Showing papers on "Phase-shift keying published in 1995"

Cdma: Principles of Spread Spectrum Communication

Abstract: 1. Introduction. Definition and Purpose. Basic Limitations of the Conventional Approach. Spread Spectrum Principles. Organization of the Book. 2. Random and Pseudorandom Signal Generation. Purpose. Pseudorandom Sequences. Maximal Length Linear Shift Register Sequences. Randomness Properties of MLSR Sequences. Conclusion. Generating Pseudorandom Signals (Pseudonoise) from Pseudorandom Sequences. First- and Second-Order Statistics of Demodulator Output in Multiple Access Interference. Statistics for QPSK Modulation by Pseudorandom Sequences. Examples. Bound for Bandlimited Spectrum. Error Probability for BPSK or QPSK with Constant Signals in Additive Gaussian Noise and Interference. Appendix 2A: Optimum Receiver Filter for Bandlimited Spectrum. 3. Synchronization of Pseudorandom Signals. Purpose. Acquisition of Pseudorandom Signal Timing. Hypothesis Testing for BPSK Spreading. Hypothesis Testing for QPSK Spreading. Effect of Frequency Error. Additional Degradation When N is Much Less Than One Period. Detection and False Alarm Probabilities. Fixed Signals in Gaussian Noise (L=1). Fixed Signals in Gaussian Noise with Postdetection Integration (L>1). Rayleigh Fading Signals (L>/=1). The Search Procedure and Acquisition Time. Single-Pass Serial Search (Simplified). Single-Pass Serial Search (Complete). Multiple Dwell Serial Search. Time Tracking of Pseudorandom Signals. Early-Late Gate Measurement Statistics. Time Tracking Loop. Carrier Synchronization. Appendix 3A: Likelihood Functions and Probability Expressions. Bayes and Neyman-Pearson Hypothesis Testing. Coherent Reception in Additive White Gaussian Noise. Noncoherent Reception in AWGN for Unfaded Signals. Noncoherent Reception of Multiple Independent Observations of Unfaded Signals in AWGN. Noncoherent Reception of Rayleigh-Faded Signals in AWGN. 4. Modulation and Demodulation of Spread Spectrum Signals in Multipath and Multiple Access Interference. Purpose. Chernoff and Battacharyya Bounds. Bounds for Gaussian Noise Channel. Chernoff Bound for Time-Synchronous Multiple Access Interference with BPSK Spreading. Chernoff Bound for Time-Synchronous Multiple Access Interference with QPSK Spreading. Improving the Chernoff Bound by a Factor of 2. Multipath Propagation: Signal Structure and Exploitation. Pilot-Aided Coherent Multipath Demodulation. Chernoff Bounds on Error Probability for Coherent Demodulation with Known Path Parameters. Rayleigh and Rician Fading Multipath Components. Noncoherent Reception. Quasi-optimum Noncoherent Multipath Reception for M-ary Orthogonal Modulation. Performance Bounds. Search Performance for Noncoherent Orthogonal M-ary Demodulators. Power Measurement and Control for Noncoherent Orthogonal M-ary Demodulators. Power Control Loop Performance. Power Control Implications. Appendix 4A: Chernoff Bound with Imperfect Parameter Estimates. 5. Coding and Interleaving. Purpose. Interleaving to Achieve Diversity. Forward Error Control Coding - Another Means to Exploit Redundancy. Convolutional Code Structure. Maximum Likelihood Decoder - Viterbi Algorithm. Generalization of the Preceding Example. Convolutional Code Performance Evaluation. Error Probability for Tailed-off Block. Bit Error Probability. Generalizations of Error Probability Computation. Catastrophic Codes. Generalization to Arbitrary Memoryless Channels - Coherent and Noncoherent. Error Bounds for Binary-Input, Output-Symmetric Channels with Integer Metrics. A Near-Optimal Class of Codes for Coherent Spread Spectrum Multiple Access. Implementation. Decoder Implementation. Generating Function and Performance. Performance Comparison and Applicability. Orthogonal Convolutional Codes for Noncoherent Demodulation of Rayleigh Fading Signals. Implementation. Performance for L-Path Rayleigh Fading. Conclusions and Caveats. Appendix 5A: Improved Bounds for Symmetric Memoryless Channels and the AWGN Channel. Appendix 5B: Upper Bound on Free Distance of Rate 1/n Convolutional Codes. 6. Capacity, Coverage, and Control of Spread Spectrum Multiple Access Networks. General. Reverse Link Power Control. Multiple Cell Pilot Tracking and Soft Handoff. Other-Cell Interference. Propagation Model. Single-Cell Reception - Hard Handoff. Soft Handoff Reception by the Better of the Two Nearest Cells. Soft Handoff Reception by the Best of Multiple Cells. Cell Coverage Issues with Hard and Soft Handoff. Hard Handoff. Soft Handoff. Erlang Capacity of Reverse Links. Erlang Capacity for Conventional Assigned-Slot Multiple Access. Spread Spectrum Multiple Access Outage - Single Cell and Perfect Power Control. Outage with Multiple-Cell Interference. Outage with Imperfect Power Control. An Approximate Explicit Formula for Capacity with Imperfect Power Control. Designing for Minimum Transmitted Power. Capacity Requirements for Initial Accesses. Erlang Capacity of Forward Links. Forward Link Power Allocation. Soft Handoff Impact on Forward Link. Orthogonal Signals for Same-Cell Users. Interference Reduction with Multisectored and Distributed Antennas. Interference Cancellation. Epilogue. References and Bibliography. Index.

