Method of direction finding of radio emission sources in conditions of multipath

 

(57) Abstract:

The invention relates to the field of radio and, in particular, can be used for direction finding systems of mobile radio communication. Achievable technical result is to develop a method of direction finding, providing a more accurate assessment of the bearing when the effects of multipath component. The aim is achieved in that in the known method of direction finding, including the reception of signals on the N-element antenna array, forming the scanning signals in a predetermined angular sector, the calculation of the weights and the subsequent multiplication of the weights with the corresponding signals of the scanning, storing the received signals, the choice of these values of the angle corresponding to the signal with the maximum amplitude, the signals take, calculate the weights and Peremohy weights with the corresponding scanning signals during the transmission of the information package and guard interval, respectively, and then subtract the resulting signal, calculated during the guard interval of the resulting signal, calculated transmission interval information package, remember raznosnab provides an exception multipath component from processing. This leads to improved accuracy of direction finding in terms of the impact of multipath. 5 Il.

The invention relates to the field of radio and direction finding of radio emission sources using adaptive antenna arrays and, in particular, can be used for direction finding in conditions of multipath propagation, for example, in cellular and batch systems mobile radio.

There is a method of direction finding of radio emission sources, which consists in calculating the weights (VK) adaptive antenna array (AAR), the multiplication of the weighting coefficients to corresponding scanning signals, memorizing the received signals for all discrete values of the angle of scan, and then select from them the values of the angle corresponding to the signal with the maximum amplitude (see B. D. Rao, Hari K. V. Statistical performance analysis of the minimum-norm method. //IEE Proc. - 1989, v. 139. - Pt.F. - N3.- P. 125-134; Gabriel U. F. Spectral analysis methods sverhrazdutaya using adaptive grids //TIER, so 68, No. 6, S. 21-28). Thus the calculation of the VC is carried out using signals from outputs of antenna elements (AE) and a priori information about the limiting factor directional (KND) of the main lobe diagrams napravlennogo environment is stationary (at least locally);

the useful signal and the interfering effects are not correlated with each other.

However, the known technical solution has several disadvantages, the main of which are the low accuracy of direction finding of radio emission sources (RES) and low resolution at the direction finding Iran in multipath conditions, such as IRI systems mobile radio. This is because in radio communication systems with mobile objects specified assumptions about the stationarity of the signal-jamming environment (sve) and correlativeness signals and interference at the point of reception is not performed. Therefore, the accuracy of direction finding on Iran and resolution of the DFS decrease.

The closest to the technical nature of the claimed invention is a method of direction finding of radio emission sources in conditions of multipath propagation (see T. J. Shan, M. Wax, Kalath T. Spatial Smoothing for Direction of Arrival Estimation of Cogerent Signals//IEEE trans. v. ASSP-33, No. 3, p. 527). Prototype method involves the preliminary formation of an N-element antenna array of K overlapping sublattices and reception of signals on the K-sublattices. Then carry out the reception of signals at the antenna elements included in the K-sublattices, and the parameters of the signals received us what this angular sector and calculate the control signal. The calculation of the control signal produced by measuring the total amplitude of interference, noise and useful signal on one of the AE chosen as a reference. Then calculates weighting coefficients for each of the averaged signal. The calculation of the weighting factor is carried out by multiplying the averaged signal parameters and the corresponding value of the control vector. After that Peremohy weights with corresponding signals of the scan. The received signals remembered for all discrete values of the scan angle and perhaps the value of the scan angle corresponding to the signal with the maximum amplitude. This value of scan angle and will correspond to the angle of arrival of the signal IRI (the direction to the source of radio emission).

This approach realizes the possibility of finding Iran in multipath conditions, including exposure correlated with signal interference.

Using the prototype method involves a violation of the correlation signals and multipath component at the input of the antenna array, by changing the position of the phase center of the AR. In this case, the ratio between the phases of signals is s IRI, penetrazione buildings and elements of the terrain and came to a point of reception in different ways.

However, the prototype has several disadvantages that limit its use. First, this method has low accuracy and low resolution when the moving direction finding Iran in difficult signal-to-noise conditions (at low relationship power signal to the power sum of the interference and noise). The reason for such deterioration of the accuracy characteristics is a partial suppression signal IRI due to the correlation of each multipath component with the background belongs to the signal and other multipath components (other rays). In addition, the deterioration of the accuracy characteristics determined by the inefficient use of the antenna array. because the degree of freedom of the AP are not used to improve the accuracy of the estimates of the bearing, and the decorrelation of input actions [4].

Secondly, the prototype method is effective only when exposed to a relatively strong strongly correlated component [4]. This is because at small signal power to the interference power and noise, and also when the values of the coefficient mezhluchevoy correlation less than 0.9 there are significant not the existing level of development components and requires complex switching devices and processing. This complicates its practical implementation.

