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 an adaptive Rake receiver and a receiving method.

Background technique

In the field of wireless communication, multipath refers to the propagation phenomenon of radio signals from the transmitting antenna to the receiving antenna through multiple paths, the scattering of the radio waves by the atmosphere, the reflection and refraction of the radio waves by the ionosphere, and the effect of the mountains, buildings and other surface objects on the radio waves. Reflections cause multipath propagation. Multipath will cause signal fading. Fading, as a kind of multiplicative interference, seriously affects the performance of the communication system, so corresponding measures must be taken to overcome it. The existing more effective anti-fading measure is to use diversity reception. Diversity reception is to disperse and receive several synthesized signals with different fading conditions at the receiving end, and then combine them in a certain way to make the total received signal. The noise ratio is improved, and the influence of fading is reduced; the diversity methods include space diversity, frequency diversity, angle diversity, polarization diversity, time diversity, etc. Rake receiver is a time diversity receiving technology, which has good resistance to multipath fading. Effect.

In 1989, QUALCOMM Corporation of the United States conducted the first CDMA experiment, which verified that the DS spread spectrum signal waveform is very suitable for the transmission of multipath channels, and the key technologies of CDMA such as Rake receiver, power control and soft handover. In 1996, it promoted the commercial operation of narrowband CDMA IS-95, industrialized the RAKE receiver, and also promoted the rapid development of Rake reception technology.

Although the structure of the 4-interdigital Rake receiver used in the current project is simple, its performance is limited; and the existing Rake receiver with higher performance has higher algorithm complexity, which is not conducive to engineering implementation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to eliminate the multipath interference in the spread spectrum communication system, and to provide an adaptive Rake receiver and a receiving method.

The technical scheme that realizes the object of the present invention is:

An adaptive Rake receiver, comprising a tap delay module, a despreading module, a channel estimation module, a combining module and a decision module;

The tap delay module is used to delay the received signal as the input of the despreading module;

The despreading module performs despreading processing on the received signal that has undergone the tap delay as the input of the channel estimation module;

The channel estimation module calculates the signal subspace of the despread signal through a fast approximate power iterative subspace tracking algorithm, and uses the signal subspace as the weight coefficient of each finger;

The combining module combines the result of multiplying the despread signal and the weight coefficient on each finger as the input of the decision module;

The judgment module performs sampling judgment on the combined signal to obtain symbol data.

An adaptive Rake receiving method, comprising the following steps:

Step 1: Tap and delay the received signal;

Step 2: despread the tap-delayed signal;

Step 3: The despreading signal is used as the input of the fast approximate power iterative subspace tracking algorithm to obtain the weight coefficient of each finger;

Step 4: Multiply the despread signal of each finger by the weight coefficient of each finger and combine them;

Step 5: Perform sampling judgment on the combined signal to obtain symbol data.

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

(1) The present invention does not require a pilot signal, and can extract channel parameters from the received signal through processing; (2) The present invention is based on snapshot processing, with low algorithm complexity and easy hardware implementation; (3) Applicable to any orthogonal Amplitude modulation (QAM) modulated signal; (4) Strong adaptability to multi-path channels, can solve a large number of multi-path channels; effectively use multi-path phenomenon to improve the received signal gain; (5) After using the Rake receiver in the invention , the original receiver system does not need a special code synchronization module, saving more hardware resources.

Description of drawings

FIG. 1 is a structural diagram of an adaptive Rake receiver of the present invention.

FIG. 2 is a circuit diagram of an adaptive Rake receiver of the present invention.

FIG. 3 is a flowchart of the adaptive Rake receiving method of the present invention.

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

FIG. 5 is a schematic diagram of the bit error rate performance of the new Rake receiver when there are 4 to 12 cross indices in an embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating the variation of the bit error rate with the increase of the number of multipaths in an embodiment of the present invention.

Detailed ways

1 and 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 to delay the received signal as the input of the despreading module;

The despreading module performs despreading processing on the received signal that has undergone the tap delay as the input of the channel estimation module;

The channel estimation module calculates the signal subspace of the despread signal through a fast approximate power iterative subspace tracking algorithm, and uses the signal subspace as the weight coefficient of each finger;

The combining module combines the result of multiplying the despread signal and the weight coefficient on each finger as the input of the decision module;

The judgment module performs sampling judgment on the combined signal to obtain symbol data.

