RU2172065C1 - Method of correlation processing of wide-band signals with frequency shift - Google Patents

Abstract

FIELD: radio engineering, communication systems with wideband signals. SUBSTANCE: technical objective of invention lies in increase of immunity to structural noises by value of the order of 60-80 dB which ensures stage-by-stage correlation processing of signals of users of various levels. At first stage power signals of nearest users are correlation-processed. Correlation processing of weak signals of remote users is conducted at second stage after rejection of reconstructed signals of nearest users from input mixture. EFFECT: increased noise immunity. 7 dwg

Description

 The invention relates to the field of radio engineering and can be used in communication systems with broadband signals.

 Known methods for correlation processing of broadband signals implemented in devices protected by patents of the Russian Federation (N 2038697, H 04 B 1/10, N 2034403, H 04 B 1/10).

 These methods are used in communication systems with code division multiplexing and cannot be used for processing broadband signals with a frequency shift.

 A known method of correlation processing of broadband signals with a frequency shift, implemented in a multicast system with the choice of an arbitrary subscriber (see N. G. Petrovich, MK Razmakhnin. "Communication systems with noise-like signals", publishing house "Sov. Radio", Moscow, 1969, pp. 127-130), the disadvantage of which is low noise immunity to structural interference.

 The closest in technical essence to the proposed method is the method implemented in the correlator with a set of filters tuned to different frequencies, given in the monograph by G. I. Tuzov "Statistical theory of the reception of complex signals", M., "Sov.radio", 1977 ., p. 111, fig. 3.3, adopted as a prototype.

The block diagram of the device in which the prototype method is implemented is shown in FIG. 1, where the following notation is used:
1 - multiplier;
2 ₁ -2 _N - first, second, ..., N-th band filters;
3 - signal copy generators.

The prototype device contains a multiplier 1, the input of which is the input of the device, N bandpass filters 2 ₁ -2 _N and a signal copy generator 3, while the output of the signal copy generator 3 is connected to the reference input of the multiplier 1, the output of which is connected to the combined inputs of the bandpass filters 2 ₁ -2 _N , the outputs of which are the outputs of the device.

 The device prototype works as follows.

 The input mixture containing broadband phase-shifted signals of near and far subscribers that differ in frequency carrier frequency shifts (which are address signs of subscribers) is fed to the input of the base station of the communication system with a frequency shift, where in block 1 are multiplied with the reference signal of generator 3, synchronous with input signals of subscribers. The result of multiplication, which is a convoluted narrow-band signal of subscribers, after filtering in N band-pass filters, each of which selects a signal from its subscriber, is output to the device.

In FIG. 2 shows an enlarged diagram of a prototype device, where it is indicated:
1 - block multiplication;
2 - filtration unit;
3 - signal copy generator.

In FIG. 2 blocks 2 ₁ -2 _{N are} combined into one signal filtering block 2.

 The prototype method implemented in the device shown in FIG. 1 and 2, based on the multiplication of the input mixture containing broadband signals with a frequency shift, with a synchronous reference signal, filtering the result of the multiplication in N frequency channels.

 The prototype method consists in the fact that the input mixture containing N wideband signals with a frequency shift (the frequency shift of the carrier frequency is the address attribute of the subscriber) coming from near and far subscribers is multiplied with a reference signal common to all N signals and synchronous with all N signals. The result of multiplying the input mixture with a synchronous reference signal, which is a convolution of wideband signals with a frequency shift - narrowband signals that differ in frequency are filtered in N frequency channels, each of which selects a signal from one of the subscribers.

 The disadvantage of the prototype method is the low noise immunity to structural interference.

 To eliminate this drawback in the method, which consists in multiplying the input mixture from the signals of near and far subscribers with a common synchronous reference signal for all N subscribers and in filtering the result of multiplication in N frequency channels, after filtering, measure signal levels in N frequency channels, then select signals a large level (signals of near subscribers), from which estimates of structural interference are formed due to the multiplication in each of the N channels of selected high-level signals with a synchronous reference signal, and The generated estimates of structural interference after limiting and summing are used as a reference signal for rejecting structural interference from the input mixture, which is then multiplied with the same synchronous reference signal. In this case, the result of multiplication is filtered in N frequency channels.

 The proposed method for processing broadband signals with a frequency shift involves the following sequence of actions on the input signal.

 In the correlator of a base station of a broadband frequency-shift communication system receiving signals from near and far subscribers, the input mixture, the content of N broadband signals, the address sign of which is the frequency shift of the carrier frequency, is multiplied with a synchronous reference signal.

 The result of multiplication, which is a convolution of broadband signals of subscribers - narrowband signals that differ in frequency are filtered.

 The filtering result is used to measure the levels of received signals.

 According to the measurement results, high-level signals, signals of near subscribers are distinguished, and structural interference estimates are formed from them. To do this, restore high-level signals due to the multiplication in each of the N channels of selected high-level signals with the same synchronous reference signal. High-level reconstructed signals limit and sum. The total signal is used as a reference signal when performing the procedure of rejection of signals of a high level (structural interference) from the input mixture.

 The input mixture after rejecting structural interference from it (high-level signals) is multiplied with a synchronous reference signal, the result of the multiplication is filtered in N frequency channels.

An example of hardware implementation of the proposed method is presented in FIG. 3, where the following notation is used:
1 ₁ , 1 ₂ - the first and second blocks of multiplication;
2 ₁ , 2 ₂ - the first and second filtering units;
3 - signal copy generator;
4 - signal level meter;
5 - shaper estimates of structural interference;
6 - block rejection of structural interference;
7 - switching unit;
8 - block restrictions;
9 - adder.

In FIG. 3 shows the first multiplication unit 1 ₁ , the first filtering unit 2 ₁ , the signal level meter 4, the control output of which (a bus of N control outputs) is connected to the control input of the switching unit 7 in series, the signal output (bus of N signal outputs) of the meter signal levels 4 is connected to the first signal input of the switching unit 7 and the signal input of the generator of estimates of structural interference 5, the reference input of which is connected to the reference inputs of the first and second block multiplication 1 ₁ and 1 ₂ and with the output of the generator a signal copy 3, and the output of the structural interference estimator 5 by the bus through the restriction unit 8 and the adder 9 is connected to the reference input of the structural interference rejection unit 6, the signal input of which is connected to the signal input of the first multiplication unit 1 ₁ and is the device input, and the output of the unit rejection of structural interference 6 is connected to the signal input of the second block multiplication 1 ₂ , the output of which through the filter block 2 ₂ bus is connected to the second signal input of the switching unit 7, the output of which is the output of the device.

 A device that implements the inventive method works as follows.

T - длительность информационного символа), являющимся адресом абонента, поступает на блок 1₁, где перемножается с опорным сигналом (копией сигнала), формируемой блоком 3. В результате перемножения широкополосные фазоманипулированные сигналы N абонентов сворачиваются в узкополосные сигналы, отличающиеся между собой частотами, которые подаются на блок 2₁. В блоке 2₁ узкополосные сигналы фильтруются с помощью гребенки из N полосовых фильтров, каждый из которых настроен на свою частоту, отфильтрованные сигналы поступают на блок 4. В блоке 4 в каждом из N каналов сигнал усиливается и детектируется, полученные огибающие сигналов сравниваются с порогом. Команды о превышении ("1") или непревышении ("0") порогов подаются на блок 7.An input mixture containing broadband phase-shifted signals from N subscribers, differing among themselves in the frequency shift of the carrier frequencies (equal for adjacent channels

T is the duration of the information symbol), which is the subscriber’s address, goes to block 1 ₁ , where it is multiplied with a reference signal (copy of the signal) formed by block 3. As a result of multiplication, the broadband phase-shifted signals of N subscribers are collapsed into narrow-band signals that differ in frequency with each other served on the block 2 ₁ . In block 2 _1, narrow-band signals are filtered using a comb of N band-pass filters, each of which is tuned to its own frequency, the filtered signals are sent to block 4. In block 4, in each of the N channels, the signal is amplified and detected, the resulting signal envelopes are compared with a threshold. Commands about exceeding ("1") or not exceeding ("0") thresholds are sent to block 7.

 Narrow-band signals whose levels have exceeded the threshold are fed simultaneously to blocks 5 and 7. In block 5, they are restored to high-level broadband signals (signals of near subscribers). This is achieved due to the multiplication (phase manipulation) of narrow-band signals transmitted to the output of block 4 by the reference signal of block 3. From the output of block 5, broadband signals of a high level (structural interference assessment) through block 8, which limits them, and block 9, which sums them are fed to block 6, where the notion of structural interference detected in block 4 is performed.

From the output of block 6, the input mixture, from which structural interference is excluded, is fed to block 1 ₂ , where it is multiplied with a reference signal (copy of the signal) generated by block 3. By multiplying with a synchronous reference signal in block 1 ₂ , convolution of the wideband signals of remote subscribers is carried out (low level signals). In block 2 _2, coiled narrow-band low-level signals are filtered each in its own band-pass filter, and then they are supplied to block 7, which commutes N frequency channels to the output of the device.

 Block 7 through the use of control commands from block 4, provides the passage of signals of large and small levels to different outputs of block 7.

The block diagram of block 4 is shown in FIG. 4, where the following notation is used:
41 ₁ -41 _N - delay element;
42 ₁ -42 _N - key;
43 ₁ -43 _N - amplifier;
44 ₁ -44 _N - detector;
45 ₁ -45 _N - comparison block with a threshold.

 Block 4 consists of N channels, each of which contains a delay element 41 and a key 42 connected in series, as well as an amplifier 43, a detector 44, a threshold comparison unit 45, the output of which is connected to the control input of the key 42 and at the same time is the channel output, the output of the key 42 is the signal output of the channel, the inputs of the delay element 41 and the amplifier 43 are combined among themselves and are the input of the channel.

 Block 4 operates as follows. In each of the N channels, the signal is amplified in block 43, detected in block 44, compared with a threshold in block 45. At the same time, in each channel, the signal through delay element 41 is supplied to key 42. The delay value of block 41 is chosen equal to the delay in the path consisting of blocks 43, 44, 45. Commands about exceeding ("1") or not exceeding ("0") the threshold from the outputs of block 45 are sent to the control output. Narrow-band signals that exceed the thresholds are fed simultaneously to the signal input of block 7 (bus of N wires) and the signal input of block 5 (bus of N wires).

The block diagram of block 5 is shown in FIG. 5, where the following notation is used:
51 ₁ -51 _N - multiplier;
52 ₁ -52 _N - band-pass filter;
53 ₁ -53 _N - delay element.

Block 5 contains N channels, each of which contains a series-connected multiplier 51 and a band-pass filter 52. The inputs of blocks 51 ₁ ... 51 _N are the signal inputs of block 5, and the outputs of blocks 52 ₁ ... 52 _N are the outputs of block 5. Block 5 also contains delay elements 53 ₁ ... 53 _N , the combined inputs of which are the reference input of block 5, the outputs of blocks 53 ₁ ... 53 _{N are} connected to the corresponding reference inputs of blocks 51 ₁ ... 51 _N.

 Block 5 operates as follows.

 Narrow-band signals that exceeded the thresholds in block 4 are supplied to the corresponding blocks 51, where they are multiplied with the reference signal generated by block 3, supplied to the blocks 51 via the corresponding delay elements 53. As a result of multiplication (phase shift keying), the narrow-band signals become broadband phase-manipulated signals similar to in structure to the corresponding signals in the input mixture. In the corresponding blocks 52, the generated signals are filtered, while the bandwidth of the blocks 52 is chosen equal to the spectral width of the corresponding broadband signals in the input mixture. Thus, at the output of block 5, structural interference estimates (copies of high-level signals) are formed.

 Block 8 contains N channels, each of which contains a limiter. In block 8, voltage levels are normalized in each of the N channels. In the adder 9, the normalized voltages of the N channels are summed using, if necessary, when combining the channels of decoupling elements (resistors, emitter followers, etc.).

The block diagram of block 6 is shown in FIG. 6, where the following notation is used:
61, 63 - multiplier;
62 - notch filter;
64, 65 are delay elements.

 Block 6 contains in series a first delay element 64, the input of which is the signal input of the block, a first multiplier 61, a notch filter 62, a second multiplier 63, the output of which is the output of the block, and a second delay element 65, while the reference input of block 6 is connected to the reference input of block 61 directly, and with the reference input of block 63 is connected through a delay element 65.

 Block 6 works as follows.

 The input mixture from the input of the device through the delay element 64 is fed to the signal input of the block 61, the reference input receives a mixture of estimates (copies) of structural interference from the output of the block 9. The delay value of the block 64 is selected so as to ensure the synchronism of the signals at the inputs of the block 61. By multiplying the input mixture with the estimates of structural interference in block 61, the convolution of broadband structural interference is narrowed into narrow-band interference, which are rejected in block 62. At the same time, weak signals (low-level signals) from subscribers in block 61 receive additional manipulation of the mixture of estimates of structural interference, which is removed in block 63 due to multiplication with the same reference signal from block 9 through block 65.

 Thus, the structural noise is rejected and therefore does not pass to the output of block 6, and the signals of the remote subscribers pass through it with almost no distortion. The delay value of blocks 64 and 65 is selected when setting up the device so that synchronization of the multiplied signals is ensured.

The block diagram of block 7 is shown in FIG. 7, where the following notation is used:
71 ₁ -71 _N - inverter;
72 ₁ -72 _N is the key;
73 ₁ -73 _N is the first amplifier;
74 ₁ -74 _N is the second amplifier.

 Block 7 contains N first channels, each of which contains block 74, N second channels, each of which contains serially connected blocks 72 and 73 and N third channels, each of which contains block 71, while the outputs of the first amplifiers 73 are connected to the corresponding outputs second amplifiers 74, the inputs of which are the first N inputs of block 7, and the outputs are N outputs of block 7. The second N inputs of block 7 are connected to the corresponding signal inputs of blocks 72, while the N sending inputs of block 7 are connected through the corresponding blocks 7 1 with corresponding key control inputs 72.

The signals of near subscribers from block 4 are fed to the inputs of blocks 74 ₁ -74 _N , where they are amplified, and from their outputs to the outputs of block 7.

The signals of the remote subscribers are fed to the second input of block 7 from block 2 ₂ . Through the keys 72 ₁ -72 _N and the first amplifiers 73 ₁ -73 _N they are supplied to the outputs of block 7. Keys 72 ₁ -72 _{N are} controlled by the commands of block 4 received through inverters 71 ₁ -71 _N. When the command “1” appears on the control outputs of block 4, the keys 72 corresponding to them are locked, due to this, the signals of the near subscribers from the outputs of block 4 are transmitted to the output of the block 7, and the signals of remote subscribers are transmitted from the outputs of block 2 ₂ , while the control commands of the block 4, a ban on the passage of signals of those channels of block 2 ₂ that are open in block 4 is made. Blocks 73 ₁ -73 _N , 74 ₁ -74 _N provide the passage of signals in one direction, thereby eliminating the mutual influence of blocks 4, 5, 2 ₂ .

Blocks 1 ₁ and 1 ₂ are multipliers, the signal and reference inputs of which signals are fed through delay elements, the values of which are selected when setting up the device in such a way as to ensure synchronization of the multiplied signals taking into account their delay in the equipment.

 The prototype method provides simultaneous correlation processing at the base station of the signals of both near and far subscribers. Powerful signals of near subscribers have an interfering effect on the reception of signals of remote subscribers, due to the presence of emissions of the cross-correlation function of broadband signals in the frequency domain, so the prototype has low noise immunity to structural interference. The inventive method is based on measuring the levels of received signals in the correlator of the base station and using a two-stage correlation processing procedure. At the first stage, correlation processing of powerful signals of near subscribers is carried out. Correlation processing of weak signals of remote subscribers is carried out at the second stage after notching from the input mixture of the restored signals of near subscribers (structural interference). This ensures an increase in noise immunity to structural interference by an amount of the order of (60-80) dB, which is determined by the degree of suppression of structural interference during their rejection.

Claims (1)

 A method for correlation processing of broadband signals with a frequency shift, based on multiplying the input mixture from near and remote signals with a synchronous reference signal common to all subscribers, and filtering the result of multiplication in N frequency channels, characterized in that after filtering the signal levels in N frequency channels are compared with a threshold, signals of nearby subscribers that exceed the threshold are fed to the output of the device and at the same time form estimates of structural interference from them by multiplying them with a synchronous reference After the restriction and summing, the generated estimates of structural interference are used as a reference signal for rejecting structural interference from the input mixture, the input mixture, from which structural interference is excluded, is multiplied with the same synchronous reference signal, due to the multiplication, the reconciliation of the wideband signals of remote subscribers is performed, coiled narrowband signals of remote subscribers are fed to the output of the device.

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