JP2642381B2 - Wireless communication signal transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a radio communication system in which a random access is made from each terminal to a central station in a mobile communication system having a plurality of terminals and a central station for controlling the terminals. The present invention relates to a communication signal transmission system.

[Conventional technology]

In a mobile communication system or the like having a plurality of terminals and a central station, there is random access as a technique in which a large number of terminals temporally multiplex a radio channel of the same frequency from a terminal to a central station, a so-called uplink. The simplest method for realizing such random access is the pure Aloha method. This is to send a signal to the central station immediately when a call is generated at the terminal,
If signals from a plurality of terminals collide and are not correctly received at the central station, retransmission is performed after random delay. In addition, in the pure Aloha method, the time axis is slotted according to the signal length, and the slot Aloha method in which all transmissions are synchronized with this, the terminal that generated the signal observes the communication path, and transmission from other terminals is not observed CMSA system that transmits only when the central station observes the main communication path and transmits a busy tone (BT) in another frequency band while signal transmission from any one terminal is observed.
BTMA method in which terminals know the use status of communication channels based on the presence or absence of BT and make outgoing calls, and the central station notifies each terminal by sending an empty signal to indicate that the communication channel is free, and each terminal sends an empty signal. There is ISMA system communication that transmits after confirming.

[Problems to be solved by the invention]

When wireless communication signals are transmitted by random access, the most problematic is collision between signals transmitted to the central station.

However, in the above-described conventional pure Aloha method, the probability of signal collision is high, and therefore, the signal throughput decreases and the signal transmission incomplete rate increases. On the other hand, in the slot Aloha system, CSMA, BTMA, and ISMA systems, control is performed to reduce the collision rate, and throughput and signal transmission incomplete rate characteristics can be improved to some extent. However, even if such control is performed, the occurrence of a collision cannot be made zero at all, so that the deterioration of characteristics due to the collision remains a problem. Therefore, in the case of a signal collision, a signal surviving method is conceivable in which if there is a level difference between the signals, the largest one can be accurately received by the central station. Therefore, if this surviving effect is increased, the characteristics can be improved even when a collision occurs. However, in the conventional method described above,
Since the transmission power is constant for each terminal, the level difference is not so large at the time of collision, and the effect of surviving the signal at the time of collision cannot be expected. In the case of reception at the central station, the signal of a terminal far from the central station has a lower received signal level than the signal of a terminal close to the central station. From the near terminal, the far terminal is forced to repeat the retransmission, and as a result, it will not be received because the specified time has passed, or even if it can be received, the delay will increase. As a result, there is a problem that unfairness occurs depending on the location of the terminal.

An object of the present invention is to provide a wireless communication signal transmission method that solves the above-mentioned problem and that can improve the signal survival rate at the time of collision and significantly improve the signal transmission incomplete rate characteristics and throughput. With the goal.

[Means for solving the problem]

According to the wireless communication signal transmission method of the present invention, in wireless communication in which a plurality of terminals randomly access a central station, the terminal changes the transmission power of a transmission signal according to the type of signal transmitted to the central station or the content of information.

(Operation)

By changing the transmission power of the transmission signal according to the type of the transmission signal from the terminal to the central station or the content of the information, for example, the transmission power of the calling signal can be increased and the transmission power of the other signals can be reduced. As a result, even if the call signal collides with another signal, the survival rate of the call signal is improved, and the signal transmission incomplete rate and the throughput can be significantly improved.

〔Example〕

Hereinafter, drawings of embodiments of the present invention will be described in detail.

FIG. 1 is a diagram showing the overall principle configuration of a land mobile communication system to which the wireless communication signal transmission system of the present invention is applied.

In FIG, 1 is ground center station which controls the whole In the center of the radio zone, 2 ₁ to 2 _n is the mobile station which is mounted in an automobile or the like, i.e., a terminal, the respective terminals 2 ₁ to 2 _n is , with respect to the center station 1, the transmission power is provided with transmitting and receiving means 3 ₁ to 3 _n which transmits a random or periodically varying signals.

