transmits the MBSFN transmission information before
scheduling. However, the MBMS controller may transmit the
MBSFN transmission information after scheduling.
In addition, the mobile station may transmit radio
channel quality information to the DF relay node after
MBSFN transmission from the base transceiver station to
the DF relay node. Furthermore, it is necessary that the
DF relay node should give the mobile station notice of
relay start timing before unicast communication. MBMS data
is transmitted to the DF relay node by the MBSFN
transmission.
On the basis of the radio channel quality
information transmitted from the mobile station, the DF
relay node which receives the MBMS data generates MBMS
control information to be transmitted to the mobile
station by the use of at least one of MBMS control
information transmitted from the MBMS controller and MBMS
control information included in the MBMS data transmitted
from the base transceiver station. The DF relay node
transmits the MBMS control information to the mobile
station as control information for unicast communication
and then transmits the MBMS data.
The MBMS controller which receives a request to
transmit the MBMS control information transmits the MBMS
control information including, for example, information
regarding a service received by the mobile station to the
DF relay node via the base transceiver station. Control
information indicative of a part of service data which has
already been received by the mobile station can be taken
as a concrete example of the MBMS control information
regarding the service. This control information is
important in maintaining the continuity of the service.
On the basis of the above MBMS control information,
the DF relay node generates a MBMS control signal and
generates a MCCH which is a logical channel. This MCCH is
mapped to a MCH which is a transport channel, and is
radio-transmitted via a PMCH which is a radio channel.
If MBMS control information is not transmitted from
the MBMS controller or if the DF relay node cannot
generate a MBMS control signal (cannot generate a MCCH,
for example) , then the DF relay node informs the mobile
station that it cannot relay MBSFN transmission, and does
not relay MBSFN transmission.
If the number of mobile stations which request
MBSFN transmission relay is smaller or greater than a
threshold set in advance, then the DF relay node does not
relay MBSFN transmission and informs the mobile stations
that the DF relay node does not relay MBSFN transmission.
A mobile station which is informed that the DF
relay node cannot relay MBSFN transmission performs hand-
over to another relay node or the base transceiver station.
To be concrete, the mobile station measures receiving
power from other relay nodes or the base transceiver
station and selects a relay node or the base transceiver
station from which receiving power is the highest as a
hand-over destination, and performs hand-over to it.
On the basis of the channel quality (or an
indicator of the quality) of a downlink between the relay
node 20a and the mobile station 30-2 transmitted from the
mobile station 30-2, the scheduler 2a included in the
relay node 20a then performs scheduling in the same way
that is used for transmitting unicast data between the
relay node 20a and the mobile station 30-2. The scheduler
2a determines radio resources for transmitting MBMS data
and a MBMS control signal and a modulation scheme.
The scheduler 2a may equally perform scheduling of
unicast data and relayed MBMS data or preferentially
perform scheduling of unicast data or relayed MBMS data.
In addition, the scheduler 2a may perform scheduling of
unicast data communication and MBMS data communication
separately.
As stated above, the relay node 20a receives the
MBMS control information and performs scheduling. If the
relay node 20a can relay MBSFN transmission as a result of
scheduling, then the relay node 20a informs the mobile
station 30-2 which makes a request to relay MBSFN
transmission that the relay node 20a can relay MBSFN
transmission.
That is to say, the relay node 20a uses control
information for giving the mobile station 30-2 notice that
the relay node 20a relays the MBMS data in the unicast
communication format. The mobile station 30-2 which
receives the notice receives a downlink physical control
channel (DPCCH). By doing so, the mobile station 30-2
extracts control information (MCS and the like) for
downlink unicast data communication and receives a
downlink radio channel PDSCH including the MBMS data in
accordance with the MBMS control information.
If the mobile station 30-2 which receives the PDSCH
radio channel can receive the MBMS data without errors,
then the mobile station 30-2 returns an ACK to the relay
node 20a. If the mobile station 30-2 receives the MBMS
data including errors, then the mobile station 30-2
returns a NACK to the relay node 20a (MBMS data relay
method in which an ACK or a NACK is not returned can be
adopted).
A process performed for relaying MBMS data will now
be described. When the relay node 20a receives MBMS data
transmitted from the base transceiver station 43a, the
relay node 20a converts the received data mapped to a slot
format using an extended CP to a slot format using a
normal CP. The relay node 20a then performs coding and
modulation on the data and transmits the data to the
mobile station 30-2.
