The paper proposes a new multiple access communications system based on the combination of multitone transmission and direct sequence spectrum spreading (DS/SS). Multitone transmission is proposed because the associated larger symbol duration is favorable to combat the effects of multipath propagation. The multiple access capability of the system is achieved by means of DS/SS which also helps to combat the presence of several paths. On the other hand, DS/SS is also attractive to decrease the multiple access interference. The performance of this system is investigated for a multipath, slowly Rician fading and frequency selective channel, and a suboptimal receiver based on matched filters. The multiple access interference is also taken into account, A model for the computation of the bit error probability is derived for QPSK modulation of the orthogonal tones by the spread symbols. The system performance is investigated for selection diversity and maximal ratio combining (RAKE reception). Then the influence of the number of tones is investigated for given bandwidth, bit rate and transmission power. The positive effect of a multitone spread spectrum transmission is demonstrated. >

Multitone spread spectrum multiple access communications system in a multipath Rician fading channel

A digital radio transceiver uses a differential 4-ary frequency shift keying (D4FSK) modulation scheme to achieve a radio that is low cost, miniaturizable, low in power consumption and high in spectral efficiency. An adaptive digital 'slicer' (31) looks at a digitized FM video signal produced in the receiver to determine if the data sent is a 00, 01, 10 or 11. The digitized FM video signal is first processed by a differential decoder (31), the output of which is input to a peak detector. The peak detector outputs a signal upon the occurrence of a three-step transition. Two and three step transitions are separately detected and used to perform digital clock recovery. A carrier detect circuit uses a digital bit filter to produce a carrier detect signal (CD) that is reliable and glitch-free. The digital radio transceiver uses frequency hopping spread spectrum transmission (23). A switchable loop bandwidth frequency synthesizer provides for glitch-free switching between a wide hopping bandwidth and a narrow bandwidth between hops.

Digital communications equipment using differential quaternary frequency shift keying

From the Publisher:
This volume is dedicated to a range of CDMA and MC-CDMA transmission aspects of systems designed for communicating over fading wireless channels.
Currently, a technical in-depth book on this subject, which has a similar detailed exposure of the recent advances in CDMA, M-ary CDMA and MC-CDMA, is unavailable. A further attraction of the joint treatment of these topics is that it allows the reader to view their design trade-offs in a comparative context.
Divided into five main parts:
Part I  provides a detailed introduction to the subject of CDMA systems designed for employment in various application
Part II  deals with the currently hot topic of genetic algorithm assisted multiuser detection
Part III  gives a detailed account of new, reduced-complexity M-ary CDMA schemes
Part IV  considers a range of novel MC-CDMA schemes which have the potential of supporting numerous design objectives
Part V  provides an overview of the 3G wireless system proposals and characterises the expected network capacity gains attained with the aid of adaptive CDMA systems
By providing an all-encompassing self-contained treatment this groundbreaking volume will have appeal to researchers, postgraduate students, academics practising research and development engineers working for wireless communications and computer networking companies, as well as senior undergraduate students and technical managers in the field.

Single and Multi-Carrier CDMA: Multi-User Detection, Space-Time Spreading, Synchronisation and Standards

Recently, an algebraic decoding algorithm suggested by Truong (2005) for some quadratic residue codes with irreducible generating polynomials has been designed that uses the inverse-free Berlekamp-Massey (BM) algorithm to determine the error-locator polynomial. In this paper, based on the ideas of the algorithm mentioned above, an algebraic decoder for the (89, 45, 17) binary quadratic residue code, the last one not decoded yet of length less than 100 , is proposed. It was also verified theoretically for all error patterns within the error-correcting capacity of the code. Moreover, the verification method developed in this paper can be extended for all cyclic codes without checking all error patterns by computer simulations.

Algebraic Decoding of the $(89, 45, 17)$ Quadratic Residue Code

The purpose of this paper is to conduct performance analysis for a frequency-hopped spread spectrum multiaccess network which is subject to the threat of multipath interference. Baseband modulation is done through frequency shift keying and signal detection is accomplished by a noncoherent type receiver. The quality of a signal is affected by the channel noise, multiuser interference, and multipath interference. Performance analysis is conducted on the basis of bit error rate. Due to the sophistication of the system exact analysis is not feasible. The accuracy of approximation is checked against simulations. One major discovery Is that when signal-to-noise ratio is low, multipath interference on the contrary may help to enhance the quality of the signal. Another discovery is that when signal-to-noise ratio is high enough, multipath/multiuser interference becomes the bottleneck of performance. The effect of channel noise can be eliminated by maintaining a large signal-to-noise ratio while spread spectrum technique is employed to reduce the effect of multipath/multiuser interference. >

Using frequency hopping spread spectrum technique to combat multipath interference in a multiaccessing environment

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. >

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

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. >

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

The paper is concerned with the bit error rate (BER) performance of multiple hops/ symbol fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) systems operating through an indoor radio multipath Rayleigh fading channel. M-ary frequency-shift-keying (MFSK) modulation with noncoherent square-law envelope demodulation and Reed-Solomon (RS) coding is considered. Results obtained in this study show that an FFH-SSMA system is not sensitive to the changes in the number of paths. Employing RS coding with an increased number M of MFSK signals yields a significant improvement in BER performance. Assuming a given system bandwidth, using a single hop per symbol is the best solution when the multiaccess interference can be large. Using several hops per symbol is more advantageous when the multiaccess interference is small.

J. Wang

Papers

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

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

Multiple hops/symbol fast frequency-hopping spread spectrum multiple access with coding for indoor radio