CN101345726A - Signal channel estimation method for reducing memory space - Google Patents
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Abstract
The invention discloses a channel estimation method of reducing storage space, for overcoming the drawback that the channel estimation method uses a plurality of storage space in an orthogonal frequency division multiplexing system of prior art, the invention is mainly applied in the channel estimation of a Time-Invariance Channel and a Slow Time-Variance Channel, wherein doe-element in time domain uses value of effective data sub-carrier on a front code-element, to save storage space when operating, except for ensuring performance of channel estimation algorithm, meanwhile complexity of the algorithm is reduced and cost of a receiver is reduced.
Description
Technical field
The present invention relates to a kind of channel estimation methods that reduces memory space, particularly relate to a kind of value and copy as value on the previous code element pilot frequency locations the valid data subcarrier, saving the operation time of channel estimating, and can reduce the channel estimation methods of employed memory space.
Background technology
OFDM (Orthogonal Frequency Division Multiplexing, OFDM) be high speed transmission technology under a kind of wireless environment, be adapted at transmitting high speed data in the wireless mobile channel of multipath transmisstion and Doppler frequency displacement (DopplerShift).It can effectively resist multipath effect, remove inter-symbol-interference, contrary frequency selectivity decline (Frequency-Selection Fading), and channel utilization height.Orthogonal frequency division multiplexi is successively adopted by systems such as European digital audio broadcast (DAB), European digital video broadcasting (DVB), IEEE802.11 WLAN (wireless local area network).
Be in frequency domain (frequencydomain), given channel to be divided into many orthogonal sub-channels (sub-channel) on the above-mentioned orthogonal frequency division multiplexi principle with efficient data transmission, on each subchannel, use a subcarrier to modulate (modulation), and each subcarrier parallel transmission.But, whole channel is not to be smooth, so have frequency selectivity, but because frequency band is narrower, each subchannel is a relatively flat, and what carry out on each subchannel is narrow band transmission, so signal bandwidth is less than the correlation bandwidth of channel, therefore each subcarrier is not through just producing distortion behind the channel, and whole like this signal still can hold its shape through behind the channel.Orthogonal frequency division multiplexi is that its allows subcarrier spectrum to overlap with respect to the difference of general multi-carrier transmission, as long as satisfy between subcarrier mutually orthogonally, then can separate (demodulation) from the subcarrier of aliasing and go out data-signal.Because orthogonal frequency division multiplexi allows the subcarrier spectrum aliasing, its spectrum efficiency improves greatly, is a kind of modulation system efficiently.
Wherein, when above-mentioned modulation signal arrives receiving terminal by wireless channel; because effect (the Inter-Symbol Interference of the intersymbol interference that channel multipath effect is brought; cause wave distortion because of channel frequency characteristic is undesirable; thereby the stack of the value that to cause actual sampling decision value be this symbol pulses waveform and other all impulse waveforms hangovers; and cause the phenomenon of judgement difficulty intersymbol interference) at receiving terminal; at this moment; no longer keep good quadrature between the subcarrier with making; thereby before transmission, need between each code element, insert protection at interval; if protection is at interval greater than maximum delay expansion (time-delay extension); during then all time delays will can not extend to next code element less than protection multipath signal at interval, thereby effectively eliminated intersymbol interference.
Known technology OFDM demodulation (demodulation) system architecture diagram as shown in Figure 1, this framework comprise analog digital converting unit (ADC) 101, orthogonal detection unit (quadraturedetector) 102, fast fourier transform module (FFT) 103, data demodulation unit (datademodulator) 104 and code element sequential lock unit (symbol timing synchronizer) 111 etc.When this system moves, there is an orthogonal frequency-division multiplex singal to transmit into, will be by a tuner (tuner, not shown in the figures) receive, after antenna receives this analog orthogonal frequency-division multiplex singal,, reduce to Low Medium Frequency etc. by high frequency through this tuner frequency modulation, consequent continuous signal (serial) is converted to digital signal after being taken a sample by analog digital converting unit 101.
