CN110868248A - Short burst collision signal separation method - Google Patents

Abstract

The invention provides a short burst collision signal separation method, which mainly solves the problem of short burst signal collision in uplink competitive access in the existing satellite Internet of things system. The method comprises the following specific steps: (1) obtaining collision signal samples and clean copy signal samples sent by two terminals; (2) calculating a covariance matrix R and a cross-correlation vector p using the clean replica signal samples and the collision signal samples; (3) calculating a collision signal separation weight w according to the covariance matrix R and the cross-correlation vector p obtained in the step (2); (4) and carrying out cancellation processing by utilizing the collision signal separation weight w to realize collision signal separation. The invention provides a method for separating collision signals by utilizing an open-loop self-adaptive filtering method based on the short-time stationarity characteristic and the minimum mean square error criterion of a satellite channel so as to improve the operation efficiency of the signal separation process in random access.

Description

Short burst collision signal separation method

Technical Field

The invention belongs to the technical field of satellite communication, and particularly relates to a short burst collision signal separation method. The method can be used for a satellite internet of things system which adopts the short burst signal for uplink access, and clean copy signals in collision signals are separated through the self-adaptive filter, so that the separation of the uplink received short burst collision signals is realized.

Background

In a satellite internet of things system, the main service of a terminal is to forward acquired data to a ground station through a satellite for processing, and most of services have the characteristics of low speed, strong burstiness and the like. And because of the requirement of low power consumption, the complex access control and the connection-oriented multiple access technology are not suitable for the satellite internet of things system.

The random multiple access technology has the advantages of flexible access, simple system deployment and the like, and can be well adapted to short data packet burst services of the Internet of things, but because the random access adopts a competition mode to seize resources, the situation of data packet collision and collision can occur, and the conventional random multiple access technology does not support signal collision.

Aiming at the problems, the main solution is to eliminate interference, and separate the data packets with collision by adopting the interference elimination technology at the receiving end. Researchers have proposed a diversity time slot multiple access method based on contention resolution, which utilizes the idea of time diversity to achieve collision signal separation by requiring a terminal to repeatedly send multiple copies of a data packet within one data frame, and combining an iterative interference cancellation technique to separate colliding data packets. However, most of the existing separation methods are based on loops and are not suitable for separating short burst collision signals.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a method for separating short burst collision signals, so as to improve the operation efficiency of the signal separation process in random access, reduce the computational complexity, and effectively apply the signal separation method to a multiple access method based on contention resolution diversity time slots.

The technical scheme of the invention is as follows: and respectively calculating a covariance matrix and a cross-correlation vector under the condition of obtaining collision signal samples and clean replica signal samples, and then performing self-adaptive weight calculation and cancellation processing to realize collision signal separation. The method comprises the following specific steps:

(1) in the collision signal separation stage, N collision signal samples d ═ d received by satellite are respectively obtained₁,d₂,…,d_N]^TAnd clean replica signal sample x ═ x₁,x₂,…,x_N]^TTherein, []^TRepresenting a transpose;

(2) calculating a covariance matrix R and a cross-correlation vector p using the clean replica signal samples x and the collision signal samples d;

(3) calculating a collision signal separation weight w ═ R according to the covariance matrix R and the cross-correlation vector p obtained in the step (2)^-1p, wherein [ ·]^-1Representing the matrix inversion.

(4) And performing collision cancellation processing by using the separation weight w to realize the separation of collision signals.

Compared with the prior art, the invention has the following advantages:

the invention provides a method for separating collision signals by utilizing open-loop adaptive filtering based on the characteristic of short-time stationarity of a satellite channel and aiming at solving the problem of separating short burst collision signals in a diversity time slot multiple access method based on contention.

Drawings

FIG. 1 is a flow chart of an implementation of the present invention;

FIG. 2 is a simulation of a crash signal and a clean replica signal prior to separation of the crash signal in accordance with the present invention;

FIG. 3 is a comparison of signal simulation plots before and after separation of the crash signal in accordance with the present invention;

FIG. 4 is a graph of bit error rate performance obtained by 10 million Monte-Carlo experiments after demodulating the separated signals.

Detailed Description

Referring to fig. 1, the specific implementation steps of the present invention are as follows:

step 1, obtaining collision signal samples and clean copy signal samples sent by two terminals (terminal 1 and terminal 2).

