CN1564555A - Processing method of protecting interval for modem procedue - Google Patents
Processing method of protecting interval for modem procedue Download PDFInfo
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- CN1564555A CN1564555A CN 200410029669 CN200410029669A CN1564555A CN 1564555 A CN1564555 A CN 1564555A CN 200410029669 CN200410029669 CN 200410029669 CN 200410029669 A CN200410029669 A CN 200410029669A CN 1564555 A CN1564555 A CN 1564555A
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Abstract
The method decides if the signal dropping into the guard interval of direct route in demodulation window in delay multi-path is dadded back to demodulation window for making demodulation, according to the signal state information in demodulation window of common OFDM and the signal state information of pilot frequecy. Namely if the SINR of the signal in demodulation window of common OFDM is higher than a preset threshold or the BER is higher than a preset threshold, the demodulation of OFDM will not select the signal sampling in guard interval; otherwise, the signal dropping into the guard interval of direct route in the demodulation window in delay multi-path will be added back to demodulation window for making demodulation.
Description
Technical field
The present invention relates to wireless communication system, particularly a kind of method of in the OFDM demodulating process, using signal sampling in the protection at interval and a kind of before the OFDM demodulation to protecting blank signal to carry out pretreated method.
Background technology
OFDM (OFDM) is suitable for the advantage of high code check multi-carrier transmission and is extensively proved.Two big restraining factors in particularly transmitting, i.e. frequency selective fading channels and intersymbol interference (ISI) utilize parallel data and protection to solve at interval usually respectively.When OFDM transmits high code rate data in noiseless parallel narrow band channel, utilize Fourier transform processing to avoid the very complicated equilibrium of computing., the protection that surpasses the channel delay diffusion is inserted between the OFDM symbol at interval to eliminate ISI.At different application, the OFDM protection occurs with the form of " circulating front/rear sewing " or silence period (zero filling) at interval.Therefore present most of ofdm system has a large amount of work to do about OFDM demodulation Cyclic Prefix based on Cyclic Prefix.On the other hand, zero filling method can be saved quite a few transmitting power.Inside a protection equaled the system of 1/4 OFDM mark space at interval, transmitting power saved 20% than cyclic prefix scheme.But its cost is the susceptibility that has increased timing offset, and the potential orthogonality that may cause losing between subcarrier is arranged.
Raising is exactly to utilize to protect interim to receive the orthogonality of signal restoring signal based on a way of zero filling method ofdm system performance.In fact protect interval sampling to comprise and postpone sinusoidal afterbody, therefore can be added back to the OFDM demodulation window in theory.On the other hand, this process has been introduced extra noise to demodulation window.If improper to protection interval sampling signal processing, signal strengthens the noise intensity that the gain that brings can be increased and offsets.
Summary of the invention
One of purpose of the present invention provides a kind of signal that utilizes in the protection at interval, and it is added back to the demodulation method that carries out demodulation in the demodulation window.
Another object of the present invention provide with the signal in the protection at interval be added back to carry out demodulation in the demodulation window before, the signal in the protection is at interval carried out pretreated method.
The objective of the invention is to realize by following technological means:
A kind of OFDM demodulation method, the method is according to the signal condition information in the conventional OFDM demodulation window or according to the pilot signal state information, and the interior at interval signal of direct projection trail protection of falling whether decision will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window;
If the SINR of the interior signal of conventional OFDM demodulation window is higher than a default thresholding or BER is lower than a default thresholding, the signal sampling in the protection is not at interval just selected in the OFDM demodulation for use; Otherwise the signal of direct projection trail protection at interval of falling that the OFDM demodulation will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.Perhaps, if the SINR of pilot signal is higher than default thresholding, the signal sampling in the protection is not at interval just selected in the OFDM demodulation for use; If the BER of pilot signal is lower than default thresholding, the signal sampling in the protection is not at interval just selected in the OFDM demodulation for use; Otherwise the signal of direct projection trail protection at interval of falling that the OFDM demodulation will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.
