Hybrid DS/SFH spread-spectrum multiple access with predetectiondiversity and coding for indoor radio

The authors derive close upper and lower bounds on the average bit error probability for hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems with noncoherent DPSK demodulation, using predetection diversity (selection combining and equal gain combining) in conjunction with interleaved channel coding (Hamming (7,4) code and BCH (15,7) code) operating through indoor radio channels. A multipath Rayleigh fading model is assumed for the indoor radio channel. The results show that the DS portion of the modulation combats the multipath interference, whereas the FH portion is a protection against large multiaccess interference. It is shown that, for the considered types of channel coding, the use of predetection diversity is still essential for obtaining satisfactory error performance     

Relationship between performance and timing recovery mechanisms for a DECT link in dispersive channels

The performance of DECT (digital European cordless telecommunications) radio links under dispersive channel conditions is studied as a function of clock recovery strategies. It is shown that due to the non-optimal sampling, analytical and practical results based on fixed timing will not be acceptable above delay spreads of approximately 40ns. On the other hand, a burst-adaptive clock recovery scheme can more than double this range.<>     

Design and analysis of a jitter-free clock recovery scheme for QAMsystems

Performance of the digital clock recovery scheme proposed by F.M. Gardner (1986), when applied to quadrature-amplitude-modulation (QAM) microwave radio communication systems is investigated. In particular, it is shown how to improve such a scheme by means of appropriate prefiltering of the incoming signal. The impulse response of the shaping filter is designed to achieve pattern-jitter-free clock recovery in the case of an ideal transmission channel. The impact of multipath fading on synchronizer performance is evaluated by means of computer simulation     

Adaptive MAPSD algorithms for symbol and timing recovery of mobileradio TDMA signals

Dual-mode adaptive algorithms with rapid convergence properties are presented for the equalization of frequency selective fading channels and the recovery of time-division multiple access (TDMA) mobile radio signals. The dual-mode structure consists of an auxiliary adaptive filter that estimates the channel during the training cycle. The converged filter weights are used to initialize a parallel bank of filters that are adapted blindly during the data cycle. When the symbol timing is known, this filter bank generates error residuals that are used to perform approximate maximum a posteriori symbol detection (MAPSD) and provide reliable decisions of the transmitted signal. For channels with timing jitter, joint estimation of the channel parameters and the symbol timing using an extended Kalman filter algorithm is proposed. Various methods are described to reduce the computational complexity of the MAP detector, usually at the cost of some performance degradation. Also, a blind MAPSD algorithm for combining signals from spatially diverse receivers is derived. This diversity MAPSD (DMAPSD) algorithm, which can be easily modified for the dual-mode TDMA application, maintains a global set of MAP metrics even while blindly tracking the individual spatial channels using local error estimates. The performance of these single-channel and diversity MAPSD dual-mode algorithms are studied via computer simulations for various channel models, including a mobile radio channel simulator for the IS-54 digital cellular TDMA standard     

Performance evaluation of a novel M-detector for coherent receiverantenna diversity in a GSM-type mobile radio system

Powerful adaptive detectors such as the maximum-likelihood (ML) detector based on the Viterbi algorithm (VA) are required at the receivers for GSM type mobile radio systems in order to combat the effect of frequency-selective fading radio channels. The use of diversity techniques like receiver antenna diversity leads to a further improvement of the receiver performance. Hence, ML detectors for coherent receiver antenna diversity (CRAD) have attracted the attention of many authors. However, the complexity of the defector for CRAD can be considerably decreased when the VA is replaced with the M-algorithm, which is a suboptimum tree search algorithm. In the course of this paper, the M-detector is extended to CRAD in the case of maximal-ratio combining (MRC), equal-gain combining (EGC), and selection combining (SC), and its performance in GSM type mobile radio systems is studied by simulations using the radio channel models rural area (RA), typical urban (TU), and bad urban (BU) specified by COST 207. It is demonstrated that this novel M-detector for CRAD can perform similarly to the ML detector for CRAD thus being a favorable alternative     

Performance analysis of direct-sequence spread-spectrum multiple-access communication in an indoor Rician-fading channel with DPSK modulation

The bit error probability for direct-sequence spread-spectrum multiple-access (DS/SS-MA) in indoor radio channels is evaluated, assuming differential phase-shift-keying (DPSK) modulation, both for selection diversity and for maximal-ratio combining. The indoor radio environment is modelled as a Rician fading channel.<>     

Optimum diversity combining and equalization overinterference-limited cellular radio channel

