JP2749237B2 - Mobile communication base station transmitting apparatus and mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system for performing communication using code division multiplexing (CDMA) between a base station and a mobile station.

[0002]

2. Description of the Related Art The code division multiplexing (CDMA) system is a communication system in which an information sequence to be transmitted under the same frequency is spread and multiplexed with different spreading codes for each channel. The detailed configuration and functions are described in "Spread Spectrum Communication System" by RCDixon. Here, an outline of a scheme called direct spread CDMA will be described.

FIG. 7 shows a configuration of a transmitting apparatus in a typical CDMA communication system. n information sequences S1, S
, Sn are input to multipliers 11, 12,..., 1n,
.., C from the spreading code generation circuit 2
n. Multipliers 11, 12,
, 1n are combined by the combiner 3 at the same timing to generate a transmission signal.

On the other hand, a signal received by a receiving device (not shown) is despread by the same spreading codes C1, C2,..., Cn as those used in the transmitting device, so that the original information sequences S1, S2,. , Sn are generated.

Here, the spreading codes C1, C2,..., Cn are usually code sequences having good autocorrelation characteristics (when the time offset of two correlated code sequences is τ, a strong correlation is obtained only at τ = 0). Value, otherwise the correlation value is small)
And a code sequence having good cross-correlation characteristics, that is, a code sequence having low correlation with other spreading codes (a code sequence whose cross-correlation value is smaller than a certain value which is an arbitrary time offset) is selected.

[0006]

However, there are few classes of code sequences that satisfy the requirements of the above-mentioned spreading codes.
Also, the number of spreading codes included in each class is small. Therefore, the conventional CDMA communication system in which different spreading codes are assigned to each communication channel has a drawback that the number of usable communication channels is small and it is not suitable for a mobile communication system having a large subscriber capacity.

An object of the present invention is to provide a CDMA mobile communication system capable of effectively increasing the number of communication channels using a limited number of spreading codes.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a base station for a mobile communication system having a plurality of base stations and a plurality of mobile stations, and performing communication using code division multiplexing between the base stations and the mobile stations. In the mobile communication base station transmission device provided in the above, after spreading a plurality of information sequences to be transmitted to a plurality of mobile stations with the same spreading code, the cell size corresponding to the base station becomes larger as the cell size becomes larger. The transmission timing is offset by the transmission timing offset interval set as described above, and transmission is performed. More specifically, the mobile communication base station transmitter includes a plurality of spreading units that spread a plurality of information sequences to be transmitted to a plurality of mobile stations, respectively, with the same spreading code, and output signals of the plurality of spreading units. A plurality of transmission timing offset means for offsetting each transmission timing by a transmission timing offset interval set to be wider as the size of a cell corresponding to the base station is larger, and output signals of the plurality of transmission timing offset means And a transmission signal generator for transmitting a transmission signal generated by the transmission signal generator to a plurality of mobile stations.

Further, the present invention relates to a mobile communication system having a plurality of base stations and a plurality of mobile stations and performing communication using code division multiplexing between the base stations and the mobile stations. After spreading a plurality of information sequences to be transmitted to the mobile station with the same spreading code, each transmission timing is set at a transmission timing offset interval set to be wider as the size of the cell corresponding to the base station is larger. The mobile station receives one of the signals transmitted from the base station transmitting apparatus at a predetermined transmission timing to the mobile station. Then, there is provided a receiving device that obtains an information sequence by despreading the received signal using the same spreading code as that used in the transmitting device. More specifically, the base station sets a plurality of spreading means for spreading a plurality of information sequences to be respectively transmitted to a plurality of mobile stations with the same spreading code, and sets a transmission timing of each of output signals of the plurality of spreading means to the above. A plurality of transmission timing offset means for offsetting at a transmission timing offset interval set to be wider as the size of the cell corresponding to the base station is larger, and a transmission signal obtained by combining output signals of the plurality of transmission timing offset means. And transmission means for transmitting the transmission signal generated by the transmission signal generation means to a plurality of mobile stations, wherein the mobile station is transmitted from a transmission device of the base station. Receiving means for receiving one of the signals transmitted to the mobile station at a predetermined transmission timing; And a despreading means for obtaining information sequence by despreading using the same spreading code as the spreading code using a signal received by means transmitting device.

