JPH0685512B2 - Wireless communication system - Google Patents

Description

The present invention relates to a wireless communication system for providing a plurality of services, and more particularly to a wireless communication system suitable for a mobile communication system.

"Prior Art" When providing a plurality of services (for example, voice, facsimile, data communication, etc.) in mobile communication, it is assumed that the transmission quality (for example, bit error rate) required for them is different.

In mobile communication, a wireless base station that is normally connected to a fixed communication network is installed in the center of the service area, and mobile stations that freely move within the service area are connected to the fixed communication network through the wireless base station. . The range in which the mobile station can communicate (called the zone radius) is the transmission quality required for communication and the base station /
It depends on the transmission power of the mobile station.

In general, facsimile and data communication require stricter transmission quality than voice communication, so in a system with transmission power set for voice communication, the same transmitter and receiver are used to receive facsimile and data communication services. In such a case, the user cannot receive the facsimile or data communication service except near the center of the service area. Therefore, in order to perform high quality facsimile and data communication in all areas where voice communication is possible, it is necessary to increase transmission power during facsimile and data communication.

Controlling the transmission power for each service is relatively troublesome, and increasing the transmission power increases the distance between wireless communication systems that use the same frequency, thus degrading the frequency utilization rate, especially for mobile radio. In that case, it is necessary to increase the distance between service areas that use the same frequency, resulting in poor effective use of the frequency.

An object of the present invention is to provide a wireless communication system that enables a plurality of services having different transmission qualities to be provided in the same area by the same transmitter with the same transmission power.

[Means for Solving the Problems] According to the present invention, the same transmitter transmits the signal of the service with the same transmission power and different required transmission quality, and the signal of the service is changed into the required transmission quality. Different transmission characteristic improvement processing is performed depending on the situation, and in this case, the greater the required transmission quality, the greater the improvement effect.

In this way, all services can be communicated under the same zone radius and transmission power, for example.

[Embodiment] FIG. 1 shows an example of a mobile communication system for explaining an embodiment of the present invention. The voice signal input terminal 1, the facsimile signal input terminal 2 and the data signal input terminal 3 are respectively connected to the switch 5 via the signal processing circuit 4 for improving the transmission characteristics. In this embodiment, error correction coding and time diversity are used as the transmission characteristic improving technique, and the signal input terminals 1, 2 and 3 are respectively connected to the error correction coding circuits 4a, 4b and 4c in the signal processing circuit 4. The output sides of the error correction coding circuits 4a, 4b, 4c are respectively connected to the time diversity circuits 4d, 4e, 4f, and these time diversity circuits 4d, 4e, 4f are connected to the transmitter 6 via the switch 5. Switched and connected. The transmission signal of the transmitter 6 is transmitted as a radio wave from the transmission antenna 7.

The radio wave is received by the receiving antenna 8 and supplied to the receiver 9. The output side of the receiver 9 is switched and connected via a switch 10 to any circuit corresponding to a voice signal, a facsimile signal and a data signal in a signal processing circuit 11 for improving transmission characteristics. The signal processing circuit 11 has an audio signal output terminal 1
2, facsimile signal output terminal 13, data signal output terminal 1
4 is connected.

The encoded audio signal is input to the audio signal input terminal 1. After the error correction coding circuit 4a adds check bits to the coded voice signal, the time diversity circuit 4d sends the same signal a plurality of times at intervals (for the operation of time diversity, refer to Japanese Patent Application No. 56- 191814
See). Similarly, the facsimile signal and the data signal are also input to the switch 5 through the error correction coding circuits 4b and 4c and the time diversity circuits 4e and 4f, respectively. The switch 5 selects any one of a voice signal, a facsimile signal and a data signal and supplies the selected signal to the transmitter 6. The signal is modulated by the transmitter 6 and transmitted from the transmission antenna 7.

The transmission signal is received by the antenna 8, demodulated and decoded into a baseband signal by the receiver 9, and then input to the signal processing circuit 11. The signal processing circuit 11 is a circuit which reverses each processing of the signal processing circuit 4 and is provided for each of a voice signal, a facsimile signal and a data signal, and performs demodulation and decoding signals after time diversity processing and then error correction coding. After the processing, the voice signal is output to the voice signal output terminal 12, the facsimile signal is output to the facsimile signal output terminal 13, and the data signal is output from the data signal output terminal 14.

In this case, according to the present invention, a voice signal, a facsimile signal,
Performing time diversity with different correction capabilities and different number of branches for each data signal, that is, the higher the required transmission quality, the higher the error correction capability of the error correction code,
Increase the number of time diversity branches. For example, the facsimile signal has a higher correction capability of the error correction code than the voice signal and the number of time diversity branches is increased.

In this way, a plurality of services that require different transmission qualities can be provided under the same transmission power and the same zone radius.