On the basis of a transmission control signal
transmitted from the relay node 20a by the use of a DPCCH,
the mobile station 30-2 sets a demodulation scheme and a
decoding scheme. By receiving a PDSCH by which unicast
data is transmitted, the mobile station 30-2 receives the
MBMS data.
In the above description the mobile station 30-2
makes a request via the relay node 20a to relay MBSFN
transmission. As a result of hand-over, however, the base
transceiver station or its upper radio channel control
station may request the relay node 20a to relay MBSFN
transmission.
Furthermore, the relay node 20a generates a MCCH.
However, the following method may be used. The relay node
20a manages the MBMS control information. When the relay
node 20a transmits the MBMS data, the relay node 20a
informs the MBMS controller 41 of the MBMS control
information and the MBMS controller 41 generates a MCCH.
As has been described, the relay node 20a relays
MBMS data which it receives to the mobile station 30-2 in
the unicast communication format. As a result, it is
possible to relay the MBMS data without causing
interference.
In addition, a radio data format using an extended
CP is converted to a radio data format using a normal CP
at communication format conversion time. As a result,
transmission can be performed with a coding rate decreased
and the number of parity bits increased. Therefore, a
transmission characteristic or a transmission rate can be
improved.
Moreover, on the basis of the quality of a downlink
between the relay node 20a and the mobile station 30-2
transmitted from the mobile station 30-2, scheduling is
performed in the same way that is used for transmitting
unicast data between the relay node 20a and the mobile
station 30-2. By doing so, an optimum transmission method
can be selected. As a result, a transmission
characteristic or a transmission rate can be improved.
Operation for converting the MBSFN communication
format to the single cell MBMS communication format and
performing relay transmission will now be described as a
second embodiment. FIG. 14 illustrates the structure of a
radio communication system. The structure of a radio
communication system la-2 is the same as that of the radio
communication system la-1 illustrated in FIG. 12. The
radio communication system la-2 differs from the radio
communication system la-1 in that a communication format
conversion unit 21 converts the MBSFN communication format
to the single cell MBMS communication format.
A mobile station 30-2 makes a request to relay
MBSFN transmission. A base transceiver station 43a
requests a MBMS controller 41 to transmit MBMS control
information to a relay node 20a. This is the same with the
first embodiment.
The MBMS controller 41 which is requested to
transmit the MBMS control information transmits the MBMS
control information to the relay node 20a in response to
the request. On the basis of the transmitted MBMS control
information, the relay node 20a generates a control signal
and generates a MCCH which is a logical channel. The relay
node 20a maps this MCCH to a DL-SCH (Downlink Shared
Channel) which is a transport channel, and performs single
cell MBMS transmission by the use of a PMCH which is a
radio channel.
With single cell MBMS transmission a short CP can
be used. This is the same with unicast transmission.
Accordingly, the relay node 20a receives MBMS data
transmitted from the base transceiver station 43a by the
use of an extended CP, and performs demodulation and
decoding. After that, the relay node 20a converts the
format of the MBMS data to the format using a normal CP,
performs coding and modulation on the MBMS data, and
transmits the MBMS data to the mobile station 30-2. This
is the same with the first embodiment.
A third embodiment will now be described. In the
third embodiment a base transceiver station carries out a
MBMS scheduling function. In addition, a plurality of
relay nodes is installed.
FIG. 15 illustrates the structure of a radio
communication system. A radio communication system la-3
includes a MBMS controller 41, a MBMS GW 42, base
transceiver stations 43a-l and 43b, a relay node RN, and
mobile stations 30-1 through 30-3. The base transceiver
station 43a-l includes a MBMS scheduler 4.
AF relay nodes RNAF and DF relay nodes RNDF may
mingle. The case where AF relay nodes RNAF and DF relay
nodes RNDF mingle in a cell of the base transceiver station
43a-l or one DF relay node is in a cell of the base
transceiver station 43a-l (FIG. 15 indicates a relay node
group in which AF relay nodes RNAF and DF relay nodes RNDF
mingle as a relay node RN) and where the base transceiver
station 43a-l performs scheduling of communication between
all the relay nodes and the mobile station 30-2 will be
described (AF relay node does not perform demodulation or
decoding, so it does not carry out communication format
conversion).
FIG. 16 is a sequence diagram of operation. FIG.
