WO2002039686A1

WO2002039686A1 - A channel estimating method and apparatus thereof

Info

Publication number: WO2002039686A1
Application number: PCT/CN2000/000420
Authority: WO
Inventors: Cosmos Zhang; Daoben Li
Original assignee: Linkair Communications, Inc.
Priority date: 2000-11-09
Filing date: 2000-11-09
Publication date: 2002-05-16
Also published as: CN1402922A; CN1188957C; AU2001212666A1

Abstract

The present invention discloses a method and apparatus of time division pilot channel estimation using in the spread spectrum communication technology, which obtain the phase and amplitude estimation value of the channel using the adjacent pilot signals, and correct the amplitude of one of the pilot symbol utilizing the power control instruction know to the receiver corresponding to the pilot signal, and acquire channel estimation result among the traffic signal by interposing values. The present invention can be suitable to various modulating manner, especially multi-level modulating manner in the CDMA system with power control, so as to significantly improve the performance of the mobile communication system.

Description

Channel estimation method and device

The present invention relates to the fields of wireless spread-spectrum communication and digital mobile communication, and in particular, to a channel estimation method suitable for various modulation modes under high data rate transmission and a device for implementing the method. Background of the invention

In modern high-speed mobile communications, due to the requirements for high data rates, research on multilevel 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. To overcome these effects of fading channels, effective channel estimation must be performed. Especially in the third generation of mobile communications, mobile stations are required to adapt to high data rate requirements and to endure a deep fading environment with a Doppler frequency shift of about 500 Hz. For this reason, there are already several solutions in the prior art.

For example, the solutions proposed by Nokia and Errisson in Europe in Wideband Code Division Multiple Access (WCDMA) use a joint estimation of continuous pilot channels and dedicated pilot channels in their forward channels, while using dedicated estimates in their reverse channels. Pilot channel estimation (see 3GPP TS25.211). The dedicated pilot channel estimation method 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, so that Eliminate the impact of the channel on the transmitted signal. In this dedicated pilot channel structure, since the pilot signal and the service signal are time-division multiplexed, the channel estimation of the service signal is obtained by interpolation calculation based on the channel characteristics estimated by the pilot symbols before and after it. Therefore, this method is only feasible for single-level modulation, such as QPSK used in WCDMA, because in single-level modulation In this mode, the channel estimation only needs to estimate the change of the phase characteristics of the channel, but does not need to estimate the change of the amplitude, that is, in the single-level modulation mode, it is not necessary to consider the influence on the estimation of the channel amplitude due to power control. However, for multi-level modulation methods, such as 16QAM, 64QAM, etc., due to the inevitable power control in the CDMA system, the amplitude of adjacent pilot symbols will be affected not only by the channel's amplitude fading, but also by the power control. The magnitude of the adjacent pilot symbols not only reflects the change in channel amplitude during this time period, but also includes the change in transmit power caused by power control. Therefore, there is a large error in the estimated value of the channel amplitude obtained by using this dedicated pilot channel estimation method, which cannot accurately and effectively guarantee the correctness of the channel estimation, and furthermore cannot guarantee the application of higher-dimensional Modulation. Summary of the invention

The channel estimation method and device for high data rate transmission and high-speed mobile environment provided by the present invention are obtained by adding a time division dedicated pilot channel estimation method commonly used in the prior art? Wenjin can greatly reduce the estimation error of the channel amplitude caused by the power control technology, and can adapt to various modulation modes, especially the multilevel modulation mode in a CDMA system with power control.

A time division pilot channel estimation method applied in a code division multiple access (CDMA) system provided by the present invention is that when channel estimation is performed by using the time division pilot method, after obtaining amplitude estimates of adjacent pilot symbols, First use the power control command corresponding to the pilot symbol known by the receiver to modify the amplitude value of one of the pilot symbols to eliminate the influence of power control on the signal amplitude, and then obtain the service signal in between by interpolation. Channel estimation results.