Wherein can dynamically adjust in time the signals sampling amount of falling in the direct projection trail protection interval of choosing in the demodulation window in the delay multipath; Also can adjust according to the instantaneous estimation wireless or diffusion of wire message way time delay; Also can adjust according to the statistical estimate wireless or diffusion of wire message way time delay; Also can determine by communication channel time delay diffusion estimated value.When channel situation is relatively stable, postpone in the multipath signals sampling the choose amount of direct projection trail protection at interval of falling in the demodulation window, can be set with the time delay diffusion of wireless or wire message way and equate.When channel situation is over time and when changing, can be set the time delay diffusion of being a bit larger tham wireless or wire message way.Described pilot signal can periodically be inserted the time domain sequences in OFDM or the multicarrier symbol code stream.Described pilot signal can be embedded within the training signal in OFDM or the multicarrier symbol code stream.Described default thresholding can be cancelled.The signal of falling sampling in the direct projection trail protection interval in the delay multipath in the demodulation window adds the top of conventional OFDM demodulation window in a looping fashion to.Signal that falling sampling in the direct projection trail protection interval in the delay multipath in the demodulation window can carry out preliminary treatment before being recycled the top that is added back to conventional OFDM demodulation window.Described preprocessing process comprises time-domain windowed and time-domain filtering, and the coefficient of filtering and windowing is by the cognitive features decision of communication channel.Time-frequency conversion among the described OFDM in described OFDM demodulating process signal sampling in used protection at interval carries out after being recycled the top that is added back to conventional OFDM demodulation window.
The present invention can improve the OFDM demodulation performance and not increase transmission of power.The noise intensity that the gain that the present invention can avoid signal to strengthen bringing can be increased and offsetting.By using SNR or the BER thresholding that adds, the present invention can reduce the complexity of receiver simultaneously.
Description of drawings
Fig. 1 is OFDM symbolic code flow diagram according to an embodiment of the invention.
Fig. 2 is according to one embodiment of the invention, the schematic diagram of direct signal and one tunnel multipath signal that postpones, and the OFDM demodulation window is locked on the direct signal.
Fig. 3 is the processing module schematic block diagram before the standard OFDM demodulator according to an embodiment of the invention.
Fig. 4 is one action illustration intention of using pilot tone in the OFDM symbol.
Embodiment
Below in conjunction with accompanying drawing, the present invention will be described in detail:
Signal condition information in the described conventional OFDM demodulation window comprises: the signal condition in the conventional OFDM demodulation window comprises Signal Interference and Noise Ratio (SINR), the error rate of decoded signal (BER), time delay wireless or wire message way spread.The pilot signal state comprises Signal Interference and Noise Ratio (SINR), the error rate of decoded signal (BER), the time delay diffusion of wireless or wire message way.The method is according to signal condition information in the conventional OFDM demodulation window or pilot signal state information, and the interior at interval signal of direct projection trail protection of falling whether decision will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.
Fig. 1 has described OFDM symbol code stream.Each symbol all comprises protection at interval, and its protection is divided into prefix and suffix two parts at interval.In addition, every the OFDM of some symbol, be inserted into a beacon/pilot signal.
In the present invention, the signal in the protection at interval is not always need be added back in the demodulation window to go.For example, if reprocessing BER (bit error rate of last OFDM demodulation symbol in the last cycle) is lower than a default thresholding, receiver can select not use the signal in the protection at interval, to reduce the demodulating process complexity.
Similarly, if reprocessing SINR (Signal Interference and Noise Ratio of last OFDM demodulation symbol in the last cycle) is higher than a default thresholding, receiver can select not use the signal in the protection at interval, to reduce the demodulating process complexity.
If preliminary treatment BER (error rate of beacon signal in the last cycle) is higher than a default thresholding conversely speaking,, receiver can select to use the signal in the protection at interval, to improve demodulation performance.
Similarly, if preliminary treatment SINR (Signal Interference and Noise Ratio of beacon signal in the last cycle) is lower than a default thresholding, receiver can select to use the signal in the protection at interval, to improve demodulation performance; For example, if the thresholding of the SINR of " QPSK+ sign indicating number " is 3, and pretreated SINR is estimated as near this thresholding, be necessary so to use protection at interval the internal symbol sampling to improve performance.In others, if when pretreated SINR is estimated as much larger than this thresholding, the symbol sampler in can abandoning protecting at interval simply.
Fig. 4 has enumerated the example of using pilot tone in the OFDM symbol.Fig. 2 has compared direct signal and one tunnel multipath signal that postpones.The OFDM demodulation window is locked on the direct signal.Sampled signal outside the demodulation window (all or part of) is added back to demodulation window, to improve demodulation.
Utilization to signal in the protection at interval of the present invention is described in detail below:
If s (t), t ∈ [O, T] is by being received ofdm signal, and the demodulation window cycle is T.If g (t), t ∈ [T, T+T
g] for protecting interval T
gThe interior signal that is received is seen Fig. 2 example.
According to the present invention, at first received signal in the part protection at interval is added to s (t), go among the t ∈ [O, T]:
x(t)＝s(t)+g(t+T)w(αT
g)；t∈[O，T]
W (α T
g) be that size is α T
gRectangular window.X (t) signal that produces is delivered to the standard OFDM demodulator.