16 is an example of a process performed in the case of
centralized scheduling. In three respects FIGS. 16 and 13
differ. Firstly, a mobile station transmits information
(radio channel quality information) indicative of the
quality of a radio channel between a DF relay node and the
mobile station to a base transceiver station via the DF
relay node.Secondly, the base transceiver station performs
whole scheduling of communication by all mobile stations
including a mobile station under the control of the DF
relay node and a mobile station which communicates
directly with the base transceiver station on the basis of
the radio channel quality information, information
indicative of the quality of a radio channel between the
base transceiver station and the mobile station which
communicates directly with the base transceiver station,
and the like. The quality of the radio channel between the
base transceiver station and the mobile station which
communicates directly with the base transceiver station is
measured by this mobile station. Thirdly, control
information regarding a MBSFN transmission relay method
determined as a result of the scheduling and MBMS data are
transmitted to the mobile station via the DF relay node.
The following method is also discussed as a method
for scheduling communication between the relay node RN and
the mobile station 30-2. The base transceiver station 43a-
1 performs whole scheduling of communication by the relay
node RN in the cell of the base transceiver station 43a-l.
The base transceiver station 43a-l performs in this
way scheduling of transmission and receiving by one or
more relay nodes RN which are in the cell of the base
transceiver station 43a-l and which perform relay. This
method is referred to as centralized scheduling in the
sense that a central base transceiver station performs
scheduling.
In unicast transmission or single cell MBMS
transmission information indicative of the quality of a
radio channel between the relay node RN and the mobile
station 30-2 transmitted from the mobile station 30-2 to
the relay node RN is transmitted from the relay node RN to
the base transceiver station 43a-l.
The base transceiver station 43a-l collects radio
channel quality information transmitted from DF relay
nodes RNDf and the mobile station 30-1 with which the base
transceiver station 43a-l directly communicates in the
scheduler 4 and perform scheduling. The base transceiver
station 43a-l then transmits scheduling information to
each DF relay node RNDF by the use of a radio channel.
A DF relay node RNDF which receives the scheduling
information generates a control signal on the basis of
MBMS control information and generates a MCCH which is a
logical channel. The DF relay node RNDF maps this MCCH to
a MCH which is a transport channel, and radio-transmits
the MCH by the use of a PMCH which is a radio channel.
When the DF relay node RNDF receives MBMS data, changes its
communication format to the unicast communication format
or the single cell MBMS communication format, and
transmits the MBMS data to the mobile station 30-2.
A fourth embodiment will now be described. In the
above description MBSFN transmission is performed between
the base transceiver station and the relay node. In the
fourth embodiment, however, unicast transmission is
performed between a base transceiver station and a relay
node and MBSFN transmission is performed between the relay
node and a mobile station.
FIG. 17 illustrates the structure of a radio
communication system. A radio communication system la-4
includes a MBMS controller 41, a MBMS GW 42, base
transceiver stations 43a-2, 43b, and 43c, a relay node 20b,
and mobile stations 30-1 through 30-3.
The base transceiver station 43c transmits unicast
data in the unicast communication format to the mobile
station 30-1. The base transceiver station 43b transmits
MBMS data in the MBSFN communication format to the mobile
stations 30-2 and 30-3.
The base transceiver station 43a-2 includes a
communication format conversion unit 21-1 and the relay
node 20b includes a communication format conversion unit
21-2. The communication format conversion unit 21-1
included in the base transceiver station 43a-2 converts
the MBSFN communication format to the unicast
communication format and transmits MBMS data in the
unicast communication format. The communication format
conversion unit 21-2 included in the relay node 20b
converts the unicast communication format to the MBSFN
communication format and transmits the MBMS data in the
MBSFN communication format.
Operation will be described. When a relay of MBSFN
transmission is requested from the mobile station 30-2 to
the relay node 20b, the relay node 20b gives the base
transceiver station 43a-2 and the MBMS controller 41 a
notice of this request. The MBMS controller 41 which
receives the notice gives the MBMS GW 42 instructions to
transmit MBMS data to be transmitted to the mobile station
30-2 and the relay node 20b for relay to the base
transceiver station 43a-2 (at least at a time
corresponding to a delay caused by a relay process
performed by the relay node 20b, for example) before
normal MBSFN transmission timing.
The base transceiver station 43a-2 receives the
MBMS data and the communication format conversion unit 21-
1 included in the base transceiver station 43a-2 converts
the format including an extended CP used for normal MBSFN
transmission to the format including a normal CP. The base
transceiver station 43a-2 transmits the MBMS data in the
unicast communication format to the relay node 20b.
