CN101814931B - Doppler frequency shift estimation and compensation method in TD-SCDMA (Time Division-Synchronization Code Division Multiple Access) system - Google Patents

Abstract

A method for estimating and compensating Doppler frequency shift in a TD-SCDMA system, comprising: after a mobile terminal receives a time slot containing data of the mobile terminal, by comparing the channel estimation sequence of the current time slot with a comparison time slot The phase difference obtains the Doppler frequency offset value of the received signal in the current time slot. And the compensation method of Doppler frequency shift in the TD-SCDMA system, comprises: after the mobile terminal receives the time slot that contains this mobile terminal data, obtains by comparing the phase difference of the channel estimation sequence of current time slot and a comparison time slot The Doppler frequency offset value of the received signal in the current time slot is combined with the joint detection, and the above-mentioned received signal is corrected in the joint detection. The present invention improves the accuracy of channel estimation, eliminates the influence of Doppler frequency shift on correct reception and demodulation, reduces the bit error rate, thereby improving system performance, and is especially suitable for TD-SCDMA mobile terminals under high-speed motion scene.

Description

Doppler Frequency Shift Estimation and Compensation Method in TD-SCDMA System

technical field

The present invention relates to mobile communication technology, in particular to a method for estimating and compensating Doppler frequency shift in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) system.

Background technique

TD-SCDMA (Time Division Synchronous Code Division Multiple Access) mobile communication system is a third-generation mobile communication system based on time division duplex and code division multiple access. It has the characteristics of flexible uplink and downlink configuration, low code rate, and high spectrum utilization.

As shown in Figure 1, in the TD-SCDMA system, the basic unit of data transmission is a radio frame. 7 regular time slots (TS0~TS6) and 3 special time slots (downlink synchronization code segment DwPTS, guard interval GP and uplink synchronization code segment UpPTS) form a subframe, and two subframes (subframe #1 and subframe #2 ) constitute a wireless frame with a duration of 10ms. The data of the mobile terminal user is transmitted in regular time slots. A regular time slot has a duration of 675 μs and consists of 864 chips (chips), and each chip has a duration of 0.78125 μs. These chips are divided into four parts: namely two data segments (352 chips each), a training code segment (midamble) (144 chips) and a 16-chip length guard interval GP; each data segment consists of The data of multiple mobile terminal code channels to be transmitted is formed by spreading, scrambling, and aliasing; the training code segment is formed by shifting the basic midamble code allocated by the system, and its function is used as a training sequence for channel estimation.

According to the current TD-SCDMA technology, it supports a maximum mobile speed of 120km/h for mobile terminals. However, in real life, high-speed trains with a speed of more than 250 kilometers per hour have appeared, and a high-speed rail network with a higher speed of 300km/h to 500km/h will spread all over the country in the near future, which poses a challenge to the existing TD wireless technology. a big challenge. When the mobile terminal is in a state of high-speed motion, the Doppler frequency shift suffered by the wireless signal transmitted in space will become very serious, and as the carrier frequency increases, the Doppler frequency shift increases, and the Doppler frequency shift It is directly proportional to the carrier frequency and the speed of the mobile terminal, namely:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; RF</span>}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; v</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}$

Among them, f _d represents the Doppler frequency offset value, f _RF represents the carrier frequency, v represents the speed of mobile terminal movement, c represents the speed of light, which is equal to 3*10 ⁸ m/s, θ represents the direction of mobile terminal movement and the incident radio wave The angle between mobile terminals. On the mobile terminal side, the Doppler frequency shift effect causes a deviation between the frequency of the local demodulated carrier and the signal actually received by the mobile terminal, and this frequency deviation accumulates over time, causing the demodulated symbols to differ from the standard The modulation symbols of , are shifted (distorted) in phase. Especially for the TD system, because it is a low code rate system, the duration of each chip is longer, so the phase distortion of the demodulated symbol accumulated on each chip becomes larger, which will greatly affect Correct reception and demodulation of mobile terminals.

On the other hand, the mobile terminal of TD-SCDMA generally adopts the joint detection technology when performing receiving demodulation. Joint detection uses the prior information in multiple access interference to regard the separation of all mobile terminal signals as a unified process, and converts the received aliased chip signals into demodulated symbols for each mobile terminal in one step , thereby reducing the mutual interference between multiple mobile terminals and increasing the system capacity. However, the effectiveness of joint detection technology is based on accurate channel estimation. The implementation of existing TD channel estimation uses Steiner-based low-cost fast Fourier transform FFT/fast Fourier inverse transform IFFT plus subsequent Detection Threshold method for removing noise taps. This technique is described in Steiner B.BAIEP. "Low cost channel estimation in the uplink receiver of CDMAmobile radio systems" Frequenz 1993, 47(12): 292-298 and Kang Shaoli et al. "Improvement of Low Cost Channel Estimation Method in TD-SCDMA System "Journal of Communications, Volume 23, Issue 10, 125-130 has detailed explanations. This channel estimation technology is based on time slots, that is, the channel is considered to be fixed within a time slot; but in fact, the fading experienced by the mobile terminal when it is moving is modulated by the Doppler frequency shift, that is, In fact, the channel is time-varying within a time slot, and the channel value estimated by the existing estimation method is actually the average value of the channel within a time slot period. Therefore, there is an error between the estimated channel obtained by this estimation method and the real channel, especially when the mobile terminal is moving at a high speed, the error is very large. If the estimated channel with error is brought into the joint detection In the matrix, it will cause repeated superposition and amplification of interference, thus affecting the correct decoding of data.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for estimating and compensating the Doppler frequency shift in the TD-SCDMA system, so as to overcome the adverse effect on the correct reception of data due to the movement of the mobile terminal.