[0010]

As described above, in the CDMA mobile communication system of the present invention, the base station spreads a plurality of information sequences using the same spreading code, and transmits the spread signals to the mobile station at different transmission timings. Accordingly, by performing transmission timing offset multiplexing in which each spread signal has a unique transmission timing offset, the same number of communication channels as the number of transmission timing offsets are formed using the same spreading code. .

Further, in the present invention, particularly in a transmitting device of a base station, the transmission timing offset interval is set to the base station.
Varied depending on the size of the corresponding cell, the cell Le small base station taking narrowing the transmission timing offset interval, and can accommodate a large number of mobile stations, taking a wide transmission timing offset interval is large base station of the cell To avoid overlapping delay profiles.

On the other hand, each mobile station receives only signals transmitted from the transmitted signal to the mobile station, that is, its own station at a predetermined transmission timing,
By despreading this using the same spreading code used in the transmitting device, the original information sequence is reproduced. In this case, the base station sets the transmission timing offset interval in accordance with the cell size, so that the signal transmitted from the base station having a large cell size to the mobile station can be received by the delay to be received. The information sequence can be correctly reproduced by capturing only the profile part.

[0013]

Embodiments of the present invention will be described below. FIG.
FIG. 2 is a block diagram illustrating a configuration of a transmission device provided in a base station, and illustrates a transmission device that simultaneously transmits to n mobile stations.

In FIG. 1, a spreading code generation circuit 10 is controlled by a control unit 31 to generate information sequences S1, S2,.
A spreading code is generated in synchronization with n. Multipliers 11, 12,
, 1n perform a process of spreading the information sequences S1, S2,..., Sn by multiplying the information sequences S1, S2,.

The transmission timing adjusting circuits 21, 22,... 2
n is controlled by the control unit 31, and the multipliers 11, 12,
.., 1n, the transmission timing is adjusted by giving different delay amounts (offsets) respectively corresponding to n mobile stations. This operation is called a transmission timing offset. Specifically, the control unit 31 instructs the transmission timing adjustment circuits 21, 22,..., 2n on the reference symbol timing interval. The transmission timing setting unit 32 sets the interval of the reference symbol timing,
This is to notify the control unit 31.

The combiner 33 includes a transmission timing adjustment circuit 2
The transmission signal is generated by combining the output signals of 1, 22,... 2n.

FIG. 2 shows two cells having different sizes of areas to which the two base stations belong, respectively.
The size of cell 1 is larger than that of cell 2. The transmission timing setting unit 32 controls the control unit 31 according to the size of the cell.
The interval of the reference symbol timing to be notified is set.
Thereby, the transmission timing offset interval is set according to the size of the cell.

Next, the operation of the transmitting apparatus will be described. The information sequences S1, S2,..., Sn to be transmitted are
, 1n are spread by the same spread signal from the spread signal generation circuit 10, and the transmission timing is adjusted by the transmission timing adjustment circuits 21, 22,. By being synthesized,
Transmission timing offset multiplexed transmission signals are generated at transmission timing offset intervals according to the cell size. The generated transmission signal is output from a transmission circuit unit (not shown) and transmitted to n mobile stations via a wireless line.

By the way, in a mobile communication system, as the size of a cell increases, the possibility that the distance between the base station and the mobile station increases increases, and the mobile station that is far away easily receives multipath with a large delay time. . In this case, assuming that the transmitting device of the base station performs the transmission timing offset by the reference symbol timing offset as shown in FIG. 3A, the delay spread becomes large and wide in a mobile station that has received a multipath with a large delay amount. Would.
Therefore, if the reference symbol timing offset interval is short, the correlation output in the receiver of the mobile station may overlap with the delay spread of the correlation output at the adjacent reference symbol timing as shown in FIG. However, the original information sequence may not be correctly reproduced.

