JP2000183852A - Cdma communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the number of channels which can be used at the same time without increasing the number of orthogonal codes. SOLUTION: (A) shows an example wherein information symbol stream or bit stream to be transmitted by channels CH1 to CHn are shown and one octal multi-valued symbol or three information bits are grouped every one- symbol period and made to correspond to octal symbols. (B) shows the result of spread modulation carried out with orthogonal codes corresponding to respective symbol streams for each channel. According to an information symbol value corresponding to each symbol period or information bit value, one slot is selected for each channel as specifically ruled and only in the selected slot period, an orthogonal code characteristic of the channel is generated to generate a spread modulated signal for the channel. Generated spread modulated signals as many as the channels are put together to generate a code-division multiplex signal, which is further modulated with another spread code or a carrier to generate a transmit signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CDMA (Code D)
ivision Multiple Access) communication method, more specifically,
The data modulation / demodulation method in the code division multiple access communication method is applicable to, for example, mobile communication, a mobile phone, a wireless LAN, and the like.

[0002]

2. Description of the Related Art FIG. 4 is a diagram for explaining an example of a transmission signal for each channel in a conventional CDMA system.
(A) shows an information bit sequence to be transmitted for each channel from CH1 to CHn. Each information bit is exclusive with the orthogonal code (1 to n) unique to each channel for each period indicated by the slot number in the figure. Multiplied by a logical OR gate, a continuous spread signal in which orthogonal codes and inverted orthogonal codes are mixed is generated for each channel as shown in FIG.
Then, a code division multiplexed signal is synthesized by adding all of these n spread signals. The spread signal in (B) is synchronized for each slot, and in each slot, orthogonal codes are simply multiplied by positive and negative codes according to information bits, so that orthogonality between channels is maintained even after multiplexing. ing. The receiving side multiplies each channel with a unique orthogonal code in synchronization with the received signal to obtain a correlation, whereby only information bits corresponding to the unique orthogonal code can be reproduced.

FIGS. 5 and 6 show the configuration required for the above processing separately for a transmitter and a receiver. In the transmitter shown in FIG. 5, an information bit sequence of n channels and a channel unique to each channel are shown. Codes that are orthogonal to each other are prepared, their corresponding ones are multiplied by exclusive OR circuits (11 _{1 to} 11 _n ), and their outputs are summed up by a summation circuit (12) to produce a code division multiplexed signal. , Which is branched into two, each of which is further multiplied by a different spreading code (13 ₁ ,
13 ₂ ) Carriers (cos ωt, sin ωt) orthogonal to each other after passing through low-pass filters (14 ₁ , 14 ₂ )
Are multiplied by (15 ₁ , 15 ₂ ), then added (16) and spread to obtain a transmission signal. Various configurations other than four-phase spreading, such as two-phase spreading using only one spreading code and one carrier, are conceivable for the spreading unit and the frequency conversion unit after generating the code division multiplexed signal.

FIG. 6 shows a configuration of the receiver shown in FIG. 5. First, a received signal is branched into two parts, each of which is applied with a mutually orthogonal carrier wave (cos ωt, sin ωt) (2).
11 ₁ , 21 ₂ ) After quadrature detection and passing through filters (22 ₁ , 22 ₂ ), in-phase and quadrature components are despread by the same spreading code (Ich spreading code, Qch spreading code) on the transmitting side ( 23 ₁ , 23 ₂ ) are added (24) to reproduce a code division multiplexed signal. Here, for the sake of simplicity, it is assumed that the frequency and the phase of the carrier wave in the transmission / reception unit are kept the same by using means such as a carrier wave phase compensation circuit and an automatic frequency control circuit. Then, the reproduced code division multiplexed signal is branched by the number of channels, and the correlation between each code and the orthogonal code unique to each channel is obtained by a correlator (25 _{1 to} 25 _n ). Will be played. Similar to the transmitter, the frequency conversion unit and the first despreading unit may have various configurations other than the configuration shown in the figure, such as two-phase spreading using only one spreading code and one carrier.

