Showing papers on "Phase-shift keying published in 1994"

Analysis of a simple successive interference cancellation scheme in a DS/CDMA system

Abstract: Compensating for near/far effects is critical for satisfactory performance of DS/CDMA systems. So far, practical systems have used power control to overcome fading and near/far effects. Another approach, which has a fundamental potential in not only eliminating near/far effects but also in substantially raising the capacity, is multiuser detection and interference cancellation. Various optimal and suboptimal schemes have been investigated. Most of these schemes, however, get too complex even for relatively simple systems and rely on good channel estimates. For interference cancellation, estimation of channel parameters (viz. received amplitude and phase) is important. We analyze a simple successive interference cancellation scheme for coherent BPSK modulation, where the parameter estimation is done using the output of a linear correlator. We then extend the analysis for a noncoherent modulation scheme, namely M-ary orthogonal modulation. For the noncoherent case, the needed information on both the amplitude and phase is obtained from the correlator output. The performance of the IC scheme along with multipath diversity combining is studied. >

Maximum-likelihood differential detection of uncoded and trellis coded amplitude phase modulation over AWGN and fading channels/spl minus/metrics and performance

Abstract: This paper derives metrics for maximum-likelihood differential detection of uncoded and trellis coded MPSK and QAM transmitted over Rayleigh and Rician fading channels. Receiver structures based on these metrics are proposed and their error probability performance analyzed and/or simulated. The results represent a generalization of the notion of multiple symbol differential detection, previously introduced by the authors for MPSK over an AWGN, to the fading channel and other modulations. For the coded cases, ideal interleaving/deinterleaving is assumed and furthermore the presence or absence of channel state information. An interesting side result is that for a constant envelope modulation transmitted over a fading channel with unknown but rapidly-varying phase error (the other extreme to the slowly-varying phase error case normally assumed for differential detection), under certain practical assumptions, it is shown that the optimum receiver is of the limiter-discriminator type. >

Adaptive trellis-coded multiple-phase-shift keying for Rayleigh fading channels

Abstract: An adaptive scheme for trellis-coded modulation of MPSK signals, called adaptive trellis-coded multiple-phaseshift keying (ATCMPSK), is proposed for slowly Rayleigh fading channels. The adaptive scheme employs a slightly modified rate 1/2 convolutional encoder and the corresponding Viterbi decoder to realize a family of codes of different rates which are employed according to channel conditions. During poor channel conditions, trellis-coded QPSK (TCQPSK) together with repetition schemes are employed. As channel conditions improve, higher rate schemes such as trellis-coded 16 PSK are used. An interleaving/ deinterleaving method suitable for the adaptive scheme is proposed. Theoretical bounds for the error performance and an exact expression for the throughput of the proposed adaptive scheme are derived, and are compared against simulation results. Simulations have been performed to measure the performance of the scheme for different parameters and some nonideal conditions. It is shown that ATCMPSK results in considerable improvement in bit-error-rate (BER) performance of MPSK signals. Under ideal conditions, gains in the range of 3-20 dB are achieved over conventional fixed rate pragmatic trellis-coded schemes.

Performance analysis of DS/CDMA with noncoherent M-ary orthogonal modulation in multipath fading channels

Abstract: The performance of a DS/CDMA system using M-ary orthogonal modulation with noncoherent demodulation is evaluated. The system operates in a multipath fading channel. A RAKE receiver structure with equal gain combining is used for demodulation. An approximation to the bit error probability is given which depends only on the first- and second-order moments of the multipath energies. The analysis results are compared with the results from computer simulations. It is seen that the approximation is accurate for multipath energies with realistic coefficient of variation. The system performance is also evaluated in terms of the capacity, which is defined as the number of users that can be supported at a given bit error probability. The approximation is used to evaluate the capacity reductions due to power variations caused by multipath fading. >

Optimal decoding of coded PSK and QAM signals in correlated fast fading channels and AWGN: a combined envelope, multiple differential and coherent detection approach