The purpose of the claimed technical solution is to develop a method of direction finding, providing a more accurate assessment of the spatial parameters of the emitters of cellular mobile radio systems (MTEF) when exposed to a multipath component.

This objective is achieved in that in the known method of direction finding of radio emission sources, including reception of signals on the N-element antenna array, forming the scanning signals in a predetermined angular sector, the calculation of the weights and the subsequent multiplication of the weights with the corresponding signals of the scanning, storing the received signals for all discrete values of the angle of scan, and then select from them the values of the angle corresponding to the signal with the maximum amplitude, re-accept signals, calculate weighting coefficients Peremohy weights with the corresponding scanning signals for each discrete value of the scan angle during the transmission of the information package and guard interval, respectively, then subtract the resulting signal calculated during protect Aminat differential signals for all discrete values of the angle of scan, of which choose the angle value corresponding to the signal with the maximum amplitude.

Listed set of essential features provides an exception multipath component from processing through the use of a priori information about the temporal structure of the radiated signals, and reduces the unwanted effects of the medium of propagation of radio waves, and in turn increases the accuracy of direction finding and increased resolution.

The claimed technical solution is illustrated by drawings on which:

Fig. 1 - scheme of the organization of information exchange in a cellular mobile radio communication;

Fig. 2 - temporal structure of the signal cellular mobile radio GSM;

Fig. 3 is an illustration of the essence of the claimed method;

Fig. 4 - illustration of the effectiveness of the inventive method;

Fig. 5 - a device that implements the claimed method of direction finding Iran in conditions of multipath.

The implementation of the inventive method is explained in the following. The majority of currently communications systems, especially communication systems with mobile objects, is constructed in accordance with [5]. When this functional pair of elements is unctionally components in the standard for pan-European digital cellular system, mobile radio GSM interact in accordance with various alarm systems, including STS # 7 [8]. In the future, the essence of the claimed method is illustrated on the example of the MTEF GSM. The use of this method for MTEF other standards will differ only temporal characteristics of network control protocols.

Under the Protocol is a set of rules and formats of communication mechanism between components of the same level of interacting systems [8, 9]. The network control protocols available to the public.

Thus, for MTEF any standard always has a priori information about the time structure of the signals radiated in the space of the functional elements (mobile and base stations) within the system. In MTEF GSM data is exchanged frames, each of which is divided into eight time positions period 576,9 ISS (Fig. 2). The physical meaning of temporary positions, which are otherwise called time Windows - the time during which radiates the carrier, the modulated digital data stream or data used by a single user.

Digital information stream is a sequence of packets that are placed in these temporary positions (boxes). Pak is hraneniya radio waves.

At the end of each time window has a guard interval. For a system of the GSM standard length guard interval ranges from 8.25 to 68.25 bits (the bit time is 3.75 μs, the guard interval is 30.5 or 252 μs (Fig. 2). Under the protective interval refers to the period of time at the beginning and end of the time window within which information and service symbols do not transmit signals do not radiate).

Thus, it becomes possible to separate in time the processing of the useful signal (the signal emitted by the element of the system) and nuisance impacts. To do this, the parameters of signals received antenna elements (AE) during radiation information package and during the guard interval, calculated weighting factors. This action is based on the performance of the antenna array spatial filter [10]. In this case, the filter weight coefficients contain information about the direction of arrival of the signals interfering influences (noise) and multipath component.

In the proposed method the calculation of the VC based on direct appeal sample correlation matrix (KM) noise (signal and noise), and a priori information acitivies coefficient gain of the antenna array). So, in the case of the criterion of minimum output power limitation on gain (KU) AP expression for calculation of the vector of weights (IHC) has the form:

W = R-1xxC; (1)

where is a normalizing factor;

Rxx= E{X(t)X (t)+} = RSS+ RPSH- correlation matrix of input actions,

E {.} - operation is the mathematical expectation;

X(t) = S(t) + P(t) + W(t) - total N-dimensional vector of input actions, components of which are the signals from the outputs of the AE;

S(t) = A(t)[1exp{ic1} exp{ic2} ... exp{icN}] is the vector of the useful signal;

P(t) is the total interference vector, defined as

(2)

Pk(t) - vector of interfering effects, correlated with the signal;

P(t) = B(t)[1exp{in1(m)2} ... exp{in1(m)N}] - vector interference;

W(t) = [W1W2...Wn] is the vector of thermal noise with variance 2m;

Rcc= E{S(t)S(t)+} - correlation matrix of the useful signal;

RPSH= E{(P(t) + W(t))(P(t) + W(t))+} - correlation matrix interfering influences;

the vector Ct= [1 0 ... 0] limits the gain value of the antenna array by the value of the input to the first antenna element, what began to rise towards the source of the useful signal (interference);

d is the distance between the elements of art;

- wavelength source signal (interference);

c(n)- direction of arrival signal (interference);

A(t) B(t) is the complex envelope of the desired signal and interference, respectively;

L, M is the number of correlated and uncorrelated interfering influences.