By varying the transmission power of the thus transmitted signal randomly or periodically, it increases the variance of the signal power level difference of the collision between signals, thereby the survival rate of the signal at the time of collision of each terminal 2 ₁ to 2 _n And the signal transmission incompletion rate characteristics and throughput can be improved.

Next, a specific example of a terminal having a function of randomly varying transmission power according to the wireless communication signal transmission method of the present invention will be described.

For Example I Figure 2 is terminal 2 ₁ (other terminals 2 ₂ to 2 _n is also the same,
Only explanation for the terminal 2 _1. 1) showing the internal configuration of
This is an embodiment of the present invention.

In the figure, 10 is an encoder for encoding transmission information of the terminal 2 _1, 11 modulator for frequency modulating the digital information from the encoder 10, a power amplifier 12 for power-amplifying the modulation signal,
13 is a processing circuit for generating a voltage for controlling the amplification factor of the power amplifier 12, 14 is a random number generation circuit for randomly changing the control voltage from the processing circuit 13, and 15 is a transmission / reception distributor. The output signal from the power amplifier 12 is added to the device 15, and an antenna 16 for transmission and reception is connected.

Reference numeral 17 denotes a detector for FM detection of the signal received by the transmission / reception distributor 15, and reference numeral 18 denotes a decoder for decoding a detection output from the detector 17.

In the circuit having the above configuration, an output signal obtained by modulating transmission information from the encoder 10 by the modulator 11 is amplified by the power amplifier 12 and radiated from the antenna 16 through the transmission / reception distributor 15. At this time, by applying an output signal from the random number generation circuit 14 to the processing circuit 13, a control voltage that changes at random is created, and by applying this control voltage to the power amplifier 12, the transmission power from the power amplifier 12 is randomized. To change. Therefore, the antenna through the transmission / reception distributor 15
The transmission power level transmitted from 16 also changes randomly. This transmission signal is transmitted to the central station 1 through the uplink of the central station.

On the other hand, a signal transmitted on the downlink from the central station is received by the transmission / reception distributor 15 through the antenna 16, detected by the detector 17, and converted into analog information by the decoder 18.

FIG. 3 is an example of the transmission power distribution characteristic output by the configuration of FIG. 2 in which the horizontal axis indicates the transmission power and the vertical axis indicates the occurrence frequency, and each straight line 30 ₁ to 30 _n is a random number. The transmission power levels of N stages output as a result of the conversion are shown, and 31 is the total width Δ (dB) of the transmission power to be randomized. Also, a straight line 31
₁ 'height to 30 _n represents the frequency of occurrence of each transmit power level.

Accordingly, if the terminal transmits transmission signals of each of the N transmission power levels at randomized levels as shown in FIG. 3 at the occurrence frequency shown in the figure, the signal survival rate at the time of collision is improved, and the signal throughput is improved. Is improved, and the signal transmission non-completion rate is improved.

Embodiment II FIG. 4 is a configuration diagram of a terminal in a case where transmission power of a terminal is determined so that a reception level at a central station is constant when randomization is not performed, and randomization is performed based on the transmission power. is there. However, by taking the average over a certain period of time, utilizing the fact that the correlation between the propagation characteristics of the downlink and the uplink is close to 1, the reception level at the central station of the uplink is calculated from the average reception level of the downlink. This is the case when asking.

In the figure, the terminal is an encoder as in the case of FIG.
10, a modulator 11, a power amplifier 12, a processing circuit 13, a random number generation circuit 14, a transmission / reception distributor 15, an antenna 16, a detector 17, a decoder 18, and a reception level averaging processing circuit
Reference numeral 19 denotes an average reception level obtained by time-averaging the envelope detection output from the detector 17, and the output is input to the processing circuit 13.

