JP3363014B2 - Propagation path selection method in wireless communication system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a propagation path in a wireless communication system for performing communication between a base station having a plurality of directional antennas and a single antenna or a plurality of terminals each having a plurality of directional antennas. The present invention relates to a selection method, that is, a method for selecting an optimal propagation path from a large number of propagation paths between a base station and a terminal in order to minimize the influence of distortion from the propagation path.

[0002]

2. Description of the Related Art In a cellular radio communication system using an angle modulation method, when performing communication at a high bit rate,
There is a problem that communication quality is greatly deteriorated due to multipath interference. Multipath interference is interference caused by a transmitted signal reaching a receiver through a plurality of propagation paths due to signal reflection at a reflecting object. That is, it is a phenomenon in which signals strengthen or weaken depending on whether the phase relationship of each received signal in which the time of arrival has passed through different propagation paths is in-phase or anti-phase. .

Conventionally, several methods for reducing multipath interference have been considered. One is a method using an adaptive automatic equalizer. The adaptive automatic equalizer is a device that constructs a filter having a transfer characteristic in which the impulse response of the transmission path is inverted and reproduces the original waveform from the signal waveform distorted in the propagation path. Such a filter can be realized by, for example, a transversal filter including a delay line with a tap and a weighting device that adjusts a tap gain given to an output or an input of each tap. However, such filters require sophisticated digital signal processing techniques,
Since the circuit scale becomes large, it is difficult to mount it on a wireless terminal such as a mobile terminal or a mobile terminal that requires small size and light weight and low power consumption.

As another method for reducing multipath interference, a method using spread spectrum technology is considered. In the spread spectrum communication system, the transmitter performs modulation in two stages. In the primary modulation, a modulation signal used in ordinary narrow band transmission is created, and in the secondary modulation, a code sequence called pseudo random noise is multiplied with the primary modulation signal to widen the band. Then, the receiver removes the interference component by multiplying the same code sequence as the pseudo random noise sequence used for the secondary modulation,
The signal before the secondary modulation is taken out. However, this method has a problem that the transmission band is widened and the frequency utilization efficiency is lowered.

In order to reduce multipath interference without using such an adaptive automatic equalizer or spread spectrum technique, the antennas of the base station and the terminal are composed of a plurality of directional antennas to obtain the best communication quality. A wireless communication system has been proposed which has a function of selecting an optimum propagation path corresponding to an optimum combination of given antennas. In this system,
A known signal sequence is assigned to a part of the transmission signal from the base station. The selection of the optimum antenna combination is performed by the following procedure.

First, a base station transmits a known signal sequence using one of the directional antennas, synchronizes at the terminal, and then receives at one of the directional antennas of the terminal. By measuring the quality of the known signal sequence, the rank of the propagation path due to the combination of both antennas is registered. Next, the antenna of the base station is switched to another antenna while the antenna for receiving the known signal sequence of the terminal is fixed, and the rank of the propagation path is similarly registered. When the propagation path rank corresponding to the combination with one antenna of the terminal is registered for all the directional antennas of the base station, the antenna of the terminal is switched this time and the same operation is performed.

Thus, the rank of the propagation path is determined for all the combinations of antennas of the base station and the terminal, and the combination of antennas corresponding to the propagation path with the highest rank is selected as the antenna for data communication. That is, when the terminal determines the propagation path with the highest rank, it informs the base station which directional antenna has been selected, and based on this, the base station uses the selected antenna to send and receive data to and from the terminal. I do. According to this method, it is possible to mitigate the effects of multipath by using a plurality of directional antennas and only adding a relatively simple circuit to the wireless transmission / reception unit and without lowering the frequency utilization efficiency during communication. it can.

As a method of determining the rank of the propagation path in such a wireless communication system, a method of measuring the quality of all the propagation paths a plurality of times has been proposed. When a propagation path is selected using the results of multiple measurements, the influence on the selection of the optimum propagation path is reduced even if the propagation environment temporarily changes due to the passage of people.

However, in this conventional optimum propagation path selection method, a plurality of directional antennas respectively provided in the base station and the terminal are temporally switched, and the propagation path is selected for all combinations of the antennas of the terminal and the base station. In order to measure quality, the number of measurements and the measurement time increase in proportion to the number of directional antennas used. That is, assuming that the number of directional antennas of the base station is a and the number of directional antennas of the terminal is b, basically there are a × b propagation paths, which is the same in the conventional method. Only the number of measurements must be taken. Therefore, when the number of antennas increases, it takes a very long time to measure the quality of all the propagation paths, and the time of each measurement is different, so the quality of the propagation path changes, and the optimum propagation is not always possible. You will not be able to select a path. In addition, in order to increase the reliability of the selection of the optimal propagation path against changes in the propagation environment due to the passage of people or moving objects in the propagation path, quality measurement is performed multiple times for each propagation path. It takes a long time.

[0010]

As described above, a plurality of directional antennas of the terminal and the base station are temporally switched, the quality of the propagation path is measured for all combinations of antennas, and the optimum propagation is based on this. In the method of selecting a path, when the number of directional antennas used is large, it takes a long time to measure the quality of all propagation paths, and the quality changes because the measurement time is different. Unable to select the propagation path to
Further, if the quality of each propagation path is measured a plurality of times in order to improve the reliability of the selected propagation path, there is a problem that a longer time is required.

The present invention provides an optimum path selection method in a wireless communication system capable of accurately selecting an optimum propagation path between a base station and a terminal in which at least a base station antenna is composed of a plurality of directional antennas. The purpose is to

[0012]

In order to solve the above problems, the present invention provides at least one base station having a plurality of directional antennas for base stations and a plurality of wireless terminals having at least one terminal antenna. In a wireless communication system for communication between terminals, when selecting an optimal propagation path from multiple propagation paths between multiple base station directional antennas and terminals, (a) from the base station via multiple directional antennas. And simultaneously transmit known signal sequences with different frequencies to the terminal, (b) analyze the frequency of the known signal sequence received by the terminal, and measure the quality of multiple propagation paths from each frequency spectrum. Based on this, a plurality of propagation paths are ranked, and (d) the optimum propagation path is determined based on the result of this ranking.

According to this method, basically, a plurality of directional antennas for base stations simultaneously transmit known signal sequences having different frequencies only once, so that quality measurement of all propagation paths and ranking based on them can be performed. Since this is possible, the time required to select the optimum propagation path is greatly reduced.