Then by the digital signal of orthogonal detection unit 102 receptions through conversion, it is carried out orthogonalization, with conversion of signals is fundamental frequency (baseband) signal, if at the orthogonal FDM communication system that generally is used for DTV receiver (DVB-T), promptly utilize several data of input in frequency band (band), it is divided into the orthogonal frequency-division multiplex singal of several quadratures (orthogonal).Above-mentioned fundamental frequency signal is transferred to fast fourier transform module (FFT) 103 and code element sequential lock unit 111 simultaneously, wherein code element sequential lock unit 111 detects the code element sequential (symbol timing) of fundamental frequency signal, make fast fourier transform module 103 effective code element be captured out according to its testing result, after fast fourier transform, by time domain (time domain) conversion of signals to frequency domain (frequency domain) signal, and be several subcarriers (subcarriers) by data demodulation unit 104 with fundamental frequency signal demodulation (demodulate), the signal that is transmitted with recasting.
OFDM demodulating system as shown above, realizing serial (serial) when the time domain signal after parallel (parallel) is converted to frequency-region signal by fast fourier transform module 103, generally all is directly to carry out (synchronization), phase noise elimination and channel estimating (channelestimation) synchronously.
When signal transmitted, the amplitude of each subcarrier and phase place all can change at random cause decline in time domain and frequency domain owing to the influence of factors such as carrier wave frequency deviation, timing slip and frequency selective fading, produce intersymbol interference thus.Therefore, above-mentioned channel estimating problem to be solved is the multipath fading (multi-path fading) that is produced when receiving terminal detects signal in Channel Transmission by channel estimation methods, so that carry out the demodulation work of signal more accurately.
In the known technology, method at channel estimating is to utilize the intellectual of scattered pilot (scatter pilot), power ascension characteristic and its distinctive placement pattern to carry out channel estimating, utilize scattered pilot to carry out the estimation of subchannel on its relevant position, carry out filtering interpolation respectively in time domain and frequency domain both direction then, obtain final channel estimation results at last, please refer to the schematic diagram that scattered pilot in the DTV receiver shown in Figure 2 system is placed pattern.
Channel estimation method is finished at frequency domain, owing to the characteristic that time domain convolution (Convolution) frequency domain multiplies each other, can obtain the input value Y (k) of the channel estimation module shown in formula one:
Y(k)＝H(k)·X(k)+I(k)+N(k) k＝0，1...N-1
-------------------------------formula one;
Wherein, X (k) expression transmitting terminal data and pilot tone, the channel estimation value of H (k) for trying to achieve, I (k) and N (k) they are distracter, and k is a sub-carrier positions, and N represents sub-carrier number, utilizes formula one can obtain the locational subchannel estimated result of scattered pilot, that is:
Because the independence of the time-domain and frequency-domain of channel, make the locational subchannel of valid data estimate to transfer to by the two-dimensional interpolation filtering of time domain, frequency domain respectively time domain and frequency domain one dimension filtering interpolation are obtained.After obtaining the channel estimation value of pilot positions, the channel response of Data Position (channel response) then can obtain by the channel response interpolation (Interpolation) of adjacent pilot frequencies signal.
It at first is the filtering interpolation of time domain direction, because the filtering interpolation on the time domain direction need be stored a little symbol data, required code element number is decided by interpolation method, here the complexity and the cost of channel estimation method have been embodied, because it needs a large amount of memory spaces to come the memory code metadata.Consideration for algorithm on the simple and performance, in the present channel estimation method, the method for filtering interpolation of time domain direction is a linear interpolation, places pattern from scattered pilot shown in Figure 2 and can see, needs to store 4 complete code elements at least and just can finish linear interpolation filtering.After finishing linear interpolation filtering, carry out the filtering interpolation on the frequency domain direction again, it generally is to use low pass FIR (Finite Impulse Response) filter.