In order to solve the above problems, the present invention provides a method for estimating the Doppler frequency offset value in a Time Division Synchronous Code Division Multiple Access TD-SCDMA system, comprising:

After receiving the time slot containing the data of the mobile terminal, the mobile terminal obtains the Doppler frequency offset value of the received signal of the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of a compared time slot.

Further, the above method can also have the following features:

The mobile terminal stores preset n range intervals of the absolute value of the Doppler frequency offset value and a comparison time slot corresponding to each range interval, wherein the n range intervals cover the The absolute value of all possible Doppler frequency offset values, n≥1;

The mobile terminal obtains the received signal Doppler frequency offset value of the mobile terminal by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot:

Judging which range interval the absolute value of the predicted value of the Doppler frequency offset value of the current time slot is in;

Determining a corresponding comparison time slot based on the determined range interval;

By comparing the phase difference between the current time slot and the compared time slot on the corresponding path, the phase offset of the received signal caused by the Doppler frequency shift in the length of each chip of the time slot is estimated.

Further, the above method can also have the following features:

The pre-judgment value of the Doppler frequency offset value of the current time slot is the Doppler frequency offset value of the previous processing time slot of the mobile terminal;

The Doppler frequency offset value of the last processing time slot of the mobile terminal refers to: the estimated value of the mobile terminal in the time slot stored in the mobile terminal when processing the last time slot containing the data of the mobile terminal The Doppler frequency offset value on the strongest path of the mobile terminal, or the maximum Doppler frequency offset value of the mobile terminal in each path of the time slot, or the weighted sum of the above two items.

Further, the above method can also have the following features:

The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes:

Intercepting the training sequence of the comparison time slot, performing channel estimation, and estimating the average channel impulse response of each mobile terminal in the comparison time slot;

Intercept the training sequence of the current time slot, perform channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot;

Carry out the phase subtraction of the mobile terminal part of the average channel impulse response of the current time slot and the comparison time slot according to the corresponding path, and then divide by the chip interval length between the above two time slots to obtain the result of the Doppler frequency shift. The received signal phase offset of the mobile terminal on each path and each chip.

Further, the above method can also have the following features:

When n=2, the range interval includes: A=[0, X), B=[X, +∞), and the comparison time slot corresponding to the range interval A is the current time slot in the previous subframe For time slots with the same time slot number, the comparison time slot corresponding to the range interval B is the TS0 time slot in the subframe where the current time slot is located, where the value of X is determined according to engineering practice.

Further, the above method can also have the following features:

The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes:

When the comparison time slot is the TS0 time slot in this frame, intercept the training sequence of the TS0 time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the comparison time slot; when the comparison When the time slot is the same time slot as the current time slot in the previous frame, the average channel impulse response of the comparison time slot is obtained according to the saved record of the mobile terminal;

Intercept the training sequence of the current time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot period;

The mobile terminal phase-subtracts the channel estimate value of the strongest path in the current time slot and the comparison time slot, and then divides by the chip interval length between the current time slot and the comparison time slot to obtain the Doppler frequency The phase offset of the received signal of the mobile terminal on each chip caused by the shift.

The present invention also provides a method for compensating Doppler frequency shift in a time division synchronous code division multiple access TD-SCDMA system, comprising:

After receiving the time slot containing the data of the mobile terminal, the mobile terminal obtains the Doppler frequency offset value of the received signal of the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of a compared time slot, and combines the joint detection , correcting the received signal in joint detection.

Further, the above method can also have the following features:

The mobile terminal stores preset n range intervals of the absolute value of the Doppler frequency offset value and a comparison time slot corresponding to each range interval, wherein the n range intervals cover the The absolute value of all possible Doppler frequency offset values, n≥1;

The mobile terminal obtains the received signal Doppler frequency offset value of the mobile terminal by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot:

Judging which range interval the absolute value of the predicted value of the Doppler frequency offset value of the current time slot is in;

Determining a corresponding comparison time slot based on the determined range interval;

By comparing the phase difference between the current time slot and the compared time slot on the corresponding path, the phase offset of the received signal caused by the Doppler frequency shift in the length of each chip of the time slot is estimated.

Further, the above method can also have the following features:

The pre-judgment value of the Doppler frequency offset value of the current time slot is the Doppler frequency offset value of the previous processing time slot of the mobile terminal;

The Doppler frequency offset value of the last processing time slot of the mobile terminal refers to: the estimated value of the mobile terminal in the time slot stored in the mobile terminal when processing the last time slot containing the data of the mobile terminal The Doppler frequency offset value on the strongest path of the mobile terminal, or the maximum Doppler frequency offset value of the mobile terminal in each path of the time slot, or the weighted sum of the above two items.

Further, the above method can also have the following features:

The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes:

Intercepting the training sequence of the comparison time slot, performing channel estimation, and estimating the average channel impulse response of each mobile terminal in the comparison time slot;

Intercept the training sequence of the current time slot, perform channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot;

Carry out the phase subtraction of the mobile terminal part of the average channel impulse response of the current time slot and the comparison time slot according to the corresponding path, and then divide by the chip interval length between the above two time slots to obtain the result of the Doppler frequency shift. The received signal phase offset of the mobile terminal on each path and each chip.

