JPH02121428A - Adaptive antenna equipment - Google Patents

Abstract

PURPOSE:To attain sufficient interference wave suppressing function without increasing a desired signal loss even if power of an interference wave is small by providing an idle time slot in a frame to activate the adaptive antenna in the time slot period. CONSTITUTION:An idle time slot 3 not making communication is set in a time division multiplex system frame 1 and the time in the time slot period is used as a study period observing a surrounding radio wave environment. The adaptive antenna uses information of a surrounding radio wave environment in the study period only to decide the weight of antenna. The decided antenna weight is fixed in other time slot period 2. Thus, even when the interruption wave is smaller in comparison with a desired signal, sufficient interference wave suppressing function is attained.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application) The present invention provides a method for determining the directivity of an antenna by learning the surrounding α wave environment in a wireless communication system using a time division multiplexing system. The present invention relates to an adaptive antenna device whose purpose is to suppress unnecessary interference waves and obtain a high S/N ratio through control.

(Prior Art) In general, time division multiplexing (hereinafter abbreviated as TDM) is a method of communication using time slots allocated within a TDM frame to prevent multiple signals from overlapping in time. It is a multiplex method. TDM is a frequency division method (FD
Compared to M), it has advantages such as good compatibility with digital signal transmission consisting of various speeds, high frequency utilization efficiency, and ability to downsize the base station. Currently, time division multiple access using TDM (TD
MA) is becoming mainstream. Furthermore, TDM is also employed in terrestrial digital microwave communication systems that use multilevel modulation technology. Furthermore, the TDMA system is considered to be promising in future rural wireless communications and land mobile communications, and its application is being considered.

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

Methods to reduce the effects of such interference waves include giving due consideration to line design, limiting the amount of coverage of communicating stations, physically constructing barriers against interference, and using antennas with low side ropes. etc. are being carried out.

One method for reducing the side rope of an antenna is to apply an adaptive antenna that suppresses interference waves in the spatial domain by automatically controlling the directivity of the antenna and forming a zero point of directivity in the direction in which the interference waves arrive. is possible. As shown in FIG. 3, an adaptive antenna is a plurality of antennas 11. A weight circuit 12 connected to each antenna 11 weights the received signal, a combiner 13 combines the weighted signals, and the weight of the weight circuit 12 is calculated from the output signal of the combiner 13 and the signal received by each antenna 11. It is comprised of a signal processing circuit 14 that makes decisions using a certain predetermined algorithm. The adaptive antenna algorithm is M S N (Maximum
S/N) method, PI (Power Invers)
ion) method, SLC (Sideiobe Ca
n celler) method etc.-1) 16. Regarding these, there are the following documents. IEEE Transact
ion.

Antenna and Popagation, AP
-24, September 1976 What these algorithms have in common is that weighting is determined so as to minimize the output signal strength of combiner 13 in FIG. Hereinafter, taking SLC as an example, its operating principle will be explained in detail.

In SLC, one of the antennas 11 is used as a main antenna that has a gain in the direction of arrival of a desired signal, and the other antennas are auxiliary antennas that have a gain that is about the same as the side lobe level of the main antenna. Furthermore, 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 multiplies the signal received by the auxiliary antenna by the output signal of the combiner 13, and integrates the result to determine antenna weighting. As is clear from Fig. 3, the SLC consists of a weight circuit 12, a synthesizer 1
3. Since it is composed of a feedback loop consisting of the signal processing circuit 14, the antenna weighting converges to the optimal weight with a certain time constant so that the output power of the combiner 13 is minimized. . If we consider this from the perspective of antenna directivity, we can see that even if the direction of arrival of a signal is unknown, the zero point of directivity is automatically formed in the signal direction. This is why adaptive antennas control directivity while following and learning from the surrounding radio wave environment.

However, the conventional adaptive antenna has two major drawbacks as shown below. Generally, an adaptive antenna is used when the electrons of the interference wave are sufficiently large compared to the power of the desired signal. This is clear from the example of the operating principle of the SLC described above. In other words, if the power of one interference wave is large, the output of the combiner 13 is also dominated by interference waves, so
Minimizing the output power corresponds to suppressing interference waves. However, on the other hand, if the desired signal is larger than the interference wave, the antenna weights are determined to suppress the desired signal, resulting in a large loss of the desired signal and using an adaptive antenna may have the opposite effect. turn into. In other words, since conventional adaptive antennas have the property of effectively suppressing signals with large power, it is difficult to apply adaptive antennas in situations where the interference wave level is low.

