IPC분류정보
국가/구분 |
United States(US) Patent
등록
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국제특허분류(IPC7판) |
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출원번호 |
US-0339961
(1993-10-19)
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발명자
/ 주소 |
- Davis Mark E. (Carlsbad CA)
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출원인 / 주소 |
- Hughes Aircraft Company (Los Angeles CA 02)
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인용정보 |
피인용 횟수 :
44 인용 특허 :
0 |
초록
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An adaptively-tuned filter (80) for use within the receiver (14) of a multiple-access code division (CDMA) communication system permits spectrally-inefficient transmissions to be made from each transmitter (12) used with such system, thereby simplifying the transmitter circuits, yet still achieves a
An adaptively-tuned filter (80) for use within the receiver (14) of a multiple-access code division (CDMA) communication system permits spectrally-inefficient transmissions to be made from each transmitter (12) used with such system, thereby simplifying the transmitter circuits, yet still achieves a signal-to-noise ratio (SNR) that approaches the SNR achieved when spectrally-efficient transmissions are made. The adaptive filter (80) also compensates for signal distortions resulting from multiple signal paths. The receiver (14) includes RF receiving circuits (60, 62), a matched filter (64), downconversion circuits (66, 68, 92), sampling circuits (70, 71, 72), a time acquisition circuit (76), an adaptive filter (80), a decimator circuit (75), a despreader circuit (77), and an accumulator circuit (78). The adaptive filter (80) includes, e.g., two LMS gradient filters (96a, 96b), or equivalent, that operate independently in parallel, with an accurate bit decision being used to select the tap signals to be used as the starting point for the next bit. The filters (80, 96) function as a fractionally-spaced chip-MSE equalizer that improves the bit-SNR in the presence of sufficient multi-access noise, and also provides narrowband noise rejection.
대표청구항
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A direct-sequence multiple-access code division (DS-CDMA) communication system comprising: a multiplicity of transmitters, each of said transmitters including: means for generating a CDMA waveform signal, said CDMA waveform signal comprising an RF carrier signal modulated with an informational data
A direct-sequence multiple-access code division (DS-CDMA) communication system comprising: a multiplicity of transmitters, each of said transmitters including: means for generating a CDMA waveform signal, said CDMA waveform signal comprising an RF carrier signal modulated with an informational data signal comprising a sequence of data bits, each data bit having a bit time of TB, and each data bit being modulated with a waveform signature signal, said waveform signature signal comprising a train of Nc chip pulses, each chip pulse being separated from an adjacent chip pulse by Tc seconds such that NCㆍTC=TB, each chip pulse of said train of chip pulses having an amplitude set by a binary spreading code unique to each transmitter; means for transmitting the CDMA waveform signal from each of said multiplicity of transmitters so that the chip pulses are transmitted having a spectrally inefficient, substantially non-flat, power spectrum within the band ±1/TC; and a receiver comprising: means for receiving the CDMA waveform signals transmitted from each of said multiplicity of transmitters and stripping the RF carrier signal therefrom, thereby leaving a data input signal to said receiver that comprises said sequence of data bits, with each data bit being modulated with the waveform signature that is unique to each transmitter; sampling means for sampling the data input signal at a prescribed sampling rate to produce a series signal xm; adaptive filter means coupled to receive said series signal xm and subject it to a prescribed transfer function that produces a filtered output signal ym, said transfer function being adapted to compensate for the spectrally inefficient substantially non-flat power spectrum of the transmitted chip pulses within the band ±1/TC, thereby improving the signal-to-noise ratio (SNR) of the signal ym, and said transfer function further being adapted to compensate the series signal xm for signal distortions caused by multiple signal paths of the CDMA waveform signal as it is transmitted from the transmitter to the receiver; decimator means for decimating the filtered output signal ym by a prescribed decimation factor D to produce a decimated series signal zn; timing acquisition means responsive to the series signal xm for generating the binary spreading code of a user of interest and a timing signal that controls when within a data bit of said data input signal the sampling means samples the data input signal; despreading means connected to said decimator means and responsive to said timing signal for identifying the beginning and ending points of a data bit within said series signal zn that originates with said user of interest by multiplying the series signal zn by an aligned spreading code cn; and accumulation means for summing said series signal zn, as aligned by the spreading code cn, over the data bit to produce a data decision signal.
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