DESCRIPTION
WIRELESS COMMUNICATION DEVICE
Technical Field
The present invention relates to a wireless communication
device for transmitting a random access signal when a mobile
terminal synchronizes itself with a base station.
Background Art:
In EUTRAN (Evolved UTRAN), which is currently being
examined as the next generation system according to the 3GPP,
a handover performed between different cells respectively
covered by different base stations in response to the moving
of a mobile terminal station is handled as a hard handover. In
order to perform a hard handover, a line that connects a mobile
terminal and a base station before the moving of the mobile
terminal is disconnected, and thereafter a line between the
mobile terminal and another base station covering the movement
destination is connected. Although a handover can be performed
in a short period even when that handover is a hard handover
by obtaining system information on the base station covering
the movement destination immediately before performing the
handover, the transmission of user data is interrupted during
the handover.
In the EUTRAN, the usage of a CAZAC (Constant Amplitude
Zero Auto Correlation) sequence as a sign used in the preamble
portion of a data frame is dominant. The preamble portion of
a data frame contains a random access signal transmitted in an
uplink line. A Zadoff-Chu sequence, a GCL sequence, etc. can
be used as a CAZAC sequence. An expression expressing a
Zadoff-Chu sequence is given below, where L represents a
sequence length, and k represents a sequence index.
Particularly when the length 1 is a prime number, an excellent
autocorrelation characteristic and a cross-correlation
characteristic are obtained.

[Expression 1]

Fig. 1 is a block diagram illustrating an example of a
circuit generating, from a CAZAC sequence, a preamble portion
of a random access signal used in a wireless uplink according
to the EUTRAN.
A CAZAC sequence with a length of M(L) is subject to a
serial/parallel conversion, and is input into a DFT unit 10,
and thereafter is Fourier-transformed into a parallel signal
with parallel number M. This signal is input into a subcarrier
mapping unit 11, and is mapped into N subcarriers. The
subcarrier signals obtained by mapping the CAZAC sequence are
input into an IFFT unit 12, and are subject to an inverse Fourier
transform, and thereafter are input into a parallel/serial
conversion unit 13. A signal with parallel number N output from
the IFFT unit 12 is converted into a serial signal by the
parallel/serial conversion unit 13, and is output as a random
access preamble sequence.
Further, according to the EUTRAN, the maximum system
bandwidth (a sending/receiving bandwidth used in a wireless
transmission line by base stations) for transmission and
reception in the radio section is 20MHz, and the
transmission/reception minimum bandwidth for terminal
stations is currently set to be 10MHz. This means that terminal
stations are capable of transmitting and receiving signals
having a bandwidth of at least 10MHz. Also, it is considered
that cells can be arranged in such a manner that base stations
having different system bandwidths are adjacent to each other.
In order to permit terminal stations to perform the initial
search and to become a handover target easily regardless of the
system bandwidths, synchronization channels and broadcast

signal channels (a broadcast signal channel is a channel for
transmitting information on cells and base stations, and is
referred to as a broadcast channel hereinafter) are arranged
around the middle of the downlink transmission bandwidth.
However, it is also considered that synchronization channels
can be arranged at two or three; portions in a transmission
bandwidth when the system transmission bandwidth is 20MHz.
This is based on the consideration of the existence of a mobile
terminal station transmitting and receiving signals having a
bandwidth of 10MHz.
In any of the cases described above, synchronization
channels are not always inserted into all subframes, and a
synchronization channel is set to be inserted into every 5, 10
or 20 subframes to be transmitted.
According to the EUTRAN, a handover between adjacent
cells covered by different base stations is handled as a hard
handover, and in a hard handover, when a mobile terminal station
starts a handover while it is transmitting data, a downlink
transmission being performed targeting that mobile terminal
station is interrupted, and the downlink data is transferred
to the base station in the handover destination from the base
station that has been communicating with that mobile terminal
device. Also, a buffer in a base station has to accumulate the
downlink data for the mobile terminal device until the handover
is completed, and as a period required for performing a handover
becomes longer, the amount of data that is accumulated in a
buffer increases as well. Similarly, uplink data to be
transmitted from the mobile terminal station to the base station
has to be prevented from being transmitted when a handover has
started, and has to be accumulated in a buffer in a mobile
terminal station. In such a case, some data may be discarded
in a process of the handover, which requires retransmission
using a higher-level layer in the case of normal data. Further,
when a handover has started with successive pieces of data being
transmitted on the basis of the HARQ (Hybrid Automatic Repeat

request), the order of sequence numbers assigned to the
successive pieces of data may be changed. Also, when a handover
is performed while an audio communication is being performed
using speech packets, the downlink speech packets are
transferred to the base station in the handover destination;
however, it is impossible to avoid an interruption. Also, audio
communication is real time communication, and accordingly all
speech packets transferred are not always utilized effectively
in the transfer destination.
Because of the above facts, it is not desirable for a
handover to consume a long period of time regardless of whether
data being transmitted is normal data or speech packets.
In a process of a handover, a terminal station has to
capture a downlink synchronization channel transmitted from the
base station in the handover destination, has to synchronize
itself with the base station, and has to transmit a random access
signal in an uplink channel. If a random access signal can be
transmitted immediately after the completion of the downlink
synchronization, time consumed by a handover can be reduced.
Also, when CAZAC sequences are used as the preamble
portions of random access signals, the values of the PAPR
(peak-to-average power ratio) of the preamble portions vary
depending upon the values of the index k even when the length
1 of the CAZAC sequences used does not vary.
Fig. 2 depicts a PAPR characteristic of a preamble signal
having a bandwidth of 5MHz and using a Zadoff-Chu sequence.
The sequence length of the Zadoff-Chu sequence used in
the illustration of Fig. 2 is fixed; however, the index k is
changed to various values in order to check the values of the
PAPR. This graph illustrates that differences equal to or
greater than 3dB can be caused in the values of the PAPR depending
on the values of the index. The higher the PAPR a sequence has,
the greater the peak power in comparison with the average power.
If a signal waveform of a preamble portion is not to be
distorted upon the transmission of the preamble portion by a

