A sequency multiplexing technique for mobile communication systems

We discuss evaluations of bit error probabilities in SSMA (spread spectrum multiple access) communication systems using binary spreading sequences of Markov chains and the designing of binary spreading sequences of Markov chains optimal in terms of bit error probabilities. We study SSMA communication systems using binary spreading sequences of Markov chains and give a necessary and sufficient condition that the distribution of the normalized MAI (multiple-access interference) is Gaussian. Based on this result, we discuss theoretical evaluations of bit error probabilities in such systems based on the CLT (central limit theorem) and those based on the SGA (standard Gaussian approximation). We compare these theoretical evaluations with experimental results and also discuss the optimum spreading sequences of Markov chains in terms of bit error probabilities based on the CLT.

In this report we consider adaptive multistage interference cancellation within asynchronous spread spectrum multiple access (SSMA) communication systems using spreading sequences of Markov chains. We show that for synchronous systems, the empirical mean of the multiple access interference (MAI) at the second stage of interference cancellation satisfies the large deviations principle (LDP) with the convex, good rate function. By refinement of the large deviations analysis, we obtain exact asymptotics of bit error probabilities in such systems. We also discuss evaluations of bit error probabilities in asynchronous systems based on the LDP.

In this paper, a binary direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system with an additive white Gaussian noise channel and a correlation receiver are considered. The signature sequences are m-sequences or random sequences when the number of users is small and are random sequences, Gold sequences, or Kasami sequences when the number of users is large. Simulation results are obtained to verify a variety of bounds provided in other literature and to compare system performance when employing different signature sequences. >

In this paper, M-ary spread spectrum multiple access (M-ary/SSMA) communication systems utilizing multicarrier techniques are evaluated by theoretical analysis. The multiple access capability of the multicarrier M-ary/SS system is evaluated by theoretical analysis in the presence of frequency selective fading and partial band interference. Moreover, the multicarrier M-ary/SS system is compared with the multicarrier direct-sequence spread-spectrum (multicarrier DS/SS) system. As a result, the BER of the multicarrier M-ary/SSMA system is better than that of the multicarrier DS/SSMA system when the number of users is small and E/sub b//N/sub 0/ is low. The BER of the multicarrier M-ary/SSMA system can he improved by increasing the number of carriers. Moreover the multicarrier M-ary/SSMA system is superior to the single carrier M-ary/SSMA system using a RAKE receiver in the presence of narrowband interference.

The performance of synchronous and asynchronous, binary and quaternary (with and without offset) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems using random signature sequences and arbitrary chip waveforms is investigated. The average probability of error at the output of the correlation receiver is evaluated using a characteristic-function approach for these systems. Numerical results are presented that illustrate performance comparisons between systems using random and deterministic signature sequences, synchronous and asynchronous systems, systems with rectangular or sinewave chip waveforms, and binary and quaternary systems with the same data rates and bandwidth. In all cases, the accuracy of the Gaussian approximation is also examined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The performance of noncoherent reception in hybrid direct-sequence/slow-frequency-hopped (DS/SFH) spread-spectrum multiple access (SSMA) communication systems operating through indoor wireless multipath and fading channels is investigated. The system with differential-phase-shift keying (DPSK) modulation and predetection combining is examined. Approximations are obtained for the multiuser probability of error by using a Gaussian approximation for the multiple-access and multipath interference.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The aim of the research described in this paper is to eliminate self-interference during the transmission of simultaneous signals over a common channel. Code-division multiple-access (CDMA) communication systems, also termed spread-spectrum multiple access (SSMA) systems, make use of a transmission bandwidth greatly in excess of the information bandwidth. A synchronous CDMA technique known as Sequence Segment Keying (SSK) that provides zero co-channel interference has been proposed and described by Darnell [1]. Previous work in this area has concentrated on the system aspects of SSK describing the application within the design of a practical radio communication system [2]. This paper provides a comprehensive analysis of this communication scheme by introducing a novel mathematical modet of an SSK system. This has been initially tested by computer simulation and verified for an unlimited number of simultaneous users. The conditions imposed on the pseudorandom (PR) bearer sequences for SSK limit those sequences which can be utilised. The lack of large sequence sets restricts the number of simultaneous users and to overcome this problem the use of independent varying chip periods for each PR bearer sequence is examined. This allows sequences that do notmeet specified period criteria to be adjusted so that they are locked into the required sequence length ratios, thus providing a larger sequence set than was previously possible and hence increasing the flexibility and viability of SSK systems.