Further, the above method can also have the following features:

The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes:

When the comparison time slot is the TS0 time slot in this frame, intercept the training sequence of the TS0 time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the comparison time slot; when the comparison When the time slot is the same time slot as the current time slot in the previous frame, the average channel impulse response of the comparison time slot is obtained according to the saved record of the mobile terminal;

Intercept the training sequence of the current time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot period;

The mobile terminal phase-subtracts the channel estimate value of the strongest path in the current time slot and the comparison time slot, and then divides by the chip interval length between the current time slot and the comparison time slot to obtain the Doppler frequency The phase offset of the received signal of the mobile terminal on each chip caused by the shift.

Further, the above method can also have the following features:

The correction of the received signal of each mobile terminal in the joint detection specifically includes:

Compensating the average channel impulse response of each mobile terminal in the current time slot period after multiplying the obtained phase offset by the spreading factor SF;

Multiplying the spreading code, channel code and scrambling code of each mobile terminal to obtain the composite spreading code of each mobile terminal respectively;

Using the compensated average channel impulse response and the composite spreading codes of each mobile terminal to construct a joint detection matrix A, and use the joint detection matrix A to perform joint detection on the data segment in the current time slot to obtain the corrected demodulation symbol.

Further, the above method may also include:

Using the obtained demodulation symbols to compare the phases of the standard modulation symbols in the constellation diagram, the obtained phase difference is smoothed to the phase frequency offset value and/or the largest phase frequency offset value of each mobile terminal, and the processed The final result is saved as the Doppler frequency offset value of this time slot.

Compared with the prior art, the present invention improves the accuracy of channel estimation, eliminates the influence of Doppler frequency shift on correct reception and demodulation, reduces the bit error rate, thereby improving system performance, and is especially suitable for TD- The scene of SCDMA mobile terminal moving at high speed. Adjust the accuracy of estimating the Doppler frequency offset by selecting an appropriate comparison time slot, and estimate the Doppler frequency offset by calculating the phase difference between the comparison time slot and the current time slot, and in a preferred case, the mobile terminal Only the phase shift of the received signal caused by the Doppler frequency shift on the strongest path (main path) is estimated and compensated, which reduces the complexity of the method implementation; in addition, the mobile terminal can also store and compare the time slot Channel estimation sequence to further reduce method complexity and system overhead.

Description of drawings

FIG. 1 is a schematic diagram of a frame structure of TD-SCDMA in the prior art;

FIG. 2 is a schematic diagram of phase shifts caused by Doppler frequency shift modulation of each path of a wireless channel in a conventional time slot in an embodiment of the present invention;

Fig. 3 is the flowchart of the method in the embodiment of the present invention;

4 is a schematic diagram of a Steiner channel estimation sequence and a channel window corresponding to each mobile terminal in an embodiment of the present invention;

Fig. 5 is the structural diagram of joint detection A matrix in the embodiment of the present invention;

Fig. 6 is the system simulation result in the embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be described in more detail below with reference to the drawings and embodiments.

For a TD time slot propagating on a wireless channel, it will be convolutionally modulated by the impulse response of the wireless channel. The impulse response consists of two parts: 1. Fading caused by multipath effects: Since the duration (675μs) of a TD time slot is much smaller than the coherence time of the spatial channel, this part can be considered as an approximate Fixed; 2, phase shift caused by Doppler effect The offset 2πf _d ^k t changes linearly with time within the duration of a time slot, as shown in Figure 2, where c _i represents the i-th chip on the time slot, and each oblique line represents the phase on the corresponding path Offset (since the included angles between each radial direction and the moving direction of the mobile terminal are different, so the slope of each slanted line, that is, f _d ^k is also different). Expand the spatial channel of a mobile terminal in a time slot length by chips sequentially, and get:

$\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; cof</span>}}_{\mathrm{<span\; class="notranslate">\; fading</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="f\; d"\; filenames="H2009100065791E00031.png,H2009100065791E00041.png"\; state="\{\{state\}\}">f</figure-callout></span><figure-callout\; id="1"\; label="f\; d"\; filenames="H2009100065791E00031.png,H2009100065791E00041.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}^{\mathrm{<span\; class="notranslate">d</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; cof</span>}}_{\mathrm{<span\; class="notranslate">\; fading</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="f\; d"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">f</figure-callout></span><figure-callout\; id="2"\; label="f\; d"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}^{\mathrm{<span\; class="notranslate">d</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; co</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; fading</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}& \\ <span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span>& <span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 864</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; cof</span>}}_{\mathrm{<span\; class="notranslate">\; fading</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 864</span>}}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; c</span>}{\mathrm{<span\; class="notranslate">\; of</span>}}_{\mathrm{<span\; class="notranslate">\; faading</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="f\; d"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">f</figure-callout></span><figure-callout\; id="2"\; label="f\; d"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}^{\mathrm{<span\; class="notranslate">d</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 864</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; co</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; fading</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100065791E00031.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 864</span>}}}& \end{array}\right.$

Among them, h(chip_i) represents the channel impulse response on the i-th chip (i ranges from 1 to 864), cof _{fading_k} represents the fading coefficient of the k-th path, Indicates the phase offset on the i-th chip caused by the Doppler frequency shift f _d ^k on the k-th path.

Hereinafter, the phase offset of the received signal per chip caused by the Doppler frequency shift is referred to as the Doppler frequency offset value for short.

