AFC in OFDM modulation by shift of a window along a reception sample sequence

• US 5,596,582 A
• Filed: 05/25/1995
• Issued: 01/21/1997
• Est. Priority Date: 05/26/1994
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation, Nippon Hoso Kyokai
• Inventors: Sato, Toru, Saito, Masafumi
• Primary Examiner(s): Kizou, Hassan
• Application Number:
  US08/450,540
• Time in Patent Office: 607 Days
• Field of Search: 370/19, 370/21, 370/23, 370/69.1, 370/70, 370/100.1, 370/105.1, 370/105.4, 370/106, 375/260, 375/295, 375/343, 375/354, 375/355, 375/365, 375/366, 375/368, 375/347
• US Class Current: 370/509
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

In a receiver for an OFDM modulated transmission signal including at least one synchronizing symbol in each frame, the synchronizing symbol is located by stepwise shifting a window along a reception sample sequence to make a cross-correlation calculator (55) calculate cross-correlation values between a stored pattern produced from a pattern memory (53) and sequence portions picked up by the window, a maximum selector (57, 59) select two successive maxima of the cross-correlation values at a time interval substantially equal to a frame period, and a controllable clock generator (61-65) generate a clock sequence at the time interval for use in sampling the sample sequence. On a transmitter side, the at least one synchronizing symbol may either be preceded by a null period or be a main synchronizing symbol preceded by an auxiliary synchronizing symbol for use in roughly defining ranges in which the window should be shifted.

Claims

1. A method of transmitting a sequence of data as a transmission signal and of receiving said transmission signal as a reproduction of said sequence of data, said method comprising the steps of:

converting said sequence of data to data symbols by orthogonal frequency division multiplex modulation;

composing said data symbols into successive frames by adding synchronizing patterns to said frames;

transmitting said successive frames as said transmission signal;

receiving said transmission signal as a received signal;

sampling reception samples from said received signal in response to a clock sequence of a clock frequency to produce a reception sample sequence;

detecting synchronization patterns in said reception sample sequence;

generating said clock sequence in response to said synchronization patterns; and

reproducing said reproduction by orthogonal frequency division multiplex demodulation of said reception sample sequence, wherein

said composing step comprises the steps of;

storing at least one synchronizing symbol to produce a stored synchronizing symbol sequence, and

using a synchronizing symbol from said stored synchronizing symbol sequence as one of said synchronizing patterns in each frame, and wherein

said detecting step comprises the steps of;

storing a pattern comprising a synchronization pattern identical with said synchronizing symbol to produce a stored pattern sequence,

calculating, responsive to said stored pattern sequence, a cross-correlation value between said synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence,

selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that gives two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames, said ones of candidate patterns being selected to decide said time interval successively as time intervals each of which substantially coincides with said frame period,

averaging a prescribed number of said time intervals into a mean, interval, and

controlling said clock frequency in response to said time interval using said mean interval as said time interval.

2. A method of transmitting a sequence of data as a transmission signal and of receiving said transmission signal as a reproduction of said sequence of data, said method comprising the steps of:

converting said sequence of data to data symbols by orthogonal frequency division multiplex modulation;

composing said data symbols into successive frames by adding synchronizing patterns to said frames;

transmitting said successive frames as said transmission signal;

receiving said transmission signal as a received signal;

sampling reception samples from said received signal in response to a clock sequence of a clock frequency to produce a reception sample sequence;

detecting synchronization patterns in said reception sample sequence;

generating said clock sequence in response to said synchronization patterns; and

reproducing said reproduction by orthogonal frequency division multiplex demodulation of said reception sample sequence, wherein

said composing step comprises the steps of;

storing a main synchronizing symbol and an auxiliary synchronizing symbol, consecutively preceding said main synchronizing symbol, to produce a stored synchronizing symbol sequence, and

using said main synchronizing symbol from said stored synchronizing symbol sequence as one of said synchronizing patterns in each frame, and wherein

said detecting step comprises the steps of;

storing a pattern comprising a synchronization pattern identical with said main synchronizing symbol to produce a stored pattern sequence,

detecting auxiliary synchronizing patterns, while said received signal is subjected to said sampling step, to produce position estimations of where said main synchronizing symbol appears in said reception sample sequence;

calculating, responsive to said stored pattern sequence, a cross-correlation value between said synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence, said cross-correlation values being calculated with said window stepwise shifted only in said position estimations,

selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that gives two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames, and

controlling said clock frequency in response to said time interval.

