Pilotless carrier phase-synchronization via LDPC code feedback

Abstract

Abstract-This paper addresses the carrier-phase estimation problem under the low SNR conditions often encountered in turbo and LDPC-coded applications. In [1] a decision-directed carrier synchronization (DDCS) circuit that uses soft information from an iterative LDPC decoder was presented for BPSK and QPSK constellations with constant phase offsets. In this work, we present a method that is able to handle arbitrary constellations with a random-walk phase noise process. Loop SNR equations are derived and the performance for different constellations is shown. An extension of the DDCS algorithm is described that uses a search and tracking method based on measuring the number of satisfied LDPC constraint-node equations equations at the decoder and is able to track arbitrary carrier phase.

Performance of decoder-based algorithms for signal synchronization for DSSS waveforms

“…In this work, we use the complex conjugate (cq [10] of the estimated symbol, X, as feedback to remove modulation of the incoming waveform. The DDCS technique uses soft estimates of the current decoded symbol to remove the mod ulation of the incoming input samples Ip and Q p (the index n has been dropped from the notation):…”

“…In order to analyze the statistical properties of the loop's phase error, the same derivation detailed in [10], based on the work of Simon [14], can be applied. When a Costas loop or a decision-directed loop multiplies signal and noise terms to remove the modulation present on the incoming symbols, a "squaring loss " or "demodulation loss " term is created.…”

“…The results shown in Fig.9, and 10 use the enhanced max-Iog MAP algorithm for symbol decoding. [7][8][9][10] show the steady-state bit-error rate (BER) and frame-error rate (FER) performance of the decoder-based signal synchronization algorithm applied to a GPS waveform. Figure 7 uses the (648,324) LDPC code from IEEE 802. lIn standard, while Fig.…”

“…The resulting architectures are often said to employ turbo synchronization [5]. Algorithms of this type can can be found in [5][6][7][8][9][10].…”

“…In the past [10], our algorithm was used for non-spread M-ary modulations using an LDPC code as an error correcting code. In this work we focus on the use of direct-sequence spread spectrum modulations that use either LDPC or turbo codes as their error correcting code.…”