According to the method of the present invention, the method may further include the following steps:

a) despreading and demodulating the received signal;

b) separating the pilot signal and the service signal from the despread demodulated signal; C) Separating the amplitude and phase of the pilot signal, and obtaining an estimated value of the amplitude and phase of the channel;

d) for the obtained channel amplitude estimation value, between adjacent pilot symbols, using a power control command known to the receiver and corresponding to the pilot symbol to modify the amplitude value of one of the pilot symbols, To eliminate the effect of power control on signal amplitude;

e) obtaining the channel estimation result of the service signal between the pilot symbols through interpolation according to the channel phase estimation value and the modified amplitude estimation value obtained above;

f) using the channel estimation result to perform phase compensation on the service signal;

g) Perform maximum ratio combining on service signals after phase compensation compensation, judge and output data.

The above-mentioned modified amplitude value of a pilot symbol may be: when the power control command is to increase transmit power, then multiply the amplitude estimated value of the previous pilot symbol by 10 ¹ , or the estimated amplitude value of the next pilot symbol Multiply by ιΛο ^; When the power control command is to reduce transmit power, multiply the estimated amplitude of the previous pilot symbol by ΙΛΟ ⁵⁵ , or multiply the estimated amplitude of the next pilot symbol by ιο; where △ is the power control Step size.

A time division pilot channel estimator applied in a code division multiple access (CDMA) system provided by the present invention includes at least:

A signal demodulation and despreading device to despread and demodulate a received signal;

A splitter that separates a pilot signal and a service signal;

The pilot channel estimator uses the pilot signal to perform channel estimation to obtain an estimated value of the channel amplitude and phase;

The arithmetic unit 1 uses the power control command corresponding to the pilot symbol known by the receiver between adjacent pilot symbols to modify the obtained channel amplitude estimation value to modify one of the adjacent pilot symbols. The amplitude of each pilot symbol to eliminate the influence of power control on the signal amplitude;

The arithmetic unit 2 obtains the channel estimation result of the service signal between the pilot symbols by interpolation according to the channel phase estimation value and the modified amplitude estimation value obtained above;

The phase compensator uses the above channel estimation result to perform phase compensation on the service signal; and a merger and decision unit combines the phase-compensated service signal to determine and output data.

According to the channel estimator of the above technical solution, the arithmetic unit 1 may be a multiplier, and its inputs are the amplitude estimates of the channels output by the pilot channel estimator and the power output by the power control command generator in the receiver. Control commands; and

When the power control command between adjacent pilot symbols is to increase transmission power, multiply the estimated amplitude value of the previous pilot symbol by 1 or multiply the estimated amplitude value of the next pilot symbol by 1 / 10∞; To reduce the transmission power, the power control command between adjacent pilot symbols is to multiply the estimated amplitude of the previous pilot symbol by l / io, or to multiply the estimated amplitude of the next pilot symbol by

10 ^Γο ; where △ is the power control step size.

The channel estimator according to the above technical solution may further include a delayer, and the channel estimation result of the corresponding pilot symbol service signal obtained through the interpolation of the operator 2 is sent to the phase compensator to the service after the delayer delays. The signal is phase compensated.

According to the channel estimator of the above technical solution, the merging and deciding device may be a maximum ratio merging and deciding device, which performs maximum ratio merging on the phase-compensated service signal, determines and outputs data.

A signal receiving system in a code division multiple access (CDMA) system to which the present invention is applied includes a receiving antenna, an intermediate frequency radio frequency demodulation section, a despreading section, a channel estimation and decision section, a decoding and source recovery section, wherein: The channel estimation and decision part adopts the time division pilot channel estimator of the present invention, including a splitter, a pilot channel estimator, an operator 1, an operator 2 and a phase compensation and merging and decision device, wherein the despreading is performed. The demodulated signal separates the pilot signal and the service signal through a splitter, estimates the phase and amplitude of the channel through the pilot channel estimator, and corrects the estimated amplitude through the arithmetic unit 1 to eliminate power control on the signal amplitude. The influence of the channel estimation result of the service signal between the corresponding pilot symbols is obtained by the operator 2 through interpolation, the channel estimation result is output to the phase compensation device, the phase compensation is performed on the service signal, and the phase compensation is performed in the combination and decision device. The subsequent service signals are combined, judged and output data.

The signal receiving system according to the above technical solution, wherein the arithmetic unit 1 may be a multiplier, and its inputs are the amplitude estimates of the channels output by the pilot channel estimator and the power output by the power control command generator in the receiver. Control commands; and

When the power control command between adjacent pilot symbols is to increase the transmission power, the estimated amplitude value of the previous pilot symbol is multiplied by ¹ ο, or the estimated amplitude value of the next pilot symbol is multiplied by ι / ΐο ^¾ ; When the power control command between adjacent pilot symbols is to reduce the transmission power, multiply the estimated amplitude value of the previous pilot symbol by ι / ΐο, or multiply the estimated amplitude value of the next pilot symbol by

10 ^; where Δ is the power control step size.

According to the signal receiving system of the above technical solution, the merging and deciding device may be a maximum ratio merging and deciding device, which performs maximum ratio merging on the phase-compensated service signal to determine and output data.

The signal receiving system according to the above technical solution may further include a delayer, and the channel estimation result of the corresponding pilot symbol service signal obtained through the interpolation of the operator 2 is sent to the phase compensator to the service after being delayed by the delayer. The signal is phase compensated.

Here, the power control step size can be transmitted to the transmitter in real time by signaling. The receiver may be set by the system and announced in the form of broadcast, etc.

The channel estimation technology disclosed in the present invention uses the power control bits formed in the receiver and a certain power control step to eliminate the estimation error of the channel amplitude caused by the adoption of the power control technology in the existing channel estimation technology. Thus, the channel estimation in the multilevel modulation mode is realized.

Compared with the dedicated pilot channel estimation technology in the prior art, the channel estimation technology disclosed in the present invention overcomes the defect that the time division dedicated pilot channel estimation in the prior art cannot be applied to a high-dimensional modulation method, and not only retains the existing All the advantages of the dedicated time-division pilot channel estimation in the technology can be applied to various modulation modes. And in the presence of power control

In the CDMA system, the channel estimation technology disclosed in the present invention is adopted, and both theoretical analysis and computer simulation have proved that this method can bring a significant improvement in the performance of the mobile communication system. Brief description of the drawings

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

Fig. 2 is a block diagram of a preferred embodiment according to the present invention.

Fig. 3 shows the performance comparison between the simulation curve of the present invention and the prior art under the 16QAM modulation mode. Mode of Carrying Out the Invention

The present invention is described in detail below with reference to the drawings. Referring to FIG. 1, FIG. 1 shows a simple CDMA mobile communication system. The source generator 101 generates a signal, which is encoded by the encoder 102, and after being spread by the spreader 103, the spread spectrum signal is sent to the modulator 104 for intermediate frequency and radio frequency modulation, and then the signal power is transmitted through the transmitting antenna 105. At the receiver end, the receiving antenna 106 receives the signal power, and then it is demodulated by the demodulator 107 into a baseband signal. The despreader 108 completes the despreading process, and the channel estimation circuit 109 completes the translation. The channel estimation required by the code and source recovery circuit 110, and according to the difference between the received signal and the interference level, a power control command is generated and transmitted to the transmitting end via the power control loop 111 for power control.

In the existing CDMA system, power control technology is commonly used, and it is generally divided into open loop power control, closed loop power control and outer loop power control. Among them, closed-loop power control has the highest frequency, and its purpose is to partially track fast fading. Closed-loop power control requires an adjustment of the transmitted signal power within 0.5-lms.

Due to the existence of power control, new content is introduced to channel estimation, especially for channel estimation in the time division dedicated pilot channel mode. Because in general, the interval between adjacent time division pilot signals is roughly equivalent to the power control time period. In this way, different pilot signals are in different power control time periods. Therefore, the change in the amplitude of adjacent pilot signals not only reflects the change in channel amplitude characteristics during the time period, but also reflects the change in transmit power due to power control during the time period. In the single-level modulation mode, since the channel estimation only needs to estimate the change in the phase characteristics of the channel, and the change in the amplitude does not need to be estimated, there is no impact due to the power control as described above when the time-division dedicated pilot method is used Because power control does not change the phase characteristics of the signal. However, in multilevel modulation, this problem becomes prominent. Because both the amplitude and phase of the received signal contain the transmitted signal information, they must be obtained accurately and reliably. This requires that the channel estimation must complete both the amplitude and phase estimation of the channel.

