WO2002021711A1

WO2002021711A1 - A method of channel estimation and the receive system for implementing said method

Info

Publication number: WO2002021711A1
Application number: PCT/CN2000/000264
Authority: WO
Inventors: Yu Zhang; Daoben Li
Original assignee: Linkair Communications, Inc.
Priority date: 2000-09-06
Filing date: 2000-09-06
Publication date: 2002-03-14
Also published as: CN1454412A; AU2000268172A1

Abstract

The present invention discloses a method and a system for spread frequency spectrum. The method comprises : after demodulating and dispreading by receive end the high frequency modulated signal sending by mobile station or base station, performing the channel estimation to the fade channel by the judgement fedd back channel estimation loop. Using the method of the present invention can save the transmit power of the base station or the mobile station, and can effectively overcome the influence of the signal amplitude and phase, can satisfy the application of high rate transform and high speed moving environment, can apply to the forward (base station to mobile station) and reverse (mobile station to base station) channels without any changing and can be easily performed.

Description

Method for channel estimation and receiving system implementing the method

Technical field

The present invention relates to the technical field of wireless spread-spectrum communication and digital mobile communication, and in particular, to a channel that can be applied to forward and reverse channels separately without any modification, and simultaneously meets the requirements of high data rate transmission and applications in high-speed mobile environments. Estimation method and signal receiving system implementing the method. Background of the invention

In modern high-speed mobile communications, due to the requirements for high data rates, research on high-dimensional state phase shift keying (PSK) modulation schemes has gradually become one of the core contents in wireless communications. However, multipath and large Doppler frequency shifts have been the main bottlenecks that limit the application of multilevel and multiphase modulation methods in high-speed mobile environments. In a high-speed mobile environment, the main factor affecting the performance of a PSK system is the effect of fast fading on the amplitude and phase of the PSK system. Especially in the deep fading environment, the amplitude deep fading will seriously degrade the performance of the system. To overcome these effects of fading channels, effective channel estimation must be performed. Especially in the third generation mobile communication system, mobile stations are required to adapt to the requirements of high data rate transmission and to withstand a deep fading environment with a Doppler frequency shift of about 500 Hz. To this end, several solutions already exist in the prior art. For example, the main solution proposed by Qualcomm in the third-generation mobile communication standard IS-2000 is to use continuous pilot channel estimation, that is, to use a common pilot channel (for downlink channels) or a dedicated pilot Channel (for uplink channel), the receiver obtains channel information by demodulating the pilot channel. In Europe, Nokia and Errisson proposed in WCDMA a joint estimation using continuous pilot channels and dedicated pilot channels. Compared with the IS-2000 pilot channel estimation algorithm, the algorithm adds an interval to the service channel. The pilot symbols in the channel information and pilot channel estimates from the pilot symbols The obtained channel information is weighted to obtain the final channel estimation value.

The continuous pilot is only used in the downlink communication of the CDMA communication system from the base station to the mobile station. At this time, the transmitting end uses a dedicated channel to conduct the frequency signal, and transmits with the signals of other channels. The signals of other channels at the receiving end are related to this pilot signal to eliminate the phase offset caused during the channel transmission process, so that each channel demodulates the original information. Continuous pilots can to some extent eliminate the effects of deep fading caused by high-speed movement. However, the pilot channel is required to be transmitted together with the signals of all other channels, and a dedicated channel is occupied. Therefore, the transmit power of the transmitter must be increased. Therefore, continuous pilot is only used in downlink communication (from base station to mobile station) of synchronous CDMA system. The dedicated pilot is to transmit a pilot symbol at a certain interval in each channel of the transmitting end, and use the channel parameters estimated by the pilot symbol to perform channel compensation on the data symbols following the pilot symbol to eliminate channel pairing. Effects of transmitted signals. It is easy to see from the principle of dedicated pilots that in a high-speed mobile environment, because the correlation between adjacent symbols is reduced, the compensation of data symbols following the pilot symbol channel estimation value is obviously Inaccurate, so this solution cannot effectively overcome the effects of deep fading on signal amplitude and phase, and cannot guarantee the application of higher-dimensional modulation methods in high-speed mobile environments. At the same time, the interference to the service signal is large, the implementation is complicated, and it is not suitable for the development trend of adaptive antennas in the future. Summary of the Invention

An object of the present invention is to provide a method for channel estimation that can be applied to forward and reverse channels separately without any modification, and simultaneously satisfies high data rate transmission and applications in high-speed mobile environments, and a signal receiving method for implementing the method. System to overcome the technical problems and deficiencies in the prior art solutions described above.

A channel estimation method applied in the spread spectrum communication technology of the present invention includes at least the following steps: an initial channel estimation is obtained through a service channel-assisted pilot symbol; The service data gives new channel estimation values symbol by symbol through the decision feedback method.

According to the above technical solution, the decision feedback method includes at least the following steps: for the high-frequency modulated signal transmitted by the transmitting end, the current data symbol is first despread and demodulated at the receiving end, and then the channel estimation information fed back by the previous symbol is used Perform phase compensation, complete the judgment of the current symbol information, and estimate the channel characteristics. At the same time, the channel estimation information of the current symbol is fed back to the next data symbol for phase compensation to complete the channel estimation of the next symbol.

Initial channel information is provided by the first auxiliary pilot symbol. The auxiliary pilot symbols inserted at intervals in the service data signal again give the reference value of the channel estimation. The transmission interval of this pilot symbol can be changed.

According to the above technical solution, the decision feedback method further includes the following steps:

(1) An initial channel estimate is obtained by demodulating and despreading the first auxiliary pilot symbol, and output through a first delayer;

(2) the latter data symbol uses the channel estimation information to perform phase compensation;

(3) Perform maximum ratio consolidation and judgment;

(4) Perform channel estimation;

(5) feedback the channel estimation value via the first delayer output;

(6) Repeat steps (2) to (5) with the next data symbol.

For the subsequent auxiliary pilot symbols, steps (2) and (3) are omitted, and steps (4), (5), and (6) are directly performed to newly give the reference value of the channel estimation.

A signal receiving system for realizing the above method of the present invention includes an antenna, an intermediate frequency and a radio frequency demodulation section, a despreading section, a channel estimation and decision section, and a decoding and source recovery section, which are characterized in that the channel estimation and the The decision part includes a decision feedback estimator, which is used for channel estimation and decision by passing the signal received by the antenna and demodulated and despread through a decision feedback channel estimation loop.

The decision feedback channel estimation loop includes a phase compensation section, a maximum ratio combining, and a decision The first delayer feedbacks the channel estimation information of the previous symbol output to the phase compensation section, performs phase compensation on the current signal after demodulation and despreading, and sends it. The maximum ratio combining and decision section is performed for maximum ratio combining and decision. The decision output is input to the channel estimation section together with the demodulated and despread current signal to perform channel estimation to output the current channel estimation amplitude and phase information. The estimation information is then fed back through the first delayer and output for the next symbol to perform phase compensation.

The novel channel estimation method for high data rate transmission and mobile environment proposed by the present invention is characterized in that an initial channel estimation is obtained by using a service channel-assisted pilot symbol, and the service data after the pilot symbol is determined by a decision feedback algorithm. The symbol gives a new channel estimate. For the high-frequency modulation signal sent by the mobile station or base station, the current symbol is first demodulated and despread at the receiving end, and the current symbol information is judged to estimate the channel characteristics. The channel estimation is completed using the current decision symbol information, that is, completed at the current symbol. After demodulation and despreading, the phase compensation is completed by using the estimated channel characteristics; then the maximum ratio combining and decision are performed; and then using the currently determined symbol information, the channel estimation of the next symbol is completed for phase compensation of the next symbol. Maximum ratio merger and decision. The role of the pilot symbols in the first is that the first pilot symbol provides initial channel information, and the second is that the pilot symbols inserted at intervals in the service signal are used to prevent erroneous decisions from causing erroneous channel estimation, which causes erroneous propagation .

According to the method of the present invention, the performance of the system is less affected by the moving speed of the mobile station, that is, less affected by the fast fading caused by Doppler frequency shift, so it can effectively overcome the deep fading caused by high data transmission and high speed movement Effect on signal amplitude and phase. At the same time, the transmission power of the signal is saved, the interference to the service signal is small, and the delay is small. Moreover, it can be applied to the forward (base station to mobile station) and reverse (mobile station to base station) channels without any changes, respectively. And the future development of adaptive antennas does not affect the application of this method, and the scope of application is broad.

Compared with the continuous pilot channel estimation method and the dedicated pilot channel estimation method in the prior art, the method of the present invention can save the transmission power of a signal, that is, occupy the transmission power of a base station or a mobile station. The advantages of low signal transmission power, simple implementation, small interference to service signals, and small time delay can effectively overcome the effects of deep fading on signal amplitude and phase. And it can be applied to the forward (base station to mobile station) and reverse (mobile station to base station) channels without any changes. And it can better adapt to the development of adaptive antennas in the future, and has a wide application range. Brief description of the drawings

Figure 1 is a block diagram of a simple CDMA mobile communication system.

Figure 2 is a block diagram of an overall receiver according to the method of the present invention.

Fig. 3 is a block diagram of a preferred embodiment of the method according to the present invention.

Fig. 4 is a block diagram of a preferred embodiment of the method according to the present invention.

Fig. 5 is a block diagram of a preferred embodiment of the method according to the present invention.

Fig. 6 is a block diagram of a preferred embodiment of the method according to the present invention.

Figure 7 is a schematic diagram of the system frame structure. Mode of Carrying Out the Invention

The present invention is described in detail below with reference to the drawings. FIG. 1 is a block diagram of a simple CDMA mobile communication system. A signal is generated by a source generator 101, encoded by an encoder 102, spread by a spreader 103, and then modulated by an intermediate frequency and a radio frequency modulator 104 into a high frequency modulation symbol. The antenna 105 transmits. At the receiving end, it is received by the receiving antenna 106, demodulated by the intermediate frequency and radio frequency demodulator 107, and after despreading by the despreader 108, channel estimation and judgment are performed by 109, and then output by the decoding and source recovery section 110.

Referring to FIG. 2, the decision feedback channel estimation loop realizes the estimation of the characteristics of the fading channel by using a service channel auxiliary pilot symbol and a decision feedback algorithm. First, the amplitude and phase information of the channel can be directly obtained from the demodulated and despread pilot symbols, and provided to the next symbol through the first delayer 115 in FIG. 2. The next symbol uses this channel information to complete phase compensation by 112. End 113 Combined at the maximum ratio, this symbol is determined by 114. This new channel information is then fed back to 112 and provided to subsequent symbols for use.

Pilot symbols can approximate the accurate estimation of channel fading characteristics. This estimate is used to give the initial amplitude and phase references for the demodulation and decision circuits. The traffic channel after the pilot symbol is given a new channel estimate value by symbol by the decision feedback algorithm, and the compensation for the channel characteristics is adjusted from time to time. To prevent erroneous propagation, pilot symbols are inserted after every certain service signal, and the amplitude and phase reference values of the channel estimates are given again. FIG. 7 shows the positions of the pilot symbols, that is, the first symbol of each subframe is a known pilot symbol, the pilot symbol is a service symbol, and several subframes constitute a transmission frame structure. The figure shows that the pilots of the system do not occupy continuous common physical channels. Each mobile user has its own specific pilot symbol. The pilot's spreading code can be the same as or different from that of the user. In the forward channel, pilot signals can also be spread using the same spreading code in the same cell or sector. The pilot symbols transmit known symbols, and the transmission interval can be changed, and it is not affected by the moving speed of the mobile station. Figure 3 is a first preferred embodiment of the present invention. Referring to FIG. 3, the receiver completes the phase compensation of the current symbol according to the channel estimation value obtained by the previous symbol (which may be a pilot or a service), merges and decides the maximum ratio, and obtains the decision information of the symbol. Then it is input to the divider 117 together with the demodulated and despread data output by the second delayer 116, and the symbol information in the data is removed to obtain new channel amplitude and phase information, and then this new The channel information is fed back to 112 and provided to subsequent symbols. The above process can be expressed by the following formula: (k) = (find, (k) + n _d (k)) ld {k); ...... ₍₁ )