mobile terminal station, the back-off amount of the
transmitting power of the transmission unit power amplifier of
the mobile terminal station has to increase as the PAPR of the
CAZAC sequence used as the preamble increases. As an amplifier
operates with a greater back-off amount, the amplifier consumes
more power. In other words, a transmission unit power amplifier
presents a linear amplification characteristic with a smaller
input power, whereas this amplification characteristic becomes
non-linear with an input power around and greater than a certain
input power value that is determined by the amplifier itself,
and thereby the amplification ratio is saturated and decreases.
When a signal using a CAZAC sequence with a high PAPR as a
preamble is to be amplified, the difference between the average
power and the peak power in this signal is great so that the
peak power is not linearly amplified due to the saturation,
resulting in a distortion in the signal if the position at which
the average power is input is around the saturation region of
the amplification characteristic of the amplifier.
Accordingly, elimination of the distortion in a signal requires
lowering of the average power of a signal input into the
amplifier so that the power does not reach the region in which
the amplification characteristic of the amplifier is saturated.
A point including the average power of an input power or an output
power in the amplification characteristic of an amplifier is
referred to as an operating point, and an amount of a reduction
from the output saturation point is referred to as a back-off
amount.
Non-patent document 1 discloses specifications for the
EUTRAN. Non-patent document 2 includes a description about
CAZAC sequences such as a Zadoff-Chu sequence, etc.
Non-patent document 1:
3GPP TR25.814
Non-patent document 2:

3GPP TSG RAN1LTE Ad Hoc R1-061710
Disclosure of the Invention
It is an object of the present invention to provide a
wireless communication device that can minimize a period during
which data transmission is interpreted instantaneously for a
handover so that a handover is effectively performed in a mobile
communication system in which handovers are performed.
When a handover is performed, a mobile terminal station
is near the edge of a cell, and accordingly a transmission power
required to generate a preamble signal transmitted from such
a mobile terminal station so that it can be successfully
received by the reception unit of the base station is greater
than that required to generate the same preamble signal
transmitted from another mobile terminal station near the base
station. Also, a transmission power required to transmit a
preamble portion of a random access signal from a mobile
terminal station near the edge of a cell having a large radius
can sometimes be greater than the maximum transmission power
of the mobile terminal station.
Further, when a handover is performed, a terminal station
has to capture a downlink synchronization channel transmitted
from the base station in the handover destination, has to
synchronize itself with the base station, and has to transmit
a random access signal in an uplink channel. If a random access
signal can be transmitted immediately after the success in the
downlink synchronization, the time consumed by a handover can
be reduced. Therefore, the present invention uses a wireless
communication device dividing uplink and downlink frequency
bandwidths into narrower frequency bandwidths, assigns data to
the narrower frequency bandwidths, and performs wireless
communication, the wireless communication device comprising:
synchronization signal capturing unit for capturing, when
receiving a notice requiring a handover to be performed, a
synchronization signal transmitted from a base station in a

handover destination; and synchronization establishment
signal transmission unit for transmitting a synchronization
establishment signal for establishing synchronization with a
base station in the handover destination, by using a frequency
position in an uplink frequency bandwidth at a time point later
than a timing of capturing the synchronization signal by a
prescribed period.
Desirably, a frequency position for transmitting a
synchronization signal in a downlink frequency bandwidth is the
same as a frequency position for transmitting a synchronization
establishment signal in an uplink frequency bandwidth. For
example, when a frequency position for transmitting a
synchronization signal in a downlink frequency bandwidth
corresponds to the center frequency, a synchronization
establishment signal is transmitted at the central frequency
position in an uplink frequency bandwidth. It is an object of
the present invention to suppress an increase in the backing
off of transmission power caused by a signal (such as a preamble
portion of a random access signal) transmitted from a place
distant from a radio base station.
The present invention uses a mobile station establishing
an uplink wireless connection by transmitting a random access
signal through a random access channel after receiving a
synchronization channel transmitted from a radio base station
in a handover destination, comprising: a preamble generating
unit for restricting a CAZAC sequence used as a preamble of the
random access signal to a prescribed CAZAC sequence from among
a plurality of CAZAC sequences with different indexes, and
generating the preamble of the random access signal using the
prescribed CAZAC sequence.
Brief Description of the Drawings
Fig. 1 is a block diagram illustrating an example of a
circuit generating, from a CAZAC sequence, a presamble portion
of a random access signal used in a wireless uplink according

