JP2003115820A - Cdma mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To vary an information transmission speed by changing a diffusion coefficient in a CDMA mobile communication system. SOLUTION: A transmission speed control part 11 on the side of transmission determines the code length of a spread code and a number of repetitions on the basis of the transmission speed of an information signal. A spread code generation part 12 generates the spread code of a correspondent code length and a delay part 13 generates a spread code repeating that code just for the applied number of repetitions. A signal diffusion part 14 diffuses one bit of information with the spread code repeatedly using the spread code of a short cycle from the delay part 13 and the information is transmitted from a signal transmission part 15. In a receiving part, a correspondent spread code is generated by a transmission speed control part 25, a spread code generation part 24 and a delay part 23 and inversely diffused. Otherwise, by diffusing the information signal by using one part of the spread code of a long cycle, the information transmission speed can be varied at much shorter intervals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code division multiple access (hereinafter referred to as "CDM").
"A". ) System is used for the mobile communication system.

[0002]

2. Description of the Related Art There is known a technique for efficiently accommodating, in a mobile radio communication system, a multimedia terminal having various information transmission speeds such as a data device and an image transceiver in addition to a mobile phone. Variable spreading factor transmission and multi-code transmission are the main techniques of this kind in the CDMA system. There are the following documents regarding the system using the variable spreading factor transmission. “Orthogonal Forward Link Using Orthogonal Multi-S
preading Factor Codes for Coherent DS-CDMA Mobile R
adio ”IEICE Trans. Commun., Vol. E81-B, No.4, pp.
777-784, Apr. 1998.

Multi-code transmission will be briefly described with reference to FIG. The multicode transmission here means a signal for one mobile station from the base station or a signal for one base station from one mobile station. FIG. 6 assumes a signal having a transmission rate 8 times the basic transmission rate. The information signal is spread by the spreading code in the base station or the mobile terminal and transmitted. The information signal is converted into eight parallel signals, and each signal is spread using spreading codes code 1, code 2, code 3, ..., Code 8. Orthogonal code is used for spreading code,
The spreading codes (code 1 to code 8) are orthogonal to each other.
In multi-code transmission, the number of signals (code number) transmitted at the same time is determined according to the transmission speed. Therefore, when modulating / demodulating a signal, modulators and demodulators for the number of codes are required. In particular, in a mobile station that transmits / receives at a high transmission rate, the device scale increases accordingly.

On the other hand, in variable spreading factor transmission, the spreading factor of an information signal is determined by its transmission rate. When an information signal having a transmission rate twice as high as the basic transmission rate is transmitted using the same frequency band, the spreading factor becomes one half of that at the transmission at the basic transmission rate. On the contrary, if the transmission rate is ½, the spreading factor is doubled. FIG. 7 is a diagram showing an example of transmission with a variable spreading factor. In FIG. 7A, 1 of the information signal
Bits are spread with a spreading code of 8 chips. In (b), 1 bit of the information signal is spread with a spreading code of 4 chips. Since the transmission frequency bands are the same, the chip length (the interval of one chip) is the same. As a result, in (b), the spreading factor is halved and the signal transmission rate is doubled. Since the spreading factor is halved, in order to maintain the communication quality, the transmission power A of the signal needs to be about twice that in the case of (a). In variable spreading factor transmission, the spreading factor changes depending on the transmission speed, so if the modulator and demodulator have a function that supports variable spreading factor transmission, a pair of modulator and demodulator can send and receive signals. . Therefore, the scale of the device is not increased.

In the downlink of CDMA, signals for each mobile station are collectively transmitted from the base station. That is, the signal for each mobile station is transmitted in multicode. Since orthogonal signals are used as spreading codes and multi-code transmission is performed, the signals are orthogonal to each other, so that the signals for mobile stations do not interfere with each other during transmission. In the uplink, signals from mobile stations are randomly transmitted, so that the signals cannot be synchronized with each other, and signals from other mobile stations all interfere. Since the downlink can perform synchronous transmission, a higher capacity than the uplink can be obtained. However, due to the influence of multipath, perfect orthogonality cannot be maintained at the time of downlink reception, resulting in a decrease in capacity.