Performance of maximal-ratio diversity systems in a correlated Nakagami-fading environment

Abstract: The bit error rate (BER) performance of an M-branch maximal-ratio combiner (MRC) for the detection of signals in a correlated Nakagami-fading channel is analyzed. Coherent and incoherent detection of frequency shift-keying (FSK) and phase-shift keying (PSK) signals are considered. It is assumed that the fading parameters in each diversity branch are identical. The effect of correlation is studied by assuming two types of correlation among the quadrature components of the signals in each diversity branch. Outage probabilities are also calculated for the digital radio communication systems via the correlated fading channel. >

Wireless Digital Communications: Modulation and Spread Spectrum Applications

Abstract: 1. Introduction to Wireless, Cellular, Digital, PCS-Mobile Radio. Summary. Mobile Communications: Evolution and Fundamentals. International Mobile Satellite, Low Earth Orbit, and Medium Altitude Orbit Satellite Frequency Bands. Personal Communication Systems (PCS) Universal Digital PCS. Standards: The Importance of National and International Standardization. Mobile Personal Computers (PC) and Personal Communication Systems (PCS). U.S. and World Cellular Markets. 2. Speech Coding for Wireless Systems Applications. Introduction to Digital Signal Processing (DSP) Techniques in Wireless Telephone and Broadcast Systems. Speech Coding Techniques for Audio and Voice. American and European Speech Codes. 3. Radio Propagation and Cellular Engineering Concepts. Introduction. Fundamental Radio Propagation and System Concepts. Fundamentals of Antenna Gain. Propagation Characteristics. Models of Multipath-Faded Radio Signals. Instrumentation and Measurements for Laboratory and Field Tests. Delay-Spread Field Measurement Results. Industry Standards for Propagation Models. Problems. 4. Digital Modulation-Demodulation (MODEM) Techniques. Introduction. Baseband Transmission Systems. Modem Principles and Architectures. Interference. Definitions and Performance of Spectral and Power Efficiency. Performance in Complex Interference-Controlled Mobile Systems. Advantages of Coherent Demodulation over Noncoherent Systems. Advanced Modulation Methods. Adaptive Equalization for Frequency- Selective Faded and Delay-Spread Systems. Synchronization of Burst Demodulators: Carrier Recovery and Symbol Timing Recovery. Problems. 5. Coding: Error Correction and Detection. Error Control Requirements. Interleaving. Block Coding. Convolutional Coding. Price of Error Correction: Reduced Throughput? Word-Error Rate, False-Alarm Rate, and Probability of Bit Error. Repetition Transmission and Majority-Voting System: Concepts and Performance. Automatic Repeat Request. 6. Spread-Spectrum Systems. Introduction. Fundamental Concepts of Spread-Spectrum Systems. Pseudo-noise Sequences. Performance of Direct- Sequence Spread-Spectrum Systems. Code Division Multiple Access (CDMA): Direct-Sequence (DS) and Frequency-Hopped (FH) Spread-Spectrum Systems. Frequency-Hopping Spread-Spectrum Systems. Synchronization of Spread-Spectrum Systems. Spread- Spectrum Applications in Cellular, PCS, and Mobile Communications. Problems. 