JP2007243498A - Communication system and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid interference in advance in an ad hoc network using a terminal having an adaptive antenna. <P>SOLUTION: A beacon sending means 13 of the terminal 1 sends a beacon signal of a fixed length of the own terminal 1 when other terminals do not transmit a signal. A beacon detection means 14 of the terminal 1 detects the beacon signal from M-1 peripheral terminals. An eigenvalue/eigenvector calculation means 15 calculates the detected beacon signal to obtain the maximum eigenvalue of all the terminals for storage, thus obtaining a sending weighting factor and the estimated value of power to the peripheral terminals of the terminal 1. In the terminal that does not communicate, when the estimated value of the power becomes a threshold or more, the terminal 1 stops transmission. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication system and a communication method that can avoid interference with other terminals in advance in an ad hoc network using a terminal equipped with an adaptive antenna.

  Conventionally, a network configuration technique called an ad hoc network is known. In an ad hoc network, since there is no base station for centrally managing terminal information, each terminal autonomously establishes communication with a counterpart.

  On the other hand, an adaptive antenna technique in which a plurality of element antennas are arranged in one terminal to form directivity is also known. In this technique, the directivity is expressed by changing and synthesizing the amplitude and phase of a transmission signal and a reception signal by a digital signal processing technique.

  FIG. 1 shows an outline of an adaptive antenna. In general, the adaptive antenna 9 includes a plurality of element antennas 91, an adaptive control processor 92, a weight coefficient setting unit 93, and an adder 94.

  In the adaptive antenna 9, the weighting coefficient of each element antenna can be changed according to a change in usage environment or the like. Thereby, directivity can be given to a transmission signal. Further, in receiving, following the movement of the transmission source, it is possible to give directivity to signal reception, and it is also possible not to receive a signal from a specific direction.

  FIG. 2 schematically shows the directivity of the adaptive antenna 9. FIG. 2 shows spatial characteristics of signal power that can be radiated by the adaptive antenna 9 or signal power that can be received. The element antennas are indicated by a1 to a6.

  As shown in FIG. 2, the adaptive antenna 9 can direct a peak (PEAK) in a desired direction while directing a null (NULL) in a certain signal arrival direction by processing a received signal.

  For example, in FIG. 3, it is assumed that transmission from the terminal TC to the terminal TD occurs when transmission from the terminal TA to TB is performed. In such a situation, when the terminal TC transmits a signal having the same frequency as the frequency used between the terminal TA and the terminal TB using an antenna having no directivity to the terminal TD, the signal from the terminal TA is being received. Interference is given to the terminal B.

  At this time, if the terminals TA, TB, TC, and TD are provided with the adaptive antenna 9, as shown in FIG. 4, the terminal TB directs a null toward the terminal TC, so that interference of the same frequency arrives from the terminal TC. However, the communication between the terminal TA and the terminal TB is not affected. With such a mechanism, the adaptive antenna 9 can increase the number of terminals that can simultaneously communicate at the same frequency.

T. T. et al. UEDA S. TANAKA S. R. D. S. S. BANDYOPADHYAY, “Location-Aware Power-Efficient Directional MAC Protocol in Ad Hoc Networks Using Directional Antenna,” IEICE Trans. on Commun. , Vol. E87-B No. 5 pp. 1085-1094, May 2004.

  However, the adaptive method shown in FIG. 4 has the following problems. The adaptive antenna 9 shown in FIG. 2 has a function of spatially blocking an interference signal, but when the arrival angle of the desired wave and the interference wave is too close, the separation capability (resolution) is limited. For example, when six antennas are arranged in a circular shape at half-wavelength intervals, a signal having an arrival angle difference of about 30 ° or less cannot be separated.

  It is considered that a situation in which the desired signal and the interference signal arrive at the same time with such an angle difference occurs frequently. In such a case, even if the terminal is equipped with the adaptive antenna 9, interference cannot be avoided.

  Conventionally, when an adaptive antenna is used in a wireless ad hoc network, such a problem is hardly studied (see Non-Patent Document 1).

  An object of the present invention is to perform advance interference avoidance (FIA) in an ad hoc network using a terminal equipped with an adaptive antenna, that is, when it is estimated that interference occurs in advance with respect to another terminal. It is an object of the present invention to provide a communication system and a communication method capable of canceling transmission.