to the EUTRAN;
Fig. 2 depicts a PAPR characteristic of a preamble signal
having a bandwidth of 5MHz and using a Zadoff-Chu sequence;
Fig. 3 illustrates the first principle of an embodiment
of the present invention;
Fig. 4 illustrates the second principle of an embodiment
of the present invention;
Fig. 5 illustrates a sequence used when a handover is
performed on the basis of an embodiment of the present invention
(first);
Fig. 6 illustrates a sequence used when a handover is
performed on the basis of an embodiment of the present invention
(second);
Fig. 7 illustrates a sequence used when a handover is
performed on the basis of an embodiment of the present invention
(third);
Fig. 8 is a block diagram illustrating a mobile terminal
station according to an embodiment of the present invention;
Fig. 9 is a block diagram illustrating a configuration
of a movement origin base station when a handover is performed
according to the present invention; and
Fig. 10 is a block diagram illustrating a configuration
of a movement destination base station when a handover is
performed according to the present invention.
Best Modes for Carrying Out the Invention
In an embodiment of the present invention, the measures
as described below are taken.
[1] The timing and frequency at which a mobile terminal station
can transmit an asynchronous random access signal to the
movement destination base station (the base station in the
handover destination) is determined by a timing that is on a
sub-band in an uplink radio section of the movement destination
cell, said sub-band corresponding to a sub-band (a frequency

domain in which a synchronization channel is transmitted as one
of plural frequency domains obtained by dividing the entire
wireless transmission bandwidth used for radio communications)
in which a synchronization channel is transmitted in a downlink
radio section in the movement destination cell and that is a
timing (in the subframe corresponding to the timing) offset by
a prescribed period from a position of the downlink
synchronization channel of the movement destination cell.
However, the lengths of preamble portions of asynchronous
random access signals may vary depending upon the sizes of the
cells. For example, in the case of a large cell, a preamble
portion of an asynchronous random access signal can sometimes
occupy plural successive subframes in a large cell; however,
the timing at which transmission of an asynchronous random
access signal starts is a timing offset by the same prescribed
period from a position of a synchronization channel.
When a handover is performed, information on the lengths
of the preambles of asynchronous random access signals used in
the movement destination cell is reported from the base station
in the movement origin to a mobile terminal station for which
a handover is being performed.
Additionally, the time offset level is set to a unique
value to be used as a common value for all cells in a single
mobile communication system. The time offset level can be
stored in a storage unit in a mobile terminal station beforehand,
and also can be designated by the base station in the handover
origin or the handover destination. Using a constant time
offset level as described above eliminates the need for a base
station to search the entire communication frequency band for
the random access signal transmitted from each of the mobile
terminal stations during a particular period. This makes it
possible to establish connections between the base stations and
the mobile terminal devices in a shorter time.
For a mobile terminal station, it is possible to transmit
a random access signal at a timing identified by a prescribed

offset time (T) on the basis of the position of the
synchronization channel used, for the establishment of
synchronization. Accordingly, compared to a case in which
random access signals are received at non-constant timings, the
level of necessity at which a needlessly large buffer in base
stations has to be secured for absorbing the inconstantness is
lowered.
With respect to a synchronization channel, a transmission
opportunity (a point in time that is subsequent by the amount
of the T offset time) of transmitting a random access signal
for every single synchronization channel can be set to once and
also to twice or more. For example, transmission opportunities
can be set at points in time subsequent by the amounts of the
offset times T and T2 for transmitting random access signals.
Even when a collision occurs in the first transmission, the next
signal can be transmitted without waiting for the transmission
of the synchronization channel.
Desirably, the value of T is set to be shorter than a
transmission cycle of the synchronization channel. Further,
it is appropriate and advantageous to set the value of T to be
equal to or shorter than five subframes, and particularly to
be three or four subframes in view of performing both an
acquisition process and a transmission process of the
synchronization channel.
[2] The timing and the frequency for the transmission of the
random access signal during the above handover are prevented
from being used by another terminal station for which a handover
is not being performed.
In other words, a timing and frequency for transmitting
a random access signal that are different from those for the
mobile station for which a handover is being performed are
assigned to a terminal station for which a handover is not being
performed.
Thereby, the likelihood that random access signals will

collide with each other in the reception unit of the base station
in the movement destination (handover destination) and the time
consumed by a handover can both be reduced.
[3] When there is no terminal station for which a handover to
a cell covered by a base station is going to be performed, the
scheduler of the base station assigns the timing and frequency
described in [2] (which are exclusively for a terminal station
for which a handover is being performed) to uplink signals
transmitted from other terminal stations in the cell to the base
station. The determination of whether or not there is a
terminal station for which a handover is going to be performed
is made on the basis of, for example, the signaling (a notice
reporting the start of a handover, information on a terminal
station for which a handover is being performed, or an
instruction requesting the securing of radio resources for a
mobile terminal station that is entering to the cell) relating
to handovers transmitted from the base stations in adjacent
cells or from an aGW (access Gate Way, which corresponds to a
base station control device in W-CDMA systems) and also on the
basis of a control signal transmitted from a terminal station
to the base station in the handover destination in order to
directly (or indirectly) report the completion of a handover.
Thereby, it is possible to avoid reduction in the use
efficiency of radio resources that would be caused if the radio
resources (timing and frequency for transmission of a random
access signal by a mobile terminal station for which a handover
is being performed) are not used while there is no terminal
station for which a handover is going to be performed.
[4] As an index of the CAZAC sequence applied to a preamble
portion used with the timing and frequency for transmitting a
random access signal when a handover is performed, an index with
a small PAPR in the preamble portion is used.
It is possible to reduce the output power back-off amount