On the other hand, in the present invention, such a problem is avoided by setting the transmission timing offset interval according to the size of the cell. FIGS. 4A and 4B
Represents an example of the transmission timing offset in the transmission device of the base station belonging to the cell 1 and the cell 2 in the present embodiment, using the reference symbol timing.

In the transmitter of the base station of cell 1, as shown in FIG. 4 (a), a plurality (n) of reference points are set within a time defined by one symbol length Ts of information sequences S1, S2,. The symbol timings T11, T12,..., T1n are set, and the delay amounts corresponding to the respective reference symbol timings are given by the transmission timing adjustment circuits 21, 22,. If A is a reference time, the delay amount of each reference symbol timing with respect to this reference time A is d11 at timing T11, d12 at T12, and T12.
In 1n, it is d1n. Reference symbol timing T1
The time intervals of 1, T12,..., T1n are set to a value corresponding to the sum of the delay spread at the time of reception by the mobile station and the guard time.

In the transmission device of the base station of cell 2, as shown in FIG.
, T2n are set, and the delay amount with respect to the reference time A is d21 at the timing T21 and d2 at the timing T22.
2, and d2n for T2n. The time interval between the reference symbol timings T21, T22,..., T2n is set to a value corresponding to the sum of the delay spread at the time of reception by the mobile station and the guard time.

Here, cell 1 and cell 2 are different in size as shown in FIG. 2, and in cell 1 having a large area, there is a high possibility that the delay spread is greatly increased depending on the location in the area. , As shown in FIGS. 4A and 4B, the reference symbol timings d11, d12,.
The offset interval of d1n (d11, d12−d11,
..) Is replaced with the reference symbol timing d21 in cell 2,
, d2n offset intervals (d21, d22
−d21,...).

FIG. 5 is a block diagram showing a configuration of a receiving device provided in each mobile station for receiving a signal transmitted from the transmitting device of FIG. 1, and using a matched filter as a correlator. Is shown. This receiving device includes a matched filter 41, a demodulator 42, a reference symbol timing extraction circuit 43, a control unit 44, and a reception timing setting unit 45. The matched filter 41 detects a correlation between the spread code provided from the control unit 44 and the received signal. The reference symbol timing extraction circuit 43 extracts the reception timing of the signal to the own station from the correlation output of the matched filter 41, and outputs the reception timing to the demodulator 4
Notify 2.

The demodulator 42 reproduces the original information sequence Si (i = 1, 2,..., N) based on the output of the matched filter 41 and the output of the reference symbol timing extraction circuit 43. The demodulator 42 is preferably a RAKE demodulator. For details of the RAKE demodulator, see, for example, Reference 2: U. Grob, ALWelti, E. Zollinger, R. Kung and H. Kauf.
mann, "Microcellular Direct-Sequence Spread-Spectru
m Radio System Using N-Path RAKE Receiver ", IEEE JS
AC, Vol. SAC-8, No. 5, pp. 772-780, June, 1990.

The control section 44 gives the spread code to the matched filter 41 and also gives its own information when the reference symbol timing extraction circuit 43 extracts the timing. The reception timing setting section 45 sets an interval of the reception timing, and notifies the control section 44 of the interval.

Next, the operation of the receiver provided in the mobile station will be described. The received signal, that is, the signal transmitted from the transmitting device in the base station having the configuration shown in FIG. 1 and received by the receiving device shown in FIG.
1 is input. The matched filter 41 includes a control unit 44
In the transmitting apparatus of FIG. 1, the same spreading code as the spreading code generated by the spreading code generating circuit 10 is given. By despreading the spread code by correlation with the received signal, the correlation output is obtained. Occur.

