Antenna diversity technique for future space telemetry modulation scheme

A full-spectrum combining (FSC) technique for future telemetry modulation schemes is described and its performance is analyzed assuming imperfect carrier and symbol synchronization. The combining system consists of a bank of phase-difference maximum likelihood estimators (MLEs) to align the signals before coherently maximal-ratio combining them and then demodulate the data with a single receiver chain. First, the performance of these MLEs is derived by finding the probability density function of the estimate error process and then determining the variance of this error process and consequently comparing it to the Cramer-Rao lower bound. Next, the performance of this full-spectrum combining technique is derived for PCM/PM/NRZ, a modulation scheme currently proposed by the International Consultative Committee Space Data Systems (CCSDS) for use in future standard telemetry systems. The performance of this antenna diversity technique is determined in terms of: 1) symbol S/N ratio degradation; and 2) symbol error rate loss. The results are verified by simulation for an array of two identical ground antennas.<
>