In the circuit having the above configuration, the modulation signal output from the modulator 11 is amplified by the power amplifier 12 and radiated from the antenna 16 through the transmission / reception distributor 15. At this time, detector 17
The average reception level is obtained by the reception level averaging processing circuit 19 from the output of the above, and from the output of the reception level averaging processing circuit 19 and the output of the random number generation circuit 14, the average reception level at the central station when the randomization is not performed is constant. A control voltage for randomly changing the output of the power amplifier 12 based on the transmission power is created, and the power amplifier 12 is controlled by this. As a result, desired transmission power can be obtained.

Next, an improvement effect when this embodiment is applied to a land mobile communication system will be described. In land mobile communication, propagation characteristics are the superposition of three components: distance fluctuation, slow short-term average value fluctuation over a section of about several tens of meters, and sudden instantaneous value fluctuation over a section of about several tens of meters. The fluctuation is represented by a component attenuated by a power of distance, the short-term average value fluctuation is represented by a lognormal distribution, and the instantaneous value fluctuation is represented by a Rayleigh distribution. The standard deviation of short-term average value fluctuation in an urban area is about 6 (dB) in power level (dB value). If the time for averaging the reception levels is long to some extent, the instantaneous value fluctuations are averaged, and the correlation between the propagation characteristics of the uplink and the downlink is close to 1. Can be determined.

Also, by reducing the averaging time to a certain extent, the variance of the average reception level of the central station can be reduced, but if it is further shortened, the variance increases due to the influence of instantaneous value fluctuation. If the averaging time is increased, the distance characteristics are compensated, but the variance increases due to the influence of the median value, and the standard deviation approaches 6 (dB). In the following, a case where the averaging time is appropriately set and the standard deviation σ ₀ = 3 (dB) of the average reception level (dB) at the central station is quantitatively evaluated.

In the present embodiment, it is assumed that the transmission power in the N stages shown in FIG. 3 appears with a uniform probability. FIG. 5 shows that two branches of diversity are used on the central station side and N
= 2 indicates a non-reception rate of a signal at the time of two-signal collision when randomization is performed.

In FIG. 5, Δ = 0 (dB) corresponds to the case of the conventional pure Aloha system. In addition, as is clear from the characteristic curve of FIG. 3, as the randomization width Δ (dB) of the transmission power increases, the non-reception rate of the signal at the time of collision decreases and the survival probability increases.

FIG. 6 is a characteristic diagram of a signal transmission incomplete ratio with respect to a traffic amount when the number of retransmissions is limited to a finite number (N ₀ = 10). A characteristic curve 32 indicates that the method of this embodiment is a pure Aloha method. The signal transmission incomplete rate when applied, and the characteristic curve 33 represents the signal transmission incomplete rate according to the conventional pure Aloha method.

FIG. 7 is a throughput characteristic diagram with respect to the traffic amount when the number of retransmissions is similarly limited to a finite number (N ₀ = 10). , And a characteristic curve 35 represents the throughput of the conventional pure Aloha method, respectively. Here, λ represents the occurrence probability of a call, t ₀ represents the signal length, and the case where the total width of randomization is Δ = 30 (dB) is shown.

In FIG. 6, when the uncompleted rate is 0.01, it can be seen that when the total width of randomization is 30 dB, about 40% more subscribers can be accommodated than when no randomization is performed. In FIG. 7, it can be seen that the maximum throughput is improved by about 40% by applying this method.

In the second embodiment, the effect of applying the present scheme to the pure Aloha scheme in which a function of compensating for the distance property among the propagation properties is added to the terminal has been described. The same effect can be exerted even when applied to

Embodiment II In wireless communication, when a plurality of signal types and information contents are transmitted on the same channel, the required signal transmission reliability and transmission delay characteristics may differ from each other. Therefore, in the present embodiment, a case where there are two types of signals will be described by taking, as an example, an uplink transmission control channel of a car telephone system currently provided for land mobile communication.

In the transmission control channel, a call signal and a location registration signal are transmitted. Since the calling signal is transmitted when a telephone user makes a call, it must be received by the central station within a connection delay time allowed after the call. In contrast, location registration signals are not usually of the nature that must be transmitted so quickly. An embodiment in which the transmission power of the calling signal is controlled to be large and the transmission power of the location registration signal is controlled to be small will be described in detail with reference to FIG.

FIG. 8 is a block diagram of a terminal for realizing the above control. 4, the transmission / reception system of the terminal includes an encoder 10, a modulator 11, a power amplifier 12, a processing circuit 13, a transmission / reception distributor 15, an antenna 16, a detector 17, and a decoder 18 as in the case of FIG. In addition, the average reception level is obtained by time-averaging the envelope detection output from the detector 17,
A reception level averaging processing circuit that outputs this to the processing circuit 13
And an information determining circuit for determining whether the information transmitted from the output of the encoder 0 is a calling signal or a location registration signal.
And a judgment output from the information judgment circuit 20 is inputted to the processing circuit 13.

In the signal transmission system configured as described above,
The modulated signal output from the modulator 11 is power-amplified by the power amplifier 12 and radiated from the antenna 16 through the transmission / reception distributor 15. At this time, the average reception level is obtained from the output of the detector 17 by the reception level averaging processing circuit 19, and the output and the output signal of the information decision unit 20 are added to the processing circuit 13, so that the average reception at the central station is at the level. Based on the transmission power at which the power becomes constant, a control voltage for changing the output of the power amplifier 12 is generated in accordance with the content of the transmission information, and the transmission voltage of the power amplifier 12 is controlled by the control voltage. As a result, specific transmission information, for example, a call signal that needs to be received by the central station within the connection delay time can be a desired transmission power with a high survival rate.

By performing such control, most of the outgoing call signal survives even if it collides with the location registration signal. Therefore, even in a system where the number of location registrations is large, the capacity of the transmission control channel is not suppressed by the location registration. . In addition, most of the location registration signal is not received when it collides with the outgoing call signal. However, by increasing the number of retransmissions, the location registration signal can be reliably transmitted during a time when there is no outgoing call signal.

Therefore, by changing the transmission power according to the type of the transmission signal or the content of the transmission information, more calls can be processed within the limited number of radio channels, and the number of mobile stations can be increased.

The signal transmission method of the present invention can also be applied to a combination of the embodiments I and III, that is, a configuration in which the transmission power according to the type of transmission signal or the content of information is changed randomly or periodically. Further, the combination of the embodiments I, II, and III, that is, the transmission level of the terminal is determined so that the reception level at the central station is constant, and the transmission power according to the transmission level and the type of the transmission signal or the content of the information. Can be applied randomly or periodically.

〔The invention's effect〕

As described above, according to the present invention, the transmission power of the transmission signal is changed according to the type of the transmission signal from the terminal to the central station or the content of the information. Can be improved, and the throughput and signal transmission incomplete rate of the entire system can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the overall configuration when the wireless communication signal transmission system of the present invention is applied to a land mobile communication system. FIG. 2 is a diagram showing the configuration of a transmission / reception system of a terminal according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram showing an example of transmission power distribution according to the embodiment of the present invention, FIG. 4 is a configuration diagram of a transmission / reception system of a terminal in the second embodiment of the present invention, and FIG. FIG. 6 is a characteristic diagram showing a signal non-reception rate at the time of collision in the embodiment, FIG. 6 is a characteristic diagram showing a signal transmission incomplete ratio in the second embodiment of the present invention, and FIG. 7 is a throughput in the same second embodiment. FIG. 8 is a configuration diagram of a transmission / reception system of a terminal according to the third embodiment of the present invention. 1 Central station 2 _{1 to} 2 _n Terminal 3 _{1 to} 3 _n Transmission / reception means 10 Encoder 11 Modulator 12 Power amplifier 13 Processing circuit 14 Random number generation circuit 15 … Tx / Rx 16… Antenna 17… Detector 18… Decoder 19… Reception level averaging processing circuit 20 …… Information judgment circuit

Claims (1)

(57) [Claims] 1. A wireless communication system in which a plurality of terminals randomly access a central station, the terminal comprising means for changing transmission power of a transmission signal in accordance with a type of a signal transmitted to the central station or contents of information. A wireless communication signal transmission system, characterized in that: