WO2010094191A1

WO2010094191A1 - Method and terminal of doppler frequency offset estimation and compensation in td-scdma system

Info

Publication number: WO2010094191A1
Application number: PCT/CN2009/074235
Authority: WO
Inventors: 朱昀; 王曼
Original assignee: 中兴通讯股份有限公司
Priority date: 2009-02-19
Filing date: 2009-09-25
Publication date: 2010-08-26
Also published as: CN101814931A; CN101814931B

Abstract

A method and terminal of Doppler frequency offset estimation and compensation in time division synchronous code division multiple access (TD-SCDMA) system are provided. The method includes the following steps: pre-judging which range interval an absolute value of the Doppler frequency offset in the current time slot is within; by comparing a phase difference in the corresponding path of the current time slot with a comparative time slot corresponding to the range interval, estimating phase offset amount of each chip length of the received signals caused by the Doppler frequency offset; according to the phase offset amount and by combining the existing joint detection technique, eliminating the phase offset of the received signals caused by the Doppler frequency offset by modifying an A matrix in the joint detection.

Description

Method and terminal for Doppler frequency shift estimation and compensation in TD-SCDMA system

Technical field

The present invention relates to mobile communication technologies, and in particular, to a method for estimating and compensating Doppler frequency shift in a 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 rate.

As shown in FIG. 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 one subframe, two subframes (subframe #1 and subframe #2) Form a radio frame with a duration of 10ms. The data of the mobile terminal user is transmitted in a regular time slot. A regular time slot has a duration of 675 μ _δ and is composed of 864 chips. Each chip has a duration of 0.78125 μ _δ. These chips are divided into four parts: That is, two data segments (352 chips each), one training code segment (midamble) (144 chips), and a guard interval GP of 16 chip length; each data segment is composed of multiple mobile terminal codes to be transmitted. The track data is composed of spread spectrum, scrambling and aliasing; the training code segment is formed by the displacement of the basic midamble code assigned by the system, and its role is used as a training sequence for channel estimation.

According to the current TD-SCDMA technology, the maximum moving speed of the mobile terminal is 120 km/h. However, in real life, high-speed trains with speeds of up to 250 km per hour have emerged, and high-speed rail networks with higher speeds of 300 km/h to 500 km/h will be spread all over the country in the near future, which proposes existing TD wireless technologies. A big challenge. When the mobile terminal is in a high-speed motion state, the Doppler shift of the wireless signal transmitted by the space becomes very serious, and as the carrier frequency increases, the Doppler shift increases, and the Doppler shift Proportional to the carrier frequency and the speed of the mobile terminal, ie: c

Where, represents the Doppler frequency offset value, /? represents the carrier frequency, and V represents the speed of the mobile terminal motion. Degree, c represents the speed of light, equal to 3*10 ⁸ m/s, indicating the angle between the direction of movement of the mobile terminal and the incident of radio waves to the mobile terminal. On the mobile terminal side, the Doppler shift effect causes a deviation between the local demodulation carrier and the frequency of the signal actually received by the mobile terminal, and the deviation of this frequency accumulates in time, resulting in demodulation symbols and standards. The modulation symbol is deflected (distorted) in phase. Especially for the TD system, since it is a low bit rate system, the duration of each chip is longer, so the phase distortion of the demodulated symbols accumulated on each chip becomes larger, which will greatly affect Correct reception and demodulation of the mobile terminal.

On the other hand, TD-SCDMA mobile terminals generally employ joint detection techniques when performing reception demodulation. Joint detection utilizes a priori information in multiple access interference to treat the separation of all mobile terminal signals as a unified process, converting the received aliased chip signals into demodulation symbols for each mobile terminal in one step. , thereby reducing interference between multiple mobile terminals and increasing system capacity. However, the effectiveness of the joint detection technique is based on accurate channel estimation. The implementation of the existing TD channel estimation uses Steiner's low-cost fast Fourier transform FFT/inverse fast Fourier transform (IFFT) plus subsequent The method of detecting thresholds to remove noise taps. "This technique is based on Steiner B. BAIEP. «Low cost channel estimation in the uplink receiver of CDMA mobile radio systems) Frequenz 1993, 47(12): 292-298 and Kang Shaoli et al. "Low-cost channel estimation method in TD-SCDMA system" The improvement is described in the Journal of Communications, Vol. 23, No. 10, 125 130. This channel estimation technique is considered to be fixed in a time slot, but the fading experienced by the mobile terminal during motion is modulated by Doppler shift. That is to say, the channel is actually time-varying in one time slot, and the channel value estimated by the existing estimation method is actually the channel average value in one slot time period. Therefore, there is an error between the estimated channel obtained by the estimation method and the real channel, especially when the mobile terminal is in a state of high-speed motion, the error is large, and if the estimated channel with error is brought into the joint In the detection matrix, repeated superposition and amplification of the interference is caused, thereby affecting the correct decoding of the data.

Summary of the invention

In order to solve the prior art problem, the present invention provides a method for estimating and compensating for Doppler shift in a TD-SCDMA system to overcome the adverse effect on the correct reception of data due to the movement of the mobile terminal. The invention provides a method for estimating a Doppler frequency offset value in a time division synchronous code division multiple access TD-SCDMA system, which comprises:

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

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

The mobile terminal stores a preset range range of absolute values of the Doppler frequency offset values and n comparison time slots corresponding to each range interval, wherein the range range covers the segment by section The absolute value of all possible Doppler frequency offset values, "> 1;

The step of obtaining the Doppler frequency offset value of the current time slot received signal by the phase difference between the current time slot and the channel estimation sequence of the comparison time slot includes:

Determining which of the above range ranges the absolute value of the pre-determined value of the Doppler frequency offset value of the current time slot;

Determining, by the determined range interval, a comparison time slot corresponding to the range interval;

The phase offset of the received signal caused by the Doppler shift in the current time slot per chip length is estimated by comparing the current time slot with the phase difference of the determined comparison time slot on each path.

Further, in the above method:

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

The Doppler frequency offset value of the processing time slot of the mobile terminal is: the mobile terminal stored in the mobile terminal and estimated when processing the last time slot containing the mobile terminal data at the time The Doppler frequency offset value of the strongest path of the slot, or the weighted sum of the maximum Doppler frequency offset value of the mobile terminal in each path of the time slot, or the above two Doppler frequency offset values.

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

The step of estimating the phase offset of the received signal per chip length of the current time slot caused by the Doppler shift by comparing the current time slot and the determined phase difference of the compared time slots on the respective paths Includes:

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

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

And phase-reducing the current mobile terminal portion of the average channel impulse response in the current time slot and the comparison time slot by a path, and dividing the length of the chip interval between the two time slots to obtain a Doppler frequency shift The current signal phase offset of the current mobile terminal on each path and per chip.

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

When "=2, the range interval includes: A=[0, X) and Β=[Χ, +οο), and the comparison slot corresponding to the range interval 为 is the previous subframe and the current slot. For a time slot having the same time slot number, the comparison time slot corresponding to the range interval B is the TS0 time slot in the subframe in which the current time slot is located, wherein the value of X is determined according to the actual project.

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

When the comparison time slot is the TS0 time slot in the current frame, the training sequence of the TS0 time slot is intercepted, channel estimation is performed, and an average channel impulse response of each mobile terminal in the comparison time slot is estimated; When the time slot is a time slot in the previous frame that is in the same time slot as the current time slot, the average channel impulse response of the comparison time slot is obtained according to the saved record of each mobile terminal;

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

The current mobile terminal phase subtracts the current time slot from the channel estimation value of the strongest path in the comparison time slot, and divides the current time slot and the chip interval length of the comparison time slot to obtain a Doppler frequency shift. The resulting phase offset of the received signal on the current mobile terminal per chip.

The 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 current time slot received signal by using the phase difference between the current time slot and the channel estimation sequence of the comparison time slot, Joint detection, the received signal is corrected in joint detection.

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

The mobile terminal stores a preset range interval of absolute values of the Doppler frequency offset values and n comparison time slots corresponding to each range interval, wherein the range range covers the segment by section The absolute value of all possible Doppler frequency offset values, "> 1;

The step of obtaining a Doppler frequency offset value of the current time slot received signal by the phase difference between the current time slot and the channel estimation sequence of the comparison time slot includes:

The phase offset of the received signal caused by the Doppler shift in the current time slot per chip length is estimated by the phase difference between the current time slot and the comparison time slot on each path.

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

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

The Doppler frequency offset value of the processing time slot of the mobile terminal is: the mobile terminal stored in the mobile terminal and estimated by the mobile terminal in processing the last time slot containing the mobile terminal data in the time slot. The Doppler frequency offset value of the strongest path, 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 Doppler frequency offset values.

