JP2721203B2 - Adaptive antenna device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention is to control the directivity of an antenna by learning the surrounding radio wave environment in a wireless communication system using a time division multiplex system. The present invention relates to an adaptive antenna apparatus for suppressing unnecessary interference waves and obtaining a high S / N ratio.

(Prior Art) Generally, in a time division multiplexing method (hereinafter, abbreviated as TDM), communication is performed using time slots allocated in a TDM frame so that a large number of signals do not overlap in time. It is a multiplex system. TDM has advantages over frequency division schemes (FDM), such as better compatibility with digital signal transmission at various speeds, higher frequency use efficiency, and the ability to reduce the size of base stations. At present, time division multiple access (TDMA) using TDM is becoming the mainstream in satellite communications. TDM is also used in digital terrestrial microwave communication systems using multi-level modulation technology. Furthermore, the application of the TDMA system to future rural radio communication and land mobile communication is being considered, even if it is promising.

A major problem in various communication systems using such a TDM system is deterioration of communication quality due to interference waves from other communication systems. For example, in satellite communications, interference from terrestrial radio systems using the same frequency band and system interference from other satellites caused by the launch of many satellites in geosynchronous satellite orbits, and terrestrial digital microwave communication systems In, coexistence with existing FDM / FM communication systems is a major problem.

As a method of reducing the influence of such an interference wave, a sufficient consideration should be given to the line design, the installation place of the communicating station is limited, a barrier against interference is physically constructed, and the antenna is set to a low side lobe. And so on.

One way to reduce the side lobe of an antenna is to apply an adaptive antenna that automatically controls the directivity of the antenna and forms a zero point in the direction of arrival of the interference wave to suppress the interference wave in the spatial domain. Conceivable. As shown in FIG. 3, the adaptive antenna includes a plurality of antennas 11, a weighting circuit 12 connected to each antenna 11 for weighting a received signal, a combiner 13 for combining the weighted signals, a combiner 13 output signals and each antenna 11
And a signal processing circuit 14 that determines the weight of the weight circuit 12 from the signal received by using a predetermined algorithm. MSN (Aaximum S / N) method, PI (Power Inversion)
And the SLC (Sideiobe Can celler) method. For these, there are the following documents. IEEE Transaction, Anten
na and Popagation, AP-24, September 1976 A common feature of these algorithms is that the weight is determined so as to minimize the output signal power of the combiner 13 in FIG. Hereinafter, the operation principle of the SLC will be described in detail using an example. In the SLC, one of the antennas 11 is a main antenna having a gain in the arrival direction of a desired signal, and the other antenna is an auxiliary antenna having a gain on the side lobe level of the main antenna. Further, the weight circuit 12 connected to the main antenna is always fixed, and the other weight circuits are controlled by the signal processing circuit 14. The signal processing circuit 14 includes a signal received by the auxiliary antenna and a synthesizer.
Multiplication with the 13 output signals is performed, and the result is integrated to determine the weight of the antenna. As is clear from FIG. 3, the SLC is composed of a feedback loop composed of the weight circuit 12, the combiner 13, and the signal processing circuit 14, so that the weight of the antenna is determined so that the output power of the combiner 13 is the minimum. It converges to the optimal weight while having a certain time constant so that Considering this from the viewpoint of the directivity of the antenna, it corresponds to the fact that the zero point of directivity is automatically formed in the signal direction even if the arrival direction of the signal is unknown. This is why the adaptive antenna controls the directivity while learning following the surrounding radio wave environment.

However, the conventional adaptive antenna has the following two major disadvantages. Generally, an adaptive antenna is used when electrons of an interference wave are sufficiently large in comparison with the power of a desired signal. This is clear from the above-described example of the operation principle of the SLC. That is, if the power of the interference wave is large, the output of the combiner 13 is also dominated by the interference wave, so minimizing the output power corresponds to suppressing the interference wave. However, conversely, when the desired signal is larger than the interference wave, the antenna weight is determined so as to suppress the desired signal, the desired signal loss increases, and the use of an adaptive antenna has an adverse effect. Would. That is, the conventional adaptive antenna has a property that a signal having higher power is more effectively suppressed, so that it is difficult to apply the adaptive antenna in a situation where an interference wave level is small.

The second disadvantage is that the desired signal received by the weight jitter suffers from a small but unnecessary modulation. As described above, the adaptive antenna determines the antenna weight using signal multiplication and integration, that is, signal correlation. The antenna weight in the converged state is the optimum weight that minimizes the output power of the combiner when viewed from the average, but it fluctuates instantaneously due to modulation of the desired signal or interference wave, and thermal noise components. doing. This is called weight jitter. When such weight jitter exists, the weight circuit 12 operates instantaneously, and the amplitude and phase of the desired signal are modulated, albeit minutely. As a result, the weight jitter causes a phase error and an amplitude distortion in the desired signal, and thus worsens the error rate.

