EP0689313A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
AFC for OFDM using windowing
Assignee: NEC Corp
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Filing: 1995-05-26
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Granted: —
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Expires: 2015-05-26
Abstract
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.
Inventors
- 👤 Toru C/O Nec Corporation Sato
- 👤 Masafumi C/O Nhk Hosogijutsukenkyusyo Saito
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 01:40
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/26; H04L27/2601; H04L27/2647; H04L27/2655; H04L27/2657; H04L27/2668; H04L27/2673; H04L27/2675
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
314 words
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 samples 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; characterised in that: said composing step comprises the steps of: storing a stored symbol comprising a synchronizing symbol to produce a stored symbol sequence comprising stored synchronizing symbols; and using responsive to said stored sequence said synchronizing symbol as one of said synchronization patterns in each frame; said detecting step comprising the steps of: storing a stored 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 value for said reception sample sequence; selecting from said candidate patterns, as reproductions of said 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 controlling said clock frequency in response to said time interval.
Claim 2
Dependent Claim
75 words
A method as claimed in claim 1, characterised in that: said selecting step selects said ones of candidate patterns to decide said time interval successively as time intervals each of which substantially coincides with said frame period; said detecting step further comprising between said selecting and said controlling steps the step of averaging a prescribed number of said time intervals into a mean interval; said controlling step using said mean interval as said time interval.
Claim 3
Dependent Claim
59 words
A method as claimed in claim 1 or 2, characterized in that: said stored symbol comprises said synchronizing symbol as a main synchronizing symbol and an auxiliary synchronizing symbol consecutively preceding said main synchronizing symbol; said using step using said main synchronizing symbol as said one of synchronizing patterns; said synchronization pattern being identical with said main synchronizing symbol.
Claim 4
Dependent Claim
63 words
A method as claimed in claim 3, characterised in that: said detecting step comprises before said calculating step the step of detecting said auxiliary synchronizing symbol in said received signal to produce position estimations where said main synchronizing symbol successively appears in said reception sample sequence; said calculating step calculating said cross-correlation values with said window stepwise shifted only in said position estimations.
Claim 5
Dependent Claim
139 words
A method as claimed in claim 1 or 2, characterized in that: said stored symbol comprises said synchronizing symbol and a null symbol consecutively preceding said synchronizing symbol and being substantially equal in duration to said synchronizing symbol; said clock sequence defining successive frame intervals and successive symbol intervals in each frame interval, said each frame interval being defined in response to said clock frequency to be substantially identical with said frame period; said detecting step comprising between said calculating and said controlling steps the step of defining a null period which one of said symbol intervals comprises when said one of symbol intervals indicates presence of said null symbol in a sequence of said cross-correlation values in said frame interval; said controlling step suspending control of said clock frequency in each frame interval except for said null period.
Claim 6
Dependent Claim
113 words
A transmitter device responsive to a sequence of data for producing a transmission signal, said transmitter device comprising: converting means (25, 27) for converting said sequence of data to data symbols by orthogonal frequency division multiplex modulation; composing means (41, 43) for composing said data symbols into successive frames by adding synchronizing patterns to said frames; and producing means (29, 45) for producing said successive frames as said transmission signal; characterised in that said composing means comprises: storing means (41) for storing a stored symbol comprising a synchronizing symbol to produce a stored symbol sequence; and using means (43) for using said synchronizing symbol as one of said synchronizing patterns in each frame.
Claim 7
Dependent Claim
48 words
A transmitter device as claimed in claim 6, characterised in that: said stored symbol comprises said synchronizing symbol as a main synchronizing symbol and an auxiliary synchronizing symbol consecutively preceding said main synchronizing symbol; said using step using said main synchronizing symbol as said one of synchronizing patterns.
Claim 8
Dependent Claim
37 words
A transmitter device as claimed in claim 6, characterised in that said stored symbol comprises said synchronizing symbol and a null symbol consecutively preceding said synchronizing symbol and being substantially equal in duration to said synchronizing symbol.