If there is no power control, the same method as the phase estimation of the channel can be used, that is, the channel amplitude and phase characteristics estimated by adjacent pilot symbols are used, and according to a given algorithm, such as a linear interpolation algorithm or a Gaussian interpolation The algorithm performs interpolation to obtain an estimated value of the channel amplitude and phase of the service signal between the pilot symbols.

But there is almost no CDMA system without power control. Therefore, for the multi-level modulation method, the above-mentioned method for estimating the channel amplitude theoretically has errors and Defects. Because as described above, the magnitude of the adjacent pilot symbols not only reflects the change in channel amplitude during this time period, but also includes the change in transmit power caused by power control. Therefore, if there is no improvement, there will be errors in the estimated value of the channel amplitude. If the step size of the power control, that is, the change value of the transmission power in the adjacent power control period is relatively large, such as IdB or 2dB, the error in the estimation of the channel amplitude due to the power control will also be large, which may The performance of the time division pilot channel method is drastically deteriorated or even unusable.

As mentioned above, for closed-loop power control, the control command is to measure the signal interference level of the receiver, so that the power control command is fed back to the transmitter. If the received signal quality is too low, the transmitter is required to increase a power control step size. The transmit power is reduced, and the transmit power is reduced by one power control step. That is to say, the receiver knows clearly and does not need any form of signaling to notify the receiving end of the power control action taken on any corresponding time period of the received signal, that is, to increase or decrease the transmission power. Therefore, when channel estimation is performed using the time-division pilot method, after obtaining the amplitude values of adjacent pilot symbols, the estimated value of the channel amplitude of the service signal is not obtained through interpolation immediately, because it will introduce power-induced Error due to change in transmit power. We can use the power control action already known between the receiver and the corresponding pilot symbol to modify the amplitude value of one of the pilot symbols. For example, if the power control performed during this time period is to increase the transmission power, then the increase of this transmission power will inevitably lead to an increase in the amplitude value of the latter pilot symbol. The calculation of the increase value is simple. Assume that the step size of the power control is A dB, the amplitude increase value of the corresponding pilot symbol is 1 (^ times. This is the error of the channel amplitude estimation value due to the presence of power control. It can be seen that the larger the power control step size Δ, the greater the impact The more obvious it is, before performing the interpolation calculation, divide the amplitude estimate of the next pilot symbol through a divider and divide by

10¾, or multiply the estimated amplitude of the previous pilot symbol by 10 °. If the power control performed during this time period is to reduce the transmission power, then modify the guidance according to the same principle. The amplitude estimated value of the frequency symbol, that is, before the interpolation calculation is performed, the amplitude estimated value of the subsequent pilot symbol is passed through a multiplier and multiplied by 10. Or, the amplitude estimation value of the previous pilot symbol is passed through a divider and divided by 10 ^. Through such simple modification, the influence of power control on multi-level modulation time-division dedicated pilot channel estimation is eliminated, thereby achieving correct channel estimation.

Referring to FIG. 2, FIG. 2 illustrates a channel estimator according to the present invention for estimating the characteristics of a fading channel through pilot symbols and an interpolation algorithm. First, the despread signal is obtained by the demodulation and despreading device 112, and then the despread pilot signal and the service signal are obtained respectively through the splitter 113; the pilot signal is used for channel estimation, so it uses the pilot channel estimation The generator 114 obtains the channel amplitude and phase estimation values, where the amplitude value contains the influence of power control and must be removed; the power control bit generator 115 outputs the power control bit "1" or "0". Feedback to the transmitting end for actual power adjustment. On the other hand, it is used to determine whether the multiplier of the multiplier 116 is 10 ^ or Δ is the power control step size, and its unit is dB. The influence of power control is removed by the channel amplitude estimation value after the multiplier, so that the channel estimation of the service signal can be performed after 117, and the channel estimation value (including amplitude and phase) of the service signal can be obtained, and then passed through the delay 118. It is provided to the phase compensator 119 and the maximum ratio combining and judging device 120 to perform a service signal decision.

The above embodiments have clearly assumed that the size of the power control step size Δ is already known by the receiver, otherwise the receiver cannot know exactly the size of the channel amplitude estimate value that should be estimated for the pilot signal. There are two ways to get this step size: 1) The transmitter sends the step size to the receiver in real time through signaling; 2) The system sets a relatively fixed step size and announces it in the form of a broadcast.

Referring to FIG. 3, FIG. 3 shows a simulation performance curve comparison between the present invention and the prior art in a 16QAM modulation mode. In the figure, the abscissa is Eb / No, the unit is db, and the ordinate is the symbol error rate. Among the two curves shown in the figure, a dashed curve is provided according to the present invention. The system performance curve obtained by the channel estimation method simulation. The other solid curve is that the channel estimation method applied in the single-level modulation method is directly applied to the 16QAM modulation method without using the method provided by the present invention. Simulation results. It can be clearly seen from the simulation curve that the improved method of the present invention can bring about significant performance improvement, which is about 1-2 dB. A rough estimate shows that this is equivalent to bringing a 26% -58% increase in capacity to a CDMA system. Since the method disclosed in the present invention does not bring much complexity to the system, the gain brought by using the method disclosed in the present invention is undoubtedly worthwhile.

The idea of the present invention is applied to a signal receiving system in a code division multiple access (CDMA) system. The signal receiving system includes a receiving antenna, an intermediate frequency radio frequency demodulation part, a despreading part, a channel estimation and decision part, a decoding and a source recovery. section. The channel estimation and decision part is a time division pilot channel estimator using the technology of the present invention, which utilizes the power control bits formed in the receiver and a certain power control step size to eliminate the effects of power control in channel estimation on channel estimation. The estimation error of the channel amplitude, so as to realize the channel estimation in the multilevel modulation mode. According to the method described in the present invention, for those of ordinary skill in the art, there may be more embodiments. Although the present invention only provides the embodiment in the 16QAM modulation mode, for a higher-dimensional modulation mode, Those skilled in the art can obviously implement the present invention and obtain good channel estimation results.

Claims

Claim

1. A time division pilot channel estimation method applied in a code division multiple access (CDMA) system, which is characterized by:

When channel estimation is performed by using the time division pilot method, after obtaining the amplitude estimation values of adjacent pilot symbols, the power control command corresponding to the pilot symbols known by the receiver is used first. The amplitude value of the pilot symbol is used to eliminate the influence of power control on the signal amplitude, and the channel estimation result of the service signal in between is obtained by interpolation.

2. The channel estimation method according to claim 1, wherein the correction of the amplitude value of a pilot symbol comprises:

When the power control command is to increase the transmission power, the amplitude estimate of the previous pilot symbol is multiplied by 10 ^, or the amplitude estimate of the next pilot symbol is multiplied by 1/10. ;

When the power control command is to reduce transmission power, multiply the estimated amplitude of the previous pilot symbol by 1/10 ^, or multiply the estimated amplitude of the next pilot symbol by

Where Δ is the power control step size.

3. The channel estimation method according to claim 2, characterized in that said power control step size is transmitted by the transmitter to the receiver in a real-time signaling manner.

4. The channel estimation method according to claim 2, wherein the step size of the power control is set by the system and announced in a broadcast form.

5. The channel estimation method according to claim 1, further comprising the following steps:

Despread and demodulate the received signal;

Separating pilot signals and service signals from the signals obtained by despreading and demodulating;

Separate the amplitude and phase of the pilot signal and obtain an estimate of the amplitude and phase of the channel Count

For the obtained channel amplitude estimates, between adjacent pilot symbols, the power control command corresponding to the pilot symbols known by the receiver is used to modify the amplitude value of one of the pilot symbols to eliminate The effect of power control on signal amplitude;

Obtaining a channel estimation result of a service signal between pilot symbols by interpolation according to the channel phase estimation value and the modified amplitude estimation value obtained above;

Use the channel estimation result to perform phase compensation on the service signal;

Carry out the maximum ratio combining of the service signals after phase compensation compensation, judge and output the data.

6. The channel estimation method according to claim 5, wherein the correction of the amplitude value of a certain pilot symbol comprises:

When the power control command between adjacent pilot symbols is to increase the transmission power, multiply the estimated amplitude value of the previous pilot symbol by 10 ^, or multiply the estimated amplitude value of the next pilot symbol by 1/10 ^; When the power control command between adjacent pilot symbols is to reduce the transmission power, the estimated amplitude value of the previous pilot symbol is multiplied by 1/10. , Or multiply the amplitude estimate of the next pilot symbol by

10 ^ °; where △ is the power control step size.

7. A time-division pilot channel estimator applied in a code division multiple access (CDMA) system, which is characterized by including at least:

A splitter that separates a pilot signal and a service signal;

The arithmetic unit 1 corrects the amplitude of a pilot symbol among adjacent pilot symbols by using a power control command known to the receiver and corresponding to the pilot symbol between adjacent pilot symbols. Value to eliminate the effect of power control on signal amplitude; The arithmetic unit 2 obtains the channel estimation result of the service signal between the pilot symbols through interpolation according to the channel phase estimation value and the modified amplitude estimation value obtained above;

8. The channel estimator according to claim 7, wherein said operator 1 is a multiplier, and its inputs are the amplitude estimates of the channels output by the pilot channel estimator and the power control commands in the receiver, respectively. A power control command output by the generator; and

When the power control command between adjacent pilot symbols is to increase the transmission power, the estimated amplitude value of the previous pilot symbol is multiplied by 1, or the estimated amplitude value of the next pilot symbol is multiplied by 1/10 ^; The power control command between adjacent pilot symbols is to reduce the transmission power, then multiply the estimated amplitude of the previous pilot symbol by 1/10 ^, or multiply the estimated amplitude of the next pilot symbol by

10 ^; where △ is the power control step size.

9. The channel estimator according to claim 8, characterized in that the power control step size is transmitted by the transmitter to the receiver in a real-time signaling manner.

10. The channel estimator according to claim 8, wherein the step size of the power control is set by the system and announced in a broadcast form.

11. The channel estimator according to claim 7, further comprising a delayer, wherein the channel estimation result of the corresponding pilot symbol service signal obtained by interpolation by said operator 2 is delayed by the delayer. The phase compensator is sent to perform phase compensation on the service signal.

12. The channel estimator according to claim 7, wherein the merging and deciding device is a maximum ratio merging and deciding device, which performs maximum ratio merging on the phase-compensated service signal, and judges and outputs data.

13. A signal receiving system applied in a code division multiple access (CDMA) system, including It includes a receiving antenna, an IF radio frequency demodulation part, a despreading part, a channel estimation and decision part, a decoding and source recovery part, and is characterized by:

The channel estimation and decision part is a time-division pilot channel estimator, including a splitter, a pilot channel estimator, an operator 1, an operator 2 and a phase compensation and merging and decision device, which is despread and demodulated. The pilot signal and the service signal are separated by a splitter, the phase and amplitude of the channel are estimated by the pilot channel estimator, and the estimated amplitude is corrected by the operator 1 to eliminate the influence of the power control on the signal amplitude The channel estimation result of the service signal between the corresponding pilot symbols is obtained by the operator 2 through interpolation, the channel estimation result is output to a phase compensation device, the phase compensation is performed on the service signal, and the phase compensation is performed in the merging and decision device. The business signals are combined, and the data is judged and output.

14. The signal receiving system according to claim 13, wherein said operator 1 is a multiplier, and its inputs are the amplitude estimates of the channels output by the pilot channel estimator and the power control commands in the receiver, respectively. A power control command output by the generator; and

When the power control command between adjacent pilot symbols is to increase the transmission power, the estimated amplitude value of the previous pilot symbol is multiplied by 1 °, or the estimated amplitude value of the next pilot symbol is multiplied by; To reduce the transmit power, the power control command between pilot symbols is to multiply the amplitude estimate of the previous pilot symbol by 1/10 ⁵ or the amplitude estimate of the next pilot symbol to be multiplied by

10 where △ is the power control step size.

15. The signal receiving system according to claim 13, wherein the merging and deciding device is a maximum ratio merging and deciding device, which performs maximum ratio merging on the phase-compensated service signal to determine and output data.

16. The signal receiving system according to claim 13, further comprising a delayer, and a signal of a corresponding pilot symbol service signal obtained through interpolation by said arithmetic unit 2. The channel estimation result is sent to the phase compensator after the delay of the delayer to perform phase compensation on the service signal.