CN1312625A - Dynamic average length regulating method and device for channel estimation - Google Patents
Dynamic average length regulating method and device for channel estimation Download PDFInfo
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Abstract
The invention method includes the following steps: (1). estimating maximum Doppler frequency-shift of moving channel; (2) calculating optimum average length according to the maximum Doppler frequency-shift; (3). making dynamic regulation according to the calculated optimum average length. Said invented equipment includes instantaneous channel parameter estimator, maximum Doppler frequency-shift estimator, optimum average length calculating device and M data accumulation average calculating devices, in which the instantaneous channel parameter estimator is connected with maxium Doppler frequency-shift estimator and M data accumution average calculating devices simultaneously. Said invention is simple and easy to make calculation, can be used in any CDMA communication system with continuous pilot, including 3GPP WCDMA and 3GPP2 CDMA 2000 system, and can greatly raise receiving performance of RAKE receiving machine.
Description
The present invention is in the field of CDMA (code division multiple access) cellular communication systems.
The CDMA cellular communication technology has a great potential for development due to its characteristics of simple frequency planning, large system capacity, strong multipath resistance, good communication quality, small electromagnetic interference, and the like, and is a mainstream technology for future mobile communications including the third generation. CDMA spread spectrum signal receivers are divided into coherent and non-coherent receivers. Coherent receivers need to know the phase information of the received signal, while noncoherent receivers do not need the phase information of the received signal, but require that the transmitted signal is in a quadrature modulation mode. The invention mainly considers the dominant coherent receiving mode in the future CDMA cellular system.
There is a multipath fading phenomenon in the mobile communication system, which causes severe multipath interference. In a CDMA cellular mobile communication system employing spread spectrum technology, amplitude and phase information of a multipath signal can be estimated by receiving a Pilot signal with certain information, thereby enabling multipath diversity and coherent reception. A coherent spread spectrum receiver for diversity processing of multi-path fading signals is called RAKE receiver, which can carry out phase correction and maximum ratio combining processing on a plurality of single-path signals carrying the same information and having mutually independent fading characteristics, thereby achieving the purposes of overcoming multi-path fading and improving the interference ratio of received signals.
In order to realize coherent reception, channel estimation is performed by estimating time-varying parameters of a fading channel. The requirement on the channel estimation has two aspects of timeliness and accuracy, wherein timeliness refers to that when the channel changes rapidly, the channel estimation can track the change of the channel rapidly; the accuracy refers to that the accuracy of channel estimation is improved as much as possible on the premise of ensuring the timeliness. In the CDMA system with continuous pilot system, the classical method used for channel estimation is that each branch of the RAKE receiver uses the sampled values of a plurality of continuous channel data estimated by pilot symbols to average to suppress the estimated noise, and the larger the average interval is, the smaller the interference caused by the noise is. On the other hand, the averaging method in a certain interval is based on the channel parameter changing slowly in this range, and the estimation interval in which the channel parameter changes slowly changes with the moving speed (doppler shift) of the mobile station, and the interval is smaller when the moving speed is larger, and vice versa. In comprehensive consideration, the length of the channel estimation has a relative balance point, and the point can take both the time-varying characteristic of the channel and the noise suppression into consideration. In a RAKE receiver of a conventional continuous pilot CDMA system, the average length of a channel estimator is set to a fixed value. For the third generation integrated service mobile communication system, if a fixed average length is adopted, the longer the moving speed is, the shorter the time for the channel to be relatively stable is, and the shorter the average length of the channel estimator should be, and as the average length of the channel estimation is shortened, the noise component contained in the channel estimation value is gradually increased, and the accuracy of the channel estimation is reduced. In order for the RAKE receiver to achieve speed adaptation from stationary to 500 km/h, the method of using a fixed average length for channel estimation is not the best solution, so we must dynamically adjust this estimation length.
The invention aims to determine the optimal average length during channel estimation according to different moving speeds of a mobile station, thereby establishing dynamic modulation on the average length of the channel estimation, overcoming the estimation error caused by channel estimation with fixed average length and greatly improving the receiving performance of a RAKE receiver.
The method and the device are realized according to the following schemes:
the invention provides an adjusting method for dynamically adjusting the average length of channel estimation, which has the following basic thought: firstly, estimating the maximum Doppler frequency shift of a channel, and then dynamically adjusting the average length by using a closed formula of the optimal channel estimation average length.