Further to simplify the notation, the dependence of quantities on time is omitted.

It should be noted that the method of calculating the VC on the criterion of minimum output power limitation on the gain of the AR (MWMO) with accuracy up to a constant multiplier coincides with the method of determining direction finding sources of radio emission on the criteria of maximum entropy [2], where the calculation expression vector VK is defined as

W = R-1xxC. (3)

To extract information about the direction of arrival (bearing) of the signal, interference, and multipath component (MLK) weighting factors are multiplied with the pre-formed signals scan. The scanning signals simulate the change of the phase shift between the individual AE depending on each of the possible directions of the source for the on the antenna element is determined by the propagation time of radio waves between the antenna elements for each of the possible values of the direction to the source of radio emission in a given angular sector. The effect on the formation of the scanning signals is as follows. Pre-determined angular sector scan and on the basis of the required accuracy calculate the sampling rate and the number of discrete values of the angle in a given sector scan. Then, in accordance with the calculated discrete values of the angle scanning compute the value of the phase shift between the antenna elements of the lattice. The expression for calculating the phase of the signal scan on each AE for discrete values of the angle in a given sector scan is:

SC= (2d/a)sin(SC), (4)

where (SC) - scan angle varying within a given angular sector scan [SCminSCmax];

the wavelength of the signal IRI;

d - the distance between the individual AE and the selected item as a reference.

Calculated this way, the scanning signals in vector form are:

S() = A[1exp{iW1}exp{iW2}...exp{icN}], (5)

To extract information about the direction of arrival of input actions contained in the weights of the adaptive antenna array Peremohy vector signal scanning and weighting coefficients AP, predstavlen) [2] and allows to extract information about the direction of arrival of input actions, contained in the weights of the adaptive antenna array.

To determine the bearing to the source of the useful signal on the background of false bearings formed MLK and nuisance effects (noise), in the proposed method the calculation of the VC carried out synchronously with the network Protocol of the communication system. Thus the calculation of the VC is carried out separately during the guard interval between information packets during the transmission of the information package.

These actions are based on the assumption that, depending on the radio propagation conditions and, in particular, on the characteristics of the urban environment, the delay time of the signal due to multipath propagation of radio waves is in the range of 8-12 ISS [11]. Therefore, within 8 to 12 μs after the end of radiation information package to the input of the antenna system will receive only signals reflected from elements of urban development, as well as the interfering signals IRI. Then received during the guard interval PSM will only contain directions to sources of interference. Given the relatively slow movement of mobile objects, radiation and signal-interfering furnished within the time of radiation of one informationfree guard interval and count them constant across time radiation subsequent information package.

In the case of the calculation of the VC in the moments of the radiation signal information packages IRI receive spatial power spectrum, containing, along with the directions on the sources of multipath component and the interference direction to the signal source. Further information about the direction of arrival of a signal useful Iran is extracted by suppressing bearings formed of multipath components or nuisance effects (noise). To do this, subtract the signal characterizing the function of a spatial spectrum obtained in moments guard interval from the signal characterizing the function of the spatial spectrum calculated in the moments of the radiation information package. The resulting spectrum will contain only information about the direction to the source of the useful signal.

The expression for calculating functions of the spatial spectrum with the representation of signals and noise vector has the form [3]:

D(t) = [WStcto(SC)]-1, (6)

where S() = A[1exp(iW1}exp{iW2}...exp{icN}] is the vector of signals scanning, modeling the phase change depending on each of the possible directions for the source of radio emission in a given angular sector, resouse PSM, obtained using (6) during the transmission of the information packet by the source, emitting a signal from a direction 30o(Fig. 3A) and during the guard interval, when in point come only interfering signals and multipath components (Fig. 3b).

It is obvious that the function describing the MSM received during the guard interval, does not contain counts bearing useful Iran. Therefore, it becomes possible to extract useful Iran against the background of interfering sources and multipath component.

For this purpose, the inventive method serves to synchronize the operation of the control device (adaptive processor) with a network Protocol of the communication system and to carry out the calculation of the IHC separately during the guard interval between information packets during the transmission of the information package. Then the expression (1) takes the form:

W1= R-1PSHC (7)

W2= R-1xxC (8)

where W1the vector of weighting coefficients, calculated during the guard interval;

W2the vector of weighting coefficients, calculated during the transmission of the information package.

The value of IHC obtained using expression (8), with the ia function, characterizing the MSM during the guard interval has the form:

D1() = [W1Stcto(SC)]-1, (9)

and to calculate features characterizing the MSM during the transmission of the information packet is determined by the expression (4).