The relay node 20b receives the MBMS data in the
unicast communication format and the communication format
conversion unit 21-2 included in the relay node 20b
converts the format using a normal CP to the format
including an extended CP. The relay node 20b transmits the
MBMS data in the MBSFN communication format to the mobile
station 30-2.
As a result, it is possible to perform MBSFN
transmission between the base transceiver station 43a-2
and the relay node 20b without interfering with
communication between the base transceiver station 43b and the
mobile station 30-2. In addition, the base transceiver station
43a-2 transmits the MBMS data before normal MBSFN transmission
timing, so the mobile station 30-2 can receive and combine the
MBMS data transmitted via the relay node 2 0b and the MBMS data
transmitted from the base transceiver station 43b.
FIG. 18 is a sequence diagram of transmission of MBMS
data before normal MBSFN transmission timing.
(51) The base transceiver station 43a-2 transmits MBMS
data in the unicast communication format to the relay node 20b,
for example, at least at a time corresponding to a delay caused
by a relay process performed by the relay node 20b (a time
corresponding to a delay caused by a series of processes, that
is to say, by a demodulation and decoding process and a coding
and modulation process performed by the relay node 20b which is,
for example, a DF relay node) before normal MBSFN transmission
timing.
(52) The relay node 20b performs the demodulation and
decoding process and the coding and modulation process on the
MBMS data.
(53) The communication format conversion unit 21-2
included in the relay node 20b converts the unicast
communication format to the MBSFN communication format and
converts the format using a normal CP to the format using an
extended CP.
(54) The relay node 20b transmits the MBMS data in the
MBSFN communication format to the mobile station 30-2.
(55) The base transceiver station 43b transmits the
MBMS data in the MBSFN communication format to the mobile
station 30-2.
(56) The mobile station 30-2 receives and
synthesizes the MBMS data transmitted via the relay node
20b and the MBMS data transmitted from the base
transceiver station 43b.
In the above sequence diagram the base transceiver
station 43a-2 transmits MBMS data in the unicast
communication format before normal MBSFN transmission
timing and the relay node 20b converts the unicast
communication format to the MBSFN communication format.
However, when the base transceiver station 43a-2 transmits
MBMS data in the MBSFN communication format before normal
MBSFN transmission timing, the relay node 20b also
converts the MBSFN communication format to the unicast
communication format.
A modification of the above radio communication
systems will now be described. In the above description
the format using an extended CP is used for MBSFN
transmission for the purpose of making it easy to receive
MBSFN transmission from a remote base transceiver station
and increasing the number of pieces of MBMS data which can
be received and synthesized, that is to say, for the
purpose of making it possible to receive MBMS data for
which a propagation delay is long.
The fact that the use of an extended CP makes it
possible to receive MBMS data for which a propagation
delay is long shows that the radius of a cell can be
increased. Accordingly, in the modification an extended CP
is used for transmitting data which is not limited to MBMS
data in a cell that is wider than a cell in which a normal
CP is used.
If a relay node is installed in a cell with a long
radius in the modification, then the relay node performs
communication by the use of a normal CP because the radius
of a cell of the relay node is short for its use.
FIG. 19 illustrates the structure of a radio
communication system. A radio communication system lb
includes a base transceiver station 43a, a relay node 20c,
and mobile stations 30-1 and 30-2 (MBMS controller 41, a
MBMS GW 42, and the like are not illustrated) . The relay
node 20c includes a radio transmission and receiving unit
2c-l and a communication format conversion unit 2c-2.
A cell 51 is a cell of the base transceiver station
43a and a cell 52 is a relay area of the relay node 20c.
The relay node 20c and the mobile station 30-1 are within
the cell 51. The mobile station 30-2 is outside the cell
51 and is within the cell 52.
The radio transmission and receiving unit 2c-l
performs a radio transmission and receiving process with
the base transceiver station 43a or the mobile station 30-
2. When the communication format conversion unit 2c-2
communicates with the base transceiver station 43a, the
communication format conversion unit 2c-2 performs
communication by the use of a first radio data format
using a first redundant portion (extended CP, for example)
When the communication format conversion unit 2c-2
communicates with the mobile station 30-2, the
communication format conversion unit 2c-2 performs
communication by the use of a second radio data format
using a second redundant portion (normal CP, for example)
that is shorter than the first redundant portion.
