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Spread Spectrum Techniques and Applications, 1994. IEEE ISSSTA '94., IEEE Third International Symposium on

Date 4-6 July 1994

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Displaying Results 1 - 25 of 119
  • Proceedings of IEEE 3rd International Symposium on Spread Spectrum Techniques and Applications (ISSSTA'94)

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    Freely Available from IEEE
  • The effect of multipath fading on the radiometric detection of frequency hopped signals

    Page(s): 243 - 247 vol.1
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    The effect of fading due to multipath is seldom accounted for in the assessment of the vulnerability of frequency hopped communications systems to radiometric intercept threats. However, the results derived in the paper illustrate that fading due to multipath could significantly improve the ability of a radiometer to detect frequency hopped signals transmitted at sea View full abstract»

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  • An interference suppressor for CW and narrow-band signals using filter bank on CDMA communications

    Page(s): 521 - 525 vol.2
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    A novel digital interference suppression method based on Fourier transform has been proposed. Since the frequency power spectrum of CW and narrow band interference signals are larger than that of the spread-spectrum signal, these interference signals can be reduced by limiting the signal level in the frequency domain. The proposed method is composed of FDM/TDM transform using a filter bank and an amplitude limiter adjusted to the spectrum of the spread-spectrum signal. The received signals are divided into separate narrow frequency bands in real time using a frequency function and the amplitude of these signals is limited. This signal processing reduces the interference signals. This paper describes the principle design of the transform circuit and explains the optimum limiting technique. In particular, the proposed digital processing model is compared with the analog processing model which has already been reported. In addition, the adjustment level of the amplitude limiter for the DS and FH spread-spectrum signal is shown. Finally, the improvement in interference suppression using FFT and the optimum limiting limiter is demonstrated with measured the eye pattern of the correlated signal. The performance of this suppressor is shown by measuring the bit error rate in the presence of CW interference signals and Gaussian noise View full abstract»

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  • A new scheme for the coded SSMA systems

    Page(s): 560 - 563 vol.2
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    A new scheme for coded spread spectrum multiple access (SSMA) systems is presented. The new scheme employs a four-dimensional modulation which combines the FSK and PSK modulation. The corresponding receiver structure is discussed and a realization method is given. The bandwidth expansion and performance comparisons show that the scheme presented is more attractive over the coded MPSK SSMA systems View full abstract»

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  • Acquisition-based capacity estimates for CDMA with imperfect power control

    Page(s): 325 - 329 vol.1
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    One of the major advantages of a code division multiple access (CDMA) system is the flexibility in frequency assignment, which allows all the users to share the same frequency band and, possibly, to partially overlay the spectrum allocation of different services. However, before synchronism to the desired sequence is achieved, the presence of multiple access interference (MAI) is a major impairment which determines the performance of the code acquisition sub-system. It has been argued that the acquisition performance in the presence of MAI may pose limits to the capacity of a CDMA system which are more stringent than those coming from bit error probability specifications. We introduce a general definition for acquisition-based capacity of a CDMA system. This quantity is evaluated for an acquisition sub-system with non-coherent correlator/detector and straight serial search in the time uncertainty region. The effect of imperfect power control is also analysed, showing that the capacity may be substantially decreased when the residual standard deviation of the received power level is above 1 dB View full abstract»

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  • The performance of GMSK as a modulation scheme for direct sequence CDMA

    Page(s): 554 - 559 vol.2
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    The processing gain of a direct sequence spread spectrum communications system using GMSK modulation is analysed. Multiple access interference is considered, rather than broadband white noise. Monte-Carlo methods are used. It is shown that the processing gain in a GMSK based system is lower than is possible in an equivalent system using QPSK. It is further shown that this processing gain need not be lost if adjacent systems are allowed to overlap in frequency. The optimum time-bandwidth product is found to be between 0.1 and 0.2 View full abstract»

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  • An overview of TU Delft research on CDMA

