CN107154813B - Adaptive Rake receiver and receiving method - Google Patents

Abstract

The invention discloses a self-adaptive Rake receiver and a receiving method, wherein the receiver comprises a tap delay module, a de-spread module, a channel estimation module, a merging module and a judgment module; the tap delay module is used for delaying the received signal and is used as the input of the de-spread module; the de-spreading module de-spreads the received signals after tap delay and takes the de-spread signals as the input of the channel estimation module; the channel estimation module calculates a signal subspace of the despread signal through a fast approximate power iteration subspace tracking algorithm, and the signal subspace is used as a weight coefficient of each interdigital; the combining module combines the result of multiplying the despread signals on each interdigital by the weight coefficient, and the result is used as the input of the judging module; and the judgment module performs sampling judgment on the combined signal to obtain symbol data. The invention does not need pilot signals, and can extract channel parameters from received signals through processing; the invention is based on snapshot processing, has low algorithm complexity and is easy to realize hardware.

Description

Adaptive Rake receiver and receiving method

Technical Field

The invention relates to the technical field of spread spectrum communication, in particular to a self-adaptive Rake receiver and a receiving method.

Background

In the field of wireless communication, multipath refers to the phenomenon of propagation of radio signals from a transmitting antenna to a receiving antenna through multiple paths, and multipath propagation is caused by scattering of radio waves by the atmosphere, reflection and refraction of radio waves by an ionosphere, and reflection of radio waves by surface objects such as mountains and buildings. Multipath causes fading of the signal, which is a multiplicative interference that severely affects the performance of the communication system and must be overcome accordingly. The existing effective anti-fading measures are diversity reception, wherein the diversity reception is to combine and concentrate a plurality of composite signals with different fading conditions received dispersedly at a receiving end in a certain way, so that the signal-to-noise ratio of the total received signals is improved, and the fading influence is reduced; the diversity mode has space diversity, frequency diversity, angle diversity, polarization diversity, time diversity, etc. the Rake receiver is one time diversity receiving technology and has excellent effect of resisting multipath fading.

The first CDMA experiment was performed in 1989 by QUALCOMM corporation of america, which verified that the DS spread spectrum signal waveform is very suitable for the transmission of multipath channels, and the key CDMA techniques such as Rake receiver, power control and soft handoff. The commercial operation of the narrow-band CDMA IS-95 IS promoted in 1996, so that the RAKE receiver IS industrialized, and meanwhile, the great development of the Rake receiving technology IS promoted.

The 4-interdigital Rake receiver adopted in the prior engineering has a simple structure but limited performance; the existing Rake receiver with higher performance has higher algorithm complexity and is not beneficial to engineering realization.

Disclosure of Invention

The invention aims to eliminate multipath interference in a spread spectrum communication system and provides a self-adaptive Rake receiver and a receiving method.

The technical scheme for realizing the purpose of the invention is as follows:

a self-adaptive Rake receiver comprises a tap time delay module, a de-spread module, a channel estimation module, a combination module and a judgment module;

the tap delay module is used for delaying the received signal and is used as the input of the de-spread module;

the de-spread module is used for de-spreading the received signals subjected to tap delay and used as the input of the channel estimation module;

the channel estimation module calculates a signal subspace of the despread signal through a fast approximate power iteration subspace tracking algorithm, and takes the signal subspace as a weight coefficient of each interdigital;

the merging module merges the result of multiplying the despread signal on each interdigital by the weight coefficient and takes the merged result as the input of the judgment module;

and the judgment module is used for sampling and judging the combined signals to obtain symbol data.

An adaptive Rake receiving method, comprising the steps of:

step 1: carrying out tap time delay on a received signal;

step 2: de-spreading the signal after tap delay;

and step 3: the despread signals are used as the input of a fast approximate power iteration subspace tracking algorithm to obtain the weight coefficient of each interdigital;

and 4, step 4: multiplying the despread signals of all the fingers by the weight coefficients of all the fingers and combining;

and 5: and sampling and judging the combined signals to obtain symbol data.

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

(1) the invention does not need pilot signals, and can extract channel parameters from received signals through processing; (2) the method is based on snapshot processing, has low algorithm complexity and is easy to realize hardware; (3) applicable to any Quadrature Amplitude Modulation (QAM) modulated signal; (4) the adaptability to multipath channels is strong, and the problem of channels with a large number of multipath can be solved; the multipath phenomenon is effectively utilized, and the received signal gain is improved; (5) after the Rake receiver in the invention is adopted, the original receiver system does not need a special code synchronization module, and more hardware resources are saved.

Drawings

Fig. 1 is a block diagram of an adaptive Rake receiver according to the present invention.