In downlink transmission the base transceiver
station 43a transmits data Dl in the format using an
extended CP. When the relay node 20c receives the data Dl,
the communication format conversion unit 2c-2 transmits
data D2 the format of which is converted to the format
using a normal CP to the mobile station 30-2.
In uplink transmission the mobile station 30-2
transmits data D2 in the format using a normal CP to the
relay node 20c. When the relay node 20c receives the data
D2, the communication format conversion unit 2c-2
generates data Dl by converting the format to the format
using an extended CP, and transmits the data Dl to the
base transceiver station 43a.
As a result, the mobile station 30-1 within the
cell 51 receives data in the format using an extended CP,
so the mobile station 30-1 receives and synthesizes plural
pieces of data. Accordingly, receiving quality can be
improved. In addition, the relay node 20c relays data in
the format using a normal CP to the mobile station 30-2,
so transmission can be performed with a coding rate
decreased and the number of parity bits increased.
Therefore, a transmission characteristic can be improved.
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.
Explanation of Reference Signs
1 radio communication system
lr, 2r, 3r radio station
21 communication format conversion unit
dl, d2, d2a radio signal
CLAIMS
1. A radio communication system comprising:
a first radio station which performs communication
by the use of a first radio signal;
a second radio station; and
a third radio station which is in an area common to
a radio communication area of the first radio station and
a radio communication area of the second radio station,
wherein:
the second radio station includes a communication
format conversion unit which converts, upon receiving a
second radio signal which is a scrambled radio signal and
is indistinguishable from the first radio signal, a
communication format of the second radio signal; and
the communication format conversion unit generates
a third radio signal by converting a communication format
of a scrambled radio signal which is based on the second
radio signal and is distinguishable from the first radio
signal, and communicates with the third radio station by
the use of the third radio signal.
2. A radio communication system comprising:
a first base station which performs communication
by the use of a first radio signal;
a second base station which transmits a second
radio signal which is a scrambled radio signal and is
distinguishable from from the first radio signal;
a relay node which performs a relay process on the
second radio signal; and
a mobile station which is within a radio
communication area of the first base station and a relay
area of the relay node,
wherein:
the relay node includes a communication format
conversion unit which converts a communication format of
the second radio signal; and
the communication format conversion unit generates
a third radio signal by converting a communication format
of a scrambled radio signal which is based on the second
radio signal and is distinguishable from the first radio
signal, and relay-communicates with the mobile station by
the use of the third radio signal.
3. The radio communication system according to
claim 2, wherein when the communication format conversion
unit converts the communication format of the second radio
signal to a communication format of the first radio signal,
the communication format conversion unit replaces a
redundant portion added to the second radio signal with a
redundant portion used in the first radio signal and
generates the third radio signal.
4. The radio communication system according to
claim 2, wherein:
the first radio signal is a normal communication
signal and the second radio signal is a broadcast signal;
and
the communication format conversion unit converts a
broadcast format which is a communication format of the
broadcast signal to a normal communication format which is
a communication format of the normal communication signal,
and generates the broadcast signal in the normal
communication format as the third radio signal.
5. The radio communication system according to
claim 4, wherein the communication format conversion unit
replaces, at the time of converting the broadcast format
to the normal communication format, a first redundant
portion added to the broadcast signal with a second
redundant portion used in the normal communication signal,
and transmits the broadcast signal to which the second
redundant portion is added as the third radio signal.
6. The radio communication system according to
claim 2, wherein:
the first radio signal is a broadcast signal and
the second radio signal is a normal communication signal;
and
the communication format conversion unit converts a
normal communication format which is a communication
format of the normal communication signal to a broadcast
format which is a communication format of the broadcast
signal, and generates the normal communication signal in
the broadcast format as the third radio signal.
7. The radio communication system according to
claim 6, wherein the communication format conversion unit
replaces, at the time of converting the normal
communication format to the broadcast format, a first
redundant portion added to the normal communication signal
with a second redundant portion used in the broadcast
signal, and transmits the normal communication signal to
which the second redundant portion is added as the third
radio signal.
8. The radio communication system according to
claim 2, wherein:
the first radio signal is unicast data and the
second radio signal is MBMS data; and
the communication format conversion unit converts a
MBSFN communication format which is a communication format
of the MBMS data to a unicast communication format which
is a communication format of the unicast data or a single
cell MBMS communication format, and generates the MBMS
data in the unicast communication format or the single
cell MBMS communication format as the third radio signal.
