Multiple-access noise rejection filter for a DS-CDMA system
First Claim
1. A direct-sequence multiple-access code division (DS-CDMA) communication system comprising:
- (1) a multiplicity of transmitters, each including;
(a) a first signal generator that generates an analog baseband waveform signal having a plurality of bits, each bit having a time period of TB, said bits being digitally encoded with data that is to be transmitted,(b) a second signal generator that generates a unique signature waveform signal having a spectrally inefficient power spectrum, said unique signature waveform signal being made up of a sequence of chip waveform signals, each chip waveform signal in said sequence of chip waveform signals having a duration of TC seconds, a polarity controlled by a unique spreading code, and a bandwidth substantially corresponding to an allowed channel bandwidth, said spectrally inefficient power spectrum being spectrally inefficient and substantially non-flat within a band ±
1/TC,(c) a first modulator that modulates each bit of the analog baseband waveform signal with the unique signature waveform signal to yield a direct sequence spread waveform signal,(d) a first filter for filtering the direct sequence spread waveform signal,(e) an RF generator that generates an RF carrier signal, said RF carrier signal having a carrier frequency that is the same for all of said multiplicity of transmitters,(f) a second modulator that modulates said RF carrier signal with the filtered direct sequence spread waveform signal, and(f) a transmitter that transmits the modulated RF carrier signal; and
(2) at least one base-station receiver comprising;
(a) an RF receiver that receives the transmitted modulated RF carrier signals from each of the multiplicity of transmitters,(b) a second filter that filters the modulated RF carrier signal to improve the signal-to-noise ratio (SNR) and to compensate for the spectrally inefficient substantially non-flat power spectrum of the signature waveform signal within the band ±
1/TC, and(c) a spread spectrum receiver that processes the filtered modulated RF carrier signal to despread such signal in order to identify a particular signature waveform signal contained therein, downconvert such signal to remove the RF carrier therefrom, and integrate such signal over a bit time to determine its informational content, said informational content over several bit times comprising the digital data transmitted by a particular one of said multiplicity of transmitters.
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Accused Products
Abstract
A direct-sequence multiple-access code division (DS-CDMA) communication system accommodates a multiplicity of separate transmitters (12) and at least one base-station receiver (14). Each transmitter generates a transmitted signal (16) at a common carrier frequency. Each transmitter has an assigned spreading code. Each bit time within the transmitted signal includes a unique signature waveform (21) generated from the spreading code that identifies the source of the transmitted signal. For a given transmitter, the transmitted signals from the other transmitters represent "multi-access noise" that may adversely degrade the signal-to-noise ratio (SNR) of that transmitter'"'"'s signal at the receiver. Each transmitter operates using a spectrally inefficient power spectrum, i.e., a non-flat power spectrum, that simplifies the transmitter circuits. Each transmitter includes a clock source (26), a signature waveform generator (28), a data generator (30, 32), a first multiplier (42), a low pass filter (44), and RF generator (46), a second multiplier (48), a bandpass filter (50), a power amplifier (52) and a broadcast antenna (54). The receiver processes the received waveform signal on a bit-by-bit basis in the absence of knowledge of the other transmitters'"'"' spreading codes. An adaptive linear filter (66) included within the receiver (14) operates to make the SNR for the spectrally-inefficient transmitted signals approach asymptotically the SNR that would be received from a spectrally-efficient transmitted signal. Additionally, the receiver rejects narrowband interference, thereby providing superior performance over a spectrally-efficient system with no narrowband noise rejection.