in a transmission signal amplifier when transmitting a preamble
portion. If a back-off amount is reduced, (1) the average
transmission power can be increased, and (2) the likelihood of
a transmission power shortage can be reduced, and this is
advantageous for a terminal station for which a handover is
being performed and which needs a high transmission power due
to it being near the edge of a cell and distant from the base
station.
Indexes with small values of the PAPR are, for example,
indexes other than indexes with values of the PAPR of 6dB or
higher in Fig. 2. Also, as indexes with relatively small values
of the PAPR, indexes can be selected from the ranges of between
1 and 75, 132 and 168, and 225 and 298. When these ranges are
expressed using the sequence length L, indexes can be selected
from ranges of between 1 and L/3, L/2-L/16 and L/2+L/16, and
2L/3 and L-1.
[5] Information on the index of the CAZAC sequence applied to
the preamble portion used with the timing and frequency for
transmitting a random access signal so as to perform a handover
is reported from the terminal station for which a handover is
being performed to the base station in the handover origin.
[6] As an index of the CAZAC sequence applied to a preamble
portion used for a handover, an index with a small PAPR is used.
A small PAPR used here is a PAPR that causes only a slight backing
off of the operating point of a transmission signal amplifier
so that a random access signal transmitted within a normal
transmission power from a mobile terminal station near the edge
of a cell covered by a base station can normally be received
by the base station. A sequence having the correct index that
should be used for whatever situation the mobile station is in
is calculated and determined beforehand.
[7] Information on the index of the CAZAC sequence applied to

the preamble portion used for a handover is reported from the
base station in the handover source to the terminal station for
which a handover is going to be performed when the handover is
actually performed.
Fig. 3 illustrates the first principle of an embodiment
of the present invention.
Fig. 3 illustrates arrangements of the downlink and
uplink signals in the frequency and time directions, with the
horizontal axis representing the frequencies and the vertical
axis representing the time. A synchronization channel is set
around the center frequency of the system bandwidth among
subframes transmitted in the downlink. A synchronization
channel is not contained in all subframes transmitted in the
downlink, but is contained in, for example, every five or ten
subframes to be transmitted. Before the synchronization is
established between a mobile terminal station and a base station,
the uplink and downlink signals are asynchronous. Thus, in an
embodiment of the present invention, when a synchronization
channel is detected in a downlink signal, a random access signal
is contained (accommodated) in an uplink subframe corresponding
to the time point subsequent to that time by the time offset
Toffset, and the signal is transmitted to a base station from
a mobile terminal. The frequency used for accumulating the
random access signal is near the center frequency in the system
bandwidth of the uplink because a downlink synchronization
channel is near the center frequency of the system bandwidth.
In the example of Fig. 3, a slot shaded with diagonal lines is
used for transmitting a random access signal. A random access
signal to be transmitted can be inserted into plural successive
subframes; however, only an uplink subframe corresponding to
a time point subsequent to the synchronization channel by the
time offset Toffset can be used as the subframe for starting
the transmission of the random access signal regardless of the
length of the random access signal. If the transmission of a
random access signal fails (when a response signal is not

transmitted from the base station), the random access signal
is inserted into the same position (uplink subframes subsequent
to the timing of another synchronization channel to be
transmitted subsequently by the time offset Toffset), and is
retransmitted. As a matter of course, when plural
opportunities to transmit a random access signal have been given
to a single synchronization channel, the random access signal
can be transmitted at the next transmission opportunity.
Fig. 4 illustrates the second principle of an embodiment
of the present invention.
In Fig. 4, similarly to the example in Fig. 3, uplink and
downlink signals are illustrated with the horizontal axis
representing the frequencies and the vertical axis representing
the time. In Fig. 4, a configuration is employed in a case in
which the system bandwidth is wide and the receiving band of
a receiving mobile terminal station is only half the system
bandwidth. A downlink signal has synchronization channels set
around two frequencies in a single subframe (however,
synchronization channels may be set at three or more positions).
In an embodiment of the present invention, a frequency used for
transmitting a random access signal of a terminal station for
which a handover is being performed is a frequency in the
frequency band of the uplink signal, said frequency
corresponding to the frequency at which synchronization
channels are set in the system bandwidth of the uplink signal.
For example, when synchronization channels are near the center
portions respectively of two bands obtained by dividing the
frequency band of the downlink, random access signals as well
are near the center portions respectively of two bands obtained
by dividing the frequency band of the uplink. The timing of
starting a transmission of a random access signal is in a
subframe of an uplink signal corresponding to a time point
subsequent to the time point of the detection of a
synchronization signal in a downlink signal by the time offset
Toffset. In Fig. 4, portions shaded with diagonal lines are

slots in which the transmission of random access signals starts .
Because there are synchronization channels in two slots in a
downlink signal, there are also two slots that can be used for
transmitting a random access signal in an uplink signal. A
random access signal to be transmitted can be inserted into
plural successive subframes; however, only an uplink subframe
corresponding to a time point subsequent to the synchronization
channel by the time offset Toff set can be used as the subframe
for starting the transmission of the random access signal
regardless of the length of the random access signal. If
transmission of a random access signal fails (when a response
signal is not transmitted from the base station), the random
access signal is inserted into the same position (uplink
subframes subsequent to the timing of another downlink
synchronization channel to be transmitted subsequently by the
time offset Toffset) to be retransmitted.
Figs. 5 through 7 illustrate sequences for performing a
handover according to an embodiment of the present invention.
Fig. 5 illustrates the first example. In Fig. 5, a
(mobile) terminal station transmits to the movement destination
base station a result of measuring a received power of a signal
(a pilot signal or the like) transmitted from a neighboring cell,
and the movement origin base station determines that it should
perform a handover (1) . Then, the movement origin base station
transmits information confirming that a handover is going to
be performed, information on the mobile terminal station, and
the like. Obtaining the information from the movement origin
base station, the movement destination base station sets a
timing and frequency to be used for transmitting a random access
signal exclusively for the mobile terminal station for which
the handover is going to be performed in such a manner that the
set timing and frequency are not assigned to an uplink data
transmission by another mobile terminal station for which a
handover is not going to be performed (2). As already described,
the above timing is a timing subsequent to the reception of the

synchronization signal by the terminal station by the time
offset, and the above frequency is a frequency in the uplink
corresponding to the frequency used for transmitting a downlink
synchronization channel. When there is no terminal station for
which a handover is going to be performed during a period between
a state in which the terminal station is communicating with the
movement origin base station and the state of (2), the timing
and frequency for transmitting a random access signal of a
terminal station for which a handover is being performed can
be assigned to a terminal station for which a handover is not
going to be performed. When the movement destination base
station has completed the setting of (2), system information
including the sequence index of the CAZAC sequence of the random
access signal used for the handover is transmitted to the
movement source base station. At that time, a CAZAC sequence
with a small PAPR is selected to be transmitted. As was already
described, indexes with small PAPRs are, for example, indexes
other than indexes with PAPRs of 6dB or higher in Fig. 2. Also,
indexes can be selected from the ranges of between 1 and 75,
132 and 168, and 225 and 298 as indexes with relatively small
PAPRs. When these ranges are expressed using the sequence
length L, indexes can be selected from ranges of between 1 and
L/3, L/2-L/16 and L/2+L/16, and 2L/3 and L-1.
However, the setting of (2) can be performed after the
transmission of the system information, etc. to the movement
origin base station. The movement origin base station that
received the system information, etc. transmits to the mobile
terminal station for which a handover is being performed system
information on the movement destination cell including the
sequence index of the CAZAC sequence used for the handover in
order to instruct the mobile terminal station to start the
handover. Thereafter, while still having data to transmit to
the terminal station, the movement origin base station
transfers that data to the movement destination base station.
However, such data may also be transferred after the handover

has succeeded.
Having received an instruction to start the handover, the
terminal station starts synchronizing itself with the movement
destination cell. The terminal station captures a downlink
synchronization channel from the movement destination base
station (4) , and transmits a preamble portion of a random access
signal (synchronization establishment signal) to the movement
destination base station. Control information or the like may
be included in the preamble portion in a multiplexing manner
(code multiplexing, time multiplexing, etc.). For a
transmission of the preamble portion of the random access signal,
timing and frequency for the transmission of a random access
signal exclusively for a terminal station for which a handover
is being performed are used. When the movement destination base
station has received the preamble portion of the random access
signal and succeeded in properly recognizing the sequence in
the preamble portion, a preamble portion reception confirmation
and the timing and frequency for transmitting uplink data are
reported to the terminal station. Having received this
information, the terminal station transmits a handover
completion report signal to the movement destination base
station. The movement destination base station, having received
this signal, transmits the handover completion report signal
to the movement origin base station after a process necessary
for establishing a wireless link with the terminal station is
completed. Thereafter, the movement destination base station
restarts releasing the timing and frequency for a transmission
of a random access signal exclusively for a terminal station
for which a handover is being performed so that they can be used
for transmitting uplink data for terminals for which a handover
is not being performed (5).
The period between (2) and (5) in Fig. 5 is a period during
which a timing and frequency for transmission of a random access
signal of a terminal station for which a handover is being
performed are exclusively assigned to the terminal station for

which a handover is being performed. After setting (5), a
timing and frequency for transmission of a random access signal
of a terminal station for which a handover is being performed
are assigned to a terminal station for which a handover is not
being performed when there is not a terminal station for which
a handover is being performed.
Fig. 6 illustrates the second example. In Fig. 6, a
(mobile) terminal station transmits to the movement origin base
station a result of measuring a received power or the like of
a signal (pilot signal or the like) from a neighboring cell,
and the movement destination base station determines that a
handover is to be performed (1) . Thereafter, the movement
origin base station transmits information confirming that a
handover is going to be performed, information on the mobile
terminal station, and the like to the movement destination base
station. Obtaining the information from the movement origin
base station, the movement destination base station sets a
timing and frequency to be used for transmitting a random access
signal exclusively for the mobile terminal station for which
the handover is going to be performed in such a manner that the
set timing and frequency are not assigned to uplink data
transmission by another mobile terminal station for which a
handover is not going to be performed (2) . As already described,
the above timing is a timing subsequent to the reception of the
synchronization signal by the terminal station by the amount
of time in the time offset, and the above frequency is a frequency
in the uplink corresponding to the frequency used for
transmitting a downlink synchronization channel. When there is
no terminal station for which a handover is going to be performed
during a period between the state in which the terminal station
is communicating with the movement origin base station and the
state of (2) , the timing and frequency for transmitting a random
access signal of a terminal station for which a handover is being
performed can be assigned to a terminal station for which a
handover is not going to be performed. In the first example

illustrated in Fig. 5, when the movement destination base
station has completed the setting of (2), system information
including the sequence index of the CAZAC sequence of the random
access signal used for the handover is transmitted to the
movement source base station. However, the setting of (2) may-
be performed after the transmission of the system information,
etc. to the movement origin base station. However, in the
second example illustrated in Fig. 6, which of the sequences
is to be used as the CAZAC sequence for the random access signal
is determined beforehand by system design or the like, and
information on the CAZAC sequence is not included in the
information transmitted from the movement destination base
station to the mobile terminal station via the movement origin
base station. The movement origin base station transmits the
system information on the movement destination cell to the
mobile terminal station, and instructs the mobile terminal
station to start the handover. Thereafter, when the movement
origin base station still has data to transmit to the terminal
station, it transfers that data to the movement destination base
station. However, such data may also be transferred after the
handover has succeeded.
Having received an instruction to start the handover, the
terminal station starts synchronizing itself with the movement
destination cell (3). The terminal station captures a downlink
synchronization channel transmitted from the movement
destination base station (4) , and transmits a preamble portion
of a random access signal to the movement destination base
station. Control information or the like may be included in
the preamble portion in a multiplexing manner (code
multiplexing, time multiplexing, etc.). For the transmission
of the preamble portion of the random access signal, the timing
and frequency for the transmission of a random access signal
exclusively for a terminal station for which a handover is being
performed are used. When the movement destination base station
has received the preamble portion of the random access signal