Before performing the following steps, the following settings need to be made to the terminal: the terminal stores n (n≥1) preset range intervals of absolute values of Doppler frequency offset values, and the n range intervals cover The absolute value of all possible Doppler frequency offset values; in addition, it also saves a comparison time slot slot[i] corresponding to each range interval (the value of i is 1~n), That is, slot[i] corresponds to the i-th range interval, and the corresponding relationship can be: as the range interval gradually approaches infinity, the comparison time slot corresponding to each range interval gradually approaches the current time slot, which can be understood as falling The greater the absolute value of the Doppler frequency offset value within a certain range interval, the closer the corresponding comparison time slot is to the current time slot. Among them, the comparison time slot is a time slot before the current time slot, which may be a time slot whose time slot number is smaller than the current time slot in the subframe where the current time slot is located, or may be a time slot before the current time slot. A certain time slot in a certain subframe of .

Preferably, set n=2, that is, set the range intervals of the absolute value of the Doppler frequency offset value as follows: interval A=[0, X), interval B=[X, +∞], and the value of X can be determined by engineering Actually OK. The comparison time slot corresponding to interval A is the time slot having the same time slot number as the current time slot in the previous subframe; the comparison time slot corresponding to interval B is the TS0 time slot in the subframe where the current time slot is located. The reason why these two time slots are used as comparison time slots is that there is always a training sequence in the training code segment of these two time slots, so that it can be ensured that subsequent channel estimation is practicable. Certainly, other arbitrary time slots before the current time slot can also be selected for the comparison time slot, such as the previous time slot of the current time slot, but it is necessary to ensure that there is a training sequence in the training code segment of the comparison time slot.

对移动终端正确接收、解调符号产生的影响，包括：The present invention eliminates the Doppler frequency shift factor through several steps

The impact on the correct reception and demodulation of symbols by mobile terminals, including:

(1) predicting which range interval the absolute value of the Doppler frequency offset value on the current time slot is in;

(2) Estimate the phase offset of the received signal caused by the Doppler frequency shift on each chip length by comparing the phase difference between the current time slot and the corresponding comparison time slot of the range interval on the corresponding path;

(3) According to the phase offset and the existing joint detection technology, the phase offset of the received symbols caused by the Doppler frequency shift is eliminated by modifying the A matrix in the joint detection.

(4) When demodulating the received symbols, finely adjust the previously estimated Doppler frequency offset while demodulating.

After performing steps (1) and (2), the Doppler frequency offset value of the mobile terminal can be preliminarily estimated; and the deviation caused by Doppler frequency shift can be compensated by performing step (3) subsequently. After step (4) is executed, the Doppler frequency offset value of the mobile terminal in the current time slot is estimated more accurately.

In step (1), the pre-judgment value of the Doppler frequency offset is the Doppler frequency offset value estimated by the mobile terminal in the last processing time slot. Preferably, the Doppler frequency offset value estimated for the time slot with the same time slot number as the current time slot in the previous subframe is processed.

In step (2), comparing the phase difference between the current time slot and the comparison time slot on the corresponding path refers to: first obtain the channel estimation sequence of the two time slots; then perform path matching on the two sequences; obtain the corresponding path After the phase difference is divided by the corresponding chip interval, the phase offset of the mobile terminal on each path and each chip length is obtained. Among them, in order to obtain the channel estimation sequence, it is necessary to perform several actions such as intercepting the training code, performing FFT transformation, and IFFT inverse transformation for the corresponding time slot. Let me repeat.

In addition, after channel estimation is performed on the current time slot, the estimation sequence can be saved. In this way, when the subsequent time slot is used as the comparison time slot, since the channel estimation sequence of the time slot is saved in the terminal, the channel estimation process of the time slot can be omitted, and the channel estimation sequence can be directly used as the channel estimation sequence of the comparison time slot. Estimated sequence.

It can be seen from step (3) that the elimination of Doppler frequency shift deviation is realized by combining the existing technology of TD-joint detection. However, in the present invention, the generated joint detection matrix A is modified, specifically including: the b vector of the generated A matrix is convoluted by the modified channel estimation sequence and the composite spreading code, and the modified channel The estimation sequence is formed by modulating the upper Doppler frequency offset value with the estimated average channel estimation sequence, which ensures that the corrected channel estimation sequence is no longer fixed within a time slot.

Preferably, in a typical TD mobile terminal high-speed motion scenario, it is only necessary to estimate the phase offset of the strongest path of the mobile terminal and correct the channel estimation of the strongest path, and to modify the joint detection A matrix to eliminate Doppler shift deviation.

In step (4), in order to improve the accuracy of the estimation, the previously estimated Doppler frequency offset is fine-tuned during demodulation, and the Doppler frequency offset value of the strongest path after fine adjustment or the Doppler frequency offset of each path is used The maximum value of the Doppler frequency deviation is used as the Doppler frequency deviation value of the current time slot, and this value is stored in the mobile terminal as the Doppler frequency deviation prediction value of the next processing time slot.

In summary, as shown in Figure 3, the mobile terminal repeatedly performs the following steps for each time slot data received by the mobile terminal that contains the data of the mobile terminal:

Step 301: The mobile terminal uses the estimated Doppler frequency offset value of the last processing time slot stored on it as a pre-judgment value (for the first receiving time slot, the pre-judgment value is 0 or a pre-specified value), and Determine which range interval the absolute value of the predicted value falls into;

Step 302: Select the corresponding comparison time slot according to the range interval that falls into, and intercept the training sequence of the comparison time slot, use the improved Steiner method to do the first channel estimation, and obtain the time of each mobile terminal in the comparison time slot Average channel impulse response within the segment;

Step 303: Intercept the training sequence of this time slot, do the second channel estimation, and estimate the average channel impulse response of each mobile terminal in this time slot;

Certainly, the order of performing channel estimation on the current time slot and the comparison time slot is not in particular order, as long as the average channel impulse response in the two time slots is obtained.

