A LOW-COST FADING AND SIMULCAST SYSTEM USING DIGITAL FILTERS
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-27
In a typical one-way messaging environment, all base stations transmit the same information signal at approximately the same time (simulcast). This results in delay spread and multipath interference. In the delay-spread case, the same signal arrives at the receiver at different times. Depending on the amount of delay, severe waveform distortions may result in the demodulated signal and errored mes- sages or no message reception may occur. Multipath interference is created by multiple reflec- tions of the transmitted signal from several struc- tures. The resultant received waveform is a sum of time and, sometimes, frequency shifted versions of the original transmission, and, depending on the channel characteristics, the received signal may be greatly distorted. Multipath causes large fluctua- tions (fading) in the received signal due to the changing phasor sum of signal components arriving at the receiver antenna via different paths. Deep fades, as much as 40 dB , can occur. This large drop in the signal level can cause unrecoverable errors in the demodulator.