Further, the present invention provides a wireless communication system for performing communication between at least one base station having a plurality of directional antennas for a base station and a plurality of wireless terminals each having a plurality of directional antennas for a terminal, In order to select an optimum propagation path from among a plurality of propagation paths between a plurality of directional antennas for base stations and a plurality of directional antennas for terminals,
(a) The base station transmits a known signal sequence with different frequencies to the terminal simultaneously through a plurality of base station directional antennas,
(b) The terminal analyzes the known signal sequences respectively received via the directional antennas for a plurality of terminals to measure the quality of a plurality of propagation paths from each frequency spectrum, and (c) based on this measurement result, The propagation paths of (1) are ranked, and (d) the optimum propagation path is determined based on the result of this ranking.

In such a system in which the base station has a plurality of directional antennas and the terminal has a plurality of directional antennas, even when the directional antennas for the terminals are switched one by one, the propagation path is measured. , It is possible to measure the quality of all propagation paths and rank them based on the simultaneous transmission of a known signal sequence from multiple directional antennas for base stations as many times as the number of directional antennas for terminals. The time required to select the propagation path is greatly reduced.

[0016] Further, if the quality measurement of the propagation path for the known signal sequence received by each terminal directional antenna and the ranking process based on it are performed in parallel, known signals from a plurality of directional antennas for base stations are obtained. Basically, the simultaneous transmission of the sequence only needs to be performed once, and the time required for selecting the optimum propagation path is further shortened.

It is desirable that the plurality of known signal sequences simultaneously transmitted from the plurality of base station directional antennas be a plurality of continuous waves having different frequencies, that is, a sine-wave signal that does not include much harmonic components. Further, it is desirable that the frequency intervals of the plurality of continuous waves be set to values larger than the reciprocal of the transmission duration of the known signal sequence and sufficiently smaller than the reciprocal of the propagation delay time differences of the plurality of propagation paths.

By thus setting the frequency intervals of a plurality of continuous waves which are known signal sequences, the influence of the propagation delay time difference caused by the distance difference of the plurality of propagation paths and the distortion of each propagation path caused by the frequency difference. It is possible to correctly measure the quality of the propagation path without being affected by the difference in the amount, and as a result, the reliability of the selection of the optimum propagation path is improved.

The frequency analysis of a plurality of known signal sequences composed of continuous waves having different frequencies is preferably performed by fast Fourier transform capable of high speed processing. In this case, by setting the size of the fast Fourier transform window in the fast Fourier transform to the reciprocal of the frequency interval of a plurality of continuous waves, the fast Fourier transform of each continuous wave transmitted from the directivity for each base station The orthogonality is maintained, and the quality of the propagation path can be measured more accurately.

It is desirable that the frequency of each continuous wave that is a plurality of known signal sequences is equal to or close to the carrier frequency used for communication. By doing so, it is possible to measure the quality of the propagation path in the data communication frequency band, and by determining the propagation path based on this, it is possible to effectively improve the communication quality during actual data communication.

The quality of the plurality of propagation paths is measured by measuring the power of each frequency spectrum of the known signal sequence received by the terminal or measuring the distortion of each frequency spectrum. The method of measuring the power of the frequency spectrum can easily measure the quality of the propagation path with a simple circuit configuration, and the method of measuring the distortion can measure the quality of the propagation path more accurately.

In the present invention, the optimum propagation path is determined after repeating the transmission of the known signal sequence from the base station to the terminal, the quality measurement of a plurality of propagation paths and the ranking for each propagation path a plurality of times. You may do it.
As a result, the influence of the quality measurement of the propagation path due to fluctuations in the propagation environment is reduced, and the reliability of selection of the optimum propagation path is improved. In this case, the known signal sequence need only be transmitted for the number of times the quality of the propagation path is measured, and the time required for the measurement can be greatly reduced as compared with the conventional method of performing a plurality of measurements.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a wireless communication system according to an embodiment of the present invention. This wireless communication system includes at least one wireless base station (hereinafter referred to as a base station) 1 and a plurality of wireless terminals (hereinafter referred to as terminals) 3. The base station 1 has a plurality of narrow directional beams B
The base station antenna 2 has a plurality of directional antennas 2-1, 2-2, 2-3, 2-4 shown in FIG. 2, which form 1, B2, B3, B4 respectively. Hereinafter, the directional antennas 2-1, 2-2, 2-3, 2-4 will be referred to as base station directional antennas. The base station 1 is configured to be able to simultaneously transmit known signal sequences of different frequencies via the directional antennas 2-1, 2-2, 2-3, 2-4 for each base station as described later. ing.

Directional antennas for base stations 2-1, 2-2,
2-3 and 2-4 are narrow directional beams B1 and B, respectively.
2, B3 and B4 are arranged as a whole so as to cover all directions of 360 ° in the communication service area of the base station 1. In addition, here, the number of narrow directional beams, that is, the directional antennas for base stations 2-1, 2-2, 2-3, 2
Although the number of -4 was set to 4, it goes without saying that these numbers are not particularly limited to four. On the other hand, the terminal 3 has an omnidirectional terminal antenna 4.

In addition to the components for normal communication (data transmission / reception) with the terminal 3, such as the switch 10 for switching between transmission and reception, the transmission circuit 11 and the reception circuit 12, the base station 1 performs optimum propagation. As components for path selection, a continuous wave generator 13 that generates a continuous wave that is a known signal sequence and an optimum propagation path selector 14 are included.

The continuous wave generator 13 continuously supplies different frequencies f ₁ , f ₂ , f ₃ , f ₄ supplied to the directional antennas 2-1, 2-2, 2-3, _2-4 for base stations. It is a circuit that generates waves. Here, the continuous wave is typically a sine wave, and refers to an AC signal in which energy is mainly concentrated in the fundamental wave component and the harmonic component is not included so much. The optimal propagation path selection unit 14 uses the path information transmitted from the terminal 3 as described below to determine the optimal propagation path, that is, the base station directional antennas 2-1, 2-2, 2-3, for communication with the terminal 3. The antenna used for communication is selected from 2-4.

FIG. 2A shows an example of the configuration of the continuous wave generator 13, which is composed of a plurality of oscillators 41, 42, 43 and 44 which oscillate at frequencies f ₁ , f ₂ , f ₃ and f ₄ , respectively. It

FIG. 2B shows another example of the configuration of the continuous wave generator 13, which is a frequency synthesizer 50 for generating signals having frequency differences 3Δf, 2Δf, Δf, 0 and four multipliers 5.
1, 52, 53, 54, an oscillator 55 that oscillates a continuous wave of frequency f ₀ , and four filters 56, 57, 58,
It consists of 59. In the multipliers 51, 52, 53, 54, the signals with the frequency differences 3Δf, 2Δf, Δf, 0 and the continuous wave with the frequency f ₀ from the oscillator 55 are respectively multiplied, and f
Continuous waves having frequencies of ₀ ± 3Δf, f ₀ ± 2Δf, f ₀ ± Δf, f ₀ are generated, respectively. Multipliers 51, 52, 5
The outputs of 3, 54 pass through filters 56, 57, 58, 59, respectively, to remove unnecessary components, and then the directional antennas for base stations 2-1, 2-2, 2-3, 2-4.
Is supplied to each.