This paper presents the comparative analysis of Nth-order diversity combining and equalization over an interference-limited cellular radio channel. The method of combining diversity and equalization has been analyzed previously. However, cochannel interference (CCI) was not considered, and the number of equalization taps was assumed to be infinite. A quadrature amplitude modulation (QAM) is used in our signal analysis. In modeling the multipath radio, we take into account CCI generated by frequency reuse and additive white Gaussian noise (AWGN). The performance evaluations are made of average error probability and outage probability. The average error rate is determined by using a Monte Carlo simulation for a set of channel parameters such as signal-to-noise ratio (SNR), signal-to-interference ratio (SIR), and equalization coefficients determined for this channel. In the error-rate estimation, we analyze and compare the results of system performance obtained by the upper bound approach and the moment estimation method. We also investigate the tradeoff of the performance improvement in terms of average error probability and equalizer complexity (the number of equalization taps)     

ADFC-CH: adjusted disjoint finite cover rendezvous algorithms for cognitive radio networks

Establishing communications in a cognitive radio networks (CRNs) requires communicating nodes to “rendezvous” before transmitting their data packets. Channel hopping (CH) rendezvous algorithms can provide guaranteed rendezvous for CRNs without common control channels. A new rendezvous algorithm named adjusted disjoint finite cover rendezvous (ADFC-CH) is proposed, which can be used in more general cognitive radio networks such as synchronous clock, heterogeneous model, symmetric role, and anonymous information. The relationship between the concept in mathematics called disjoint finite cover (DFC) and rendezvous process is built in ADFC-CH. The ADFC-CH produces a channel sequence by constructing the DFC which is a function of network scale called LOCK. So the algorithm can be fit for the diversity of the network requirement by adjusting the value LOCK. Simulation results show that ADFC-CH can achieve better performance over the exiting channel hopping protocols such as SSB, L-DDP and DSCR.     

Hybrid DS/SFH-SSMA with predetection diversity and coding overindoor radio multipath Rician-fading channels

The authors investigate the bit-error-rate (BER) performance of hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems operating over a multipath Rician-fading channel (which models indoor radio propagation in factories). They consider both phase-shift-keying (PSK) modulation with coherent demodulation and differential phase-shift-keying (DPSK) modulation with noncoherent demodulation. Predetection multipath diversity (maximal ratio combining for coherent reception and equal gain combining for noncoherent reception) and simple interleaved channel coding are employed for improving the BER performance. The BER of both coherent and noncoherent hybrid systems is obtained using a Gaussian interference approximation     

Reconfigurable radio receiver with fractional sample rate converter and multi-rate ADC based on LO-derived sampling clock

A composite radio receiver back-end and digital front-end, made up of a delta-sigma analogue-to-digital converter (ADC) with a high-speed low-noise sampling clock generator, and a fractional sample rate converter (FSRC), is proposed and designed for a multi-mode reconfigurable radio. The proposed radio receiver architecture contributes to saving the chip area and thus lowering the design cost. To enable inter-radio access technology handover and ultimately software-defined radio reception, a reconfigurable radio receiver consisting of a multi-rate ADC with its sampling clock derived from a local oscillator, followed by a rate-adjustable FSRC for decimation, is designed. Clock phase noise and timing jitter are examined to support the effectiveness of the proposed radio receiver. A FSRC is modelled and simulated with a cubic polynomial interpolator based on Lagrange method, and its spectral-domain view is examined in order to verify its effect on aliasing, nonlinearity and signal-to-noise ratio, giving insight into the design of the decimation chain. The sampling clock path and the radio receiver back-end data path are designed in a 90-nm CMOS process technology with 1.2V supply.     

Secrecy outage performance analysis of MIMO underlay cognitive radio networks with delayed CSI and transmitter antenna selection

Cognitive radio network is an emerging solution to deal with spectrum scarcity and to utilize the radio spectrum in opportunistic and efficient manner. Secure data transmission is one of the important issues in these kind of networks. This work studies the secrecy outage performance of a multiple-input multiple-output underlay cognitive wiretap radio network system over Rayleigh fading channel with delayed channel state information. This work considers that the secondary transmitter is equipped with multiple antennas and confidential information is transmitted from to multiantenna receiver in the presence of multiantenna eavesdropper. Further, the transmit antenna selection scheme is considered at secondary transmitter to reduce the complexity of antenna selection and to make it more practicable. To improve the quality of signal, this work considers maximal ratio combining (MRC) at secondary receiver, while selection combining and MRC techniques are utilized at the eavesdropper. The closed form expression for exact, asymptotic, and intercept secrecy outage probability has been derived, and the simulation is done for the validation of analytical results. The derived results reveal deterioration of channel secrecy performance with outdated channel state information, and the eavesdropper with outdated channel state information has also an adverse effect. Moreover, the diversity order that can be achieved in underlay cognitive radio network with outdated channel state information is unity.     