Step 304: Match the channel estimation values of the current time slot and the comparison time slot according to the mobile terminal and the corresponding path, perform phase subtraction of the two matched channel sequences according to the path, and then divide by the difference between the current time slot and the comparison time slot The chip interval length of , estimate the phase offset of each mobile terminal receiving the signal on each path and each chip caused by the Doppler frequency shift, that is, the Doppler frequency offset of each mobile terminal on each path value;

Step 305: multiply the phase offset of each mobile terminal obtained in step 304 on each path and each chip by the spreading factor SF to obtain the phase offset factor of each mobile terminal on each path and the duration of each symbol length, And use this factor to modify the channel estimation sequence of the current time slot, use the modified estimated channel sequence and composite spreading code to perform convolution operation, and construct the modified joint detection A matrix;

Step 306: Use the modified A matrix to perform joint detection on the received signal of the current time slot, and obtain the demodulated symbols of each mobile terminal at one time.

Step 307: Compare these demodulation symbols with the nearest standard modulation symbol in the constellation diagram (the standard modulation symbol is the standard complex modulation symbol sent after modulation by the transmitter, for example, for QPSK modulation, the standard modulation symbol is: +i, 1,-1,-i) do phase comparison, and the gained phase difference is smoothed to obtain the phase offset; then use this phase offset to fine-tune the mobile terminal estimated in step 304 at the channel maximum in this time slot. Doppler frequency offset value of strong path;

Step 308: Determine the Doppler frequency offset value of this time slot and save it in the next receiving time slot of the mobile terminal for reference and comparison. The Doppler frequency offset value of the current time slot is the Doppler frequency offset value on the strongest path of the mobile terminal fine-tuned in step 307, or the largest Doppler frequency offset value in each path of the mobile terminal value, or a weighted sum of the two above.

When the mobile terminal is in a high-speed motion scene, in the above steps 305-308, only the phase offset of the strongest path of the mobile terminal can be estimated, the channel estimation of the strongest path can be corrected, and the joint detection A matrix can be corrected , to eliminate the Doppler shift bias.

The present invention will be further described below with a specific example.

Assume that a certain TD mobile terminal is performing a 12.2kbps voice service, the service feature is that the mobile terminal occupies a fixed time slot in each subframe, and the downlink spreading factor SF=16.

Initially configure the terminal: pre-set 2 range intervals by the absolute value of the Doppler frequency offset: interval A = [0, 1*10 ^-3 radians/chip), interval B = [1*10 ^-3 radians /chip, +∞). (The selected boundary between the two intervals is equal to 1*10 ^-3 radian/chip, the corresponding speed of the mobile terminal is 120 km/h, and the maximum Doppler frequency shift fd _max is 222 Hz).

Set the comparison time slots of the corresponding two range intervals: corresponding to interval A, the comparison time slot is the time slot with the same time slot number as the current time slot in the previous subframe; corresponding to interval B, the comparison time slot is the TS0 of this subframe time slot.

The pre-judgment value of the initial Doppler frequency offset value is set to 0.

The mobile terminal repeats the following steps for the received time slots containing the data of the mobile terminal in each subframe:

Step 1: According to which range interval the absolute value of the Doppler frequency offset value of the predicted time slot falls in, a corresponding comparison time slot is selected (for the first subframe, the predicted value is 0, for the following subframes frame, the pre-judgment value is the Doppler frequency offset value of the slot with the same slot number as the current slot in the previous subframe)

When the pre-judgment value falls into the interval A, it is considered that the mobile terminal is in a small Doppler frequency offset state, and the time slot with the same time slot number as the current time slot in the previous subframe is selected as the comparison time slot;

When the predicted value falls into interval B, it is considered that the mobile terminal is in the Doppler frequency offset state, so more accurate Doppler frequency offset estimation is required, and the TS0 time slot in this subframe is selected as the comparison time slot.

Step 2: intercept the training sequence of the comparison time slot for channel estimation, and obtain the average channel response ch_est1 of each mobile terminal on the comparison time slot. The specific method of channel estimation adopts the improved Steiner method, which can be divided into the following two sub-steps:

Step 2.1, intercept the training sequence receiver_mid ₁ of the comparison time slot and perform FFT transformation, then divide by the FFT transformation of the basic training sequence mid_basic, and then perform IFFT transformation on the result to obtain the channel estimation sequence (Channel_Estimation):

Channel_Estimation=IFFT(FFT(receiver_mid ₁ )/FFT(mid_basic)) (2)

The basic training sequence is initially assigned to each cell by the system and notified to the mobile terminal.

Step 2.2, as shown in Figure 4, remove the path with power greater than ε in the channel estimation sequence corresponding to each mobile terminal obtained in step 2.1 as a noise path, and the remaining sequence ch_est1 is the average channel response. (wherein, ε=r ² ·σ ² , r ² represents the threshold signal-to-noise ratio, σ ² represents the noise power, the values of r and σ can be selected according to the actual engineering, r<1).

