605 research outputs found
Symbol timing recovery for generalized minimum shift keying modulations in software radio receiver
A new symbol timing estimator for generalized MSK signals is proposed. It is based on the squaring algorithm and has a feedforward structure. The proposed timing estimator is fully-digital and is suitable for implementation in software radios. The performance in AWGN channel is compared with the Modified Cramer-Rao bound and that of the ML algorithm. The proposed timing estimator is found to have a performance close to that of the ML algorithm, but with a lower implementation complexity.published_or_final_versio
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
Joint symbol and chip synchronization for a burst-mode-communication superregenerative MSK receiver
In this paper we describe a superregenerative (SR)
MSK receiver able to operate in a burst-mode framework where
synchronization is required for each packet. The receiver is based
on an SR oscillator which provides samples of the incoming
instantaneous phase trajectories. We develop a simple yet effective
technique to achieve joint chip and symbol synchronization
within the time limits of a suitable preamble. We develop some
general results and focus on the case of the IEEE 802.15.4 MSK
physical layer. We provide details on a VHDL implementation on
an FPGA where the most complex digital processing block is an
accumulator. Simulation and experimental results are provided
to validate the described technique.Peer ReviewedPostprint (published version
Asymptotic equivalence between the unconditional maximum likelihood and the square-law nonlinearity symbol timing estimation
This paper provides a systematic approach to the
problem of nondata aided symbol-timing estimation for linear
modulations. The study is performed under the unconditional
maximum likelihood framework where the carrier-frequency
error is included as a nuisance parameter in the mathematical
derivation. The second-order moments of the received signal are
found to be the sufficient statistics for the problem at hand and they
allow the provision of a robust performance in the presence of a
carrier-frequency error uncertainty. We particularly focus on the
exploitation of the cyclostationary property of linear modulations.
This enables us to derive simple and closed-form symbol-timing
estimators which are found to be based on the well-known square
timing recovery method by Oerder and Meyr. Finally, we generalize
the OM method to the case of linear modulations with
offset formats. In this case, the square-law nonlinearity is found
to provide not only the symbol-timing but also the carrier-phase
error.Peer Reviewe
Symbol timing recovery for GMSK modulation based on squaring algorithm
A new all-digital symbol timing estimator for GMSK signals is proposed. It is based on the squaring algorithm and has a feedforward structure. Performance in AWGN channel is assessed by computer simulation, and is compared with the modified Cramer-Rao bound and other existing algorithms. The performance of the proposed estimator is shown to be close to that of ML algorithm.published_or_final_versio
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