Adaptive Delta Modulation for Companded PCM Coding and Decoding

An Adaptive Delta Modulator and demodulator are used as the first and last stages in a system for coding and decoding telephone signals intomu = 255Companded Pulse Code Modulation. The system objectives are to devise an economic coder and decoder that is reliable, free of potentiometer adjustments, and convenient for automated manufacturing for large quantity production. The strategy is a shift of circuit emphasis from analog to digital in order to take full advantage of low-cost, low-speed digital processing technology such as MOS/LSI to achieve the desired objectives. The system structure, digital signal processing, system implementation, and performance of the prototype are discussed in this paper.     

Performance Analysis of Joint Adaptive Modulation and Diversity Combining Over Fading Channels

Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, capitalizing on recent developments in adaptive combining, we propose three joint adaptive modulation and diversity combining (AMDC) schemes. With these schemes, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error-rate requirement. We accurately analyze these three AMDC schemes in terms of processing power consumption, spectral efficiency, and error-rate performance. Selected numerical examples show that the proposed AMDC systems meet the target error-rate requirement while achieving high spectral efficiency with low processing power consumption     

Adaptive Companded Pulse Code Modulation

In this paper, a novel quantization scheme-adaptive companded pulse code modulation (ACPCM)-is proposed. It is shown that, for fine quantization of analog signals, ACPCM will outperform the widely used PCM and DPCM in the sense of minimizing the meansquared quantizing error. For autoregressive (AR)signals, ACPCM is shown to reduce to DPCM. Some examples and simulations are given to demonstrate the method.     

A Microprocessor-Based PSK Modem for Packet Transmission Over Satellite Channels

This paper describes a microprocessor-based modem developed for use in a packet switching network over satellite channels. This digital modem can process both BPSK and QPSK packets with near optimum error rate performance over channels with marginal signal energy-to-noise density ratio. Of principal concern is the development of the discrete time algorithms which form the basis of the microinstruction program. The processing of a packet can be decomposed into two basic stages: (1) the detection of the packet preamble and the rapid estimation of signal parameters (symbol timing and carrier frequency offset) for the specific packet, and (2) the demodulation of the data portion of the packet including the tracking of both symbol timing and carrier offset phase, phase ambiguity resolution and data symbol estimation. The paper concludes with details on the performance of the modem under operational conditions and a brief discussion of implementation of the processor.     

256-QAM Modem Performance in Distorted Channels

Performance degradations of 256-QAM modems in distorted channels are studied in this correspondence. Illustrative linear, parabolic, and sinusoidal amplitude and group delay channel distortions, caused by filter imperfections and/or by selective radio fades, are investigated. To enable an easy comparison with 64-QAM systems, we present the degradations of these systems in the same figures as those of 256-QAM modems. It is shown that linear (slope) group delay and sinusoidal (ripple) amplitude distortions cause the most significant performance degradations.     

Block-Differential Modulation Over Doubly Selective Wireless Fading Channels

Block-Differential Modulation Over Doubly Selective Wireless Fading Channels Differential encoding is known to simplify receiver implementation because it bypasses channel estimation. However, over rapidly fading wireless channels, extra transceiver modules are necessary to enable differential transmission. Relying on a basis-expansion model for time- and frequency-selective (doubly selective) channels, we derive such a generalized block-differential (BD) codex and prove that it achieves maximum Doppler and multipath diversity gains, while affording low-complexity maximum-likelihood decoding. We further show that existing BD systems over frequency-selective or time-selective channels follow as special cases of our novel system. Simulations using the widely accepted Jakes model corroborate our theoretical analysis.     

Delta Modulation of Data Signals

This paper is an analytical study to determine the performance of single-integration delta-modulation(DeltaM)encoders with inputs which are various voice-band data signals. Signal-to-quantizing noise ratiosS/Nare calculated forDeltaMbit rates from 16 to 96 K bits/s. The input data signals studied are phase modulation at 1200 and 2400 bits/s, partial response at 4800 and 9600 bits/s, and single sideband at 4800 bits/s. Predictions of the performance of these modems, when transmitted over theDeltaMsystems, are based on the calculatedS/Nratios.     