The method comprises the following steps: (1) estimating the maximum Doppler frequency shift of a mobile channel; (2) calculating the optimal average length according to the maximum Doppler frequency shift; (3) and dynamically adjusting according to the calculated optimal average length.
The following are introduced in connection with the formulas, respectively.
1. Estimation of the maximum doppler shift of the channel: the Pilot channel (Pilot) in a CDMA system is used to convey a Pilot sequence that is known in advance, and may be used for system timing and carrier extraction, channel estimation, handoff, etc.
Let the number of fingers used by the RAKE receiver be L, consider the L-th finger. The received pilot channel data is despread in relation to the scrambling code and channel code of the pilot channel of the transmitted signal to obtain the pilot receiving symbol sequence rl (n) affected by the fading channel, i.e. the received pilot channel data
rl(n)=dp(n)cl(n)+v(n)
cl(n)=clI(n)+jclQ(n) [ formula 1]
dp(n)=dpI(n)+jdpQ(n) wherein dp(n) is a transmission symbol of a pilot channel, cl(n) is the channel parameter of the nth symbol interval of the first path, and v (n) is complex additive white Gaussian noise. r islThe sampling time interval of (n) and v (n) is the symbol intervalΔt. The sequence of channel parameters estimated from the pilot symbols is:wherein,
is cl(n) an instantaneous estimate of the sign, z (n) being the estimated white noise introduced by v (n) with a variance σ2 n。
Let xl,T(n) isEnvelope of (a), we use xl,T(N) estimating the maximum Doppler shift ω of the channel at a value in the interval 1. ltoreq. n.ltoreq.Nd. The RAKE receiver can distinguish small multipath time delay and search the strongest path as the first path. The following variable G was constructed:
ωdthe estimation of (d) is:
2. calculating an optimal average length
When estimating the channel parameter of the nth point by using the continuous pilot frequency, an averaging method is adopted, namelyInput into an average system model with an average length of 2N +1, as shown in FIG. 1.
Thereby obtaining a new estimated sequence of channel parametersConsists of three parts at the right end of the following equation:
wherein epsilons(n) is the error due to the average length, εz(n) is an error due to noise. EpsilonTotal(n) is the sum of the two errors.
The invention provides a complete error average power expression. OmegadIs the channel maximum doppler shift. Therefore, the mean square error due to averaging is:
at known ωdAnd symbol interval deltatThen, the optimal average time 2N +1 at different motion speeds can be obtained from the above formula. Let M =2N +1, then]It is understood that the most preferable M is an integer which minimizes the following expressionWherein a =6.51 × 10-4(ωdΔt)4σ2 l,b=σ2 n[ equation 8)]By using the basic inequality, the method is easy to obtain Then [ equation 7 ]]Taking the minimum value, the average length shown in FIG. 1 can be taken
3. After the optimal average length is obtained, the instantaneous channel parameters are dynamically adjusted by a data accumulation averager, namely, the instantaneous channel parameter estimation is accumulated, summed and averaged.
The device of the invention is shown in fig. 2, which comprises an instantaneous channel parameter estimator 1, a maximum doppler shift estimator 2, an optimal average length calculator 3 and M data accumulation averagers 4, wherein the instantaneous channel parameter estimator 1 is simultaneously connected with the maximum doppler shift estimator 2 and the M data accumulation averagers 4.
The invention has the advantages that:
(1) the invention is simple and easy to operate, and can be used in any CDMA mobile communication system with continuous pilot frequency, including 3GPP WCDMA and 3GPP2 CDMA2000 systems.
(2) The estimation error caused by channel estimation with fixed average length is overcome, and the receiving performance of the RAKE receiver is greatly improved.
Description of the drawings:
FIG. 1 is a schematic diagram of continuous pilot averaging method for estimating channel parameters at the nth point
FIG. 2 is a general block diagram of an apparatus for channel estimation with dynamic adjustment of optimal average length
FIG. 3 is an instantaneous channel parameter estimator
FIG. 4 is a diagram of a maximum Doppler shift estimator
FIG. 5 is a diagram of an optimal average length calculator for channel estimation
FIG. 6 is a diagram of M data accumulation averagers
FIG. 7 is a block diagram of an exemplary embodiment of a channel estimation apparatus using dynamically adjusting the optimal average length
The following detailed description of the embodiments is given in conjunction with the apparatus of the invention:
the device of the invention is shown in fig. 2, which comprises an instantaneous channel parameter estimator 1, a maximum doppler shift estimator 2, an optimal average length calculator 3 and M data accumulation averagers 4, wherein the instantaneous channel parameter estimator 1 is simultaneously connected with the maximum doppler shift estimator 2 and the M data accumulation averagers 4.