A Mobile Radio Single-Frequency "Two-Way" Diversity System Using Adaptive Retransmission from the Base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "twoway diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

Performance Improvement by Microdiversity for Wideband Signals in Frequency Selective Fading Indoor Channels with Co-Channel Interference

A comprehensive analytical bit-error-rate (BER) model is presented to analyse the performance of antenna-microdiversity for wideband BPSK modulated signals in the frequency selective fading multipath channel, specified by its complex impulse response. The model includes the disturbance by intersymbol interference (ISI) and co-channel interference (CCI), as well as the channels' impact on the carrier phase- and clock recovery in the receiver. The channel impulse responses at the antenna elements are determined by taking into account the direction of arrival of the individual paths. Computational BER- and SNIR-gain results (SNIR = signal-to-noise+interference-ratio) show that a substantial performance improvement is achieved with antenna combining for wideband signals which suffer ISI and/or CCI. For the indoor multipath channel with exponentially decaying power delay profile, the performance enhancement is compared for several antenna combining schemes. Quasi-coherent equal gain combining (QCEGC) is proposed as an novel EGC scheme based on a less accurate phase estimation technique. For wideband signals, QCEGC shows a slight performance degradation when compared to maximal ratio combining or minimum mean square error combining (MMSEC), but has a much lower implementation complexity. In the channel with CCI, where the best performance is achieved with MMSEC, QCEGC performs very poor.     

A mobile radio single-frequency "Two-way" diversity system using adaptive retransmission from the base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "two-way diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

Multiple hops/symbol FFH-SSMA with MFSK modulation and Reed-Solomoncoding for indoor radio

A multiple-hopes-per-symbol fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) system for indoor radio communication is treated. The data are Reed-Solomon (RS) encoded and then modulate a carrier by means of M-ary frequency-shift-keying (MFSK) The indoor radio channel is described as a multipath (Rayleigh or Rician) slowly fading channel. The receiver uses predetection diversity by linearly combining the squared enveloped of the different hops of the same MFSK symbol. The bit error rate (BER) performane is evaluated, and how the performance is influenced by various parameters, such as the number of hops per symbol, the size of the symbol alphabet, the ratio of specular power to fading power, and the ratio of nonreference user power to reference user power, is investigated     

A flexibly configurable spatial model for mobile radio channels

The application of multiple directive antennas, i.e., directional diversity, may lead to significant capacity benefits in cellular mobile radio systems. A flexibly configurable statistical channel model for mobile radio systems using directional diversity is presented. The parameters of this model, which is available as a FORTRAN77 program, can be easily adjusted to various propagation areas such as, for example, rural, urban, microcellular, and picocellular environments. Therefore, the model is well suited to perform simulations, evaluations, and comparisons of mobile radio systems. Simulation results concerning a code-division multiple-access (CDMA) mobile radio system which uses multiple directive base station (BS) antennas in combination with joint detection illustrate the application of the presented channel model     

Decorrelating detector with diversity combining for single user frequency-selective rayleigh fading multipath channels

Diversity combining techniques are applied in mobile radio communications as a means of performance improvement in a fading multipath environment. Adaptive equalizers which incorporate diversity combining were shown to combat intersymbol interference (ISI) caused by multipath provided that the fading is sufficiently slow. However, for fast fading rates, noncoherent techniques are often desirable. In this paper, we examine the performance of several coherent and noncoherent detectors that make use of diversity combining. In particular, the decorrelating filter is shown to provide reliable performance for a frequency-selective Rayleigh fading multipath channel with ISI. Numerical and simulation results are presented for a channel with two independent Rayleigh fading paths. Signal design issues which arise in the implementation of the decorrelating detector and the zero-forcing equalizer are discussed.     

Optimum combining in digital mobile radio with cochannel interference

This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maximize the output signal-to-interference-plus-noise ratio. Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical cellular mobile radio systems show that optimum combining increases the output signal-to-interference ratio at the receiver by several decibels. Thus, systems can require fewer base station antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays.     

Optimum Combining in Digital Mobile Radio with Cochannel Interference

This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maximize the output signal-to-interference-plus-noise ratio. Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical cellular mobile radio systems show that optimum combining increases the output signalto-interference ratio at the receiver by several decibels. Thus, systems can require fewer base station antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays.