The Theory of Operation of an Equal-Gain Predetection Regenerative Diversity Combiner with Rayleigh Fading Channels

Dynamic response of Granlund predetection diversity combiners

“…Halpern [2] proved this to be true for any phase modulation index. This is true because in the first mixing process, a phase modulated signal is multiplied by itself with inverted spectrum (i.e., the conjugation process).…”

“…This result was arrived at by Halpern [2] in an analysis using ideal filters. His restriction was that the feedback filter have essentially zero delay and pass the signal bandwidth undistorted.…”

“…The Granlund combiner has been studied by [1][2][3][4]. The Granlund combiner uses a regenerative technique that operates on the signals received from diversity paths.…”

“…One notable difference between the combiner proposed by [1] and the one proposed by [3] is that [3] used automatic gain control (AGC) to maintain regeneration and [1] used a hard limiter. Reference [2] analyzed performance of an "equal gain combining" (see [5]) version of the Granlund combiner which used limiting in the forward and reverse paths. The performance against phase modulated signals in a Rayleigh fading environment was analyzed using ideal filters.…”

Four Channel Predetection Combiner for use with Troposcatter Communication Systems

“…The bandwidth of 49 MHz filter is dependent upon system requirement (10 MHz for 120 channels). The 21-MHz crystal filter has to be only as wide ~ is necessary to pass the unmodulated Rayleigh fading carrier without introducing excessive noise [3]. A 25 kHz (3-dB) bandwidth has been selected to make adequate allowance for phase shift resulting from propagation conditions and carrier frequency variation.…”