CN101394385B - Method for promoting OFDM system based on time domain processing combined channel estimation - Google Patents
Method for promoting OFDM system based on time domain processing combined channel estimation Download PDFInfo
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Abstract
A method for improving the performance of an orthogonal frequency division multiplexing system based on time domain processing in association with channel estimation relates to the technical field of mobile communication, and solves the problems of the prior orthogonal frequency division multiplexing system such as poor system performance resulting from signal distortion generated by reducing peak-to-average power ratio. The orthogonal frequency division multiplexing system comprises the following steps: in a transmitter, subjecting time domain signals after IFFT to linear filter interpolation to reduce the peak-to-average power ratio, and transmitting the time domain signals through a transmission channel after insertion of a cyclic prefix and parallel/serial conversion; in a receiver, subjecting the received signals to serial/parallel conversion and linear inverse transformation to obtain two parallel time domain received signal sequences; removing the cyclic prefix from one of the signal sequence and subjecting to FFT to obtain a frequency domain signal sequence D'(n); subjecting the other signal sequence to channel estimation to obtain the channel impulse response h(n), and carrying out FFT to obtain a parallel channel frequency response sequence H(n); and subjecting D'(n) and H(n) to zero-forcing equalization, parallel/serial conversion, de-mapping and demodulation to obtain bit signals. The system is suitable for the prior OFDM systems.
Description
Technical field
The present invention relates to the mobile communication technology field, be specifically related to method based on the raising ofdm system performance of time domain processing combined channel estimating.
Background technology
The frequency selective fading of multipath channel can cause received signal power to decline to a great extent, and signal to noise ratio also declines to a great extent.In Wideband Wireless Digital Communication, the topmost class interference that influences the high speed information transmission is by the caused frequency selection type decline of the multipath effect of channel, just when the rate of information throughput is higher, signal duration is short more, respective bandwidth is wide more, if signal bandwidth surpasses the channel coherence bandwidth, then the channel time disperse characteristic produces frequency selective fading to received signal, thereby make received signal overlapped, produce intersymbol interference and cause communication performance to descend.Along with the further raising of the rate of information throughput, adopt equalizer or adopt direct sequence spread spectrum to add the conventional method that Rake receives at receiving terminal, though overcome frequency selective fading, all face many obstacles in complexity and aspect of performance.
Therefore, multi-transceiver technology from basic inwardly solution this problem.It is divided into a plurality of subchannels with channel on frequency domain, the spectral characteristic that makes each subchannel is near flat all, make a plurality of mutually independently the subchannel transmission signal in receiver, merge, to realize the frequency diversity of signal, multipath channel presents frequency selective fading on frequency domain so overcome.Wherein OFDM (orthogonal frequency division multiplexi) is a kind of multicarrier data transfer mode of efficient quadrature, and it sends highspeed serial data stream demultiplexing low-speed parallel data flow simultaneously, and simultaneously different quadrature carriers is modulated.
The performance of communication system mainly is subjected to the restriction of wireless channel, selects and time-varying characteristics because wireless channel has frequency, makes that before the ofdm signal demodulation it is very necessary that channel is carried out dynamic channel estimating.From the angle of equilibrium,, also must carry out channel estimating to obtain fixed phase and the amplitude on all subcarriers in order accurately to recover the transmission signal at receiving terminal.When adopting simple frequency domain equalization to replace complicated higher-Order Time-Domain equilibrium, complexity that can simplified receiver.In ofdm system, system is responsive to deviation ratio, thus generally use coherent detection, and for the ofdm system of coherent detection, it is necessary adopting channel estimating.
Simultaneously, a major defect of ofdm signal is that PAPR (peak-to-average power ratio) is bigger, and high PAPR has proposed very high requirement to the linearity of high power amplifier HPA of system and A/D converter.When high PAPR, occur non-linearly, will produce intermodulation distortion and out-of-band radiation between subcarrier, thereby greatly reduce the performance of ofdm system.
The method of taking for the performance of improving ofdm system mainly contains: 1, by improving the accuracy that channel response is estimated, eliminate the influence of channel at receiving terminal to the transmission data, thereby improve the channel antijamming capability, reduce the generation of error code, make receiving terminal can accurately recover desired data.2,, thereby reduce the generation of error code by effectively reducing PAPR.Not have at present simultaneously by improving accuracy that channel response estimates and effectively reducing the method that PAPR improves the ofdm system performance, and present method all is that nonlinear change makes signal be easy to generate distortion phenomenon the transmitting terminal employing, thereby has influenced the performance of receiving terminal.
