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Global Telecommunications Conference, 1998. GLOBECOM 1998. The Bridge to Global Integration. IEEE

Date 8-12 Nov. 1998

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  • IEEE Globecom 1998 [front matter]

    Page(s): i - xii
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  • Author index

    Page(s): xiii - xxi
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  • Maximum-likelihood sequence estimation receiver with joint frequency offset and delay profile estimation technique

    Page(s): 3455 - 3459 vol.6
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    This paper proposes a joint frequency offset and delay profile estimation technique for TDMA mobile radio communications. In the proposed algorithm, the carrier frequency offset between transmission and reception is tracked from burst to burst, while the delay profile is estimated at the beginning of each burst. In each burst, estimated frequency offset is updated during delay profile estimation using the residual error of delay profile estimation. This technique is combined with an adaptive maximum-likelihood sequence estimation receiver for time varying multipath channels. Computer simulations have been performed to demonstrate the performance of the proposed algorithm. It is shown that the allowable frequency offset range of the proposed receiver is over 10 times as large as that of the conventional receiver without frequency offset compensation View full abstract»

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  • Hidden Markov models for burst errors in GSM and DECT channels

    Page(s): 3692 - 3698 vol.6
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    Digital communication systems operating over fading radio channels suffer burst errors which can be modeled by a hidden Markov process model. An approach is presented for constructing HMM models for GSM and DECT channels using waveform level simulation and the resulting set of HMM models are tabulated for realistic values of the fading channel parameters. The use of the HMM model for protocol design and evaluation is also illustrated along with a comparison of the computational requirements for the HMM model versus a detailed waveform level simulation approach. While the actual savings in computations that is possible with the use of HMM models depends on how often the parameters of the model have to be computed from waveform level simulation, it is shown that typical savings of two or more orders of magnitude are possible View full abstract»

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  • Direct-detection optical asynchronous CDMA systems with double optical hard-limiters: APD noise and thermal noise

    Page(s): 3233 - 3238 vol.6
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    Performance of optical asynchronous code-division multiple-access (CDMA) systems with double optical hard-limiters is analyzed in the presence of avalanche photodiode (APD) noise and thermal noise. The following effects on the optimal thresholds of double optical hard-limiters and on-off keying (OOK) decoder are clarified: sequence codes, the number of users, the received laser power, and the modulation extinction ratio. The results show that the optical asynchronous CDMA systems with double optical hard-limiters have good performance in the presence of the APD noise and the thermal noise even when the number of simultaneous users is large. Moreover the optical asynchronous CDMA systems with double optical hard-limiters are shown to be practical in the respect of setting optimal thresholds View full abstract»

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  • Performance of multicode direct-detection optical CDMA systems

    Page(s): 3227 - 3232 vol.6
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    We analyze the performance of multicode direct-detection optical code-division multiple-access (CDMA) systems supporting several kinds of data with different bit rates: each user is assigned a set of sequence codes generated from time-shifted versions of optical orthogonal codes (OOCs). We analyze the performance of multicode direct-detection optical CDMA systems by using the mean value of the maximum cross-correlation between a sequence code and a set of sequence codes. We evaluate the performance of the systems under a fixed bit rate for each sequence code. Our results show that the multicode direct-detection optical CDMA system can support several kinds of data with different bit rates in optical fiber networks. Moreover, we show that the multicode direct-detection optical CDMA system has a better performance than a system using one sequence code for each user at the same bit and chip rates View full abstract»

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  • Stochastic traffic features and queueing working conditions: a simulation study

    Page(s): 3338 - 3343 vol.6
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    The paper presents an extended simulation study aimed to the evaluation of the impact on queueing performance of different statistical features of actual traffic data. In particular the relevance of marginal distribution (PDF of the arrival rate) and memory properties (LRD-SRD) is considered, highlighting the impact of these features in different queueing scenarios, varying queue length and loading conditions. The study is carried out by means of discrete event simulation driven by actual traces (collected during measurement sessions) and synthetic sequences generated according to different models. The choice of the generation procedures is motivated by model adequacy in capturing the considered statistical features of actual traffic. The analysis emphasises the need of a proper methodology (which takes into account working conditions) in model selection for realistic queueing performance evaluation View full abstract»

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  • Multiple access on narrowband interference channels

    Page(s): 3270 - 3275 vol.6
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    We investigate the influence of narrowband interference on different multiple access techniques including classic frequency-division multiple access (FDMA), time-division multiple access (TDMA), code-division multiple access (CDMA), and orthogonal FDMA (OFDMA). A major finding of this study is that CDMA with pseudonoise spreading sequences (PN-CDMA) does not perform any better than TDMA and that both multiple access schemes give virtually identical performance. We give a supporting interpretation of this result pointing out that TDMA is a special case of CDMA and that the argument of increased robustness to narrowband interference through spectral spreading equally applies to TDMA. Another finding is that orthogonal CDMA (OCDMA) has an entirely different behavior from TDMA and PN-CDMA in that the performance degradation is not the same for all users. Using continuous-wave (CW) interference, it was found that OCDMA can support a significant number of users at interference values which break both TDMA and PN-CDMA. We also point out some similarities between OCDMA and OFDMA, and highlight the fact that OFDMA is the most resistant multiple access technique to narrowband interference View full abstract»