Abstract: The maximum likelihood sequence estimator for the reception of coded digital phase modulated signals with single or multiamplitude constellations, transmitted over a multiplicative, frequency-nonselective (i.e., flat) correlated fast fading Rayleigh or Rician channel and corrupted by additive white Gaussian noise (AWGN), is derived. Due to this correlation, the errors caused by fading tend to occur in bursts. In the analysis, no assumption simplifying the problem is made. For fast fading the authors consider the most general case where both phase and amplitude distortion resulting from the fading process could change significantly and thus cannot be assumed to be constant over a number of transmitted symbols. It is shown that the estimator's hardware structure consists of a combination of envelope, multiple differential and coherent detectors. With multiple differential detectors they define a receiver structure consisting of a combination of more than one distinct differential detectors each of them employing a progressively increasing (by the symbol duration) time-delay element. The outputs of these detectors are jointly processed by means of an algorithm which is presented in a recursive form. The derivation of this new receiver is general enough to accommodate trellis coded phase shift keying (PSK) and quadrature amplitude modulated (QAM) systems. Differentially encoded signals, such as the /spl pi//4-shift differential quadrature phase shift keying (DQPSK) scheme can also be incorporated. In order to reduce the overall receiver implementation complexity, several reduced complexity, near-optimal versions of the algorithm are presented. These reduced complexity receivers are based on the use of only a few multiple differential detectors. Performance evaluation results for reduced complexity trellis coded /spl pi//4-shift DQPSK, /spl pi//4-shift 8-DQAM (differential quadrature amplitude modulation) and 8-DPSK (differential phase shift keying) systems have demonstrated that the proposed receivers significantly reduce the error floors caused by fading. >

A six-port direct digital millimeter wave receiver

Abstract: A novel approach is proposed for direct demodulation of various digitally modulated signals at microwave/millimeter wave frequencies using a six-port phase/frequency discriminator (SPFD). The proposed six-port direct digital receiver is capable of handling PSK and QAM as well as their varieties. Preliminary measurements on demodulation of DBPSK signals at 26.5 GHz, 33 GHz and 40 GHz have revealed great potential of this new receiver. >

Markov characterization of digital fading mobile VHF channels

Abstract: We apply techniques for the modeling of error sequences on digital communication channels to results of experiments undertaken on mobile VHF channels. The experiments were carried out using four different modulation schemes at some of the different standardized signaling rates. The modulation schemes used were: FSK @ 300 baud, DPSK @ 1200 baud, QPSK @ 1200 baud, and 8-ary PSK @ 1600 baud, and in each case, subcarrier modulation was used. The experiments were undertaken for urban as well as freeway environments. Fritchman-partitioned Markov chain models were derived throughout, and from the models, block error probability distributions were derived. These block error probability distributions or P(m,n) give the probability that a block of n bits will contain exactly m errors. We present P(/spl ges/m,n) for 7-, 15-, 31-, 63-, 127-, and 255-b blocks, for the above-mentioned modulation schemes, in the mobile VHF environments mentioned. P(/spl ges/m,n) denotes the probability that at least m errors will occur in a block of n bits. Furthermore, the P(/spl ges/m,n) information presented here, should give some indication of the performance to be expected from block error-correcting schemes. >

Multilevel polarization shift keying: optimum receiver structure and performance evaluation

Abstract: Multilevel digital coherent optical modulation schemes based on the state of polarization of a fully polarized lightwave are proposed and analyzed. Based on the complete statistical characterization of the Stokes parameters, extracted through appropriate signal processing in the presence of shot and additive Gaussian noise, the optimum maximum likelihood receiver operating symbol by symbol is derived. The exact performance in terms of the average symbol error probability is found. Optimum constellations for the case of equipower 4, 8, 16 and 32 signals are found on the basis of the minimization of the error probability for a given average power. Their performance turns out to be promising as compared to other standard modulation techniques. The spectral analysis of polarization modulated signals is presented. A new receiver structure, which solves the problem of the excess penalties incurred in the presence of channel dichroism, is proposed and analyzed. >

Optical transmission of narrow-band millimeter-wave signals by resonant modulation of monolithic semiconductor lasers

Abstract: We demonstrate the use of monolithic semiconductor lasers as efficient narrow-band (20-300 MHz) millimeter-wave optical transmitters at a cavity round-trip resonant frequency of 45 GHz. The modulation efficiency within the passband is >10 dB above that of a conventional laser diode at frequencies below relaxation oscillation. At an input RF drive power of 10 dBm, a carrier-to-noise ratio of 90 dB (1 Hz) is achieved. We also present a system demonstration of this technique in which 50 Mb/s digital data is transmitted at a 45 GHz subcarrier over optical fiber. This is the highest subcarrier frequency transmission reported to date. >

Symbol synchronizer using modified early/punctual/late gate technique

Abstract: A method and apparatus for synchronizing symbol timing for a QPSK demodulator. A matched filter pair outputs respective "early-punctual-late" signals. The early and late signals are input to a symbol synchronizing estimator that produces an interpolation control signal used by the filters to synchronize the symbol timing to the sample timing. The punctual signal is output as an information bearing signal representing the received inphase and quadrature signals. The matched filters are interpolating matched filters. The symbol synchronizing estimator normalizes the early and late signals in a manner that allow the demodulator to "flywheel" over signals having a low signal to noise ratio below a predetermined threshold.