and has succeeded in properly recognizing the sequence of the
preamble portion, a preamble portion reception confirmation and
timing and frequency for transmitting uplink data are reported
to the terminal station. Having received this information, the
terminal station transmits a handover completion report signal
to the movement destination base station. The movement
destination base station, having received this signal,
transmits the handover completion report signal to the movement
origin base station after a process necessary for establishing
a wireless link with the terminal station is completed.
Thereafter, the movement destination base station restarts
assigning timing and frequency for transmission of a random
access signal exclusively for a terminal station for which a
handover is being performed as timing and frequency for
transmitting uplink data for terminals for which a handover is
not being performed.
The period between (2) and (5) in Fig. 6 is a period during
which the timing and frequency for the transmission of a random
access signal of a terminal station for which a handover is being
performed are exclusively assigned to a terminal station for
which a handover is being performed. After setting (5), the
timing and frequency for the transmission of a random access
signal of a terminal station for which a handover is being
performed are assigned to a terminal station for which a
handover is not being performed when there is not a terminal
station for which a handover is being performed.
Fig. 7 illustrates the third example. In Fig. 7, a
(mobile) terminal station transmits to the movement origin base
station a result of measuring a received power or the like of
a signal (pilot signal or the like) from a neighboring cell,
and the movement destination base station determines that a
handover is to be performed (1). Thereafter, the movement
origin base station transmits information confirming that a
handover is going to be performed, information on the mobile
terminal station, and the like. In the third example, timing

and frequency are set beforehand to be exclusively for the
transmission of a random access signal for a mobile terminal
station for which a handover is being performed in order to
prevent the timing and frequency from being used for other
purposes. As was already described, the above timing is a
timing subsequent to the reception of the synchronization
signal by the terminal station by the amount of time in the time
offset, and the above frequency is a frequency in the uplink
corresponding to the frequency used for transmitting a downlink
synchronization channel. The movement destination base
station transmits to the movement origin base station the system
information, including the sequence index of the CAZAC sequence
for the random access signal used for the handover. The
movement origin base station transmits the system information
on the movement destination base station to the mobile terminal
station, and instructs the mobile terminal station to start the
handover. Thereafter, the movement origin base station has
data yet to be transmitted to the terminal station, it transfers
that data to the movement destination base station. However,
such data may also be transferred after the handover has
succeeded.
Having received an instruction to start the handover, the
terminal station starts synchronizing itself with the movement
destination cell (2) . The terminal station captures a downlink
synchronization channel from the movement destination base
station (3) , and transmits a preamble portion of a random access
signal to the movement destination base station. For the
transmission of the preamble portion of the random access signal,
the timing and frequency for the transmission of a random access
signal exclusively for a terminal station for which a handover
is being performed are used. When the movement destination base
station has received the preamble portion of the random access
signal and succeeded in properly recognizing the sequence of
the preamble portion, a preamble portion reception confirmation
and a timing and frequency for transmitting uplink data are

reported to the terminal station. Having received this
information, the terminal station transmits a handover
completion report signal to the movement origin base station
after a process necessary for establishing a wireless link with
the terminal station.
Fig. 8 is a block diagram illustrating a mobile terminal
station according to an embodiment of the present invention.
When a receiving antenna has received a signal, a radio
unit 10 demodulates the signal and a decoding unit 11 decodes
the signal in order to obtain user data/speech packets, a
control signal, sequence information used for a handover, and
a handover instructing signal. Outputs from the DFT unit 10
are input into a downlink synchronization channel receiving
process unit 13. Thereafter, a process of receiving a
synchronization channel is performed, and a reception result
is input into a handover operation control unit 14. The
handover operation control unit 14 controls a receiving
frequency control unit 12, a sequence determination unit 1.5,
and a random-access-signal transmission-timing-and-frequency
determination unit 19. The reception frequency control unit
12 controls frequency used when receiving a synchronization
channel. The sequence determination unit 15 determines a
sequence to be used for a random access signal. As an example,
a sequence used for a random access signal may be reported from
the radio base station in the handover origin. The
random-access-signal transmission-timing-and-frequency
determination unit 19 determines a timing and frequency for a
random access signal.
In response to the determination by the
random-access-signal transmission-timing-and-frequency
determination unit 19, a transmission frequency control unit
20 controls a radio unit 28 and a modulation unit 27 in order
to transmit a random access signal at the timing and frequency
determined in the present invention. When which sequence is
to be used has been determined by the sequence determination