7. Diversity Techniques for Mobile-Wireless Radio Systems. Introduction. Concepts of Diversity Branch and Signal Paths. Combining and Switching Methods. Carrier-to-Noise and Carrier-to-Interference Ratio Performance Improvements. Average Pe Performance Improvement. Summary. Problems. 8. Personal Mobile Satellite Communications. Introduction. Integration of GEO, LEO, and MEO Satellite and Terrestrial Mobile Systems. Personal Satellite Communications Programs. 9. Cellular and Wireless Systems Engineering. Introduction. Access Methods: TDMA (TDD and FDMA) Spread-Spectrum Frequency-Hopping Direct-Sequence CDMA and CSMA. Comparison of Linearly Amplified BPSK, DQPS and DQPSK and Nonlinearly Amplified (NLA) GMSK, GFSK, 4-FM, and FQPSK Radio Equipment (Coherent and Noncoherent). Radio Link Design of Digital Wireless Cellular Systems. Spectrum Utilization in Digital Wireless Mobile Systems. Capacity and Throughput (Message Delay) Study and Comparison of GMSK, GFSK, and FQPSK Modulated Wireless Systems. Time Division Multiple Access Wireless Cellular Systems. Code Division Multiple Access Spread-Spectrum Digital Cellular IS-95 System. Standards for Wireless Local Area Networks. Wireless Personal Communications. Problems. Appendices. Statistical Communication Theory: Terms, Definitions, and Concepts. Software Package of CREATE-1 (Disk Enclosed). Dr. Feher Associates Patented Filter, Digital Signal Processing, and Correlated Modulation/RF Amplification Means: GMSK, GFSK, FBPSK and FQPSK Implementations of Digcom, Inc. Licensed Technologies. Abbreviations and Acronyms. Bibliography. Index.

Closed-form blind symbol estimation in digital communications

Abstract: We study the blind symbol estimation problem in digital communications and propose a novel algorithm by exploiting a special data structure of an oversampled system output. Unlike most equalization schemes that involve two stages-channel identification and channel equalization/symbol estimation-the proposed approach accomplishes direct symbol estimation without determining the channel characteristics. Based on a deterministic model, the new method can provide a closed-form solution to the symbol estimation using a small set of data samples, which makes it particularly suitable for wireless applications with fast changing environments. Moreover, if the symbols belong to a finite alphabet, e.g., BPSK or QPSK, our approach can be extended to handle the symbol estimation for multiple sources. Computer simulations and field RF experiments were conducted to demonstrate the performance of the proposed method. The results are compared to the Cramer-Rao lower bound of the symbol estimates derived in this paper.

Computer and measurement simulation of a new digital receiver operating directly at millimeter-wave frequencies

Abstract: A novel digital millimetric receiver (DMR) scheme is introduced. Using a six-port phase/frequency discriminator (SPD) in conjunction with a digital signal processor (DSP), the receiver performs various PSK and QAM demodulations directly at microwave and millimeter-wave frequencies. An important feature of the new DMR is that hardware imperfections such as phase/amplitude imbalance are readily eliminated by a simple calibration procedure. The concept is proved through computer simulation and measurements at 26.5 GHz. This receiver scheme is proposed for small/medium capacity digital terminals typically found in various wireless communication networks.

