Digital signal frame and interleaver synchronizer

Details Digital signal frame and interleaver synchronizer Digital signal frame and interleaver synchronizer

1999-08-30

2003-09-23

Patel, Ajit (Department: 2664)

Multiplex communications

Generalized orthogonal or special mathematical techniques

Particular set of orthogonal functions

C370S343000, C375S260000, C375S350000

Reexamination Certificate

active

06625113

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to Orthogonal Frequency Division Multiplexing (OFDM) systems, and is more particularly related to transmitting and receiving digital information within a Frequency Modulated (FM) signal band using OFDM.
BACKGROUND OF THE INVENTION
As is well-known, the center frequencies of adjacent FM bands/channels are separated by 200 kHz. As is also well-known, analog signals within the audio band are typically frequency modulated onto a FM carrier for transmission to a receiver. It is now possible to also transmit information (e.g., analog/digital information) in the upper and lower side bands of a FM carrier signal. This is broadly illustrated in
FIG. 1
, in which transmitter
105
transmits via antenna
125
an analog host signal supplied by source
110
over a FM carrier (represented by signal a
1
). It also transmits digital versions of signals supplied by source
115
in the upper and lower side bands (represented by side band signals b
1
and b
2
), respectively, of the FM carrier. We have recognized that it is likely that the host signal, a
2
, as well as the first adjacent FM signals, c
1
and c
2
, will interfere with the side band signals (represented by the shaded portions of signals b
3
and b
4
) during the transmission of the FM signal from antenna
125
to a receiver antenna
205
. Disadvantageously, such interference makes it extremely difficult for receiver
200
to recover the signal transmitted in the side bands, since the inference sorely corrupts the side band signal.
SUMMARY OF THE INVENTION
We have recognized that such interference may be sufficiently minimized by filtering the side band signal at the receiver to allow receiver processes to perform successfully frame synchronization and interleaver functions on the filtered signal. In accordance with an aspect of the invention, such filtering is done using a simple bandpass filter.
We have further recognized that, although such filtering renders the side band signal sufficiently clean to recover frame synchronization and interleaver signals, it nevertheless corrupts the information carried in that signal, thereby making it extremely difficult to recover the information. We deal with this problem by using the filtered version of the received side band signal for frame and interleaver synchronization functions and, after such functions have been performed using a shifted version of the received side band signal to recover such information, all in accordance with an aspect of the invention.
In accordance with another aspect of the invention, the extent of such shifting is determined as a function of the number of signal samples that the filtered signal had to be shifted to obtain frame synchronization, e.g., to locate the beginning of a frame.
These and other aspects of the invention are described in the following detailed description and ensuing claims.


REFERENCES:
patent: 5282222 (1994-01-01), Fattouche et al.
patent: 5995483 (1999-11-01), Marchok et al.
patent: 6160791 (2000-12-01), Bohnke
patent: 6181714 (2001-01-01), Isaksson et al.
patent: 6243413 (2001-06-01), Beukema
patent: 6285654 (2001-09-01), Marchok et al.
patent: 6359926 (2002-03-01), Isaksson et al.
patent: 6363128 (2002-03-01), Isaksson et al.

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