JP2002159061A - Cdma mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lighten the burdens imposed upon a base station and a CDMA mobile communication system at the time of performing multi-code transmission. SOLUTION: When a mobile terminal MS-b in a soft hand-off area performs the multi-code transmission, the terminal MS-b transmits part of multi-code signals to one base station BS1 and the remaining code signals to a separately connected base station BS2 in an incoming circuit. In an outgoing circuit, a plurality of base stations (BS1 and BS2) transmits different code signals to the mobile terminal MS-b. Consequently, the burden imposed upon one base station is lightened and a more efficient system can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a code division multiple access (hereinafter referred to as "CDM").
A ") mobile communication system.

[0002]

2. Description of the Related Art There is known a technique for efficiently accommodating, in a mobile radio communication system, multimedia terminals having various information transmission speeds, such as data devices and image transceivers, in addition to mobile phones. The main such techniques in the CDMA system include variable spreading factor transmission and multi-code transmission. There are the following documents as techniques in such a field. "Mobile radio access suitable for multimedia: W-CD
MA "Sawabashi, Adachi, IEICE Technical Report SST98-41 (1998-12), pp.
1-8

[0003] Multicode transmission will be briefly described with reference to FIGS. 10 and 11. Here, it is assumed that a data signal having a transmission rate five times the basic transmission rate is transmitted. FIG. 10 shows a schematic configuration of a transmission side in a base station or a mobile terminal, and FIG. It is a figure showing an example. The information signal is spread and transmitted by a spread signal in a modulation unit of a mobile terminal or a base station. In FIG. 10, an information signal is converted into five parallel signals by a serial / parallel converter (S / P converter) 51. Each signal is output to a corresponding one of the spread code codes in the code signal generation circuit units 52 to 56.
It is spread using 1, code2, code3, code4 and code5. In the CDMA system, spreading and despreading are performed using the same code between transmission and reception, so that it is necessary to accurately synchronize signals on the receiving side. Therefore, in general, synchronization acquisition is facilitated by transmitting the synchronization signal simultaneously with the information signal. This synchronization signal is sometimes called a pilot signal. Since the synchronization signal is not information-modulated (ie, all 1s or all -1s), it can be handled as a known signal on the receiving side. In the figure, a synchronization signal is spread with a spreading code code 0 by a synchronization signal generation circuit section 57 and sent to a signal transmission section 58 together with each code signal from the code signal generation circuits 52 to 56. As shown in FIG. 11, the synchronization signal and the information signal are transmitted in synchronization. code 0 and co
de 1 to code 5 are orthogonal signals. Therefore, no interference occurs between the information signal and the synchronization signal in the same terminal. However, it will interfere with other terminal signals,
Measures have been taken, such as making the transmission power of the synchronization signal lower than that of the information signal.

With reference to FIG. 12, a description will be given of a general uplink connection method. In a mobile communication system, each base station controls an area around itself. This area is called a cell. The cell is generally determined by the signal power from the base station. Cell that is controlled by the base station BS1
Set to 1. As shown in FIG. 12, mobile terminal M in cell 1
S_a and MS_b connect to the base station BS1 and transmit signals to BS1 via the uplink. Here, it is shown that MS_a is transmitting with 4 multicodes and MS_b is transmitting with 5 multicodes. FIG. 13 is a diagram showing a connection method in a downlink. As in the case of FIG. 12, a case where mobile terminals MS_a and MS_b are located in cell1 is shown, and mobile terminals MS_a and MS_b are connected to base station BS1 and receive signals from BS1 via the downlink. I do. Here, B
From S1, 4 multicodes are transmitted to MS_a and 5 multicodes are transmitted to MS_b. Also, generally, CD
In the MA system, soft handoff is used. A mobile terminal near a cell boundary (soft handoff region: SH region) can perform stable handoff by connecting to a plurality of base stations. FIG. 14 shows an example of soft handoff. As shown in this figure, a mobile terminal MS_b located in the soft handoff area is connected at the same time as the base stations BS1 and BS2, and both base stations transmit the same signal to MS_b on the downlink.

[0005]

However, when the required transmission amount at a mobile terminal (multi-code terminal) that performs multi-code transmission is large, the number of code signals transmitted at one time increases, which causes an excessively large amount of data for the system. It will give a load. In the uplink, the transmission power from the mobile terminal increases, causing large interference with the connected base station and the adjacent base station. In addition, since the base station requires demodulation circuits for the number of code signals, the call loss rate of the base station itself or the call loss rate of another mobile terminal increases. Also in the downlink, since the base station requires code signal generation circuits (modulation circuits) for the number of code signals, the call loss rate increases. Since the base station allocates transmission power to each code signal, especially when the mobile terminal is near a cell boundary, the transmission power for the multi-code terminal becomes very large. When a terminal is in a soft handoff state, a plurality of base stations will transmit to this terminal with high power.
When the maximum transmission power in the base station is determined, allocating large power to the multicode terminal causes insufficient power to be allocated to other terminals, resulting in deterioration of communication quality.

Accordingly, an object of the present invention is to provide a CDMA mobile communication system capable of reducing the load on the base station and the load on the system when performing multi-code transmission.

[0007]

In order to achieve the above object, a CDMA mobile communication system according to the present invention is a mobile communication system for transmitting signals having various information transmission rates using a multicode signal. The terminal connects to a plurality of base stations and transmits a different code signal to each base station when transmitting a multicode signal. Another CDMA mobile communication system of the present invention is a CDMA mobile communication system that transmits signals having various information transmission rates using a multicode signal. In a CDMA mobile communication system, a mobile terminal connected to a plurality of base stations is provided. Each of the base stations transmits a different code signal. Still another CDMA mobile communication system according to the present invention is a CDMA mobile communication system for transmitting signals having various information transmission rates using a multi-code signal. When transmitting a code signal, a part of the multi-code signal is transmitted to each of the base stations, and the other code signals are transmitted to some of the base stations. This is transmitted to the base station. Still another aspect of the present invention provides a CDMA mobile communication system for transmitting signals having various information transmission rates using a multicode signal.
When transmitting a multi-code signal to a mobile terminal connected to a plurality of base stations, for a part of the multi-code signal, the code signal is transmitted from the base station to the mobile terminal, Other code signals are transmitted from some base stations to the mobile terminal. Still further, different power values are set for the code signal transmitted to each of the base stations or the code signal transmitted from each of the base stations. Furthermore, a different signal spreading factor is set for a code signal transmitted to each of the base stations or a code signal transmitted from each of the base stations.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
A first embodiment of the mobile communication system A will be described. This embodiment relates to the operation in the uplink. As shown, a mobile terminal MS_a located near the base station BS1 connects to the base station BS1, and
In response, a signal is transmitted using 4 multicodes. Also, it is assumed that the mobile terminal MS_b is in a soft handoff region (SH region) between the base stations BS1 and BS2, and can be connected to both base stations. However, the mobile terminal MS_b is the base station BS
Since BS1 is closer to BS1, BS1 is set as a main connection destination base station. Here, it is assumed that the mobile terminal MS_b requests the BS1 to perform communication using 5 multicodes. At this time, the base station BS1
If the number of users under control is large and there is no demodulation circuit for 5 code signals, the connection request from the mobile terminal MS_b is rejected. Since the mobile terminal MS_b is in the soft handoff area and can be connected to the base station BS2, it issues a similar request to BS2. At this time, it is assumed that there is no demodulation circuit for 5 code signals even in BS2. According to the conventional method, in this case, the connection request itself from MS_b is rejected,
Connection is permitted by reducing the number of transmission code signals in MS_b.

On the other hand, in the present invention, the mobile terminal MS_b
Requests a plurality of connectable base stations to connect different code signals. For example, base station BS
Assuming that demodulation circuits for three code signals can be used in mobile station 1, mobile terminal MS_b transmits a spreading code code to BS1.
Request connection of three code signals spread by 1 to code 3. Also, for base station BS2, spreading code code 4
And a connection of two code signals spread by code5. In the following, spreading codes code 1, code 2,
,..., Code 5 are referred to as code signal 1, code signal 2,.

As described above, even when the number of demodulation circuits available in one base station is insufficient, the reception of a part of the code signal is allocated to the adjacent base station, so that the connection request rejection of the multi-code signal is rejected. Can be avoided. Also, even if the base station BS1 has a large number of usable demodulation circuits and can accept a connection request from the mobile terminal MS_b, if the multicode transmission amount in the MS_b is large, the base station BS1 should connect to the MS_b. Thus, the number of usable demodulation circuits in the base station may decrease, and connection requests from other mobile terminals may not be accepted. For this reason, a call loss in BS1 can be reduced by pre-allocating a part of the code signal in MS_b to base station BS2. Furthermore, when it is assumed that all code signals can be assigned to the base station BS2, since the distance from the mobile terminal MS_b to the base station BS2 is longer than the distance to the base station BS1, higher transmission power is required. The transmission power value increases for each code signal. When the number of transmission codes in the mobile terminal MS_b is large, the transmission power becomes very high and the base station BS1
The amount of interference with the light also increases. By allocating a code signal to a plurality of base stations as in the present invention, it is possible to suppress an increase in interference power.

FIG. 2 shows a C of the present invention operating as described above.
FIG. 2 is a block diagram illustrating a main configuration of a mobile terminal in a DMA mobile communication system. Here, this mobile terminal MS_b
However, as described above, a case where a 5-multicode signal is transmitted is shown. In this figure, an information signal is converted by an S / P converter 11 into five parallel signals C1 to C5.
Each of the signals C1 to C5 is converted into a corresponding spread code code 1 to co at a corresponding code signal generation circuit 13 to 17, respectively.
The signal is spread by de 5 and becomes code signal 1 to code signal 5. The signal transmission unit 19 transmits each code signal together with the synchronization signal from the synchronization signal generation circuit 18. Here, the code control unit 12 determines which code signal is transmitted to each base station (BS1, BS2) based on information from the base stations (BS1, BS2) (information such as the number of available demodulation circuits and communication quality at the base station). It decides whether to allocate to the station, and transmits it to the S / P converter 11 and each of the code signal generation circuits 13 to 17.

FIG. 3 is a diagram showing an example of a multicode signal transmitted from the mobile terminal configured as described above. As shown in this figure, in this example, code signal 1, code signal 2 and code signal 3 are assigned to base station BS1, and code signal 4 and code signal 5 are assigned to base station BS2. When a multi-code signal as shown in FIG. 3 is transmitted from the mobile terminal MS_b, the base station BS1 receives the code signals 1 to 3, and the base station BS2 receives code signals 4 and 5. Base stations BS1 and B
Each code signal received in S2 is sent to a control station (not shown), and the control station combines all the code signals 1 to 5 transmitted from the mobile terminal MS_b, and sends them to the destination of the signal. Become.

Next, an embodiment of the CDMA mobile communication system of the present invention applied to the downlink of the present invention will be described with reference to FIG. As in the case of FIG. 1, the mobile terminal MS_a connects to the base station BS1 and requests the BS1 to transmit a signal with 4 multicodes. It is assumed that the mobile terminal MS_b is in the soft handoff area between the base stations BS1 and BS2 and can connect to both base stations. Where M
Since S_b is closer to BS1, BS1 is set as a main connection destination base station. Here, it is assumed that the mobile terminal MS_b has requested the base station BS1 to transmit with 5 multicodes. At this time,
Since the base station BS1 has a large number of users in charge and does not have a modulation circuit for 5 code signals, it rejects the connection request from MS_b. Since the mobile terminal MS_b is in the soft handoff area and can be connected to the base station BS2, MS_b issues a similar request to the base station BS2. At this time, BS2
However, it is assumed that there is no modulation circuit for five code signals. According to the conventional method, in this case, the connection request itself from MS_b is rejected, or the connection is permitted by reducing the number of transmission code signals at the base station.