Here, the number of simultaneous communication channels will be briefly considered. Assuming that the number of orthogonal codes is n, the signal power of the desired channel is 1 / n of the total power when all the codes are used at the same time and the interference signal power from the other channels is the remaining (n− 1) / n, and therefore the ratio between the desired signal power and the interference signal power is approximately 1 / n. If one cycle of the orthogonal code is exactly adjusted to one information bit, the spreading gain is n. Therefore, after despreading, only the desired signal power becomes n times, so that the ratio between the desired signal power and the interference signal power becomes almost 1 Becomes In this situation, the interference is too great for satisfactory information transmission.
Therefore, in practice, it is necessary to reduce the information rate to increase the spreading gain and increase the signal power after despreading, or to limit the number of simultaneously connected channels to reduce interference power from other channels. This causes a decrease in the transmission speed of the entire system and a decrease in the number of simultaneously connected channels.

[0006]

SUMMARY OF THE INVENTION Code division multiple access (C)
In the (DMA) communication system, multiplex transmission is performed by using code sequences orthogonal to each other in order to perform communication simultaneously with a large number of mobile stations and carrying data of different mobile stations. The longer the code length of this orthogonal code sequence is, the more the number of simultaneous communication channels can be increased.However, due to frequency band limitations and demands for information transmission speed, it is not possible to increase the number of simultaneous communication channels, and the code length is limited. The number is also limited. Furthermore, even within this limited number of channels, it is difficult to achieve strict orthogonality between channels due to fading, etc., and as the number of simultaneous connections increases, inter-channel interference increases, and the transmission quality of each channel deteriorates. I do. Therefore, depending on the propagation environment, the actual number of simultaneous connections is considerably less than the number of orthogonal codes.

It is an object of the present invention to increase the number of channels that can be used simultaneously without increasing the number of orthogonal codes, and to make it possible to use the increased number of channels as simultaneously as possible. It is another object of the present invention to provide a CDMA modulation / demodulation method for reducing CDMA. Another object is to reduce the power consumption of the transmitter and the receiver, to reduce the size and cost by reducing the circuit scale.

Therefore, in the present invention, the orthogonal code is not always transmitted for each channel, but only one slot period is selected according to the information signal for every fixed number of slots, and the orthogonal code is output. To reduce the interference wave power for other channels in the propagation path. As a result, a signal of a certain channel becomes an interference wave of another channel, so that the transmission power of all the channels becomes 1 / M, so that the interference wave power for the demodulation target channel is statistically averaged to 1 / M. It becomes M. On the other hand, the transmission power during the period in which the orthogonal code corresponding to the demodulation target channel is being transmitted (the selected slot period) is not different from the conventional case. Therefore, the average signal-to-interference wave ratio is improved by M times compared to the conventional one, and the transmission characteristics are improved.

Further, since the transmission power at the transmitter can be greatly reduced, the power consumption can be greatly reduced by applying the method of the present invention to the mobile station, and the talk time per one charge can be extended accordingly, and the battery can be extended. Since the size and weight of the device can be reduced, convenience is increased. On the receiving side, the effective number of simultaneous transmission channels at the same number of transmission channels as the conventional one is 1 / M of the conventional one.
Therefore, the number of levels of the multiplexed signal is reduced to about 1 / M on average. Therefore, if a certain amount of overflow is allowed, the number of bits of the A / D converter in the receiving unit can be reduced by about log ₂ M bits, the number of bits of the demodulation calculation process thereafter can be reduced, and the circuit scale can be reduced. Power consumption can be reduced. Further, the number of usable channels can be doubled or quadrupled by using a certain orthogonal code and a code obtained by inverting the sign of the orthogonal code as another communication channel.

[0010]

According to a first aspect of the present invention, there is provided a CDMA (Code Division Multiple Access) system for connecting information signals of a plurality of channels by code division multiple access using mutually orthogonal codes.
ccess) In a communication system, a multi-valued information symbol sequence of a plurality of channels is prepared as an information signal to be transmitted, each period obtained by dividing each symbol period by a value equal to or greater than the number of symbol states is defined as a slot, and each symbol is provided for each channel. For each period, one slot is selected according to a certain rule for the information symbol value at that time, and a channel-specific orthogonal code is generated in accordance with the selected slot period to generate a transmission signal for the channel. This is characterized in that multiplexed signals are obtained by adding the transmission signals for the number of channels.

According to a second aspect of the present invention, there is provided the CD according to the first aspect.
In the MA communication system, the information signal of each channel is 2
The present invention is characterized in that a value information bit string is used, and a result obtained by dividing each of these into a fixed number is converted into a multi-valued symbol and used as the multi-valued information symbol string.

