Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2001-12-05
2004-04-20
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S063100, C455S278100, C455S283000, C455S225000, C455S284000, C455S296000, C455S303000, C455S306000, C455S307000
Reexamination Certificate
active
06725017
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
NOT APPLICABLE
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
NOT APPLICABLE
REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK
NOT APPLICABLE
BACKGROUND OF THE INVENTION
This invention relates to a radio frequency or optical communication system in which a relay station is used to aid communication between a device and one or more other devices, and more particularly to an improvement allowing more efficient use of the available channel resource.
Self-interference cancellation is a theoretically efficient technique for removing interference on a channel containing a remote signal and a near signal in relayed communication between two or more devices involving the transmission of different signals within the same frequency band at the same time. In the example of communication between two devices, such transmission results in a composite signal that includes two signals, one originating from each device. As each device attempts to receive the signal originating from the other device (remote signal), it is hindered by interference caused by the signal originating from itself (near signal). Thus, self-interference cancellation works by generating a cancellation signal resembling the device's own near signal and using the cancellation signal to remove at least a portion of the near signal from the composite signal to obtain a signal closer to the desired remote signal. A number of self-interference cancellation and related techniques have been disclosed in U.S. Pat. Nos. 5,596,439 and 6,011,952, both issued to Dankberg et al., U.S. Pat. No. 5,280,537 issued to Sugiyama et al., U.S. Pat. No. 5,625,640 issued to Palmer et al., U.S. Pat. No. 5,860,057 issued to Ishida et al., and U.S. patent application Ser. No. 09/925,410 entitled METHOD AND APPARATUS FOR RELAYED COMMUNICATION USING BAND-PASS SIGNALS FOR SELF-INTERFERENCE CANCELLATION.
However, special problems exist when a composite signal containing multiple channels requires self-interference cancellation. Self-interference may exist on fewer than all the channels. If the number of channels containing self-interference is less than the total number of channels, unnecessary resources and equipment may be committed, and there may be avoidable signal degradation.
A typical multi-channel satellite communication facility is shown in FIG.
1
. Typically, an RF transmitter
102
, a transmit antenna
104
, an RF receiver
106
, and a receive antenna
108
are located outdoors, while IF and baseband equipment are located indoors. The indoor and outdoor systems are connected via cables that carry multi-channel IF signals, comprising a transmit IF path
107
and a receive IF path
109
. Individual IF transmit signals
111
from a number, M, of IF modulators
110
are combined in a multi-port signal combiner
112
to produce a multi-channel IF transmit signal on the transmit IF path
107
. The multi-channel IF transmit signal is translated to the RF transmission frequency by the RF transmitter
102
which then amplifies the signal and broadcasts it via the transmit antenna
104
.
The RF receiver
106
may share the transmit antenna
104
, or it may have a receive antenna
108
of its own. The RF receiver
106
performs the complementary function to the RF transmitter
102
, outputting a multi-channel IF received signal via the receive IF path
109
to a multi-port signal splitter
114
that distributes individual IF receive signals
115
to a number, D, of IF demodulators
116
. Digital baseband data from the facility's users comes into the IF modulators
110
for transmission and is output to the facility's users from the IF demodulators
116
. Note that a signal splitter or a signal combiner as discussed in the present invention may be implemented using the same device (signal splitter/combiner) which performs either function. Also, multi-port splitter/combiners as discussed in the present invention may be implemented as either a single device or as a number of devices in serial and/or parallel configurations.
In many practical systems, the above mentioned communication facility will broadcast to an intermediate site (such as a satellite transponder) which will rebroadcast the signal such that the originating facility will also receive its own signal. In such systems, the multi-channel IF received signal becomes a composite signal (multi-channel composite IF received signal).
FIG. 2
is an example frequency plot which shows the separate components of a multi-channel composite IF received signal. For clarity, only a few selected channels are shown. Note that although no absolute frequency is indicated in this plot, all of the signals shown are contained within the IF band that is used by the facility
100
. Note also that “channel” refers generally to a particular frequency band occupied by one or more signal. However, a signal said to occupy a particular channel may not be perfectly contained within the associated frequency band. Often such a signal has some portions extending into neighboring channels. Such interference between channels occurs in many communication systems and is not discussed further in the present application.
The Relayed Remote (RR) signal is composed of the D signals (RR
1
to RR
D
) originating from remote terminals and destined for the local demodulators. The Relayed Near (RN) signal is composed of the M signals (RN
1
to RN
M
) that are due to the facility's own transmissions. That is, the RN signal has been transmitted and then relayed back to the facility. Thus, the multi-channel composite IF received signal (the “composite received signal”) is the sum of the RR and the RN signals, as shown in FIG.
2
.
Since the M signals corresponding to VR and the D signals corresponding to RN can overlap in frequency, the total number of channels in the composite received signal can vary. If no overlap exists, the total number of channels is simply M+D. However, if there is overlap such that S channels are shared, the total number of channels is M+D−S. In more general terms, the composite received signal has a total number of M+D−S channels (where S=0 indicates the condition that no overlap exists).
In this example, the first channel (CH
1
) and the last channel (CH
M+D−S
) of the composite received signal are shared (bi-directional), and the second channel (CH
2
) and the third channel (CH
3
) are not shared. In order to properly demodulate the RR signal contained in the shared channels, the composite received signal must be processed to remove the interfering RN signal. To simplify this self-interference removal, it may be helpful to take advantage of the Local Near (LN) signal, which is the IF signal that is output from the combination of the IF modulators and input to the RF transmitter. The desired output signal, shown in the bottom of the figure, contains all of the RR channels and any RN channel that did not overlap in frequency with any RR channel.
As can be seen from
FIG. 2
, the number of shared frequency channels may indeed be less than the total number of channels that exist in the multi-channel composite IF received signal. A technique is needed for performing efficient self-interference cancellation only on those channels where self-interference is present. Is also desirable to dynamically select channels for self-interference cancellation without the need to physically reconfigure the relevant subsystems.
SUMMARY OF THE INVENTION
Multi-channel self-interference cancellation is provided in relayed electromagnetic communication between a first device and one or more other devices on one or more shared frequency channels. Specifically, near signals are generated at the first device and transmitted to a relay station. A composite signal is received at the first device from the relay station containing relayed versions of the near signals and relayed versions of remote signals transmitted from the one or m
Blount Richard
Irvine David H.
Torres Marcos
Trost William
ViaSat Inc.
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