In the most existing ofdm system, be loaded with pilot frequency information on the part subcarrier and be used for estimating channel, because the complexity of channel, known channel estimation method has used a large amount of memory spaces, though guaranteed the performance of channel estimation method but simultaneously it has increased the complexity of its algorithm and the cost of receiver (receiver) again, therefore, should channel estimation method nonvolatile energy and can reduce its complexity and the receiver cost aspect make corresponding processing.
Summary of the invention
The object of the present invention is to provide a kind of channel estimation methods that reduces memory space, overcome known ofdm system because the complexity of channel has been used the shortcoming of a large amount of memory spaces at channel estimation method, it is except reducing the use of memory space, more can the time still possess channel estimation method under constant channel (Time-InvarianceChannel) and slow time varying channel (the Slow Time-Variance Channel) situation performance, and reduce the complexity of algorithm and the cost of receiver simultaneously.
To achieve these goals, the invention provides a kind of channel estimation methods that reduces memory space, comprise and receive information by an orthogonal FDM communication system by receiver earlier, then carry out the analog digital conversion again, to receive information translation is digital information, in transmission channel, information can be divided into subcarrier (in the frequency domain) and specific time slot (in the time domain), therefore each information then can simply be represented by code element, signal is rendered as the framework of two dimension at time-domain and frequency-domain, then, detect the beginning sample of each code element in this orthogonal FDM communication system, and by the conversion of the Fu Liye in the orthogonal FDM communication system (FFT) module each symbol data is carried out Fu Liye and change, the code element with output is stored in the medium again.
The special locational value of scattered pilot that in this storing step, the value of the valid data subcarrier of present code element is copied as previous code element, utilize the correlation of time-domain and frequency-domain to carry out channel estimating afterwards, carry out balancing operational according to results estimated again, to compensate the part of each distorted signals.
The channel estimation methods of minimizing memory space proposed by the invention mainly is under the situation of constant channel and slow time varying channel when being applied to, at this moment, the value of the valid data subcarrier of each code element can use the value on the relevant position of previous code element to replace, so as to saving the memory space of a complete code element, overcome known ofdm system because the complexity of channel has been used the shortcoming of a large amount of memory spaces at channel estimation method, reduce the complexity of algorithm and the cost of receiver simultaneously.
Describe the present invention below in conjunction with the drawings and specific embodiments, but not as a limitation of the invention.
Description of drawings
Figure 1 shows that OFDM (OFDM) the demodulating system Organization Chart of known technology;
Figure 2 shows that the schematic diagram of scattered pilot placement pattern in known technology DTV receiver (DVB-T) system;
Figure 3 shows that the schematic diagram of scattered pilot placement pattern in the applied DTV receiver of the present invention system;
Fig. 4 is shown as the one piece of data schematic diagram that distributes when orthogonal FDM communication system receives data in time domain;
Fig. 5 is the flow chart of the embodiment of channel estimation methods of the present invention;
Fig. 6 is the main flow chart of channel estimation methods of the present invention.
Wherein, Reference numeral:
Analog digital converting unit 101
Orthogonal detection unit 102
Fast fourier transform module 103
Data-modulated unit 104
Code element sequential lock unit 111
Interval d1, d2
Code element a, b, c, d
Embodiment
The present invention is a kind of channel estimation methods that reduces memory space, it mainly is under the situation of constant channel (Time-Invariance Channel) and slow time varying channel (Slow Time-Variance Channel) when being applied to, at this moment, because former and later two the channel characteristics of code element (symbol) of each code element on time domain is constant or changes very little, therefore just can use the value on the pilot frequency locations of previous code element to replace in the value of the valid data subcarrier of each code element, the present invention can save the memory space of a complete code element like this.
Above-mentioned known linear interpolation filtering method needs to store 4 complete code elements at least, accumulation just need to get up a large amount of memory spaces like this, but the present invention places pattern by scattered pilot in Fig. 2 or the DTV receiver system shown in Figure 3 and learns, on the time-domain and frequency-domain position that is distributed in two dimension among the figure of scattered pilot (stain among the figure) rule, and be position known in the system.