d (k + l) = ∑ (d (k +

Where d (k) is the data of the k-th business symbol, W is the additive white Gaussian noise with a mean value of 0 and a variance of σ ² for the k-th business symbol. The multiplicative noise of the fading channel, which represents the amplitude and phase distortion of the signal (A) is a complex number, is its estimated value, and is the decision result of the k-th symbol. L is the total number of separable paths of the channel. Fig. 4 is a second preferred embodiment of the present invention. Referring to FIG. 4, the receiver completes the phase compensation, maximum ratio combining and decision of the symbol according to the average of the channel estimation values of the previous N symbols, and obtains the channel estimation value of the symbol. Or pass the channel estimation value of the first N symbols through FIR (Finite Impulse Response Filter) or IIR (Infinite Impulse Response Filter), and use the channel estimation value of the filter for phase compensation of this symbol, and combine the maximum ratio And decision, and obtain the channel estimate of this symbol. The purpose of this is to reduce the effect of noise on the channel estimates.

This embodiment is an improvement based on the first embodiment, that is, the accumulator or the FIR or IIR low-pass filter 120 is used to suppress the bad influence on the channel estimation caused by noise and interference, and the rest is the same as the first embodiment. This significantly improves the channel estimation of mobile stations moving at low speeds, thereby also improving their service performance. For example, it can be mainly applied to the case of low speed (<50km / h) movement. Fig. 5 is a third preferred embodiment of the present invention. Please refer to Figure 5. This scheme is mainly used in the case of high-speed (> 200km / h) movement. That is to say, the receiver uses a certain algorithm (as described above) to predict the channel estimates of the current symbol based on the channel estimates of the first N symbols to complete the phase compensation, maximum ratio combining, and decision of this symbol. And get the actual channel estimate for this symbol.

This embodiment is an improvement based on the first embodiment. That is, by adding the predictor 123, the synchronization estimation of the channel is realized, and the lag characteristic of Embodiment 1 and Embodiment 2 is avoided. At the same time, in order to continue to maintain the advantages of the simpleness of the invention, a simple prediction algorithm is used. For first-order linearity The prediction algorithm can be expressed as follows:

h, (k) = (d (k) h, (k) + n _d (k)) / d (k);

¾ (k + l) = h, (k) + (h, (k) -h ^ kl)); ... ⁽²⁾

d (k + l)

Where + is the predicted value of the channel estimate obtained for the (k + 1) th symbol. Similar algorithms can be used for second-order prediction. Fig. 6 is a fourth preferred embodiment of the present invention. Please refer to FIG. 6. This scheme is mainly applied to the uplink channel. A Kalman filter is used here, which combines the advantages of the second embodiment and the third embodiment, but avoids their disadvantages. Because the second embodiment causes the obtained channel estimation value to lag behind the actual channel value, it cannot be applied to the case of high-speed movement, while the channel estimation value obtained by the third embodiment will be affected by noise more than the first embodiment. This embodiment overcomes these disadvantages, but because its algorithm is already more complicated, it is more suitable for the uplink channel, that is, the receiver is on the base station side.

This embodiment is an improvement based on the third embodiment, that is, by adding a Kalman filter 126, the predictor 123 in the third embodiment is improved, thereby maintaining the advantages of the synchronous estimation in the third embodiment and suppressing it by filtering. The adverse effects of noise. The calculation method of the Kalman filter has a well-established theory, and engineering designers can complete their design without creative work. It is obvious to those skilled in the art that according to the channel estimation method disclosed in the present invention, there are many ways to modify the disclosed invention, and in addition to the above-mentioned specific preferred modes, the present invention may have many other embodiments. . Therefore, any method or improvement that can be obtained according to the concept of the present invention shall fall within the protection scope of the claims of the present invention.

Claims

Claim

1. A channel estimation method used in spread spectrum communication technology, characterized in that the method includes at least the following steps:

An initial channel estimate is obtained by using the auxiliary pilot symbol of the traffic channel, and the service data after the pilot symbol is given a new channel estimate value by symbol by a decision feedback method.

2. The method according to claim 1, wherein the method for determining feedback comprises at least the following steps:

For the high-frequency modulation signal transmitted by the transmitting end, the current data symbol is first despread and demodulated at the receiving end, and then the channel estimation information fed back by the previous symbol is used for phase compensation to complete the judgment of the current symbol information and estimate the channel characteristics;

At the same time, the channel estimation information of the current symbol is fed back to the next data symbol for phase compensation to complete the channel estimation of the next symbol.

3. The method according to claim 1, wherein the initial channel information is provided by a first auxiliary pilot symbol.

4. The method according to claim 1, characterized in that: the auxiliary pilot symbols inserted at intervals in the service data signal, and the reference value of the channel estimation is given again.

5. The method according to claim 4, characterized in that: the first symbol of each transmission subframe is an auxiliary pilot symbol, the pilot symbol is a service data symbol, and the transmission frame structure is composed of a plurality of subframes .

6. The method according to claim 5, wherein each mobile user has its specific pilot symbol, and the spreading code of the pilot can be the same as or different from the spreading code of the user.

7. The method according to claim 5, characterized in that: the same cell or sector in the forward channel uses the same spreading code to spread the pilot symbols.

8. The method according to claim 4 or 5, characterized in that: the transmission interval of the pilot symbols can be changed.

9. The method according to claim 1 or 2, wherein the method for determining feedback further comprises the following steps:

(3) Perform maximum ratio consolidation and judgment;

(4) Perform channel estimation;

(5) feedback the channel estimation value via the first delayer output;

(6) Repeat steps (2) to (5) with the next data symbol.

10. The method according to claim 9, characterized in that steps (2) and (3) are omitted for subsequent auxiliary pilot symbols, and steps (4), (5) and (6) are directly performed, so that The reference value of the channel estimation.

11. The method according to claim 2 or 9, wherein the channel estimation comprises at least the following steps:

The demodulated and despread received data is output through a second delayer, and is input to a divider together with the known pilot symbol or the decision symbol, the symbol information in the data is removed, and the new channel amplitude and Phase information.

12. The method according to claim 11, further comprising: outputting the signal output by the divider through an accumulator, a finite impulse response filter, or an infinite impulse response filter.

13. The method according to claim 11, further comprising: outputting a signal output by the divider through a first-order or second-order predictor.

14. The method according to claim 11, further comprising: The output signal is output through a Kalman filter.

15. A signal receiving system for implementing the method according to claim 1, comprising an antenna, an intermediate frequency and a radio frequency demodulation section, a despreading section, a channel estimation and decision section, and a decoding and source recovery section, wherein: The channel estimation and decision section of the Q & A includes a decision feedback estimator for performing channel estimation and decision by passing a demodulated and despread signal received by the antenna through a decision feedback channel estimation loop.

16. The receiving system according to claim 13, wherein: the decision feedback channel estimation loop comprises a phase compensation section, a maximum ratio combining and decision section, a channel estimation section and a first delayer, wherein The channel estimation information of the previous symbol output from a delayer feedback is fed back to the phase compensation section, phase compensation is performed on the demodulated and despread current signal, and then sent to the maximum ratio combining and decision section for maximum ratio combining and decision. The output is input to the channel estimation section together with the demodulated and despread current signal to perform channel estimation, so as to output the current channel estimation amplitude and phase information. The channel estimation information is then fed back to the next delay output for the next delay. The symbols are phase compensated.

17. The receiving system according to claim 16, wherein: the channel estimation section includes a second delayer and a divider, and the demodulated and despread signal data is output through the second delayer, The known pilot symbols or decision symbols are input to the divider together, the symbol information in the data is removed, and new channel amplitude and phase information is output.

18. The receiving system according to claim 17, characterized in that: the divider can further pass an accumulator or an infinite impulse response filter or a finite impulse response filter or a first-order, second-order Output after a predictor or a Kalman filter.