Summary of the invention
Not have at present simultaneously by improving accuracy that channel response estimates and effectively reducing the method that PAPR improves the ofdm system performance in order to solve, and present ofdm system adopts at transmitting terminal all is that nonlinear change makes signal be easy to generate distortion phenomenon, thereby influence the problem of receiving terminal performance, the existing method that proposes based on the raising ofdm system performance of time domain processing combined channel estimating.
Step of the present invention is:
Emission process:
The bit stream of steps A 1, input obtains the constellation point symbol by mapping, obtains symbols streams after this constellation point symbol is modulated, and described symbols streams is through the serial/parallel parallel frequency-region signal sequence X ' (n) of being converted to;
Steps A 2, parallel frequency-region signal sequence X ' (n) and parallel pilot tone burst P ' (n) are carried out pilot tone insert, then time-domain signal sequence X (n) and the time-domain pilot signal sequence P (n) that obtains walking abreast through the IFFT conversion;
Receiving course:
Steps A 6, parallel time domain received signal sequence C (n) is handled respectively:
I, remove the frequency-region signal sequence D of carrying out the FFT conversion behind the Cyclic Prefix and obtaining walking abreast ' (n);
II, carry out channel estimating and obtain channel impulse response with time-domain pilot signal sequence P (n)
Then carry out the channel frequency response sequence that obtains walking abreast after the FFT conversion
Wherein said channel estimation process is:
Step B1, parallel time domain received signal sequence C (n) and parallel time-domain pilot signal sequence P (n) are carried out circular correlation: one, the circular correlation first time is carried out in starting point α=0 of selection circular correlation;
Two, described two sequences n ∈ [0, N
g] result of part circular correlation is the coefficient of channel impulse response for the first time
Three, according to described two sequences at n ∈ [N
g, N] and the result of part circular correlation
Obtain the average threshold value of all tap power
Four, according to average threshold T to n ∈ [0, N
g] partly carry out the backward energy detection, just initial monitoring point is N
g, the power of i tap of power ratio that obtains big and i+1 the tap of the average threshold T of power ratio of i tap is little, then obtains the i value, thereby obtains the length L=N of channel impulse response
g-i-1;
Five, at α ∈ [N
g+ L, 0] part is selected the starting point of circular correlation, then according to the N that do not coexist of circular correlation starting point
gObtain the coefficient of channel impulse response in the scope
The coefficient of step B2, all channel impulse responses that will obtain
Ask expectation, obtain channel impulse response
The thought that the present invention adopts combined channel to estimate, what its transmitting terminal adopted all is linear change, so signal is not easy to produce distortion phenomenon, and by improving the accuracy that channel response is estimated, effectively reduce PAPR, thereby improved the performance of receiving terminal, made the performance of ofdm system obtain further improvement.
Description of drawings
Fig. 1 is the theory structure schematic diagram of emitter of the present invention; Fig. 2 is the theory structure schematic diagram of receiving system of the present invention; Fig. 3 is the frame assumption diagram of pilot channel; Fig. 4 is the schematic diagram that time domain received signal sequence C (n) that walks abreast and the time-domain pilot signal sequence P (n) that walks abreast are carried out burst in the channel estimation process.
Embodiment
Embodiment one: present embodiment is described in conjunction with Fig. 1 and Fig. 2.
The employed emitter of present embodiment is by mapper 1, modulator 2, the first serial/parallel transducer 3, pilot tone inserter 4, IFFT converter (fast fourier transformer) 5, linear quantizer 6, the insertion control unit 7 of Cyclic Prefix and the first parallel/serial transducer 8 are formed, the output of mapper 1 links to each other with the input of modulator 2, the output of modulator 2 links to each other with the input of the first serial/parallel transducer 3, the output of the first serial/parallel transducer 3 links to each other with the input of pilot tone inserter 4, the output of pilot tone inserter 4 links to each other with the input of IFFT converter 5, the output of IFFT converter 5 links to each other with the input of linear quantizer 6, the output of linear quantizer 6 links to each other with the input of the insertion control unit 7 of Cyclic Prefix, insertion control unit 7 outputs of Cyclic Prefix link to each other with the input of the first parallel/serial transducer 8, and the output of the first parallel/serial transducer 8 links to each other with send channel; The employed receiving system of present embodiment is by the second serial/parallel transducer 9, linear inversion device 10, the removal control unit 11 of Cyclic Prefix, the one FFT converter (Fourier transformer) 12, channel estimator 13, the 2nd FFT converter 14, zero forcing equalization device 15, the second parallel/serial transducer 16, de-mapping device 17 and demodulator 18 are formed, the output of the second serial/parallel transducer 9 links to each other with the input of linear inversion device 10, the output of linear inversion device 10 links to each other with the input of the removal control unit 11 of Cyclic Prefix and the input of channel estimator 13 respectively, the output of the removal control unit 11 of Cyclic Prefix links to each other with the input of a FFT converter 12, the output of channel estimator 13 links to each other with the input of the 2nd FFT converter 14, the output of the output of the one FFT converter 12 and the 2nd FFT converter 14 links to each other with the input of zero forcing equalization device 15 simultaneously, the output of zero forcing equalization device 15 links to each other with the input of the second parallel/serial transducer 16, the output of the second parallel/serial transducer 16 links to each other with the input of de-mapping device 17, and the input of the output demodulator 18 of de-mapping device 17 links to each other.