3. A method of transmitting a sequence of data as a transmission signal and of receiving said transmission signal as a reproduction of said sequence of data, said method comprising the steps of:

converting said sequence of data to data symbols by orthogonal frequency division multiplex modulation;

composing said data symbols into successive frames by adding synchronizing patterns to said frames;

transmitting said successive frames as said transmission signal;

receiving said transmission signal as a received signal;

sampling reception samples from said received signal in response to a clock sequence of a clock frequency to produce a reception sample sequence;

detecting synchronization patterns in said reception sample sequence;

generating said clock sequence in response to said synchronization patterns; and

reproducing said reproduction by orthogonal frequency division multiplex demodulation of said reception sample sequence, wherein

said composing step comprises the steps of;

storing at least one synchronizing symbol and a null symbol to produce a stored synchronizing symbol sequence, said null symbol consecutively preceding said synchronizing symbol and having a duration which is substantially equal to said at least one synchronizing symbol, and

using a synchronizing symbol from said stored synchronizing symbol sequence as one of said synchronizing patterns in each frame,

said clock sequence defines successive frame intervals and successive symbol intervals in each frame interval, said each frame interval being substantially identical with said frame period and being defined in response to said clock frequency, and wherein

said detecting step comprises the steps of;

storing a pattern comprising a synchronization pattern identical with said synchronizing symbol to produce a stored pattern sequence,

calculating, responsive to said stored pattern sequence, a cross-correlation value between said synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence,

selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that gives two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames,

defining a null period which one of said symbol intervals comprises when said one of said symbol intervals indicates a presence of said null symbol in a sequence of said cross-correlation values in each frame interval, and

controlling said clock frequency in response to said time interval, said controlling step suspending control of said clock frequency in each frame period except for said null period.

4. A receiver device for receiving a transmission signal derived from successive frames, each of which is composed of at least one synchronizing symbol and a sequence of data symbols with said data symbols produced by subjecting a sequence of data to orthogonal frequency division multiplex modulation, said receiver device comprising:

receiving means for receiving said transmission signal as a received signal;

sampling means responsive to a clock sequence of a clock frequency for sampling reception samples from said received signal to produce a reception sample sequence;

detecting means for detecting synchronization patterns in said reception sample sequence;

clock generating means responsive to said synchronization patterns for generating said clock sequence; and

reproducing means for reproducing, by orthogonal frequency division multiplex demodulation of said reception sample sequence, a reproduction of said sequence of data, wherein said detecting means comprises;

storing means for storing a synchronization pattern identical with said at least one synchronizing symbol to produce a stored synchronization pattern sequence,

calculating means, responsive to said stored synchronization pattern sequence, for calculating a cross-correlation value between said synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence,

selecting means for selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that give two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames, said ones of candidate patterns being selected to decide said time interval successively as time intervals each of which substantially coincides with said frame period,

averaging means for averaging a prescribed number of said time intervals into a mean interval, and

control means for controlling said clock frequency in response to said time interval using said mean interval as said time interval.

5. A receiver device for receiving a transmission signal derived from successive frames, each of which is composed of a main synchronizing symbol, an auxiliary synchronizing symbol consecutively preceding said main synchronizing symbol, and a sequence of data symbols with said data symbols produced by subjecting a sequence of data to orthogonal frequency division multiplex modulation, said receiver device comprising:

receiving means for receiving said transmission signal as a received signal;

sampling means responsive to a clock sequence of a clock frequency for sampling reception samples from said received signal to produce a reception sample sequence;

detecting means for detecting synchronization patterns in said reception sample sequence;

clock generating means responsive to said synchronization patterns for generating said clock sequence; and

reproducing means for reproducing, by orthogonal frequency division multiplex demodulation of said reception sample sequence, a reproduction of said sequence of data, wherein said detecting means comprises;

