RU2665269C1 - Method of suppression of multiple- access interference in the digital communication system - Google Patents

Abstract

FIELD: information technology.SUBSTANCE: invention relates to the field of digital information transmission and is intended for use in receiving devices of synchronous digital communication systems. Method for suppressing multiple-access interference (MAI) in a digital communication system comprises the following operations: at each clock of the communication system, array of M≥2 decisive statistics corresponding to all of its M users; determine the maximum in terms of the level of these crucial statistics; determine the set of parameters of the elementary premise (EP) corresponding to this decisive statistics; based on the results of determining the said set of EP parameters, a reference compensation signal of the MAI component generated by the said EP is formed, the scale factor of the MAI compensation signal is generated; as the MAI compensation signal, the result of multiplying the reference compensation signal of the MAI component by a specified scale factor; subtract the MAI compensation signal from the input signal, at that all operations of the method for suppressing MAI at each clock cycle of the communication system are repeated N≤M-1 times.EFFECT: increasing the efficiency of MAI compensation, namely, reducing the level of residual MAI components.1 cl, 1 dwg

Description

The invention relates to the field of digital information transmission and is intended for use in receiving devices of synchronous digital communication systems.

In a number of situations, the noise immunity of receiving digital communication signals is limited by the interference caused by the simultaneous transmission in the same frequency band of a block of two or more elementary premises (EP) (in accordance with the terminology used, for example, in [1], EP is the pulse per the output of the transmitting part of the communication system, resulting from the formation of high-frequency oscillations based on the code of the transmitted symbol). The presence of this interference is a consequence of the lack of strict orthogonality between different EPs. These situations occur in the following two cases:

- in a single-channel communication system with the simultaneous transmission of several ES in order to increase the transmission speed [2];

- in a multi-channel communication system with code access (or with CDMA-English. Code Division Multiple Access - code division multiple access) [3].

In the aforementioned single-channel communication system, the considered interference is referred to as systemic, and in a multi-channel communication system with code access, it is called multiple access interference (PMD). The following descriptions of the prototype and the proposed method are mainly focused on a single-channel communication system with the simultaneous transmission of several electronic devices, however, accurate to some part of the terminology, all of the above can apply to a multi-channel communication system with code access. Further, for uniformity, the acronym PMD is used for both of these communication system options. In this case, a single-channel communication system with the simultaneous transmission of a block of several EIs is considered as an M-channel, in which 1 / Mth part of all information to be transmitted is transmitted on each of the M channels. The users of the single-channel communication system under consideration are actually one pair of users or a single source and a single receiver, however, it is further conditionally assumed that the system has M pairs of users. The application of the mentioned terminological conventions ensures the identity of the terminology (to the extent possible) used in the description of the prototype and the claimed object.

The analogue mentioned above is known [2], in which the transmission rate is limited by the presence of PMD. The PMD level is proportional to the number of ETs simultaneously transmitted in the same frequency range, which in turn determines the transmission rate. Therefore, the presence of PMD limits the maximum allowable transmission rate in the aforementioned single-channel communication system (as well as the number of pairs of subscribers simultaneously using the multi-channel communication system with code access). This circumstance is due to the disadvantage of this analogue, as well as the relevance of suppressing PMD.

There is a known method for suppressing PMD (see [3], section 10.5.1; this refers to the part of section 10.5.1 that begins with the 10th line from the bottom of the text on page 402), which provides for the formation of an array at each clock cycle of the communication system decisive statistics corresponding to the totality of all users, determining the maximum of the specified decisive statistics, determining the parameters of the EP corresponding to the maximum of the decisive statistics, determining the standard of the compensation signal of the PMD component generated by the specified EP, and subtracting the standard of the computer signal PMD from the input mixture. This method is selected as a prototype.

Explanations

1. Under the array of decision statistics in the present description refers to the array of results of the primary processing of the received set of EP in a mixture with background noise. So, for example, in the object described in [2], the array of decision statistics is the array that is generated during the operation of determining the maximum correlation of the received signal with a noise-like signal generated by phase modulation according to the law of one of the predefined pseudo-random sequences, and it is as a result of calculating the indicated correlation.

An example of the formation of relatively typical decisive statistics is described in detail, for example, in [5].

In [3], when describing the prototype, instead of the operation of generating decisive statistics, it is said about "... estimating user bits with the transition from strong to weaker signals ...". In this case, the concept of “strong signal” is equivalent to the concept (term) used in the present description, the decision statistics, over the array of which the operation of determining the maximum of these decision statistics is performed.

2. The operation, referred to above as “determining the parameters of the ES corresponding to this decisive statistics”, is referred to in the source text [3] as “determining the user bits”.

The disadvantage of the prototype is the low quality of compensation PMD, due to the possible mismatch of the levels of compensated EP and the reference signal compensation components of PMD. With this mismatch, as a result of the implementation of the prototype, a residual PMD component of a very substantial level is formed, which reduces the noise immunity of receiving information.

The aim of the proposed method is to increase the compensation efficiency of PMD, i.e. decrease in the level of the residual PMD component.

This goal is achieved by the fact that the method of suppressing PMD in a digital communication system, in accordance with which, at each clock cycle of the system, an array of M≥2 decision statistics corresponding to all its M users is sequentially formed, the maximum (in level) is determined from the specified decision statistics, determine the set of EP parameters corresponding to this crucial statistics, based on the results of determining the specified set of EP parameters, form the reference compensation signal of the PMD component generated by the decree EMF, and subtract the PMD compensation signal, and all operations of the PMD suppression method at each clock cycle of the communication system are repeated 2≤N≤M-1 times, additionally form the scale factor of the PMD compensation signal and use the result of multiplying the reference compensation signal as the PMD compensation signal PMD components at the specified scale factor.

A flowchart illustrating the combination of operations of the proposed method is shown in FIG. 1, where are indicated:

- 1.1 ... 1.M - formation of decisive statistics;

- 2 - determination of the maximum (by level) of the decisive statistics;

- 3 - determination of the set of EP parameters corresponding to the maximum decisive statistics;

- 4 - the formation of a reference signal for compensation of the PMD component;

- 5 - the formation of the scale factor of the compensation signal PMD;

- 6 - multiplication of the reference signal for compensation of the PMD component by a scale factor;

- 7 - subtraction of the PMD compensation signal.

To clarify the content of the operation (in fact, the totality of operations) 1.1 ... 1.M of the formation of decisive statistics, it is necessary to determine the dynamics of updating the input data and their content (or a kind of exchange protocol) of the proposed method. At each (current) clock cycle of the digital communication system, in which the inventive method functions, its input (current) block (or set) of M ES, each of which, as mentioned above, contains 1 / Mth part information transmitted on the specified measure. The duration of this measure is denoted by τ. Within the time interval that coincides with the current clock cycle, the full cycle of operations of the proposed method should be implemented. This hollow cycle contains N≤M-1 phases. First, explanations are given for the first of these phases (explanations for the operation of the proposed method in the aggregate of all phases are given below when describing its operation in dynamics).

The implementation of suppression of the PMD by the claimed method is based on the fact that upon receiving the EP block, the resulting PMD is a superposition (sum) of the components of this PMD, each of which is generated by one (corresponding to it) EP.

In the first phase of the implementation of the proposed method at the current cycle of the communication system, the current processing unit of the EP, which goes to the input of operation 7, is completely (i.e. without any changes) transmitted to the input of the set of operations 1.1 ... 1.M (here and in similar cases further when indicating a signal to the input of a certain operation, this means supplying the specified signal to the input of a device that implements the corresponding operation of the method). Each mth (for 1≤m≤M) operation 1.m provides for the implementation of the function for generating the mth decisive statistics, for example, using the transmission method described in [2] as a result of calculating the cyclic correlation function between the input for the described operation the signal and the mth support function or, equivalently, the cyclic convolution between the indicated signal and the mth support function read in the inverse time (i.e., if this function has the form S (t) for values of the time argument t in range 0 ... τ, then this same function, read in atnom time has the form S (τ-t)). The support function used in calculating the indicated convolution coincides in shape with the pseudo-noise signal at its zero cyclic time shift (see also, if necessary, the description of the object [2]). In this case, the device that implements the described function, in this example, is a correlator. In the case of using the proposed method in a communication system, for example, type MS-5 [6] (or, equivalently, “Kineplex”), the set of operations 1.1 ... 1.M is performed by a discrete Fourier transform calculator with subsequent calculation of the relevant modules ( i.e., located in the working frequency range) of the coefficients of this transformation.

The decisive statistics generated by the mth EP of the block (i.e., using the mth support function) is called the mth.

Operation 2 of determining the maximum level from the decisive statistics is implemented by comparing them sequentially, for example, as follows: first, we select an arbitrary decisive statistic, remember its level and number (index) m, and carry out a sequential comparison of its specified level with the levels of other decisive statistics ( let us assume an arbitrary order of selection of these other decisive statistics). In the process of such a sequential search of other crucial statistics, when the condition that the level of the initially selected critical statistics is exceeded by the level of other critical statistics is first fulfilled, the primary selected critical statistics are replaced with these other critical statistics (i.e., the level and number of this other critical statistics is stored), and these other crucial statistics are then deemed to be initially selected. Further, the indicated procedure (i.e., operation 2) continues until the array of all decisive statistics is exhausted. The number m of the decisive statistics, which is considered to be initially selected at the time the operation 2 ends, is the result of operation 2.

Operation 3 of determining the set of EP parameters corresponding to the maximum decisive statistics is implemented as follows. As a result of the operation 2, the number m of the EA that corresponds to the maximum decisive statistics is determined. Moreover, for example, when using the transmission method considered in [2], the indicated set of EP parameters is a cyclic time shift introduced into the pseudo-random sequence. The operation of determining the cyclic time shift introduced into the pseudo-random sequence is known; it is part of the object described in [2].

In the situation of using the proposed method as part of a communication system of type MS-5, the content of operation 3 consists in determining the initial phase of each spectral component formed as a result of the above-mentioned operation of computing the discrete Fourier transform.

The operation 4 of generating a reference compensation signal for the PMD component, for example, when using the transmission method described in [2], for example, when using the transmission method described in [2], is implemented by generating a pseudo-random sequence that matches in shape with an EF whose parameter ( namely, the cyclic time shift) is determined as a result of the operation 3. The contents of this generation procedure in the situation under consideration are given in [2].

In the situation of using the proposed method as part of a communication system of type MS-5, the content of operation 4 consists in generating a segment of a sinusoid of duration τ, and the initial phase of this sinusoid is equal to the result of determining the initial phase of the m-th spectral component formed as a result of computing the discrete Fourier transform.

The step 5 of generating the scale factor of the PMD compensation signal is realized, for example, by calculating the correlation between the result of the formation of the reference signal for compensating the PMD component and the signal in which the specified component is compensated. In this situation, the scale factor of the PMD compensation signal is taken equal to the result of calculating the indicated correlation.

Incoming communications of operation 5 are shown in Fig. 1 by dashed lines, since with the equivalent embodiment of the method with PMD compensation in the claims, it is not in the input signal but in the PC (see the penultimate paragraph of the present description) instead of the incoming communication of operation 5 from the output of operation 7 there are incoming connections of operation 5 from the outputs of the set of operations 1.1 ... 1.M

Operation 6, in accordance with its name, is implemented by multiplying the reference compensation signal for the PMD component generated as a result of operation 4 by a scale factor generated as a result of operation 5.

Operation 7, in accordance with its name, is implemented by subtracting the PMD compensation signal generated as a result of operation 6, for example, from an input signal whose implementation is stored in the buffer memory that is part of the device that implements this operation. As a result of the operation 7, the result of the indicated subtraction (i.e., the difference obtained as a result of the subtraction) is recorded in the indicated buffer memory, and the implementation of the input signal stored in the indicated buffer memory before the subtraction is erased.

All operations of the proposed method are implemented by universal programmable microprocessors. It is possible to combine the implementation of several operations of the method in one microprocessor.

The inventive method in dynamics works as follows. The dynamics of updating the input signal is described above. The above also indicates that the inventive method is designed for use in synchronous digital communication systems. Upon receipt of the proposed method for the implementation of the next block of EP (mixed with background noise), it is written to the buffer memory, which, for example, is part of the device that implements step 7. The duration of this implementation is τ. Further, this implementation is read into the input of the set of devices that implement the set of operations 1.1 ... 1.M, after which the set of operations 2 ... 7 is described sequentially, as described above in relation to the first phase of testing its function by the claimed method. As a result, the claimed method develops its function in the indicated first phase at its output — the output of operation 3 — a set of EP parameters is formed that corresponds to the maximum (in the first phase) decisive statistics (as noted above, in the considered example of a communication system operating according to the principle of the method [ 2], this set of parameters is a cyclic time shift. The specified shift is the first result of developing its function by the claimed method in the first phase. This result is issued for its conversion into a code the combination of the above-mentioned EP (see the operation of determining the combination of bits of the transmitted symbol in the description of the object [2] - this operation is beyond the scope of the proposed method.) The second result of working out its function by the claimed method in the first phase is the implementation of the signal recorded in the buffer memory included in the composition of the device that implements operation 7, in which the specified EP, which corresponded to the maximum level of decision statistics, is deleted. The latter ensures the absence and components of PMD generated by the specified EP, when the claimed object fulfills its function in the second phase.

. Такой итерационный процесс компенсации отдельных компонент ПМД (т.е. отработка заявляемым способом своей функции в третьей, четвертой и т.д. фазах) может продолжаться в пределе до тех пор, пока не будут компенсированы компоненты ПМД, порожденные всеми ЭП блока. При этом в каждой

фазе отработки заявляемым способом своей функции при расчетах по формуле (2) принимается значение

.When implementing the second phase of testing its function by the claimed method, the entire set of operations of the method is repeated with a single change, consisting in the fact that when calculating according to formula (2), the value

. Such an iterative process of compensation of individual PMD components (i.e., the development of their functions by the claimed method in the third, fourth, etc. phases) can continue in the limit until the PMD components generated by all the EI blocks are compensated. Moreover, in each

the phase of mining by the claimed method of its function in the calculations according to the formula (2), the value

.

имеет место снижение текущего уровня оставшейся к соответствующему

фазе моменту уровня ПМД, чем обеспечивается возможность правильного определения циклических временных сдвигов в том числе и тех ЭП блока, которым соответствуют решающие статистики, уровни которых на момент начала реализации заявляемого способа были сравнительно низки.As a result, testing the claimed method of its function N≤M-1 times (i.e., when implementing N phases of mining) compensated PMD components generated by the N E block. At the same time, at the output of the method, the parameters of the ES block are sequentially generated (cyclic time shifts entered on the transmitting side of the communication system), according to which codes (corresponding to the received ES (their cyclic time shifts)) are formed further. As the phase number increases, the claimed method of its function

there is a decrease in the current level remaining to the corresponding

phase to the moment of PMD level, which provides the opportunity to correctly determine cyclic time shifts, including those EP blocks, which correspond to the decisive statistics, the levels of which at the time the implementation of the proposed method were relatively low.

There is a possible implementation of the PMD compensation method, the formal difference from which described is only that operation 7 (subtraction of the PMD compensation signal) is performed not on the implementation of the input signal, but on the decisive statistics, i.e. on the results of operations 1.1 ... 1.M (the formation of a set of decisive statistics). In this case, for example, in the case of using the transmission method considered in [2] in the communication system, the compensating PMD signal generated by calculating the cyclic cross-correlation function between the signal is subtracted from each mth decisive statistics in each phase of the development by the claimed method arising from the operation 6, and a support function matching in shape with the m-th support function used in performing operation 1.m. This embodiment of the method for compensating PMD in its concept is equivalent to that described above and appearing in the claims, i.e. it is the equivalent of the proposed method.

The achievement of the technical effect in the claimed method is due to the implementation in it of a set of operations that ensure the equalization of the levels of the compensating and compensated components of the PMD generated by the set of ES units. In the absence of such equalization, compensation of PMD in the general case does not actually occur.

Used sources

1. Fano R. Transfer of information. Statistical Communication Theory. Per. from English / Ed. R.L. Dobrushin. - M .: World. 1965 .-- 440 p.: Ill.

2. Golubev A.G. A method of transmitting information in a communication system with noise-like signals. Pat. No. 2549188. Claim 01/09/14.

3. Ipatov V.P. Broadband systems and code division signals. Principles and applications. - M .: Technosphere, 2007 .-- 488 p.: Ill.

4. Okunev Yu.B. Digital transmission of information by phase-shifted signals. -M.: Radio and communication. 1991 .-- 296 pp., Ill.

5. Kostylev V.I., Slichenko M.P. Decisive statistics of the energy detector when receiving radio signals against a background of poly-Gaussian noise. Bulletin of the Voronezh State University. Series Physics. Maths. 2010. No1.

6. Equipment for the transmission of discrete information MS-5. Ed. A.M. Zaezdnogo and Yu.B. Okuneva. - M .: Communication. 1970 .-- 150 p.: Ill.

7. Levin B.R. Theoretical foundations of statistical radio engineering. 3rd ed. - M .: Radio and communications, 1989 .-- 654 p.: Ill.

Claims (2)

1. A method of suppressing multiple access interference (PMD) in a digital communication system, according to which, at each clock cycle of the communication system, an array of M≥2 decision statistics corresponding to all its M users is sequentially formed, the maximum level is determined from the specified decision statistics, determine the set of parameters of the elementary premise (EP) corresponding to this decisive statistics, on the basis of the results of determining the specified set of parameters of the EP form the reference signal of compensation components PMD generated by the specified EP, and subtract the PMD compensation signal from the input signal, and all operations of the PMD suppression method at each clock cycle of the communication system are repeated N≤M-1 times, characterized in that each execution of the set of operations of the PMD suppression method at each clock cycle the operation of the communication system forms the scale factor of the PMD compensation signal and, as the PMD compensation signal, use the result of multiplying the reference PMD component compensation signal by the specified scale factor. 2. The method for suppressing PMD in a digital communication system according to claim 1, characterized in that when the operation of generating a scale factor of the PMD compensation signal is performed, the correlation between the reference signal of compensation of the PMD component and the signal in which the compensation is performed, and the scale factor are taken equal to specified correlation.

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