In the collision signal separation stage, N collision signal samples d ═ d received by satellite are respectively obtained₁,d₂,…,d_N]^TAnd clean replica signal sample x ═ x₁,x₂,…,x_N]^TTherein, []^TIndicating transposition.

And 2, calculating a covariance matrix R and a cross-correlation vector p.

2a) The covariance matrix R is calculated using the clean replica signal samples x:

2b) the cross-correlation vector p is calculated using the clean replica signal samples x and the collision signal samples d:

wherein [ ·]^*Representing conjugation.

Step 3, calculating a collision signal separation weight w ═ R according to the covariance matrix R and the cross-correlation vector p obtained in the step 2^-1p, wherein [ ·]^-1Representing the matrix inversion.

And 4, carrying out cancellation processing by using the separation weight w to realize separation of collision signals.

4a) And estimating a terminal 1 signal in the collision signal by using the separation weight to obtain an output y of the adaptive filter:

y＝w^Hx

4b) carrying out cancellation processing on the collision signal and the output of the filter to realize the separation of the collision signal:

d-y＝d-w^Hx

wherein [ ·]^HRepresenting a conjugate transpose.

The effects of the present invention can be further verified by the following simulation.

1. An experimental scene is as follows:

taking BPSK signals as an example, the length of a transmission data packet is 50 bits, the data rate is 1000 bits/s, the sampling rate is 10kHz, the carrier frequency of a signal transmitted by the terminal 1 is 2kHz, the initial phase is 0rad, the carrier frequency of a signal transmitted by the terminal 2 is 2.5kHz, the initial phase is pi rad, and the signal-to-noise ratio difference between two received terminal signals is 3 dB.

2. Experimental contents and results:

experiment 1, calculating simulation data by using the method of the present invention to obtain simulation graphs of signals before and after separation of collision signals, wherein the simulation graphs of collision signals of two terminals and clean copy signals of the terminal 1 are shown in fig. 2, and a comparison graph of signals of the terminal 2 separated by using the method of the present invention and signals of the terminal 2 before separation is shown in fig. 3.

It can be seen from fig. 3 that short burst collision signals can be separated by the method of the present invention.

Experiment 2, in order to better evaluate the performance of the method of the present invention, the separated signal of the terminal 2 is demodulated, and then the error code performance is analyzed by using the monte carlo method, and a bit error rate curve is drawn and compared with a theoretical bit error rate curve, as shown in fig. 4. Wherein, the solid line represents the bit error rate curve obtained by the theoretical method, and the hollow circle line represents the bit error rate curve obtained by the method.

As can be seen from FIG. 4, the simulated bit error rate performance curve and the theoretical bit error rate performance curve are at the normalized SNR E_b/N₀Smaller substantially coincide, and at E_b/N₀If the ratio is large, a certain degree of deviation occurs. The simulation result is basically consistent with the theoretical analysis, and the method can realize the separation of the short burst collision signals and can obtain better separation performance.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims (3)

1. A short burst collision signal separation method is characterized in that: the method comprises the following steps:

step 1, in a collision signal separation stage, N collision signal samples d ═ d received by a satellite are respectively obtained₁,d₂,…,d_N]^TAnd clean replica signal sample x ═ x₁,x₂,…,x_N]^TWhich isMiddle school [. C]^TRepresenting a transpose;

step 2, calculating a covariance matrix R and a cross-correlation vector p by using a clean replica signal sample x and a collision signal sample d;

step 3, calculating a collision signal separation weight w ═ R according to the covariance matrix R and the cross-correlation vector p obtained in the step 2^-1p, wherein [ ·]^-1Representing matrix inversion;

and 4, performing collision cancellation processing by using the separation weight w to realize the separation of collision signals.

2. The short collision burst signal separation method according to claim 1, wherein the covariance matrix R and the cross-correlation vector p are calculated in step 2, comprising the steps of:

2a) the covariance matrix R is calculated using the clean replica signal samples x:

2b) the cross-correlation vector p is calculated using the clean replica signal samples x and the collision signal samples d:

wherein [ ·]^*Representing conjugation.

3. The method according to claim 1, wherein the step 4 of separating the collision signal by using the separation weight w comprises the following steps:

4a) and estimating a terminal 1 signal in the collision signal by using the separation weight to obtain an output y of the adaptive filter:

y＝w^Hx

4b) carrying out cancellation processing on the collision signal and the output of the filter to realize the separation of the collision signal:

d-y＝d-w^Hx

wherein [ ·]^HIndicating a conjugate rotationAnd (4) placing.

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