The second drawback is that the received desired signal is subject to slight but unnecessary modulation due to weight jitter. As mentioned above, the adaptive antenna uses signal multiplication and integration, that is, signal correlation, to determine antenna weights. The antenna weights in the converged state are the optimal weights that minimize the combiner output power in terms of average values, but instantaneously they vary depending on the modulation of the desired signal and interference waves, as well as thermal noise components. are doing. This is called weight jitter.0 When such weight jitter exists, the weight circuit 13 operates instantaneously, and modulates the amplitude and phase of the desired signal, albeit slightly. Ultimately, the weight jitter causes a phase error and amplitude distortion in the desired signal, worsening the error rate.

Communication systems using the TDM system require a higher C/N ratio than conventional FDM systems, and there are also strict requirements for carrier wave phase error and receiving system amplitude distortion. There is. Considering this situation, T
It is difficult to apply conventional adaptive antennas to DM communication systems.

(Problems to be Solved by the Invention) When a conventional adaptive antenna is applied to suppress interference waves in a TDM communication system that requires a high C/N ratio, low phase error, and low amplitude distortion, the following problems occur. Defects arise.

(11 When the power of the interference wave is small compared to the desired signal, the interference wave suppression effect decreases, and conversely the desired signal loss increases,
The C/N ratio deteriorates.

(2) Unnecessary modulation is added to the desired signal due to weight jitter, which causes phase errors and amplitude distortions, causing deterioration of the error rate.

The present invention has been made in view of the above-mentioned conventional example, and its purpose is to exhibit a sufficient interference wave suppression effect when the level of the interference wave is small compared to the desired signal, and to reduce the loss of the desired signal. An object of the present invention is to provide an adaptive antenna for a TDM communication system that can improve the C/N ratio and avoid phase errors and amplitude distortions by reducing weight jitter and avoiding the influence of weight jitter on a desired signal.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention sets an empty time slot in which no communication is performed in a TDM 7 frame in a wireless communication system using TDM, and This period will be used as a learning period to observe the surrounding radio wave environment. The adaptive antenna determines antenna weights using information about the surrounding radio wave environment only within this learning period. In other time slot periods, the determined antenna weights are fixed. In other words, the adaptive antenna performs the interference wave suppression operation similar to the conventional one within the vacant time slot period, and uses fixed weights in other time slot periods. Furthermore, the initial value of the antenna weight determined by learning within the empty time slot period is set to the antenna weight that was fixed until immediately before the start of the empty time slot.

(Operation) During the empty time slot period, no desired signal exists and only interference waves are observed.

Since the adaptive antenna operates using detailed information about the surrounding radio wave environment only within this period, antenna weights that suppress interference waves are determined. In other words, the determined antenna weights do not depend on the signal level of the desired signal at all, but only on the interference waves, so even if the interference waves are small compared to the desired signal, a sufficient interference wave suppression function can be achieved. . 'Also, since it does not attempt to suppress the desired signal,
Desired signal loss is also reduced. In other time slot periods, the determined antenna weight is fixed, so the interference wave suppression function is maintained, and at the same time,
There is no way jitter either.

As described above, since the adaptive antenna operates only within the empty time slot period, there may be cases where the weights do not fully converge to the optimal weight, for example, due to the short time of the empty time slot. In such a case,
It is necessary to make effective use of the learning effect so far by using the vacant time slot periods of consecutive multiple 'r1)M frames. This is effectively achieved by using the final information learned in the previous vacant time slot period, that is, the antenna weight that has been fixed until now, as the initial value of the antenna weight. (Example) An example of the present invention is shown below. FIG. 1(a) shows an example of the structure of a TDM frame according to the present invention. In the same figure, i
A TDM frame 1 is composed of ml 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 end time be tl and t2, respectively. It is assumed that the arrangement of this vacant time slot 3 within the TDM frame is determined in advance for the entire communication system. 1st
Figure (b) shows the situation at the input end of the adaptive antenna when interference waves are mixed into the desired signal of the TDM system. Let to be the time when the interference wave is applied.

Figure 1 ((1) shows the convergence of the antenna weights in Figure 1 ((1)).
d) shows the signal waveform at the output end of the adaptive antenna.

FIG. 2 shows an example of the configuration of the adaptive antenna of the present invention. In the figure, 4 is an antenna, 95 is a weight circuit, 6 is a combiner, 7 is a multiplier, 8 is a switch, 9 is an integrator, and IO is a synchronization circuit.

