An OFDM system uses a normal mode which has a symbol length T, a guard time TG and a set of N sub-carriers, which are orthogonal over the time T, and one or more fallback modes which have symbol lengths KT and guard times KTG where K is an integer greater than unity. The same set of N sub-carriers is used for the fallback modes as for the normal mode. Since the same set of sub-carriers is used, the overall bandwidth is substantially constant, so alias filtering does not need to be adaptive. The Fourier transform operations are the same as for the normal mode. Thus fallback modes are provided with little hardware cost. In the fallback modes the increased guard time provides better delay spread tolerance and the increased symbol length provides improved signal to noise performance, and thus increased range, at the cost of reduced data rate.

Claims

42 · 5 independent · depth 4

42 granted claims

›1.independentA receiver for receiving an orthogonal frequency division multiplex (OFDM) communications signal, the ODFM signal being transmitted using a set of sub…+13

›2.↳ 1The receiver of claim 1 further comprising a filter operative to average an input signal over K intervals, each interval having a duration T.d2+8

›3.↳ 2The receiver of claim 2 wherein the FFT block is coupled to an output of the filter.d3+1

›5.↳ 2The receiver of claim 2 further comprising a symbol timing circuit operative to provide a timing signal to the FFT block and to the filter such that t…d3

›6.↳ 2The receiver of claim 2 wherein the filter operates to sum K samples, each sample separated by T seconds.d3+1

›8.↳ 2The receiver of claim 2 further comprising a control circuit operative to set the number of averaging intervals K.d3+2

›11.↳ 1The receiver of claim 1 further comprising an antenna.d2+1

›13.↳ 1The receiver of claim 1 further comprising a filter that provides, when operating in a signaling mode in which K>1 , an average over K successive peri…d2

›14.↳ 1The receiver of claim 1 wherein a length of the guard time is KTG where TG is the same for all of the signaling modes.d2

›15.independentA receiver for receiving an orthogonal frequency division multiplex (OFDM) communications signal, the ODFM signal being transmitted using a set of sub…+1

›17.independentA method for receiving an orthogonal frequency division multiplexed (OFDM) signal, the OFDM signal being transmitted using a set of sub-carriers which…+8

›18.↳ 17The method of claim 17 wherein the step of determining an average operates to average across K parts of the OFDM symbol, each of the K parts having a …d2

›19.↳ 17The method of claim 17 wherein the average determining step operates to sum K samples, each sample separated by T seconds.d2

›20.↳ 17The method of claim 17 wherein the determined average is stored in a memory having a delay line established to receive M samples, where M corresponds …d2

›21.↳ 17The method of claim 17 further including a step of providing a control signal operative to set the number of averaging intervals K.d2+2

›24.↳ 17The method of claim 17 wherein the guard time is interposed between successive ones of the OFDM symbols.d2+1

›26.independentA receiver for receiving an orthogonal frequency division multiplex (OFDM) communications signal, the ODFM signal being transmitted using a set of sub…+15

›27.↳ 26The receiver of claim 26 wherein the plurality of signaling modes use the same set of sub-carriers.d2

›28.↳ 26The receiver of claim 26 wherein the FFT block is coupled to an output of the filter.d2+1

›30.↳ 26The receiver of claim 26 wherein the FFT block is arranged in a signal path of the receiver ahead of the filter such that the filter averages K output…d2+1

›32.↳ 26The receiver of claim 26 further comprising an antenna.d2+1

›34.↳ 26The receiver of claim 26 further comprising an analog to digital converter.d2+3

›38.↳ 26The receiver of claim 26 further comprising a control circuit operative to set the number of averaging intervals K.d2+2

›41.↳ 26The receiver of claim 26 wherein a length of the guard time is KTG where TG is the same for all of the signaling modes.d2

›42.independentA receiver for receiving an orthogonal frequency division multiplex (OFDM) communications signal, the ODFM signal being transmitted using a set of sub…

Classifications

3 codes

IPC · International Patent Classification

Section H — Electricity

H04J011/00

USPC · US Patent Classification

370/208370/210

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Phirin Sam

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1 priority documents

›Priority documents — 1

Type	Document	Date
related publication	US 20030189894 A1	9 Oct 2003

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