The outputs of the multipliers 51, 52, 53, 54 are generally f ₀ ± nΔf (n = 0, ..., 3), and
It also includes the independent frequency components of ± nΔf and f ₀ input from the frequency synthesizer 50 and the oscillator 55. The filters 56, 57, 58, and 59 remove these unnecessary frequency components to obtain f ₀ ± nΔf or f ₀ + n.
Only the frequency component of Δf or f ₀ -nΔf is taken out as a continuous wave of frequencies f ₁ , f ₂ , f ₃ , f ₄ , and the directional antennas for base stations 2-1, 2-2, 2-3, _2- are extracted. 4 respectively.

On the other hand, the wireless terminal 3 has constituent elements for normal communication (data transmission / reception) with the base station 1, such as a switch 30 for switching between transmission and reception, a transmission circuit 31, and a reception circuit 32. As components for selecting the optimum propagation path, there are a synchronization circuit 33, a frequency analysis unit 34, a spectrum measurement unit 35, a ranking unit 36, an optimum propagation path determination unit 37, and a path information generation unit 38.

The synchronizing circuit 33 is a circuit for synchronizing the timing of frequency analysis of the continuous wave, which is a known signal sequence transmitted from the base station 1, with this continuous wave. The frequency analysis unit 34 is a circuit that analyzes the frequency spectrum of a continuous wave and outputs a frequency spectrum signal, and is configured by, for example, a fast Fourier transformer. The spectrum measuring unit 35 measures the received power of the frequency spectrum signal and the like. The quality of the propagation path can be measured by this spectrum measurement. The ranking unit 36 is
The measured spectral signals are ranked. The optimum propagation path determination unit 37 uses the ranking unit 36.
Based on the ranking result of No. 1, the optimal propagation path, that is, the directional antennas for base stations 2-1, 2-2, 2-3, 2-4
Among them, the propagation path corresponding to the antenna most suitable for communication with the terminal 3 is determined. The path information generating unit 38 is information indicating the optimum propagation path determined in this way, in other words, the four directional antennas for base stations 2- constituting the base station antenna 2.
Information indicating the antenna best suited for communication with the terminal 3 among 1, 2, 2-2, 2-3, and 2-4 is generated and sent to the transmission circuit 31.

FIG. 3 shows an example of the configuration of the frequency analysis unit 34. The serial / parallel converter 71 converts an input continuous wave into a discrete parallel signal, and a discrete frequency spectrum with the parallel signal as an input. It is composed of a fast Fourier transformer 72 for converting into a signal and a parallel / serial converter 73 for converting this frequency spectrum signal into a serial signal. If the spectrum measuring unit 35 in the subsequent stage of the frequency analysis unit 34 performs parallel processing, the parallel / serial converter 73 is not necessary, and the frequency spectrum signal from the fast Fourier transformer 72 is directly input to the frequency analysis unit 34. It should be output.

Next, a schematic procedure for selecting an optimum propagation path in this embodiment will be described using the flowchart shown in FIG. Note that FIG. 4 is an example in which a single omnidirectional antenna is used as the terminal antenna 4 as described above, and the measurement result of the quality of the past propagation path is not used for determining the optimum propagation path.

First, the directional antennas 2-1 and 2-1 for base stations
At the start time of the measurement field for measuring the quality of the propagation path between -2, 2-3, 2-4 and the terminal antenna 4,
Directional antennas for all base stations 2-1, 2-2, 2-
3, 2-4, different frequencies f ₁ , f ₂ , f at the same time
Continuous waves of ₃ and f ₄ are transmitted (step S101).

The frequencies f ₁ , f ₂ , f transmitted in this way
The continuous waves of ₃ and f ₄ reach the terminal antenna 4 through their respective propagation paths and are received. Terminal antenna 4
The continuous wave received at is input to the synchronizing circuit 33 via the switch 30 in the terminal 3 and is synchronized with the start time of the measurement field (step S102). That is, the synchronization circuit 33 supplies the synchronization signal to the frequency analysis unit 34, and the frequency analysis unit 34 receiving this performs the fast Fourier transform on the continuous wave input via the switch 30,
A continuous wave signal, which is a signal on the time axis, is converted into a frequency spectrum signal (step S103). This frequency spectrum signal is input to the spectrum measuring unit 35, and spectrum measurement is performed (step S104). This spectrum measurement result is input to the ranking unit 36, which ranks the directional antennas for base stations 2-1, 2-2, 2-3, 2-4 and the terminal antenna 4 based on the spectrum measurement result. The quality of the propagation path between (when viewed from the terminal 3,
(Reception quality) ranking is performed, and rank, that is, rank information indicating the degree of quality of each propagation path is passed to the optimum propagation path determination unit 37 (step S105). The optimum propagation path determination unit 37 compares the input rank information of each propagation path and determines the propagation path with the highest rank, that is, the highest quality, as the optimum propagation path (step S1).
06). Then, path information indicating the optimum propagation path is generated from the path information generation unit 38, and is transmitted from the terminal antenna 4 to the base station 1 via the transmission / reception circuit 31 and the switch 30.

In the base station 1, the base station directional antenna 2
The path information from the terminal 3 is received through any one of -1, 2, 2, 2-3, 2-4 or a separately prepared omnidirectional antenna (step S108), and the path information is optimized based on this path information. A propagation path is selected (step S109). That is, in step S109, the four base station directional antennas 2-1, 2-2, 2-3, 2 of the base station antenna 2 are used.
-4 is selected as an antenna for communication with the terminal 3, which corresponds to the optimum propagation path.

As described above, in the present embodiment, the base station 1 is provided with a plurality of base station directional antennas 2-1, 2-2, 2-.
The quality of each propagation path is measured by simultaneously transmitting a known signal sequence composed of continuous waves of different frequencies via 3, 2-4 and measuring the frequency spectrum of each known signal sequence received by the terminal 3 side. Is determined and the optimum propagation path is determined by ranking each propagation path, and the optimum propagation path can be selected by one transmission of the known signal sequence from the base station 1.