It should be noted that only the correction capability of the error correction code or only the number of branches of time diversity may be changed according to the request of transmission quality.

"Effect of the Invention" Next, the effect of the present invention will be specifically described. A3kHz analog signal is APC-AB (adaptive prediction-adaptive bit allocation) coded as a voice signal, and G3 is used as a facsimile signal.
4.8 kb / s signal and 2.4 kb / s signal as the data signal, and the required transmission quality for these signals is 10 ^-2 and 10 respectively.
^-4, it is assumed that 10 ^-5. When 2-branch space diversity (2SD) is used as a measure against fading, the voice signal is 1.5G when the transmission power of the base station / mobile station is 15W / 3W.
In the Hz band, the zone radius is 3 km, and frequency allocation for the service area is realized by repeating a set of 9 types of frequencies. However, in the case of facsimile signals, if the transmission power is the same, the frequency for the service area is 1.4 km for the zone radius. The allocation will be realized by repeating a set of 36 kinds of frequencies.

Therefore, as shown in FIG. 2, the voice signal from the input terminal 1 is coded by the APC-AB coding circuit 15 and bit selection error correction coding (BSFEC), and the coded voice signal is 1
Output to switch 5 at 6 kb / s. The facsimile signal is subjected to error correction coding by the error correction coding circuit 4b, and then the time diversity circuit 4e performs 2-branch time diversity (2T
D) was performed and supplied to Switch 5 at 16 kb / s. That is, since the time diversity is 2 branches, 8 kb / s is output from the 1 branch, and 3 (8-4.8) kb / s thereof is used for the error correction bid. The data signal at the terminal 3 was error-correction coded by the error-correction coding circuit 4c, and then time-diversity (4TD) of four branches was performed by the time-diversity circuit 4f and supplied to the switch 5 at 16 kb / s. GM with transceiver 21
SK (BbT = 0.25) modulated and transmitted. That is, the transmission rate in the wireless section is 16 kb / s, the reception is performed by the two-branch space diversity antenna 22, the transmitter / receiver 21 demodulates it by the frequency detection 2-bit integral detection method, and the coding circuit 15 It is supplied to either one of the diversity circuits 4e and 4f for decoding.

When using only 2-branch space diversity in the presence of 40 Hz Rayleigh fading (2SD), when using 2 branch space diversity, 2 branch time diversity and error correction code (2SD-2TD-FEC), 2 branch space FIG. 3 shows the experimental measurement results of the average bit error rate for each received CNR (median value) when diversity, 4-branch time diversity and error correction code are used (2SD-4TD-FEC).

From Fig. 3, the received CNR is close to 10 dB, the voice signal has an average bit error rate of 10 ^-2 by 2SD, and the facsimile signal has an average bit error rate of 10 ^-4 by 2SD-2TD-FEC. 2SD-4TD-FEC gives an average bit error rate of 10 ^-5 . That is, if the transmission characteristics improving process as shown in FIG. 2 is performed for each of the voice signal, the facsimile signal and the data signal, the required transmission quality can be obtained with the same transmission power. When applied to the mobile radio, the zone radius is 3k
It is possible to provide not only voice signals, but also services of facsimile signals and data signals by repeating a set of nine types of frequencies for frequency allocation to the m and service areas.

As described above, according to the present invention, it is possible to provide a facsimile or data communication service even at a point where voice communication can be performed with the same transmitter and the same transmission power, and the user can use a plurality of services without being aware of the difference in services. Can receive. The present invention can be applied not only to mobile communication but also to general wireless communication.

[Brief description of drawings]

FIG. 1 is a block diagram showing a wireless communication system to which the present invention is applied, FIG. 2 is a block diagram showing an example of an experimental system to which the present invention is applied, and FIG. 3 is an average bit error rate for the experimental system shown in each drawing. FIG. 7 is a diagram showing an experimental result of a relationship of received CNR.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Nakajima 1-2356 Takeshi, Yokosuka City, Kanagawa Pref., Nippon Telegraph and Telephone Corporation, Research Institute for Communication Networks No. 2 (72) Kenkichi Hiraide 1 Takeshi, Yokosuka City, Kanagawa Prefecture Address 2356 Nippon Telegraph and Telephone Corporation, Communication Network Second Laboratory (56) Reference JP 61-13833 (JP, A) JP 55-137742 (JP, A) JP 60-241336 (JP, A) ) JP-A-57-159148 (JP, A) JP-A-59-228440 (JP, A)

Claims (1)

[Claims] 1. A method for providing a plurality of services having different required transmission qualities by wireless communication, wherein the same transmitter performs the wireless communication with the same transmission power for each service, and requests for the services. The wireless communication system is characterized in that the service signal is subjected to a transmission characteristic improvement process in which a greater improvement effect is obtained as the demand becomes stricter according to the transmission quality.