A Performance Study of Delta Modulation Systems for Voiceband Data Signals

In this paper the performance of delta modulation (DM) systems have been studied by computer simulation when the input signal to the DM coder is a voiceband data signal. First, the parameter values of three DM systems, linear DM (LDM), constant factor DM (CFDM), and continuously variable slope DM (CVSD) has been optimized for 4800 bits/s differential phase shift keying (DPSK) signal. Then, the performance of the three DM systems have been studied for ideal and noisy channels. It has been found that the peak signal-to-quantization-noise ratio (SQNR) is nearly the same regardless of coding scheme used, but CFDM yields the widest dynamic range. In a noisy channel, however, CFDM is very sensitive to channel bit errors. Considering the overall performance, CVSD appears to be the best among the three DM systems studied. Also, the performances of DM's have been compared with those of PCM and DPCM systems. In addition, we have studied the effect of DM quantization noise on modem bit error rate by the Monte Carlo simulation method. It is possible to transmit a 4800 bits/s DPSK signal at a bit error rate below 10^-5by CVSD with the rate of 32 kbits/s.     

Average SER Performance of Distributed Antenna Systems Over Shadowed Generalized-Gamma Channels for Different Modulation Schemes

Recently, much attention has been drawn to distributed antenna systems (DAS), which are proposed to improve the performance of mobile communication systems. This paper focuses on the analysis of the average symbol error rate (SER) of DAS over a generic composite channel. Initially, a new composite channel model is considered for DAS, which is a mixture of path loss, lognormal shadowing and generalized-Gamma fast fading. This composite channel model is a generic model, which includes many well-known composite channel models as special cases. Based on the channel model, the cumulative distribution function of the output signal-to-noise ratio is obtained by employing selective transmission scheme. Moreover, by averaging the channel conditions and the positions of the MS in the cell, an approximate expression of the average SER is derived, which is a unified form of expression for many commonly used modulation schemes. Numerical results show that the derived expression of the average SER can provide sufficient precision for evaluating the SER performance of DAS under different modulation schemes.     

Differential Space-Time Modulation Using DAPSK Over Rician Fading Channels

This paper studies differential space-time modulation using diversity-encoded differential amplitude and phase shift keying (DAPSK) for the multiple-input multiple-output (MIMO) system over independent but not identically distributed (inid) time-correlated Rician fading channels. An asymptotic maximum likelihood (AML) receiver is developed for differentially detecting diversity-encoded DAPSK symbol signals by operating on two consecutive received symbol blocks sequentially. Based on Beaulieu’s convergent series, the bit error probability (BEP) upper bound is analyzed for the AML receiver over inid time-correlated Rician fading channels. Particularly, an approximate BEP upper bound of the AML receiver is also derived for inid time-invariant Rayleigh fading channels with large received signal-to-noise power ratios. By virtue of this approximate bound, a design criterion is developed to determine the appropriate diversity encoding coefficients for the proposed DAPSK MIMO system. Numerical and simulation results show that the AML receiver for diversity-encoded DAPSK is nearly optimum when the average received signal-to-noise power ratios are high and the channel is heavily correlated fading and can provide better error performance than conventional noncoherent MIMO systems when the effect of non-ideal transmit power amplification is taken into account.     

OFDM Scheme for Data Transmission Over Inductive Channels

Although OFDM has become a widely used method for transmitting digital data on multicarrier frequencies in wideband digital communication, this scheme has barely been used for near field inductive communication. Therefore, in this paper, OFDM is applied to three inductive communication systems including two, three and four node systems in order to transmit data over inductive channels. Furthermore, the channel responses for these three circuits are analysed in details to clarify the accurate inductive channels for data transmission that were defined alternatively in other papers. Besides, the effects of second neighbour interaction on inductive systems are also included in this work. More importantly, the OFDM scheme has been simulated in MATLAB and implemented in MATLAB SIMULINK in order to verify the method in either theory or practice. The BER versus SNR performances obtained by simulation and implementation are compared with the theoretical results to verify the data transmission errors.     

