Patent ID: 6704344
Filing Date: 2004-03-09
Classification: H04B,H04L

Abstract:
A broad band spread spectrum communications system wherein a transmitter transits a data modulated MPSK M-ary phase shift keying spread spectrum radio frequency (RF) signal, where m data bits are grouped into one symbol, m=log2M is a positive integer and M is the number of keying: phases of MPSK signals, to a receiver, said receiver comprises:means for receiving the transmitted data modulated MPSK spread spectrum RF signals, wherein the receiving means comprises a carrier recovery and tracking means, a synchronization means and a data demodulation means, wherein in the means for receiving, the carrier recovery and tracking means comprises: a frequency generating means which generates three different frequencies fc+D, fc and fcâˆ’D, where fc represents the adjusted carrier frequency and D a positive offset to fc; two RF downconverters, each of which comprises two multipliers and a 90Â° phase shifter, wherein each down-converter has two inputs, one connected to receive the transmitted data modulated MPSK spread spectrum signals and the other one connected to receive the locally generated carrier from said frequency generating means, and two outputs which provide the I-phase and Q-phase of the base-band signals, wherein at least one downconverter is connected to receive fc+D from said frequency generating means and at least one downconverter is connected to receive fcâˆ’D from said frequency generating means; and two X-correlators each of which is connected to receive said I-phase and Q-phase of the base-band signals, wherein the I-phase and Q-phase signals are correlated with the local PN-sequence and the correlation results are processed and outputs from the two X-correlators are used to adjust the frequency generated by a VCO, which output in turn is fed to said frequency generating means.