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

The step of estimating the phase offset of the received signal in the current time slot per chip length caused by the Doppler shift by the phase difference between the current time slot and the comparison time slot on each path includes: Intercepting the training sequence of the comparison time slot, performing channel estimation, and estimating an average channel impulse response of each mobile terminal in the comparison time slot;

Current mobile terminal portion of the average channel impulse response in the current time slot and the comparison time slot The phase subtraction is performed according to the path, and the chip interval length between the two time slots is divided, and the phase shift amount of the received signal of each current path and each chip by the current mobile terminal caused by the Doppler shift is obtained.

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

The step of estimating the phase offset of the received signal in the current time slot per chip length caused by the Doppler shift by the phase difference between the current time slot and the comparison time slot on each path includes: When the time slot is compared to the TS0 time slot in the frame, the training sequence of the TS0 time slot is intercepted, channel estimation is performed, and an average channel impulse response of each mobile terminal in the comparison time slot is estimated; When the time slot is a time slot in the previous frame that is in the same time slot as the current time slot, the average channel impulse response of the comparison time slot is obtained according to the saved record of each mobile terminal;

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

The steps of correcting the received signal in joint detection include:

Multiplying the obtained phase offset by the spreading factor SF to compensate the average channel impulse response of each mobile terminal in the current slot period according to the path;

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

Constructing a joint detection matrix A by using the compensated average channel impulse response and the composite spreading code of each mobile terminal, and jointly detecting the data segments in the current time slot by using the joint detection matrix A, and obtaining the corrected Demodulation symbol.

Further, the above method may further include:

Comparing the obtained demodulated symbols with the standard modulation symbols in the constellation diagram, and obtaining the phase difference to smooth the phase frequency offset value and/or the maximum phase frequency offset value of the strongest path of each mobile terminal, and processing The resulting result is saved as the Doppler shift value of the current time slot. The present invention also provides a mobile terminal supporting estimation and compensation of Doppler shift in a time division synchronous code division multiple access TD-SCDMA system, the mobile terminal being configured to: receive data containing the mobile terminal After the time slot, the Doppler frequency offset value of the current time slot received signal is obtained by the phase difference between the current time slot and the channel estimation sequence of the comparison time slot, and combined with the joint detection, the received signal is corrected in joint detection.

Further, the mobile terminal stores a preset range range of absolute values of the Doppler frequency offset values and n comparison time slots respectively corresponding to each range interval, wherein the n ranges The interval covers the absolute value of all possible Doppler frequency offsets, " > 1;

The mobile terminal is configured to obtain a Doppler frequency offset value of the current time slot received signal by using a phase difference between the current time slot and a channel estimation sequence of a comparison time slot according to the following steps:

Determining which range of the absolute value of the pre-determined value of the Doppler frequency offset value of the current time slot is located; determining the corresponding time slot corresponding to the range interval from the determined range interval; and determining by the current time slot and the determined time slot Comparing the phase difference of the time slots on the respective paths to estimate the phase offset of the received signal caused by the Doppler shift in the current time slot per chip length;

The mobile terminal is further arranged to modify the received signal in joint detection according to the following steps:

Multiplying the obtained Doppler frequency offset value by the spreading factor SF to compensate the average channel impulse response of each mobile terminal in the current slot period according to the path;

Constructing a joint detection matrix A by using the compensated average channel impulse response and the composite spreading code of each mobile terminal, and jointly detecting the data segments in the current time slot by using the joint detection matrix A, and obtaining the modified demodulation symbol.

Compared with the prior art, the invention improves the accuracy of channel estimation, eliminates the influence of Doppler shift on correct reception and demodulation, reduces the bit error rate, thereby improving system performance, and is especially suitable for TD- SCDMA mobile terminal scenario under high speed motion. The accuracy of estimating the Doppler frequency offset is adjusted by selecting an appropriate comparison time slot, and the Doppler frequency offset is estimated by performing a phase difference operation on the comparison time slot and the current time slot, and in a preferred case, the mobile terminal Estimating and compensating only the phase shift of the received signal caused by the Doppler shift of the strongest path (main path), reducing the method The complexity of the implementation; in addition, the mobile terminal can further reduce the method complexity and system overhead by storing the channel estimation sequence of the compared time slots.