Fig. 2 is a circuit diagram of an adaptive Rake receiver according to the present invention.

Fig. 3 is a flowchart of an adaptive Rake receiving method according to the present invention.

Fig. 4 is a schematic diagram illustrating comparison of error rate performance between a Rake receiver based on a FAPI algorithm and a Rake receiver based on an SVD algorithm in the embodiment of the present invention.

Fig. 5 is a diagram illustrating the performance of the new Rake receiver with 4 to 12 fingers according to an embodiment of the present invention.

Fig. 6 is a diagram illustrating the variation of the ber with the increase of the number of multipaths in the embodiment of the present invention.

Detailed Description

With reference to fig. 1 and fig. 2, an adaptive Rake receiver includes a tap delay module, a despreading module, a channel estimation module, a combining module, and a decision module;

the tap delay module is used for delaying the received signal and is used as the input of the de-spread module;

the de-spread module is used for de-spreading the received signals subjected to tap delay and used as the input of the channel estimation module;

the channel estimation module calculates a signal subspace of the despread signal through a fast approximate power iteration subspace tracking algorithm, and takes the signal subspace as a weight coefficient of each interdigital;

the merging module merges the result of multiplying the despread signal on each interdigital by the weight coefficient and takes the merged result as the input of the judgment module;

and the judgment module is used for sampling and judging the combined signals to obtain symbol data.

With reference to fig. 3, the adaptive Rake receiving method of the present invention includes the following steps:

step 1: carrying out tap time delay on a received signal; the specific process is as follows:

the noise-free tapped delay line channel model is represented by:

wherein r is_l(t) is the received signal, h_l(t, n) is a weight coefficient of the delay line, s_l(t) is the transmitted signal, W is the bandwidth of the transmitted signal, L is the length of the tapped delay line model,

T_ma multi-path delay;

suppose that the information sequence of user j is b_jJ, where J is 1.. J, J is the total number of users, and the spreading sequence of user J is C_jThen the spread signal is

s_j＝b_jC_j

Wherein s is_jA transmit signal for user j;

after the transmission signal of the user j passes through the channel, the receiving signal of the user j is obtained:

the received signal r (t) is the sum of the received signals of all users:

assuming that the Rake receiver is composed of K +1 fingers and K ═ 2L, the received signal is subjected to tap delay to obtain a tap-delayed signal z (t):

step 2: de-spreading the signal after tap delay; the specific process is as follows:

step 2-1, forming a matrix X with K +1 rows and P columns by P pieces of Z (t)_K+1,P(t)：

Wherein, P is the spread spectrum gain;

the target user is user i, i belongs to [1, J ], and the above formula is written as:

wherein

Step 2-2, adding X_K+1,P(t) despreading to obtain a despread signal y (t):

wherein, C_iSpreading sequence for user i, N (t) for other users and channelsThe noise of (2).

And step 3: the despread signals are used as the input of a fast approximate power iteration subspace tracking algorithm to obtain the weight coefficient of each interdigital; the method specifically comprises the following steps:

calculating the weight coefficient of each interdigital by adopting a fast approximate power iteration subspace tracking algorithm

Wherein the iteration coefficient theta (t) is a matrix of (K +1) x 1 dimensions,

the weight coefficient of each interdigital at the last moment;

first, three intermediate variables W (t), V (t), and g (t) are initialized:

W(t)＝h^H(t-1)y(t)

V(t)＝D(t-1)W(t)

wherein β is a parameter of the window function, β is more than 0 and less than or equal to 1, β equals 1, which represents a rectangular window, and ε (t) is | | | y (t) |²-||W(t)||²The square root of (i), i.e.

ε²(t)＝||y(t)||²-||W(t)||²

Wherein, | y (t) | represents performing modulo operation on y (t);

the intermediate variables τ (t), η (t) and d (t) are calculated as follows:

η(t)＝1-τ(t)g²(t)

wherein the matrices W '(t), V' (t) and δ (t) are calculated as follows:

W′(t)＝η(t)W(t)+τ(t)g(t)

V′(t)＝Z(t-1)W′(t)

updating the weight coefficient:

wherein the intermediate variable e' (t) is

And 4, step 4: multiplying and combining the despread signals of each finger with the weight coefficient of each finger to obtain combined signals O (t):

wherein the content of the first and second substances,

is the weight coefficient of each finger.

And 5: and extracting one point of the combined signal to carry out symbol decision to obtain symbol data.

The present invention is further illustrated by the following specific examples.

