Coherent hybrid ds‐FFH CDMA‐basic performance in mobile radio environment

This paper proposes a coherent hybrid DS‐FFH CDMA system that combines the coherent frequency‐hopping (FFH) and the direct sequence (DS) techniques. the basic performance in the mobile radio system is analyzed. the proposed method features the following: (i) CDM by the low‐chip‐rate DS using the orthogonal codes; (ii) the frequency‐diversity effect obtained for each symbol by the maximum‐ratio synthesis of the multiple chips spread by the coherent FFH. The system configuration and the operation are described. Assuming a channel where the delayed wave components of the four waves contain respective Rayleigh fadings, a computer simulation is executed and the following transmission characteristics are revealed. (i) When there does not exist an interference wave in the 4‐chip system, the 4‐branch frequency‐diversity effect is verified. the average E_b/N_o required in order to realize the average BER of 10⁻² is 8 dB. (ii) When space diversity is combined, the average E_b/N_o required to realize the average BER of 10^‐2 is 8 dB, even if there exists an interference wave. (iii) In the dynamic fading environment, the maximum Doppler frequency that can realize the average BER of 10^‐2 for the average E_b/N_o =15 dB, is 20 Hz and 80 Hz, respectively, for the cases with and without interference.