On the other hand, in the present invention, a plurality of connectable base stations BS1 and BS2 transmit different code signals to the mobile terminal MS_b. For example, assuming that a modulation circuit for three code signals can be used in base station BS1, code signals 1, 2 and 3 are transmitted to mobile terminal MS.
Send to _b. Further, the base station BS2 transmits two signals of code signals 4 and 5 to the mobile terminal MS_b. As described above, even when the number of available modulation circuits in one base station is insufficient, the adjacent base station bears transmission of a part of the code signal, thereby avoiding rejection of a connection request for a multicode signal. It becomes possible. Further, in base station BS1, there are a large number of available modulation circuits, and mobile terminal MS
Even if the connection request from MS_b can be accepted, if the multi-code transmission amount to MS_b is large, the number of available modulation circuits is reduced by connecting to MS_b, and connection requests from other mobile terminals are reduced. May not be accepted. For this reason, by distributing a part of the code signal required for MS_b to the base station BS2 in advance, it is possible to reduce the call loss at BS1. Further, the mobile terminal MS_b
Exists near the cell boundary, the propagation loss to MS_b is large, and the base station needs to allocate a large amount of power to satisfy the communication quality required by MS_b. Mobile terminal MS
When the multi-code transmission amount for _b is large, power for the number of codes is required, so that the load on one base station becomes very large. In the downlink, transmission diversity for transmitting the same signal from a plurality of base stations is considered, but in this case, the power burden on the plurality of base stations increases. By dividing the code signal transmitted by each base station as in the present invention, it is possible to reduce the power burden on one base station.

FIG. 5 is a diagram showing a main configuration of a base station according to the present embodiment that operates as described above. Here, it is assumed that the configuration of the base station BS1 is shown, and there is a request for transmission of a 5-multicode signal from the mobile terminal. As described above, the base station BS1 transmits the three code signals of the code signals 1 to 3 as described above. It shall be transmitted to the mobile terminal MS_b. In FIG. 5, an information signal to be transmitted to the mobile terminal MS_b supplied from a control station (not shown) is converted by an S / P converter 21 into five parallel signals C1 to C5.
Of the signals C1 to C5, the signals to be transmitted from the base station (BS1) (in this example, C1 to C3) are the corresponding spreading codes code1 to code3 in the corresponding code signal generation circuits 23 to 25, respectively. Spread and code signals 1-3
Becomes Here, the code control unit 22 determines which code signal is to be transmitted to the mobile terminal MS_b based on information from a control station (not shown) located above the base station (control information that specifies a code signal to be transmitted by this base station). Judgment, said S
/ P conversion unit 21 and code signal generation circuits 23 to 25
To communicate. Accordingly, the base station BS1 transmits the code signals 1 to 3, and the code signal generation circuits 23 to 2
The information signals C1 to C3 after the parallel conversion are sent to only 5 and are spread-modulated by the respective code signal generation circuits. The signal transmission section 29 transmits the code signals together with the synchronization signal from the synchronization signal generation circuit 28. Similarly, in the base station BS2, only C4 and C5 of the five parallel signals output from the S / P converter 21 are supplied to the code signal generation circuits 26 and 27 and spread by the spreading codes code4 and code5. , Code signals 4 and 5 are generated and transmitted to the mobile terminal MS_b.

FIG. 6 is a diagram showing an example of a multicode signal received by the mobile terminal MS_b. Here, the code signals 1 to 3 are transmitted from the base station BS1, and the code signals 4 and 5 are transmitted from the base station BS2. The mobile terminal MS_b receives signals from both base stations simultaneously. Normally, the mobile terminal MS_b
It has a plurality of fingers for reception, and by allocating these to reception of signals from the base stations BS1 and BS2, it is possible to simultaneously receive signals from both base stations. However, since the distance between the mobile terminal MS_b and the base stations BS1 and BS2 is different, the code signals 1 to 3
And the code signals 4 and 5 are not necessarily received at the same timing. Therefore, it is necessary for the mobile terminal MS_b to restore the original signal by adjusting the timing of the signals received from both base stations.