Error rates for Rayleigh fading multichannel reception of MPSK signals

Abstract: This paper provides a new closed form expression for calculating the probability that an MPSK signal will lie in a particular decision region when received over N independent and identically distributed Rayleigh fading channels corrupted by additive white Gaussian noise This expression is applied to provide a unified method to derive the exact symbol error rate and bit error rate for MPSK signals considering N channel diversity reception The N channel diversity reception techniques considered are maximal ratio combining (MRC) and selection combining MRC with identical channels and dissimilar channels is considered The results for MRC can be extended to provide an approximation for the error rates of MPSK under equal gain combining >

F-modulation amplification

Abstract: Binary and Quadrature Feher's (F)-Modulation/Amplification with significantly reduced envelope fluctuations and peak radiation, increased power efficiency and transmit power delivered by connected RF (radio frequency), Infrared (IR) and other devices. A subclass of these systems has a constant envelope. Extraordinary power advantages, robust BER performance and linearly or nonlinearly amplified narrow spectrum without the pitfalls of conventional BPSK and DBPSK is attained. The FBPSK improved efficiency transmitter is compatible with conventional BPSK receivers. FBPSK modems are based on using quadrature structure where Q channel data is inserted in quadrature with I channel data. The Q channel data is the same as the I channel but is offset by one half bit (Tb/2). Further improvement in the spectrum is attained using correlation between I and Q channels. FBPSK modem is shown to meet the IEEE 802.11 specified spectral mask (-30 dB point) for wireless LAN, and leads output power gain of 6.5 dB over BPSK modems. The Crosscoupled Quadrature Structure is also suitable for digital and for analog frequency modulation (Feher's Frequency Modulation). Reduced modulation index Gaussian FSK (GFSK), multilevel FM and crosscoupled Quadrature Amplitude Modulated (QAM) transmitters and combinations of these modulations and corresponding coherent demodulators are described.

Signal processing circuit for spread spectrum communications

Abstract: In a transmitting unit, an input signal is converted into an I data sequence of an in-phase (I) symbol and a Q data sequence of a quadrature (Q) symbol, a differential encoding is performed for the I and Q data sequences according to a differential binary phase shift keying (DBPSK) modulation to produce an I code sequence and a Q code sequence, a spectrum of the I code sequence is spread by a first spreading code signal to produce an I spread spectrum signal, a spectrum of the Q code sequence is spread by a second spreading code signal to produce a Q spread spectrum signal, the I and Q spread spectrum signals are quadrature-modulated to a synthesized signal, and the synthesized signal is transmitted to a receiving unit. In the receiving unit, the synthesized signal is quadrature-demodulated to a first baseband signal and a second baseband signal, the first and second baseband signals are respectively correlated with each of the first and second spreading code signals to obtain first and second I correlated signals and first and second Q correlated signals, and a BPSK delay detection is performed for a group of the first and second I correlated signals and a group of the first and second Q correlated signals to reproduce the I and Q data sequences.

Analysis of the impact of channel estimation errors on the performance of a decision-feedback equalizer in fading multipath channels

Abstract: A coherent receiver with a decision-feedback equalizer (DFE) operating on a Rayleigh fading channel under a suitable adaptive algorithm is considered. In the analysis of a DFE, a common assumption is that the receiver has perfect knowledge of the channel impulse response. However, this is not the case in practice, and for a rapidly fading channel, errors in channel tracking can become significant. We analyze theoretically the impact of these errors on the performance of a multichannel DFE. The expressions obtained for the achievable average MPSK bit error probabilities depend on the estimation error covariance. In order to specify this matrix, we focus on a special case when a Kalman filter is used as an optimal channel estimator. In this case, the probability of bit error can be assessed directly in terms of channel fading model parameters, the most interesting of which is the fading rate. Our results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates. >

Maximum likelihood decoding of uncoded and coded PSK signal sequences transmitted over Rayleigh flat-fading channels

Abstract: The problem of maximum likelihood (ML) detection for uncoded and coded M-PSK signals on Rayleigh fading channels is investigated. It is shown that, if the received signal is sampled at baud-rate, a ML receiver employing per-survivor processing can be implemented. The error rate performance of this receiver is evaluated by means of computer simulations and its limitations are discussed. In addition, it is shown that, on a fast fading channel, the error floor in the BER curve can be appreciably lowered if more than one received signal sample per symbol interval is processed by the receiver algorithm, Finally, a sub-optimum two-stage receiver structure for interleaved coded PSK systems is proposed. Its error rate performance is assessed for simple trellis-coded modulation schemes and compared to that provided by other receiver structures.

