TH70563A - Synchronization in the broadcast of the FM system using time-division multiplexed pilot signals. - Google Patents

Abstract

DC60 (23/11/47) In an OFDM system, the transmitter broadcasts the first TDM pilot signal on the first set of subbands, followed by the second TDM pilot signal on the second set of subbands in each frame. The subbands in each set are selected from among the total N subbands in such a way that (1) the OFDM symbol for the first TDM pilot signal has at least a pilot-1 sequence of length L1 corresponding to S1, and (2) the OFDM symbol for the second TDM pilot signal has at least a pilot-2 sequence of length L2 corresponding to S2, where L2>L1, S1•L1=N and S2•L2=N. The transmitter may also broadcast an FDM pilot signal. The receiver processes the first TDM pilot signal to obtain the frame timing (for example, by performing operations on different pilot-1 sequences to achieve this) and further processes the second TDM pilot signal to obtain the symbol timing. (For example, by detecting the start of the channel's impulse response estimate derived from the second TDM pilot signal.) In an OFDM system, the transmitter broadcasts the first TDM pilot signal on the first set of subbands, followed by the second TDM pilot signal on the second set of subbands in each frame. The subbands in each set are selected from among the total N subbands in such a way that (1) the OFDM symbol for the first TDM pilot signal has at least a pilot-1 sequence of length L1 corresponding to S1, and (2) the OFDM symbol for the second TDM pilot signal has at least a pilot-2 sequence of length L2 corresponding to S2, where L2>L1, S1•L1=N and S2•L2=N. The transmitter may also broadcast an FDM pilot signal. The receiver processes the first TDM pilot signal to obtain the frame timing (for example, by performing operations on different pilot-1 sequence correlations to achieve it) and also processes A second TDM pilot signal is then used to obtain the symbol timing (for example, by detecting the start of the channel's impulse response estimate derived from the second TDM pilot signal).

Claims (43)