Packet Radio Performance Over Slow Rayleigh Fading Channels

Expressions for the throughput and average packet delay for a Pure-ALOHA single-hop packet radio system operating in slow Rayleigh fading are derived. For noncoherent frequency-shift-keying (NCFSK), an exact closed form expression is presented. For coherent phase-shift-keying (CPSK) an excellent approximation for large packet sizes is derived. This approximation technique is valid in general for other modulation schemes and for other fading channel statistical characterizations. The packet length which maximizes the useful data throughput in slow Rayleigh fading is found. The results of this investigation indicate that a packet radio system can be designed with a modest link margin for fading and achieve identical throughput performance over a nonfading channel and a fading channel with only a small increase in average packet delay for the fading channel.     

Bit Interleaved Time-Frequency Coded Modulation for OFDM Systems Over Time-Varying Channels

Bit Interleaved Time-Frequency Coded Modulation for OFDM Systems Over Time-Varying Channels Orthogonal frequency-division multiplexing (OFDM) is a promising technology in broadband wireless communications with its ability in transforming a frequency selective fading channel into multiple flat fading channels. However, the time-varying characteristics of wireless channels induce the loss of orthogonality among OFDM sub-carriers, which was generally considered harmful to system performance. In this paper, we propose a bit interleaved time–frequency coded modulation (BITFCM) scheme for OFDM to achieve both time and frequency diversity inherent in broadband time-varying channels. We will show that the time-varying characteristics of the channel are beneficial to system performance. Using the BITFCM scheme and for relatively low maximum normalized Doppler frequency, a reduced complexity Maximum Likelihood (ML) decoding approach is proposed to achieve good performance with low complexity as well. For high maximum normalized Doppler frequency, the inter-carrier interference (ICI) can be large and an error floor will be induced. To solve this problem, we propose two ICI mitigation schemes by taking advantage of the second order channel statistics and the complete channel information, respectively. It will be shown that both schemes can reduce the ICI significantly.     

Interference Analysis of Filtered Multitone Modulation Over Time-Varying Frequency- Selective Fading Channels

We consider in this paper filtered multitone (FMT) modulation over frequency-selective time-varying fading channels. Due to the phase and amplitude distortion introduced by the fading channel, not only is the orthogonality among different subcarriers destroyed, but also the perfect Nyquist sampling condition of the baseband matched filters is no longer valid. Consequently, interchannel, as well as intersymbol, interference will cause distortions to the transmitted signals. In this paper, the interference caused by the channel frequency selectivity and time variance is quantified by analyzing the demodulated signals at the receiver under several different fading-channel conditions. An analysis of the average carrier-to-interference (C/I) ratio of the FMT system is provided in order to demonstrate the underlying tradeoff between spectral efficiency and system performance. For comparison purposes with other multicarrier communication systems (or modulation techniques), the C/I ratio of the conventional orthogonal frequency-division multiplexing system is also provided and compared with that of the FMT system under the same channel conditions and spectral efficiency. Finally, numerical and simulation results are given that confirm the C/I ratio results obtained     

Bit Error Probability of Trellis-Coded Quadrature Amplitude Modulation Over Cross-Coupled Multidimensional Channels

Convolutionally encodedM-ary quadrature amplitude modulation (M-QAM) systems operated over multidimensional channels, for example dual-polarized radio systems, are considered in this paper. We have derived upper bounds on the average bit-error probability for 4QAM (QPSK) with conventional convolutional coding by means of a truncated union bound technique and averaging over the cross-polarization interference by means of the method of moments. By modifying this technique, we have found approximate upper bounds on the average biterror probability for bandwidth efficient trellis-coded QAM systems. This is an extension of our previous work [1] that was based on one dominating error event probability as a performance measure. Our evaluations seem to indicate that bandwidth efficient trellis-codedMQAM schemes offer much larger coding gains in an interference environment, e.g., a cross-coupled interference channel, than in a Gaussian noise channel. In general, our findings point out that optimum codes for a Gaussian channel are not optimum when applied in an interference environment. We note that a rate 1/2 convolutional code for example, with a code memory greater than two, if applied to two of the bits in each signal point representation, can be utilized with a simple decoder to greatly improve the performance of a QAM signal in interference. Also, we have introduced a new concept referred to as dualchannel polarization hopping in this paper which can improve the system performance significantly for systems with nonsymmetrical interference.     