According to a third aspect of the present invention, a transmission signal is obtained by multiplying a multiplexed signal in the CDMA communication system according to the first or second aspect by a further code sequence and / or a carrier. It is a characteristic.

According to a fourth aspect of the present invention, there is provided a CDMA communication system according to any one of the first to third aspects.
A known information signal is transmitted as an information symbol sequence or an information bit sequence of one channel, or only the orthogonal code of the channel is constantly output and transmitted. Alternatively, a fixed period is set in at least one slot period in each symbol period. It is characterized in that orthogonal codes are output and transmitted.

According to a fifth aspect of the present invention, in the CDMA communication system according to any one of the first to fourth aspects, two or four codes having carrier phases different by π or π / 2 are prepared for each orthogonal code. Then, the number of channels is increased by allocating each to a symbol sequence of different channel information.

According to a sixth aspect of the present invention, in the CDMA communication system according to any one of the first to fourth aspects, an orthogonal code in a slot selected for each channel and an additional binary information bit for each channel. Are multiplied by the transmission signal of the channel.

According to a seventh aspect of the present invention, in the CDMA communication system according to any one of the first to fourth aspects, two codes having carrier phases different from each other by π / 2 are prepared for each orthogonal code. Each orthogonal code is assigned to an information symbol sequence of another channel, and further, if necessary,
The transmission signal of the channel is obtained by multiplying an orthogonal code in a selected slot for each channel by an additional binary information bit for each channel.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above-mentioned problem of the prior art, the present invention does not always transmit orthogonal codes for each channel, but rather transmits one orthogonal code every fixed number of slots (symbol period). A modulation method is adopted in which only the period is selected according to the information signal and the orthogonal code is output only during that period, so that the information signal is placed at the slot position of the orthogonal code.
As a result, assuming that each symbol period is composed of M slots, a signal is transmitted from the transmitter for only one slot per symbol period, so that the transmission power per symbol period for each channel is 1 / M of the conventional one. Here, attention is paid to the slot in which the orthogonal code of the demodulation target channel in each symbol period is selectively transmitted. Although the transmission power of the demodulation target channel during this slot period is the same as the conventional one, the average value of the interference wave power of the other channels is 1 / M of the conventional one, and the ratio of the demodulation channel power to the interference wave power is (To be referred to as SI ratio) is M times that of the conventional one, and the transmission characteristics are improved. However, the transmission speed is the same as the conventional (log ₂
M) / M, the number of channels of the present invention is M / (lo
g ₂ M), and comparing the speed of the entire system with that of the conventional system, the SI ratio is inversely proportional to the number of channels and is improved by log ₂ M times. Table 1 summarizes the above results for the case of M = 2 ^k where n is the number of simultaneously connected channels.

[0018]

[Table 1]

(Inventions of Claims 1 and 2) FIG. 1 is a diagram for explaining an example of a signal structure and an operation principle in the present invention. In FIG. 1, (A) shows each channel from CH1 to CHn. Indicates an information symbol sequence or a bit sequence to be transmitted,
An example is shown in which one 8-level multi-level symbol or three information bits are grouped per symbol period to correspond to an 8-level symbol. (B) shows the result of performing spread modulation using orthogonal codes corresponding to each symbol sequence for each channel.
In the illustrated example, since the symbol value has eight values, one symbol period is divided into eight equal portions, and the slots are numbered from 0 to 7, respectively. Then, one slot is selected according to a certain rule according to an information symbol value or a plurality of information bit values corresponding to each symbol period for each channel, and an orthogonal code unique to the channel is generated for the selected slot period. As a result, a spread modulation signal for the channel is generated. The generated spread modulation signals for the number of channels are added to generate a code division multiplexed signal, and further modulated by another spreading code or carrier to generate a transmission signal. As an example of associating symbol values with slots, FIG. 1 shows an example in which symbol values are directly associated with slot numbers.
Arbitrary association is possible by using an M table or the like.

As an example, paying attention to CH1 in FIG. 1, the bit sequence in the symbol period is 101 and the symbol value is 5, so that slot number 5 is selected, and only during this period, the orthogonal code unique to CH1 is selected. 1 is sent out. Signals in other slots of this channel remain at zero.
As orthogonal codes, Wals in the narrowband CDMA standard
Although the h function is well known, any set of orthogonal codes can be applied to the present invention as long as the orthogonality of the codes in each symbol period is maintained. At this time, it is desirable to match the symbol period to an integral multiple of the period of the orthogonal code in order to maintain orthogonality.