According to the present invention, the amount of g (t) add-back is α, by the channel delay diffusion τ decision of estimating based on beacon to obtain.In some cases, α T
gBe set to equate with τ; Under other situation, α T
gMay be set to the delay between the main multipath signal of two-way; Only detect main footpath signal when also having some, α T
gBe set to zero.
Below channel delay is spread the estimation of τ:
When there is periodic beacon symbols in the OFDM code stream, based on beacon signal, beacon signal periodically is inserted in the OFDM symbol code stream through the spread spectrum modulation to the estimation of channel delay diffusion.Fig. 1 is the example of beacon in the OFDM symbols streams.
In detail, beacon signal is at first carried out despreading based on known pseudo random sequences.Contain spike in the output signal corresponding to multi-path location.The time span that first and last can detect between the multipath signal is channel delay diffusion estimated value τ.If only detect a main footpath, channel delay diffusion estimated value is made as zero.
Another kind method is output signal to be carried out channel type estimate, by the diffusion of parametric method decision channel delay, as maximum likelihood method, subspace parameter Estimation method, the Minimum Mean Square Error estimation technique.
If there is not beacon signal, channel delay diffusion τ will estimate according to the embedded regular pilot signal of OFDM symbol.Fig. 4 is an example.Estimating at multiple channel fitting algorithm for the frequency response of multipath channel can adopt.Then channel frequency response is transformed into time domain,, obtains the channel delay diffusion of time domain such as using Fourier transform.
The third situation, channel delay diffusion τ is according to beacon and the common estimation of regular pilot signal.For example, the higher value in channel delay diffusion two estimated values being set to respectively to obtain by beacon and pilot signal.
The 4th kind of situation utilizes the decision-feedback method to obtain reprocessing channel delay diffusion τ based on the ofdm signal of demodulation
PostEstimation.τ
PostDecide the at interval interior signal of protection to be used for the amount of demodulation independently or in conjunction with τ.Under the above-mentioned situation, estimate that in order to obtain the better statistics of robust performance the channel delay diffusion is estimated carrying out smoothing processing on the section (crossing over one or more OFDM symbol period) sometime.
Fig. 3 is that a kind of OFDM receiver of suggestion is realized.As shown in the figure, received signal (OFDM symbol code stream) at first enters a pilot/beacon processor.The pilot/beacon processor extracts the signal corresponding to pilot/beacon from received signal.The signal that extracts obtains channel type estimation and SINR or BER preliminary treatment and estimates through handling.Then this estimated value is outputed to protection blank signal processor; Simultaneously, the ofdm signal that ofdm demodulator obtains former demodulation is sent to BER and channel type estimator, and to reprocessing BER and/or reprocessing SINR, and the diffusion of reprocessing channel delay is estimated.The parameter value of BER and the output of channel type estimator also enters protection blank signal processor.Current and before on the basis of input signal, protection blank signal processor extracts the useful part of signal in the protection at interval, carries out time shaft translation T after the time, and it is added back to signal in the OFDM demodulation window.Output signal is sent to conventional ofdm demodulator again and carries out demodulation.In some cases, protection blank signal processor can be handled the filter or the window of signal increase time domain in the protection at interval, and purpose is further to improve signal to noise ratio.As shown in Figure 2.
Above embodiment only is used for illustrating the present invention, is not to be used for limiting the present invention.
Claims (17)
1. an OFDM demodulation method is characterized in that, the method is according to the signal condition information in the conventional OFDM demodulation window, and the interior at interval signal of direct projection trail protection of falling whether decision will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.
2. OFDM demodulation method according to claim 1 is characterized in that,
If the SINR of the interior signal of conventional OFDM demodulation window is higher than a default thresholding or BER is lower than a default thresholding, the signal sampling in the protection is not at interval just selected in the OFDM demodulation for use;
Otherwise the signal of direct projection trail protection at interval of falling that the OFDM demodulation will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.
3. an OFDM demodulation method is characterized in that, the method is according to the pilot signal state information, and the interior at interval signal of direct projection trail protection of falling whether decision will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.
4. OFDM demodulation method according to claim 3 is characterized in that,
If the SINR of pilot signal is higher than default thresholding, the signal sampling in the protection is not at interval just selected in the OFDM demodulation for use;
If the BER of pilot signal is lower than default thresholding, the signal sampling in the protection is not at interval just selected in the OFDM demodulation for use;
Otherwise the signal of direct projection trail protection at interval of falling that the OFDM demodulation will postpone in the demodulation window in the multipath is added back to and carries out demodulation in the demodulation window.
5. according to the arbitrary described OFDM demodulation method of claim 1-4, it is characterized in that, can dynamically adjust in time the signals sampling amount of falling in the direct projection trail protection interval of choosing in the demodulation window in the delay multipath.