On the error probability of linearly modulated signals on frequency-flat Ricean, Rayleigh, and AWGN channels

Abstract: The method used in Aghamohammadi and Meyr (1990) for finding the error probability of linearly modulated signals on Rayleigh frequency-flat fading channels has been applied to the more general case of Ricean fading. A signal received on a fading channel is subject to a multiplicative distortion (MD) and to the usual additive noise. Following a compensation of the MD, the signal provided to the detector may be thought to include only a single additive distortion term ("final noise"), which comprises the effects of the original additive noise, the MD, and the error in MD compensation. An exact expression for the probability density function of the final noise is derived. This allows calculation of error probability for arbitrary types of linear modulations. Results for many cases of interest are presented. Furthermore, as special cases of Ricean fading, error probability for Rayleigh fading and non-fading channels are obtained which either match the results or complete the approximate derivations formerly known from the literature. >

Coded modulation scheme employing turbo codes

Abstract: The authors present a turbo coding scheme for bandwidth-efficient modulation that outperforms turbo coding with Gray mapping by employing Ungerboeck codes as component codes. The scheme can be decoded iteratively and achieves very good bit error rates at low signal to noise ratios after a small number of iterations. 8PSK is used as an example, although the scheme can be extended to other constellations.

Bandwidth efficient QPSK in cochannel interference and fading

Abstract: The performances of QPSK in the presence of cochannel interference in both nonfading and fading environments are analyzed. Three approaches for representing the cochannel interference are investigated. These are a precise error probability method, a sum of sinusoids (sinusoidal) model, and a Gaussian interference model. In addition to determining precise results for the performance of QPSK in cochannel interference, we examine the validity of these two interference models in both additive white Gaussian noise (AWGN) environments and in different flat fading environments; Rayleigh, Ricean, and Nakagami. Nyquist pulse shaping is considered and the effects of cross channel ISI produced by the cochannel interference are accounted for in the precise interference model. Also accounted for are the random symbol and carrier timing offsets of the interfering signals. Two performance criteria are considered. These are the average bit error rate and the interference penalty. The latter is defined as the increase in signal-to-noise power ratio (SNR) required by a system with cochannel interference in order to maintain the same BER as a system without interference. Attention is given, in particular, to the outdoor microcellular fading environment. In this environment, the fading experienced by the interfering signals may be represented by a Rayleigh-fading model while the fading experienced by the desired signal may be represented by a Ricean or a Nakagami-fading model. >

Modulation identification by the wavelet transform

Abstract: There is a need, for example in surveillance of the radio spectrum, to determine the modulation type of a received signal. By knowing the modulation type, one can demodulate the incoming signal for useful information. This paper proposes the use of wavelet transform for the identification problem. Application of wavelet transform on a digital modulation signal results in distinctive patterns for different types, which enables simple processing for identification. Three identifiers for classifying PSK and FSK, M-ary PSK, and M-ary FSK are considered and the relevant statistics for optimum decision making are included. Simulations are included for performance evaluation.

ACE-8PSK: band-limited 8PSK with an Almost Constant Envelope

Abstract: 8PSK modulation is of increasing interest in satellite communications applications where bandwidth efficiency is a prime concern. However, its adoption in practical systems has been limited, largely due to its increased sensitivity to channel and transmitter imperfections as compared with QPSK and other modulation schemes. In particular, band-limited 8PSK is highly susceptible to the interference associated with adjacent channel spectral regrowth caused by transmitter nonlinearity. Spectral regrowth may lead to substantial performance degradation or make necessary an increase in the spacing between carriers. The transmitted carrier may suffer levels of spurious RF emission which exceed system specifications or spectral mask regulations. This paper proposes new low complexity trellis coding techniques which can be applied to conventional 8PSK modulation, and which lead to substantially reduced levels of spectral regrowth. When the coding is applied, the modulated signal exhibits a reduced degree of envelope fluctuation, and hence it is less affected by amplitude nonlinearity. The schemes are termed Almost-Constant-Envelope 8PSK (ACE-8PSK). Combined with outer FEC coding, ACE-8PSK can achieve greater power efficiency than QPSK, and provide significant performance advantages on the nonlinear channel in terms of bit error rate and the spectral purity of transmissions.