storing means for storing a main synchronization pattern and an auxiliary synchronization pattern to produce a stored synchronization pattern sequence, said main synchronization pattern being coincident with said main synchronizing symbol and said auxiliary synchronizing pattern consecutively preceding said main synchronization pattern and being similar to said auxiliary synchronizing symbol,

estimating means responsive to said auxiliary synchronization pattern for estimating, by detection of said auxiliary synchronizing symbol in said received signal, position estimations of where said main synchronizing symbol appears in said reception sample sequence,

calculating means, responsive to said stored synchronization pattern sequence, for calculating a cross-correlation value between said main synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence, said cross-correlation values being calculated with said window stepwise shifted only in said position estimations,

selecting means for selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that give two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames, and

control means for controlling said clock frequency in response to said time interval.

6. A receiver device for receiving a transmission signal derived from successive frames, each of which is composed of a main synchronizing symbol, an auxiliary synchronizing symbol, and a sequence of data symbols with said data symbols produced by subjecting a sequence of data to orthogonal frequency division multiplex modulation, said receiver device comprising:

receiving means for receiving said transmission signal as a received signal;

sampling means responsive to a clock sequence of a clock frequency for sampling reception samples from said received signal to produce a reception sample sequence;

detecting means for detecting synchronization patterns in said reception sample sequence;

clock generating means responsive to said synchronization patterns for generating said clock sequence; and

reproducing means for reproducing, by orthogonal frequency division multiplex demodulation of said reception sample sequence, a reproduction of said sequence of data, wherein said detecting means comprises;

storing means for storing a main synchronization pattern and an auxiliary synchronization pattern to produce a stored synchronization pattern sequence, said main synchronization pattern corresponding with said main synchronizing symbol and said auxiliary synchronizing pattern corresponding with said auxiliary synchronizing symbol,

estimating means responsive to said auxiliary synchronization pattern for estimating, while said sampling means produces said reception sample sequence, position estimations of where said main synchronizing symbol appears in said reception sample sequence,

calculating means, responsive to said stored synchronization pattern sequence, for calculating a cross-correlation value between said main synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence, said cross-correlation values being calculated with said window stepwise shifted only in said position estimations,

selecting means for selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that give two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames, and

control means for controlling said clock frequency in response to said time interval.

7. A receiver device for receiving a transmission signal derived from successive frames, each of which is composed of a synchronizing symbol, a null symbol consecutively preceding said synchronizing symbol, said null symbol having a duration which is substantially equal to said synchronizing symbol, and a sequence of data symbols with said data symbols produced by subjecting a sequence of data to orthogonal frequency division multiplex modulation, said receiver device comprising:

receiving means for receiving said transmission signal as a received signal;

sampling means responsive to a clock sequence of a clock frequency for sampling reception samples from said received signal to produce a reception sample sequence;

detecting means for detecting synchronization patterns in said reception sample sequence;

clock generating means responsive to said synchronization patterns for generating said clock sequence, wherein said clock sequence defines successive frame intervals and successive symbol intervals in each frame interval, said each frame interval being substantially identical with said frame period and being defined in response to said clock frequency; and

reproducing means for reproducing, by orthogonal frequency division multiplex demodulation of said reception sample sequence, a reproduction of said sequence of data, wherein said detecting means comprises;

storing means for storing a synchronization pattern identical with said at least one synchronizing symbol to produce a stored synchronization pattern sequence,

calculating means, responsive to said stored synchronization pattern sequence, for calculating a cross-correlation value between said synchronization pattern and each of candidate patterns derived from said reception sample sequence with a window of a predetermined time duration stepwise shifted relative to said reception sample sequence to produce successive cross-correlation values for said reception sample sequence,

selecting means for selecting from said candidate patterns, as reproductions of synchronizing symbols, ones of said candidate patterns that give two successive maxima among said cross-correlation values at a time interval substantially coincident in a standstill pattern of said reception sample sequence with a frame period of said frames,

null period defining means for defining a null period which one of said symbol intervals comprises when said one of said symbol intervals indicate a presence of said null symbol in a sequence of said cross-correlation values in each frame interval, and

control means for controlling said clock frequency in response to said time interval, said control means suspending control of said clock frequency in each frame interval except for said null period.