In specific implementation, when the comparison time slot is the time slot with the same time slot number as the current time slot in the previous subframe, since the channel estimation has been done for this time slot in the processing of the previous subframe, it is only necessary to Increase the storage of the channel estimate in the mobile terminal, and read the storage in this step, without doing steps 2.1 and 2.2;

Step 3: Intercept the training sequence of the current time slot for channel estimation, and obtain the average channel response ch_est2 of each mobile terminal in the current time slot. The specific method of channel estimation adopts the improved Steiner method, which can be divided into two sub-steps (as described in steps 2.1 and 2.2), which will not be repeated here.

After obtaining the channel estimation sequence on the current time slot, store the sequence.

Step 4. The estimated sequence of the average channel response of the current time slot and the comparison time slot is matched according to the mobile terminal and the path, and the phase subtraction of the average channel response of the strongest path of each mobile terminal is carried out, and then divided by the current time slot and Comparing the number of chips at intervals between time slots, the phase offset per chip of the received signal of the mobile terminal on the strongest path caused by the Doppler frequency shift is obtained, that is, the phase offset of the mobile terminal on the strongest path Doppler frequency offset value:

$\mathrm{<span\; class="notranslate">\; phase</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimate</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; per\; chip</span>}}^{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; phase</span>}}_{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}^{\mathrm{<span\; class="notranslate">\; ch</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; est</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; phase</span>}}_{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}^{\mathrm{<span\; class="notranslate">\; ch</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; est</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

This value can be regarded as a rough estimate of the Doppler frequency offset (fine adjustment is required in step 6). Among them, phase indicates the phase operation, strongest tap indicates the strongest path, that is, the path with the largest power in the channel response of each path, and N _chip indicates the number of chips between the current time slot and the comparison time slot:

For the TS0 time slot of this subframe selected in step 1 as the comparison time slot, N _chip = current time slot number * 864 + 352, where 352 is the total chip length of the downlink synchronization code, guard interval and uplink synchronization code.

For the time slot with the same time slot number in the previous subframe selected as the comparison time slot in step 1, the interval between the current time slot and the comparison time slot is one subframe long, and the chip interval N _chip =6400.

In this embodiment, it is preferable to only estimate the Doppler frequency offset value of the strongest path of each terminal user, and the optimal method can reduce the complexity of terminal implementation; the reason for this is that in a typical mobile terminal high-speed motion scene In general, there is a wireless signal with a direct path (that is, the radio wave can reach the mobile terminal directly from the base station antenna), and this direct path is the main factor affecting the quality of the received signal, that is, the estimated strongest path;

Step 5: Multiply the phase offset per chip of the estimated received signal on the strongest path by the spreading factor, modify the channel estimation sequence of the current time slot, and use the modified channel estimation sequence with the composite spreading code Carry out convolution operation to form a modified joint detection A matrix. Specifically divided into four sub-steps:

Step 5.1, multiply the phase offset of each chip on the strongest path of the received signal obtained in step 4 by the spreading factor SF to obtain the phase offset factor of the received signal on each symbol of the strongest path:

$\mathrm{<span\; class="notranslate">\; phase</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimate</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; per\; symbol</span>}}^{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SF</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; phase</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimate</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; per\; chip</span>}}^{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Step 5.2. Compensate the phase offset of the received signal on the strongest path per symbol length to the strongest path of the current slot average channel estimation sequence obtained in step 3, and obtain the corrected channel estimation sequence:

$\mathrm{<span\; class="notranslate">\; channel</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimate</span>}{{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; symbol</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; tap</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; strongest</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; channel</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimati</span>}{\mathrm{<span\; class="notranslate">\; on</span>}}^{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; phase</span>}<span\; class="notranslate">\; \_</span>{\mathrm{<span\; class="notranslate">\; estimate</span>}}_{\mathrm{<span\; class="notranslate">\; per\; symbol</span>}}^{\mathrm{<span\; class="notranslate">\; strongest\; tap</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>}$

Wherein, channel_estimation ^{strongest tap} represents the strongest path of the mobile terminal obtained in step 3 in the average channel estimation of the current time slot, and n represents the nth modulation symbol.

The corrected channel estimation sequence is no longer fixed in this time slot, but is modulated by the estimated Doppler frequency offset symbol-by-symbol.

Step 5.3, obtain the composite spreading code of each mobile terminal respectively by multiplying the spreading code, channel code and scrambling code of each mobile terminal $c^{\mathrm{user}}=({\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="H2009100065791E00031.png,H2009100065791E00041.png"\; state="\{\{state\}\}">c</figure-callout>}}_1^{\mathrm{user}}...c_{\mathrm{SF}}^{\mathrm{user}}):$

${\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; user</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; spreading</span>}<span\; class="notranslate">\; \_</span>{\mathrm{<span\; class="notranslate">\; code</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; user</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; channeliasation</span>}<span\; class="notranslate">\; \_</span>{\mathrm{<span\; class="notranslate">\; code</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; scrambling</span>}<span\; class="notranslate">\; \_</span>{\mathrm{<span\; class="notranslate">\; code</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Step 5.4, using the corrected channel estimation sequence obtained in step 5.2 and the composite spreading codes of each mobile terminal generated in step 5.3 to construct a joint detection matrix A.