CD3-OFDM: a new channel estimation method to improve the spectrum efficiency in digital terrestrial television systems

Abstract: The paper describes a novel channel estimation scheme (identified as CD3, coded decision directed demodulation) for coherent demodulation of OFDM (orthogonal frequency division multiplex) signals making use of any constellation format (e.g. QPSK, 16 QAM, 64 QAM). The structure of the CD3-OFDM demodulator is described, based on a new channel estimation loop exploiting the error correction capability of a forward error correction (FEC) decoder and frequency and time domain filtering to mitigate the effects of noise and residual errors. In contrast to the conventional coherent OFDM demodulation schemes, CD3-OFDM does not require the transmission of a comb of pilot tones for channel estimation and equalisation, therefore yielding a significant improvement in spectrum efficiency (typically between 5% and 15%). The performance of the system with QPSK and 64 QAM modulations is analysed by computer simulations, on AWGN and frequency selective channels. The results indicate that CD3-OFDM allows to achieve C/N performance similar to coherent demodulation with pilot tones, when the same channel coding and modulation scheme is adopted. Otherwise, when the additional capacity is exploited to increase the FEC redundancy instead of the useful bit-rate, CD3 can offer significant C/N advantages (typically from 2 to 5 dB depending on the channel characteristics). Therefore CD3-OFDM can be suitable for digital television broadcasting services over selective radio channels.

Bandwidth efficient parallel concatenated coding schemes

Abstract: We propose a new solution to parallel concatenation of trellis codes with multilevel amplitude/phase modulations and a suitable iterative decoding structure. Examples are given for throughputs 2 bits/sec/Hz with 8PSK and 16QAM signal constellations.

Square-QAM adaptive modulation/TDMA/TDD systems using modulation level estimation with Walsh function

Abstract: The authors propose a square-QAM adaptive modulation/time division multiple access/time division duplex (TDMA/TDD) system for land mobile communications to achieve high quality and high bit rate transmission in both flat and frequency selective fading environments. To further improve performance, a new modulation level estimation scheme using the Walsh function and maximum likelihood (MS) estimation is also proposed. Computer simulation confirms that the proposed system gives 8 dB better performance and four times larger delay spread immunity than that of conventional QPSK systems at BER = 10-3.

Data-aided noncoherent demodulation of DPSK

Abstract: Considers noncoherent demodulation of DPSK when the receiver has partial knowledge of the information being transmitted. This partial knowledge represents preamble symbols, pilot symbols, or past decisions when operating in a decision-feedback mode. The maximum likelihood (ML) noncoherent receiver for this case is derived. It is shown that known demodulation schemes such as multi-symbol differentially coherent receivers and decision-feedback differential receivers can be considered as special cases of this data-aided noncoherent DPSK demodulator. A simple recursive structure for this receiver is introduced and its performance analyzed. >

Differential amplitude phase shift keying (DAPSK)-a new modulation method for DTVB

Abstract: In digital terrestrial video broadcasting (DTVB) applications the objective is to transmit a high data rate of 34.368 Mbit/s in a single radio channel (bandwidth of 7 or 8 MHz). In this paper the performance of a multicarrier transmission technique, the well-known orthogonal frequency division multiplexing (OFDM) method, is analysed and the system parameters for the DTVB application are considered. A multilevel differential modulation technique, the so-called differential amplitude and phase shift keying (64-DAPSK) is proposed, in which the phase and the amplitude are used simultaneously for differential modulation. A differential modulation technique does not require any explicit knowledge about the radio channel properties in the differential channel equalization process. In an OFDM/64-DAPSK receiver it is therefore not necessary to implement a channel estimation and a frequency-domain equalizer, which reduces the computation complexity. The performance of both modulation techniques has been analysed in the uncoded case referring to Gaussian and frequency-selective Rayleigh fading channels. The results are described.