Next, an example of the configuration of the transmitter according to the present invention for generating the spread modulation signal of FIG. 1 and generating the code division multiplexed signal will be described with reference to FIG. In the transmitter of FIG. 2, an information bit sequence of n channels is prepared,
Each is input to a serial-to-parallel converter (31 _{1 to} 31 _n ) operated by a bit clock, and the parallel output is held in a register (32 _{1 to} 32 _n ) for each symbol clock to perform serial-to-parallel conversion. If the information signal is already a multi-level symbol, the symbol value is directly held in the register for each symbol clock without going through serial-parallel conversion. Subsequently, a slot number counter (33) operated by a slot clock is prepared to select a specific one slot corresponding to a symbol value for each channel, and a counter output is converted from a counter output to a corresponding symbol. By inputting to (34), a symbol value synchronized with the slot clock is output. Then, this value and the register value for each channel in each slot in each symbol period are compared with the coincidence detection circuit (35).
_{1 to} 35 _n ), and a match detection signal for selecting only one slot period in one symbol period is generated. Furthermore, each channel-specific orthogonal code to the detection signal as a control signal to control the switch (36 ₁ ~36 _n), and sends the orthogonal codes only previous selection slot period.

As described above, the orthogonal code is transmitted only for the slot period corresponding to the symbol value. Thereafter, the summation circuit (37) adds the spread signals of all the channels to generate a code division multiplexed signal. In the example of FIG. 2, the conversion table from the count value to the corresponding symbol value is used, but the count value may be used as it is for the match determination except for this. Further, if necessary, the multiplexed signal may be further multiplied by another spreading code or a carrier wave to obtain a transmission signal. In the example of FIG.
After the code division multiplexed signal is branched into two and multiplied by different spreading codes (Ich spreading code, Qch spreading code) (38 ₁ , 38 ₂ ), the low-pass filters (39 ₁ , 3 ₂ )
9 ₂ ) and then orthogonal to each other (cos
ωt, sinωt) and add them together (41)
An example in which four-phase spread signals are used as transmission signals is shown. Various configurations are conceivable for the spreading unit and the frequency conversion unit after generating the code division multiplexed signal, such as two-phase spreading using only one spreading code and one carrier, in addition to four-phase spreading.

Next, the receiver of the present invention will be described with reference to FIG. Similar to the prior art example shown in FIG. 6, a baseband (may include a low-frequency residual carrier) code division multiplexed signal is generated from a received signal by frequency conversion or despreading using a code other than an orthogonal code. Although various configurations are conceivable for this part, in FIG. 3, similarly to FIG. 6, the received signal is branched into two and the carrier waves (cos ωt, cos ωt,
sin ωt) and (51 ₁ , 52 ₂ ) quadrature detection, and after passing through filters (52 ₁ , 52 ₂ ), the same spread code (Ich spread code,
(Qch spreading code) and add the despread code (54)
To reproduce the code division multiplexed signal. Again, for simplicity, the frequency and phase of the carrier wave in the transmitting / receiving section are assumed to be kept the same using means such as a carrier phase compensating circuit and an automatic frequency control circuit, but for each in-phase and quadrature component during quadrature detection. The despreading by the orthogonal code as well as the I and Q spreading codes may be simultaneously performed by the correlator, and phase compensation or the like may be performed later based on the correlation result.

Next, the circuit after reproduction of the code division multiplexed signal shown in FIG. 3 shows an embodiment of a demodulation unit according to the first and second methods. First, the code division multiplexed signal is branched by the number of channels, and the correlation with the orthogonal code unique to each channel is obtained using correlators (55 _{1 to} 55 _n ) corresponding to the number of channels. The correlation calculation at this time is performed in synchronization with the slot cycle.
The input signal to each correlator is multiplied and integrated in each slot period, and the integrated value is output for each slot. Each threshold determination circuit followed (56 ₁ ~56 _n), to determine whether a correlation value for each slot period exceeds a specific reference value,
If it exceeds, it is determined that the orthogonal code unique to the channel corresponding to the slot period has been received, and a data read signal is sent to the corresponding register (59 _{1 to} 59 _n ).

To obtain the slot number of the orthogonal code for each received channel, a slot number counter (57) operated by a slot clock is prepared, and this output is stored in a conversion table (58) from the count value to the corresponding symbol value. Input and output the symbol value corresponding to each slot. Registers (59 _{1 to} 59 _n ) corresponding to each channel following the threshold value determination read and hold the symbol value from the conversion table only when the slot in which the read signal from the threshold value determination circuit is valid. . As a result, at the end of the symbol period, a symbol value corresponding to the slot number of the orthogonal code of each channel, that is, a transmission symbol value is reproduced in each register. By reading out the reproduced symbol value corresponding to each channel according to the symbol clock, the original symbol sequence is reproduced. This in order to further back into the bit string may be reproduced information bit string by using the parallel-serial converter that operates at bit clock (60 ₁ ~60 _n).

Also, the examples shown in FIGS. 2 and 3 show examples of the case of a base station or a multiplex transmission apparatus that performs multi-channel transmission for both transmission and reception. However, when the present invention is applied to a mobile station, The apparatus can be greatly simplified by reducing the number of channels for modulation and demodulation using orthogonal codes to the minimum required number. Data transmission is possible if a modulation / demodulation unit for at least one orthogonal code is prepared.

(Invention of Claim 4) In the invention of Claims 1 to 3, an information signal (including non-modulated) known as an information symbol sequence or information bit sequence of at least one channel is carried and transmitted, or Only orthogonal codes are always output and transmitted, or a fixed orthogonal code is output and transmitted during at least one slot period in each symbol period. Phase and frequency standards,
Timing signals for synchronization such as symbol synchronization and slot synchronization can be easily obtained. As a result, the receiving side can correctly determine the carrier phase of each orthogonal code with respect to the reference orthogonal code carrier. Knowing the relative phase of the carrier between the orthogonal codes is described later in claim 5.
It is an indispensable item for realizing the inventions of (1) to (7). According to the invention of claim 4, it is possible to transmit a pilot channel in the conventional CDMA communication system (IS95), a perch channel in wideband CDMA, and a reference signal corresponding to a pilot symbol in the present invention. Also,
Sharing and integration with the conventional CDMA system are also facilitated.

(Invention of claim 5) The invention of claims 5 to 7 is a method of increasing the number of channels by multiplexing using the carrier phase of the orthogonal code, or information is also carried on the carrier phase. This discloses a method for increasing the transmission capacity. The invention according to claim 5 is the CD according to claims 1 to 4.
In the MA communication system, two or four codes having only a carrier phase different by π or π / 2 are prepared for each orthogonal code, and each code is assigned to an information symbol sequence of another channel. The number of available channels can be doubled or quadrupled without increasing the number of codes. A code having carrier phases different by π from each other is equal to a code obtained by inverting the sign of one code. When slots overlap between channels having carrier phases different from each other by π, if both slots are output, the signals cancel each other out and the signal disappears.
One orthogonal code is not transmitted, and for symbols for which no orthogonal code is detected on the receiving side, the same symbol value as that of a channel having a carrier phase difference of π is used as the symbol value of that channel, so that the symbols of both channels are used. Normal demodulation is possible. By increasing the number of channels to twice or four times that of claims 1 to 4, it becomes possible to make the overall transmission capacity equal to or higher than that of the conventional one, and to reduce the interference wave power from other channels by the same transmission capacity. Can be reduced, and transmission characteristics are improved.

According to a sixth aspect of the present invention, in the CDMA communication system of the first to fourth aspects, an orthogonal code in a selected slot for each channel and an additional binary code for each channel are provided. In the method of multiplying the information bit (1 bit) as the transmission signal of the channel, the transmission information per symbol is increased by 1 bit without increasing the interference wave power with the same number of channels as in the inventions of claims 1 to 4, Transmission speed can be improved.

According to a seventh aspect of the present invention, in the CDMA communication system of the first to fourth aspects, two codes having carrier phases different from each other by π / 2 are prepared for each orthogonal code. Each of the two orthogonal codes is assigned to an information symbol sequence of another channel, and, if necessary, an orthogonal code in a selected slot for each channel and an additional binary information bit (1 bit) for each channel. ) Is used as the transmission signal of the channel.
The present invention is applied to two mutually orthogonal carrier waves and transmitted simultaneously to multiplex them. As a result, the number of channels is doubled as in claims 1 to 4 and claim 6, and the overall transmission capacity can be doubled. With the same transmission capacity, the power of the interference wave can be reduced and the transmission speed can be improved.