9. The radio communication system according to
claim 8, wherein the communication format conversion unit
replaces, at the time of converting the MBSFN
communication format to the unicast communication format
or the single cell MBMS communication format, an extended
CP which is a redundant portion added to data at MBSFN
transmission time with a normal CP which is a redundant
portion shorter than the extended CP, and transmits the
MBMS data to which the normal CP is added as the third
radio signal.
10. The radio communication system according to
claim 2, wherein:
the first radio signal is MBMS data and the second
radio signal is unicast data or single cell MBMS data; and
the communication format conversion unit converts a
unicast communication format which is a communication
format of the unicast data or a single cell MBMS
communication format which is a communication format of
the single cell MBMS data to a MBSFN communication format
which is a communication format of the MBMS data, and
generates the unicast data or the single cell MBMS data in
the MBSFN communication format as the third radio signal.
11. The radio communication system according to
claim 10, wherein the communication format conversion unit
replaces, at the time of converting the unicast
communication format or the single cell MBMS communication
format to the MBSFN communication format, a normal CP
which is a redundant portion added to data at unicast data
or single cell MBMS data transmission time with an
extended CP which is a redundant portion longer than the
normal CP, and transmits the unicast data or the single
cell MBMS data to which the extended CP is added as the
third radio signal.
12. The radio communication system according to
claim 2, wherein the second base station transmits the
second radio signal to the relay node at a time
corresponding to a delay caused by the relay process
performed by the relay node.
13. A relay node comprising:
a receiving unit which receives a first radio
signal; and
a communication format conversion unit which
converts a communication format of the first radio signal,
wherein when a radio station is in an area where
the radio station can receive a second radio signal and
the first radio signal which is a scrambled radio signal
and is indistinguishable from the second radio signal, the
communication format conversion unit generates a third
radio signal by converting a communication format of a
scrambled radio signal which is based on the first radio
signal and is distinguishable from the second radio signal,
and communicates with the radio station by the use of the
third radio signal.
14. A mobile station comprising:
an antenna; and
a receiving unit which performs a process for
receiving a radio signal received via the antenna,
wherein when the mobile station is in an area where
the mobile station can receive a first radio signal and a
second radio signal which is a scrambled radio signal and
is indistinguishable from the first radio signal, the
receiving unit performs a process for receiving the first
radio signal or performs a process for receiving the
second radio signal in a converted communication format
which is generated on a transceiver side and is
distinguishable from the first radio signal.
15. A radio communication method comprising:
performing, by a first base station, communication
by the use of a first radio signal;
transmitting, by a second base station, a second
radio signal which is a scrambled radio signal and is
indistinguishable from the first radio signal is
performed;
performing, by a relay node, a relay process on the
second radio signal, wherein
a mobile station is within a radio
communication area of the first base station and a
relay area of the relay node, and
the relay node includes a communication
format conversion unit which converts a
communication format of the second radio signal;
and
generating, by the communication format conversion
unit, a third radio signal by converting a communication
format of a scrambled radio signal which is based on the
second radio signal and is distinguishable from the first
radio signal, and communicating with a third radio station
by the use of the third radio signal.
16. A radio communication system comprising:
a base station;
a relay node which is within a radio communication
area of the base station; and
a mobile station which is within a relay area of
the relay node,
wherein:
communication is performed between the base station
and the relay node in a first radio format using a first
redundant portion; and
communication is performed between the relay node
and the mobile station in a second radio format using a
second redundant portion shorter than the first redundant
portion.
17. A radio apparatus for communicating with a
first radio station and a second radio station, the
apparatus comprising:
a radio transmission and receiving unit which
performs a transmission and receiving process with the
first radio station and the second radio station; and
a communication format conversion unit which
performs, at the time of communicating with the first
radio station, communication by the use of a first radio
format using a first redundant portion and which performs,
at the time of communicating with the second radio station,
communication by the use of a second radio format using a
second redundant portion shorter than the first redundant
portion.

Interference is prevented and radio transmission
quality is improved.
A radio station (1r) performs communication by the
use of a radio signal (d1). A radio station (2r) receives
a radio signal (d2) which is indistinguishable from the
radio signal (dl). A radio station (3r) is in a radio
communication area of the radio station (1r) and a radio
communication area of the radio station (2r) . A
communication format conversion unit (21) generates a
radio signal (d2a) by converting a communication format of
the radio signal (d2) to a communication format which is
distinguishable from the radio signal (dl), and
communicates with the radio station (3r) by the use of the
radio signal (d2a).