Maximum-likelihood block detection of noncoherent continuous phasemodulation

The authors examine maximum-likelihood block detection of uncoded full response continuous phase modulation (CPM) over an additive white Gaussian noise (AWGN) channel. Both the maximum-likelihood metrics and the bit error probability performances of the associated detection algorithms are considered. The special and popular case of minimum-shift-keying (MSK) corresponding to h=0.5 and constant amplitude frequency pulse is treated separately. The many new receiver structures that result from this investigation can be compared to the traditional ones that have been used in the past both from the standpoint of simplicity of implementation and optimality of performance     

Noncoherent sequence detection of continuous phase modulations

In this paper, noncoherent sequence detection, proposed in a companion paper by Colavolpe and Raheli (see ibid. vol.47, no.9, p.1376-85, 1999), is extended to the case of continuous phase modulations (CPMs). The results in the companion paper on linear modulations with intersymbol interference (ISI) are used here because a CPM signal is mathematically equivalent to a sum of ISI-affected linearly modulated components, according to the Laurent decomposition. The proposed suboptimal detection schemes have a performance which approaches that of coherent detection with acceptable complexity, allow for time-varying phase models, and compare favorably with previously proposed solutions     

Iterative decoding of convolutionally encoded signals overmultipath Rayleigh fading channels

We analyze and compare several strategies for iteratively decoding trellis-encoded signals over channels with memory. Soft-in/soft-out extensions of reduced-complexity trellis search algorithms such as delayed decision-feedback sequence estimating (DDFSE) or parallel decision-feedback decoding (PDFD) algorithms are used instead of conventional BCJR and min-log-BCJR algorithms. It has been shown that for long channel impulse responses and/or high modulation orders where the BCJR algorithm becomes prohibitively complex, the proposed algorithms offer very good performance with low complexity. The problem of channel estimation in practical implementation of turbo detection schemes is studied in the second part. Two methods of channel reestimation are proposed: one based on the expectation-maximization (EM) algorithm and the second on a simple Bootstrap technique. Both algorithms are shown to dramatically improve the performance of the classical pseudo inverse channel estimation performed initially on a training sequence     

A decision-feedback phase-tracking receiver for continuous phasemodulation

In this letter, a new recursive structure of a decision-feedback (DF) phase-tracking receiver for continuous phase modulation (CPM) is derived. This receiver uses the previously detected symbols to continuously estimate the initial phase in the current symbol and thus makes optimum coherent detection. The theoretical and simulation analyses of the error performance are given. It is shown that the BER performance of binary continuous phase frequency-shift keying (2CPFSK) and raised cosine (2RC) with a small modulation index is very close to the ideal bound, and the BER performance of GMSK is better than any previously known noncoherent detection     

Simple coherent receivers for partial response continuous phasemodulation

By using a pulse-amplitude-modulation representation of binary continuous-phase-modulation signals, the authors develops a novel optimum Viterbi sequence detector and a near-optimum Viterbi receiver with low complexity. For modulation index 0.5, where a linear receiver can be used, a minimum-mean-squared-error linear receiver filter is derived. The performance of all of these is analyzed, using the Gaussian minimum-shift-keying signal (GMSK) for illustration. It is shown that a GMSK receiver consisting of two matched filters and a four-state Viterbi algorithm performs with less than 0.24-dB degradation compared with the optimal receiver. The linear receiver is optimum for all values of E _b/N₀ (bit-energy-to-noise one-sided spectral density ratio). A design method for its filter is given. The filter is equivalent to a cascade of a matched filter and a Wiener filter estimator. Both upper and lower bounds for the bit-error probability are calculated. Simulation results which confirm the analysis are given     

Noncoherent sequence detection

New noncoherent sequence detection algorithms for combined demodulation and decoding of coded linear modulations transmitted over additive white Gaussian noise channels, possibly affected by intersymbol interference, are presented. Optimal sequence detection in the presence of a random rotation of the signal phase, assumed to be constant during the entire transmission, requires a receiver complexity exponentially increasing with the duration of the transmission. Based on proper approximations, simple suboptimal detection schemes based on the Viterbi algorithm are presented, whose performance approaches that of coherent detection. In a companion paper by Colavolpe and Raheli (see ibid., vol.47, no.9, p.1303-7, 1999), noncoherent sequence detection is extended to continuous phase modulations. In the proposed schemes, the tradeoff between complexity and performance is simply controlled by a parameter, referred to as implicit phase memory, and the number of states of a trellis diagram. Besides being realizable, these schemes have the convenient feature of allowing us to remove the constant phase assumption and encompass time-varying phase models. The proposed schemes compare favorably with other solutions previously proposed in the technical literature     

Modified Viterbi decoders for joint data detection and timingrecovery of convolutionally encoded PPM and OPPM optical signals

