JP2749238B2 - 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 between two correlated code sequences is τ, strong correlation 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 transmitting device provided in, after spreading a plurality of information sequences to be respectively transmitted to a plurality of mobile stations with the same spreading code, each at a transmission timing offset interval set according to the transmission power The transmission is performed by offsetting the transmission timing. 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 at a transmission timing offset interval set according to the transmission power,
Transmission signal generation means for combining the output signals of the plurality of transmission timing offset means to generate a transmission signal, and transmission means for transmitting the transmission signal generated by the transmission signal generation means to a plurality of mobile stations. Have.

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 respectively transmitted to the mobile station with the same spreading code, having a transmission device that transmits by offsetting each transmission timing at a transmission timing offset interval set according to the transmission power, The mobile station receives one signal transmitted at a predetermined transmission timing to the mobile station among the signals transmitted from the transmission device of the base station, and uses the received signal in the transmission device. It has a receiving device that obtains an information sequence by despreading using the same spreading code as the spreading code. For more information,
A plurality of spreading means for spreading a plurality of information sequences to be transmitted to a plurality of mobile stations with the same spreading code,
A plurality of transmission timing offset means for offsetting the transmission timing of each of the output signals of the plurality of spreading means at a transmission timing offset interval set according to the transmission power, and the output signals of the plurality of transmission timing offset means are combined. Transmission signal generating means for generating a transmission signal, and transmitting means for transmitting the transmission signal generated by the transmission signal generation means to a plurality of mobile stations. Receiving means for receiving one signal transmitted at a predetermined transmission timing to the mobile station among the transmitted signals, and the signal received by the receiving means being the same as the spreading code used in the transmitting apparatus. Despreading means for despreading using a spreading code to obtain an information sequence.

[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, especially in the transmitting device of the base station, the transmission timing offset interval is made different depending on the transmission power. A mobile station can be accommodated, and a transmission timing offset interval is widened in a base station having a large transmission power 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, by setting the transmission timing offset interval in accordance with the transmission power on the base station side, the signal transmitted from the base station having a large transmission power to the mobile station also
The information sequence can be correctly reproduced by taking in only the part of the delay profile to be received.

[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 synthesizing the output signals of 1, 2,. The transmission circuit 34
Upon receiving the designation of the transmission power from the control unit 31, it transmits the transmission signal from the combiner 33 at the designated transmission power. Control unit 3
1 instructs the transmission timing adjustment circuits 21, 22,..., 2n to set the above-described reference symbol timing intervals in accordance with the transmission power designation information sent to the transmission circuit 34. That is, when the transmission power specified for transmission circuit 34 is large, control unit 31 sets the interval of the reference symbol timing wide, and conversely, when the transmission power specified is small, it sets the interval of the reference symbol timing narrow.

FIG. 2 shows two base stations to which each belongs.
In this case, the transmission power in the cell 1 is larger than that in the cell 2. Here, the transmission timing setting unit 32 sets the reference symbol timing interval to be notified to the control unit 31 according to the transmission power, as described above. Thereby, the transmission timing offset interval is set according to the transmission power. In the present embodiment, the conditions other than the transmission power of each base station, that is, the topography of the installation position, the height and the directivity of the antenna, and the like are almost the same.
In this case, it can be predicted that the service area of the cell 1 is wider than the service area of the cell 2 as shown in FIG.

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 transmission power. The generated transmission signal is output from the transmission circuit 34 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, by setting the transmission timing offset interval according to the transmission power,
Such a problem is avoided. FIGS. 4A and 4B show examples of transmission timing offsets in the transmission devices of the base stations belonging to the cells 1 and 2 in the present embodiment, using reference symbol timings.

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 interval of 1, T12,..., T1n is about a value corresponding to the sum of the delay spread and the guard time at the time of reception of the mobile station within the service area estimated by the magnitude of the transmission power of the transmission device of the base station. Is set.

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 the sum of the delay spread and the guard time at the time of reception of the mobile station within the service area, which is also estimated by the magnitude of the transmission power of the transmission device of the base station. Is set to a value corresponding to.

Here, as shown in FIG. 2, the cell 1 and the cell 2 have different service areas due to the difference in the transmission power of the base station, and have a large transmission power of the base station, that is, a cell having a large service area. 1, in consideration of the high probability that the delay spread is greatly spread depending on the location in the area, the offset intervals of the reference symbol timings d11, d12,..., D1n as shown in FIGS. d11, d12-d11,...) are used as reference symbol timings d21, d22,
.., D2n offset intervals (d21, d22−d2
1, ...).

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.

Comparing cell 1 and cell 2, as shown in FIG. 2, cell 1 has higher transmission power than cell 2 and thus has a wider service area, so that the delay spread is wider. In the example, as shown in FIG. 3, 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.

Accordingly, if the transmission timing offset interval (reference symbol timing offset interval) is set according to the transmission power and transmission timing offset multiplexing is performed so that the delay profiles of the information sequences do not overlap as in the present invention. , 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.

In the above description, the transmission power of the base station is assumed to be constant. However, when performing transmission power control, the transmission timing offset is determined according to the maximum transmission power within the range of the transmission power controlled by the channel. By controlling the interval,
The same effect as described above can be obtained.

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 correlator that can detect a plurality of reference symbol timings, such as a combination of sliding correlators, can be used.

[0036]

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 autocorrelation characteristics and cross-correlation characteristics is used, a communication channel several times the transmission timing offset can be obtained. Moreover, a CDMA communication system having a high degree of freedom in channel selection can be realized.

Further, in the present invention, by setting the transmission timing offset interval in the transmitting device of the base station in accordance with the transmission power, the base station having a small transmission power has a narrower transmission timing offset interval so as to increase the number of mobile stations. In a base station having a large transmission power, a transmission timing offset interval is widened to avoid overlapping delay profiles, thereby ensuring high-quality communication.

[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 34 Transmission circuit 41 Matched filter 42 Demodulator 43 Reference symbol timing extraction circuit 44 Control unit 45 Reception Timing setting section

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-133152 (JP, A) JP-A-60-148245 (JP, A) JP-A-63-281536 (JP, A)

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 device , after a plurality of information sequences to be transmitted to a plurality of mobile stations are spread with the same spreading code, each transmission timing is offset at a transmission timing offset interval set according to the transmission power and transmitted. Transfer characterized by
Mobile communication 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
Off the transmission timing set according to the transmission power
Multiple transmission timings offset at set intervals
Fset 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 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 includes a plurality of mobile stations to be transmitted to a plurality of mobile stations.
After spreading the same information sequence with the same spreading code,
At the transmission timing offset interval set accordingly
Transmission that offsets each transmission timing and transmits
Device The mobile station transmits a signal transmitted from a transmitting device of the base station.
To the mobile station Transmission time
One signal transmitted by the
The same spreading code as the spreading code used in the transmitting device.
A receiving device that obtains an information sequence by despreading using
And 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 includes a plurality of mobile stations to be transmitted to a plurality of mobile stations.
Spreading means for spreading the same information sequence with the same spreading code
When, Transmission timing of each of the output signals of the plurality of spreading means
Off the transmission timing set according to the transmission power
Multiple transmission timings offset at set intervals
Fset 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.