FIGS. 6A and 6B show cell 1 and cell 2
Is an example of the correlation output of the matched filter 41 in the mobile station located at the horizontal axis, where the horizontal axis represents time and the vertical axis represents the correlation value.
As described above, the reception signal of the receiving apparatus of FIG. 5, that is, the transmission signal output from the transmitting apparatus of FIG. 1, is subjected to transmission timing offset multiplexing, and thus corresponds to the reference symbol timings T11 to T1n in the cell 1. The time position, and in cell 2 the reference symbol timing T
Large correlation values are detected at time positions corresponding to 21 to T2n.

The reference symbol timing extraction circuit 43
Information regarding the reception timing of a signal transmitted to its own station, for example, the reference time A in FIG. 4 and information on the delay amount of each reference symbol timing with respect to the time A is notified from the control unit 44 in advance. The reception timing of the own station is recognized from the output of the matched filter 41. Then, the reference symbol timing extraction circuit 43
When it is detected that the reception timing has arrived, it is notified to the demodulator 42. The demodulator 42 reproduces an information sequence Si (i = 1, 2,..., N) for the own station from the output of the matched filter 41 at the own station's reception timing notified from the reference symbol timing extraction circuit 43.

When cell 1 and cell 2 are compared with each other, as shown in FIG. 2, cell 1 has a wider service area than cell 2, so that the delay spread is wider. As described above, the transmission timing offset interval in the cell 1 is set larger than the transmission timing offset interval in the cell 2. Therefore, also in the cell 1, the receiver of the mobile station can fetch only the profile portion to be received from the correlation output of the matched filter 41, and reproduce the information sequence Si correctly.

In the direct spreading-code division multiplexing (DS-CDMA) system using a spreading code, even if signals to a plurality of mobile stations having the same spreading code sequence are transmitted simultaneously, if their delay profiles overlap, Otherwise, each mobile station can fetch only the profile portion to be received and reproduce the information sequence. This means that the information sequence of each channel can be independently demodulated and decoded even if transmission timing offset multiplexing is performed.

Therefore, as in the present invention, the transmission timing offset multiplexing (the offset interval of the reference symbol timing) is set according to the cell size, and the transmission timing offset multiplexing is performed so that the delay profiles of the information sequences do not overlap. If this is performed, the same number of independent communication channels as the transmission timing offset number n can be obtained with one spreading code. This makes it possible to obtain a communication channel n times as large as the conventional one using a limited number of spreading codes having good auto-correlation characteristics and cross-correlation characteristics, thereby realizing a CDMA mobile communication system with a large communication capacity. it can.

The demodulator 42 shown in FIG.
For example, Reference 3: Akihiro Higashi, Tadashi Matsumoto, "B
ER Performance of Adaptive RAKE Diversity (ARD) in D
PSKDS / CDMA Mobile Radio ", IEICE Technical Report, SST92-16, 1992.
It is also possible to use the moon and the ARD receiver described in Japanese Patent Application No. 4-83947 “Spread Spectrum Receiver”.

Although the matched filter 41 is used as a correlator in FIG. 5, any combination of a sliding correlator and the like can be used as long as it can detect a plurality of reference symbol timings.

[0035]

As described above, according to the present invention, after a plurality of information sequences are spread using a common spreading code, transmission timing offset multiplexing is performed to transmit to a plurality of mobile stations. This makes it possible to form independent communication channels for the number of transmission timing offsets.

Therefore, even if a code sequence containing only a small spreading code having good auto-correlation characteristics and cross-correlation characteristics is used, a communication channel having several times the transmission timing offset can be obtained, and the subscriber capacity is large. Moreover, a CDMA communication system having a high degree of freedom in channel selection can be realized.

Further, in the present invention, the transmission timing offset interval in the transmitting device of the base station is set according to the cell size, so that the transmission timing offset interval is narrowed in the base station having a small cell size. A base station having a large cell size capable of accommodating a large number of mobile stations can secure high-quality communication by avoiding overlap of delay profiles by increasing the transmission timing offset interval.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a transmission device installed in a base station according to an embodiment of the present invention.

