Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-12-01
2004-05-04
Deppe, Betsy L. (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S316000, C375S340000, C370S307000
Reexamination Certificate
active
06731690
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to communications systems, and more particularly to methods and apparatus for transmultiplexing a multi-channel communication signal in a multi-channel transceiver.
BACKGROUND OF THE INVENTION
There are numerous advantages to implementing a communications system using digital techniques. For example, there are enhanced system capacity, and reduced noise, hardware and power consumption. In communications systems having a multi-channel communication signal, multi-channel transceivers with transmultiplexers are utilized to recover individual communication channels from the multi-channel communication signal. Such a multi-channel transceiver
100
having a transmultiplexer
102
is shown in
FIG. 1
according to the prior art.
The multi-channel transceiver
100
shown in
FIG. 1
is configured as a receiver for illustrative purposes. However, it should be appreciated that operated in reverse, this multi-channel transceiver
100
operates to process multiple channels for transmission as a multi-channel radio frequency (RF) signal. As a receiver, the transceiver
100
receives multi-channel RF signals with an antenna
104
, transducer
106
, bandpass filter
108
, mixer
110
, intermediate frequency (IF) filter
112
, baseband mixer
114
, filter
116
, analog-to-digital (A/D) converter
118
and mixer
120
.
The mixer
120
mixes the digitized signal output
122
of the A/D converter
118
with a complex sinusoid of the form
ⅇ
j2π
kF
0
F
s
,
where F
s
is the A/D sample frequency, F
0
is the frequency shift, and k is the time index. This frequency shift is often used to translate a selected frequency channel such that it is centered at 0 Hz. Therefore, we refer to this operation as channel centering. This channel centering operation creates a digitized and centered multi-channel signal
124
, which is operatively coupled to the transmultiplexer
102
by commutator
126
. The transmultiplexer
102
converts the digitized and centered multi-channel signal
124
to a baseband signal using a fast Fourier transformer
128
operating on the outputs of polyphase filters
130
, and equalizes and/or matched filters each of the down-converted channels of the fast Fourier transformer
128
using equalizers
132
and/or matched filters
134
, respectively. The resulting outputs
136
of the transmultiplexer
102
are multiple communications channels separated from the digitized and centered multi-channel signal
124
originally presented to the inputs
138
of the transmultiplexer
102
.
As may be appreciated from the foregoing description of the prior art, the transmultiplexer
102
requires channel centering to avoid additional computations caused by down converting both the positive and negative images of the channels in the real-valued input signal. The channel centering operations result in complex valued signals that are presented to the transmultiplexer for channel signal conversion, thereby increasing computational requirements as compared to a transmultiplexer conversion of real value inputs. Furthermore, the polyphase filtering, equalization and matched filtering of the prior art transmultiplexer does not utilize fast Fourier transform (FFT) filtering and fast convolution to improve computational efficiency.
In view of the foregoing, is should be appreciated that it would be desirable to provide transmultiplexing methods and apparatus for use with digital transceivers that reduce channel duplication. In addition, it should be appreciated that it would be desirable to provide transmultiplexing methods and apparatus with improved computational efficiency. Furthermore, additional desirable features will become apparent to one skilled in the art from the following detailed description of a preferred exemplary embodiment and appended claims.
REFERENCES:
patent: 4241443 (1980-12-01), Sakaki et al.
patent: 5323391 (1994-06-01), Harrison
patent: 5490172 (1996-02-01), Komara
patent: 5710763 (1998-01-01), Harrison
patent: 5926455 (1999-07-01), Allpress
Bogacz Frank J.
Deppe Betsy L.
Pace Lalita
Terry L. Bruce
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