Claim 9
Dependent Claim
300 words
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 orthogonal frequency division multiplex modulation of a sequence of data, said receiver device comprising: receiving means (31) for receiving said transmission signal as a received signal; sampling means (51) 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 (53-61, 71-79) for detecting synchronization patterns in said reception sample sequence; clock generating means (63, 65) responsive to said synchronization patterns for generating said clock sequence; and reproducing means (33, 35) for reproducing, by orthogonal frequency multiplex demodulation of said reception sample sequence, a reproduction of said sequence of data; characterised in that said detecting means comprises: storing means (53) for storing a stored pattern comprising a synchronization pattern identical with said synchronizing symbol to produce a stored pattern sequence comprising synchronization patterns; calculating means (55) responsive to said stored 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 (57, 59) for selecting from said candidate patterns, as reproductions of said synchronizing symbols, ones of said candidate patterns that give two successive maxima of 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 (61) for controlling said clock generating means to adjust said clock frequency in response to said time interval.
Claim 10
Dependent Claim
81 words
A receiver device as claimed in claim 9, characterised in that: said selecting means (57, 59) selects said ones of candidate patterns to decide said time interval successively as time intervals each of which is substantially coincident with said frame period; said detecting means (53-61, 71-79) comprising, between said selecting and said control means, means (79) for averaging a prescribed number of said time intervals into a mean interval; said control means (61) using said mean interval as said time interval.
Claim 11
Dependent Claim
81 words
A receiver device as claimed in claim 9 or 10, said synchronizing symbol being a main synchronizing symbol, said at least one synchronizing symbol comprising said main synchronizing symbol and an auxiliary synchronizing symbol consecutively preceding said main synchronizing symbol, characterised in that said stored pattern comprises said synchronization pattern as a main synchronization pattern coincident with said main synchronizing symbol and an auxiliary synchronization pattern which consecutively precedes said main synchronization pattern and is similar to said auxiliary synchronizing symbol.
Claim 12
Dependent Claim
87 words
A receiver device as claimed in claim 11, characterised in that: said detecting means (53-61, 71-79) comprises, prior to said calculating means, estimating means (71, 73) responsive to said auxiliary synchronization pattern for estimating, by detection of said auxiliary synchronizing symbol in said received signal, position estimations where said main synchronizing symbol appears in said reception sample sequence; said calculating means (55) calculating, by using as the above-mentioned synchronization pattern said main synchronization pattern, said cross-correlation values with said window stepwise shifted only in said position estimations.
Claim 13
Dependent Claim
86 words
A receiver device as claimed in claim 11, characterised in that: said detecting means (53-61, 71-79) comprises, prior to said calculating means, estimating means (71, 73) responsive to said auxiliary synchronization pattern for estimating, while said sampling means (51) produces said reception sample sequence, position estimations where said main synchronizing symbol appears in said reception sample sequence; said calculating means (55) calculating, by using as the above-mentioned synchronization pattern said main synchronization pattern, said cross-correlation values with said window stepwise shifted only in said position estimations.
Claim 14
Dependent Claim
143 words
A receiver device as claimed in any of claims 9 to 13, said at least one synchronizing symbol comprising, consecutively preceding said synchronizing symbol, a null symbol which is substantially equal in duration to said synchronizing symbol, characterised in that: said clock sequence defines successive frame intervals and successive symbol intervals in each frame interval, said each frame interval being defined by said clock frequency to be substantially equal to said frame period; said detecting means (53-61, 71-79) comprising, between said calculating and said control means, means (75, 77) for defining a null period which one of said symbol intervals comprises when said one of symbol intervals indicates presence of said null symbol in a sequence of said cross-correlation values in each frame interval; said control means (61) suspending control of said clock frequency in each frame interval except for said null period.
References Cited (Backward Citations)
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