Next, various preferable conditions in this embodiment will be described. First, referring to FIGS. 5 and 6, the duration of the measurement field and the directional antenna 2 for the base station are measured.
The relationship with the frequency intervals of continuous waves transmitted from -1, 2, 2-3, and 2-4 will be described. As shown in FIG. 5, the base station 1 uses a part of the transmission time as a measurement field, and transmits a continuous wave Sr that is a known signal sequence during the measurement field. The terminal 3 receives the continuous wave Sr, determines the optimum propagation path, and further transmits path information indicating the optimum propagation path to the base station 1. Based on this,
The base station 1 selects the optimum propagation path. The continuous wave Sr shown in FIG. 5 has all the directional antennas 2-1 and 2- for the base station 1 for the duration τ of the measurement field.
The frequencies f ₁ , which are transmitted simultaneously from 2, 2, 3 and 2-4,
This shows the synthesis of continuous waves of f ₂ , f ₃ , and f ₄ .

On the other hand, FIG. 6 is a diagram showing a frequency spectrum in which the horizontal axis represents frequency and the vertical axis represents the reception power of the continuous wave Sr transmitted in the measurement field of FIG. Base station 1
Are different frequencies f ₁ , f during the measurement field duration.
Directive antenna 2 for each base station with continuous waves of ₂ , f ₃ and f ₄
-1, 2-2, 2-3, 2-4 simultaneously transmit. Here, as shown in FIG. 6, adjacent frequencies f ₁ , f ₂ , and f
If the frequency intervals of ₃ and f ₄ are all equal to Δf, and this frequency interval Δf is set to be larger than the reciprocal of the measurement field duration τ, that is, Δf> 1 / τ, the center frequency is continuous to f ₁ . The spectrum S ₁ of the wave is 0 on the frequencies f ₂ , f ₃ and f ₄ , and the spectrum S ₂ of the continuous wave whose center frequency is f ₂ is 0 on the frequencies f ₁ , f ₃ and f ₄ and the center frequency is f ₃ The continuous wave spectrum S ₃ of the frequency f
It is possible to make the spectrum S ₄ of a continuous wave having 0 on ₁ , f ₂ , f ₄ and the center frequency f ₄ to be 0 on the frequencies f ₁ , f ₂ , f ₃ .

That is, the frequencies f ₁ , f ₂ , f ₃ , f ₄
In the above, the received power spectra of continuous waves from other directional antennas for base stations are all 0, and frequencies f ₁ , f ₂ ,
It is possible to make the state of being completely unaffected by the interference of continuous waves transmitted via other directional antennas for base stations on f ₃ and f ₄ . As a result, it becomes possible to measure the quality of the propagation path by simultaneously transmitting a plurality of continuous waves having different frequencies.

Next, FIG. 7 shows that the continuous waves of frequencies f ₁ , f ₂ , f ₃ , and f ₄ transmitted from the base station 1 arrive at the terminal 3 at different times due to the distance difference between the respective propagation paths. The received signal waveform of the terminal 3 in the case of being shown is shown. Frequency f
Continuous waves CW ₁ , CW ₂ , CW of ₁ , f ₂ , f ₃ , and f _4
3 , the durations of the measurement fields of CW ₄ are all τ, and the directional antennas for base stations 2-1, 2-2, 2-3, which transmit the continuous waves CW ₁ , CW ₂ , CW ₃ , CW ₄ are shown. 2-
4 and the terminal 3 have different arrival times due to the difference in distance.

Here, if Δf> 1 / τ is set as described above, that is, the frequency difference Δf between f ₁ , f ₂ , f ₃ , and f ₄ is Δf.
Is larger than the reciprocal of the duration τ of the measurement field, the operating time τ _f of the frequency spectrum conversion in the frequency analysis unit 34 within the duration of the measurement field of all the continuous waves CW ₁ , CW ₂ , CW ₃ , and CW _4. If the measurement field is set to include CW ₁ , CW to the terminal 3,
It is not affected by the difference in arrival times of ₂ , CW ₃ , and CW ₄ . In order to improve the frequency utilization efficiency, the duration τ of the measurement field may be set longer.

FIG. 8 shows the relationship between the propagation delay between the base station 1 and the terminal 3 and the distortion on the frequency axis. One directional antenna for base station 2-i with base station 1 (i = 1, 2,
When there are a plurality of propagation paths between the terminal antenna 3 and the terminal antenna 3, the arrival time difference (propagation delay time difference) of the continuous wave at the terminal 3 due to the distance difference of the propagation paths is represented by τ.
When _m, the frequency selective fading F varying the magnitude and phase of the spectrum with a period 1 / tau _m on the frequency axis f
Occurs.

In the presence of such frequency selective fading F, the amount of distortion varies depending on the frequency used for communication. As a result, the received power spectrums P ₁ , P ₂ , P ₃ , at the terminal 3 of continuous waves of frequencies f ₁ , f ₂ , f ₃ , f ₄
Comparing the magnitudes of P ₄ , it can be seen that the amount of spectrum attenuation varies depending on the frequency.

In FIG. 8, when the frequencies of the continuous waves transmitted from the base station 1 are far apart, such as the frequencies f ₁ and f ₄ , the attenuation amounts of the spectrum are significantly different, and the base station of the base station 1 Directional antennas 2-1, 2-2, 2-
It can be seen that the quality of the propagation path determined by which of 3 and 2-4 is used greatly differs depending on the frequency of the continuous wave transmitted from the base station 1.

Therefore, in the present embodiment, the frequencies f ₁ , f ₂ , f ₃ , and f _{3 of} each continuous wave transmitted in the measurement field are
The frequency interval Δf of f ₄ is set to a value sufficiently smaller than the reciprocal 1 / τ _m of the propagation delay time difference of each propagation path. Thus, if Δf << 1 / τ _m , then f ₁ , f ₂ , f ₃ , f
_When a continuous wave of any one of the _four frequencies is transmitted, the distortion received in the propagation path is almost equal.

Therefore, if this frequency interval Δf is set to a value that is sufficiently smaller than the propagation delay time differences of all the multipaths existing between the base station antenna 2 and the terminal antenna 4, such propagation delay time differences will occur. The quality of the propagation paths can be accurately measured without being affected, and the quality of the propagation paths can be accurately compared. As a result, the highest quality optimum propagation path can be reliably determined.

