Synchronization tracking in pulse position modulation receiver
AssigneeThe Unites States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorVictor A. Vilnrotter
Life of this patent
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Abstract
A clock pulse generator for decoding pulse position modulation in an optical communication receiver is synchronized by a delay tacking loop which multiplies impulses of a data pulse by the square-wave clock pulses from the generator to produce positive impulses when the clock pulse is of one level, and negative impulses when the clock pulse is of another level. A delay tracking loop integrates the impulses and produces an error signal that adjusts the delay so the clock pulses will be synchronized with data pulses. A dead-time .tau..sub.d provided between data pulses of an interval .tau..sub.p in the data pulse period .tau.. When synchronized, the average number of positive impulses integrated will equal the average number of negative impulses over the continuous stream of data pulses.
Claims4
A method for synchronizing a receiver for a pulse position modulation channel directly from pulse position modulated data pulses received comprising the steps of
- transmitting pulse position modulated data over a channel said modulated data having a nominal slot time for each data pulse equal to .tau., and a dead time, .tau..sub.d, on each side of a data pulse of a time .tau..sub.p modulated within the slot time .tau., and
- receiving at a receiver said pulse position modulated data
- generating a square-wave clock pulse signal having a phase and two levels at said receiver of a period nominally equal to the period of a data slot time, .tau.,
- multiplying said pulse position modulated data received at said receiver by said square-wave clock pulse signal generated such that when it is of one level, the product is positive, and when it is of another level, the product is negative,
- integrating said positive and negative products in a delay tracking loop filter to produce an error signal proportional to the integrated difference of said positive and negative products, and
- adjusting the phase of said square-wave clock pulse signal proportional to the magnitude and sign of said error signal, whereby synchronization of said square-wave clock pulse signal with said data pulse slots is achieved without the use of decision aided feedback.
In a receiver for an optical pulse position modulation channel having a dead time .tau..sub.d on each side of a data pulse .tau..sub.p in a data pulse slot period .tau.,
- a voltage controlled clock generator for producing square-wave clock pulses of two levels with a cycle period .tau.,
- means for detecting photons of an optical data pulse and producing an impulse of uniform height for each photon detected,
- means for multiplying said impulses with said square-wave clock pulses to produce positive impulses when said square-wave clock pulses are of one level and negative impulses when said square-wave clock pulses are of another level, and
- a delay tracking loop filter for integrating said negative and positive impulses for producing an error signal transmitted to said voltage controlled oscillator, whereby said delay tracking loop filter causes said oscillator to produce said square-wave clock in synchronism with said data pulse slot periods.
Dependencies are inferred from the claim text.