Synchronization Techniques for Burst-Mode Continuous Phase Modulation

Synchronization is a critical operation in digital communication systems, which establishes and maintains an operational link between transmitter and the receiver. As the advancement of digital modulation and coding schemes continues, the synchronization task becomes more and more challenging since the new standards require high-throughput functionality at low signal-to-noise ratios (SNRs). In this work, we address feedforward synchronization of continuous phase modulations (CPMs) using data-aided (DA) methods, which are best suited for burst-mode communications. In our transmission model, a known training sequence is appended to the beginning of each burst, which is then affected by additive white Gaussian noise (AWGN), and unknown frequency, phase, and timing offsets. Based on our transmission model, we derive the Cramer-Rao bound (CRB) for DA joint estimation of synchronization parameters. Using the CRB expressions, the optimum training sequence for CPM signals is proposed. It is shown that the proposed sequence minimizes the CRB for all three synchronization parameters asymptotically, and can be applied to the entire CPM family. We take advantage of the simple structure of the optimized training sequence in order to design a practical synchronization algorithm based on the maximum likelihood (ML) principles. The proposed DA algorithm jointly estimates frequency offset, carrier phase and symbol timing in a feedforward manner. The frequency offset estimate is first found by means of maximizing a one dimensional function. It is then followed by symbol timing and carrier phase estimation, which are carried out using simple closed-form expressions. We show that the proposed algorithm attains the theoretical CRBs for all synchronization parameters for moderate training sequence lengths and all SNR regions. Moreover, a frame synchronization algorithm is developed, which detects the training sequence boundaries in burst-mode CPM signals. The proposed training sequence and synchronization algorithm are extended to shaped-offset quadrature phase-shift keying (SOQPSK) modulation, which is considered for next generation aeronautical telemetry systems. Here, it is shown that the optimized training sequence outperforms the one that is defined in the draft telemetry standard as long as estimation error variances are considered. The overall bit error rate (BER) plots suggest that the optimized preamble with a shorter length can be utilized such that the performance loss is less than 0.5 dB of an ideal synchronization scenario

An Architecture for High Data Rate Very Low Frequency Communication

Very low frequency (VLF) communication is used for long range shore-to-ship broadcasting applications. This paper proposes an architecture for high data rate VLF communication using Gaussian minimum shift keying (GMSK) modulation and low delay parity check (LDPC) channel coding. Non-data aided techniques are designed and used for carrier phase synchronization, symbol timing recovery, and LDPC code frame synchronization. These require the estimation of the operative Eb/N0 for which a kurtosis based algorithm is used. Also, a method for modeling the probability density function of the received signal under the bit condition is presented in this regard. The modeling of atmospheric radio noise (ARN) that corrupts VLF signals is described and an algorithm for signal enhancement in the presence of ARN in given. The BER performance of the communication system is evaluated for bit rates of 400 bps, 600 bps, and 800 bps for communication bandwidth of ~200 Hz.Defence Science Journal, 2013, 63(1), pp.25-33, DOI:http://dx.doi.org/10.14429/dsj.63.376

Investigation into PRS-precoded, constant-envelope, continuous-phase digital modulation schemes

Bibliography: leaves 78-79.Partial response signaling ( PRS) has been used successfully to improve the spectral properties of Pulse Amplitude Modulated (PAM) digital transmission systems. This thesis investigation studied the effect of PRS on frequency- and phase-modulated carrier systems, in particular on their spectral performance and their maintenance of constant envelope

A Hardware Implementation of a Coherent SOQPSK-TG Demodulator for FEC Applications

This thesis presents a hardware design of a coherent demodulator for shaped offset quadrature phase shift keying, telemetry group version (SOQPSK-TG) for use in forward error correction (FEC) applications. Implementation details for data sequence detection, symbol timing synchronization, carrier phase synchronization, and block recovery are described. This decision-directed demodulator is based on maximum likelihood principles, and is efficiently implemented by the soft output Viterbi algorithm (SOVA). The design is intended for use in a field-programmable gate array (FPGA). Simulation results of the demodulator's performance in the additive white Gaussian noise channel are compared with a Matlab reference model that is known to be correct. In addition, hardware-specific parameters are presented. Finally, suggestions for future work and improvements are discussed

Advanced Modulation and Coding Technology Conference

The objectives, approach, and status of all current LeRC-sponsored industry contracts and university grants are presented. The following topics are covered: (1) the LeRC Space Communications Program, and Advanced Modulation and Coding Projects; (2) the status of four contracts for development of proof-of-concept modems; (3) modulation and coding work done under three university grants, two small business innovation research contracts, and two demonstration model hardware development contracts; and (4) technology needs and opportunities for future missions

Reduced-Complexity Joint Frequency, Timing and Phase Recovery for PAM Based CPM Receivers

In this thesis, we present a reduced-complexity decision-directed joint timing and phase recovery method for continuous phase modulation (CPM). Using a simple linear modulation--pulse amplitude modulation (PAM)--representation of CPM, more popularly known as the Laurent representation of CPM, we develop formulations of a PAM based joint timing error detector (TED) and a phase error detector (PED). We consider the general M-ary single-h CPM model in our developments and numerical examples. We show by analysis and computer simulations that the PAM based error detector formulations have characteristics similar to the conventional (i.e., non-PAM) formulations and they render reliable performance when applied to specific CPM examples; in fact, we show the error detectors are able to perform close to the theoretical limit given by the modified Cramer-Rao bound (MCRB) and able to provide a bit error rate (BER) close to the theoretical value. Also, we investigate the false lock problem in M-ary CPMs and are able to obtain much improved performance over conventional CPM detectors with our PAM based method. Furthermore, the PAM based receivers perform well in the presence of a large frequency offset (on the order of the symbol rate) and are, in general, much more resistant to small carrier frequency variations compared to conventional CPM receivers. We use an existing PAM based frequency difference detector (FDD) for a large carrier frequency recovery. As such, the proposed method of combining the error detectors (FDD, TED and PED) provides important synchronization components for jointly recovering the respective signal attribute offsets (i.e, carrier frequency, symbol timing and carrier phase) for reduced-complexity PAM based CPM receivers, which have been missing up to this point