FIG. 2 is a diagram showing two cells having different sizes in a mobile communication system;

FIG. 3 is a diagram illustrating an example of a transmission timing offset and a correlation output when a delay profile on a receiving side overlaps;

FIG. 4 is a diagram showing an example of a transmission timing offset at a base station of cell 1 and cell 2 in the embodiment.

FIG. 5 is a block diagram showing a configuration of a receiving device installed in a mobile station in the embodiment.

FIG. 6 is a diagram showing an example of a correlation output at a mobile station of a cell 1 and a cell 2 in the embodiment.

FIG. 7 is a block diagram showing a configuration of a transmission device in a conventional CDMA communication system.

[Explanation of symbols]

10. Spread code generation circuits 11-1n ...
Multipliers 21 to 2n Transmission timing adjustment circuit 31 Control unit 32 Transmission timing setting unit 33 Combiner 41 Matched filter 42 Demodulator 43 Reference symbol timing extraction circuit 44 Control unit 45 Reception timing setting unit

Claims (4)

(57) [Claims] A mobile communication base station provided in a base station of a mobile communication system having a plurality of base stations and a plurality of mobile stations, and performing communication using code division multiplexing between the base stations and the mobile stations.
In the transmitting apparatus , after spreading a plurality of information sequences to be transmitted to a plurality of mobile stations with the same spreading code, a cell corresponding to the base station is spread.
For mobile communication characterized in that each transmission timing is offset by a transmission timing offset interval set so as to become wider as the size of the transmission becomes larger .
Base station transmitter. 2. A base station having a plurality of base stations and a plurality of mobile stations.
A mobile station that performs communication using code division multiplexing between a mobile station and a mobile station.
Mobile communication systemMobile communication base station provided in a base station
Transmission deviceAtMultiple information sequences to be transmitted to multiple mobile stations
A plurality of spreading means for spreading with one spreading code; Transmission timing of each of the output signals of the plurality of spreading means
The larger the size of the cell corresponding to the base station,
Between transmission timing offsets set to be wide
Multiple transmission timing offsets offset by intervals
Means, Output signals of the plurality of transmission timing offset means
Transmission signal generating means for generating a transmission signal by combining; A plurality of transmission signals generated by the transmission signal generation means;
Transmission means for transmitting to the mobile station.
Mobile communication base station transmitter. 3. A mobile communication system having a plurality of base stations and a plurality of mobile stations and performing communication using code division multiplexing between the base stations and the mobile stations, wherein the base station includes a plurality of mobile stations. After spreading a plurality of information sequences to be transmitted to the base station with the same spreading code,
A transmission device that offsets the transmission timing at a transmission timing offset interval set so as to be wider as the size of the cell corresponding to the mobile station is larger , One of the signals transmitted from the transmitting device, which has been transmitted to the mobile station at a predetermined transmission timing, is received, and the received signal is the same spreading code as the spreading code used in the transmitting device. A mobile communication system, comprising: a receiving apparatus that obtains an information sequence by despreading a mobile communication system. (4)A base station having a plurality of base stations and a plurality of mobile stations;
A mobile station that performs communication using code division multiplexing between a mobile station and a mobile station.
In mobile communication systems, The base station comprises: Multiple information sequences to be transmitted to multiple mobile stations
A plurality of spreading means for spreading with one spreading code; Transmission timing of each of the output signals of the plurality of spreading means
The larger the size of the cell corresponding to the base station,
Between transmission timing offsets set to be wide
Multiple transmission timing offsets offset by intervals
Means, Output signals of the plurality of transmission timing offset means
Transmission signal generating means for generating a transmission signal by combining; A plurality of transmission signals generated by the transmission signal generation means;
Transmitting means for transmitting to the mobile station, The mobile station transmits a signal transmitted from a transmitting device of the base station.
Transmission time, which is predetermined for the mobile station.
Receiving means for receiving one signal transmitted by the
When, A signal received by the receiving means is used by the transmitting device.
Despread using the same spreading code as the spread code
Mobile communication characterized by having despreading means for obtaining
system.