Buffer Control for Transmission of Blocked Data Over Fading Channels

Since fading channels are characterized by frequent signal dropouts which are long compared to packet duration, substantial buffer space must be provided at both ends of the link. Systems which rely on selective, on/off transmission to achieve low bit error rates are seriously affected by the special conditions which must be imposed on them to prevent buffer overflow or underflow. This effect can be reduced by a method of buffer control developed and analyzed in this paper, in which the average transmission rate is varied as a function of queue length in an attempt to keep the queue away from the ends of the buffer. It is shown that buffer control provides the same improvement in average error probability as does doubling the buffer size, but without the associated doubled storage cost and doubled delay. In order to simplify the analysis and keep the discussion relevant, the system is oriented to transmission of fixed length blocks or packets.     

Achievable Performance of Orthogonal STBC Over Spatially Correlated Rician Channels

The effect of spatial correlation on the performance of orthogonal space-time block codes (OSTBCs) over multiple-input-multiple-output (MIMO) Rician fading channels is studied. Asymptotic error-rate formulas for OSTBC with high average signal-to-noise ratios (ASNRs) over arbitrarily correlated Rician MIMO channels are derived in terms of the diversity and coding gains. Our results show that, in correlated fading, the phase vector phi of the channel line-of-sight (LOS) components affects the effective Rice K-factor at the OSTBC receiver output and, hence, may result in a coding gain that is significantly higher than that for independent Rician MIMO channels. Furthermore, when the channel covariance matrix is rank deficient and under some additional mild conditions, the error and outage probabilities of OSTBC achieve those in a nonfading additive-white-Gaussian-noise channel. For both cases of full-rank and rank-deficient channel covariance matrices, analytical expressions of optimal and worst case phase vectors phi, and exact upper and lower bounds of OSTBC performance are derived. These results provide new insights into the achievable performance of OSTBC over correlated Rician MIMO channels and, if incorporated into future multiple antenna systems design, will bring about significant performance enhancement     

SER Performance of Amplify-and-Forward Cooperative Diversity Over Asymmetric Fading Channels

In this paper, the performance of amplify-and-forward (AF) cooperative diversity is analyzed over asymmetric fading channels. The source–relay and the relay–destination links experience Rayleigh fading while the source–destination link is subject to generalized Gamma fading. First, the probability density function (PDF) and the moment generating function (MGF) of the source–relay–destination link and the MGF of the source–destination link are derived. Then, the symbol error rate (SER) is determined based on the MGF of the total end-to-end signal-to-noise ratio (SNR). Moreover, the SER performance of N-relay assisted AF cooperative diversity is illustrated for M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM). Based on the derived MGF expressions, the numerical results are obtained by varying the modulation types and channel parameters for different scenarios.     

On the Performance of Energy-Division Multiple Access Over Fading Channels

In this paper we consider a multiple-access scheme in which different users share the same bandwidth and the same pulse, and are discriminated at the receiver on the basis of the received energy using successive decoding. More specifically, we extend the performance analysis from the case of additive white Gaussian noise channels (presented in a previous work Salvo Rossi in Wirel Pers Commun, in press) to the case of fading channels. The presence of channel coefficients introduces a new degree of freedom in the transceiver design: unlike the AWGN case, different ordering among the users provides different transmitted energy, thus different overall system performance. Optimal ordering, in terms of minimum transmitted energy, is derived analytically. Analytical and numerical results, in terms of bit error rate and normalized throughput, are derived for performance evaluation in fading environments with optimal ordering exhibiting significant gains w.r.t. static ordering.     

Performance Analysis of Blind-Adaptive-Subspace Multiuser Detectors Over Multipath Fading Channels

Perturbation analyses for various kinds of blind-adaptive-subspace multiuser detectors are presented in this paper. Closed-form expressions are derived for the minimum-mean-square-error detector, zero-forcing detector, and group-blind detector in terms of output signal-to-interference-plus-noise ratio and bit-error rate over a multipath fading channel. Numerical results show that the analytical results match well with the simulation results for both static and dynamic environments. Furthermore, the proposed analytical results can be treated as performance bounds for other blind-adaptive singular-value-decomposition-based subspace multiuser detectors