When a high transmission rate signal to one mobile station is multicode-transmitted in a CDMA downlink, the transmission method is the same as the method of transmitting the signal to each mobile station in multicode. However, the mobile station requires demodulators for the number of multi-codes. When transmitting a high transmission rate signal to one mobile station with a variable spreading factor, it is important to maintain orthogonality with the signals for other mobile stations when the spreading factor of the signal to that mobile station is changed. . If orthogonality between signals is not maintained at the time of transmission, the capacity in the downlink decreases. Therefore, it is necessary to allocate spreading codes that maintain orthogonality even when the signal spreading factor is changed.

FIG. 8 shows an example of how to make an orthogonal code. Let A be a block of orthogonal codes. A and -A (inversion sign of A) are arranged as shown in the figure to form a block B. This time,
The code number of the block B is twice that of the block A. If A is a block of orthogonal codes with a code number of 4, the code number of B is 8. An example of block A is shown in FIG.
The block A is a set of four spreading codes F1 to F4 having a code length of 4 (code period 4). The spreading codes F1 to F4 are orthogonal to each other, and the spreading codes in the block B formed from the block A are also orthogonal to each other. As shown in FIG.
The block C can be made using the block B in the same manner. In this way, by combining a block of a certain orthogonal code and its inverted block, a block of an orthogonal code having twice the number of codes can be created. The spread rate of the signal spread by the spread code in the block B is 1/2 and the transmission rate is doubled in comparison with the signal spread by the spread code in the block C of 1 bit of the information signal.

An example of the orthogonal code created in this way is shown in FIG. It is assumed that the block A in FIG. 9A is made of spreading codes F1 to F4 shown in FIG. 9B, respectively. (A) is composed of eight columns L1 to L8, and each column is composed of four spreading code sequences, so that the total number of codes is 32. With this, up to 32 stations,
It becomes possible to allocate orthogonal spreading codes. The code length of each spreading code is 32, and the spreading factor of the signal at this time is 32. When the transmission rate of a signal for a certain mobile station is doubled, for example, it is spread using the spreading code in the block (A, A, -A, -A) indicated by X in L3. The diffusion rate at this time is 16. However, the same block as X also exists in L7. Therefore, for example, when the second spreading code in the block X (spreading code consisting of code F2, hereinafter F2 code) is used when performing double-speed transmission, the signal to another mobile station is L3. F2
The code and the F2 code in L7 cannot be used.
As an example of the case of performing quadruple speed transmission, it is assumed that the block Y (A, -A) in L4 is used. The diffusion rate at this time is 8
Becomes For example, if the F4 code in block Y is used, the F4 code in L2, L4, L6, and L8 cannot be used. By selecting the spreading code in this way, it is possible to make signals between other stations orthogonal when transmitting on the downlink.

FIG. 10 is a diagram showing an example of such variable speed transmission in the conventional system. In the example shown in this figure,
The basic rate transmission of (a) is performed using the spreading code in L4. Also, the double speed transmission of (b) is performed using the spreading code in the first half block (A, -A, -A, A) in L4, and the quad speed transmission of (c) is in L4. The spreading code in the first quarter block (that is, the block Y in FIG. 9) is used.

[0010]

However, as shown in FIG. 10, when a signal is transmitted at a transmission rate higher than the basic transmission rate, the spreading factors are 1/2, 1/4, 1/8, 1 /
16 and so on, and the transmission speed is doubled, 4 times, 8 times, 16 times.
Doubled ... On the other hand, in multi-code transmission, the transmission rate can be freely changed according to the number of codes transmitted at the same time. In a mobile communication system, it is required that the transmission rate can be freely set in order to provide more flexible service. In addition, when the number of other mobile stations in the cell or the transmission rate of signals for other mobile stations increases or when the amount of interference from adjacent cells increases, a high level is set to prevent quality deterioration or communication disconnection in the entire system. It is conceivable to temporarily reduce the transmission rate of signals that are communicating at the transmission rate. Also at this time, by freely setting the transmission speed,
More flexible response is possible. Therefore, according to the present invention, when the transmission rate is made variable by the variable spreading factor transmission, the CDMA can freely set the transmission rate at finer intervals.
It is intended to provide a mobile communication system.