The antenna 4, weight circuit 5, combiner 6, multiplier 7, and integrator 9 are the same as those shown in the conventional example. The synchronization circuit 10 detects an empty time slot in the TDM frame, generates a control signal that is ON if the time slot is an empty time slot, and OFF if the time slot is another time slot, thereby controlling the switch 8. Switch 8 is synchronous circuit 1
With a control signal of 0, the output signal of the multiplier 7 is supplied to the integrator 9 when ON, and is not supplied to the integrator 9 when OF2.

The operating principle of the present invention will be explained in detail below with reference to FIGS. 1 and 2. First, before the interference wave is applied (to
(previously). In this state, as shown in FIG. 1(a), it is not an empty time slot period, so the switch 8
is in the OFF state. At this time, the antenna weights stored in the integrator 9 are fixed. In this state, tO
Since the antenna weight is fixed when the interference wave is applied, as shown in Fig. 1(d), the C/
N deterioration occurs. Next, when time reaches tl, the synchronization circuit 10 detects that the current time is the start of an empty 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, so that the antenna weight begins to change as shown in FIG. 1(C). This change continues at t2-1, when the empty time slot (El1) ends. After t2, the switch 8 is turned OFF' under the control of the synchronization circuit 10, so the antenna weight remains fixed to the antenna weight at time t,2. During the empty time slot period from tl to t2, there is no desired signal and only interference waves are present, so the output of the synthesizer 6 during this period is also only interference waves. Since the antenna weights are successively changed so as to minimize the output power of the combiner 6, the antenna weights that suppress interference waves can be found as a result. Therefore, the antenna weight is completely unrelated to the level of the new signal, and the suppressing effect is sufficiently exerted even on interference waves with small signal power. FIGS. 1C and 1D show antenna weights during this empty time slot period and the suppression effect on interference waves.

Due to reasons such as a short vacant time slot period, the antenna weights may not converge sufficiently and interference waves may remain.

In such a case, the optimum weight for suppressing the interference waves can be found by effectively using the information learned during the vacant time slot period. This is achieved by using the final information learned in the previous vacant time slot period, that is, the antenna weights that have been fixed up until now, as the initial values of the antenna weights. This initial value setting is automatically performed by turning off the manual power of the integrator 9 using the switch 8.

Furthermore, as is clear from FIGS. 1 and 2, the antenna weights are fixed during periods other than one empty time slot. Therefore, weight jitter does not occur during the period when the desired signal exists, and does not have the same effect on the desired signal.

As a result, it is possible to avoid additional phase errors and amplitude distortions due to the introduction of the adaptive antenna.

The present invention is not limited to the above embodiments.

For example, a plurality of vacant time slot periods may be set within an ITDM frame. Further, in the above embodiment, the signal processing of the adaptive antenna is expressed in hardware, but the signal received by the antenna may be A/D converted and similar processing may be performed in software in a computer. Furthermore, when the integrator 6 is replaced with a low-pass filter,
The function of holding the antenna weight may be realized by inserting the switch 5 between the resistor and the capacitor. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

〔Effect of the invention〕

As explained above, the present invention provides an empty time slot in the TDM frame and operates the adaptive antenna within this time slot period, thereby achieving a signal even when the power of the interference wave is small compared to the desired signal. A sufficient interference wave suppression function can be achieved without increasing desired signal loss. Further, unnecessary modulation of the desired signal due to weight jitter can also be avoided.

Furthermore, by setting the initial value of the antenna weights determined by learning to the antenna weights immediately before the start of learning, it is possible to converge to the optimal weights. As described above, 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.
Stable and high-quality communication can be provided without generating new phase errors or amplitude distortions. Further, by using the present invention, it is possible to increase the degree of freedom in circuit design and to relax restrictions on the grounding location of communication stations. Furthermore,
There is no need for a large-scale barrier for suppressing interference waves, and the effect is sufficient.

[Brief explanation of the drawing]

FIG. 1 is a time chart showing the relationship between time and signals related 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... Wait circuit, 6... Combiner, 8... Switch, 10... Synchronous circuit - 1 Agent Patent attorney Yudo Nori Chika Hikaru Matsuyama Tea mouth

Claims (2)

[Claims] (1) In an adaptive antenna applied to wireless communication using time division multiplexing, an empty time slot generation means that provides an empty time slot in which no communication is performed within a frame, and a radio wave that changes sequentially within the empty time slot period. a radio wave environment storage means for storing the environment; a weight determination means for determining the antenna weight of the adaptive antenna from the output of the radio wave environment storage means; 1. An adaptive antenna device comprising: weight fixing means for fixing and using determined weights. (2) The adaptive antenna device according to claim 1, wherein the initial value of the antenna weight determined within the empty time slot period is the antenna weight that was fixed until immediately before the start of the empty time slot.