The concrete steps of present embodiment are:
Emission process:
The bit stream of steps A 1, input obtains the constellation point symbol by mapper 1, obtains symbols streams after this constellation point symbol is sent into modulator 2, after the frequency-region signal sequence X that the first serial/parallel transducer 3 obtains walking abreast ' (n);
Steps A 2, parallel frequency-region signal sequence X ' (n) are sent into pilot tone inserter 4 and parallel pilot tone burst P ' and (n) are carried out pilot tone and insert, after time-domain signal sequence X (n) that IFFT converter 5 obtains walking abreast and time-domain pilot signal sequence P (n);
Receiving course:
Steps A 6, parallel time domain received signal sequence C (n) are divided into two-way and transmit:
One tunnel frequency-region signal sequence D that obtains walking abreast of a removal control unit 11 and the FFT converter 12 by Cyclic Prefix ' (n) successively;
Another road and time-domain pilot signal sequence P (n) obtain channel impulse response by channel estimator 13
The channel frequency response sequence that obtains walking abreast by the 2nd FFT converter 14 then
Embodiment two: present embodiment is described in conjunction with Fig. 4.
This embodiment is that with the different of embodiment one the parallel time-domain pilot signal sequence C (n) described in the steps A 6 by the step of channel estimator 12 is:
Step B1, parallel time domain received signal sequence C (n) and parallel time-domain pilot signal sequence P (n) carry out circular correlation:
One, select starting point α=0 of circular correlation to carry out the circular correlation first time;
Two, two sequences n ∈ [0, N
g] result of part circular correlation is the coefficient of channel impulse response for the first time
N wherein
gBe called protection at interval;
Three, according to two sequences at n ∈ [N
g, N] and the result of part circular correlation
Obtain the average threshold value of all tap power
Four, according to average threshold T to n ∈ [0, N
g] partly carry out the backward energy detection, just initial monitoring point is N
g, the power of i tap of power ratio that obtains big and i+1 the tap of the average threshold T of power ratio of i tap is little, then obtains the i value, thereby obtains the maximum length L=N of channel
g-i-1;
Five, at α ∈ [N
g+ L, 0] part is selected the starting point of circular correlation, then according to the N that do not coexist of circular correlation starting point
gObtain the coefficient of channel impulse response in the scope
The coefficient of step B2, all channel impulse responses that will obtain
Ask expectation to obtain channel impulse response
Embodiment three: this embodiment is that with the different of embodiment one or embodiment two the delay factor τ described in the steps A 3 is the constant in [0,1], and it is to determine according to the state of channel.
The frame of pilot channel shown in Figure 3 comprises pilot signal PS and data-signal DS, they are alternate transmission in same frame, pilot signal PS is mainly used in the aid in treatment of carrying out channel estimating, in the process of handling, carry out the insertion of pilot signal according to the selection of pilot tone pattern, utilize channel estimating then, come data estimator signal DS, utilize channel information to optimize the value of transmitting terminal delay factor τ at last.