An adaptive direct conversion transmitter

Abstract: An adaptive direct conversion transmitter is presented, in which adjacent channel power measurements are used to simultaneously compensate for both power amplifier (PA) nonlinearity and quadrature modulator (QM) errors. Three main contributions are given. First, analysis is presented which shows that adjacent channel power is a quadratic function of power amplifier nonlinearity as well as quadrature modulator errors. Quadrature modulator errors are gain imbalance, phase splitter error, and DC offset errors. Second, a new optimization method is given which uses the predicted adjacent channel power surface to obtain fast convergence. Third, simulation and measured results are given for an adaptive system using offset QPSK modulation. The measured results confirm the analysis and show that a 20-dB reduction in adjacent channel power is achievable. In general, the adaptive direct conversion transmitter has applications in any system where power efficiency and spectral efficiency are important, and allows the use of smaller more efficient power amplifiers in a direct conversion architecture. >

Microdiversity on Rician Fading Channels

Abstract: formats, coherent phase shift keying (CPSK) and -noncoherent frequency shift keying (NCFSK). Results using both maximal ratio combining (MRC) and selection diversity combining (SC) are presented for comparison. Our results show that from a feasibility and practical tradeoffs point of view, the performance of an EG combiner may be as good as that of a MR combiner. The effects of gain unbalance between branches of the EG combiner on the probability distribution of SNR and on the bit error rates are also investigated. The Rician fading model may be used to model both the microcellular environment and the mobile satellite fading channel. Hence, the results of this paper may be useful in both of these areas. Furthermore, in the development of the analysis, we present an efficient method for computing the distribution of sums of Rich random variables. This may be useful for other problems involving Rician fading. The suitability of modeling a Rician fading environment by a properly chosen Nakagami model is examined. A formula for determining the corresponding values of Rician parameter K and Nakagami parameter m is also assessed.

Comparison of hybrid FDMA/CDMA systems in frequency selective Rayleigh fading

Abstract: A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signalling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal. >

Modulation and demodulation of plural channels using analog and digital components

Abstract: In the modulation and demodulation of a plurality of frequency separated channels on a radio frequency carrier by digitally coded speech or data, the speech or data is modulated on a digitally generated sub-carrier by quadrature phase shift keying and after conversion to analogue form the modulated sub-carrier is mixed with an RF carrier of fixed frequency to produce the signal for transmission. Reception and demodulation of the transmitted signal are effected by the reverse processes. Frequency multiplication is effected after the digital to analogue conversion by producing analogue samples of very short duration and applying them to a suitable filter. Frequency division during the analogue to digital conversion is effected by sub-sampling.

Adaptive modulation/TDMA scheme for personal multimedia communication systems

Abstract: The development of digital land mobile communication techniques makes it possible to use most of the modulation techniques. This paper proposes an adaptive modulation/TDMA scheme to achieve high capacity personal multimedia communication systems. TDMA is used to cope with various bit rate for multimedia services, and the modulation scheme is selected from 1/4-rate QPSK, 1/2-rate QPSK, QPSK, 16QAM and 64QAM according to the received C/I/sub c/ (power ratio of the desired signal to the co-channel interference) and the delay spread. Computer simulation confirms that the proposed system can achieve 3.5 times higher spectral efficiency than that of the conventional QPSK systems at the outage probability of 10%, and the proposed system is also effective to improve the delay spread immunity.

