JPH11341553A - Spread spectrum communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the spread spectrum communication system that ensures a high communication capacity stably by reducing a loss of a communication capacity of a channel through multiplexing processing in this invention different from a conventional spread spectrum communication equipment having a problem of not stably reserving a prescribed communication capacity. SOLUTION: In the spread spectrum communication system, a high frequency circuit 9 amplifies a received signal, an inverse spread circuit 10 applies inverse spread processing to the signal, a signal power measurement circuit 13 measures signal power from the signal that is inversely spread, a noise power measurement circuit 14 measures noise power from the signal that is inversely spread, an Eb/10 calculation circuit 15 and a control circuit 16 generate a command to control transmission power according to the results of measurement and a transmission circuit 17 adjusts the transmission power of an information signal with the command and sends and outputs the information signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system using a code division multiple access system.

[0002]

2. Description of the Related Art In a spread spectrum communication system using a code division multiple access system (hereinafter, SSMA system: spread spectrum multiple access system), the number of multiplexes (the number of simultaneous communication stations) indicating line utilization efficiency is a typical example. A comparison is made with another multiple access system, the frequency division access (FDMA) system.
Here, line synchronization is an ideal state that is completely established,
The characteristics of each transceiver are the same. Here, the relationship between the modulation method, the encoding method, etc. of the primary modulation and the characteristics is ignored for simplicity.

FIG. 4 shows the basic configuration of an SSMA communication system, and FIG. 5 shows the basic configuration of an FDMA communication system. The total power and bandwidth that can be used in the transmission channels of the configuration diagrams shown in FIGS. 4 and 5 are Pr [W] and W [H, respectively.
z], the power spectrum density of the noise is set to No / 2 [W / H].
z].

In order to quantify the quality of a transmission channel, the following Transmission Channel Standard (Transmission Channel Standard:
When TCS is defined, the following equation (Equation 1) is obtained.

[0005]

(Equation 1)

The channel capacity of the transmission channel is given by the following equation (Equation 2).

[0007]

(Equation 2)

Assuming that the bandwidth required for the primary modulation is B and the number of multiplexes is M, the communication capacity per channel in the FDMA system is represented by the following equation (Equation 3).

[0009]

(Equation 3)

Here, since C _T = M · C _F (W = MB), it is understood that the FDMA system does not cause a loss in communication capacity due to multiplexing. In the SSMA system, the relationship between W and B is not easily linked, and is related as the processing gain _GP . Communication capacity and the CN ratio at the primary demodulation stage per channel of SSMA system, when the average power per channel P, and spreading code frequency is f _PN, the following equation [Expression 4] [Formula 5].

[0011]

(Equation 4)

[0012]

(Equation 5)

Ec indicates the line utilization efficiency and is defined by the following equation [Equation 6].

[0014]

(Equation 6)

Here, Ec in the equation [Equation 6] is SSMA to the maximum value _{GP of the} channels that can be multiplexed in the FDMA system.
It shows the ratio with the number of channels multiplexed by the method. According to the comparison between Equations (2) and (4), multiplexing causes a loss in communication capacity in the SSMA system. The cause is a decrease in the CN ratio in the primary demodulation stage. Assuming that there is no such loss in the line, CN ratio of SSMA method,
(C / N) _S and CN ratio of FDMA system, (C / N) _F
Are determined, the relationship between the line utilization efficiency Ec and the transmission channel standard (TCS) is determined.

The CN ratio of the primary demodulation stage input is set to 6 dB (= TC
Assuming that S), when _GP ≧ 20 dB, Ec is about 10%, and the multiplexing number in the SSMA system, that is, the number of simultaneous communication stations is about 1/10 of the FDMA system.

[0017]

From the results shown above, the SSMA system has other FDM as a multiple access.
A, there is a major disadvantage in principle compared to the TDMA system.

The present invention has been made in view of the above circumstances, and the number of multiplexing (number of simultaneous communication stations) of the SSMA system, which is a problem of the prior art, is smaller than that of other multiple access systems such as the FDMA and TDMA systems. It is an object of the present invention to provide a communication system in which the disadvantage of being small in principle is solved, and as a multiple access system, there is almost no practical loss of communication capacity of a line due to multiplexing.

[0019]

SUMMARY OF THE INVENTION To achieve the above object, a communication system according to the present invention comprises a plurality of subscribers and a base station which transmit power of a specific station and other subscriptions independently of each other. By measuring the noise-like power and the noise power of the transmitter and the base station, and measuring the ratio of the transmission power to the noise power, that is, the effective signal-to-noise ratio by the power ratio, the transmitted station is measured. In this case, an appropriate transmission power value is transmitted as data to control the transmission power.

That is, the result that the number of multiplexes in the SSMA system is small is based on the assumption that the powers of all transmitting stations are equal. Also, physical conditions and hardware device configurations are different depending on the reverse link (transmission from the subscriber to the base station) and the forward link (transmission from the base station to the subscriber). It needs to be changed depending on the conditions.

The signal power in order to control the transmission power _{E S = N · Ec (E} S: signal power, N: the spreading code length, Ec: 1 signal power per chip) and Io = I / W
(I: noise power from other uncorrelated subscribers, W: spreading bandwidth), for example, for the reverse link:
By transmitting a command for controlling transmission from the base station to the subscriber, it is possible to control transmission from the subscriber to the base station.

In the conventional method, transmission control is performed by measuring only the signal power. However, in this method, the usage status of the subscriber is not known and a predetermined communication capacity can be achieved. It has the disadvantage of not being able to.

[0023]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram for performing SSMA transmission control according to an embodiment of the present invention. FIG. 1 shows transmission control in the base station. The reception input from the antenna is subjected to predetermined amplification or frequency conversion by the high frequency line 9 and output to the despreading circuit 10. The despreading circuit 10 performs control such as timing extraction of a spreading code and despreading, and outputs an information-modulated signal for the subscriber. This output is output to the power measurement / calculation unit 1
2 is input.

The input despread output is input to a signal power measurement circuit 13 and a noise power measurement circuit 14, where the signal power and noise for the subscriber are measured (calculated), and Eb /
It is input to the Io calculation circuit 15. Eb / Io calculation circuit 1
5, the signal power measurement circuit 13 and the noise power measurement circuit 14
Are normalized to the value of Eb / Io and calculated.
This output is input to the control circuit 16, generates a command for controlling the transmission output on the subscriber side, and is output to the transmission device 17 in a predetermined format.

FIG. 4 shows an SSM according to an embodiment of the present invention.
FIG. 2 is a configuration diagram for performing transmission control of the A system. In FIG.
The input high-frequency (intermediate frequency) signal from the high-frequency circuit 9 is input to the first multiplier 18 and the second multiplier 19, and the in-phase component of the carrier wave from the carrier oscillator 25 and 9
The components shifted by 90 ° by the 0 ° phase shifter 24 are respectively multiplied to form a baseband signal or an intermediate frequency signal. The first filter (LPF (BPF)) 20 and the second filter
(LPF (BPF)) 21 is output.

In the LPFs (BPFs) 20 and 21, the respective signals are low-pass (band) -filtered to become signals in a required band. These signals are converted into L signals by a parallel (L) demodulator 22.
Signals from independent multipath channels are separated,
Demodulated. This signal is input to the maximum ratio combiner 23,
The phases of the signals corresponding to the respective paths are controlled to be in-phase, and weighting is performed in accordance with the reliability to perform the synthesis.

This output is separated from the signal for demodulating the information signal and the input to the power measurement / calculation unit 12 and output. Power measurement / calculation unit 12, control circuit 16, and transmission device 17
Is the same as that described with reference to FIG.

FIG. 3 is a configuration diagram of a parallel (L) demodulator. LPF (BPF) 20 and LPF (BPF)
21 is multiplied by a multiplier 27 and a multiplier 28 as an in-phase component and a 90 ° phase-shift component, respectively, with a spread signal having a timing synchronization established from a lead-lag gate tracking loop 26, and a Hadamard sequence (M) correlation is obtained. Container 29
Gives a correlation output of M orthogonal Hadamard sequences,
Is output.

[0029]

According to the transmission power control system of the SSMA system according to the present invention, another FDMA system or TD
Eliminating the drawback of multiplexing loss compared to the MA system, the number of simultaneous communication stations can be reduced to about 0.8 by applying an appropriate transmission power control method, for example, compared to the FDMA system.
It has been confirmed by the examples that the value reaches about 1.0.

Further, even in a multipath communication path in which rice fading occurs, it is possible to measure the signal power and the noise power and their ratios.
The multiplexing of the A method can be realized easily and practically.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing SSMA transmission control according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing transmission control of the SSMA scheme according to the embodiment of the present invention.

FIG. 3 is a configuration diagram of a parallel demodulator according to the embodiment of the present invention.

FIG. 4 is a principle configuration diagram showing an SSMA communication system.

FIG. 5 is a principle configuration diagram showing an FDMA communication system.

[Explanation of symbols]

1: Primary modulator, 2: Spread modulator, 3: Adder,
4 ... spread demodulator, 5 ... primary demodulator, 6 ... FDMA multiplexer, 7 ... adder, 8 ... FDMA demultiplexer,
9: High frequency circuit, 10: Despreading circuit, 11: Information modulation / demodulation circuit, 12: Power measurement / calculation unit, 13: Signal power measurement circuit, 14: Noise power measurement circuit, 15: Eb
/ Io calculation circuit, 16: control circuit, 17: transmission device, 18: first multiplier, 19: second multiplier,
20 ... first filter (LPF (BPF)), 21 ...
Second filter (LPF (BPF)), 22: parallel (L) demodulator, 23: maximum ratio combiner, 24: 9
0 ° phase shifter, 25 carrier oscillator, 26 lead-lag gate tracking loop, 27, 28 multiplier,
29 ... Hadamard (M) sequence correlator

Claims (1)

[Claims] 1. A mobile or fixed communication system using a transmission system in which multiple access is performed by modulation different from information modulation for spreading the bandwidth in a transmission system using a band wider than the bandwidth used for information transmission. A subscriber having an antenna, a receiver and a transmitter, and controlling, controlling, and exchanging each subscriber the base station having an antenna, a receiver and a transmitter, via the base station In a communication system in which information signals are transmitted between subscribers, in a receiver of a communicating subscriber, a signal power transmitted from a corresponding base station for the multiple subscriber received by the subscriber for the multiple access. And a first noise power for measuring signal power and other noise power for a subscriber and a base station other than the subscriber used for code division other than the power. Measurement Means for measuring the first signal power, and first power adjusting means for decreasing or increasing the transmission power of the subscriber according to the result of the means for measuring the first noise power. Means for measuring a second signal power for measuring a signal power transmitted from a corresponding subscriber to the base station for multiple access received by the base station at a receiver of the base station which performs communication; Means for measuring signal power and other noise power for the base station and subscribers other than the base station and subscriber used for code division other than the power, and a second noise power measuring means; A second power adjusting means for reducing or increasing the transmission power of the base station according to the result of the means for measuring the power and the means for measuring the second noise power. Tram spread communication system.