Differential detection via the Viterbi algorithm for offsetmodulation and MSK-type signals

The differentially coherent reception of two families of constant-envelope signals, the linear offset quaternary phase shift keying and the binary partial response continuous phase modulation with index 0.5, is addressed. When the conventional (PSK-type) differentially coherent detector is used, a large performance degradation, compared with that of coherent receiver, is observed. The reason for this is the presence of an inherent intersymbol interference (ISI) in the signal and also noise enhancement and correlation introduced by the receiver filter. A differential detection strategy which compensates for ISI and avoids noise enhancement is presented. A phase estimate that takes into account the presence of the inherent ISI is derived. This phase estimate is then used in the decision metric of a coherent receiver. The resulting decision rule can be implemented using the Viterbi algorithm. Simple Viterbi receivers with good performance are obtained. Simulation results are given     

A New Soft‐Fusion Approach for Multiple‐Receiver Wireless Communication Systems

In this paper, a new soft‐fusion approach for multiple‐receiver wireless communication systems is proposed. In the proposed approach, each individual receiver provides the central receiver with a confidence level rather than a binary decision. The confidence levels associated with the local receiver are modeled by means of soft‐membership functions. The proposed approach can be applied to wireless digital communication systems, such as amplitude shift keying, frequency shift keying, phase shift keying, multi‐carrier code division multiple access, and multiple inputs multiple outputs sensor networks. The performance of the proposed approach is evaluated and compared to the performance of the optimal diversity, majority voting, optimal partial decision, and selection diversity in case of binary noncoherent frequency shift keying on a Rayleigh faded additive white Gaussian noise channel. It is shown that the proposed approach achieves considerable performance improvement over optimal partial decision, majority voting, and selection diversity. It is also shown that the proposed approach achieves a performance comparable to the optimal diversity scheme.     

Adaptive symbol-by-symbol reception of MPSK on the Gaussian channelwith unknown carrier phase characteristics

An adaptive version of the optimum, decision-aided, symbol-by-symbol receiver obtained in our previous works for M-ary phase shift keying over the Gaussian channel with unknown carrier phase characteristics is considered. It uses a first-order adaptive filter for carrier reference tracking, and the filter gain is adapted on-line based on the observed signal samples using a least-mean-square-error criterion. The phase tracking performance of the filter in the steady-state tracking mode is analyzed using a linearized model. The phase tracking error variance is minimized due to the risk function used in designing the filter gain adaptation algorithm. The bit-error probability for quadrature phase shift-keying is obtained, both analytically and via computer simulations     

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     

Frequency-Domain Turbo Equalization and Multiuser Detection for DS-UWB Systems

One of the major challenges in direct sequence-ultra wideband (DS-UWB) receiver design is intersymbol interference (ISI). Several equalization schemes to eliminate ISI in DS-UWB systems have been proposed in the literature. It was shown that frequency-domain (FD) equalization techniques can offer better trade off between performance and complexity compared to timedomain equalization schemes for DS-UWB systems on highly dispersive channels. In this paper, we derive low-complexity FD minimum mean square error turbo equalization schemes for single-user binary phase shift keying (BPSK) and quaternary bi-orthogonal keying (4BOK) DS-UWB systems. For multiuser DS-UWB systems, we combine FD turbo equalization schemes with soft interference cancelation to obtain multiuser FD turbo detectors. The bit error rate performance gain due to turbo detection is shown to be significant, particularly for multiuser DS-UWB systems.     

New Simple Closed-Form BER Expressions for MRC Diversity BPSK in Correlated Rayleigh Fading and CCI

Exact closed-form expressions are derived for the bit error rate of binary phase shift keying in Rayleigh fading channels with maximal ratio combining diversity in the presence of cochannel interference and additive white Gaussian noise. The desired signal and the interferer signals are subject to correlated Rayleigh fading and binary phase shift keying modulation is used by all users.     

Error probability of digital modulation in satellite mobile, landmobile, and Gaussian channels with narrow-band receiver filter

It is shown how to derive formulas for the error probability for M-ary differential phase shift keying with differential phase detection (DPD) and M-ary frequency shift keying with DPD, limiter-discriminator detection and limiter-discriminator-integrator detection in the satellite mobile channel (SMC) with narrowband receiver filter if such formulas are available for the Gaussian channel. The modification of the formulas involves only a redefinition of the noise power and autocorrelation function. Since the SMC contains as special cases the land mobile (Rayleigh) channel and the Gaussian channel, the derived formulas are valid for these channels as well. In fact the formula for the land mobile channel is in many cases reduced to a closed form, which does not contain an integral. The author computes the error probability for the four systems, and compares their performance assuming a third-order butterworth filter and M=2,4,8 symbols     

The search for optimized shaping filters suitable for vsat systems

The satellite communications industry has seen the emergence of VSAT (very small aperture terminal) systems with the promise of high growth in the next decade. The system design of the VSAT ground station has generally followed traditional satellite communication system design, namely featuring data transmission using QPSK (quadrature phase shift keying) or BPSK (binary phase shift keying) and 50 per cent raised cosine shaping filters with quasilinear transmission. Transmitter power is strictly limited and is at a premium for the VSAT transmitter which usually consists of a non-linear solid-state power amplifier (SSPA). Consequently it is important to operate the SSPA so that the maximum power is obtained, which means that the SSPA should be operated close to its saturation point. In so doing considerable distortion can be introduced, which leads to intersymbol interference (ISI) in the receiver and an associated degradation in error rate. Although constant envelope BPSK or QPSK solves the intersymbol interference problem and enables operation at the saturating point of the SSPA, the sinx/x spectral shape has unacceptable sidelobe levels. This paper gives results of a search for a pulse shaping filter characteristic that is bandlimited and yet has improved performance over the traditional root 50 per cent cosine roll-off filter when used in a VSAT ground station with a SSPA. The performance improvement due to improved shaping filtering is maintained over a range of output levels of the SSPA. Performance evaluation results using computer simulation are presented.     

Error performance analysis of a jointly optimal single-cochannel-interferer BPSK receiver

An analytical solution is derived for the average error-rate performance of a jointly optimal binary phase-shift keying receiver operating in the presence of one cochannel interferer and additive white Gaussian noise. The solution takes different analytical forms, depending on the region of signal-to-interference ratio. The regions depend, in turn, on the phase difference between the desired signal and the interferer signal.     

A fully digital noncoherent and coherent GMSK receiver architecturewith joint symbol timing error and frequency offset estimation

We propose a fully digital noncoherent and coherent Gaussian minimum shift keying (GMSK) receiver architecture with joint frequency offset compensation and symbol timing recovery. Carrier phase offset can be estimated if the coherent demodulation mode is adopted. The converted base-band complex signal is first frequency discriminated and then passed through a digital filter which performs a fast Fourier transform (FFT). The frequency offset can be estimated from the DC component of the FFT, and the symbol timing error can be estimated from the phase angle of the FFT at a specified frequency which is equal to an integral multiple of half the bit rate. These two estimated parameters are then used for frequency offset compensation and symbol timing recovery during a preamble period. Coarse carrier phase can be estimated by averaging sampled in-phase and quadrature-phase signals and finding its phase angle within the preamble period after carrier frequency offset is estimated and compensated. The bit error rate (BER) performance of this GMSK receiver architecture is assessed for an additive white Gaussian noise (AWGN) channel by computer simulation     

BER Calculation and Investigation of Optimal Single User Detector for a BPSK Signal Contaminated by Cochannel Interferer

We propose an optimal single user detector (OSUD) for a binary phase shift keying (BPSK) signal corrupted by a cochannel interferer and additive white Gaussian noise (AWGN). We obtain an analytical expression for the detector bit error rate (BER). The capacity of this channel is also investigated to interpret the BER performance of the optimal detectors.     