  In order to achieve the above object, in the communication system according to claim 1, a plurality of terminals equipped with an adaptive antenna exchange beacon signals that are signals including terminal information, and each of the terminals is connected to the adaptive antenna. A communication system for setting directivity, wherein the terminal includes a monitoring unit that monitors a signal transmitted from one or more other terminals in a communication area, and the monitoring unit includes all of the other terminals. A beacon transmission means for transmitting a beacon signal including the terminal information of the own terminal when it is detected that no signal is transmitted, and a beacon signal including the terminal information of the other terminal transmitted by the other terminal. Beacon detection means for detecting all, and the feature amount representing the environment between the terminal and each of the other terminals extracted from the beacon signal at all other ends Calculating the interference value given to any of the other terminals by the terminal based on the environmental feature quantity saved in the feature quantity saving means when a communication request occurs, Pre-interference avoidance means for determining communication stop when the interference value exceeds a predetermined value is provided.

  The invention according to claim 2 is the communication system according to claim 1, further comprising eigenvalue / eigenvector calculation means for calculating a maximum eigenvalue and an eigenvector as the environmental feature quantity of the other terminal, wherein the feature quantity storage means is the eigenvalue -The calculation result by the eigenvector calculation means is stored.

  According to a third aspect of the present invention, in the communication system according to the first or second aspect, the terminal is used as a terminal of an ad hoc network.

  The communication method according to claim 4 is a communication method in which a plurality of terminals having an adaptive antenna exchange beacon signals which are signals including terminal information, and each terminal sets the directivity of the adaptive antenna. The terminal monitors a signal transmitted from one or more other terminals in the communication area, and the monitoring means detects that all of the other terminals are not transmitting signals. The beacon signal including the terminal information of the own terminal is transmitted, the beacon signal including the terminal information of the other terminal transmitted by the other terminal is detected for all the other terminals, and the terminal extracted from the beacon signal and the terminal The feature quantity representing the environment between each other terminal is saved for all other terminals, and when a communication request is generated, the terminal Calculate an interference value to be given to one of the terminals, when the interference value exceeds a predetermined value, characterized in that to determine the communication stop.

  According to a fifth aspect of the present invention, in the communication method according to the fourth aspect, a maximum eigenvalue and an eigenvector are calculated as the environmental feature amount of the other terminal, and the calculation result is stored.

  The invention according to claim 6 is the communication method according to claim 4 or 5, wherein the terminal is used as a terminal of an ad hoc network.

  ADVANTAGE OF THE INVENTION According to this invention, the magnitude | size of the interference which an own terminal gives to another terminal can be estimated, and transmission can be stopped before giving interference.

  An embodiment of the present invention will be described with reference to FIG. In FIG. 5, the terminal 1 includes an adaptive antenna 11, a channel monitoring unit 12, a beacon sending unit 13, a beacon detecting unit 14, an eigenvalue / eigenvector calculating unit 15, an eigenvalue / eigenvector storing unit 16, and a weight calculating unit. 17 and prior interference avoiding means 18 are provided.

  As shown in FIG. 6, the adaptive antenna 11 includes the terminal 1 including N element antennas a <b> 1 to aN. In the case of signal reception, a signal received by each element antenna is frequency-converted by a radio frequency band front end (RF-FA) 111 and then sampled by an analog / digital converter (ADC) 112. The sampled signal is sent as a signal y to a signal processing circuit (not shown) via a weight coefficient setting unit 113 and an adder 114. In the case of transmission, a signal is sent from the signal processing circuit to the element antennas a1 to aN through the reverse path.

  In the present embodiment, it is assumed that there are M terminals in total.

  The channel monitoring means 12 shown in FIG. 5 can monitor signals from other terminals.

  The beacon sending means 13 sends a beacon signal when the channel monitoring means 12 detects that no signal is sent from another terminal.

  The beacon detection means 14 detects a beacon signal transmitted from another terminal.

  The eigenvalue / eigenvector calculation means 15 is based on the beacon signal of the terminal transmitted from the beacon transmission means 13 and the beacon signal from the other terminal detected by the beacon detection means 14, and the maximum eigenvalue and eigenvector (features) relating to the own terminal and the other terminal. Amount) is calculated. For convenience of explanation, the eigenvalue / eigenvector calculating means 15 is shown in FIG.

  The eigenvalue / eigenvector storage means 16 stores the calculation result by the eigenvalue / eigenvector calculation means 15.

  When a communication request is generated, the weight calculation unit 17 calculates a weighting factor for each element antenna a1 to aN of the adaptive antenna based on the eigenvalue / eigenvector stored in the eigenvalue / eigenvector storage unit 16.