    Page(s): 319 - 324 vol.1
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    This paper presents an overview of the research work carried out by the faculty members and students of the Delft University of Technology (TU Delft), The Netherlands in the field of code division multiple access. They have investigated CDMA systems considering direct sequence (DS), slow frequency hopping (SFH), hybrid SFH/DS, hybrid CDMA/inhibit sense multiple access (ISMA), multi-carrier (MC)-CDMA, interference cancellation, dynamic code channel allocation, synchronization, receiver structure and overlay CDMA/TDMA systems for macro-, micro- and pico-cellular systems as well as for land mobile satellite systems. The effect of forward error correction (FEC) coding and of diversity techniques on CDMA systems performance is also analyzed. Computer simulation has been performed to verify the basic assumptions, such as approximating by multi-users interference by a Gaussian random variable, in the analysis. Results of these investigations are summarized and discussed View full abstract»

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  • Influence of data modulation and Doppler effects on the performance of a delay locked loop

    Page(s): 598 - 602 vol.2
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    The influence of Doppler effects on the tracking performance of a noncoherent second-order delay-locked loop (DLL) operating on a data modulated signal is investigated. For the performance analysis the author considers the tracking accuracy (steady state error and jitter) of the linear DLL and the reliability of the nonlinear loop. The nonlinear analysis concerning the loop reliability makes use of an asymptotic expansion for the mean exit time (mean time to lose lock, MTLL) which has been derived by applying the singular perturbation method. In particular, the author gives optimal loop parameters and the optimal bandwidth of the bandpass filter in the loop arms to achieve a maximum MTLL. Due to Doppler effects the optimal loop parameters are rather different using either linear or nonlinear analyses View full abstract»

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  • Consumer communications based on spread spectrum techniques

    Page(s): 138 - 145 vol.1
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    This paper shows consumer applications of spread spectrum techniques in the following areas: power line communication, data carrier, radio remote control, ISM wireless LAN, vehicle to vehicle communication, and digital TV broadcasting. One of the most difficult problems for a spread spectrum communication system is how to synchronize the receiver to the transmitted signal. The sliding correlator method is the typical and simplest, but needs a long acquisition time for synchronisation. Matched filter and convolver methods need much shorter acquisition time and SAW devices are adapted to them View full abstract»

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  • Carrier frequency offset-spread spectrum multiple access (CFO-SSMA) method

    Page(s): 314 - 318 vol.1
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    A novel spread spectrum multiple access method employing only a single PN code is proposed. This new method, named “CFO-SSMA (carrier frequency offset-spread spectrum multiple access)”, utilizes a single PN code commonly assigned to all users with different carrier frequencies. The amount of the frequency offset between carriers is determined by the information rate, which is very small as compared with the bandwidth of the spread spectrum signal. CFO-SSMA employs a receiver using a surface acoustic wave (SAW) matched filter, which has an advantage of rapid signal acquisition over the conventional receiver, but has a disadvantage of difficulty to change the PN code pattern. CFO-SSMA defeats this disadvantage, because there is no need to change the matched filer in accordance with the channel to be recovered. The concept and basic performance of CFO-SSMA is discussed in this paper. The optimum bandwidth of the receive filter as well as the BER performance of CFO-SSMA are also shown View full abstract»

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  • Doppler optimised compression filters

    Page(s): 534 - 538 vol.2
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    The problem of designing radar detection filters that minimise sidelobe levels in both Doppler and the range co-ordinates is considered. The new algorithm for Doppler optimised mismatch filter is constructed. The generalization enables sidelobe suppression for the polyphase and complex multilevel sequences. For minimax filter coefficients calculation, the iterative reweighted least-square procedure is successfully applied. Considerable experimental results are obtained, especially for polyphase sequences View full abstract»

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  • A channel access protocol for multihop FH-SS packet radio networks

    Page(s): 228 - 232 vol.1
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    This paper proposes and studies the performance of a channel access protocol specifically designed for multihop frequency-hopping spread spectrum packet radio networks. This protocol takes into account inherent FH-SS characteristics such as the time overhead for hopping pattern synchronization, the capture effect, and interference rejection. An accurate simulation model has been built to evaluate the protocol's performance in terms of end-to-end packet throughput and end-to-end delay. The simulation results show that as the traffic load increases the data link layer performance is much more sensitive to the acknowledgment and pacing strategy than to the parameters of the channel access protocol. The best results are obtained when active acknowledgment packets piggy-back other packets (data, control, update route, etc.) View full abstract»