Two novel Viterbi decoders, known as joint Viterbi decoder (JVD) and enhanced Viterbi decoder (EVD), for synchronization and data detection are introduced and analyzed for convolutionally-encoded (CE) optical pulse-position modulation (PPM) and overlapping PPM (OPPM) channels. For the JVD algorithm, a count metric is employed to perform the Viterbi decoding in the absence of synchronization. For the EVD algorithm, a memory array is utilized to reduce the computation time of the JVD algorithm. With the aid of a previously proposed upper-bound and taking advantage of the minimal asymptotic normalized timing error (MANTE) concept, approximate performance measures for the EVD and JVD receivers are obtained     

Noncoherent decision-feedback multiuser detection

The problem of noncoherent multiuser detection for multipulse modulation over the Gaussian multiuser channel is studied. It is assumed that neither the energies nor the carrier phases of the signals of any of the users are available at the receiver. Previously, a post-decorrelative generalized likelihood ratio test (GLRT) based detector was proposed as a solution to this problem. In this paper, we introduce the concept of noncoherent decision feedback (DF) that forms the basis for an improved solution to the same problem. The users are detected sequentially in some fixed order, and the decision for a particular user takes advantage of the reduction of uncertainty associated with the signal space resulting from decisions already made for previous users. In contrast to coherent DF, therefore, the feedforward and feedback transformations in the noncoherent case are themselves functions of the matched filter outputs. An efficient implementation of the noncoherent DF detector for M-ary modulation and ρ-dimensional signal space requires O(M_ρ) computational complexity per user. Upper and lower bounds on its symbol error probability are obtained. It is shown that significant improvements over the post-decorrelative GLRT-based detector are often possible. Sufficient conditions are obtained which guarantee, without ignoring error-propagation effects, that the high signal-to-noise performance of the DF strategy can be as good as its genie-aided version in which perfect past users' decisions are used     

Performance of a satellite modem transmitting convolutionally and differentially encoded 8PSK signals

The paper studies a digital satellite modem for mobile systems. The modem transmits a convolutionally and differentially encoded eight-phase-shift-keyed (CDE8PSK) signal over a satellite link and employs a near-maximum-likelihood decoder at the receiver. The signal can tolerate phase ambiguities that are multiples of 4 radians, which normally result from the carrier recovery loop at the receiver. However, the carrier recovery loop is not considered here. The high-power amplifier (HPA) at the earth-station transmitter may introduce non-linear distortion to the CDE8PSK signal, and predistortion may or may not be used. Several different earth-stations are assumed to have simultaneous access to a given transponder on the satellite, in an arrangement of frequency division multiple access, but the satellite transponder is assumed to be linear. Thus the CDE8PSK signals that occupy the immediately adjacent frequency bands can introduce adjacent-channel interference (ACI) to the desired CDE8PSK signal. Extensive computer-simulation tests have been carried out to evaluate the effects of non-linear distortion with predistortion, in the presence of ACI, on the tolerance of the modem to additive white Gaussian noise. Four different bandwidths of the transmitted signal are considered, together with three different arrangements of the demodulator. The predistorter operates on the baseband signal at the input to the modulator and assumes a prior knowledge of the HPA characteristics. In all simulation tests, an equivalent baseband model of the transmission system is used, and the results are used to determine the preferred modem design.     

Noncoherent sequence detection of CPM

Schemes in which noncoherent sequence detection based on the Viterbi algorithm are proposed for linearly modulated signals transmitted over additive white Gaussian noise channels, have recently been proposed by the authors. These schemes are attractive because their performance closely approaches that of coherent receivers with acceptable complexity, and they avoid the drawbacks of phase-locked loops. The authors extend these results to M-ary continuous phase modulation (CPM) signals     

Noncoherent detection of periodic signals

In this paper the optimal Bayes detector for a general periodic waveform having uniform delay and additive white Gaussian noise is examined. It is shown that the detector is much more complex than that for the we!l-known cases of pure sine waves (i.e., classical noncoherent detection)and narrow-hand signals. An interpretation of the optimal processor is presented, and several implementations are discussed.     

Noncoherent detection for trellis-coded MPSK

This letter shows several methods for improving the decoding of noncoherent trellis-coded M-ary phase-shift keying. We propose two new metrics for the basic decision-feedback algorithm. These metrics are derived based on the idea of reducing the effect of incorrect amplitude of the reference signal. We also propose a new decoding algorithm that uses a simple way to estimate the metric of the future sequence     

Noncoherent detection in asynchronous multiuser channels

The noncoherent demodulation of multiple differentially phase-shift-keyed signals transmitted simultaneously over an asynchronous code-division multiple-access (CDMA) channel with white Gaussian background noise is considered. A class of bilinear detectors is defined with the objective of obtaining the optimal bilinear detector. The optimality criterion considered is near-far resistance that denotes worst-case asymptotic efficiency over the signal energies and phases which are unknown at the receiver. The optimal bilinear detector is therefore obtained by solving a minimax optimization problem. In the finite packet length case, this detector is shown to be a time-varying multiinput multioutput linear decorrelating filter followed by differential decision logic. In the limit as packet lengths go to infinity, the time-varying decorrelating detector is replaced by a time-invariant multiinput multioutput decorrelating filter. Several properties of the optimally near-far resistant detector are established     

