Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-06-14
2001-09-11
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S144000, C375S148000, C375S153000
Reexamination Certificate
active
06289039
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to spread-spectrum communications, and more particularly to spread-spectrum communications using parallel channels, preferably employing orthogonal chip-sequence signals, with error rate and data rate feedback.
DESCRIPTION OF THE RELEVANT ART
In a packet-communications spread-spectrum multi-cell system, high-speed data can be implemented with the prior art method of parallel channels, using parallel chip-sequence signals. By using multiple correlators or matched filters, multiple-orthogonal chip-sequence signals can be sent simultaneously thereby increasing the data rate while still enjoying the advantage of a high processing gain. The multiple chip-sequence signals behave as multiple users in a single location. Multipath is ameliorated by a RAKE receiver, and the interference to be overcome by the processing gain is that generated by other users, in the same or adjacent cells. When such interference occurs, it is called a collision.
Normally, when a remote station is within a cell or cell sector, as illustrated in
FIG. 1
, the path differences from base stations located in the adjacent cells ensure that the interference is small enough so as not to cause the error rate of the wanted signal to deteriorate below a usable level. When the remote station is near the edge of the cell, however, the interference can be substantial as the interference can result from two adjacent cells.
One method that has been used to overcome this problem in a conventional spread-spectrum system is to increase the processing gain in order to increase the immunity from interference. To do this, in a fixed bandwidth system, the data rate is reduced, and the integration time of the correlator or the length of the matched filter is increased accordingly. This method, however, changes the length of the correlator sequence, or changes the size of the matched filter; both of which impact the architecture of the receiver. In addition, with increased integration times, the chip-tracking loop and phase-tracking loop have to function flawlessly and the allowable frequency offset must be reduced, requiring at least a frequency locked loop.
Another method in the prior art is to repeat the symbols sequentially and add the result of the individually received symbols. This method changes the timing of the receiver and the framing of the data at the transmitter.
SUMMARY OF THE INVENTION
A general object of the invention is to vary the throughput of a transmitted spread-spectrum signal.
Another object of the invention is to set the throughput of a transmitted spread-spectrum signal based on a required error rate at a spread-spectrum receiver.
An additional object of the invention is to control a data rate of a spread-spectrum transmitter from a spread-spectrum receiver, using a closed loop method.
According to the present invention, as embodied and broadly described herein, a spread-spectrum system is provided comprising, at a spread-spectrum transmitter, a demultiplexer, a plurality of forward-error-correction (FEC) encoders and interleavers, a plurality of spread-spectrum processors, a combiner, and a modulator. At a spread-spectrum receiver, the system comprises a demodulator, a plurality of spread-spectrum despreaders, a multiplicity of adders, a multiplicity of FEC decoders and de-interleavers, a command processor, and a multiplexer.
The demultiplexer demultiplexes input data into a plurality of data channels. The plurality of forward-error-correction encoders and interleavers FEC encodes and interleaves the plurality of data channels, as a plurality of FEC encoded and interleaved channels, respectively.
The plurality of spread-spectrum processors spread-spectrum processes the plurality of FEC encoded and interleaved channels as a plurality of spread-spectrum channels. The plurality of spread-spectrum channels uses a plurality of chip-sequence signals to define a particular spread-spectrum channel. Preferably, the plurality of chip-sequence signals is a plurality of orthogonal chip-sequence signals, however, a plurality of quasi-orthogonal chip-sequence signals may be used.
The combiner combines the plurality of spread-spectrum channels as a code-division-multiplexed signal. The modulator transmits the code-division-multiplexed signal with the plurality of spread-spectrum channels, over a communications channel.
At the receiver, the demodulator translates the code-division-multiplexed signal to a processing frequency, and the plurality of spread-spectrum despreaders despreads the code-division-multiplexed signal into a plurality of despread channels, respectively.
The multiplicity of adders is electronically controlled by an adder-control signal. The multiplicity of adders adds at least two despread channels to generate a multiplicity of added channels.
The multiplicity of FEC decoder and de-interleavers generates a syndrome signal from an error rate of the multiplicity of added channels. The multiplicity of FEC decoders and de-interleavers, FEC decodes and de-interleaves the multiplicity of added channels, as a multiplicity of decoded channels.
In response to the syndrome signal, the command processor determines a desired-data rate, and generates a data-rate command signal having the desired data rate for the spread-spectrum transmitter. The command processor also generates the adder-control signal for adding together a number of despread channels of the plurality of despread channels, and generates a multiplexer signal having a number of decoded channels to multiplex together. The multiplexer multiplexes the multiplicity of decoded channels to generate an estimate of the input data.
The data-rate command signal is sent to the spread-spectrum transmitter. The data-rate command signal controls into how many data channels the demultiplexer demultiplexes the input data. Assume the demultiplexer, by way of example, demultiplexes input data into 16 parallel channels. If the processor in the receiver determines, as a response to the syndrome, that the input data are to be sent at twice the power of a single data channel of the plurality of data channels, then pairs of data channels in the plurality of data channels have identical data, with a resulting eight sets of data having different data per set. Each set of data comprises two data channels with identical data.
Additional objects and advantages of the invention are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 5579304 (1996-11-01), Sugimoto et al.
patent: 5673286 (1997-09-01), Lomp
patent: 5926500 (1999-07-01), Odenwalder
patent: 6075809 (2000-06-01), Naruse
patent: 6192066 (2001-02-01), Asanuma
Chartered David Newman
Linex Technologies Inc.
Vo Don N.
LandOfFree
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