Refer to Figure 5 for the structure of A matrix. It consists of N V blocks, N represents the number of modulation symbols, each V block is arranged by U b vectors, U represents the number of mobile terminals, and each b vector is composed of the corrected channel estimation and composite spreading code volume Accumulate to get:

${\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}}_{\mathrm{<span\; class="notranslate">\; symbol</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; user</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Channel</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Estimation</span>}{{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; symbol</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; user</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; user</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Among them, Channel_Estimation _{symbol_n} ^user_u represents the corrected channel estimation of the uth mobile terminal on the nth symbol, and c ^user_u represents the composite spreading code of the uth mobile terminal; Represents a convolution operation.

Step 6: Use the modified A matrix to perform joint detection on the data segment of the current time slot to obtain the demodulation symbols of each mobile terminal

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

That is, the Doppler frequency shift elimination of the demodulated symbols is realized. Among them, I represents the identity matrix, σ represents the noise power, and e represents the received data segment chips; A ^H represents the Hermitian transformation of matrix A, and A ^-1 represents the inverse transformation of matrix A.

Step 7: In order to obtain a more accurate Doppler frequency offset estimate, fine-tune the rough estimate of the Doppler frequency offset estimated in step 4, specifically including the following steps:

A, the demodulation symbol obtained in step 6 is compared with the standard modulation symbol, and the gained phase difference is smoothed, and the obtained result fine-tunes the rough estimate of the Doppler frequency offset, specifically including:

A1. Compare the obtained demodulation symbol with the phase of the standard modulation symbol _dstd , and average the obtained phase difference:

Δphase'=AVG(phase(d)-phase(d _std )) (9)

Here, AVG represents an averaging operation, and specifically refers to averaging all (all users) demodulated symbols obtained through joint detection.

A2. Use the obtained Δphase' to fine-tune the rough estimate of the Doppler frequency offset estimated in step 4:

$\mathrm{<span\; class="notranslate">\; \&Delta;phase</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimate</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; per\; chip</span>}}^{\mathrm{<span\; class="notranslate">\; tap</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; strongest</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; phase</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; estimate</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; per\; chip</span>}}^{\mathrm{<span\; class="notranslate">\; tap</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; strongest</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; phase</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}{\mathrm{<span\; class="notranslate">\; SF</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

即本移动终端在本时隙上的多普勒频偏值，根据该值可以得到多普勒频移值f_d。This value can be considered as

That is, the Doppler frequency offset value of the mobile terminal in the current time slot, and the Doppler frequency offset value f _d can be obtained according to this value.

B. Save the phase offset Δphase_estimation _{per chip} ^{tap_strongest} of the adjusted strongest diameter obtained in step A2 as the Doppler frequency offset value of this time slot in the mobile terminal, as a preview for the next subframe processing Judgment.

Repeat steps 1-7 for the next subframe data.

As shown in Fig. 6, it can be seen that after adopting the method of the present invention, the bit error rate of the mobile terminal is significantly reduced.

Of course, the present invention can also have other various embodiments, and those skilled in the art can make various corresponding changes and deformations according to the present invention without departing from the spirit and essence of the present invention, but these corresponding Changes and deformations should belong to the scope of protection of the appended claims of the present invention.

Claims (14)