Noncoherent detection scheme for GSM system

A receiver employing frequency discriminator demodulation and maximum likelihood sequence estimator detection is proposed for the GSM mobile telephone system. Computer simulated bit error rates based on two ray and GSM propagation models are presented. The proposed scheme is more tolerant to carrier frequency offset than a coherent system     

Noncoherent detection of preamble-signal-assisted differentiallyphase-encoded APSK signals

A noncoherent detection scheme for differentially encoded amplitude- and phase-shift-keyed data transmission, assisted with differentially phase-shift-keyed preamble signals, is presented and analyzed for an additive white Gaussian noise channel. It is analytically shown that, despite a controllable reduction in bandwidth efficiency, the proposed scheme yields an error performance approaching that of the quadrature amplitude modulation scheme with ideal coherent detection within a loss of approximately 1 dB     

Noncoherent maximum-likelihood block detection of orthogonalNFSK-LDPSK signals

This paper investigates the noncoherent block detection of orthogonal N frequency-shift keying (FSK)-L differential phase shift keying (DPSK) signals transmitted over the additive white Gaussian noise channel, based on the principle of maximum-likelihood (ML) sequence estimation. By virtue of a union bound argument, asymptotic upper bounds for the bit error probability of the developed ML block receiver are derived and verified by simulation. It is analytically shown that the noncoherent NFSK-LDPSK ML block receiver performs comparably with the ideal coherent NFSK-L phase shift keying (PSK) receiver for L = 2 and 4, as the observation block length is large enough. Furthermore, substantial performance improvement can be achieved by the ML block detection of the NFSK-LDPSK signal with L > 2 by increasing the observation block length     

Decision feedback sequence estimation for continuous phasemodulation on a linear multipath channel

An approach to reduced-complexity detection of partial response continuous phase modulation (CPM) on a linear multipath channel is presented. The method, referred to as decision feedback sequence estimation (DFSE), is based on a conventional Viterbi algorithm (VA) using a reduced-state trellis combined with decision feedback (DF). By varying the number of states in the VA, the receiver structure can be changed gradually from a DF receiver to the optimal maximum-likelihood sequence estimator (MLSE). In this way different tradeoffs between performance and complexity can be obtained. Results on the receiver performance, based on minimum distance calculations and bit error rate simulations, are given for Gaussian minimum-shift keying modulation on typical mobile radio channels. It is shown that for channels with a long memory, a significant complexity reduction can be achieved at the cost of a moderate degradation in performance     

Noncoherent sequence detection receiver for Bluetooth systems

The design of power efficient receivers for Bluetooth systems is a challenging task due to stringent complexity constraints. In this paper, we tackle this problem and present a receiver design consisting of a single filter and a subsequent noncoherent sequence detector. This receiver outperforms the conventional discriminator detector by more than 4 dB for typical Bluetooth channels. Thereby, the proposed noncoherent sequence detection (NSD) algorithm is both favorably low complex as it operates on a two-state trellis and highly robust against channel phase variations caused by low-cost local oscillators. The particular filter design accomplishes effective out-of-band interference suppression. Different from previous work on sequence detector receivers published in the literature, we take possible variations of the Bluetooth modulation parameters into account, and we also devise efficient methods for combined NSD and forward error correction decoding. Hence, the presented receiver design is an attractive solution for practical Bluetooth devices.     

Noncoherent multistage multiuser detection of M-ary orthogonal signals

In recent years, a great deal of research has been performed on methods of alleviating the performance degradations suffered by code division multiple access (CDMA) systems due to multiple access interference. In this paper, we consider a multistage detector for noncoherent CDMA using M-ary orthogonal signals. Using a decorrelating detector as its first stage, the detector iteratively estimates the multiple access interference affecting the desired signal, subtracts the estimated interference, and forms symbol estimates for each of K users. Through numerical examples, the bit error performance of the proposed detector is demonstrated to be superior to that of previous detectors for the same signalling scheme. This revised version was published online in June 2006 with corrections to the Cover Date.     

Noncoherent sequence detection in frequency nonselective slowlyfading channels

A new class of noncoherent sequence detection (NSD) algorithms for combined demodulation and decoding of any coded linear and continuous phase modulations, transmitted over additive white Gaussian noise (AWGN) channels, has been previously presented. In this paper, this class is generalized to the case of frequency nonselective Rayleigh or Rice slowly fading channels, in the presence or absence of channel state information. Coded linear modulations, namely M-ary phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM), are considered. The proposed detection schemes have a performance which approaches that of coherent detectors, are very robust to phase and frequency instabilities, and compare favorably to other solutions previously proposed in the technical literature