Optical PPM synchronization for photon counting receivers

Optical PPM Combining Loss for Photon Counting Receivers

“…In [7], the standard deviation of the slot synchronization error for a system utilizing an inter-symbol guard time was found to be, in the region of interest, well approximated by…”

“…To facilitate synchronization to the symbol and slot boundaries of the received signal, an inter-symbol-guard time, equal to one slot duration, is included in the transmitted symbol sequence [7]. Assuming a timing estimate error, εT s , of less than half a slot, for a signal arriving in the k th slot the expected counts, conditioned on this error, for the k § 1¡ th , k th , and k D 1¡ th slots are…”

“…Assuming equal signal and background fluxes along with equal timing estimation error variances [7] for each detector, we will consider an equal gain combiner whereby the synchronized counts from each receiver are summed to form the composite slot statistic (see Figure 1). For the i th slot the composite slot count is…”

“…Each element will be independently synchronized using timing estimates facilitated by the inclusion of an inter-symbol guard time [7]. Synchronization errors in each element associated with this technique are incorporated into the the probability of uncoded PPM symbol error.…”

Deep space acquisition and tracking with single photon detector arrays

“…The laser beacon can be modulated to allow background subtraction of scattered light and upwelling radiance from Earth. The DOT project chose a nested modulation scheme composed of a fixed data rate 2-PPM (pulse-position modulation) outer code with two inter-symbol guard time slots and a variable data rate 16-PPM inner code with four inter-symbol guard time slots [5], [10]. The effect of the nested modulation scheme is to create a square wave sync pattern for "lockin" detection of the laser beacon.…”