135 Citations
19 Claims
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1. A direct-sequence multiple-access code division (DS-CDMA) communication system comprising:
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(1) a multiplicity of transmitters, each including; (a) a first signal generator that generates an analog baseband waveform signal having a plurality of bits, each bit having a time period of TB, said bits being digitally encoded with data that is to be transmitted, (b) a second signal generator that generates a unique signature waveform signal having a spectrally inefficient power spectrum, said unique signature waveform signal being made up of a sequence of chip waveform signals, each chip waveform signal in said sequence of chip waveform signals having a duration of TC seconds, a polarity controlled by a unique spreading code, and a bandwidth substantially corresponding to an allowed channel bandwidth, said spectrally inefficient power spectrum being spectrally inefficient and substantially non-flat within a band ±
1/TC,(c) a first modulator that modulates each bit of the analog baseband waveform signal with the unique signature waveform signal to yield a direct sequence spread waveform signal, (d) a first filter for filtering the direct sequence spread waveform signal, (e) an RF generator that generates an RF carrier signal, said RF carrier signal having a carrier frequency that is the same for all of said multiplicity of transmitters, (f) a second modulator that modulates said RF carrier signal with the filtered direct sequence spread waveform signal, and (f) a transmitter that transmits the modulated RF carrier signal; and (2) at least one base-station receiver comprising; (a) an RF receiver that receives the transmitted modulated RF carrier signals from each of the multiplicity of transmitters, (b) a second filter that filters the modulated RF carrier signal to improve the signal-to-noise ratio (SNR) and to compensate for the spectrally inefficient substantially non-flat power spectrum of the signature waveform signal within the band ±
1/TC, and(c) a spread spectrum receiver that processes the filtered modulated RF carrier signal to despread such signal in order to identify a particular signature waveform signal contained therein, downconvert such signal to remove the RF carrier therefrom, and integrate such signal over a bit time to determine its informational content, said informational content over several bit times comprising the digital data transmitted by a particular one of said multiplicity of transmitters. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A direct sequence code-division multiple-access (DS-CDMA) receiver for use with a plurality of transmitters, each transmitter being configured to asynchronously transmit a spectrally-inefficient CDMA signal (s.sup.(k) (t)) at the same carrier frequency, said spectrally-inefficient CDMA signal having a substantially non-flat power spectrum within a band ±
- 1/TC, the CDMA signal transmitted by a particular transmitter having information data bits therein, of duration TB, encoded with a unique signature waveform that identifies the particular transmitter as the source of its transmitted CDMA signals, the signature waveform comprising a train of chip pulses separated by a time period TC, each having a polarity defined by a unique spreading code, with NC chip pulses being included within each data bit, whereby NC ×
TC =TB, the CDMA signals transmitted by any of said plurality of transmitters other than a transmitter of interest representing a form of noise, said DS-CDMA receiver including;a front-end receiver that receives the spectrally-inefficient substantially non-flat CDMA signals transmitted by each of said transmitters within the band ±
1/TC ;a chip matched filter having a frequency response H*(ω
) matched to a frequency response of each of said transmitters, said matched filter being coupled to the front-end receiver so as to filter the CDMA signals received by said front-end receiver;a sampling circuit that samples an output of said chip matched filter at a prescribed sampling rate and produces a series signal xm ; and an adaptive filter coupled to receive the series signal xm that generates an output series signal ym therefrom, said adaptive filter including means for compensating for the spectrally-inefficient substantially non-flat power spectrum of the CDMA signals within the band ±
1/TC transmitted by a transmitter of interest so as to improve the signal-to-noise ratio (SNR) of the output series signal ym ;a decimator that decimates the series signal ym and produces a series signal zn ; a despreader that despreads the signal zn and identifies individual data bits that originated from a transmitter of interest; and means for determining the informational content of the individual data bits obtained from the despreader. - View Dependent Claims (11, 12, 13, 14)
- 1/TC, the CDMA signal transmitted by a particular transmitter having information data bits therein, of duration TB, encoded with a unique signature waveform that identifies the particular transmitter as the source of its transmitted CDMA signals, the signature waveform comprising a train of chip pulses separated by a time period TC, each having a polarity defined by a unique spreading code, with NC chip pulses being included within each data bit, whereby NC ×