BRIEF abstract

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

2 is a schematic diagram of phase offset caused by Doppler shift modulation of each path of a wireless channel in a regular time slot segment according to an embodiment of the present invention;

3 is a flow chart of a method in an 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 according to an embodiment of the present invention;

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

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

Preferred embodiment of the invention

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

For a TD time slot that propagates over a wireless channel, it is subject to convolutional modulation of the wireless channel impulse response. The impulse response consists of two parts: 1. Fading caused by multipath effect: Since the duration of a TD slot (675 s) is much smaller than the coherence time of the spatial channel, this part can be considered to be within a slot time period. Approximately fixed; 2, the phase offset caused by the Doppler effect _e - ^{] The} offset ² varies linearly with time over a time slot duration, as shown in Figure 2, where the , a chip, each diagonal line indicates the phase offset on the corresponding path (the slope of each diagonal line is different because the angle between each radial direction and the moving direction of the mobile terminal is different). The spatial channels of a mobile terminal in a time slot length are sequentially expanded by chips, to obtain:

- h(chip_l) = [cof _fadmg eP _C0 f _{fadmg 2} -e- ^j2 ^ ...,cof _{fadmg L} . _e ² '

...+... — ― — (1 )

Hchip—864) = [cof _fadmg , . e- , _cof ^ _ ₂ . _e - ^J '1, cof _{fadmg L} . _e ^] "^ ] where h(chip_i) represents the channel impulse response on the lth chip ( The range of I is

1-864), c. f _{fadi k} represents the fading coefficient of the kth path, and ² ” represents the Doppler frequency on the first path The phase offset on the second chip caused by the shift. Hereinafter, the phase shift amount of the received signal per chip caused by the Doppler shift is simply referred to as a Doppler shift value.

Before performing the following steps, you need to make the following settings for the terminal: The range of the preset absolute value of «(1) Doppler frequency offset value is saved on the terminal, and the η range interval covers the segment by section. The absolute value of all possible Doppler frequency offset values; in addition, there is a comparison time slot slot[z] corresponding to each range interval, the value of , is slot [ z] corresponds to the zth range interval, and the corresponding relationship may be: as the range interval gradually approaches infinity, the comparison slot corresponding to each range section gradually approaches the current slot, that is, it may be understood as falling on a certain The larger the absolute value of the Doppler frequency offset value in the range interval, the closer the corresponding comparison time slot is to the current time slot. The comparison time slot is a certain time slot before the current time slot, which may be the current time slot. The slot number in the subframe in which the subframe is located is smaller than a certain slot in the current slot, or may be a slot in a subframe before the subframe in which the current slot is located.

Preferably, setting "=2, that is, setting the absolute range of the Doppler frequency offset value is: interval A = [0, X), interval Β = [Χ, + οο], the value of X can be engineered Actually determined. The comparison slot corresponding to the interval 是 is the slot with the same slot number in the previous subframe as the current slot; the comparison slot corresponding to the interval B is the TS0 slot in the subframe in which the current slot is located. The reason why these two time slots are used as comparison time slots is because there are always training sequences in the training code segments of the two time slots, so that the channel estimation afterwards can be guaranteed to be implemented. Of course, the comparison time slot may also select any other time slot before the current 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.

The present invention eliminates the effects of the Doppler shift factor on the correct reception and demodulation of symbols by the mobile terminal through several steps, including:

(1) predetermining which of the above range ranges the absolute value of the Doppler frequency offset value on the current time slot;

(2) estimating a phase offset of the received signal per chip length caused by the Doppler shift by comparing the phase difference of the comparison slot corresponding to the current slot and the range interval on the corresponding path;

(3) According to the phase offset combined with the existing joint detection technology, through the joint detection The A matrix is used to eliminate the phase offset of the received symbols caused by the Doppler shift.

(4) When the received symbol is demodulated, the previously estimated Doppler frequency offset is finely adjusted while demodulating.

The above steps are all performed by the mobile terminal provided by the present invention to support estimation and compensation of Doppler shift in the TD-SCDMA system.

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

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

In step (2), comparing the phase difference between the current time slot and the comparison time slot on the corresponding path means: first obtaining the channel estimation sequence of the two time slots; then performing path matching on the two sequences; obtaining 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 the length of each chip is obtained. In order to obtain the channel estimation sequence, it is necessary to perform the operations of intercepting the training code, performing the FFT transform, and performing the inverse inverse transform of the IFFT on the corresponding time slot. The implementation of the channel estimation uses the improved steiner method, which belongs to the prior art category. No longer comment.

In addition, after the 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 stored in the terminal, the channel estimation process for the time slot can be omitted, and the channel estimation sequence is directly used as the channel for comparing the time slot. Estimate the sequence.