[0011]

In order to achieve the above object, the CDMA mobile communication system of the present invention can change the transmission rate by changing the signal spreading factor.
In a DMA mobile communication system, a 1-bit signal is spread using a spreading code which is an original spreading code once or a plurality of times, and a code length of the original spreading code or The spreading factor of the signal is made variable by changing at least one of the repetition numbers. Further, another CDMA mobile communication system of the present invention is a CDMA mobile communication system capable of varying a transmission rate by changing a signal spreading rate,
A 1-bit signal is spread by using a spreading code created by using all or a part of the original spreading code, and for spreading the 1-bit signal of the original spreading code. The signal spreading factor is made variable by changing the ratio of the portion used for. Furthermore, still another CDMA mobile communication system of the present invention makes the transmission rate of the signal variable by changing the spreading factor of the signal by any one of the above-described methods for each one bit or every plural bits of the signal. Is.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described with reference to FIGS. First, the variable rate transmission method used in the first embodiment of the present invention will be described with reference to FIG. Here, it is assumed that the block Y (A, -A) shown in FIG. 9 is used as the original spreading code. FIG. 2A shows a state in which one bit of the information signal is spread by the spreading code in the block Y, and shows transmission at a transmission rate four times the basic transmission rate. This is similar to the transmission in the conventional method shown in FIG. In FIG. 2B, the spreading code in the block Y is 2
One bit of the information signal is spread repeatedly and spread twice, resulting in a double transmission rate. The portion surrounded by a thick line is the information signal 1
Become a bit. In FIG. 2C, the spreading code in the block Y is repeated three times to spread one bit, and in this case, the transmission rate is 4/3 times. In (d) of FIG. 2, the spreading code in the block Y is spread by a spreading code that is repeated four times, and transmission is performed at the basic transmission rate. In this way, by spreading one bit of the information signal by the spreading code that is generated by repeating the original orthogonal spreading code one to a plurality of times, the transmission rate can be changed with a finer change width compared to the conventional method. You can When the maximum transmission speed is 8 times,
In addition to 4, 2, 1x speed transmission, 8/3, 8/5, 4
Transmission at ⅓ and 8/7 times speed is possible. Further, it is possible to maintain orthogonality with the signal between other stations.

FIG. 1 is a diagram showing a main configuration of a transmission section and a reception section according to the first embodiment of the present invention.
(A) is a transmitter (for example, a base station transmitter), and (b) is a receiver (for example, a mobile station receiver). In the transmission section of FIG. 1A, the transmission rate control section 11 calculates the transmission rate from the information signal. Alternatively, the speed information is directly obtained from the device or the like that sends the information signal. Transmission rate control unit 1
In 1, the code length of the spreading code used for signal spreading and the number of repetitions of the code are determined from the obtained speed information. In the example of FIG. 2, it is assumed that the spreading code length of the same length as the spreading code in the block Y is selected. From the example of FIG. 9, the code length of the spread code in the block Y is 8. When performing the quadruple rate transmission of FIG. 2A, the transmission rate control unit 11 sends information of the code length 8 and the repetition number 1. That is, 1 bit of the signal is spread by the spreading code having the code length of 8. In the example of FIG. 9, when the code length is 8, there are two blocks (A, A) and (A, −A), and there are eight types of spreading codes. Which code to use depends on the spreading code. The generation unit 12 selects. Figure 2
In the case of the 4/3 times speed transmission of (c), the transmission speed control unit 11 sends information of code length 8 and repetition number 3.
When the double speed transmission of (b) is performed, there are a method of repeating the spreading code of code length 8 twice and a method of repeating the spreading code of code length 16 once. The former is used when the maximum transmission speed of the information signal is four times, and the latter is used when the maximum transmission speed is two times. This is because the number of codes that can be used at the same time is limited when a spread code having a short code length is used. In the spread code generator 12,
The spread code having the code length given from the transmission rate control unit 11 is generated and transmitted. In the delay unit 13, the spread code generation unit 1
The spreading code generated in 2 is delayed by the code length and is repeated by the number of repetitions given from the transmission rate control unit 11 to generate a spreading code used for spreading one bit of the information signal, It is sent to the diffusion unit 14. The signal spreading unit 14 spreads the 1-bit information signal by the spreading code from the delay unit 13. The information signal spread by the signal spreader 14 is transmitted from the signal transmitter 15.