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15. A code-division multiple access (CDMA) communication system that detects with an approximately maximized signal-to-noise ratio (SNR) whether the bits of a transmitted data signal used within such system represent a logical "1" or a logical "0", said CDMA communication system including:
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a plurality of transmitters, each of which includes means for transmitting data signals having information data bits therein of bit time TB, encoded with a unique signature waveform, the signature waveform comprising a sequence of chip pulses separated by a time period TC, each of said plurality of transmitters transmitting at the same data rate and chip rate as are transmitted by others of the transmitters at the same time; means within each transmitter for generating the sequence of chip pulses to define a unique chip sequence within each bit time of the data signal to be transmitted, said unique chip sequence serving to identify a particular transmitter from which the transmitted signal originates; means for shaping the chip pulses of each sequence of chip pulses so that each has a spectrally-inefficient, substantially non-flat power spectrum within a frequency band of ±
1/TC ;means for transmitting the shaped sequence of chip pulses as part of each data bit that is transmitted by the particular transmitter, whereby each data bit transmitted is encoded with said unique chip sequence; a base-station receiver; means within said base-station receiver for receiving the sequence of chip pulses; matched filter means within the receiver for filtering the sequence of chip pulses in accordance with a matched filter transfer function configured to match the power spectrum of the transmitted chip pulses; means for sampling the sequence of chip pulses passed through the matched filter at a specified rate to produce a sampled series of pulses, xm (i); linear filter means for filtering the sampled series of pulses, xm (i), in accordance with a prescribed transfer function so as to produce a sequence of pulses ym (i), said prescribed transfer function being adapted to;
(a) compensate for the spectrally-inefficient substantially non-flat shape of the power spectrum within the band ±
1/TC of the transmitted pulses, (b) compensate for the transfer function of the matched filter, and (c) produce a net transfer function for the series of pulses ym (i) that is substantially flat over all frequencies within the allowed frequency band, thereby maximizing the SNR of the series ym (i); andmeans for determining whether the sequence of pulses ym (i) represents a data bit that is a logical "1" or a logical "0".
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16. A method of detecting with a maximized signal-to-noise ratio (SNR) whether the bits of a transmitted data signal used within a code-division multiple access (CDMA) communications system represent a logical "1" or a logical "0", said CDMA communications system including a plurality of transmitters, each of which includes means for transmitting data signals at the same data rate and chip rate as may be transmitted by others of the transmitters at the same time, and a base-station receiver adapted to receive said transmitted data signals, said method comprising the steps of:
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(a) generating a sequence of chip pulses separated by a time period TC that define a unique chip sequence within each bit time of the data signal to be transmitted, said unique chip sequence serving to identify a particular transmitter from which the transmitted signal originates; (b) shaping the chip pulses of each sequence of chip pulses generated in step (a) so that each has a spectrally-inefficient substantially non-flat power spectrum within a frequency band ±
1/TC ;(c) transmitting the sequence of chip pulses shaped in step (b) as part of each data bit that is transmitted by the particular transmitter, whereby each data bit transmitted is encoded with said unique chip sequence; (d) receiving the sequence of chip pulses at the receiver; (e) passing the sequence of chip pulses received in step (d) through a matched filter, said matched filter having a transfer function adapted to match the power spectrum of the transmitted chip pulses; (f) sampling the sequence of chip pulses passed through the matched filter in step (e) at a specified rate to produce a sampled series of pulses, xm (i); (g) passing the sampled series of pulses, xm (i), through a linear filter to produce a sequence of pulses ym (i), said liner filter being configured to exhibit a transfer function that compensates for the spectrally-inefficient substantially non-flat shape of the power spectrum of the transmitted pulses within the frequency band ±
1/TC, as well as the transfer function of the matched filter, to produce a net transfer function for the series of pulses ym (i) that is substantially flat over all frequencies within the frequency band ±
1/TC, thereby maximizing the SNR of the series ym (i); and(h) determining whether the sequence of pulses ym (i) represents a data bit that is a logical "1" or a logical "0". - View Dependent Claims (17, 18, 19)
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Specification