Next, the spectrum measuring section 35 will be described. FIG. 9 shows received power spectra P ₁ , P ₂ , P ₃ , P ₄ of continuous waves of frequencies f ₁ , f ₂ , f ₃ , f ₄ from the base station 1 received by the terminal 3. The spectrum measuring unit 35 receives these received power spectra P ₁ , P ₂ ,
The magnitudes of P ₃ and P ₄ , that is, the electric powers E ₁ , E ₂ , E ₃ ,
The quality of each propagation path is measured by measuring E ₄ , and the measurement result is given to the ranking unit 36.

FIG. 10 shows the received power spectra P ₁ , P ₂ , P ₃ , P ₄ of continuous waves of frequencies f ₁ , f ₂ , f ₃ , f ₄ from the base station 1 received by the terminal 3 as frequencies. It is expressed on the coordinate axes represented by the axis f, the real axis I, and the imaginary axis Q. In this case, the spectrum measuring unit 35 measures the spectrum size E of the received power spectra P ₁ , P ₂ , P ₃ , and P _4.
By measuring the spectral distortion from ₁ , E ₂ , E ₃ , E ₄ and the phase shifts θ ₁ , θ ₂ , θ ₃ , θ _{4 with} respect to the phase of the continuous wave at the time of transmission of the base station 1, each propagation path is measured. The quality may be measured and the measurement result may be given to the ranking unit 35.

As described above, the spectrum measuring section 35 may measure only the magnitude (power) of the spectrum, or by measuring the phase shift of the spectrum with respect to the phase of the transmission signal in addition to the magnitude of the spectrum. May be measured. According to the former, the quality of the propagation path can be easily measured by using a simple circuit in the spectrum measuring unit 35, and according to the latter, the quality of the propagation path can be measured more accurately.

Next, the relationship between the carrier frequency used for data communication and the frequency of a continuous wave which is a known signal sequence for selecting the optimum propagation path will be described. FIG. 11 shows the relationship between the carrier frequency and the frequencies f ₁ , f ₂ , f ₃ , and f ₄ of the continuous wave. The power spectrum Pd of the data signal spreads on the frequency axis f centering on the carrier frequency fc. The power spectrum of continuous waves of frequencies f ₁ , f ₂ , f ₃ , f ₄ can be represented by P ₁ , P ₂ , P ₃ , P ₄ . When the spectrum distortion due to multipath, that is, the frequency selective fading F is present, the magnitude of the distortion of the power spectrum varies depending on the frequency. In addition, the magnitude of the frequency selective fading F due to multipath may differ between the carrier frequency used for data communication and other frequencies.

Therefore, in order to determine the optimum propagation path during data communication, the frequencies f ₁ , f ₂ , f ₃ , f ₄ of the continuous waves used for selecting the optimum propagation path are equal to the carrier frequency fc, or It is desirable to set the frequency close to fc. By doing so, it is possible to measure the quality of the propagation path in the actual communication frequency band, and by determining the optimum propagation path based on this, it is possible to obtain high communication quality.

Next, the measurement field and the fast Fourier transform window (FF) in the fast Fourier transformer 72 in FIG.
The relationship with (T window) will be described. FIG. 12 is a diagram showing the relationship between the measurement field 11 and the fast Fourier transform window 112. As described above, the frequency interval Δf of the continuous wave that is the known signal sequence is set to be larger than the reciprocal of the duration τ of the measurement field 111. Therefore, when the size of the fast Fourier transform window 112 is set to be equal to the reciprocal 1 / Δf of the frequency interval Δf, the size of the fast Fourier transform window 112 becomes the measurement field duration time τ or less. Therefore, if the start time of the fast Fourier transform is adjusted appropriately, the difference in arrival time at the terminal 3 of the continuous waves transmitted from the directional antennas 2-1, 2-2, 2-3, 2-4 for the base station. It is possible to remove the influence of (difference in propagation delay time).

If the size of the fast Fourier transform window 112 is 1 / Δf, the orthogonality of each frequency spectrum of the continuous wave received by the terminal 3 after the fast Fourier transform is maintained. Fast Fourier Transformed Spectra S ₁ , S ₂ , S
_3, S _4, the orthogonality is maintained in the on frequency _{f 1, f 2, f 3} , f 4 , are not that each continuous wave frequencies _{f 1, f 2, f 3} , f 4 from interfering with each other. Therefore, if the size of the fast Fourier transform window 112 is set to be equal to the reciprocal of the frequency interval Δf as described here, there is no interference of continuous waves, so that the quality of the propagation path can be measured more accurately. it can.

The configurations of the base station 1 and the terminal 3 are shown in FIG.
However, the elements are not limited to the above, but are provided in the terminal 3 for processing up to the determination of the optimum propagation path, for example, the spectrum measurement unit 35, the ranking unit 36, the optimum propagation path determination unit 37, and the path information generation. The function of the unit 38 may be provided in the base station 1. That is, the processing result in the process of reaching the optimum propagation path determination may be transmitted to the base station 1, and the final propagation path determination may be performed inside the base station 1. In this way, the load on the terminal 3 is reduced, and it is possible to reduce the size and weight of the terminal 3, reduce the price, and reduce the power consumption. Further, this point is the same in the embodiments described below.

(Second Embodiment) FIG. 13 is a block diagram showing the internal structure of the terminal 3 in this embodiment. The same reference numerals are given to the portions corresponding to the constituent elements of the terminal 3 shown in FIG. 1, and the description will be made focusing on the differences, and in this embodiment, a storage unit 39 is newly added. The storage unit 39 stores the rank information output from the ranking unit 36 and representing the quality of each propagation path.

To the ranking unit 36, the past rank information stored in the storage unit 39 is input together with the spectrum measurement result from the spectrum measuring unit 35. And
The ranking unit 36 updates the propagation path rank based on the new spectrum measurement result and the past propagation path rank information. The updated propagation path rank information is stored in the storage unit 39 again. The updated propagation path rank information is input to the optimal propagation path determination unit 37, and the optimal propagation path determination unit 37 determines the updated propagation path with the highest rank as the optimal propagation path.

The subsequent processing is the same as that of the first embodiment. The path information generating section 38 generates path information indicating the optimum propagation path determined by the optimum propagation path determining section 37, and the transmitting / receiving circuit 31 and the switch 30. Via terminal antenna 4
From the base station 1 to the base station 1.

As described above, according to the present embodiment, the spectrum measurement can be repeated a plurality of times in the terminal 3 and the rank of the propagation path can be updated successively, so that the quality of the propagation path can be measured more accurately. , Which enables the optimal propagation path to be determined with higher reliability.