The instantaneous channel parameter estimator 1 includes: a complex multiplication apparatus 101, as shown in FIG. 3;
the maximum doppler shift estimator 2 includes: a complex modulus calculation device 201, a delay device 202, a subtracter 203, a squarer 204, a squarer 205, N-1 data accumulation averaging devices 206, N data accumulation averaging devices 207, a divider 208, a quadratic root calculation device 209 and a multiplier 210, wherein the subtracter (203) is simultaneously connected with the delay device (202), the complex modulus calculation device (201) and the squarer (204), and the divider (208) is simultaneously connected with the N data accumulation averaging devices (207), the N-1 data accumulation averaging devices (206) and the quadratic root calculation device (209), as shown in FIG. 4;
the channel estimation optimal average length calculator 3 includes: a multiplier 301, a fourth power device 302, a multiplier 303, a 5 th power root solving device 304, and the four devices are connected in series as shown in fig. 5;
the M data accumulation averagers 4 include: m data accumulation averagers 401, as shown in FIG. 6.
The following describes the devices 1, 2, 3, 4 respectively
For device 1, its input is the complex channel parameters sampled at the symbol rate of the despread pilot channel, where the complex multiplier of 101 performs the operation shown in equation 2, since the pilot data is known. The result data of device 1 are sent to device 2 and device 4, respectively.
For the device 2, its input is the instantaneous channel parameters estimated from the device 1 and its output is the estimated maximum doppler shift of the channel, which is sent to the device 3. Wherein 201 finishes the modulus operation of the input complex number, 202 and 203 finish the difference operation of two adjacent values, the result finishes the square operation by 204, and finishes the average operation by 206. 205. 207 performs the square and cumulative average of the denominator portion as shown in equation 3. 208 performs a division operation as shown in equation 3, and the result is sent to 209 for a quadratic root, and at 210 for a multiplication operation with known data 2/Δ t for obtaining the maximum doppler shift, which is sent to the device 3.
The device 3 receives the maximum doppler shift calculated by the device 2, performs the calculations shown in equations 8 and 9, and determines the optimal average length M to send to the device 4.
For the device 4, according to the optimal M value calculated by the device 3, the M data accumulation averagers 401 accumulate, sum and average the M complex numbers sent from the device 1, which is the dynamic adjustment, and the result is the estimated channel parameter after the average length is dynamically adjusted.
In fig. 7, an implementation example of the apparatus of the present invention applied to a RAKE receiver is shown, except for the apparatus of the present invention, the remaining apparatus is a general apparatus in a RAKE receiver, and functions and connections of the apparatus are as follows:
● tapped delay line
The tap delay line completes sampling of received baseband data and delay tap output, and the result is sent to a data channel related despreader and a pilot channel related despreader in a time division multiplexing mode.
● data channel correlation despreader
The data channel correlation despreader performs correlation despreading of the data channel in the sampled data output from the tapped delay line, and the result is supplied to the multiplier.
● Pilot channel correlation despreader
The pilot channel correlation despreader performs correlation despreading of the pilot channel in the sampled data output from the tapped delay line, and the result is sent to the instantaneous channel parameter estimator.
● multiplier
The multiplier performs complex multiplication of data channel data output from the data channel correlation despreader and a channel parameter estimation value output from the data averager with a length of M, i.e., performs phase correction on the received signal. The result is sent to the maximum ratio combiner of the RAKE receiver.
Claims (4)
1. A method for dynamically adjusting an average length for channel estimation, comprising the steps of:
(1) estimating the maximum Doppler frequency shift of a mobile channel;
(2) calculating the optimal average length according to the maximum Doppler frequency shift;
(3) and dynamically adjusting according to the calculated optimal average length.
2. A method of dynamically adjusting the average length for channel estimation according to claim 1, characterized in that the dynamic adjustment is accumulating, summing and averaging the instantaneous channel parameter estimates.
3. A device for dynamically adjusting average length to estimate channel is characterized by comprising an instantaneous channel parameter estimator (1), a maximum Doppler shift estimator (2), an optimal average length calculator (3) and M data accumulation averagers (4), wherein the instantaneous channel parameter estimator (1) is simultaneously connected with the maximum Doppler shift estimator (2) and the M data accumulation averagers (4).