6. according to the arbitrary described OFDM demodulation method of claim 1-4; it is characterized in that, can adjust according to the instantaneous estimation wireless or diffusion of wire message way time delay the interior at interval signals sampling amount of choosing of direct projection trail protection of falling in the demodulation window in the delay multipath.
7. according to the arbitrary described OFDM demodulation method of claim 1-4; it is characterized in that, can adjust according to the statistical estimate wireless or diffusion of wire message way time delay the interior at interval signals sampling amount of choosing of direct projection trail protection of falling in the demodulation window in the delay multipath.
8. according to the arbitrary described OFDM demodulation method of claim 1-4, it is characterized in that, can determine by communication channel time delay diffusion estimated value the calculating of falling the signals sampling amount of choosing in the direct projection trail protection interval in the demodulation window in the delay multipath.
9. OFDM demodulation method according to claim 5 is characterized in that, the interior at interval signals sampling amount of choosing of direct projection trail protection of falling in the delay multipath in the demodulation window can be set with the time delay diffusion of wireless or wire message way and equate.
10. OFDM demodulation method according to claim 5 is characterized in that, the interior at interval signals sampling amount of choosing of direct projection trail protection of falling in the delay multipath in the demodulation window can be set the time delay of being a bit larger tham wireless or wire message way and spread.
11., it is characterized in that described pilot signal can periodically be inserted the time domain sequences in OFDM or the multicarrier symbol code stream according to claim 3 or 4 described OFDM demodulation methods.
12., it is characterized in that pilot signal can be embedded within the training signal in OFDM or the multicarrier symbol code stream according to claim 3 or 4 described OFDM demodulation methods.
13., it is characterized in that default thresholding can be cancelled according to claim 2 or 4 described OFDM demodulation methods.
14., it is characterized in that the signal of falling sampling in the direct projection trail protection interval in the delay multipath in the demodulation window adds the top of conventional OFDM demodulation window in a looping fashion to according to the arbitrary described OFDM demodulation method of claim 1-4.
15., it is characterized in that the signal that falling sampling in the direct projection trail protection interval in the delay multipath in the demodulation window can carry out preliminary treatment according to the arbitrary described OFDM demodulation method of claim 1-4 before being recycled the top that is added back to conventional OFDM demodulation window.
16. according to the arbitrary described OFDM demodulation method of claim 1-4, it is characterized in that described preprocessing process comprises time-domain windowed and time-domain filtering, the coefficient of filtering and windowing is by the cognitive features decision of communication channel.
17. the conversion of the time-frequency among the described OFDM in the OFDM demodulation method according to claim 1, described OFDM demodulating process signal sampling in used protection at interval carries out after being recycled the top that is added back to conventional OFDM demodulation window.
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| CNB200410029669XA CN100571237C (en) | 2004-03-31 | 2004-03-31 | A kind of OFDM demodulation method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102291359A (en) * | 2011-09-06 | 2011-12-21 | 复旦大学 | Producing and sending device for enhancing quality of receiving optical OFDM (Orthogonal Frequency Division Multiplexing) signal by adopting time domain windowing technology |
| CN109818894A (en) * | 2018-11-19 | 2019-05-28 | 西安宇飞电子技术有限公司 | GMSK signal detecting method and detection device under multipath channel |
| CN111183602A (en) * | 2017-08-09 | 2020-05-19 | 瑞典爱立信有限公司 | Instantaneous guard interval |
-
2004
- 2004-03-31 CN CNB200410029669XA patent/CN100571237C/en not_active Expired - Fee Related
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102291359A (en) * | 2011-09-06 | 2011-12-21 | 复旦大学 | Producing and sending device for enhancing quality of receiving optical OFDM (Orthogonal Frequency Division Multiplexing) signal by adopting time domain windowing technology |
| CN102291359B (en) * | 2011-09-06 | 2014-08-06 | 复旦大学 | Producing and sending device for enhancing quality of receiving optical OFDM (Orthogonal Frequency Division Multiplexing) signal by adopting time domain windowing technology |
| CN111183602A (en) * | 2017-08-09 | 2020-05-19 | 瑞典爱立信有限公司 | Instantaneous guard interval |
| US11646846B2 (en) | 2017-08-09 | 2023-05-09 | Telefonaktiebolaget Lm Ericsson (Publ) | Transient protection interval |
| CN109818894A (en) * | 2018-11-19 | 2019-05-28 | 西安宇飞电子技术有限公司 | GMSK signal detecting method and detection device under multipath channel |
| CN109818894B (en) * | 2018-11-19 | 2021-12-07 | 西安宇飞电子技术有限公司 | GMSK signal detection method and detection device under multipath channel |
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| CN100571237C (en) | 2009-12-16 |
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