  The prior interference avoidance means 18 calculates an interference value given to any of the other terminals by the terminal based on the weight coefficient calculated by the weight calculation means 17, and when the interference value exceeds a predetermined value, a communication stop instruction Is sent to a communication control circuit (not shown). The communication stop instruction can be given by software, or a transmission stop signal can be sent directly to the adaptive antenna 1, for example.

Hereinafter, the processing procedure of the terminal 1 will be described in detail. In the present embodiment, the processing procedure in the terminal 1 consists of two stages: a beacon exchange phase and a communication phase.
《Beacon exchange phase》
In the beacon exchange phase, beacon signals are exchanged between terminals 1 and eigenvectors are calculated in each terminal 1.

  First, the channel monitoring means 12 of the terminal 1 monitors the channel by CSMA (Carrier Sense Multiple Access), and confirms that no other terminal is transmitting a signal around the terminal. When the other terminal is not transmitting a signal, the beacon sending means 13 sends a beacon signal of a certain length of the terminal 1.

  The beacon signal is assigned a transmission terminal ID, and the terminal 1 that has received the beacon signal can specify another terminal that has transmitted the beacon signal.

  On the other hand, since the other terminal also sends a beacon signal when a terminal other than the other terminal is not sending a signal in the same manner as described above, the beacon detection means 14 of the terminal 1 Can detect a beacon signal. Next, the eigenvalue / eigenvector calculation means 15 calculates the beacon signal detected by the beacon detection means 14.

  Calculation of the eigenvector in each terminal 1 is performed as follows.

  The eigenvalue / eigenvector calculation means 15 of the terminal 1 calculates the beacon signal of the mth other terminal (m = 1, 2,..., M−1).

  The terminal 1 calculates a (N × N) correlation matrix using the received signal samples of the element antennas a1 to aN by the equation (1).

ここで、

here,

は大きさ（Ｎ×１）のｍ番目の他端末の受信信号ベクトルであり、λ（＝−∞，・・・，−１，０，１・・・，＋∞）は、サンプル時刻を表す整数である。また、Ｌは取得したサンプル数である。

Is a received signal vector of the mth other terminal of size (N × 1), and λ (= −∞,..., −1, 0, 1... + ∞) represents the sample time. It is an integer. L is the number of acquired samples.

  Next, when eigenvalue decomposition is performed on the equation (1), the equation (3) is obtained.

ここで、Λ^(m)は大きさ（Ｎ×N）のｍ番目の他端末の固有値行列であり、対角要素に固有値λ₁ ^(m)，λ₂ ^(m)，・・・，λ_N ^(m)を含み、それ以外の要素は「０」である。

Here, lambda ^(m) is the m-th other terminals eigenvalue matrix of size (N × N), the eigenvalues lambda ₁ ^(m) on the ^{_{diagonal, λ 2 (m), ···}} , λ N ^The other elements including ^(m) are “0”.

ここで、固有値は大きい順から順番を付け、
λ₁ ^(m)≧λ₂ ^(m)≧・・・≧λ_N ^(m)
の関係となっているものとする。

Here, the eigenvalues are ordered in descending order,
λ ₁ ^(m) ≧ λ ₂ ^(m) ≧ ・ ・ ・ ≧ λ _N ^(m)
It is assumed that

V ^(m) is an eigenvalue matrix of the m-th other terminal having a size (N × 1), and is represented by Expression (4).

Here, v _n ^(m) (n = 1,..., N) is an eigenvector of a size (N × 1) corresponding to the nth eigenvalue, and is expressed by equation (5).

It is expressed. Of these, only the maximum eigenvalue λ ₁ ^(m) and the corresponding eigenvector ν ₁ ^(m) are stored in the eigenvalue / eigenvector storage means 16. This is repeated, and the maximum eigenvalues and eigenvectors of all terminals other than the own terminal 1 are stored in the eigenvalue / eigenvector storage means 16.

《Communication phase》
In the communication phase, transmission weighting coefficient calculation and transmission weighting coefficient check are performed.
Communication request is generated in the terminal 1, the communication partner terminal, the terminal m _1.
At this time, the weight calculation means 17 calculates the weight coefficient w of the adaptive antenna of the size (N × 1) used for transmission by calculating the equation (6).

ここで、Ｒ_IIは（Ｎ×N）の行列であり、ｍ₁番目の最大固有値およびその対応固有ベクトルを除いたＭ−１個の最大固有値および対応固有ベクトルから得られる。具体的には、（７）式により得られる。

Here, R _II is an (N × N) matrix, and is obtained from M−1 maximum eigenvalues and corresponding eigenvectors excluding the m ₁ th maximum eigenvalue and its corresponding eigenvector. Specifically, it is obtained by the equation (7).