Embodiment four: what this embodiment and embodiment one or embodiment two different were that the zero forcing equalization device described in the steps A 7 14 adopts is the equalizer of single tap, the time domain combined estimated signal sequence that obtains walking abreast
Claims (3)
1. based on the method for the raising ofdm system performance of time domain processing combined channel estimating, it is characterized in that its step is: emission process:
The bit stream of steps A 1, input obtains the constellation point symbol by mapping, obtains symbols streams after this constellation point symbol is modulated, and described symbols streams is through the serial/parallel parallel frequency-region signal sequence X ' (n) of being converted to;
Steps A 2, parallel frequency-region signal sequence X ' (n) and parallel pilot tone burst P ' (n) are carried out pilot tone insert, then time-domain signal sequence X (n) and the time-domain pilot signal sequence P (n) that obtains walking abreast through the IFFT conversion;
Steps A 3, with parallel time-domain signal sequence X (n) by the interpolation processing that transmitting terminal delay factor τ carries out filtering, the time-domain signal sequence Z (n) that obtains walking abreast;
Steps A 4, carry out parallel/serial conversion together with time-domain pilot signal sequence P (n) after in parallel time-domain signal sequence Z (n), inserting Cyclic Prefix, then launch by send channel;
Receiving course:
Steps A 5, the signal that receives is carried out serial/parallel conversion and linear inversion, time domain received signal sequence C (n) that obtains walking abreast and time-domain pilot signal sequence P (n);
Steps A 6, parallel time domain received signal sequence C (n) is handled respectively:
I, remove the frequency-region signal sequence D of carrying out the FFT conversion behind the Cyclic Prefix and obtaining walking abreast ' (n);
II, carry out channel estimating and obtain channel impulse response with time-domain pilot signal sequence P (n)
Then carry out the channel frequency response sequence that obtains walking abreast after the FFT conversion
Wherein said channel estimation process is:
Step B1, parallel time domain received signal sequence C (n) and parallel time-domain pilot signal sequence P (n) are carried out circular correlation: one, the circular correlation first time is carried out in starting point α=0 of selection circular correlation;
Two, described two sequences n ∈ [0, N
g] result of part circular correlation is the coefficient of channel impulse response for the first time
Three, according to described two sequences at n ∈ [N
g, N] and the result of part circular correlation
Obtain the average threshold value of all tap power
Four, according to average threshold T to n ∈ [0, N
g] partly carry out the backward energy detection, just initial monitoring point is N
g, the power of i tap of power ratio that obtains big and i+1 the tap of the average threshold T of power ratio of i tap is little, then obtains the i value, thereby obtains the length L=N of channel impulse response
g-i-1;
Five, at α ∈ [N
g+ L, 0] part is selected the starting point of circular correlation, then according to the N that do not coexist of circular correlation starting point
gObtain the coefficient of channel impulse response in the scope
The coefficient of step B2, all channel impulse responses that will obtain
Ask expectation, obtain channel impulse response
Steps A 7, with parallel frequency-region signal sequence D ' (n) and parallel channel frequency response sequence
Send into the zero forcing equalization device, the estimated signal sequence that obtains walking abreast
Steps A 8, with parallel estimated signal sequence
Carry out parallel/serial conversion, obtain bit signal after separating mapping, demodulation then.
2. the method for the raising ofdm system performance based on time domain processing combined channel estimating according to claim 1, it is characterized in that the delay factor τ described in the steps A 3 is [0,1] constant in, it is to determine according to the characteristic of the state of channel.
3. the method for the raising ofdm system performance based on time domain processing combined channel estimating according to claim 1, what it is characterized in that the zero forcing equalization device employing described in the steps A 7 is the equalizer of single tap, the parallel time domain combined estimated signal sequence that obtains
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| CN102868656B (en) * | 2011-07-04 | 2015-01-28 | 吴嶽 | Method of using mixed signal spread spectrum technology to reduce orthogonal frequency division multiplexing signal peak |
| CN103813825B (en) | 2011-09-22 | 2017-01-18 | 皇家飞利浦有限公司 | Method and apparatus for monitoring and controlling pressure support device |
| CN102752260B (en) * | 2012-07-13 | 2014-11-19 | 中国空间技术研究院 | Time-frequency estimation method of OFDM (Orthogonal Frequency Division Multiplexing) structure of satellite CMMB (China Mobile Multimedia Broadcasting) system |
| EP3001596B1 (en) * | 2013-07-02 | 2017-11-15 | Huawei Technologies Co., Ltd. | Information processing method and device |
| GB2513677B (en) * | 2013-10-17 | 2015-09-02 | Imagination Tech Ltd | Channel impulse response |
| JP6362786B2 (en) * | 2015-08-03 | 2018-07-25 | 三菱電機株式会社 | Transmitter |
| CN112866198A (en) * | 2020-12-30 | 2021-05-28 | 西安电子科技大学 | Physical layer frame structure optimization method for low-power wide area network |
| CN115695094A (en) * | 2021-07-26 | 2023-02-03 | 中移物联网有限公司 | Channel estimation method, device and communication equipment |
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| CN1463083A (en) * | 2003-06-18 | 2003-12-24 | 清华大学 | Method for inserting pilot frequency and estimating parameters of channel for equilibrium in frequency doman |
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