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  • Co-channel interference cancellation in optical synchronous CDMA communication systems

    Page(s): 579 - 583 vol.2
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    Three co-channel interference cancellation techniques are proposed for synchronous optical CDMA communication systems. Modified prime sequence optical codes that exhibit a grouping characteristic are employed. In the first technique the desired user collects primary decisions from receivers of all interfering users and subtracts them, after properly weighting, from its received signal. In the second and third techniques the desired user collects photodetector outputs from users in its same group and subtracts them from its received signal after a proper scaling View full abstract»

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  • Block demodulation-an overview

    Page(s): 36 - 42 vol.1
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    We consider the use of block demodulation, or multi-symbol detection, in receivers for digital transmission. After reviewing the rationale behind it, we examine its performance for intersymbol-interference channels and for differential and double-differential detection of PSK View full abstract»

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  • Complex valued spreading sequences with good crosscorrelation properties

    Page(s): 500 - 504 vol.2
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    This paper examines the performance of sets of pseudorandom (PR) sequences using the criterion of least mean-square (MS) values of the aperiodic cross-correlation (CC). The MS correlation values are averaged over all elements in the set rather than the more traditional approach of taking the MS correlation values of randomly selected elements as representative. This is intended to give an indication of the performance of the set as a whole. This paper introduces a new family of constant amplitude, complex valued sequences designed using the criterion of least MS value of the CC values of all sequences in the set. This family of sequences is compared with well known sequences on the basis of correlation values and frequency characteristics and is shown to offer a wider range and better combination of correlation values. The paper also provides a limit on the lower bound of the value of the MS CC for the new family of complex sequences and members of the family are given for which the average MS value of the CC asymptotically approaches this bound. The potential trade off of CC values for auto-correlation (AC) is also illustrated View full abstract»

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  • 4-phase DS-CDMA mobile radio receiver in non-Gaussian environment

    Page(s): 440 - 444 vol.2
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    The aim of the paper is to investigate the performance of digital mobile radio communications using the RAKE receiver under impulsive environments. The performances studies are carried out in terms of spectral efficiency and bit error probability. The assumed modulation technique is QPSK. The signature sequences used for spreading the signal are complex valued and characterized by different correlation properties; the possible choices lead to a performance comparison based on the properties of the sequences in order to maximize the number of users per cell View full abstract»

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  • Additional interference in a RAKE receiver implementation of a CDMA power control mechanism

    Page(s): 425 - 429 vol.2
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    A direct sequence CDMA power control mechanism in a multipath fading environment is considered. The greatest attention is devoted to the additional interference in a RAKE receiver with a limited number of branches, i.e. the multipath “range” exceeds the number of branches of the RAKE, when an ideal power control on the tracked rays is assumed. Analytical expressions are derived under the assumption of relatively slow multipath Rayleigh fading and an illustrative numerical application is then given View full abstract»

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  • FH-SSMA with band-efficient modulations over cellular radio channels

    Page(s): 218 - 222 vol.1
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    We present frequency hopped spread-spectrum multiple-access (FH-SSMA) employing band-efficient modulations that are phase-continuous during each hop. The particular cases of minimum-shift keying (MSK), and Gaussian minimum-shift keying (GMSK) are studied in detail. Noncoherent sequence estimation on a hop-by-hop basis is considered. Has been evaluated in selective Rayleigh fading with additive white Gaussian noise (AWGN) and the presence of multiple-access cellular interference. Power control is employed for improving the BER performance. This system performance is better than the performance of FH-SSMA with noncoherent binary FSK modulation View full abstract»

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  • Bit error probability for an adaptive diversity receiver in a Rayleigh fading channel