1. The method of transmitting pilot signals in a wireless broadcasting system utilizes orthogonal frequency division multiplexing (OFDM), which consists of transmitting the first pilot signal on the first set of frequency subbands in a time-division multiplexing (TDM) format with data, where the first set includes a small portion of the total N frequency subbands in the system, where N is an integer greater than one; and transmitting the second pilot signal on the second set of frequency subbands in TDM format with data, where the second set includes more subbands than the first. The first and second pilot signals are then used for synchronization by the receiver in the system. 2. Method of Claim 1 whereby the first and second pilot signals are transmitted periodically in frames with predetermined durations. 3. The method of claim number 2 involves sending the first pilot signal at the beginning of each frame and sending the second pilot signal in the next frame. 4. The method of claim 2 involves using the first pilot signal to detect the start of each frame, and using the second pilot signal to determine the timing of the symbol indicating the start of the received OFDM symbol. 5. Method of Claim 1 whereby the first pilot signal is sent out in the symbol OFDM one symbol. 6. The method of claim 1, where the first set includes N/2 M frequency subbands, where M is an integer greater than one. 7. Method of Claim 1 whereby a second pilot signal is transmitted in one OFDM symbol. 8. The method of claim 1, where the second set includes N/2 K frequency subbands, where K is one or more integers. 9. Method of Claim 1, whereby the second set includes N/2 subbands of frequency. 10. The method of claim 1, where the frequency subbands in each first and second set are uniformly distributed across the total frequency subbands N. 11. Method of Claim 1, whereby the receiver uses the first pilot signal to estimate the frequency error. 12. Method of Claim 1, whereby the receiver uses a second pilot signal for channel estimation. 13. The method of claim 1 is further comprised of the transmission of a third pilot signal on a third subband of frequency in a frequency division multiplexed (FDM) format with the data, whereby the receiver uses the first and second pilot signals to obtain the timing of frames and symbols, and whereby the receiver uses the third pilot signal for frequency and time tracking. 14. The method of claim number 13 involves using a third pilot signal for channel estimation. 15. The method of claim 1 also includes the generation of the first and second pilot signals using a pseudo-random number (PN) generator. 16. The method of claim 15 further includes the initialization of the PN generator as the first initial state for the first pilot signal and the initialization of the PN generator as the second initial state for the second pilot signal. 17. The method of claim number 15, while still using a PN generator to encrypt the data before transmission. 18. The methodology of claim 1 further includes the generation of a first pilot signal, a second pilot signal, or a combination of first and second pilot signals, each containing information that has been selected to minimize peak-to-average variation in the time domain waveform for the pilot signals. 19. An instrument in an orthogonal frequency division multiplexing (OFDM) system consists of a modulator that operates to provide the first pilot signal on the first set of frequency subbands in a time-division multiplexing (TDM) format with data, and to provide a second pilot signal on the second set of frequency subbands in TDM format with data, where the first set includes a small portion of the total frequency subbands N in the system, where N is an integer greater than one, and the second set includes more subbands than the first, and a transmitter unit that operates to transmit the first and second pilot signals, where the receiver in the system uses the first and second pilot signals for synchronization. 20. Instrument of Claim 19, whereby the first and second pilot signals are transmitted periodically in frames, each frame having a predetermined duration. 21. An instrument in an orthogonal frequency division multiplexing (OFDM) system consists of a path to transmit the first pilot signal onto the first set of frequency subbands in a time-division multiplexing (TDM) format with data, where the first set includes a small portion of the total N frequency subbands in the system, where N is an integer greater than one; and a path to transmit the second pilot signal onto the second set of frequency subbands in TDM format with data, where the second set includes more subbands than the first, and where the receiver in the system uses the first and second pilot symbols for synchronization. 22. Instrument of Claim 21 whereby the first and second pilot signals are transmitted periodically in frames with predetermined durations. 23. The method for achieving synchronization in a perpendicular frequency division multiplexing (OFDM) system involves processing the first pilot signal received via the communication channel to detect the start of each frame at a predetermined time. This first pilot signal is then transmitted over the first set of frequency subbands in time-division multiplexing (TDM) format with data, where the first set includes a small portion of the total frequency subbands N in the system, where N is a larger integer than one. A second pilot signal received via the communication channel is then processed to obtain the symbol timing, indicating the start of the received OFDM symbol. This second pilot signal is then transmitted over the second set of frequency subbands in TDM format with data, where the second set includes more subbands than the first. 24. Method of Claim 23 whereby the first and second pilot signals are transmitted periodically in frames, each frame having a predetermined duration. 25. The method of claim 23, whereby the processing of the first pilot signal comprises the acquisition of a detection measure by using delayed correlation between samples in a sequence of samples received for the first pilot signal as the primary, and the detection of the start of each frame using the primary detection measure. 26. The method of claim 25, whereby the beginning of each frame is further investigated using the threshold change of the measure as the basis. 27. The method of claim 26, whereby the start of a frame is detected if the detection measure exceeds the measure's threshold for a predetermined amount of time, and then during the first pilot signal. 28. The method of claim 26, whereby the start of a frame is detected if the detection measure exceeds the measure threshold for a percentage of time during the first pilot signal and remains below the measure threshold for a predetermined amount of time thereafter. 29. The method of claim 23, whereby the processing of the first pilot signal comprises the acquisition of a detection measure by using the direct correlation between the obtained sample for the first pilot signal and the expected value for the first pilot signal as the primary, and the detection of the start of each frame using the primary detection measure. 30. The method of claim 23, whereby the processing of the second pilot signal comprises the determination of the channel impulse response estimate using the received second pilot signal as the basis, the determination of the start of the channel impulse response estimate, and the determination of the symbol timing using the start of the channel impulse response estimate as the basis. 31. Method of Claim 30, where the channel impulse response estimate is determined by the channel separation terminal L, where L is an integer greater than one, and where the beginning of the channel impulse response estimate is determined by the channel separation terminal L. 32. The method of claim 31, whereby consideration of the initial determination of the channel impulse response estimate includes consideration of the determination for each position of a number of overlay positions, the power of the channel's isolation terminals within the overlay, and the initial setting of the channel impulse response estimate at the overlay position with the highest power among a number of overlay positions. 33. Method of claim 32 where the initiation of the channel impulse response estimate is set at the rightmost superposition position with maximum energy. If there are multiple superposition positions with maximum energy. 34. The method of claim 23 further incorporates processing of the first pilot signal to estimate the frequency error in the received OFDM symbol for the first pilot signal. 35. The method of claim 23 further incorporates processing of the second pilot signal to estimate the frequency error in the received OFDM symbol for the second pilot signal. 36. The methodology of claim 23 further incorporates the processing of a second pilot signal to obtain an approximation of the channel for the communication channel. 37. The method of claim 23 further includes the processing of the third pilot signal received via the frequency and time monitoring communication channel, whereby the third pilot signal is transmitted over a third set of frequency subbands in a frequency division multiplexed (FDM) format with the data. 38. The instruments in an orthogonal frequency division multiplexing (OFDM) system consist of a frame detector that processes the first pilot signal received via the communication channel to detect the start of each predetermined frame, where the first pilot signal is transmitted on the first set of frequency subbands in a time-division multiplexing (TDM) format with data, and where the first set includes a small portion of the total frequency subbands N in the system, where N is an integer greater than one; and a symbol timing detector that processes the second pilot signal received via the communication channel to obtain the symbol timing indicating the start of the received OFDM symbol, where the second pilot signal is transmitted on the second set of frequency subbands in TDM format with data, and where the second set includes more subbands than the first. 39. Instrumentation of claim 38 whereby the first and second pilot signals are transmitted periodically in frames of predetermined duration. 40. The instrument of claim 38, whereby the frame detector operates to obtain a detection measure by applying correlation between samples in a sequence of samples received for the primary pilot signal, and to detect the start of each frame using the primary detection measure. 41. The instrument of claim 38, whereby a symbol timing detector operates to obtain an estimation of the channel impulse response using a second received pilot signal as the basis. Consider determining the start of the channel impulse response estimation and obtain the symbol timing using the start of the channel impulse response estimation as the basis. 42. The tools in an orthogonal frequency division multiplexing (OFDM) system consist of a path to process the first received pilot signal via a communication channel to detect the start of each frame with a predetermined time interval. The first pilot signal is transmitted on the first set of frequency subbands in a time-division multiplexing (TDM) format with data, and the first set includes a small portion of the total frequency subbands N in the system, where N is a greater than one integer; and a path to process the second received pilot signal via a communication channel to obtain the symbol timing indicating the start of the received OFDM symbol. The second pilot signal is transmitted on the second set of frequency subbands in a TDM format with data, and the second set includes more subbands than the first. 43. Instrument of Claim 42, whereby the first and second pilot signals are transmitted periodically in frames of predetermined duration.