One of the problems associated with the transmission of information packets over a wireless communication medium is multipath fading, wherein multiple copies of an information packet reach the receiver over multiple paths with different time delays, amplitudes, and phases due to scattering and reflection and destructively interfere with each other causing the level of the received signal to fall.
If the level of the received signal falls below a usable threshold level, (characterized by a very small signal-to-noise ratio (SNR)) the channel is said to be in a "deep fade." For channels with slow fading characteristics, namely channels whose characteristics vary slowly relative to the data transmission rate, a large number of information packets may be lost if the channel is in a deep fade.
Diversity techniques are used to reduce the effects of multipath fading on slow fading channels. One form of diversity is time diversity. In this protocol, multiple copies of each information packet are interleaved in the packet stream for transmission at different times so that they are subject to independent multipath fading characteristics of the channel. In many applications, the communication delays associated with waiting for the multiple copies of each packet to be received cannot be tolerated.
Another form of diversity is switched antenna diversity. In this protocol, multiple antennas are used one at a time to transmit information packets over a slow fading wireless communication medium. The transmitter switches to another antenna channel, having independent multipath fading characteristics, when the current antenna channel is in a deep fade.
A switched antenna protocol is expensive. Each of the antennas must use a power amplifier rated at the full power P needed to transmit an information packet over the communication medium to the receiver. In addition, abruptly switching the antennas "off" and "on" may damage the power amplifiers.
There is a need for a more cost effective packet diversity transmission method and system which reduces the effects of multipath fading on slow fading channels without the communication delays associated with prior art protocols.