Adaptive Demodulation in Differentially Coherent Phase Systems: Design and Performance Analysis

This paper is devoted to an investigation of an exact average symbol error probability (SEP) for amplify and forward (AF) relaying in independent Nakagami‐m fading environments with a nonnegative integer plus one‐half m, which covers many actual scenarios, such as one‐side Gaussian distribution (m = 0.5). Using moment generating function approach, the closed‐form SEP is expressed in the form of Lauricella multivariate hypergeometric function. Four modulation modes are considered: rectangular quadrature amplitude modulation (QAM), M‐ary phase shift keying (MPSK), M‐ary differential phase shift keying (MDPSK), and π/4 differential quaternary phase shift keying (DQPSK). The result is very simple and general for a nonnegative integer plus one‐half m, which covers the same range as integer m. The tightness of theoretical analysis is confirmed by computer simulation results.

The performances of direct-sequence spread-spectrum multiple-access (DS-SSMA) systems with M-ary differential phase shift keying (MDPSK) and differential phase detector (DPD) are estimated on the satellite mobile channel (SMC) which includes Gaussian and Rayleigh channels as the special cases. The numerical results are presented for the system with one of three types of chip waveforms (rectangular, cosine and root Nyquist filtering (RNF)), and binary or complex random signature sequences. They show that the system with the complex random signature sequences outperforms the system with the binary random signature sequences on Gaussian and Rician (K = 10) channels, while on a Rayleigh channel both systems perform similarly; the system with 2 × I users and BDPSK signalling format outperforms that with I users and QDPSK for Gaussian and Rician (K = 10) channels; and from the point view of both bandwidth efficiency and antimultipath effects, the cosine pulse shaping is the best choice of the three pulse shape functions, although the system with the RNF has the highest bandwidth efficiency.

In addition to diversity, forward error correction (FEC) coding is a well-known method that can be used to improve the performance of communication on wireless fading channels. In this paper, we investigate the performance of combined diversity and FEC coding strategies. For block coding to be effective, bit errors in each code word should be independent. To render the channel memoryless, perfect bit interleaving is assumed. That is, bit errors in the code word are assumed to be independent. In this paper, we analyze the performance of M-ary differential phase shift keying (MDPSK) on frequency-selective Rayleigh fading channels using two branch postdetection equal gain (EG) combining. Both the effects of correlation between the two diversity branches and the effects of cochannel interference on the BER performance are investigated. The interferers are assumed to be MDPSK modulated signals with same symbol rate as that of the desired signal, but with random symbol timing offsets relative to the desired signal. The cochannel interference contribution is represented by a Gaussian noise whose mean and variance are equal to the mean and variance of the sum of the interfering signals.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We investigate the effects of correlation on the performance of diversity systems in wideband wireless radio environments. Specifically, the average bit error rate (BER) performance of M-ary differential phase shift keying (MDPSK) on correlated frequency-selective slow Rayleigh fading channels is analyzed. A two-branch diversity receiver with postdetection equal gain combining is considered. Nyquist pulse shaping is used and differential detection is employed at the receiver. The effects of cochannel interference on the system performance are assessed using a Gaussian interference model. To further enhance the system performance, the effects of combined diversity and forward error correction (FEC) coding on the average BER are investigated. Results using short cyclic block codes with perfect bit interleaving are obtained. The effects of the root mean square (RMS) delay spread, the amount of correlation, and the level of modulation, M, on the average BER are investigated in detail for both coded and uncoded systems. The results show that dual branch diversity combining with a correlation coefficient of 0.5 outperforms (in terms of BER) short block codes with perfect bit interleaving, and that combined diversity and coding strategies are effective in combatting the effects of frequency-selective fading.

In this paper, the authors derive the moment generating function (MGF) of the decision variable for a practical optical differential quadrature phase shift keying (DQPSK) receiver affected by phase noise and the amplifier spontaneous emission noise. The effect of the different optical filters, Gaussian, Fabry-Peacuterot (FP), and optical integrator, on the phase noise is examined. Using the saddle point approximation, the authors obtain numerically the bit error rate (BER) for the above system, as a function of the optical-signal-to-noise ratio (OSNR) and the source linewidth. The model is found to agree with previous published simulation results and the Monte Carlo simulations presented in this paper. The authors also calculate the BER floors for DQPSK inflicted by the phase noise and compare its performance with differential phase shift keying (DPSK). Finally, the authors examine the effect of interferometric demodulation on the relative intensity noise (RIN) spectra and the impact on the DQPSK system performance. In particular, the authors examine the influence of system dispersion on the receiver sensitivity

Wireless data transmission with binary phase-shift keying modulation encoded on a 92 GHz carrier is achieved using photonic components. A high-speed photodiode is used to convert the doubly-modulated optical signal to a modulated millimeter-wave carrier. A W-band Mach-Zehnder interferometer with a one-bit time delay is used to directly detect the differential phase-shift keyed millimeter-wave wireless signal without the use of a local oscillator. Field tests with antennas separated by 890 m demonstrate the ability to discriminate two phase states for differential binary phase shift keying (DBPSK) and four phase states for differential quadrature phase shift keying (DQPSK) at data rates of 2.3 Gb/s and 4.6 Gb/s, respectively.