FIG. 1B shows the configuration of the receiving section corresponding to the transmitting section. It is assumed that the speed information of the information signal is included in the header portion of the information, or is given from the transmission unit to the transmission speed control unit 25 of the reception unit via the control channel or the like. Alternatively, the spread code length and the number of repetitions may be directly notified. Similar to the transmission unit, the transmission rate control unit 25 calculates the spreading code length and the number of repetitions corresponding to the rate information, and the spreading code generation unit 24 and the delay unit 23 generate the corresponding spreading code. The signal despreading unit 22 despreads the received signal from the signal receiving unit 21 using the spreading code from the delay unit 23, and the information signal demodulating unit 26 demodulates.

Next, another embodiment of the present invention will be described. First, the variable speed transmission method used in this embodiment will be described with reference to FIG. In this embodiment, instead of repeatedly using the spreading code having a short code length as in the first embodiment, a part of the spreading code having a long code length is used. FIG. 4D shows the transmission at the basic rate. In the figure, one bit of the information signal is shown surrounded by a thick line. In this example, 1 bit of the information signal is spread using one spreading code in the block indicated by L4. In the example shown in FIG. 9, L4 is a spreading code block having a code length of 32. FIG. 4C shows a case where 4/3 times speed transmission is performed. One spreading code in L4 is selected, and 3/4 of the spreading code is used to spread one bit of the information signal. The next following bit is the remaining quarter of the spreading code.
Spread using the first half of the same spreading code as. Similarly, in the case of the double speed transmission of (b), one spreading code in L4 is selected, and ½ of the selected spreading code is used for spreading. (A)
In the case of quadruple rate transmission of, one spreading code in L4 is selected and 1/4 thereof is used for spreading. in this way,
The transmission rate of the signal can be made variable by changing the allocation rate to 1 bit of the signal by using a part of the spreading code used in the basic rate transmission without generating a spreading code with a short code length. . Further, it is possible to maintain orthogonality with the code for other stations.

FIG. 3 shows the main configuration of the transmission section and the reception section in this embodiment of the present invention. 3A shows a transmission unit and FIG. 3B shows a reception unit, and the same components as those in FIG. 1 are designated by the same reference numerals. In the transmitting unit (a), the spreading code generating unit 12 generates a spreading code having a code length used in basic rate transmission. The transmission rate control unit 11
Of the spreading codes generated by the spreading code generation unit 24, the ratio of the portion used for spreading the information signal of 1 bit is determined based on the transmission rate information of the information signal, and the information designating the ratio is coded. It is supplied to the partial selection unit 17. For example, in the case of 4/3 times speed transmission of FIG.
The information designating / 4 is output to the code part selection unit 17.
The code part selection unit 17 selects a part of the spread code from the spread code generation unit 12 at a ratio given by the transmission rate control unit 11 and sends it to the signal spread unit 14. The signal spreading unit 14 spreads the 1-bit information signal with the spreading code from the code portion selecting unit 17, and the spread information signal is transmitted from the signal transmitting unit 15. In the receiving unit of (b), it is assumed that the transmission unit provides the transmission rate control unit 25 with the speed information of the information signal, as in the case described above. Similar to the transmitting section, the transmission rate control section 25 determines the ratio corresponding to the rate information, and the spreading code generating section 24 and the code part selecting section 27 generate the corresponding spreading code. Signal despreading unit 22
Then, the received signal from the signal receiving unit 24 is despread using the spreading code from the code portion selecting unit 27, and the information signal demodulating unit 26
Demodulate with.