In the above description, S / P conversion is performed in each base station, and only the information to be transmitted by the own station among the converted signals is spread-modulated and transmitted. Without being limited, for example, when information to be transmitted to the mobile terminal MS_b is long information, from the control station, the transmission information is divided and supplied to each of the base stations. The supplied information may be S / P converted to the number of code signals assigned to the own station, spread modulated, and transmitted. For example, the first half of the transmission information is the base station BS1, and the second half is the base station B
S2, and the BS1 S / P-converts the first half into three parallel signals and supplies them to the code signal generation circuits to generate the code signals 1 to 3, thereby generating the mobile station MS_b.
And the BS2 performs S / P conversion of the latter half into two parallel signals to generate code signals 4 and 5 to generate MS_b
May be transmitted. In this case, the mobile terminal MS
In _b, the original signal is restored by following the information restored from the signal received from the base station BS1 with the information restored from the signal received from the base station BS2.

Another embodiment of the CDMA mobile communication system according to the present invention will be described with reference to FIGS. Here, FIG. 7 is a diagram illustrating a case where the present invention is applied to an uplink, and FIG. 8 is a diagram illustrating a case where the present invention is applied to a downlink. When an information signal is subjected to parallel conversion, it is possible to separate the information into high-priority information and low-priority information. In this case, the code signal generates a high-priority code signal and a low-priority code signal. For example, in music information, important information is included in a low frequency portion, and a high frequency portion relates to sound quality. For this reason,
Even if the high frequency part is deleted, the sound quality is deteriorated, but basic information of the sound can be transmitted. Therefore, when the information signal that is a music signal is parallelized to a plurality of data, the music signal is divided into signals of different frequency bands by a plurality of band filters, and the signals are coded. Each is supplied to the code signal generation circuit to generate a code signal. In this case, the code signal corresponding to the audio signal in the lower frequency band has a higher priority, and the code signal corresponding to the audio signal in the higher frequency band has the lower priority. Such a priority exists not only in music information but also in various data.

According to this embodiment of the present invention, when there are such a high-priority code signal and a low-priority code signal, a transmission error with respect to a high-priority code signal is reduced, and its reliability is reduced. Is to improve. Here, it is assumed that the code signals 1 to 3 have high priority and the code signals 4 and 5 have low priority. In the uplink, as shown in FIG. 7, the mobile terminal MS_b transmits code signals 1 to 3 to the base station BS1, and transmits code signals 1 to 5 to the base station BS2. That is, the code signals 1 to 3 having high priority are received by both BS1 and BS2, and the one having higher communication quality is selected (or signals from both base stations are combined), so that code signal 1 is obtained. -3 can be reduced. This selection or combination processing is performed by a control station located above the base stations BS1 and BS2. The control station selects one of the received signals from the base stations BS1 and BS2 based on the BER, the received power, or the like, or combines the two.

On the downlink, as shown in FIG. 8, the base station BS1 transmits code signals 1 to 3 to the mobile terminal MS_b, and the base station BS2 transmits the code signals 1 to
Send 5 By combining the code signals 1 to 3 received from both base stations in the mobile terminal MS_b, transmission errors for the code signals 1 to 3 can be reduced. As described above, according to the present embodiment, the reliability of a code signal having high importance can be increased by performing diversity between base stations for a part of the multicode signal.

Another embodiment of the CDMA mobile communication system according to the present invention will be described with reference to FIG. Here, the connection is performed on the uplink, and as in the embodiment shown in FIG. 1, code signals 1 to 3 are transmitted to base station BS1, and code signals 4 and 5 are transmitted to base station BS2. And Here, assuming that the priority of the code signals 1 to 3 is high, the transmission power P1 of the code signals 1 to 3 is set higher than the transmission power P2 of the code signals 4 and 5, so that the code signal 1 having a high priority is set. ~ 3 signal errors can be reduced. Further, even if the priority of each code signal is the same, the distance to each base station (that is, the propagation attenuation)
And the communication quality at each base station is different, so it is necessary to set power according to those parameters. When the distance to the base station BS1 is long, or when the communication quality at the base station BS1 is poor, the transmission power P1 for the code signals 1 to 3 is set.
Is set high, signal errors can be reduced.