Nearly all previous analytical results on the performance of direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems are restricted to systems in which the period <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> of the signature sequence is equal to the number <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> of chips per data symbol. In many applications, however, it is necessary to employ signature sequences whose period <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> is much larger than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> . Thus, successive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> -chip segments of the signature sequence are used to phase-code the carrier during the transmission of successive data symbols. The performance of such systems depends on the partial correlation properties of the signature sequences (rather than the aperiodic correlation properties as in the case when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N=p</tex> ). In this paper, we consider the performance of a DS/SSMA system for arbitrary values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> . As special cases of our results, we delermine the effects of partial correlation in three classes of systems: those for which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N =p</tex> , those for which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> are relatively prime, and those for which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> is a divisor of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> . We also provide two methods for the design of sequences for systems for which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> is a divisor of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> .

The authors consider a direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system with M-ary phase-shift keyed (MPSK) signaling. Users in the system use complex signature sequences. A bounding technique is used to obtain arbitrarily tight upper and lower bounds on the probability of bit error. Numerical results are presented for Frank-Zadoff-Chu (FZC) and near-optimal four-phase complex sequences, as well as binary Gold sequences, for binary phase shift keying, (BPSK), 4-PSK, and 8-PSK. Results show that complex sequences can yield better performance than binary sequences in MPSK signaling. Using complex sequences, the number of signature sequences with good correlation properties is greatly enlarged.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The performance of a hybrid direct sequence/frequency hopped (DS/FH) spread spectrum multiple access communication system is evaluated. The modulation considered is quadrature phase shift keying modulation. A mobile radio channel is investigated in the presence of interference and noise. Both deterministic and random signature sequences and memoryless random frequency-hopping patterns are considered. The maximum number of simultaneous users (capacity) at a desired level of bit error probability (10/sup -3/ - 10/sup -2/) and the spectrum efficiency are considered as performance measures. Simulation results for both synchronous and asynchronous hybrid systems are presented.

The application of selection diversity in conjunction with simple channel coding is considered for a multiuser, slowly fading, Spread-Spectrum Multiple Access (SSMA), digital radio system. For the most part, the index of performance for our study is the average bit error probability; we also give some consideration to multipath outage as a performance measure. All subscribers are assumed to communicate to a central station; that is, a star network architecture is assumed. Average power control is also assumed. The average mentioned in this context includes averaging over the channel fading statistics. The modulation is direct-sequence, spread-spectrum, binary phase-shift keying. We assume perfect timing and carrier recovery in our coherent receiver, and a slowly varying, Rayleigh fading, discrete multipath model is used. Previous analyses have found that SSMA can tolerate few simultaneous users for fading radio channels. We find that the combination of spread-spectrum modulation with low-complexity diversity and/or channel coding can restore fading-channel user levels to an acceptable figure. In addition, selection diversity plus channel coding is more effective than either method by itself. Finally, it turns out that SSMA is less sensitive to a change in the value of delay spread of a fading channel than, say, time-division multiple access. The method of moments is used to accurately assess the system error probability. Using this technique, we also assess the accuracy of assuming that the multiuser interference has a Gaussian distribution, which allows it to be analyzed by a simple method. Using this assumption, we compare selection diversity plus channel coding with the maximal-ratio-combining technique for diversity reception. Except for a high order of diversity, the former is more efficient and is always less complex than the latter.