An efficient decision feedback with center sampling differential detector for restricted bandwidth fast Rayleigh channels

An efficient decision feedback technique (EDF) is proposed to improve the performance of premodulation Gaussian minimum shift keying (GMSK) signals. Center sampling differential detector (CSDD) over restricted bandwidth (BW) fast Rayleigh channels is employed. The intersymbol interference (ISI) is partially eliminated by using the conventional decision feedback (CDF) technique. In the present modification ISI is drastically eliminated by using EDF technique resulting in the minimization of probability of error. The new receiver structure, is useful in mobile radio (MR) and mobile satellite communications where power efficiency, synchronization and implementation complexity are of primary concern. Numerical results show that the receiver structure under consideration yields a superior performance in narrowband channels where conventional differential detector (CDD) becomes unusable.     

Continuous Phase Chirp (CPC) Signals for Binary Data Communication-Part I: Coherent Detection

Chirp (linear FM) signals provide an attractive wideband digital modulation scheme in applications where interference rejection is important. This paper evaluates the error rate (performance) of coherent binary continuous phase chirp (CPC) receivers operating on the additive white Gaussian noise (AWGN) channel and determines the improvement in performance made possible by multiple bit observation. In particular, it is shown that a receiver with two bit observation, giving up to 1.75 dB signal-to-noise ratio (SNR) improvement over the optimum single bit chirp receiver, provides a good compromise between SNR gain and system complexity. Furthermore, a simple, suboptimum, average matched filter (AMF) receiver is analyzed, and it is shown that a two-bit observation is optimum, giving a performance equivalent to that of antipodal phaseshift keying (PSK). An implementation of this receiver in the form of in-phase and quadrature demodulators is also derived.     

一种多进制连续相位调制信号的符号定时跟踪方法

针对多进制连续相位调制信号(MCPFSK)的传输系统,提出一种在相位上提取定时误差的符号定时跟踪方法,并分析定时跟踪环路的特性。根据MCPFSK信号特性,接收端将信号差分、鉴相后,利用多进制信号特性提取定时误差。Matlab仿真结果表明,在加性高斯白噪声信道上,该方法能准确地估算出定时偏差,适用于MCPFSK信号的非相干差分解调系统。     

Performance of Single and Multichannel Coherent Reception under Rician Fading

In the present work, simple closed-form series solutions for the average error rate of several coherent modulation schemes such as, binary phase shift keying (BPSK), binary frequency shift keying (BFSK), differential binary phase shift keying (DBPSK), quadrature phase shift keying (QPSK), offset-QPSK, minimum shift keying (MSK), and square M-ary quadrature amplitude modulation (M-QAM), operating over frequency non-selective slow Rician fading channel and corrupted by additive white Gaussian noise (AWGN) are derived. Further, to improve the link quality, receiver antenna space diversity is considered, where multiple independent and identically distributed (i.i.d.) as well as uncorrelated signal replicas are combined before successive demodulation. The proposed linear predetection combiner follows optimum maximal ratio combining (MRC) algorithm. Starting from a novel unified expression of conditional error probability the error rates are analysed using probability density function (pdf) based approach. The derived end expressions, consisting of rapidly converging infinite series summations of Gauss hypergeometric function, are accurate, free from any numerical integration and general enough, as it encompasses as special situations, some cases of non-diversity, non-fading AWGN and Rayleigh fading. Symbol or, bit error probabilities (SEP/BEP) are graphically displayed against signal to noise ratio (SNR) per bit per channel for all the digital modulation schemes stated above with different values of diversity order L and varying values of the channel specular-to-scatter ratio or, the Rician parameter K, as found from the measured statistics of mobile and indoor wireless channels. In addition, to examine the dependence of error rate performance of M-QAM on the constellation size M, numerical results are plotted for various values of M. Selected simulation results are also provided to verify the analytical deductions. The series solutions presented in current text realize a trade-off between precision and complexity and offers valuable insight into the performance evaluation over a fading channel in a unified manner.     