In ofdm system, the signal of being imported enters system by tuner (passing through antenna), and through analog digital conversion (ADC), in this system, insert the code element of expressing each subcarrier data afterwards, between each code element, insert pilot frequency code element (pilot symbol) afterwards and carry out channel estimating, form the placement pattern of scattered pilot in the applied DTV receiver of Fig. 3 the present invention system, each code element is expressed the data of each subcarrier, on the transverse axis at frequency domain place as can be known, with 12 code elements is being distributed in this system of periodic law (in this example as among the figure d1) at interval, every 12 subcarriers that just have by the modulation of pilot tone (scattered pilot) information.Then, the position of this pilot tone is displacement in time, and this example has been skipped three positions for displacement, this system then law of character graphics displaying be that the unit weight complex becomes this pattern with 4, interval d2 as shown in the figure.
Afterwards, the expressed subcarrier data of each code element will be changed (FFT) and carry out demodulation by fast fourier, wherein demodulates information is come out, the scattered pilot that the present invention will during this time soon be captured wherein carries out channel estimating, estimate the interference volume and the characteristic of channel of this input signal, and then carry out equilibrium (equalize) computing, and output after deciphering with the correction signal data.
Above-mentioned when carrying out the computing of channel estimating, each code element need use memory space, the present invention promptly the time constant channel and slow time varying channel situation under carry out channel estimating, the channel characteristics of former and later two code element is constant or changes very little, so between each code element on time domain be do not change or difference little, the present invention promptly utilizes this characteristic, the value of the valid data subcarrier of the code element among Fig. 3 (b) is duplicated value on previous code element (a) pilot frequency locations, save the operation time that the mode of once using interpolation is carried out code element (b) channel estimating with this, more can reduce employed memory space.Especially in the DTV receiver system, each code element carries the data volume of 8K, so on time domain, will store the data volume of 4 8K at every turn, duplicates code element when estimating if borrow, and then can reduce the storage capacity of a 8K.
Then, the filtering interpolation of the present invention on frequency domain then can be undertaken by a low pass filter, and on time domain, then as the above-mentioned effect of utilizing between code element that produces linear interpolation filtering of duplicating, and can be reduced by at least once interpolation arithmetic time.
The order of general standard channel estimating is to store earlier the scattered pilot value (code element as shown in Figure 3 (a)) of first three code element of present code element respectively and reach three code element (code element (b as shown in Figure 3 thereafter at present, c, d)) all data values, then carry out the filtering interpolation (interpolation) on the time domain, carry out the filtering interpolation computing on the frequency domain again.So the step 1 coexistence has been stored up the scattered pilot value of 3 code elements and 4 complete symbol values to medium.
Fig. 4 is shown as the one piece of data that distributes when orthogonal FDM communication system receives data in time domain, for example in the 8K pattern, per 4 data then have 1 scattered pilot, and the receiver of orthogonal FDM communication system then carries out channel estimating according to this scattered pilot.The value of total (1+1/4) * 8K of one of them code element.Time t on the time coordinate in the drawings is meant the code element that t receives constantly, this code element (being " estimating target ") for needing at present to estimate, and time t-3, t-2 and t-1 represent the 3rd, second of present this code element front and first code element respectively, and time t+1, t+2 and t+3 be respectively this code element at present the back first, second with the 3rd code element.In this example, channel estimation methods of the present invention then reduces the storage capacity of a 8K by the mode of duplicating code element.Compared with aforementioned scattered pilot value of having stored 3 code elements and 4 complete symbol values known technology, promptly saved the 3rd code element in back (being " saving ") of present code element (time t) to medium.
The interpolation arithmetic flow process of one preferred embodiment of the disclosed channel estimation methods of the present invention on time domain as shown in Figure 5.
Wherein the code element of being mentioned in the step is the one piece of data that is distributed on the time domain, to carry out the code element of the code element demonstration of channel estimating at present as Fig. 4 time t, during beginning, should determine the symbol value that to estimate at present (time t), the scattered pilot of first three code element of the code element of this time t is stored in the medium, be storage time (t-3, t-2, the scattered pilot of code element t-1) (step S501) then, stores the symbol value that will estimate at present, with its data of latter two code element, be storage time (t, t+1, code element t+2) (step S503).