unit 15, the determined sequence is generated by a
preamble-signal sequence generating unit 16, and a random
access preamble signal generating unit 17 uses this sequence
in order to generate a preamble signal containing a random
access signal. This preamble signal is combined with control
information in a multiplexing manner by a multiplexing unit 18,
and the resultant information is input into a switching unit
26.
A speech packet, user data, and a result of measuring a
neighboring cell are input into a multiplexing/switching unit
21, are output in a combined (multiplexed) state or in a
one-by-one manner, and are coded by a channel coding unit 22.
A control signal as well is coded by another channel coding unit
23. Outputs from the channel coding units 22 and 23 are output
by another multiplexing/switching unit 24 in a combined
(multiplexed) state or in a one-by-one manner, are mapped onto
a physical channel by a physical channel generating unit 25,
and are input into the switching unit 26. The switching unit
26 switches between signals from the multiplexing unit 18 and
signals from the physical channel generating unit 25 to output
to the transmitting antenna via the modulation unit 27 and the
radio unit 28.
Fig. 9 is a block diagram illustrating a configuration
of a movement origin base station when a handover is being
performed according to an embodiment of the present invention.
A signal received by a receiving antenna is demodulated
by a radio unit 30, and is decoded by a decoding unit 31. A
result of measuring a neighboring cell is obtained from the
decoded signal and is used for a handover determination unit
32 to determine whether or not a handover is to be performed
for the terminal station that has sent that result. When it
has been determined that a handover should be performed,
information confirming the performing of the handover and
information on the terminal station for which the handover is
going to be performed are transmitted to the movement

destination base station.
Having received system information on the movement
destination base station and random access signal preamble
sequence information used for the handover (for example,
information on the sequence length L and the index k for
recognizing a sequence with a PAPR, or the like) transmitted
from the movement origin base station, a handover operation
processing unit 33 generates random access signal preamble
sequence information used for the handover and. a handover
starting instruction signal, and system information on the
movement destination base station. A physical channel
generating unit 34 maps the generated information onto a
physical channel. The resultant information is transmitted
through the transmitting antenna after going through a
modulation unit 35 and a radio unit 36.
Fig. 10 is a block diagram representing a configuration
of a movement destination base station when a handover is being
performed according to an embodiment of the present invention.
First, handover confirmation information and handover
target terminal information are received from the movement
origin base station of a terminal station for which a handover
is being performed. Thereafter, a handover operation
processing unit 42 transmits to the movement origin base station
random access signal preamble sequence information used for the
handover and the system information on the base station.
Further, the handover operation processing unit 42 requests
that an uplink radio resource management unit 47 prohibit other
stations from using the timing and frequency for the random
access signal of the terminal station for which the handover
is going to be performed and that it assign an uplink radio
resource to be used until the handover for the terminal station
is completed. The uplink radio resource management unit 47
transmits information on the assignment of an uplink radio
resource to the mobile terminal station via a physical channel
generating unit 48, a modulation unit 49, and a radio unit 50.

When a signal from the terminal station for which the
handover is to be performed is received via the receiving
antenna, a radio unit 40, and a decoding unit 41, a received
random access signal detection processing unit 43 attempts to
detect reception of a random access signal that may have been
received in order to determine whether or not a random access
signal was transmitted. The process of detecting the preamble
portion of a random access signal is performed by the received
random access signal detection processing unit 43 under control
of the handover operation processing unit 42 and a received
preamble confirmation unit 44. When detecting reception of a
random access signal, the received preamble confirmation unit
44 transmits reception confirmation information on the preamble
portion to the terminal station via the physical channel
generating unit 48, the modulation unit 49, and the radio unit
50. Having received the random access signal, a random access
signal receiving timing detection unit 45 detects the timing
at which the random access signal was received, and calculates
a gap in the transmission timing from the terminal station,
generates an uplink transmission timing correction information
signal, and transmits this signal to the terminal station via
the physical channel generating unit 48, the modulation unit
49, and the radio unit 50.
Receiving a terminal station handover process completion
reporting signal transmitted from the terminal station, a
handover completion determination unit 46 determines that the
handover has been completed, and transmits a request to the
uplink radio resource management unit 47 to release the timing
and frequency for the random access signal for the terminal
station for which the handover has been performed. When a
process necessary for establishing a wireless link with the
terminal station is completed, a handover completion report is
transmitted to the movement origin base station. In addition,
the synchronization channel transmitted from the movement
destination base station when a handover is performed is

transmitted via the physical channel generating unit 48, the
modulation unit 49, the radio unit 50, and the transmitting
antenna.
The above configuration corresponds to the sequence
illustrated in Fig. 5. However, configurations corresponding
to Figs. 6 and 7 will be easily conceived by those skilled in
the art.

CLAIMS
1. A wireless communication device dividing uplink and
downlink frequency bandwidths into narrower frequency
bandwidths, assigning data to the narrower frequency bandwidths
and performing wireless communication, comprising:
synchronization signal capturing means for capturing,
when receiving a notice requiring a handover to be performed,
a synchronization signal transmitted from a base station in a
handover destination; and
synchronization establishment signal transmission means
for transmitting a synchronization establishment signal for
establishing synchronization with a base station in the
handover destination by using a frequency position in an uplink
frequency bandwidth at a time point later than a timing of
capturing the synchronization signal by a prescribed period.
2. The wireless communication device according to claim 1,
wherein:
a timing and a frequency position used for transmission
of the synchronization transmission signal can be used by the
radio communication device for which a handover is being
performed.
3. The wireless communication device according to claim 2,
wherein:
when there is no wireless communication device for which
a handover is being performed in a cell of a base station, the
timing and the frequency position used for transmission of the
synchronization establishment signal are used by another
wireless communication device in the cell of the base station
for transmitting a signal other than a synchronization
establishment signal.
4. The wireless communication device according to claim 1,