Differential detection of Gaussian MSK in a mobile radio environment

Minimum shift keying with Gaussian shaped transmit pulses is a strong candidate for a modulation technique that satisfies the stringent out-of-band radiated power requirements of the mobil radio application. Numerous studies and field experiments have been conducted by the Japanese on urban and suburban mobile radio channels with systems employing Gaussian minimum-shift keying (GMSK) transmission and differentially coherent reception. A comprehensive analytical treatment is presented of the performance of such systems emphasizing the important trade-offs among the various system design parameters such as transmit and receiver filter bandwidths and detection threshold level. It is shown that two-bit differential detection of GMSK is capable of offering far superior performance to the more conventional one-bit detection method both in the presence of an additive Gaussian noise background and Rician fading.     

Performance of Partial Response CPM in the Presence of Adjacent Channel Interference and Gaussian Noise

Partial response continuous phase modulation (CPM) schemes have found wide acceptance because of their compact spectra and comparable performance with other traditional modulation schemes. Although optimum receivers are complex, simple suboptimum receivers are found to yield very good performance in special cases. Performance of such modulation schemes is of interest in a multiple user environment where adjacent channels are spaced closely to improve the system capacity. This paper presents the performance of partial response CPM in the presence of adjacent channel interference and Gaussian noise. The meansquare crosstalk in CPM systems employing MSK-type receivers is formulated. Based on this formulation, a number of modulation schemes employing different receiver filters are analyzed for their ACI rejection. Comparison of results proves that receiver filters, in addition to the spectral occupancy of the signal, play an important role in deciding the crosstalk. The error performance of various schemes evaluated using simulation technique is compared, and it is found that in the presence of adjacent channel interference, certain schemes perform better than minimum shift keying (MSK). The results of the simulation further prove the inadequacy of Gaussian assumption for the adjacent channel interference. It is seen that judicious choice of modulation scheme and receiver filter can result in better spectrum utilization.     

A RAKE Receiver With an ICI/ISI Equalizer for a CCK Modem

In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword.     

Dynamic stimulated Brillouin scattering analysis

We present a new simple analysis-including the effect of spontaneous emission-of the (dynamic) influence of stimulated Brillouin scattering (SBS) on the detected receiver eye diagram. It applies in principle for general types of modulation formats such as the digital formats of amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The analysis is formulated for a determination of the signal power depiction and intersymbol interference (ISI) caused by the combined effect of fiber dispersion, fiber attenuation and nonlinear fiber effects such as the effect of self-phase modulation (SPM) and SBS. The analysis allows a quantification of the dithering influence on the SBS threshold. Representative numerical examples are presented for two single-channel ON-OFF modulated 10-Gh/s systems utilizing Franz-Keldysh and Mach-Zehnder-type modulators     

Noncoherent detection of coherent lightwave signals corrupted byphase noise

Waves are treated that modulate by either on-off keying (OOK) or binary frequency-shift keying (FSK) and are further impaired by additive Gaussian noise. Heterodyne detection of such a waveform produces an electronic bandpass signal, which, to ease demodulation in the presence of phase noise, is noncoherently demodulated to extract the baseband pulse stream. The treatment goes beyond previous bit error rate (BER) analyses of optical heterodyne receivers for OOK and FSK. First, there is full adherence to the standard (Brownian motion) model of phase noise. Also, the receiver structure is formulated in such a way that the probability density function of the receiver output samples can be accurately determined. This permits calculations of the additive noise and phase noise tolerable when achieving bit error rates as small as 10 ^-9. Finally, the study is comprehensive regarding the range of parameters explored. Filtering at an intermediate frequency (IF) alone, as well as IF filtering plus postdetection low-pass filtering, is considered. When the receiver parameters decision threshold (for OOK) and IF filter bandwidth are optimized, large amounts of phase noise can be accommodated with only minor increases in required signal-to-noise ratio. This is especially important when the bit rate is moderate compared to the laser linewidth