Communication channel simulation method

FIELD: communications engineering; simulating digital communication channels with separate and grouping errors.

SUBSTANCE: proposed method includes evaluation of set of communication channel states S0,S1, ..., Sm - 1 and calculation of conditional error probabilities P(e/s) in each state s" i = 0, ..., m - 1 of communication channel, and error acquisition in communication channel in compliance with conditional error probability for current state of communication channel; in the process probability of error-free interval p(0i) of i bits is found, and conditional probabilities p(0i1/11), p(0i1/01) of error-free intervals of i bits are calculated with respect to them basing on probabilities p(0i) and using recurrent rules during each current time interval and preceding one on condition that for error generation use is made of two states of communication channel corresponding to combination of errors 11 or 01; random number p uniformly distributed within interval between 0 and 1 is generated; conditional probabilities p(0i1/11), p(0i1/01) are summed up starting from i = 0 resulting in sequence 0k1 that constitutes bit-by-bit stream of communication channel errors.

EFFECT: enhanced speed.

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The invention relates to the field of communication technology and can be used for modeling discrete communication channel with independent and grouping errors.

The method described in this application can be used for modeling binary symmetric channel and allows to obtain a bit stream errors necessary for testing the equipment data.

To compare the possible ways of the communication system and predict its characteristics without direct experimental tests are needed to have the various characteristics of the grouped channels. The description of the channel, allowing to calculate or evaluate its performance, is called the channel model.

Worldwide telecommunication devices are thoroughly tested for compliance with the requirements of the connection network connection (S1-PM and C1-fluorescence in Russia; FCC Part 65, Part 15 in the US; BS6305 in the UK). The tests are performed in certified laboratories of the Ministry of communications, Ministry of Railways, the Bank, MOI, MOE, and so on - in all departments, have their own channels of communication.

Large banks, government agencies, owners of data networks - all those who actively operate a funds transfer, forced to carry out comparative tests. Users interested in the stability of the device to various interferences the distortion.

For such comparative tests using different models of communication channels, allowing to obtain bit error stream of the communication channel.

In many cases, the communication channel to determine a block error statistics of the communications channel. Under block error statistics of the communications channel to understand the distribution P(t,n) probability t errors in a block of length n bits for different values of t and n (t≤n). For example, a model of the communication channel on Purtova specified block error statistics of the communications channel. The proposed method based on the block error statistics of the communications channel to receive bit error stream channel required for testing various devices.

There is a method of modeling a communication channel with independent errors, which first calculates the average probability of bit errors in the channel, and then in accordance with this likely to get errors in the communication channel [1].

The disadvantage of this method is the limited scope of its application, since the distribution of errors in real communication channels differs substantially from the distribution of independent errors.

Closest to the proposed method is a method of modeling a communication channel with the grouping errors on Markov model of the channel (prototype), namely, that first define a set of SOS is ojani communication channel s 0, s1,..., sm-1and calculate the conditional probability P(e/si) the occurrence of errors in each condition si, i=0,..., m-1 communication channel. Further in accordance with the conditional probability of error for the current state of the communication channel get errors in the communication channel. Thus the next state of the communication channel is determined by the transition probabilities P(sj/si), corresponding to the transition from the current state siin the following communication channel status sj[2].

The disadvantage of this method is the high complexity of the modeling of the communication channel at block statistics of the communications channel, because when you build a Markov model for block statistics of the communication channel required a large amount of calculations to determine the parameters of the Markov model. In many cases, to obtain affordable accuracy of the Markov model will have a large number of States, which complicates getting a bit of statistics of the communications channel. In addition, this method has poor performance, due to the fact that in each state of the communication channel is generated by only one bit error stream, and then decided to transition to the next state.

The purpose of the invention is to simplify the modeling of the communication channel by receiving the error stream directly on block statistics of the communications channel and increase rapidly Sodeistvie, since each state of the communication channel can generate a sequence of errors, consisting of one or more bits, and only then decided to transition to the next state of the communication channel.

To achieve the goal of the proposed method lies in the fact that you first determine the set of States of the communication channel s0, s1,..., sm-1and calculate the conditional probability P(e/si) the occurrence of errors in each condition si, i=0,..., m-1 communication channel. Further in accordance with the conditional probability of error for the current state of the communication channel get errors in the communication channel. What's new is that each state of the communication channel corresponds to an event of occurrence of a particular combination of errors si=0i1 in the time preceding the current time, where 0i1=0...01 - binary combination consisting of i consecutive positions in which there is no error, and one position in which an error takes place, for each state of the communication channel compute the conditional probability P(0k1/si), and errors in the communication channel are received as a sequence of the form 0k1 in accordance with the conditional probability P(0k1/si).

Implementation of the proposed method of modeling a communication channel consider the example of the modified build is dressed communication channel for Purtova [3].

Modified model of the communication channel on Purtova set block statistics of the communications channel. According to the modified model of the communication channel on Purtova probability t and more errors (t≥2) in the block length n bits is expressed by the formula:

where p is the average probability of error (p<0.5),

a - factor grouping error (0≤≤1), the value a=0 approximately corresponds to the channel with independent errors, a=1 - channel, when all the errors are concentrated in one group,

where

The likelihood of distortion of the code combination is equal to

This model error is determined by only two parameters p and as and when the various parameters of the model accurately describes many real communication channels.

Block statistics of the communications channel is determined by the equation

Block statistics channel, you in many cases are easy enough to obtain various characteristics of the communication system, for example to determine the reliability of the reception of messages protected by error correcting code. The probability of correct reception of error-correcting code that corrects t errors and having a block length n, is estimated by the formula:

Unfortunately, the task block article is of statistical data communication channel in a modified model of the communication channel on Purtova causes significant difficulties in obtaining bit error stream, required test equipment data.

Therefore, a method is proposed, which generates a bit stream errors that satisfy the block statistics of the communications channel, in particular block statistics of the modified model of the communication channel on Purtova.

Consider a binary symmetric channel. Let p(0i- probability of error-free interval of length i bits, i=0,1,.... This probability is calculated based on the formula (2)

p(0i)=1-P(≥1,i).

When building a model of a channel according to the experimental data, the probability distribution of the lengths of the error-free intervals determined directly according to the statistics of the errors of the actual communication channel.

On the basis of the probability distribution p(0ifurther compute the following probability distribution p(0i1), p(10i1), p(10i11), where 1 indicates the erroneous bits.

These probabilities are calculated by the following recurrence rules

where

True

where

or

where

or

The proposed method uses the conditional probability

where the unconditional probability p(10i+11) and p(110i1) calculated by formulas (5) and (7) respectively, and p(11)=1-2×p(0)+p(00) p(01)=p(0)-R(00).

The conditional probability p(0i1/11) and p(0i1/01) determine the probability of error-free intervals of length i bits, provided that prior to this model were generated by the combination of 11 or 01 and for generating errors is only two States of the communication channel corresponding to a combination of errors 11 and 01. In our model, only the combinations of errors and can be in the time preceding the current time, because the generated sequence of the form 0i1. When i=0 the state of the communication channel will correspond to the combinations of 11, and when i>0 - state 01. Defining the current time the state of the communication channel, then the formulas (8) and (9) calculated the conditional probability p(0i1/11) and p(0i1/01) and in accordance with these probabilities determine the sequence of the form 0k1, which is bit error stream of the communication channel. In this first generate uniformly distributed in the interval from 0 to 1 random number R and carry out the summation of the conditional probabilities p(0i1/11) or p(0i1/01), starting with i=0, and the result is a sequence 0k1, which is chosen according to the following who have rule

where the # symbol can take the value 0 or 1.

Note that to improve the performance of the model channel length undistorted k intervals for each random number, R, is taken with a certain acceptable error can be calculated in advance before the beginning of the simulation and place in the table, the entrance of which will be the value of R, and the output is the undistorted length of interval k. In the simulation process undistorted length of the intervals will be determined by the table showing the functional relationship between R and k. Because the table is limited, the "tail" of the distribution, showing the dependence between R and k, not included in the table, you must fit a suitable analytical dependence, for example, is directly proportional dependence (direct). In this event, the "tail" of the distribution, as a rule, it is unlikely and the approximation error does not significantly affect the accuracy of the simulation.

Example. The table below shows the block statistics P1(t,n) modified model of the communication channel on Purtova calculated by the formulas (1) and (2), and similar statistics P2(t,n) flow error for the proposed method of modeling the communication channel. The parameters of the modified model of the communication channel on Purtova: p=0.01, a=0.3, block length n=31, the volume flow error is to have $ 1000000 bits.

Table
t0123456
P1(t,n)0.8950.0490.0200.0110.0070.0050.003
P2(t,n)0.8960.0480.0200.0110.0060.0040.003

Statistical goodness of fit Chi - square for theoretical P1(t,n) and experimental P2(t,n) probability distribution will be equal to χ2=0.974, indicating a high degree of approximation of the proposed model and the modified model of the communication channel on Purtova.

In the proposed method, the receive bit error stream channel communication is carried out directly on the basis of block statistics of the communications channel, in particular the method is based on the use of statistics undistorted intervals. In many cases, it is possible to simplify the construction of a channel model. For example, for comparison, a Markov model modified model of the communication channel on Purtova to generate a bit stream errors and provide affordable precision, will have at least 7 status is of any. The number of independent parameters of this model are respectively not less than 49. Moreover, for obtaining the parameters of the Markov model for block statistics requires a large amount of calculations. Consider how, even when generating error stream on the basis of only two States of the communication channel, which provides high accuracy model that simplifies the implementation of the method. In addition, in each state of the channel immediately receive sequence error 0k1, consisting of one or more bits, which increases the performance of the method.

Achievable technical result of the proposed method of modeling the communication channel is to simplify the implementation and improve performance.

Sources of information

1. Seliger NB basics of data transmission. Textbook for universities, M., Bond, 1974, p.25.

2. Fleas AL Popov, O.V., Turin VIA the source Model error in the transmission channels of digital information. M.: 1971, p.64.

3. Samoilov V.M. Generalized analytical model of the channel group error distribution. The problems of radio electronics, vol. OVR, vol. 6, 1990.

The method of modeling a communication channel, namely, that determine the set of States of the communication channel s0, s1,..., sm-1and calculate the conditional probability P(e/si) the occurrence of errors in each condition s where i=0,..., m-1 of the communication channel, and in accordance with the conditional probability of error for the current state of the communication channel get errors in the communication channel, characterized in that to determine the probability of error-free interval R(0i) the length of i bits, which is based on the probability p(0i) recurrent rules compute the conditional probability p(0i1/11), p(0i1/01) error-free intervals of length i bits at any point in time and prior to that time, provided that for generating errors using two state of the communication channel corresponding to a combination of errors 11 or 01, generate uniformly distributed in the interval from 0 to 1 random number R, carry out the summation of the conditional probabilities p(0i1/11), p(0i1/01), starting with i=0, and the result is a sequence 0k1, which is bit error stream of the communication channel.



 

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FIELD: communications engineering; simulating digital communication channels with separate and grouping errors.

SUBSTANCE: proposed method includes evaluation of set of communication channel states S0,S1, ..., Sm - 1 and calculation of conditional error probabilities P(e/s) in each state s" i = 0, ..., m - 1 of communication channel, and error acquisition in communication channel in compliance with conditional error probability for current state of communication channel; in the process probability of error-free interval p(0i) of i bits is found, and conditional probabilities p(0i1/11), p(0i1/01) of error-free intervals of i bits are calculated with respect to them basing on probabilities p(0i) and using recurrent rules during each current time interval and preceding one on condition that for error generation use is made of two states of communication channel corresponding to combination of errors 11 or 01; random number p uniformly distributed within interval between 0 and 1 is generated; conditional probabilities p(0i1/11), p(0i1/01) are summed up starting from i = 0 resulting in sequence 0k1 that constitutes bit-by-bit stream of communication channel errors.

EFFECT: enhanced speed.

1 cl, 1 tbl

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EFFECT: expanded area of application of the device due to modeling of error stream on basis of block statistic of communication channel.

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