Then, second code element in front and back at the above-mentioned code element that will estimate at present (is time t-2, the code element of t+2) scattered pilot carries out interpolation arithmetic (step S505), and (be time t-3 with first code element afterwards to the 3rd code element before the code element that will estimate, the code element of t+1) scattered pilot carries out interpolation arithmetic (step S507), scattered pilot with preceding first code element (time t-1) copies as the code element (step S509) that will carry out channel estimating at present afterwards, so can reduce the storage capacity of a 8K, with the interpolation arithmetic time that reduces once.
Figure 6 shows that preferred embodiment flow chart of the present invention, the relevant channel estimation methods in ofdm system of the present invention, as being applied to information transmission between mobile communication system and the radio base station, the information-reply that will be converted and transmit in system is the original information that receives.Receive information (step S601) by the orthogonal FDM communication system in the middle of communicator and the base station by receiver during beginning, then carry out the analog digital conversion again, to receive information translation is digital information (step S603), in transmission course, the information that full range is wide is cut into the subcarrier of several carrying informations, in transmission channel, information can be divided into subcarrier (in the frequency domain) and specific time slot (timeslot, in the time domain), therefore each information then can simply be represented by code element, in this ofdm system, insert continuous code element and scattered pilot, signal is rendered as the framework of two dimension (T/F) at time-domain and frequency-domain, each code element carrying different sub carrier information.
Then, step detects the beginning sample of each code element in this orthogonal FDM communication system, in this detects step, from the code element sample after the analog digital conversion, detect, and this is begun sample (code element) export in the Fu Li leaf modular converter (step S605).Then, each symbol data is carried out Fu Liye conversion (step S607), will be stored to (step S609) in the medium through the code element of FFT conversion back output again by the conversion of the Fu Liye in the orthogonal FDM communication system (FFT) module.
The present invention copies as the locational value of previous code element pilot tone (or scattered pilot) (step S611) with the value of the valid data subcarrier of present code element especially in this storing step, reduce once computing and its calculation complexity whereby, and can reduce memory space.
Then, orthogonal FDM communication system utilizes the correlation of the time-domain and frequency-domain of channel to carry out channel estimating (step S613) by means of each symbol value that is stored in the medium simultaneously, during channel estimating, will carry out interpolation arithmetic, and first time orientation is frequency domain direction then.At last, be sent to again in the module of carrying out balancing operational, carry out balancing operational according to results estimated, with the part (step S615) that compensates each distorted signals.
Above-mentioned technology in an experiment, its performance the time there is no any change or loss under the constant channel, and the time varying channel situation is next differs 0.1 to 0.2dB slow, there is no too big loss, and its memory space has descended about 20% than known algorithm.
In sum, the channel estimation methods of the disclosed minimizing memory space of the present invention, the time constant channel and slow time varying channel the enforcement state under, utilize between each code element constantly or change very little feature, saved employed memory space when carrying out channel estimating by the replacement mode of code element.
Certainly; the present invention also can have other various embodiments; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.
Claims (9)
1, a kind of channel estimation methods that reduces memory space is characterized in that, described method includes:
One orthogonal FDM communication system receives information by a receiver;
This information is carried out the analog digital conversion;
Detect the sample at the beginning of each code element in this orthogonal FDM communication system;
Should begin sample and carry out the Fu Liye conversion;
Store the code element of this Fu Li leaf conversion back output of this process;
One valid data that carry out the code element of channel estimating are at present copied as the locational value of previous scattered pilot; And
Carry out the channel estimating computing;
The computing of borrowing above-mentioned copy step to reduce by a channel estimating, and can reduce memory space.
2, the channel estimation methods of minimizing memory space according to claim 1 is characterized in that, described method is applied in the DTV receiver system of data volume that each code element carries 8K.3, the channel estimation methods of minimizing memory space according to claim 1, it is characterized in that, in this orthogonal FDM communication system, insert this continuous code element and scattered pilot, this signal presents the framework of a two dimension on time-domain and frequency-domain, and each code element carrying different sub carrier information.
4, the channel estimation methods of minimizing memory space according to claim 3, it is characterized in that, wherein utilize the correlation of this time-domain and frequency-domain, this orthogonal FDM communication system borrows each symbol value that is stored in the medium that the attribute of each channel is carried out the channel estimating computing.
5, the channel estimation methods of minimizing memory space according to claim 1 is characterized in that, after carrying out the channel estimating calculation step, each code element is carried out a balancing operational, to compensate the part of each distorted signals.
6, the channel estimation methods of minimizing memory space according to claim 1 is characterized in that, described orthogonal FDM communication system is the system of constant channel in a period of time.
7, the channel estimation methods of minimizing memory space according to claim 1 is characterized in that, described orthogonal FDM communication system is the system of a slow time varying channel.
8, a kind of channel estimation methods that reduces memory space is characterized in that, described method includes:
Determine the symbol value that to estimate at present;
The scattered pilot of first three code element of this code element that will estimate at present is stored in the medium;
Store this symbol value that will estimate at present data of latter two code element with it;
Scattered pilot at back second code element before this code element that will estimate at present carries out interpolation arithmetic;
Carry out interpolation arithmetic at the 3rd code element before this code element that will estimate at present and the scattered pilot of first code element afterwards; And
The scattered pilot of first code element before this code element that will estimate is at present copied as the code element that this will carry out channel estimating at present;
Can reduce the storage capacity of a 8K whereby, with the interpolation arithmetic time that reduces once.
9, the channel estimation methods of minimizing memory space according to claim 8 is characterized in that, described orthogonal FDM communication system is the system of constant channel for the moment or is the system of a slow time varying channel.
10, the channel estimation methods of minimizing memory space according to claim 8 is characterized in that, described method is applied in the DTV receiver system of data volume that each code element carries 8K.
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| CN102571644A (en) * | 2010-12-09 | 2012-07-11 | 上海华虹集成电路有限责任公司 | CMMB (China Mobile Multimedia Broadcasting) channel response estimation method and device |
| CN102761501A (en) * | 2011-04-28 | 2012-10-31 | 上海华虹集成电路有限责任公司 | Method and device for evaluating signal-noise power in CMMB system |
| CN103081428A (en) * | 2010-08-20 | 2013-05-01 | 德克萨斯大学系统董事会 | Inserting and decoding replicated data symbols in wireless communications |
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| CN103081428A (en) * | 2010-08-20 | 2013-05-01 | 德克萨斯大学系统董事会 | Inserting and decoding replicated data symbols in wireless communications |
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| CN102571644A (en) * | 2010-12-09 | 2012-07-11 | 上海华虹集成电路有限责任公司 | CMMB (China Mobile Multimedia Broadcasting) channel response estimation method and device |
| CN102761501A (en) * | 2011-04-28 | 2012-10-31 | 上海华虹集成电路有限责任公司 | Method and device for evaluating signal-noise power in CMMB system |
| CN103763223A (en) * | 2014-01-20 | 2014-04-30 | 清华大学 | Sparse MIMO-OFDM channel estimation method based on space-time correlation of channel |
| CN103763223B (en) * | 2014-01-20 | 2017-01-11 | 清华大学 | Sparse MIMO-OFDM channel estimation method based on space-time correlation of channel |
| US11540279B2 (en) * | 2019-07-12 | 2022-12-27 | Meteorcomm, Llc | Wide band sensing of transmissions in FDM signals containing multi-width channels |
| CN111489721A (en) * | 2020-03-23 | 2020-08-04 | 天津大学 | Signal frame matrixing music information recording method |
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| US12022375B2 (en) | 2020-12-19 | 2024-06-25 | Meteorcomm, Llc | End of train to head of train communication over a train control network |
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