It can be seen from the step (3) that the Doppler shift deviation is combined with the prior art of the TD. The b vector of the generated A matrix is convolved by the modified channel estimation sequence and the composite spreading code. And the modified channel estimation sequence is formed by estimating the Doppler frequency offset value of the average channel estimation sequence, that is, the corrected channel estimation sequence is no longer fixed in one time slot. changing.

Preferably, in a typical TD mobile terminal high-speed motion scenario, only the mobile terminal The most strong path is used to estimate the phase offset and correct the channel estimate for the strongest path, and to correct the joint detection A matrix to eliminate the Doppler shift.

In step (4), in order to improve the accuracy of the estimation, the previously estimated Doppler frequency offset is finely adjusted during demodulation, and the finest adjusted Doppler frequency offset value or the multipath is used. The maximum value of the frequency offset value is used as the Doppler frequency offset value of the current time slot, and the value is stored as the Doppler frequency offset prediction value of the next processing time slot in the mobile terminal.

In summary, as shown in FIG. 3, the mobile terminal repeatedly performs the following steps on each time slot data received by the mobile terminal including the data of the mobile terminal:

Step 301: The mobile terminal uses the Doppler frequency offset estimation value of the last processing time slot held thereon as a pre-judgment value (for the first receiving time slot, the pre-determined value is 0 or a pre-specified value), and Determining which range of the absolute value of the predicted value falls within;

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

Step 303: intercept the training sequence of the time slot, perform a second channel estimation, and estimate an average channel impulse response of each mobile terminal in the current time slot period;

Of course, the order of channel estimation for the time slot and the comparison time slot is not sequential, as long as the average channel impulse response in the two time slots is obtained.

Step 304: Match channel estimation values of the current time slot and the comparison time slot according to the mobile terminal and the corresponding path, and perform phase subtraction according to the path of the matched two channel sequences, and divide by the current time slot and the comparison time slot. The length of the chip interval is estimated by the Doppler shift caused by the phase offset of each mobile terminal receiving signals on each path and every chip, that is, the Doppler frequency offset of each mobile terminal on each path. Step 305: Multiply the phase offset of each mobile terminal on each path and each chip by the spreading factor SF to obtain the phase offset of each mobile terminal in the length of each path and each symbol length. a factor, and using the factor to correct the channel estimation sequence of the current time slot, using the modified estimated channel sequence and the composite spreading code to perform convolution operation, and constructing the modified joint detection A matrix;

Step 306: Perform joint detection on the received current time slot signal by using the modified A matrix, and obtain demodulation symbols of each mobile terminal at one time. Step 307: The demodulation symbols are the closest standard modulation symbols in the constellation diagram (the standard modulation symbols are standard complex modulation symbols transmitted by the transmitter, for example, for QPSK modulation, the standard modulation symbols are: +i, 1 , -1 , -i ) phase comparison, the obtained phase difference is smoothed to obtain a phase offset; and then the phase offset is used to fine tune the estimated channel of the mobile terminal in the time slot in step 304. Doppler frequency offset of the strong path;

Step 308: Determine the Doppler frequency offset value of the time slot and save it to the next receiving time slot of the mobile terminal for reference comparison. The Doppler frequency offset value of the current time slot is a Doppler frequency offset value of the strongest path of the mobile terminal finely adjusted in step 307, or the largest Doppler frequency offset among the paths of the mobile terminal. Value, or a weighted sum of the two above.

When the mobile terminal is in a high-speed motion scenario, in the above steps 305-308, only the phase shift amount estimation of the strongest path of the mobile terminal and the channel estimation of the strongest path may be corrected, and the joint detection A matrix may be modified. To eliminate Doppler shift deviation.

The invention will now be further illustrated by a specific example.

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

Initial configuration of the terminal: Pre-set the range of the range of the absolute value of the Doppler frequency offset: interval A = [0, 1 * 10 - ³ radians / chip), interval B = [l * 10 - ³ radians /chip, . (The two selected boundary interval is equal to 1 * 10_ ³ rad / chip, the speed of the mobile terminal corresponds to 120km / h, the maximum Doppler shift ^ is 222 Hz).

The comparison time slot of the corresponding two range intervals is set: corresponding to the interval A, the comparison time slot is the time slot of the same time slot number as the current time slot in the previous subframe; corresponding to the interval B, the comparison time slot is the TS0 of the current subframe Time slot.

The initial value of the initial Doppler shift value is set to zero.