Optimum linear diversity receivers for mobile communications

Abstract: This paper analyzes and quantifies the performance of a space diversity combining receiver operating in a mobile radio environment with quaternary phase-shift-keying transmission, frequency-selective Rayleigh multipath fading, and cochannel interference (CCI) The receiver has an infinite-length filter in each branch of the diversity combiner, and the filters are optimized jointly according to the minimum mean-square-error criterion The link bit error rate is estimated accurately using Metzger's (1987) algorithm, which approximates the probability density function of the combined intersymbol interference (ISI) and CCI The authors present numerical performance results showing the influence of the diversity order, the number of dominant cochannel interferers, the multipath channel's delay spectrum, and the root-mean-square delay spread The results show that, under certain conditions, the optimum linear receiver can almost completely eliminate all ISI and CCI while providing near-optimum noise filtering >

Performance analysis of a multilevel coded modulation system

Abstract: A modified version of the multilevel coded modulation scheme of Imai and Hirakawa (1977) is presented and analyzed. In the transmitter, the outputs of the component codes are bit interleaved prior to mapping into 8-PSK channel signals. A multistage receiver is considered, in which the output amplitudes of the Gaussian channel are soft limited before entering the second and third stage decoders. Upper bounds and Gaussian approximations for the bit error probability of every component code, which take into account errors in previously decoded stages, are presented. Aided by a comprehensive computer simulation, it is demonstrated in a specific example that the addition of the interleaver and soft limiter in the third stage improves its performance by 1.1 dB at a bit error probability of 10/sup /spl minus/5/, and that the multilevel scheme improves on an Ungerboeck's code with the same decoding complexity. The rate selection of the component codes is also considered and a simple selection rule, based on information theoretic arguments, is provided. >

Method for the transmission of reference signals in an OFDM system

Abstract: Various methods, such as OFDM, QPSK and QAM modulation, are used for the terrestrial transmission of digital radio signals. One of the main problems with such systems is synchronization when a receiver is switched on or tuned into another channel. The invention calls for the power of the signal during part of the length of the synchronization symbol to be fixed at zero or almost zero. During another part of the time, a modulation can be utilized which differs from the modulation used in the rest of the signal and which includes at least one sequence with optimun auto-correlation characteristics, e.g. a number of CAZAC sequences or a bit sequence modulated on a centrally positioned carrier, the interval between the bits in the sequence or sequences being equal to the time intervals used in scanning the OFDM symbols or a multiple of these time intervals, or half the effective length of the symbol is used with only every other carrier. As a result, only a single symbol is necessary for synchronisation. In a receiver, rough synchronisation is carried out at zero power using the part-symbol, followed by processing of the received signal component of the synchronisation symbol and follow-up control of the oscillator.

Achievable performance over the correlated Rician channel

Abstract: The correlated Rician channel is a useful model for a slowly fading channel, in which the complex fading process is composed of two quadrature Gaussian processes with a given autocorrelation function. For slow fading the correlation between adjacent symbols is relatively high. The authors investigate the achievable error probabilities over the channel, employing coherent detection and ideal side information on the realization of the fading processes at the receiver. An underlying decoding delay constraint which precludes the use of (ideal) interleaving is assumed. Coded BPSK performance is addressed both with and without the piecewise constant approximation (according to which the fading value remains constant during the symbol duration). For the latter case, that is no piecewise constant approximation, the analysis relies on the Fredholm determinant associated with the fading process autocorrelation function. The authors focus on the exponentially correlated channel. The "worst case" pairs of codewords are identified. The exponential behavior of the error probability with random coding (and i.i.d. Gaussian inputs) is analyzed, and the behavior of the cut-off rate and capacity is addressed. The results enhance the insight to the effect of the basic parameters governing the performance and these are examined in view of previous works and compared to relevant performance results for the block-fading channel model. >

Upper bounds on the bit error rate of optimum combining in wireless systems

Abstract: The paper presents upper bounds on the bit error rate (BER) of optimum combining in wireless systems with multiple cochannel interferers in a Rayleigh fading environment. The authors present closed-form expressions for the upper bound on the bit error rate with optimum combining, for any number of antennas and interferers, with coherent detection of BPSK and QAM signals, and differential detection of DPSK. They also present bounds on the performance gain of optimum combining over maximal ratio combining. These bounds are asymptotically tight with decreasing BER, and results show that the asymptotic gain is within 2 dB of the gain as determined by computer simulation for a variety of cases at a 10/sup -3/ BER. The closed-form expressions for the bound permit rapid calculation of the improvement with optimum combining for any number of interferers and antennas, as compared with the cpu hours previously required by Monte Carlo simulation. Thus, these bounds allow calculation of the performance of optimum combining under a variety of conditions where it was not possible previously, including analysis of the outage probability with shadow fading and the combined effect of adaptive arrays and dynamic channel assignment in mobile radio systems. >

Multiuser detection scheme based on canceling cochannel interference for MFSK/FH-SSMA system