In communication systems using the TDM system, a higher C / N ratio is required than in the conventional FDM system, etc., and strict requirements are also placed on carrier phase errors and amplitude distortion of the receiving system. I have. Under these circumstances, it is difficult to apply a conventional adaptive antenna to a TDM communication system.

(Problems to be Solved by the Invention) When a conventional adaptive antenna is applied to a TDM communication system that requires a high C / N ratio, a low phase error, and a low amplitude distortion for interference wave suppression, the following problem occurs. Disadvantages arise.

(1) When the power of the interference wave is smaller than that of the desired signal, the effect of suppressing the interference wave is reduced, the loss of the desired signal increases, and the C / N ratio is deteriorated.

(2) Unwanted modulation is added to the desired signal due to the weight jitter, causing a phase error and an amplitude distortion to cause a deterioration in an error rate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional example, and has as its object to exhibit a sufficient interference wave suppressing effect when the level of an interference wave is smaller than a desired signal, and to achieve a desired signal loss. Another object of the present invention is to provide an adaptive antenna for a TDM communication system capable of improving a C / N ratio and avoiding a phase error and an amplitude distortion by reducing the influence of a weight jitter on a desired signal and reducing a phase error and an amplitude distortion.

[Configuration of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention sets an empty time slot in which no communication is performed in a TDM frame in a wireless communication system using TDM, Inside is the learning period for observing the surrounding radio wave environment. The adaptive antenna determines the antenna weight using information on the surrounding radio wave environment only during this learning period. In other time slot periods, the determined antenna weight is fixed. In other words, the adaptive antenna performs the same interference wave suppression operation as in the related art during the above-mentioned idle time slot period, and uses a fixed weight in other time slot periods. Further, the initial value of the antenna weight determined by learning during the empty time slot period may be an antenna weight fixed until immediately before the start of the empty time slot.

(Operation) During the empty time slot period, the desired signal does not exist, and only the interference wave is observed. Since the adaptive antenna operates using information of the surrounding radio wave environment only during this period, the antenna weight for suppressing the interference wave is determined. That is, since the determined antenna weight does not depend on the signal level of the desired signal at all, and depends only on the interference wave, a sufficient interference wave suppressing function can be realized even when the interference wave is smaller than the desired signal. . In addition, since it does not operate to suppress the desired signal, the desired signal loss is reduced. In other time slots, the determined antenna weight is fixed, so that the interference wave suppressing function is maintained and there is no way jitter.

As described above, since the adaptive antenna operates only during the idle time slot period, it is conceivable that the optimum weight may not be sufficiently converged, for example, because the idle time slot time is short. In such a case, it is necessary to effectively use the learning effect up to now by using an empty time slot period of a plurality of continuous TDM frames. This is effectively achieved by adopting, as the initial value of the antenna weight, the final information learned in the immediately preceding empty time slot period, that is, the antenna weight fixed so far.

(Example) An example of the present invention is shown below. FIG. 1A shows a configuration example of a TDM frame of the present invention. In the figure, 1TD
The M frame 1 is composed of m time slots 2, and the i-th time slot 2 is an empty time slot 3 in which no communication is performed. Let the start time and the end time be t1 and t2, respectively. It is assumed that the arrangement of the empty time slot 3 in the TDM frame is predetermined in the entire communication system. FIG. 1 (b)
The situation at the input end of the adaptive antenna when an interference wave is mixed in a desired signal of the TDM system is shown. The time during which the interference wave is applied is defined as to. FIG. 1 (c) shows the convergence of the antenna weights, and FIG. 1 (d) shows the signal waveform at the output end of the adaptive antenna.

FIG. 2 shows a configuration example of the adaptive antenna of the present invention. In the figure, 4 is an antenna, 5 is a weight circuit, 6 is a combiner, 7 is a multiplier, 8 is a switch, 9 is an integrator, and 10 is a synchronous circuit. The antenna 4, the weight circuit 5, the combiner 6, the multiplier 7, and the integrator 9 are the same as those shown in the conventional example. The synchronization circuit 10 detects a vacant time slot in the TDM frame, and turns on during a vacant time slot period, and turns off during another time slot period.
, And controls the switch 8. The switch 8 operates so that the output signal of the multiplier 7 is supplied to the integrator 9 when ON and not supplied to the integrator 9 when OFF according to the control signal of the synchronization circuit 10.

Hereinafter, the operation principle of the present invention will be described in detail with reference to FIG. 1 and FIG. First, before the interference wave is applied (to
Think before). In this state, it is not an empty time slot period as shown in FIG.
Is in the OFF state. At this time, the antenna weights stored in the integrator 9 are fixed. In this state, when an interference wave is applied at to, the antenna weight is fixed, so that C / N degradation due to the interference wave occurs as shown in FIG. 1 (d). Next, when the time reaches t1, the synchronization circuit 10 detects that the current time is the start of the idle time slot period, and turns on the switch 8. As a result, the output signal from the multiplier 7 is supplied to the integrator 9, and FIG.
The antenna weight starts to change as shown in FIG. This change continues until t2 when the empty time slot period ends. t2
Thereafter, since the switch 8 is turned off under the control of the synchronization circuit 10, the antenna weight remains fixed at the antenna weight at time t2. During the vacant time slot period from t1 to t2, the desired signal does not exist and only the interference wave exists,
During this period, the output of the combiner 6 is also only the interference wave. Since the antenna weights are sequentially changed so as to minimize the output power of the combiner 6, an antenna weight for suppressing the interference wave is obtained as a result. From this, the antenna weight is completely irrelevant to the level of the desired signal, and a sufficient suppression effect is exerted even on an interference wave having a small signal power. FIGS. 1 (c) and 1 (d) show the antenna weight and the suppression effect on the interference wave during the empty time slot period.

The antenna weight may not converge sufficiently and an interference wave may remain due to a reason such as a short idle time slot period. In such a case, the optimal weight for suppressing the interference wave can be obtained by effectively using the information learned during the empty time slot period. This is achieved by adopting, as the initial value of the antenna weight, the final information learned in the immediately preceding empty time slot period, that is, the antenna weight fixed so far. This initial value setting is automatically performed when the input of the integrator 9 is turned off by the switch 8.

Further, as is clear from FIGS. 1 and 2, the antenna weight is fixed during periods other than the idle time slot period. Therefore, no weight jitter occurs during the period in which the desired signal exists, and the desired signal is not affected at all.
As a result, new phase errors and amplitude distortion due to the introduction of the adaptive antenna can be avoided.

The present invention is not limited to the above embodiment. For example, a plurality of empty time slot periods may be set in one TDM frame. Further, in the above embodiment, the signal processing of the adaptive antenna is represented by hardware, but the signal received by the antenna may be A / D converted and the same processing may be performed by software in a computer. Further, the integrator 6
If a low-pass filter is used instead, switch 5
May be inserted between the resistor and the capacitor to realize the function of retaining the antenna weight. In short, the present invention can be variously modified and implemented without departing from the gist thereof.

〔The invention's effect〕

As described above, the present invention provides an empty time slot in the TDM frame, and operates the adaptive antenna during this time slot period, even when the power of the interference wave is smaller than the desired signal, A sufficient interference wave suppressing function can be exhibited without increasing the desired signal loss. In addition, unnecessary modulation to a desired signal due to weight jitter can be avoided. Furthermore, by setting the initial value of the antenna weight obtained by learning as the antenna weight immediately before the start of learning, it is possible to converge on the optimum weight. Thus, by applying the adaptive antenna of the present invention to a TDM communication system, it is possible to suppress interference waves and achieve a high C / N ratio, and to stably generate no new phase error or amplitude distortion. And high quality communication can be provided. Further, by using the present invention, it is possible to increase the degree of freedom in circuit design and to ease the restriction on the grounding place of the communication station. Further, a large-scale barrier for suppressing interference waves is not required, and a sufficient effect is exhibited.

[Brief description of the drawings]

FIG. 1 is a time chart showing the relationship between time and signals according to the present invention, FIG. 2 is a diagram showing one configuration of the present invention, and FIG. 3 is a diagram showing a conventional example. 4 ... antenna, 5 ... weight circuit, 6 ... synthesizer, 8 ... switch, 10 ... synchronous circuit.

Claims (2)

(57) [Claims] An adaptive antenna apparatus applied to wireless communication using a time-division multiplexing system, comprising: an empty time slot generating means for providing an empty slot in a frame where no communication is performed; Radio wave environment storing means for storing a radio wave environment to perform, weight determining means for determining an antenna weight of the adaptive antenna so as to suppress an interference wave during the idle time slot period based on an output of the radio wave environment storing means, An adaptive antenna apparatus, comprising: a weight fixing unit that is fixed to the weight determined by the weight determining unit during a time slot period other than the empty time slot period. 2. The adaptive antenna apparatus according to claim 1, wherein an initial value of the antenna weight determined within the empty time slot period is an antenna weight fixed until immediately before the start of the empty time slot. .