Examples

The simulation parameters of the receiver in this embodiment are shown in the following table:

TABLE 1 simulation parameters

When the number of multipaths is 20 and the Rake receiver cross index is 10, the performance of the Rake receiver based on the fast power iteration subspace tracking algorithm (FAPI algorithm) and the Rake receiver based on the SVD algorithm are compared as shown in fig. 4. As can be seen from fig. 4, for the blind adaptive Rake receiver, the FAPI algorithm has a lower error rate than the SVD algorithm. This is because the FAPI algorithm can use the data of each frame and adjust the weight coefficients better and better by using the data of each frame, while the SVD algorithm only uses the data of the current frame and does not use the previous results, so the FAPI algorithm has better performance.

When the multipath number is 20, the fork index of the novel Rake receiver is from 4 to 12, and the influence of different fork numbers on the performance of the novel Rake receiver is shown in figure 5. As can be seen from fig. 5, as the cross index increases, the error rate performance of the novel Rake receiver improves; and when the fork index is between 9 and 12, the bit error rates are almost the same, which also verifies that K ≈ 2L is a reasonable design criterion.

When the new Rake receiver has a fork index of 10, a signal-to-noise ratio of a transmitted signal is-5 dB, and the number of multipaths is changed from 1 to 451, the error rate performance of the new Rake receiver is shown in fig. 6, wherein the abscissa represents the number of multipaths, and the ordinate represents the error rate. It can be seen that the bit error rate is 10 no matter the number of multipaths^-5Nearby; therefore, the novel Rake receiver based on the FAPI algorithm is suitable for various multipath numbers, and the error rate performance of the novel Rake receiver cannot be deteriorated along with the increase of the multipath numbers.

Claims (1)

1. An adaptive Rake receiving method, comprising the steps of:

step 1: carrying out tap time delay on a received signal; the method specifically comprises the following steps:

the noise-free tapped delay line channel model is represented by:

wherein r is_l(t) is the received signal, h_l(t, n) is a weight coefficient of the delay line, s_l(t) is the transmitted signal, W is the bandwidth of the transmitted signal, L is the length of the tapped delay line model,

T_ma multi-path delay;

suppose that the information sequence of user j is b_jJ, where J is 1.. J, J is the total number of users, and the spreading sequence of user J is C_jThen the spread signal is

s_j＝b_jC_j

Wherein s is_jA transmit signal for user j;

after the transmission signal of the user j passes through the channel, the receiving signal of the user j is obtained:

the received signal r (t) is the sum of the received signals of all users:

assuming that the Rake receiver has K +1 fingers and K ═ 2L, the received signal is subjected to tap delay to obtain a tap-delayed signal z (t):

step 2: de-spreading the signal after tap delay; the method specifically comprises the following steps:

step 2-1, forming a matrix X with K +1 rows and P columns by P pieces of Z (t)_K+1,P(t)：

Wherein, P is the spread spectrum gain;

the target user is user i, i belongs to [1, J ], and the above formula is written as:

wherein

Step 2-2, adding X_K+1,P(t) despreading to obtain a despread signal y (t):

wherein, C_iThe spreading sequence for user i, n (t) the noise from other users and channels;

and step 3: the despread signals are used as the input of a fast approximate power iteration subspace tracking algorithm to obtain the weight coefficient of each interdigital; the method specifically comprises the following steps:

calculating the weight coefficient of each interdigital by adopting a fast approximate power iteration subspace tracking algorithm

Wherein the iteration coefficient theta (t) is a matrix of (K +1) x 1 dimensions,

the weight coefficient of each interdigital at the last moment;

first, three intermediate variables W (t), V (t), and g (t) are initialized:

W(t)＝h^H(t-1)y(t)

V(t)＝D(t-1)W(t)

wherein β is a parameter of the window function, β is more than 0 and less than or equal to 1, β equals 1, which represents a rectangular window, and ε (t) is | | | y (t) |²-||W(t)||²The square root of (i), i.e.

ε²(t)＝||y(t)||²-||W(t)||²

Wherein, | y (t) | represents performing modulo operation on y (t);

the intermediate variables τ (t), η (t) and d (t) are calculated as follows:

η(t)＝1-τ(t)g²(t)

wherein the matrices W '(t), V' (t) and δ (t) are calculated as follows:

W′(t)＝η(t)W(t)+τ(t)g(t)

V′(t)＝Z(t-1)W′(t)

updating the weight coefficient:

wherein the intermediate variable e' (t) is

And 4, step 4: multiplying and combining the despread signals of each finger with the weight coefficient of each finger to obtain combined signals O (t):

wherein the content of the first and second substances,

is the weight coefficient of each finger;

and 5: and extracting a point from the combined signal O (t) for symbol decision to obtain symbol data.

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