As described above, the transmission rate can be easily changed by repeating the spreading code having a short cycle or using a part of the spreading code having a long cycle. Therefore, for the same information signal, more flexible variable-rate transmission can be performed by changing the spreading code length for each bit or for each plurality of bits. Still another embodiment of the present invention capable of more flexible variable speed transmission will be described with reference to FIG. FIG. 5 shows an example of spreading a signal by using a part of the spreading code in the block L4, as in the method shown in FIG. As shown in the figure, in this embodiment, the first 1 bit of the information signal is spread using 1/2 of the spreading code. That is, double speed transmission is performed. The next 1 bit is spread using the subsequent 1/4 of the spreading code. That is, four-times speed transmission is performed. Such diffusion,
By repeating the transmission, it is possible to perform triple speed transmission on average. Further, by repeating spreading with spreading codes having different code lengths for every plural bits, it is possible to obtain an arbitrary average transmission rate. Since one spreading code in L4 is continuously used and only the ratio assigned to 1 bit of the signal is changed, the spreading factor can be easily changed. Even when the spreading code having the short cycle shown in FIG. 2 is repeated, more flexible variable speed transmission can be realized by changing the spreading code length for each one bit or for every plural bits.

[0018]

As described above, according to the present invention,
By repeatedly using the spreading code or by using a part of the spreading code to spread the information signal, the information transmission rate can be made variable at a finer interval. Further, in this case, the average transmission rate can be changed more flexibly by changing the code length of the spread code for each bit or for every plural bits.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention, in which (a) shows a transmitting unit configuration and (b) shows a receiving unit configuration.

FIG. 2 is a diagram illustrating a variable speed transmission method according to the first embodiment of the present invention.

3A and 3B are diagrams showing a configuration of another embodiment of the present invention, in which FIG. 3A shows a transmitting unit configuration and FIG. 3B shows a receiving unit configuration.

FIG. 4 is a diagram illustrating a variable speed transmission method according to another embodiment of the present invention.

FIG. 5 is a diagram illustrating still another embodiment of the present invention.

FIG. 6 is a diagram explaining multi-code transmission.

FIG. 7 is a diagram illustrating variable spreading factor transmission.

FIG. 8 is a diagram illustrating how to create an orthogonal code.

FIG. 9 is a diagram showing an example of an orthogonal code.

FIG. 10 is a diagram showing variable speed transmission according to a conventional method.

[Explanation of symbols]

11, 25 Transmission rate control unit 12, 24 Spread code generator 13, 23 Delay section 14,22 Signal despreader 15 Signal transmitter 17, 27 Code portion selection unit 21 signal receiver 26 Information signal demodulator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Takeo             Kanagawa Prefecture Yokosuka City Hikarinooka No. 3-4 Stock Association             YRP Mobile Communication Infrastructure Research Institute             Inside the laboratory F term (reference) 5K022 EE02 EE11 EE21                 5K067 AA03 AA33 CC10 HH21

Claims (3)

[Claims] 1. A CDMA mobile communication system capable of varying a transmission rate by changing a spreading rate of a signal, wherein spreading is made by repeating a spreading code based on a 1-bit signal one or more times. The CDMA mobile communication system is adapted to spread using a code, and the signal spreading factor is made variable by changing at least one of the code length of the original spreading code or the number of repetitions thereof. . 2. A CDMA mobile communication system in which the transmission rate can be varied by changing the spreading factor of the signal, and the CDMA mobile communication system is formed by using all or part of the spreading code which is the basis of a 1-bit signal. Spreading is performed using a spreading code, and the spreading rate of the signal can be made variable by changing the ratio of the portion used for spreading the 1-bit signal in the original spreading code. Characteristic CDM
A mobile communication system. 3. The CDMA mobile communication system according to claim 1, wherein the transmission rate of the signal is made variable by changing the spreading factor of the signal for each one bit or every plural bits of the signal.