(Third Embodiment) FIG. 14 is a diagram showing the internal configurations of the terminal antenna and the terminal 3 in this embodiment. The same reference numerals are given to the portions corresponding to the constituent elements of the terminal 3 shown in FIG.
In this embodiment, the terminal antenna has a plurality of directional antennas (hereinafter, referred to as terminal directional antennas) 4-1 and 4-.
It is composed of 2,4-3,4-4. Further, the switch 30a provided inside the terminal 3 is provided for the terminal directional antennas 4-1, 4-2, 4-3, 4-4 at the time of transmission / reception switching, data communication, and propagation path quality measurement. Also switch. Further, also in the present embodiment, as in the second embodiment, a storage unit 39 for storing the rank information from the ranking unit 36 is provided.

The operation of this embodiment is as follows. In the terminal 3, the terminal directional antennas 4-1 and 4-
A measurement field is received by any one of 2, 4, 3 and 4-4, and a continuous wave that is a known signal sequence of the measurement field is input to the synchronization circuit 33 via the switch 30a, and the synchronization circuit 33 receives the continuous wave. When the measurement fields are synchronized, the switch 30a is switched to input the continuous wave received by the terminal directional antenna 4-1 to the frequency analysis unit 34.

The frequency analysis unit 34 performs a fast Fourier transform on the input continuous wave to convert the signal on the time axis into a frequency spectrum signal. This frequency spectrum signal is input to the spectrum measuring section 35, and spectrum measurement is performed. This spectrum measurement result is input to the ranking unit 36, and based on the spectrum measurement result, the ranking unit 36 directs the base station directional antennas 2-1 and 2-2.
The quality of the propagation paths between the 2-3 and 2-4 and the terminal directional antenna 4-1 is ranked, and rank information indicating the rank of each propagation path is output. This rank information is stored in the storage unit 39.

Next, the switch 30a is switched, and the continuous wave received by the other terminal directional antennas 4-2, 4-3 and 4-4 is similarly converted into a frequency spectrum signal by the frequency analysis unit 34. Conversion and spectrum measurement unit 35
The spectrum measurement and the ranking by the ranking unit 36 are sequentially performed, and the rank information is stored in the storage unit 39.

Thus, the directional antennas 4-for all terminals are
When the storage of the rank information is completed for the case of using 1,4-2,4-3,4-4, the propagation that gives the highest rank among the rank information stored in the storage unit 39 in the optimum propagation path determination unit 37. The path is determined as the optimum propagation path, path information indicating the optimum propagation path is generated by the path information generation unit 38, and the transmission / reception circuit 31 and the switch 30 are generated.
Via any one of the terminal antennas 4-1, 4-2, 4-3, 4-4 or a plurality of antennas to the base station 1.

As described above, according to the present embodiment, the terminal antenna is not an omnidirectional antenna, but a plurality of terminal directional antennas 4-1, 4-2, 4-3, 4-4. At, the optimal propagation path can be determined and selected.

Also in this embodiment, a plurality of base station directional antennas 2-1 and 2-1, as in the previous embodiments.
By transmitting continuous waves of different frequencies simultaneously from 2-2, 2-3, and 2-4, the directional antenna for terminals 4-
Even when the propagation paths are measured by switching 1, 4-2, 4-3, and 4-4 one by one, the directional antenna for the base station is used only for the number of times corresponding to the number of directional antennas for the terminal (4 times in this example). By simultaneously transmitting continuous waves from the active antennas 2-1, 2-2, 2-3, 2-4, it is possible to measure the quality of all propagation paths and perform ranking based on them, and to select the optimum propagation path. The time required can be greatly reduced.

(Fourth Embodiment) FIG. 15 is a diagram showing the internal configuration of the terminal antenna and the terminal 3 in the present embodiment. The same reference numerals are given to the portions corresponding to the constituent elements of the terminal 3 shown in FIG.
In this embodiment, as in the embodiment shown in FIG. 14, the terminal antennas are a plurality of terminal directional antennas 4-1 and 4-2.
It is composed of 4-3 and 4-4. Also, the terminal 3
The switch 30a provided inside the switch switches transmission / reception and also switches the terminal directional antennas 4-1, 4-2, 4-3, 4-4 during data communication.

In the present embodiment, the frequency analysis units 34-1, 34-2, 34-3 are individually provided corresponding to the terminal directional antennas 4-1, 4-2, 4-3, 4-4. ，
34-4 and spectrum measuring units 35-1, 35-2,
35-3 and 35-4 are provided.

The operation of this embodiment is as follows. In the terminal 3, the terminal directional antennas 4-1 and 4-
When the continuous wave which is the known signal sequence of the measurement field is received by 2, 4, 3 and 4-4 and is input to the synchronization circuit 33 and the synchronization circuit 33 synchronizes the measurement field,
Directional antennas for terminals 4-1, 4-2, 4-3, 4-4
The continuous waves received by the frequency analyzers 34-1, 34-
2, 34-3, 34-4, respectively. In the frequency analysis units 34-1, 34-2, 34-3, 34-4,
Fast Fourier transform is performed on each input continuous wave to convert a signal on the time axis into a frequency spectrum signal. These frequency spectrum signals are input to the spectrum measuring units 35-1, 35-2, 35-3, 35-4, respectively, and spectrum measurement is performed. These spectrum measurement results are input to the ranking unit 36a.

In the ranking unit 36a, the base station directional antennas 2-1, 2-2, 2-3, 2-4 of the base station 1 and the terminal directional antennas 4-1 and 4-2 of the terminal 3 are used. , 4-
The quality of all the propagation paths (4.times.4 = 16 propagation paths in this example) corresponding to the combination of 3 and 4-4 is ranked and the rank information is output. The rank information output from the ranking unit 36a is input to the optimum propagation path determination unit 37, and the propagation path with the highest rank is determined as the optimum propagation path.

The subsequent processing is the same as in the first to third embodiments, the path information generating section 38 generates path information indicating the optimum propagation path determined by the optimum propagation path determining section 37, and the transmitting / receiving circuit Terminal 3 via 31 and switch 30a
Directional Antennas for Terminals Antennas 4-1, 4-2, 4-
It is transmitted toward the base station 1 from any one of the antennas 3 and 4 or a plurality of antennas.

As described above, according to the present embodiment, the terminal antennas are a plurality of terminal directional antennas 4-1, 4-2, and 4.
In the case of being configured with -3, 4-4, it is possible to simultaneously measure and rank the quality of the propagation path for all the directional antennas 4-1, 4-2, 4-3, 4-4 for terminals. This greatly reduces the operating time required to determine and select the optimal path.