The mobile terminal repeats the following steps for the received time slot 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 pre-determined time slot falls within, a comparison time slot is selected correspondingly (for the first subframe, the pre-judgment value is 0, and the subsequent sub- Frame, the pre-judgment value is the Doppler frequency offset value of the previous slot number slot with the same slot number in the previous subframe) When the pre-judgment value falls in the interval A, it is considered that the mobile terminal is in the small Doppler frequency offset state, and the time slot of the same subframe number as the current time slot in the previous subframe is selected as the comparison time slot;

When the pre-judgment value falls into the interval B, it is considered that the mobile terminal is in the majority of the Pulse frequency offset state, so it is necessary to make a more accurate Doppler frequency offset estimation, and select the TS0 time slot in the subframe 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_estl of each mobile terminal on the comparison time slot. The specific method of channel estimation uses the improved steiner method, which can be divided into the following two sub-steps:

Step 2.1: intercepting the training sequence of the comparison time slot receiver-mid to perform FFT transformation, and then dividing by the FFT transformation of the basic training sequence mid-bas, and then performing the IFFT transformation on the result, and obtaining the channel estimation sequence 歹¹ J (Channel_ Estimation):

Channel—Estimation = IFFT^^^ ⁶⁰ ^^-^^^ ¹ ^^^ basic)) (2) The basic training sequence is initially allocated by the system to each cell and notified to the mobile terminal. Step 2.2: As shown in FIG. 4, the path whose power is greater than ε in the channel estimation sequence corresponding to each mobile terminal obtained in step 2.1 is removed as a noise path, and the remaining sequence ch_estl is the mobile terminal in the comparison time slot. Average channel response. (where f = r ² . ² , represents the threshold SNR, σ represents the noise power, and the values of r and σ can be selected according to the actual project, r < l ).

In a specific implementation, when the comparison slot is a slot with the same slot number as the current slot in the previous subframe, since the channel has been estimated in the processing of the previous subframe, only Adding the storage of the channel estimate to the mobile terminal, and reading the storage in this step, without having to perform 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 on the current time slot. The specific method of channel estimation uses the improved steiner method, which can be divided into two sub-steps (as described in steps 2.1 and 2.2), and will not be described here.

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

Step 4: respectively, the estimated sequence of the average channel response of the current time slot and the comparison time slot is matched by the mobile terminal and the path, and the average channel response of the strongest path of each mobile terminal is phase-reduced, and then divided by the current time slot and Comparing the number of interval chips between the slots, the phase offset of the received signal of the mobile terminal on the strongest path caused by the Doppler shift is obtained, that is, the mobile terminal is at the strongest path. Doppler frequency offset value: ^phase —estimation ;^ = - ^phase — _{( 3}

N _c hip

When the comparison time slot is far apart from the current time slot, the phase difference between the two will be n times 2 r flipping.

Indicates the phase of the comparison slot, and η is the estimated number of 2 r flips that occurred.

This value can be considered as a rough estimate of the Doppler shift (which needs to be fine-tuned in step 6). Wherein, · indicates phase calculation, strongest top indicates the strongest path, that is, the path with the largest power in the channel response of each path, and N _c/n indicates the number of chips between the current time slot and the comparison time slot:

For the TS0 time slot in which the subframe is selected in step 1, the comparison time slot is used, N _{c / n} = the current time slot number *864 + 352, where 352 is the total code of the downlink synchronization code, the guard interval and the uplink synchronization code. length.

For the time slot in which the same slot number in the previous subframe is selected in step 1, the interval between the current slot and the comparison slot is one subframe length, and the chip interval is N _chip =64QQ.

In this embodiment, it is preferable to estimate only the Doppler frequency offset value of the strongest path of each terminal user, and the preferred method can reduce the complexity of the terminal implementation; the reason for the establishment is that the mobile terminal moves at a high speed in a typical mobile terminal. In the scenario, there is usually a direct-path wireless signal (that is, radio waves can reach the mobile terminal directly from the base station antenna), and the 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 of each of the estimated received signals on the strongest path by the spreading factor, correct the channel estimation sequence of the current time slot, and use the corrected channel estimation sequence and the composite spreading code. A convolution operation is performed to form a modified joint detection A matrix. Specifically divided into four sub-steps: The correction of the Doppler shift can also be achieved by multiplying the received time slot by the estimated Doppler shift phase shift on each chip. Then do not perform ^ί'爹 on the joint detection matrix, go to step 6.

Step 5.1: Multiply the phase offset of each received chip by 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:

Phase _estimation °;^ = SF * phase _estimation °X ^tap ( 4 ) Step 5.2. Compensate the phase offset of the received signal at the strongest path per symbol length to step 3 In the strongest path of the current slot average channel estimation sequence obtained in the obtained, the corrected channel estimation sequence is obtained:

= channel _estimation ^stionm * ₍ 5) where ^{channel_estimation} - represents the strongest path of the mobile terminal obtained in step 3 in the current slot average channel estimate, and n represents the nth modulation symbol.

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

Step 5.3: Multiplying a spreading code, a channel code, and a scrambling code of each mobile terminal to obtain a composite spreading code c ^USCT = (cf ... c^ ^er ) of each mobile terminal:

c" ^ser = spreading _code" ^ser * channeliasation _code _i * scrambling _code _i (6) Step 5.4, constructing using the corrected channel estimation sequence obtained in step 5.2 and the composite spreading code of each mobile terminal generated in step 5.3 Joint detection matrix A.

The structure of the A matrix is shown in Figure 5. It consists of N V blocks, N represents the number of modulation symbols, and each V block is arranged by [/ b vectors, U represents the number of mobile terminals, and each b vector is corrected by channel estimation and composite spreading code. Convolution obtained:

―" = Channel _ Estimation' : - J—„® c ( 7 ) where Channel _ Estimation ::- _n represents the corrected channel estimate of the Uth mobile terminal on the “symbol, c,-” indicates the _M mobile terminal composite spreading code; 2 denotes convolution operation. Step 6: Joint detection of data segments of the current time slot by using the modified A matrix to obtain demodulation symbols of each mobile terminal.

d = (I + a - ² A ^H Ay ^l - A ^H e ( 8 ) that achieves Doppler shift cancellation for demodulated symbols. Where I represents the identity matrix, representing the noise power, and e represents the received Data segment chip; represents the Hermitian transformation of matrix A, representing the inverse transformation of matrix A.

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

A. Compare the demodulated symbols obtained in step 6 with the standard modulation symbols, and obtain the phase. The difference is smoothed, and the result is fine-tuned to the rough estimate of the Doppler shift. The details include:

Al, the obtained demodulation symbol is compared with the phase of the standard modulation symbol ^, and the obtained phase difference is averaged:

Aphase - A VG(phasefd) - phase(d _std )) ( 9 ) Here, AVG denotes an operation of averaging, specifically, averaging all (all users) demodulated symbols obtained by joint detection.

A2. Fine-tune the rough estimate of the Doppler frequency offset estimated in step 4 by using the obtained:

/phase _ ( 10 )

The value can be regarded as e- ^{; 2 8 Ρ} , that is, the Doppler frequency offset value of the mobile terminal in the time slot, according to which the Doppler frequency shift value f _d can be obtained.

B, and after adjusting the amount of phase shift obtained in Step A2 is the strongest path ^ hase- estimation ^ ^gest, the present time slot as a Doppler frequency offset value stored into the mobile terminal, processing the next subframe as Pre-judgment.

Repeat steps 1-7 for the next subframe data.

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

It is a matter of course that the invention may be embodied in various other forms and modifications without departing from the spirit and scope of the invention.

Industrial applicability

Compared with the prior art, the invention improves the accuracy of channel estimation, eliminates the influence of Doppler shift on correct reception and demodulation, reduces the bit error rate, thereby improving system performance, and is especially suitable for TD- SCDMA mobile terminal scenario under high speed motion.

Claims

Claim

A method for estimating a 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 current time slot received signal by the phase difference between the current time slot and the channel estimation sequence of a comparison time slot.

2. The method of claim 1 wherein

The mobile terminal stores a preset range range of absolute values of the Doppler frequency offset values and n comparison time slots respectively corresponding to each range interval, wherein the range range is segment by segment Covers the absolute value of all possible Doppler shift values, > 1 ;

Determining which range of the absolute value of the pre-determined value of the Doppler frequency offset value of the current time slot is located; determining the comparison time slot corresponding to the range of the range from the determined range interval;

The phase offset of the received signal caused by the Doppler shift in the current slot per chip length is estimated by the current slot and the phase difference of the determined comparison slot on each path.

3. The method of claim 2, wherein

The Doppler frequency offset value of the processing time slot of the mobile terminal is: the mobile terminal stored in the mobile terminal and estimated by the mobile terminal when processing the last time slot containing the mobile terminal data Determining the Doppler frequency offset value of the strongest path of the processing time slot, or the maximum Doppler frequency offset value of the mobile terminal in each path of the last processing time slot, or the above two The weighted sum of the Pule frequency offset values.