[0031]

According to the first aspect of the present invention, a multi-valued information symbol sequence of a plurality of channels is prepared as an information signal to be transmitted, and each period obtained by dividing each symbol period by a value equal to or greater than the number of symbol states is defined as a slot. , One slot is selected for each channel according to a certain rule for the information symbol value at that time for each symbol period, and an orthogonal code unique to the channel is generated in accordance with the selected slot period. And the number of generated transmission signals is added to form a multiplexed signal, so that the number of slots per symbol is M and the transmission signal power per channel is greatly reduced to 1 / M of the conventional level. it can. Therefore, if the present invention is applied to a mobile station, power consumption can be significantly reduced, the talk time per charge can be extended accordingly, and the size and weight of the battery can be reduced, thus increasing convenience. Next, since the signal of a certain channel becomes an interference wave of another channel, the transmission power of all the channels becomes 1 / M, so that the interference wave power for the demodulation target channel is statistically averaged to be 1 / M. Become. on the other hand,
The transmission power during the period in which the orthogonal code corresponding to the demodulation target channel is being transmitted (the selected slot period) is the same as the conventional one. Therefore, the average signal-to-interference wave ratio is improved by M times compared to the conventional one, and the transmission characteristics are improved.

On the receiving side, the effective number of simultaneous transmission channels at the same number of transmission channels as in the prior art is 1 /
M, the number of levels of the multiplexed signal is 1 / M on average.
To a degree. Therefore, if a certain amount of overflow is allowed, the number of bits of the A / D converter in the receiving unit is log ₂ M
The number of bits can be reduced by about one bit, and the number of bits for the subsequent demodulation calculation processing can be reduced, so that the circuit scale can be reduced and power consumption can be reduced. Further, in the present invention, since multi-valued symbols are used as transmission signals, multi-bit data can be transmitted in parallel as it is, and there is no need to synchronize symbols during serial-parallel conversion.

According to the second aspect of the present invention, a binary information bit sequence is used as an information signal of each channel, and a result obtained by dividing each of the binary information bit sequences into multi-level symbols is converted into a multi-level symbol. Since it is used as a value information symbol sequence, the invention of claim 1 can be applied to a serial information bit sequence, and the same effect can be obtained.

According to the third aspect of the present invention, the transmission signal is obtained by multiplying the multiplexed signal according to the first or second aspect of the invention by another code sequence and / or one of the carrier waves. The present invention can be applied to wireless transmission in a band. Further, by applying a spreading code different from the orthogonal code, a plurality of base stations and the like can be distinguished, and the same orthogonal code can be reused in another base station.

According to the fourth aspect of the present invention, a known information signal (including unmodulated) is transmitted as an information symbol sequence or an information bit sequence of at least one channel, or only the orthogonal code of the channel is constantly output. Transmit,
Also, since a fixed orthogonal code is output in at least one slot period in each symbol period, the receiving side uses this reference signal to determine the carrier phase and frequency reference required for demodulation, symbol synchronization, slot synchronization, etc. , A timing signal for synchronization is easily obtained, and demodulation processing is facilitated. Thereby, on the receiving side, it is possible to correctly determine the carrier phase of each orthogonal code with respect to the carrier of the reference orthogonal code, and to implement information according to claims 5 to 7 in which information is also carried on the carrier phase. . Further, according to the present invention, a pilot channel and a wideband CDMA in a conventional CDMA communication system (IS95) are provided.
In the present invention, a reference signal corresponding to a perch channel and a pilot symbol can be added to the present invention and transmitted, so that sharing and fusion with a conventional CDMA communication system can be facilitated.

According to the fifth aspect of the present invention, two or four carrier waves differing in carrier phase by π or π / 2 for each orthogonal code, respectively.
Since two codes are prepared and assigned to different channel information symbol sequences, the number of channels can be doubled or quadrupled, and the number of users who can talk at the same time can be greatly increased as compared with the inventions of claims 1 to 4.

According to the sixth aspect of the present invention, a signal obtained by multiplying an orthogonal code in a slot selected for each channel by an additional binary information bit for each channel is used as a transmission signal of the channel. It is possible to increase the transmission speed with the same transmission quality as in the inventions 1 to 4.

