System for improving the quality of a received radio signal

摘要

A delay spread is created in a digital radio signal to reduce the coherence bandwidth and facilitate frequency hopping to reduce the effect of fading losses within an enclosed propagation environment The delay spread is introduced into the signal in several ways. One technique disclosed employs a transmitter with two separate antennas one of which transmits the digital signal and the other of which transmits the same signal after a phase delay has been introduced into the signal. The carrier frequency of the signals is hopped between at least two frequencies and the receiver processes the resulting signals. In another embodiment, a single transmit antenna is used but the signal is received by two different antennas with the output signal from one of those antennas being phase delayed before combining it with the other prior to processing by the receiver circuitry. Phase delay is also introduced at baseband into the signals to be transmitted by rotating the I and Q components of the waveforms before modulation.