In conjunction with Fig. 3, the adaptive Rake receiving method of the present invention comprises the following steps:

Step 1: Tap and delay the received signal; the specific process is:

The noise-free tapped delay line channel model is expressed as:

T_m为多径延时；where r _l (t) is the received signal, h _l (t,n) is the delay line weight coefficient, s _l (t) is the transmitted signal, W is the bandwidth of the transmitted signal, and L is the tapped delay line the length of the model,

T _m is the multipath delay;

Assuming that the information sequence of user j is b _j , where j=1...J, J is the total number of users, and the spreading sequence of user j is C _j , the spread spectrum signal is

s _j =b _j C _j

where s _j is the signal sent by user j;

After the transmitted signal of user j passes through the channel, the received signal of user j is obtained:

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

Assuming that the Rake receiver consists of K+1 interdigitated fingers, and K=2L, the received signal is tap-delayed to obtain the tap-delayed signal Z(t):

Step 2: Despread the tap-delayed signal; the specific process is:

Step 2-1. A matrix X _K+1,P (t) with K+1 rows and P columns is formed by P Z(t):

Among them, P is the spread spectrum gain;

The target user is user i, i∈[1,J], the above formula is written as:

in

Step 2-2, despread X _K+1,P (t) to obtain the despread signal y(t):

Among them, C _i is the spreading sequence of user i, and N(t) is the noise from other users and channels.

Step 3: The despreading signal is used as the input of the fast approximate power iterative subspace tracking algorithm to obtain the weight coefficient of each finger; the specific steps include:

Using fast approximate power iterative subspace tracking algorithm to calculate the weight coefficient of each finger

为上一时刻各叉指的权重系数；where the iteration coefficient Θ(t) is a (K+1)×1-dimensional matrix,

is the weight coefficient of each finger at the previous moment;

First initialize three intermediate variables W(t), V(t) and g(t):

W(t)=h ^H (t-1)y(t)

V(t)=D(t-1)W(t)

where β is the parameter of the window function, 0<β≤1, β=1 represents a rectangular window, ε(t) is the square root of ||y(t)|| ² -||W(t)|| ² , which is

ε ² (t)=||y(t)|| ² -||W(t)|| ²

Among them, ||y(t)|| represents the modulo operation on y(t);

Calculate the intermediate variables τ(t), η(t) and D(t) as follows:

η(t)=1-τ(t)g ² (t)

where 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)

Update the weight coefficients:

where the intermediate variable e'(t) is

Step 4: Multiply the despread signal of each finger by the weight coefficient of each finger and combine them to obtain the combined signal O(t):

为各叉指的权重系数。in,

is the weight coefficient of each finger.

Step 5: Extracting a point from the combined signal for symbol decision to obtain symbol data.

The present invention will be further described below with reference to specific embodiments.

Example

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

Table 1 Simulation parameters

When the multipath number is 20 and the cross index of the Rake receiver is 10, the performance comparison between the Rake receiver based on the fast power iterative subspace tracking algorithm (FAPI algorithm) and the Rake receiver based on the SVD algorithm is shown in Figure 4. As can be seen from Figure 4, for the blind adaptive Rake receiver, the FAPI algorithm has a lower bit error rate than the SVD algorithm. This is because the FAPI algorithm can use the data of each frame and use the data of each frame to adjust the weight coefficients better and better, while the SVD algorithm only uses the data of the current frame and does not use the previous results, so The performance of the FAPI algorithm is better.

When the multipath number is 20, the cross index of the new Rake receiver is from 4 to 12, and the effect of different cross index on the performance of the new Rake receiver is shown in Figure 5. As can be seen from Figure 5, the bit error rate performance of the new Rake receiver is improved with the increase of the cross index; and when the cross index is between 9 and 12, the bit error rate is almost the same, which also verifies that K≈2L is a reasonable design criterion.

When the cross index of the new Rake receiver is 10, the signal-to-noise ratio of the transmitted signal is -5dB, and the number of multipaths changes from 1 to 451, the BER performance of the new Rake receiver is shown in Figure 6, where the abscissa is the number of multipaths , and the ordinate is the bit error rate. It can be seen that regardless of the number of multipaths, the bit error rate is around 10 ^-5 ; therefore, the new Rake receiver based on the FAPI algorithm is suitable for various multipath numbers, and its bit error rate performance does not vary with the multipath number. increase and worsen.

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,

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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