1. an estimation method of Doppler frequency offset value in a time division synchronous code division multiple access TD-SCDMA system, it is characterized in that, After receiving the time slot containing the data of the mobile terminal, the mobile terminal calculates the phase difference between the current time slot and the channel estimation sequence of a comparison time slot, and obtains the Doppler frequency offset value of the received signal in the current time slot; Wherein, the corresponding relationship between the absolute value of the preset Doppler frequency offset value and the comparison time slot in the mobile terminal; The calculation of the phase difference between the current time slot and the channel estimation sequence of a comparison time slot includes: selecting the corresponding comparison time slot according to the absolute value of the pre-judgment value of the Doppler frequency offset value of the current time slot; The pre-judgment value of the Doppler frequency offset value of the current time slot is the Doppler frequency offset value obtained by the mobile terminal in a previous processing time slot. the 2. The method of claim 1, wherein, The calculation of the phase difference between the current time slot and the channel estimation sequence of a comparison time slot to obtain the Doppler frequency offset value of the current time slot received signal also includes: Calculate the phase difference between the current time slot and the comparison time slot on the corresponding path, divide the calculated phase difference by the chip interval length of the current time slot and the comparison time slot, and obtain the signal received by the mobile terminal Phase offset per chip length for this slot. the 3. The method according to claim 2, characterized in that, The corresponding relationship between the absolute value of the Doppler frequency offset value preset in the mobile terminal and the comparison time slot specifically includes: Range intervals of the absolute values of n Doppler frequency offset values and a comparison time slot corresponding to each range interval, wherein, the n range intervals cover the absolute values of all possible Doppler frequency offset values segment by segment value, n≥1. the 4. method as claimed in claim 2 is characterized in that, The Doppler frequency offset value obtained by the last processing time slot of the mobile terminal refers to: the estimated value of the mobile terminal obtained when processing the last time slot containing the data of the mobile terminal stored in the mobile terminal at that time The Doppler frequency offset value on the strongest path of the slot, or the maximum Doppler frequency offset value of the mobile terminal in each path of the time slot, or the weighted sum of the above two items. the 5. The method of claim 2, wherein, The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes: Intercepting the training sequence of the comparison time slot, performing channel estimation, and estimating the average channel impulse response of the mobile terminal in the comparison time slot; Intercept the training sequence of the current time slot, do channel estimation, and estimate the average channel impulse response of the mobile terminal in the current time slot; Carry out the phase subtraction of the mobile terminal part of the average channel impulse response of the current time slot and the comparison time slot according to the corresponding path, and then divide by the chip interval length between the above two time slots to obtain the result of the Doppler frequency shift. The received signal phase offset of the mobile terminal on each path and each chip. the 6. method as claimed in claim 3 is characterized in that, When n=2, the range interval includes: A=[0, X), B=[X, +∞), the comparison time slot corresponding to the range interval A is the current time slot in the previous subframe For time slots with the same time slot number, the comparison time slot corresponding to the range interval B is the TS0 time slot in the subframe where the current time slot is located, where the value of X is determined according to engineering practice. the 7. method as claimed in claim 6 is characterized in that, The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes: When the comparison time slot is the TS0 time slot in this frame, intercept the training sequence of the TS0 time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the comparison time slot; when the comparison When the time slot is the same time slot as the current time slot in the previous frame, the average channel impulse response of the comparison time slot is obtained according to the saved record of the mobile terminal; Intercept the training sequence of the current time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot period; The mobile terminal subtracts the phase difference between the current time slot and the channel estimation value of the strongest path in the comparison time slot to obtain a phase difference, and then divides it by the chip interval length of the current time slot and the comparison time slot to obtain a multiple The phase offset of the received signal of the mobile terminal on each chip caused by the Puler frequency shift. the 8. a kind of compensation method of Doppler frequency shift in the time division synchronous code division multiple access TD-SCDMA system, it is characterized in that, After receiving the time slot containing the data of the mobile terminal, the mobile terminal obtains the Doppler frequency offset value of the received signal of the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of a compared time slot, and combines the joint detection , correcting the received signal in the joint detection; Wherein, the mobile terminal saves preset n range intervals of absolute values of Doppler frequency offset values and a comparison time slot corresponding to each range interval, wherein the n range intervals are segment by segment Covers the absolute value of all possible Doppler frequency offset values, n≥1; Obtain the Doppler frequency offset value of the current time slot received signal by comparing the phase difference between the current time slot and the channel estimation sequence of a comparison time slot, including: judging the absolute value of the predicted value of the Doppler frequency offset value of the current time slot The value is located in which range interval above, and the corresponding comparison time slot is determined by the judged range interval; The pre-judgment value of the Doppler frequency offset value of the current time slot is the Doppler frequency offset value obtained by the mobile terminal in a previous processing time slot. the 9. method as claimed in claim 8 is characterized in that, The mobile terminal obtains the Doppler frequency offset value of the received signal of the mobile terminal by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which also includes: By comparing the phase difference between the current time slot and the comparison time slot on the corresponding path, and dividing the phase difference obtained by the comparison by the chip interval length of the current time slot and the comparison time slot, it is estimated that the Doppler frequency shift The resulting phase offset of the received signal per chip length of the slot. the 10. The method of claim 9, wherein, The Doppler frequency offset value obtained by the mobile terminal in the last processing time slot refers to: the estimated value of the mobile terminal at that time when processing the last time slot containing the data of the mobile terminal stored in the mobile terminal. The Doppler frequency offset value on the strongest path of the slot, or the maximum Doppler frequency offset value of the mobile terminal in each path of the time slot, or the weighted sum of the above two items. the 11. The method of claim 9, wherein, The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes: Intercepting the training sequence of the comparison time slot, performing channel estimation, and estimating the average channel impulse response of each mobile terminal in the comparison time slot; Intercept the training sequence of the current time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot; The mobile terminal part of the average channel impulse response of the current time slot and the comparison time slot is subtracted according to the corresponding path to obtain the phase difference, and then divided by the chip interval length between the above two time slots to obtain the Doppler frequency The phase offset of the received signal of the mobile terminal on each path and each chip caused by the shift. the 12. The method of claim 9, wherein, The mobile terminal obtains the Doppler frequency offset value of the signal received by the mobile terminal in the current time slot by comparing the phase difference between the current time slot and the channel estimation sequence of the compared time slot, which specifically includes: When the comparison time slot is the TS0 time slot in this frame, intercept the training sequence of the TS0 time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the comparison time slot; when the comparison When the time slot is the same time slot as the current time slot in the previous frame, the average channel impulse response of the comparison time slot is obtained according to the saved record of the mobile terminal; Intercept the training sequence of the current time slot, do channel estimation, and estimate the average channel impulse response of each mobile terminal in the current time slot period; The mobile terminal subtracts the phase difference between the current time slot and the channel estimation value of the strongest path in the comparison time slot to obtain a phase difference, and then divides it by the chip interval length between the current time slot and the comparison time slot to obtain a multiple The phase offset of the received signal of the mobile terminal on each chip caused by the Puler frequency shift. the 13. The method according to any one of claims 9 to 12, characterized in that, The correction of the received signal of each mobile terminal in the joint detection specifically includes: Compensating the average channel impulse response of each mobile terminal in the current time slot period after multiplying the obtained phase offset by the spreading factor SF; The composite spreading code of each mobile terminal is obtained by multiplying the spreading code, channel code and scrambling code of each mobile terminal; Using the compensated average channel impulse response and the composite spreading codes of each mobile terminal to construct a joint detection matrix A, and use the joint detection matrix A to perform joint detection on the data segment in the current time slot to obtain the corrected demodulation symbol. the 14. The method of claim 13, further comprising: Using the obtained demodulation symbols to compare the phases of the standard modulation symbols in the constellation diagram, the obtained phase difference is smoothed to the phase frequency offset value and/or the largest phase frequency offset value of each mobile terminal, and the processed The final result is saved as the Doppler frequency offset value of this time slot. the

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