Further, code signals 1 to 3 and code signal 4
In (5) and (5), the spreading factor in the signal spreading can be set differently. Assuming that the priority of the code signals 1 to 3 is high, the spreading factor for the code signals 1 to 3 is set higher than that of the code signals 4 and 5 (since the signal band is the same, the code signals 1 to 3 are set). 3 is reduced). By increasing the spreading factor in this way, it is possible to reduce signal errors for the code signals 1 to 3.

[0023]

As described above, the CDMA of the present invention
According to the mobile communication system, the multi-code signal transmission is shared by a plurality of base stations, so that the load on one base station is reduced and a more efficient system is obtained. Further, by transmitting the same code signal to a plurality of base stations or transmitting the same code signals from a plurality of base stations, the reliability of the code signal can be improved. Furthermore, by setting the transmission power of some code signals high or setting the spreading factor high, it is possible to reduce signal errors for the code signals.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an embodiment applied to an uplink of a CDMA mobile communication system according to the present invention.

FIG. 2 is a diagram showing a main configuration of a mobile terminal in the embodiment shown in FIG.

FIG. 3 is a diagram for explaining multicode transmission in the embodiment shown in FIG.

FIG. 4 is a diagram schematically illustrating an embodiment applied to a downlink of a CDMA mobile communication system according to the present invention.

FIG. 5 is a diagram showing a main configuration of a base station in the embodiment shown in FIG.

FIG. 6 is a diagram for explaining multicode transmission in the embodiment shown in FIG.

FIG. 7 is a diagram schematically illustrating another embodiment of the present invention applied to an uplink.

FIG. 8 is a diagram schematically illustrating another embodiment of the present invention applied to a downlink.

FIG. 9 is a diagram for explaining multi-code transmission according to still another embodiment of the present invention.

FIG. 10 is a diagram illustrating a configuration of a transmission unit in a conventional multicode transmission system.

FIG. 11 is a diagram for explaining multicode transmission.

FIG. 12 is a diagram illustrating a connection method in an uplink.

FIG. 13 is a diagram illustrating a connection method in a downlink.

FIG. 14 is a diagram illustrating a connection method on a downlink in a soft handoff area.

[Explanation of symbols]

 11, 21 S / P conversion section 12, 22 Code control section 13-17, 23-27 Code signal generation circuit 18, 28 Synchronization signal generation circuit 19, 29 Signal transmission section BS1, BS2 Base station MS_a, MS_b Mobile terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K022 EE02 EE21 5K067 AA13 AA33 BB04 BB21 CC10 EE02 EE10 GG08 JJ12

Claims (6)

[Claims] 1. A CDMA mobile communication system for transmitting signals having various information transmission rates using a multicode signal, wherein a mobile terminal is connected to a plurality of base stations and transmits a multicode signal. A CDMA mobile communication system transmitting different code signals to each base station. 2. A CDMA mobile communication system for transmitting signals having various information transmission rates using a multicode signal, wherein each base station has a different code for a mobile terminal connected to a plurality of base stations. A CDMA mobile communication system for transmitting a signal. 3. In a CDMA mobile communication system for transmitting signals having various information transmission rates using a multicode signal, a mobile terminal is connected to a plurality of base stations and transmits a multicode signal. For some code signals of the multi-code signal, transmit to each of the base stations,
The other code signal is transmitted to some of the base stations.
A mobile communication system. 4. In a CDMA mobile communication system for transmitting signals having various information transmission rates using a multicode signal, when transmitting a multicode signal to a mobile terminal connected to a plurality of base stations, Some of the multi-code signals are transmitted from each of the base stations to the mobile terminal, and other code signals are transmitted from some of the base stations to the mobile terminal. A CDMA mobile communication system, comprising: 5. A different power value is set for a code signal transmitted to each of the base stations or a code signal transmitted from each of the base stations.
5. The CDMA mobile communication system according to any one of claims 1 to 4. 6. The method according to claim 1, wherein a different signal spreading factor is set for a code signal transmitted to each of the base stations or a code signal transmitted from each of the base stations. A CDMA mobile communication system according to