wherein:
the synchronization establishment signal is a signal
including a prescribed signal sequence in a preamble portion
in a data frame.
5. A mobile station establishing an uplink wireless
connection by transmitting a random access signal through a
random access channel after receiving a synchronization channel
transmitted from a radio base station in a handover destination,
comprising:
a setting unit for setting a timing of transmitting the
random access signal to be later than the timing of receiving
the synchronization channel by a prescribed period.
6. A mobile station establishing an uplink wireless
connection by transmitting a random access signal through a
random access channel after receiving a synchronization channel
transmitted from a radio base station in a handover destination,
comprising:
a preamble generating unit for restricting a CAZAC
sequence used as a preamble of the random access signal to a
prescribed CAZAC sequence from among a plurality of CAZAC
sequences with different indexes, and generating the preamble
of the random access signal using the prescribed CAZAC sequence.
7. A mobile station according to claim 6, wherein:
the prescribed CAZAC sequence has a PAPR smaller than
PAPRs of the plurality of CAZAC sequences.
8. A mobile station according to claim 6, wherein:
when a Zadoff-Chu sequence is used as the CAZAC sequence,
a sequence whose index is selected from a range of between 1
and L/3, L/2-L/16 and L/2+L/16, and 2L/3 and L-l is used as the
prescribed CAZAC sequence, where L is a sequence length.

9. The wireless communication device according to claim 4,
wherein:
a wireless communication device for which a handover is
being performed uses a signal sequence by which a
peak-to-average power ratio (PAPR) in the preamble portion used
by the wireless communication device for which a handover is
being performed is smaller than a peak-to-average power ratio
in a preamble portion in a data frame used when another wireless
communication device for which a handover is not being performed,
transmits a signal at a timing and frequency other than a timing
or frequency for transmission of the synchronization
establishment signal.
10. The wireless communication device according to claim 4,
wherein:
the signal sequence is a CAZAC sequence.
11. A base station in a wireless communication system
dividing uplink and downlink frequency bandwidths into narrower
frequency bandwidths, assigning data to the narrower frequency
bandwidths and performing wireless communication, comprising:
synchronization signal transmission means for
transmitting a synchronization signal through a downlink so
that a terminal station can recognize a base station;
handover notice receiving means for receiving a handover
notice reporting that a terminal station in a cell covered by
another base station is going to move to a cell of the base
station itself through a process of a handover;
synchronization establishment signal reception means for
receiving, when receiving a handover notice, a synchronization
establishment signal transmitted from a terminal station moving
to a cell of the base station itself through a process of a
handover, using a frequency position in an uplink frequency
bandwidth corresponding to a frequency position in a downlink
frequency bandwidth of the synchronization signal at a

prescribed timing; and
transmission timing reporting means for reporting a
transmission timing to the terminal station when the terminal
station transmits a signal through an uplink on the basis of
the timing of receiving the synchronization establishment
signal.
12. The base station according to claim 7, further
comprising:
signal sequence reporting means for reporting to the
terminal station a signal sequence to be used for the
synchronization establishment signal.
13. The base station according to claim 7, wherein:
a terminal station for which a handover is not being
performed is prevented from using the frequency position and
the prescribed timing used for transmission of the
synchronization establishment signal by the terminal station
moving to a cell of the base station itself through a process
of a handover.
14. The base station according to claim 8, wherein:
the signal sequence is a CAZAC sequence.
15. A method of controlling a wireless communication device
dividing uplink and downlink frequency bandwidths into narrower
frequency bandwidths, assigning data to the narrower frequency
bandwidths, and performing wireless communication,
comprising:
capturing, when receiving a notice requiring a handover
to be performed, a synchronization signal transmitted from a
base station in a handover destination; and
transmitting a synchronization establishment signal for
establishing synchronization with a base station in a handover
destination by using a frequency position in an uplink frequency

bandwidth corresponding to a frequency position in a downlink
frequency bandwidth used for transmission of the
synchronization signal at a time point later than a timing of
capturing the synchronization signal by a prescribed period.
16. A method of controlling a base station in a wireless
communication system dividing uplink and downlink frequency
bandwidths into narrower frequency bandwidths, assigning data
to the narrower frequency bandwidths, and performing wireless
communication, comprising:
transmitting a synchronization signal through a downlink
so that a terminal station can recognize a base station;
receiving a handover notice reporting that a terminal
station in a cell covered by another base station is going to
move to a cell of the base station itself through a process of
a handover;
receiving, when receiving a handover notice, a
synchronization establishment signal transmitted from a
terminal station moving to a cell of the base station itse] f
through a process of a handover, using a frequency position in
an uplink frequency bandwidth corresponding to a frequency
position in a downlink frequency bandwidth of the
synchronization signal at a prescribed timing; and
reporting a transmission timing to the terminal station
when the terminal station transmits a signal through an uplink
on the basis of the timing of receiving the synchronization
establishment signal.

When a handover is performed, a mobile station receives, from the movement origin base station, information on the movement destination base station and information relating to a sequence to be used for transmitting a random access signal to the movement destination base station. The mobile station receives a synchronization channel signal transmitted from the movement destination base station. Thereafter, the mobile
station transmits the random access signal to the movement destination base station at a timing offset by a prescribed period from a timing of receiving a synchronization channel and
at a frequency corresponding to that of the synchronization channel. A position of the timing/frequency used for transmitting the random access signal for the handover is used
exclusively by the random access signal transmitted from the mobile terminal for which a handover is being performed or is used exclusively at the same time by a plurality of mobile stations for which handovers are performed. Thereby, interference between random access signals transmitted from a plurality of mobile stations are suppressed to zero or to a low level in order to increase the percentage of normal reception of the random access signals by the handover destination base station. This reduces the chance that a random access signal
will have to be retransmitted, resulting in a shorter period of time being consumed by a handover.