    Page(s): 450 - 454 vol.2
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    The bit error probability is determined for an adaptive diversity receiver using decision directed feedforward channel estimation. The channel is assumed to be a nonselective Rayleigh fading channel with AWGN. The analysis is valid for all feedforward estimation structures which use an FIR-type estimation filter. The analysis can be applied also to Rake receivers in a frequency selective Rayleigh fading channel. Numerical results are presented for an adaptive diversity receiver which uses either an FIR-type minimum mean-square error (MMSE) filter or a moving average (MA) filter as the estimation filter. The results show that the MA filter performs poorly compared to the MMSE filter at large signal-to-noise ratios and large Doppler spreads. However, at small signal-to-noise ratios and Doppler spreads the filters do not show any remarkable difference in the performance View full abstract»

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  • Information theory aspects of spread-spectrum communications

    Page(s): 16 - 21 vol.1
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    A novel definition of a spread-spectrum system as a communications system in which the Fourier bandwidth is much greater than the Shannon bandwith (the number of dimensions of signal space used per second) is proposed. Six different communication systems are analyzed in terms of this definition. It is shown that there is a fundamental difference between the bandwidth expansion due to coding and due to “spectrum spreading”. It is further shown that spectrum spreading plays no role in increasing the capacity of the system, but can perform other useful roles such as providing low probability of interception of the signal, good electromagnetic compatibility, and a multiple-access capability View full abstract»

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  • On narrowband interference suppression using DFB filter in DSSS systems under impulsive channel conditions

    Page(s): 530 - 533 vol.2
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    In this paper the extension analysis of the recently proposed direct sequence spread spectrum (DSSS) receiver using decision feedback filter (DFB) under narrowband interference (NBI) and impulsive channel conditions is presented. The results, obtained by theoretical analysis and computer simulation in term of the output signal to interference ratio (SIR), show that the impulsive noise does not deteriorate the excellent performance of the DFB receiver in the NBI suppression. The impulsive noise influence on the receiver performance can be adequately expressed through the increase of the total noise power View full abstract»

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  • Interference suppression for CDMA overlays of narrowband waveforms

    Page(s): 61 - 68 vol.1
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    An overview of the performance of CDMA networks which overlay narrowband signals in order to increase the spectral efficiency is presented. Such systems employ interference suppression filters in the CDMA receivers to minimize the interference caused by the narrowband waveforms. The results presented in this paper include the effects of multipath fading, as well as both intracell and intercell interference for cellular systems View full abstract»

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  • An integrated all digital diversity receiver for spread spectrum communications over multipath fading channels

    Page(s): 367 - 371 vol.2
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    In this paper is described the architecture of an integrated multipath combining diversity receiver for direct sequence spread spectrum communication systems using differential binary phase shift keying modulation. A general structure of path combiner is proposed. Simulated performance over a multipath fading channel for two different path combining algorithms implemented on this architecture are presented View full abstract»

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  • Realistic simulations of CDMA mobile radio systems using joint detection and coherent receiver antenna diversity

    Page(s): 193 - 197 vol.1
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    Due to time variant multipath propagation, both intersymbol interference and multiple access interference occur at CDMA receivers. These degrading effects can be combatted by joint detection (JD) techniques. In order to reduce the performance impairments resulting from time variance, coherent receiver antenna diversity (CRAD) can be used. A system model of CDMA mobile radio systems using various JD techniques in combination with CRAD is introduced. This system model is an evolution of the pan-European GSM and takes important real world aspects such as imperfect channel estimation, nonlinear amplification and D/A and A/D conversion into account. The viability of JD with CRAD is demonstrated by bit error rate simulations of this system model. It is shown that by using JD with two receiver antennas in bad urban areas, Eb/N0<8 dB per antenna is sufficient for a bit error rate of 10-2, and Eb/N0<11 dB per antenna is required for a bit error rate of 10-3 View full abstract»

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  • Optimum PN sequences for CDMA systems

    Page(s): 27 - 35 vol.1
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    Most known methods for the design of hopping patterns for frequency-hopped code-division multiple-access (CDMA) systems and for the design of signature sequences for direct-sequence CDMA systems provide sequences that can be viewed as codewords (or the images of codewords) from low-rate Reed-Solomon codes. This paper surveys sequence designs for CDMA systems from this viewpoint View full abstract»

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