(Fifth Embodiment) Next, referring to the flow chart shown in FIG. 16, as shown in the third and fourth embodiments, the terminal antennas have a plurality of terminal directional antennas 4-1 and 4-1. 4-2, 4-3, 4-4 (4-m, m = 1,
2, 3, 4), and a plurality of base station directional antennas 2-1, 2-2, 2-3, 2-4 of the base station 1 and terminal directional antennas 4-1 and 4-1 of the terminal 3. 4-2, 4-3
A procedure for selecting an optimum selection path when the optimum propagation path is determined and selected by measuring the quality of each propagation path between the 4-4 and 4-4 N times will be described.

First, in the terminal 3, the counter value (measurement number counter value) n for counting the number of times of measurement of the propagation path is set to 1
(Step S201). Next, the known signal sequence in the measurement field period is the terminal directional antenna 4-1.
M = 1 is set so that the measurement can be performed via the received signal (step S202).

At the measurement field start time, all base station directional antennas 2-1, 2-2, 2 of the base station 1 are reached.
From -3 and 2-4, frequencies f ₁ and f that are known signal sequences
Continuous waves of ₂ , f ₃ , and f ₄ are simultaneously transmitted (step S203).

The frequencies f ₁ , f ₂ , and f transmitted in this way
The continuous waves of ₃ and f ₄ respectively pass through their own propagation paths, and the terminal directional antennas 4-1 to 4-2 of the terminal 3 are connected.
3, 4-4 is reached and received. The continuous wave received is synchronized with the start time of the measurement field (step S204). After the end of the measurement field, the terminal 3 performs a fast Fourier transform on the continuous wave input in the frequency analysis unit to convert the signal on the time axis into a frequency spectrum signal (step S205), and further performs spectrum measurement of this frequency spectrum signal. That is, the quality of the propagation path between the directional antennas 2-1, 2-2, 2-3, 2-4 for the base station and the directional antenna 4-1 for the terminal is measured (step S206).

Next, based on the spectrum measurement result obtained in step S206, the directional antenna for base station 2-
1, 2-2, 2-3, 2-4 and terminal directional antenna 4
-1 is the quality of the propagation path between the two (when viewed from the terminal 3,
Based on the reception quality) and the measurement results of the quality of the past n-1 propagation paths, the propagation paths are ranked (step S07), and rank information indicating the rank of each propagation path is stored. (Step S208).

Thereafter, m is incremented by 1 each time the processing of step S208 is completed (step S210),
Directional antennas 4-2, 4-3, 4 for other terminals of the terminal 3
The procedure of steps S203 to S208 is repeated for -4. Then, when m = 4 in step S209, that is, the directional antenna 2- for each base station of the base station 1
1 of the quality of the propagation path between 1, 2-2, 2-3, 2-4 and all the base station directional antennas 2-1, 2-2, 2-3, 2-4 of the terminal 3. When the ranking of the measurement results of the second time is completed, the process proceeds to step S211.

After that, the number-of-measurements counter value n is incremented by 1 (step S212), each time step S212 is performed.
The procedure from 202 to S209 is repeated. Then, when n = N in step S211, that is, the base station directional antennas 2-1, 2-2, 2-3, 2-4 and the terminal directional antennas 4-1, 4-2, 4-3. , 4-4, the quality measurement and ranking of each propagation path between N and
From the rank information which is the ranking result for N times stored in step S208, the propagation path with the highest rank, that is, the highest quality is determined as the optimum propagation path (step S213). Then, the path information indicating the optimum propagation path is generated, and the terminal directional antennas 4-1 and 4-1 are generated.
It is transmitted toward the base station 1 from any one of 4-2, 4-3, and 4-4, or a plurality of antennas.

In the base station 1, the directional antenna 2 for the base station is used.
The path information from the terminal 3 is received through any one of -1, 2, 2-2, 2-3, and 2-4 or a separately prepared omnidirectional antenna (step S215), and optimal based on this path information. A propagation path is selected (step S216). That is, in step S216, one of the four directional antennas for base stations 2-1, 2-2, 2-3, 2-4 corresponding to the optimum propagation path is selected as the antenna for data communication with the terminal 3. It

As described above, in this embodiment, the optimum propagation is performed after repeating the transmission of the known signal sequence from the base station to the terminal, the quality measurement of a plurality of propagation paths, and the ranking for all the propagation paths a plurality of times. By determining the path, the influence of the quality measurement of the propagation path due to changes in the propagation environment is reduced, and the reliability of the selection of the optimum propagation path is improved. In this case, the known signal sequence needs to be transmitted only the number of times the quality of the propagation path is measured, which is advantageous in that the time required for the measurement can be greatly reduced as compared with the conventional method of performing the measurement a plurality of times.

[0082]

As described above, according to the present invention, between a base station having a plurality of base station directional antennas and a plurality of wireless terminals, or a base station having a plurality of base station directional antennas. In a wireless communication system for communicating with a plurality of wireless terminals each having a directional antenna for a plurality of terminals, a known signal sequence with different frequencies is simultaneously transmitted to the terminal via a plurality of directional antennas for a base station. ,
The known signal sequence received by the terminal is frequency-analyzed, the quality of each propagation path between the base station and the terminal is measured from each frequency spectrum, and each propagation path is ranked, and the optimal propagation path is based on this ranking result. By determining
The optimum propagation path can be accurately selected in a short time.

When the terminal has a plurality of directional antennas, the measurement of the quality of the propagation path for the known signal sequence received by the directional antenna for each terminal and the ranking processing based on the measurement are performed in parallel. Basically, the simultaneous transmission of the known signal sequence from the directional antenna for the base station is basically required only once, and the time required to select the optimum propagation path from a large number of propagation paths can be shortened more efficiently. .

Further, a plurality of known signal sequences simultaneously transmitted from a plurality of directional antennas for base stations are set as a plurality of continuous waves having different frequencies, and their frequency intervals are larger than the reciprocal of the transmission duration of the known signal sequence, Also, by setting a value that is sufficiently smaller than the reciprocal of the propagation delay time difference of multiple propagation paths, the influence of the propagation delay time difference caused by the distance difference of the carrying path and the difference in the distortion amount of each propagation path caused by the frequency difference. The quality of the propagation path can be accurately measured without being affected by, and the reliability of selection of the optimum propagation path is further improved.

Further, frequency analysis of a plurality of known signal sequences consisting of continuous waves having different frequencies is performed by fast Fourier transform capable of high speed processing, and at this time, the size of the fast Fourier transform window is set to the frequency interval of each continuous wave. By setting the reciprocal of the above, it becomes possible to more accurately measure the quality of the propagation path while maintaining the orthogonality of each continuous wave transmitted from each base station directivity after the fast Fourier transform.

Also, the quality of the propagation path in the data communication frequency band can be measured by selecting the frequency of each continuous wave, which is a plurality of known signal sequences, to be equal to or close to the carrier frequency used for communication. And by determining the propagation path based on this,
It is possible to effectively improve the communication quality during actual data communication.

Further, the transmission of the known signal sequence from the base station to the terminal, the quality measurement of a plurality of propagation paths, and the ranking are repeated a plurality of times for all the propagation paths so that the optimum propagation path is determined. By doing so, the influence of propagation path quality measurement due to fluctuations in the propagation environment due to human movement, etc. is reduced, the reliability of the selection of the optimum propagation path is improved, and the transmission of a known signal sequence is performed by measuring the propagation path quality. It is only necessary to perform the above-mentioned number of times, and the time required for the measurement can be significantly shortened as compared with the conventional method of performing a plurality of measurements.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wireless communication system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a base station antenna and a continuous wave generation unit in the same embodiment.

FIG. 3 is a block diagram showing a configuration example of a frequency analysis unit in the same embodiment.

FIG. 4 is a flowchart showing an optimum propagation path selection procedure in the same embodiment.

FIG. 5 is a diagram showing a continuous wave that is a known signal sequence of a measurement field in the same embodiment.

FIG. 6 is a diagram showing a frequency spectrum of a continuous wave that is a known signal sequence received by the terminal according to the first embodiment.

FIG. 7 is a diagram showing a received signal waveform of a continuous wave which is a known signal sequence received by the terminal in the embodiment.

FIG. 8 is a diagram showing the relationship between distortion on the frequency axis and the frequency of a continuous wave that is a known signal sequence in the same embodiment.

FIG. 9 is a diagram showing a received power spectrum of a continuous wave which is a known signal sequence received by the terminal in the embodiment.

FIG. 10 is a diagram showing a received power spectrum of a continuous wave which is a known signal sequence received by the terminal in the embodiment.

FIG. 11 is a diagram showing the relationship between the frequency band of data and the frequency of a continuous wave that is a known signal sequence in the same embodiment.

FIG. 12 is a diagram showing a relationship between a fast Fourier transform window and a frequency interval of a continuous wave that is a known signal sequence in the same embodiment.

FIG. 13 is a block diagram showing a configuration of a terminal according to another embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration of a terminal according to another embodiment of the present invention.

FIG. 15 is a block diagram showing a configuration of a terminal according to still another embodiment of the present invention.

FIG. 16 is a flowchart showing an optimum propagation path selection procedure in the same embodiment.

[Explanation of symbols]

1 ... Wireless base station 2 ... Base station antenna 2-1 to 2-4 ... Directional antenna for base station 3 ... Wireless terminal 4 ... Terminal antenna 4-1 to 4-4 ... Directional antenna for terminal 10 ... switch 11 ... Base station transmission circuit 12 ... Base station receiving circuit 13 ... Continuous wave generator 14 ... Optimal propagation path selection unit 30, 30a ... Switch 31 ... Terminal transmitting circuit 32 ... Terminal receiving circuit 33 ... Synchronous circuit 34, 34-1 to 34-4 ... Frequency analysis unit 35, 35-1 to 35-4 ... Spectrum measuring unit 36, 36a ... Ranking section 37 ... Optimal propagation path determination unit 38 ... Path information generation unit 39 ... Storage unit 41-42 ... Oscillator 50 ... Frequency synthesizer 51-54 ... Multiplier 55 ... Oscillator 56-58 ... Filter 71 ... Series / parallel converter 72 ... Fast Fourier transformer 73 ... Parallel / serial converter 111 ... Measurement field 112 ... Fast Fourier transform window

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B ⁷ /02-7/12 H04L 1/02-1/06 H04B 7/24-7/26 H04Q 7/00-7 / 38

Claims (6)

(57) [Claims] 1. A wireless communication system for communicating between at least one base station having a plurality of base station directional antennas and a plurality of wireless terminals having at least one terminal antenna, wherein: A method of selecting an optimum propagation path from a plurality of propagation paths between a directional antenna and the terminal, wherein a known signal sequence of different frequencies is simultaneously transmitted to the terminal from the base station via the plurality of directional antennas. The quality of the plurality of propagation paths is measured from each frequency spectrum by frequency-analyzing the known signal sequence received by the terminal, and the plurality of propagation paths are ranked based on the measurement result. A propagation path selection method in a wireless communication system, characterized in that the optimum propagation path is determined based on the result of the attachment. 2. A plurality of bases in a wireless communication system for communicating between at least one base station having a plurality of directional antennas for a base station and a plurality of wireless terminals each having a plurality of directional antennas for a terminal. A method for selecting an optimum propagation path from among a plurality of propagation paths between a station directional antenna and the plurality of terminal directional antennas, wherein the base station via the plurality of base station directional antennas Simultaneously transmitting known signal sequences of different frequencies to the terminal, the terminal analyzes the frequency of the known signal sequences respectively received via the plurality of terminal directional antennas in the plurality of propagation paths from each frequency spectrum. The quality is measured, the plurality of propagation paths are ranked based on the measurement result, and the optimum propagation path is calculated based on the result of the ranking. A method for selecting a propagation path in a wireless communication system. 3. The plurality of known signal sequences are a plurality of continuous waves having different frequencies, and the frequency intervals of the plurality of continuous waves transmitted as the known signal sequences from the plurality of base station directional antennas are the same. The wireless communication system according to claim 1 or 2, wherein the wireless communication system is set to a value that is greater than the reciprocal of the transmission duration of the known signal sequence and sufficiently smaller than the reciprocal of the propagation delay time differences of the plurality of propagation paths. Optimal Propagation Path Selection Method in. 4. The plurality of known signal sequences are a plurality of continuous waves having different frequencies, and the frequency analysis is performed by a fast Fourier transform in which the size of the fast Fourier transform window is set to the reciprocal of the frequency interval of the plurality of continuous waves. The optimum propagation path selection method in the wireless communication system according to any one of claims 1 to 3, wherein the method is performed by conversion. 5. The plurality of known signal sequences are a plurality of continuous waves having different frequencies, and the frequencies of these continuous waves are equal to or close to the carrier frequency used for the communication. 5. An optimum propagation path selection method in the wireless communication system according to any one of 1 to 4. 6. The optimum propagation path after repeating the transmission of the known signal sequence from the base station to the terminal and the quality measurement and ranking of the plurality of propagation paths a plurality of times for all the propagation paths. The optimum propagation path selection method in the wireless communication system according to claim 1 or 2, wherein