Then, the resulting signals characterizing the MSM, are determined by the expression:

Dp() = D()-D1(), (10)

The resulting signals characterizing PSM calculated using (10), do not contain values bearings formed MLK and nuisance impacts (Fig. 3b).

To illustrate the effectiveness of the inventive method of Fig.4 shows the dependence of the errors in direction finding, the ratio of signal power of Iran to the power sum of the interference and noise (OSPS) obtained when using the prototype method (expression (6)) and the claimed method (10) with the following characteristics signal-to-noise:

The operating frequency is 900 MHz

Interelement distance is /2

The number of antenna elements (linear equidistant antenna array) - 7

The number of signals 1

The number of multipath component 2

The coefficient mezhluchevoy correlation 0; 0,6; 0,99

In Fig. 4 curve 1 was calculated using the method-against 3, calculated in the absence of multipath component and the interfering influences.

This sequence of steps of the claimed method can be implemented by the device (for example, adaptive antenna), a variant of which is shown in Fig. 5.

In Fig. 5 numbers denote: 1 - the antenna elements 2 - device synchronization, 3 - forming device scanning signals, 4 - weight multipliers, 5 - unit weight calculation (for example, digital processor signal processing), 6, 7 - adders, 8 - storage device 9 is a device subtraction.

The operation of this device can be explained as follows. The signals from the outputs of antenna elements fed to the input of the device computing the weights, which in moments of transmission of the information package and during the guard interval calculates weighting coefficients according to the expressions (7) and (8) respectively. Device synchronization provides the calculation of VK in the required time intervals. Thus to calculate a control signal using the output signal of one of the antenna elements, chosen as a reference. The obtained values of the weighting koaia information package and during the guard interval. The formation of the scanning signals is carried out in the device 3 by modeling the values of the phase signal IRI each antenna element for each discrete values of the angular coordinate in a given sector. Total signals representing the angular spatial range, remembered separately for time transfer of the data packet and a time guard interval in the device 8. Then the total signals calculated during the guard interval, subtract the device 9 from the total signal, calculated during the transmission of the information package. The result is suppression (compensation) of all disturbing influences in addition to the useful signal source. In further to determine the direction to the source and select the value of the scan angle corresponding to the resultant signal with the maximum amplitude. This angle will determine the direction of a useful source of radio emission.

Thus, the claimed method allows you to pelargonate the emitters of mobile radio systems under the influence of multipath component. Thus the error in the determination of the bearing is reduced from 15-20o2-3oand when Delineator

1. Rao B. D.,Hari K. V. Statistical performance analysis of the minimum-norm method //IEE Proc. - 1989, v. 139.- Pt.F. - N3.- P. 125-134.

2. Gabriel U. F. Spectral analysis methods sverhrazdutaya using adaptive grids //TIER, so 68, No. 6, S. 21-28

3. Shan T. J., M. Wax, Kalath T. Spatial Smoothing for Direction of Arrival Estimation of Cogerent Signals//IEEE trans. v. ASSP-33. N 3, P. 527.

4. Loskutova, Century About the influence of spatial smoothing on the angular resolution of multipath signals in adaptive antenna arrays // radio engineering and electronics. 1990, N 12, c. 2557-2560

5. McDonald V. H. The Cellulare Concept BSTJ, Vol. 58, No. 1, part 3, p. 15-41, Jan. 1979.

6. ETSI GSM 05.02 Multiplexing and multiple access. Feb. 1992.

7. J. E. Padgett e.t.c. Overview of Wireless Personal Communications. IEEE Commun. Mag. Vol. 39, N 1, p. 28-41, Jan. 1995.

8. Boult R. New standards steal the show at Telecom //Open System Magazine. Jan. - 1992. - 12 S.

9. Picken D. The GSM mobile telephone network: tehnical features and measurement requirements //News From Rohde &Shwarz. - N 1. - 1992. - 28 S.

10. Gusev Century, The system of spatial-temporal processing of hydroacoustic data, Leningrad: Sudostroenie, 1988. - 264 S.

11. Ponomarev, A., Telehouse D. E., Kulikov A. P. Distribution of VHF in the city. - Tomsk: Tomsk state University, 1991. - 220 C.

Method of direction finding radio cellular mobile radio systems in conditions of multipath propagation, which consists in receiving signalement antenna grid, the formation of the scanning signals in a predetermined angular sector, the calculation of the weights and the subsequent multiplication of the weights with the corresponding signals of the scan, remembering resulting from the multiplication result signals and corresponding scanning signals, wherein these steps are performed repeatedly in the period of the guard interval of each time window cellular mobile radio, and then subtract the resulting signals calculated during the guard interval from the respective output signals calculated during the reception of the information packet each time window cellular mobile networks, remember differential signals for all discrete values of the angle of scan, then select from them the difference signal with the maximum amplitude, and the corresponding angle scanning accept as the bearing of the source of radio emission.

 

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