ここで、インデックスｐは、ｍ₁番の最大固有値およびその対応固有ベクトルを除いたＭ−１個の最大固有値および対応固有ベクトルに新たに振りなおした１からＭ−１までの番号である。つまり、この総和の中に、ｍ₁番目の最大固有値およびその対応固有ベクトルは含まれていない。

Here, the index p is a number from 1 reroll the new to the maximum eigenvalue and M-1 or largest eigenvalues and corresponding eigenvectors, excluding its corresponding eigenvector number ₁ m to M-1. That is, the total sum of the m _1st eigenvalue and its corresponding eigenvector is not included in this sum.

  Next, transmission weight coefficient checking will be described.

  If the weighting coefficient vector w obtained by the equation (5) is used, high power should be transmitted with the peak directed toward the other party to be communicated, and null should be directed toward the other terminal directions without causing interference. However, there is a problem of the limit of resolution, and interference may be given to a terminal that is too close to the desired wave direction.

  In such a case, according to the present invention, the prior interference avoidance means 18 performs a check before radio wave transmission. For this reason, the value of equation (8) is calculated for the surrounding mth terminal.

これは、ｍ番目の周囲端末に与える電力の推定値となる。通信しない相手の端末において、この電力の推定値が閾値以上となる場合には送信を中止することで、事前与干渉回避を行う。

This is an estimated value of power given to the mth surrounding terminal. If the estimated value of the power is equal to or greater than the threshold value at the other terminal that does not communicate, the transmission is stopped to avoid pre-interference.

It is explanatory drawing which shows the outline | summary of an adaptive antenna. It is a figure which shows typically the directivity of an adaptive antenna. It is explanatory drawing which shows operation | movement of the conventional terminal which is not provided with an adaptive antenna. It is explanatory drawing which avoids interference by an adaptive antenna. It is a functional block diagram of the terminal used with the communication system of this invention. It is explanatory drawing which shows the adaptive antenna mounted in the terminal of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Terminal 11 Adaptive antenna 12 Channel monitor means 13 Beacon transmission means 14 Beacon detection means 15 Eigenvalue / eigenvector calculation means 16 Eigenvalue / eigenvector storage means 17 Weight calculation means 18 Prior interference avoidance means a1 to aN Element antenna

Claims (6)

A plurality of terminals equipped with an adaptive antenna exchange beacon signals, which are signals including terminal information, and each terminal sets a directivity of the adaptive antenna,
The terminal
Monitoring means for monitoring a signal transmitted by one or more other terminals in communication range;
A beacon sending means for sending a beacon signal including terminal information of the own terminal when the monitoring means detects that all of the other terminals are not sending signals;
Beacon detection means for detecting beacon signals including terminal information of other terminals transmitted by other terminals for all of the other terminals;
Feature quantity storage means for storing the feature quantity representing the environment between the terminal and each other terminal extracted from the beacon signal for all other terminals;
When a communication request occurs, based on the environmental feature value stored in the feature value storage means, the interference value that the terminal gives to any of the other terminals is calculated, and the interference value exceeds a predetermined value Pre-interference avoidance means to determine when to stop communication,
A communication system comprising: An eigenvalue / eigenvector calculating means for calculating a maximum eigenvalue and an eigenvector as the environmental feature quantity of the other terminal;
The feature amount storage means stores a calculation result by the eigenvalue / eigenvector calculation means,
The communication system according to claim 1.   The communication system according to claim 1 or 2, wherein the terminal is used as a terminal of an ad hoc network. A plurality of terminals equipped with an adaptive antenna exchange beacon signals that are signals including phase terminal information, and each terminal sets a directivity of the adaptive antenna.
The terminal
Monitor the signal sent by one or more other terminals within range,
When the monitoring means detects that all of the other terminals are not transmitting signals, it transmits a beacon signal including terminal information of its own terminal,
A beacon signal including terminal information of another terminal transmitted by another terminal is detected for all of the other terminals;
The feature amount representing the environment between the terminal and each other terminal extracted from the beacon signal is stored for all other terminals,
When a communication request occurs, the interference value given to any of the other terminals by the terminal is calculated based on the stored environmental feature amount, and when the interference value exceeds a predetermined value, the communication stop is determined. A communication method characterized by: Calculating the maximum eigenvalue and eigenvector as the environmental feature quantity of the other terminal, and storing the calculation result;
The communication method according to claim 4.   The communication method according to claim 4 or 5, wherein the terminal is used as a terminal of an ad hoc network.

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