Due to a world wide surge in the intelligent vehicle highway system (IVHS), the field of automatic vehicle identification (AVI) has been rapidly growing. The use of spread spectrum communications has not yet pervaded the AVI market. However, in the already cramped electromagnetic environment, spread spectrum techniques have gained significant popularity in many growing areas of wireless communication. AVI is perfectly suited to benefit. The fundamental advantage of spread spectrum technology in AVI applications is its invulnerability to interference and its ability to operate alongside narrow band communication systems already in place. The second advantage is the ease of licensing for spread spectrum AVI, since it does not require a dedicated frequency spectrum. It is also possible for several spread spectrum AVI systems to operate simultaneously in the vicinity of each other, using different spreading codes. This article concentrates on architecture as well as applied key signal processing techniques for a proposed direct sequence spread spectrum (DSSS) AVI system. A functional block diagram that outlines the major components of the system is presented. The system consists of three major functional parts: interrogator, transponder, and trigger. Free flow of traffic can be maintained only if the interrogator can isolate each vehicle in a common interrogation zone. DSSS allows this through code division multiple access (CDMA). The triggering system is based on the principles of speed enforcement radar. The proposed digital modulation scheme is BPSK. The DSSS modulator applies a Gold pseudo-random (PN) code to spread the spectrum of the binary signal. Despreading is carried out through the use of a PN matched filter. The antenna is assumed to have a 60/spl deg/ half-power radiation field and is placed on an existing overpass approximately 6 meters above the roadway. With 50 mW antenna transmit power, link budget analysis indicates that sufficient bit energy-to-noise power spectral density ratio is available at the receiver to generate an excellent bit error rate without requiring error control coding.

The cell capacity is determined for a direct-sequence code-division multiple-access (CDMA) communications system that employs power control of the transmitted signal in the presence of doubly selective fading. The influence of the power-control delay and the delay spectrum and Doppler spread of the channel on the cell capacity and the effectiveness of the power-control method is examined. The sensitivity of the performance of the power control to the chip rate of the direct-sequence waveform and the number of taps in the RAKE receiver is also discussed. Both open-loop and closed-loop power control. Are considered.

This paper proposes a new blind interference suppression scheme for direct-sequence code-division multiple-access (DS-CDMA) mobile communication systems. The proposed detector, the orthogonalizing matched filtering (OMF) detector, consists of a bank of despreading filters and a signal combiner. The received composite signal is first despread by the filters in the bank. The despreading filter outputs are then weighted and combined. The weight vector is adaptively determined and updated so that the average combined signal power is minimized while keeping the combiner's response to the desired signal constant. The proposed algorithm for OMF weight updating requires neither knowledge about other users' spreading sequences nor desired user's signal reference. The similarity between the proposed OMF detector and Applebaum's sidelobe canceller adaptive array is discussed in detail. Results of computer simulations are shown to demonstrate the OMF performance in various mobile communications environments.

Present day services and its users need new technology so as to integrate multimedia services along with existing ones within the same Bandwidth. Future communication networks need wide Bandwidth & high speed access. Ever since the World war 2, spread spectrum techniques have been widely used in a variety of military and civilian applications. A method of Spread Spectrum Multiple Access technique called Frequency Hopping/Multiple Carrier Direct Sequence-Code Division Multiple Access (FH/MC DS-CDMA), is an emerging system for future communication system. In this work an FH/MC DS-CDMA scheme is synthesized in VLSI chip of Xilinx's XC4000 architecture. The adoptability of the proposed system for future generation mobile as well as existing generation is always higher. Multiple carriers can be allotted as per user requirements with high secrecy and multiple encryptions. The performance analysis for the above scheme is shown supportive in terms of BER, power requirements, complexity, etc., compared to existing and evolving techniques. Here as a part of the research work a method for quick tracking of frequency hopped signals is performed in on-chip.