According to the seventh aspect of the present invention, two codes having carrier phases different from each other by π / 2 are prepared for each orthogonal code, and each of the two orthogonal codes is assigned to an information symbol sequence of another channel. Further, if necessary, a signal obtained by multiplying an orthogonal code in a selected slot for each channel by an additional binary information bit for each channel is used as a transmission signal of the channel. 4
Thus, the number of users who can talk at the same time can be doubled, and the total transmission capacity can be doubled. Further, with the same transmission capacity, the power of the interference wave can be reduced as compared with the conventional case, and the transmission characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a signal configuration example and an operation principle according to the present invention.

FIG. 2 is a diagram illustrating a configuration example of a transmitter according to the present invention for generating the spread modulation signal of FIG. 1 and generating a code division multiplexed signal.

FIG. 3 is a diagram illustrating a configuration example of a receiver according to the present invention corresponding to the transmitter in FIG. 2;

FIG. 4 is a diagram for explaining an example of a transmission signal for each channel in a conventional CDMA system.

FIG. 5 is a diagram illustrating a configuration example of a conventional transmitter.

FIG. 6 is a diagram illustrating a configuration example of a receiver with respect to FIG. 5;

[Explanation of symbols]

31 _{1 to} 31 _n ... S / p converter, 32 _{1 to} 32 _n ... register, 33 ... slot counter, 34 ... conversion table, 3
5 ₁ to 35 _n ... coincidence detection circuit, 36 ₁ ~ 36 _n ... switch,
37 ... sum operation circuit, 38 _{1 to} 38 _n ... multiplier, 39 ₁ to
39 _n : filter, 40 ₁ to 40 _n : multiplier, 41: adder, 51 _{1 to} 51 _n : multiplier, 52 _{1 to} 52 _n : filter,
53 _{1 to} 53 _n ... Multipliers, 54... Adders, 55 _{1 to} 55 _n .
Correlators, 56 _{1 to} 56 _n Threshold decision circuit, 57 slot counter, 58 conversion table, 59 _{1 to} 59 _n register, 60 _{1 to} 60 _n S / P converter.

Claims (7)

[Claims] 1. A code division multiple access (CDMA) system for code division multiplexing access to information signals of a plurality of channels using mutually orthogonal codes.
ivision Multiple Access) In a communication system, a multi-valued information symbol sequence of a plurality of channels is prepared as an information signal to be transmitted, and each symbol period is divided by a value equal to or greater than the number of symbol states to form a slot. For each symbol period, one slot is selected in accordance with a certain rule for the information symbol value at that time, and a channel-specific orthogonal code is generated in accordance with the selected slot period to generate a transmission signal for the channel. CDMA communication system characterized in that multiplexed signals are obtained by adding transmission signals for the number of generated channels. 2. The CDMA communication system according to claim 1, wherein a binary information bit sequence is used as an information signal of each channel, and a result obtained by dividing each of the binary information bit sequences into a multi-level symbol is converted into a multi-level symbol. A CDMA communication system, wherein the CDMA communication system is used as a value information symbol sequence. 3. The CDMA communication system according to claim 1, wherein the multiplexed signal in the CDMA communication system according to claim 1 or 2 is further multiplied by another code sequence and / or a carrier wave to obtain a transmission signal. method. 4. The CD according to claim 1, wherein:
In the MA communication system, a known information signal is transmitted as an information symbol sequence or an information bit sequence of at least one channel, or only orthogonal codes of the channel are constantly output and transmitted, or at least one channel in each symbol period is transmitted. A CDMA communication system characterized in that a certain orthogonal code is output and transmitted during one slot period. 5. The CD according to claim 1, wherein:
In the MA communication system, two or four codes having carrier phases different by π or π / 2 are prepared for each orthogonal code, and the number of channels is increased by assigning each to a symbol sequence of different channel information. Characteristic CDMA communication system. 6. A CD according to any one of claims 1 to 4.
In the MA communication system, a transmission signal of the channel is obtained by multiplying an orthogonal code in a slot selected for each channel by an additional binary information bit for each channel. 7. A CD according to any one of claims 1 to 4.
In the MA communication system, two codes having carrier phases different from each other by π / 2 are prepared for each orthogonal code, and each of the two orthogonal codes is assigned to an information symbol sequence of another channel. A CDMA communication system characterized in that a signal obtained by multiplying an orthogonal code in a selected slot for each channel by an additional binary information bit for each channel is used as a transmission signal of the channel.