The capacity of a direct-sequence code-division multiple-access (DS/CDMA) system is limited by multiple-access interference (MAI) and the near-far problem. Multiuser receivers provide solutions to these problems, but they require knowledge of parameters of the MAI and are computationally complex. Adaptive single-user receivers do not require knowledge of MAI parameters and need fewer computations. In this paper, we propose noncoherent receivers for M-ary differential phase-shift keying (MDPSK) signals. The performance of the proposed noncoherent receiver approaches that of a coherent MPSK receiver. The noncoherent receiver consists of a linear equalizer and a decision-feedback differential detector (DF-DD). The bit error rate (BER) performance comparisons of different proposed receivers are shown by the simulations.

This paper presents recent progress toward the realization of ultrahigh-speed coherent optical transmission with a single-channel bit rate of more than 1 Tbit/s using ultrashort pulse technology and an advanced modulation format. We first describe Tbit/s optical time-division multiplexing (OTDM) transmission employing differential binary or quadrature phase shift keying. We present our recent demonstrations of single-polarization 640-Gb/s differential phase-shift keying and 1.28-Tb/s differential quadrature phase-shift keying transmissions over 525 km, which employ an ultrafast optical Fourier transformation technique. We then focus on coherent optical transmission using quadrature amplitude modulation (QAM) with a multiplicity of 512 that enables us to achieve an ultrahigh spectral efficiency of more than 10 b/s/Hz. Finally, we demonstrate a novel ultrahigh-speed, spectrally efficient coherent pulse transmission combining OTDM and QAM. A 400 Gb/s, 32 RZ/QAM signal was successfully transmitted over 225 km on a single carrier at 10 Gsymbol/s × 4-OTDM.

In this paper, a novel differential demodulator for OFDM combining traditional differential demodulation with neural computation has been introduced for differential detection. Simulations using a two-path channel model and M-ary differential phase shift keying (MDPSK) modulation have been run to investigate the performance characteristics of the proposed scheme. The results show that it adapts very well to channel conditions with both strong delay and Doppler spread. The new structures are superior when compared to the traditional differential demodulation in frequency selective fast fading channels without any extra computing complexity.KeywordsOrthogonal Frequency Division MultiplexChannel EstimationOrthogonal Frequency Division Multiplex SystemOrthogonal Frequency Division Multiplex SymbolDelay SpreadThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

New expressions are derived for the cumulative distribution function (CDF) of the phase difference between two signals perturbed by additive Gaussian noise, for mobile radio channels characterised by: (i) Rician fading and lognormal shadowing, so called Rice-lognormal (RLN) channels; (ii) Nakagami fading and lognormal shadowing, so called Nakagami-lognormal (NLN) channels. New CDF curves for the phase difference as functions of the Rice K factor, Nakagami m factor and shadowing spread are presented. The new formulae are applied to compute the symbol error rate of M-ary differential phase shift keying (MDPSK) signals in RLN and NLN channels.

Performance Analysis of Different Phase Shift Keying Modulation Schemes in Aeronautical Channels

The accurate performance evaluation of differential amplitude and phase-shift keying (DAPSK) with postdetection equal gain combining (EGC) over generalized fading channels is of great theoretical interest and practical importance. In this paper, by using a decision variable-based moment generating function approach, exact error probability results for DAPSK over generalized Rician and Nakagami fading channels are derived, taking into account the effects of all the system and fading channel parameters. Several maximum likelihood (ML)-based detectors that do not require channel state information (CSI) are proposed for generalized Rician fading channels, and an exact bit error probability (BEP) union bound for the ML detection is derived. Assuming CSI, a performance upper bound for DAPSK with EGC is also presented. Simulation and numerical results show when both detectors have no CSI, the conventional DAPSK detector may perform closely to (though worse than) the ML detector. However, the EGC receiver with CSI performs substantially better than the ML detector without CSI, and very closely to the coherent APSK detector.

In this paper, we propose a novel rate-adaptive system where the receiver adjust demodulation schema to the channel condition, by using controlled soft demodulation (CSD) and rateless erasure code. In CSD, the receiver demodulates only those reliable bits which determined by log likelihood ratio (LLR) criterion and treats non-demodulated bits as deleted. Dynamic LLR threshold strategy and fix LLR threshold strategy were presented to supply some implementations of this system. We analyzed the performance of these strategies over an additive white Gaussian noise channel, and compared the results with the Adaptive Demodulation system. The adaptive solutions were also provided, by analyzing the simulation results with the Raptor codes. The analysis indicates that the CSD system could avoid some defects of traditional rate-adaptive schemes, such as feedback overhead and complexity of the system, it also has better performance than the Adaptive Demodulation system, with much more flexible approach.

In this paper, rate adaptive forward error correction systems for land mobile satellite communication are studied. For link performance evaluation, a simplified L-band land mobile satellite three state communication channel is introduced. A code rate adaptive system using multilevel coded modulation schemes with iterative decoding is presented. A new cost function based on the E/sub b//N/sub 0/ is given for performance evaluation of such systems. Based on this cost function, we show that rate adaptive systems can achieve extra coding gains between 3.9 dB and 9.0 dB.

Kalman filtering (KF) and hidden Markov model (HMM) signal processing techniques are coupled to demodulate signals transmitted through noisy fading channels. The demodulation scheme presented can be applied to both digital M-ary differential phase shift keyed (MDPSK) and analog frequency modulated (FM) signals. Adaptive state and parameter estimation algorithms are devised based on the assumption that the transmission channel introduces time-varying gain and phase changes, modelled by a stochastic linear system, and has additive Gaussian noise. Our technique is to use an HMM filter, for signal estimation, coupled with a KF, for channel parameter tracking. The approach taken can easily be generalised for other transmission schemes, such as continuous phase modulated (CPM) signals. >