Abstract: The paper proposes and investigates a multiuser detection scheme baseEEon canceling cochannel interference (CCI) to improve spectral efficiency or to increase user capacity in an MFSK (multilevel frequency shift keying)/FH-SSMA (frequency hopping-spread spectrum multiple access) system. In the MFSK/FH-SSMA system, an address code is employed as a hopping sequence to hop the carrier frequency in MFSK. In the proposed scheme, it is assumed that the address codes of all users in MFSK/FH-SSMA are known. Then, candidates of the transmitted vector which are regenerated from the time-frequency matrices decoded by all the users' address codes are added with logical OR operation to produce candidates of the received matrix. The candidates of the received matrix are utilized in order to estimate a pattern of all users' data symbols which has the most number of coincident entries with the received matrix. Its BER (bit error rate) performance is evaluated by theoretical analysis and computer simulation in order to show the improvement of user capacity. Moreover, the authors investigate a hybrid scheme combining a multiuser detection scheme and the decoding scheme of an error-correcting code for the coded MFSK/FH-SSMA system. >

Multi-Carrier CDMA in an Indoor Wireless Radio Channel

Abstract: Narrowband communications has the desirable property of being relatively immune to intersymbol interference but has the undesirable property of being susceptible to flat fading. With conventional Division Multiple Access-Spread Spectrum (CDMA-SS), resistance is achieved by spreading the signal energy over a larger ba. However, the process of providing resistance to deep fade signal is affected by delay spreads to a greater extent, and experiences considerable inter-chip interference. Multi-Carrier CDMA (MC-CDMA) addresses the issue of how to spread the signal bandwidth without increasing the adverse effects of the delay spread. With MC-CDMA, the data symbol is transmitted over many phase-shift keying (BPSK) modulated subcarriers. The scope of this project involves investigating the performance of this modulation / multiple-access technique in an indoor wireless network.

for Satellite Communication Systems

Abstract: List of Figures 3List of Tables 51 INTRODUCTION 62 MODEM/CODEC THEORY lU2.1 MODEM Theory 102.1.1 BPSK (Binary Phase Shift Keying) i02.1.2 QPSK (Quadrature Phase Shift Keying) 122.1.30QPSK (Offset QPSK) 152.1.4 MSK (Minimum Shift Keying) 162.2 CODEC Theory 202.2.1 Convolutional Encoder 202.2.2 Viterbi Decoder 213 SYSTEM DESIGN 233.1 System Specifications 233.2 System Interfazes 243.3 IF Frequency 253.4 System Structure 264 TRANSMITTER DESIGN 294.1 Modulator Design 294.1.1 Q2334 Direct Digital Synthesizer 304.1.2 Modulator Design. 334.2 Encoder/Decoder Design 384.2.1 Parallel and Serial Data Modes 394.2.2 Synchronization Status Monitor Design 404.2.3 Monitoring Channel Bit Error Rate (BER) 424.2.4 The Other Considerations 434.3 D / A Converter 43

An adaptive maximum likelihood receiver for correlated Rayleigh-fading channels

Abstract: The paper develops a receiver structure for random Gaussian signals in additive noise based on the classic maximum likelihood (M-L), estimator-correlator derivation of Kailath [1960], and applies it to differential phase shift keying (DPSK) on the correlated Rayleigh-fading channel. It is shown to lower the error floor found in the performance of conventional DPSK receivers by orders of magnitude. In addition, the maximum-likelihood procedure is shown to make uncorrelated symbol decisions. The performance of both conventional and optimal receivers, which require knowledge of the channel statistics, is examined analytically. A recursive, channel-adaptive version of the optimal receiver, utilizing decision feedback to estimate the channel statistics, is developed. Its simulated performance shows no penalty compared to theoretical calculations which require explicit knowledge of the channel statistics. >

A coherent spread-spectrum diversity-receiver with AFC for multipath fading channels

Abstract: A direct-sequence spread-spectrum (DSSS) coherent RAKE-receiver demodulating M-ary phase-shift keyed (MPSK) signals is presented for microcellular communication systems with frequency-selective fading channels. Since the channel fading is due to multipath propagation, the received signal contains multipath or time diversity which is resolved at the receiver by a RAKE-structure. The maximum-likelihood (ML) rule is invoked to estimate the phases, and the combining factors of the receiving paths, as well as the frequency offset between the carrier of the receiver and the transmitter. The ML algorithm is simplified by using decision-directed feedback. The resulting digital algorithms for synchronization, data demodulation, and frequency error detection (FED) are well suited for digital implementation because of their fairly low numerical complexity. Analytical expressions of the bit error probability versus signal-to-noise ratio (SNR) and versus frequency offset are presented. In addition, experimental results using Monte-Carlo simulations have also been carried out. The results show a negligible influence of the decision-direction above a certain SNR, as well as a "robust" transient behavior of the phase estimation and the automatic frequency control (AFC) scheme. >