4. An apparatus for dynamically adjusting average length for channel estimation according to claim 3, wherein:
(1) the instantaneous channel parameter estimator (1) comprises: a complex multiplication device (101);
(2) the maximum Doppler shift estimator (2) comprises: the device comprises a complex modulus calculating device (201), a time delay device (202), a subtracter (203), a squarer (204), a squarer (205), N-1 data accumulation averaging devices (206), N data accumulation averaging devices (207), a divider (208), a quadratic root calculating device (209) and a multiplier (210), wherein the subtracter (203) is simultaneously connected with the time delay device (202), the complex modulus calculating device (201) and the squarer (204), and the divider (208) is simultaneously connected with the N data accumulation averaging devices (207), the N-1 data accumulation averaging devices (206) and the quadratic root calculating device (209);
(3) the channel estimation optimal average length calculator (3) comprises: a multiplier (301), a fourth power device (302), a multiplier (303) and a 5 th power root solving device (304), wherein the four devices are connected in series;
(4) the M data accumulation averagers (4) comprise: m data accumulation averagers (401).
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2003021980A1 (en) * | 2001-09-03 | 2003-03-13 | The Research Institute Of Telecommunication Transmission, Mii | A method and equipment for regulating dynamically an average area of a channel estimation |
| WO2004109949A1 (en) * | 2003-06-05 | 2004-12-16 | Huawei Technologies Co., Ltd. | Method for estimation of maximum doppler frequency |
| CN100345453C (en) * | 2003-09-16 | 2007-10-24 | 三星电子株式会社 | Apparatus and method for estimating a velocity of a mobile terminal in a mobile communication system |
| CN100350760C (en) * | 2006-01-04 | 2007-11-21 | 东南大学 | Multi antenna channel feedback method based on instantaneous and statistic channel information |
| CN100359959C (en) * | 2004-06-01 | 2008-01-02 | 华为技术有限公司 | Method for implementing channel estimation in OFDMA system |
| CN101425987B (en) * | 2007-10-30 | 2011-05-04 | 华为技术有限公司 | Channel estimation method and apparatus |
| CN101212433B (en) * | 2007-12-25 | 2011-12-28 | 北京创毅视讯科技有限公司 | Channel estimating method and device |
| CN104702539A (en) * | 2015-01-29 | 2015-06-10 | 武汉剑通信息技术有限公司 | CDMA 2000 reverse-access channel balancing method |
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2001
- 2001-04-29 CN CNB011155698A patent/CN1150710C/en not_active Expired - Fee Related
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2003021980A1 (en) * | 2001-09-03 | 2003-03-13 | The Research Institute Of Telecommunication Transmission, Mii | A method and equipment for regulating dynamically an average area of a channel estimation |
| US7376176B2 (en) | 2001-09-03 | 2008-05-20 | The Research Institute Of Telecommunication Transmission, Mii | Method and equipment for regulating dynamically an average area of a channel estimation |
| WO2004109949A1 (en) * | 2003-06-05 | 2004-12-16 | Huawei Technologies Co., Ltd. | Method for estimation of maximum doppler frequency |
| CN100345453C (en) * | 2003-09-16 | 2007-10-24 | 三星电子株式会社 | Apparatus and method for estimating a velocity of a mobile terminal in a mobile communication system |
| US7302267B2 (en) | 2003-09-16 | 2007-11-27 | Samsung Electronics Co., Ltd. | Apparatus and method for estimating a velocity of a mobile terminal in a mobile communication system |
| CN100359959C (en) * | 2004-06-01 | 2008-01-02 | 华为技术有限公司 | Method for implementing channel estimation in OFDMA system |
| CN100350760C (en) * | 2006-01-04 | 2007-11-21 | 东南大学 | Multi antenna channel feedback method based on instantaneous and statistic channel information |
| CN101425987B (en) * | 2007-10-30 | 2011-05-04 | 华为技术有限公司 | Channel estimation method and apparatus |
| CN101212433B (en) * | 2007-12-25 | 2011-12-28 | 北京创毅视讯科技有限公司 | Channel estimating method and device |
| CN104702539A (en) * | 2015-01-29 | 2015-06-10 | 武汉剑通信息技术有限公司 | CDMA 2000 reverse-access channel balancing method |
| CN104702539B (en) * | 2015-01-29 | 2018-03-30 | 武汉剑通信息技术有限公司 | A kind of equalization methods of CDMA2000 Reverse Access Channels |
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