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Joint LDPC Decoding and Timing Recovery Using Code Constraint Feedback

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In traditional receiver architectures, symbol acquisition and tracking are performed using phase lock techniques that are independent of the channel code decoding process. In burst reception scenarios, bandwidth inefficient piloting must often be embedded in a transmission in order to accelerate acquisition and or to aid symbol time tracking at low signal-to-noise ratios. In this paper we show that outputs from the constraint node side of a bi-partite decoding graph can be used to direct estimation of symbol frequency and phase in a pilotless Low-Density Parity-Check (LDPC) coded transmission. We focus on the problem of a fixed symbol frequency/phase offset between transmitter and receiver and demonstrate that the technique is capable of pulling-in arbitrarily large frequency offsets with complexity that grows logarithmically with offset size. Relatively large timing offsets may occur in receivers that need to determine baud rates autonomously while finer offsets are often due to crystal oscillator mismatches and Doppler-induced frequency shifts. Combining the constraint node observations with a properly calibrated PLL allows successful tracking of both a fixed frequency offset and a random phase walk.

About the Speaker

Christopher R. Jones is with the Jet Propulsion Laboratory in Pasadena California where he works on problems related to Low-Density Parity-Check (LDPC) codes. Specific interests include protograph selection and lifting to achieve low error-floors, universal encoder/decoder architectures, hybridization with ARQ protocols, and integration with timing / carrier recovery techniques. Chris’ background includes a Ph.D.in Electrical Engineeing from the University of California Los Angeles and five years as a communications engineer with Broadcom Corporation.

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