AFC circuit for QPSK demodulator

Abstract: AFC circuit for QPSK demodulator including, a circuit for obtaining quadrature related detection signals by multiplying a modulated input signal with quadrature related local oscillation frequency signals from a quadrature phase local oscillator, digital converter for converting the detection signals into corresponding digital signals by sampling them with quadrature related clocks which have a frequency two times higher than a symbol rate of the input signal, frequency error detecter for detecting a frequency error between the quadrature related digital signals using a symbol timing sample value and a symbol intermediate timing sample value in the converted digital signals, first validity determinator for determining whether the frequency error signal is valid or not through a detection of the pattern of the modulated input signal from sample values before and after the symbol timing so as to result a first validity signal, second validity determinator for deetermining whether the frequency error signal is valid or not through a detection of an absolute sample value of the symbol intermediate timing so as to result a second validity signal, and valid frequency error extractor for extracting the frequency error signal as a frequency control signal for controlling the oscillation frequency of the local oscillator when the frequency error signal has been proved to be valid by the first and the second validity signals.

Higher-order differential phase shift keyed modulation

Abstract: Advanced modulation/demodulation techniques which are robust in the presence of phase and frequency uncertainties continue to be of interest to communication engineers. The authors are particularly interested in techniques which accommodate slow channel phase and frequency variations with minimal performance degradation and which alleviate the need for phase and frequency tracking loops in the receiver. They investigate the performance sensitivity to frequency offsets of a modulation technique known as binary double differential phase shift keying (DDPSK) and compare it to that of classical binary differential phase shift keying (DPSK). They also generalize their analytical results to include n/sup -th/ order, M-ary DPSK. The DDPSK (n=2) technique was first introduced in the Russian literature circa 1972 and was studied more thoroughly in the late 1970s by Pent and Okunev. They present an expression for the symbol error probability that is easy to derive and to evaluate numerically. They also present graphical results that establish when, as a function of the signal energy-to-noise ratio and normalized frequency offset, binary DDPSK is preferable to binary DPSK with respect to performance in additive white Gaussian noise. Finally, they provide insight into the optimum receiver from a detection theory viewpoint. >

Multipath propagation effects on a CDMA cellular system

Abstract: The performance of the reverse link of a code division multiple access cellular system is evaluated. At the base station, the signal from each user is demodulated by a coherent BPSK RAKE receiver. Parameters for the model of the impulse response of the channel were taken from measurements of the digital cellular channel in Toronto. The signal-to-noise ratio (SNR) for a received signal is used to measure the performance of the reverse link. The variation in SNR of received signals at the base station should be as small as possible to reduce interference in the network. A power control scheme to lower the variation in SNR of the received signals is analyzed. The effects of lowering the bandwidth of the transmitted signal were also investigated. >

Tight bounds on the error probability of coded modulation schemes in Rayleigh fading channels

Abstract: This paper presents a tight upper bound on the bit error performance of coded modulation schemes in Rayleigh fading channels. Upper and lower bounds on the pairwise error probability are first derived. The upper bound is then expressed in a product form to be used with the transfer function bounding technique. This upper bound has the same simplicity as the union-Chernoff bound while providing closer results to the exact expression. Examples for the case of four-state and eight-state TCM 8PSK schemes are also given to illustrate the tightness and the application of this upper bound. >

A comparative analysis of linear multiuser detectors for fading multipath channels

Abstract: In this paper, we compare two linear multiuser receivers for synchronous CDMA frequency-selective Rayleigh fading channels. The first receiver consists of a bank of matched filters followed by a linear transformation and an optimal combiner for each user. The second consists of a bank of RAKE receivers followed by a linear transformation. We consider receivers for both coherent and differentially coherent PSK demodulation. While the conventional single-user receiver's performance is severely limited by near-far effects in the multiuser environment, both of these multiuser receivers mitigate the near-far problem and provide significant performance gains for moderate to high SNRs. It is shown that the second receiver has a uniformly lower error rate than the first and that its performance gains relative to the first increase as the number of users and received multipaths increases.