4. The method of claim 2, wherein

The step of estimating the phase offset of the received signal per chip length of the current time slot caused by the Doppler shift by the phase difference between the current time slot and the determined comparison time slot on each path Includes:

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

And phase subtracting the current mobile terminal portion of the average channel impulse response in the current time slot from the comparison time slot by a path, and dividing by the chip interval length between the current time slot and the comparison time slot, The phase shift of the received signal at each path and per chip of the current mobile terminal caused by the Doppler shift.

5. The method of claim 2, wherein

6. The method of claim 5, wherein

The step of estimating the phase offset of the received signal per chip length of the current time slot caused by the Doppler shift by the phase difference of the current time slot and the determined comparison time slot on each path includes :

When the comparison time slot is a TS0 time slot in the current frame, the training sequence of the TS0 time slot is intercepted to perform channel estimation, and an average channel impulse response of each mobile terminal in the comparison time slot is estimated; When the comparison time slot is a time slot in the previous frame that is in the same time slot as the current time slot, the average channel impulse response of the comparison time slot is obtained according to the saved record of each mobile terminal;

7. A method for compensating Doppler 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 current time slot received signal by using the phase difference between the current time slot and the channel estimation sequence of the comparison time slot, and combines the joint detection. The received signal is corrected in joint detection.

8. The method of claim 7, wherein

The phase offset of the received signal per chip length of the time slot caused by the Doppler shift is estimated by the current time slot and the phase difference of the determined comparison time slots on the respective paths.

9. The method of claim 8 wherein

The Doppler frequency offset value of the processing time slot of the mobile terminal is: the mobile terminal stored in the mobile terminal and estimated by the mobile terminal when processing the last time slot containing the mobile terminal data Determining the Doppler frequency offset value of the strongest path of a processing time slot, or the maximum Doppler frequency offset value of the mobile terminal in each path of the last processing time slot, or the above two The weighted sum of the Pule frequency offset values.

10. The method of claim 8 wherein

The step of estimating the phase offset of the received signal per chip length of the current time slot caused by the Doppler shift by the phase difference of the current time slot and the determined comparison time slot on each path includes : Intercepting the training sequence of the comparison time slot, performing channel estimation, and estimating an average channel impulse response of each mobile terminal in the comparison time slot;

11. The method of claim 8 wherein:

The step of using a phase difference between the current time slot and the determined comparison time slot on each path, the phase offset of the received signal caused by the Doppler shift in the current time slot per chip length, includes: When the comparison time slot is the TS0 time slot in the current frame, the training sequence 歹 ij of the TS0 time slot is intercepted, channel estimation is performed, and an average channel impulse response of each mobile terminal in the comparison time slot is estimated; When the comparison time slot is a time slot in the previous frame that is in the same time slot as the current time slot, the average channel impulse response of the comparison time slot is obtained according to the saved record of each mobile terminal;

The method according to any one of claims 7 to 11, wherein the step of correcting the received signal in joint detection comprises:

Constructing the compensated average channel impulse response and the composite spreading code of each mobile terminal The detection matrix A is combined, and the joint detection matrix A is used to jointly detect the data segments in the current time slot, and the modified demodulation symbols are obtained.

13. The method of claim 12, further comprising:

The obtained demodulation symbol is compared with the standard modulation symbol in the constellation diagram, and the obtained phase difference smoothes the phase frequency offset value of the strongest path of each mobile terminal and/or the maximum phase frequency offset value of each mobile terminal. , the processed result is saved as the Doppler frequency offset value of the current time slot.

14. A mobile terminal supporting estimation and compensation of Doppler shift in a time division synchronous code division multiple access TD-SCDMA system, the mobile terminal being configured to: receive a time slot containing data of the mobile terminal Then, the Doppler frequency offset value of the current time slot received signal is obtained by the phase difference between the current time slot and the channel estimation sequence of the comparison time slot, and combined with the joint detection, the received signal is corrected in the joint detection.

The mobile terminal of claim 14, wherein

The mobile terminal stores a preset range range of absolute values of the Doppler frequency offset values and n comparison time slots respectively corresponding to each range interval, wherein the range range is segment by segment Covers the absolute value of all possible Doppler shift values, "> 1;

Multiplying a spreading code, a channel code, and a scrambling code of each mobile terminal to obtain a composite spreading code of each mobile terminal; Constructing a joint detection matrix A by using the compensated average channel impulse response and the composite spreading code of each mobile terminal, and jointly detecting the data segments in the current time slot by using the joint detection matrix A, and obtaining the modified demodulation symbol.