Near-far resistant detection of CDMA signals via isolation bit insertion

Abstract: This paper presents a novel scheme for near-far resistant CDMA detection: isolation bit insertion (IBI). At the transmitter, isolation bits are inserted into the information bit sequence before modulation, and a practical linear decorrelating detector (LDD) is obtained at the receiver. All the advantages that an LDD theoretically offers are retained and realised in practice. >

Asymptotical performance of M-ary and binary signals over multipath/multichannel Rayleigh and Rician fading

Abstract: This paper presents a general framework for computing the asymptotic error probability (i.e., at high average SNRs) of M-ary and binary signaling schemes over Rician and Rayleigh fading diversity channels. A general theorem (Theorem 1) relates the asymptotic error rate of multipath and multichannel receivers (over AWGN, ISI free channels) to the multidimensional integral of the conditional error probability. Two other theorems are presented for the particular cases where the conditional error probability is a function of the sum of received SNRs (Theorem 2) or received amplitudes (Theorem 3). Theorems 2 and 3 are related for linear coherent systems, and closed form expressions are obtained for equal gain combining systems. Detection structures for typical diversity schemes (coherent/noncoherent maximal ratio and equal gain combining, and quadratic noncoherent combining) are considered. We analyze the asymptotic error rates of some M-ary signaling schemes (MPSK/MPAM with Kth order diversity and orthogonal signals with K=1 and with coherent and noncoherent detection). Binary signaling is also considered in our study.

Simple coding scheme to reduce peak factor in QPSK multicarrier modulation

Abstract: The authors present a simple half-rate coding scheme to limit the peak factor of QPSK multicarrier waveforms to less than one quarter that of the uncoded carrier, using Rudin-Shapiro polynomials.

Pilot symbol assisted modulation and differential detection in fading and delay spread

Abstract: Pilot symbol assisted modulation (PSAM) has previously been shown to give good performance in flat fading, noise and cochannel interference. The present paper analyzes its performance in ISI due to frequency selective fading, and provides a similar analysis of differential detection for comparison. The paper also introduces a method for performing the formidable average over transmitted data patterns simply, and with an analytical result, PSAM is shown to be sensitive to RMS delay spread, though it always gives better performance than differential detection. >

Performance of modulation-level-controlled adaptive-modulation under limited transmission delay time for land mobile communications

Abstract: The performance of an adaptive-modulation/time division duplex (TDD) scheme to support constant-bit-rate services under transmission delay time constraint conditions is evaluated in this paper. According to the received signal conditions, the modulation levels or transmission modes are selected from transmission-off, QPSK, 16QAM, or 64QAM by using the reciprocity of the propagation path characteristics in the TDD systems. Moreover, the transmission delay time is limited to keep data transmission rate constant by the memory buffer. The received signal condition is estimated by using extrapolation of pilot symbol or estimated received signal distortion at the decision stage. The performance is evaluated by computer simulation in case of 32 ksymbol/s transmission and is compared with the performance of conventional trellis-coded (TCM) 32QAM. The results show that the proposed method improves the BER performance and delay spread immunity of a system transmitting data at a constant rate under multipath fading conditions and the performance is better than that of TCM-32QAM in Rayleigh fading conditions with small Doppler frequency.

Computational simplified detection of digitally modulated radio signals providing a detection of probability for each symbol

Abstract: The invention provides simple and reliable detection of π/4 shifted DQPSK modulated digital signals in a single-subscriber-unit, a multiple-subscriber unit (MSU) or a base transceiver station (BTS) of a fixed-wireless system, and is also directly applicable to other digital cellular or personal communication systems which utilizes a binary or M-ary PAM, FSK or PSK digital modulation scheme with differential or coherent encoding and time- and/or frequency-multiplexing. It offers great simplicity while providing soft-decision information for the later stage decoding of information bits encoded with an error correcting code. For each received sample z k+L and its estimated one z k+L , a Euclidean distance function is calculated. This Euclidean distance u(z k+L |v k+L , . . . , v k ) is then added to the function derived from the previous iteration g(v k+L-1 , . . . , v k ), to yield a new Euclidean distance function f(v k+L , . . . , v k ). Then a series of comparisons are carried out to find the minimum Euclidean distance with respect to each symbol within the channel memory span except v k . These minimum Euclidean distances are then added up to yield M values. The symbol corresponding to the minimum distance is the detected symbol. The same M Euclidean distance values are also used for soft decision derivation for use with an error detecting code. A simple measure of the accuracy of each symbol is calculated from the two shortest Euclidean distances. In particular, by taking the ratio of the difference to the sum of those two distances, the overall implementation of the demodulator becomes especially computationally efficient.

Information transmission system

Abstract: A system for transmitting information over an OFDM channel using phase shift keying encoding employs a bit mapping encoder to reduce the crest factor (ratio of peak voltage to RMS voltage). For a 16 subchannel OFDM system using QPSK encoding, a first set of four symmetrically positioned pairs of subchannels is used to encode two bits of information on each subchannel. A second set of four symmetrically positioned pairs of subchannels is used to encode only one bit of information on each subchannel, with the resultant phasor for each pair of the second set of pairs of subchannels being orthogonal to the resultant phasor for one of the pairs of the first set of subchannels. With this arrangement, the crest factor is reduced.

Symbol-aided channel estimation with nonselective Rayleigh fading channels

Abstract: New algorithms are proposed to implement coherent detection of PSK signals transmitted over frequency-flat Rayleigh channels. Channel gain estimates are derived both from known symbols multiplexed with the data stream and from tentative data decisions. The performance of these algorithms is assessed by computer simulation with uncoded and trellis-coded modulation. Comparisons are also made with differentially coherent detection (DPSK) and with perfect coherent detection (corresponding to ideal knowledge of the fading process). Simulation results demonstrate that these algorithms can track adequately the severe fading fluctuations encountered on a Rayleigh channel and that their superiority over DPSK becomes impressive with fast fading.

Optical transmission of narrowband millimeter-wave signals

Abstract: We describe experimentally and theoretically three techniques used to transmit narrowband millimeter-wave (MM-wave) analog signals over optical fiber: 1) narrowband MM-wave optical transmitters based on resonant modulation of monolithic semiconductor lasers, 2) feedforward optical modulation, and 3) a passively mode-locked laser operating in an optoelectronic phase-locked loop. The resonant modulation response at the cavity round-trip frequency is fully characterized for multiple-contact lasers under various bias conditions. Issues such as modulation efficiency, passband bandwidth, noise, and intermodulation distortion are addressed. A system implementation of resonant modulation is presented in which two simultaneous 2.5-Mb/s BPSK channels centered at a subcarrier frequency of 41 GHz is transmitted over 400 m of single-mode fiber. Simple microstrip matching circuits are fabricated at 41 GHz to couple the MM-wave signals into the laser. Resonant modulation of single-contact lasers is also reported. Next, implementation of a tunable MM-wave (30-300 GHz) optical transmitter based on feedforward optical modulation is presented, and the fundamental performance of this technique investigated in terms of noise and dynamic range. Feedforward modulation is used to transmit 300-Mb/s data at 39 GHz over 2.2 km of single-mode fiber. Finally, a passively mode-locked monolithic semiconductor laser operating in an optoelectronic phase-locked loop is implemented as a narrowband MM-wave optical transmitter at 46 GHz. The phase-locked loop bandwidth, MM-wave tracking capability, and fundamental limit to the stability of the MM-wave subcarrier is established. The relative merits of the three techniques are discussed and compared. The MM-wave subcarrier transmission results presented here represent the highest reported to date. >

Adaptive decision feedback equalization for digital satellite channels using multilayer neural networks

Abstract: This paper introduces an adaptive decision feedback equalization using the multilayer perceptron structure of an M-ary PSK signal through a TDMA satellite radio channel. The transmission is disturbed not only by intersymbol interference (ISI) and additive white Gaussian noise, but also by the nonlinearity of transmitter amplifiers. The conventional decision feedback equalizer (DFE) is not well-suited to detect the transmitted sequence, whereas the neural-based DFE is able to take into account the nonlinearities and therefore to detect the signal much better. Nevertheless, the applications of the traditional multilayer neural networks have been limited to real-valued signals. To overcome this difficulty, a neural-based DFE is proposed to deal with the complex PSK signal over the complex-valued nonlinear MPSK satellite channel without performing time-consuming complex-valued back-propagation training algorithms, while maintaining almost the same computational complexity as the original real-valued training algorithm. Moreover, a modified back-propagation algorithm with better convergence properties is derived on the basis of delta-bar-delta rule. Simulation results for the equalization of QPSK satellite channels show that the neural-based DFE provides a superior bit error rate performance relative to the conventional mean square DFE, especially in poor signal-to-noise ratio conditions. >