Antenna selection diversity for framed digital signal transmission in mobile radio channel

An antenna selection diversity method is proposed in which received signal levels from the antennas are measured in a time-division manner and a switching operation is performed in the preamble or postamble portion of a framed digital signal. Hence the switching noise problem is avoided. Deterioration in diversity performance, compared with the case of a post-detection diversity, can be kept within 1 dB if a frame length, normalized by the maximum Doppler frequency, is less than 1/16. With the use of this technique, base station diversity systems, where no diversity facility is required in mobile stations for both upward and downward direction of transmission, are proposed. For single-frequency time-duplexed communication, the base station uses the proposed diversity method for reception, and an antenna selected last in the reception period is used for transmission. For dual-frequency duplex communication, the base station sends a postamble signal from the antennas in a time-division manner, and then the result determined from the comparison of the received levels that correspond to the postamble signal at the mobile station is sent back to the base station and used for antenna selection for the next transmission of the information signal. The performance of the proposed diversity for a digital FM system in the Rayleigh fading channel is investigated by computer simulation