초록 ▼

A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmit

A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmitted carrier and receiver local oscillator (LO), the transmitted carrier ferquency is related to the pilot frequency. The receiver phase-locks the pilot carrier to the local oscillator, thereby providing an IF data signal with reduced frequency error. The IF data signal is multiplied by sine and cosine demodulating signals related to the local oscillator frequency to produce inphase (I) and quadrature (Q) components of the received data signal. The I and Q signals are applied to code matched filters, which produce filtered or decoded signals the amplitudes of which are related to the phase error between the demodulating signals and the IF carrier. A logic arrangement responds to the decoded signals to generate a control signal which step-corrects the demodulating signal to the correct phase. Correction can occur within one or a few bit intervals, thereby allowing burst mode communications while maintaining high throughput for the multiple users of the communication system.

대표청구항 ▼

A spread spectrum communications arrangement for communicating among a plurality of transmitter-receiver pairs by bursts of data in the form of pseudorandom sequence encoded data bits, comprising: a transmission path subject to undesirable phase or frequency effects such that the frequency of a sign

A spread spectrum communications arrangement for communicating among a plurality of transmitter-receiver pairs by bursts of data in the form of pseudorandom sequence encoded data bits, comprising: a transmission path subject to undesirable phase or frequency effects such that the frequency of a signal passing therethrough experiences a frequency offset; a pilot signal generator coupled to a sending end of said transmission path for generating a pilot signal having a pilot frequency and for applying said pilot signal to said sending end; a source of data to be transmitted; transmitting means coupled to said source of data and including first clock generating means for producing a first clock signal having a nominal frequency which is an integer submultiple of said pilot frequency for clocking said source of data to produce clocked data at a frequency which is a second integer multiple of said frequency of said first clock signal, and including a modulator coupled to said source of data for PSK modulating said clocked data with a pseudorandom sequence having a chip frequency which is a third integer multiple of said frequency of said first clock signal to produce an encoded data signal, and including up-conversion means coupled to said first clock signal generating means and to said modulator for frequency-converting said encoded data signal to a transmitting frequency to produce an encoded transmitting frequency signal, and also including transmitting means coupled to said up-conversion means for coupling said encoded transmitting frequency signal to said sending end of said transmission path whereby said transmission path offsets said pilot frequency and said transmitting frequency to produce a frequency offset pilot signal and a frequency offset encoded data signal; a receiver coupled to a receiving end of said transmission path for receiving said frequency offset pilot signal and said frequency offset encoded data signal, said receiver including downconversion means, quadrature detection means, matched filtering means and downconversion reference phase correction means; said downconversion means comprising a second clock signal generator for generating a second clock signal having a second clock frequency which is a fourth integer submultiple of said pilot frequency, a downconverter coupled to said second clock signal generator and to said receiving end of said transmission path for receiving said offset pilot signal and said offset encoded data signal for mixing said offset pilot signal and said offset encoded data signal with a signal derived from said second clock signal to produce an intermediate frequency pilot signal having a pilot intermediate frequency and an intermediate frequency data signal having a data intermediate frequency in such a manner as to make said intermediate frequency pilot signal equal to a fifth integer multiple of said second clock signal, thereby setting the offset between said fifth integer multiple of said second clock signal and said data intermediate frequency at a frequency equal to the offset between said pilot frequency and said transmitting frequency; said quadrature detection means comprising phase controllable demodulating signal generating means coupled to said second clock signal generator for generating a demodulation signal at a demodulation frequency which is a sixth integer multiple of said second clock frequency which is nominally equal to said data intermediate frequency and also comprising mixing means coupled to said demodulating signal generating means and to said downconversion means for demodulating said intermediate frequency data signal to form mutually quadrature undecoded I and Q components of demodulated data signal; said matched filtering means being coupled to receive said undecoded I and Q components for generating decoded I and Q signals having amplitudes which are together representative of the phase angle between said demodulating signal and said intermediate frequency data signal; and said downconversion reference phase correction means is coupled to said matched filtering means and to said controllable demodulation signal generating means for generating from said decoded I and Q signals a phase control signal representative of said phase difference between said demodulating signal and said intermediate frequency data signal and for applying said control signal to said demodulating signal generating means for closing a control loop for correcting said phase difference between said demodulating signal and said intermediate frequency data signal. A method for receiving spread-spectrum encoded data signals which have been upconverted to a particular frequency range and which are associated with a pilot carrier, comprising the steps of: generating a local oscillator signal; downconverting said spread-spectrum encoded data signals and said pilot signal by mixing said spread-spectrum data signals and said pilot signal to an intermediate frequency range by use of said local oscillator signal to produce an encoded IF data signal and an IF pilot signal; generating a reference frequency signal; controlling the frequency of said local oscillator signal in such a fashion that said IF pilot signal is locked to said reference frequency signal whereby said encoded IF data signals are associated with an IF carrier having an IF carrier frequency; generating mutually quadrature demodulating signals at a frequency near said IF carrier frequency; separately mixing each of said mutually quadrature demodulating signals with said encoded IF data signals to produce inphase and quadrature components of demodulated encoded data signals; match-filtering said inphase and quadrature components of said encoded data signals to produce decoded inphase and decoded quadrature signals, respectively, the amplitudes of which are related to the phase angle between said demodulating signals and said IF carrier; evaluating the amplitudes said decoded inphase and decoded quadrature signals to generate a control signal representative of said phase differences between said demodulating signals and said IF carrier; and controlling the phase of said mutually quadrature demodulating signals with said control signal in a manner selected to reduce said phase differences between at least one of said demodulating signals and said IF carrier.