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  • Throughput evaluation of a satellite switched CDMA (SS/CDMA) demand assignment system

    Page(s): 3632 - 3638 vol.6
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    This paper presents throughput evaluation of a satellite switched code division multiple access (SS/CDMA) system which operates under demand assignment control. The SS/CDMA provides both multiple access and switching to a geostationary multibeam satellite. Multiple access is resolved by space, frequency and code division. Space division is introduced by the multibeam antennae that provide frequency reuse in each beam. The spectrum is then channelized into frequency bands where each band is accessed by code division for both the uplink and the downlink. The satellite on-board performs the switching function which is also based on compatible code multiplexed switching. The switch may route both circuit calls and data packets which are assigned upon request. The on-board code division switch operates under the control of a channel assignment algorithm. We provide channel assignment algorithms for optimum, sub-optimum and random switch operation. Computer simulation has been used to evaluate the performance of the three algorithms. It is shown that their circuit call blocking probabilities are almost the same. The optimum algorithm achieves the minimum data packet delay, while the performance of the sub-optimum algorithm is slightly better than the random one. Furthermore, data packets may be routed via the switch with small delay, even with heavy load of circuit calls View full abstract»

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  • Comparison of W-CDMA and DSSS-TDMA systems

    Page(s): 3391 - 3396 vol.6
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    This paper compares a wireless telecommunication system employing W-CDMA transmissions from both terminal-to-base and base-to-terminal, with a novel system which employs spread-TDMA transmission from terminal-to-base and W-CDMA transmission from base to-terminal, thereby providing high quality performance in both directions. The systems are compared on the basis of capacity in a multipath, multiple cell, environment and on the basis of complexity. The spread spectrum receivers employed in both systems employ matched filters, which permit connectionless as well as connection-based packet switched communications at data rates up to 12 Mb/s, for multimedia or LAN applications, as well as voice communication View full abstract»

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  • Security techniques for the global information infrastructure

    Page(s): 3141 - 3146 vol.6
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    Information security has become an issue of critical importance; the potentially huge moves towards a global information infrastructure (GII) and electronic commerce heavily depend on the security issues being resolved. Before the GII and electronic commerce obtain widespread use and general acceptance, confidence is required that the security techniques being employed are sufficient to guarantee the effective protection of the information transmitted processed and stored. The authors look at the GII security requirements, the needs for security standardization, the work underway and the tasks ahead View full abstract»

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  • Maximal-ratio-combining array beamforming assisted by training sequences for SDMA mobile radios

    Page(s): 3204 - 3208 vol.6
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    This paper proposes and discusses the study of a non-blind type digital beamformer that can be applied to receiving array antennas with many elements. It can steer different beams independently to different users at the same frequency and of the same modulation type located in different unknown directions. The proposed beamformer is comprised of the combination of a spatial discrete Fourier transform (DFT) and maximal ratio combining (MRC) to training sequences in the complex baseband. Numerical simulations show that this beamformer can provide fast acquisition, sufficient beam isolation, and stable tracking without extensive computations such as those that would be needed for heavy matrix operations or nonlinear optimization View full abstract»

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  • Matched codes for ISI channels

    Page(s): 3530 - 3535 vol.6
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    The performance of a bandlimited communication system in the presence of additive white Gaussian noise depends on the minimum Euclidean distance, dmin, between different signal sequences. To further increase dmin, convolutional or trellis, coding could be used. Search results indicate that the encoder with the best free distance does not always give the best coded distance when combined with an intersymbol interference (ISI) channel. It has been seen from the results for several ISI channels that moderate coding gains can be obtained if the channel and the encoder are properly matched. Further it has been observed that if the channel is a maximum distance one then the resulting coded distance is usually higher than that for a non-maximum distance channel View full abstract»

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  • Multilevel coded 16-QAM modulation with multistage decoding and unequal error protection

    Page(s): 3548 - 3553 vol.6
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    A new construction for multilevel coded modulation with multistage decoding and unequal error protection is proposed and analyzed for both symmetric and asymmetric 16-QAM constellations. It is shown that the conventional upper bound originally derived for PSK signaling is loose when applied to QAM. A new tight approximated upper bound is proposed for 16-QAM and the partitioning considered. The proposed multilevel codes provide a larger proportion of most important bits (MIB) than in previous constructions View full abstract»

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  • More performant codes for deep-space missions: the turbo codes option

    Page(s): 3602 - 3607 vol.6
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    Rosetta is the first of a series of deep-space missions to be launched by the European Space Agency (ESA) in the next century. Using the present standard of the Consultative Committee for Space Data Systems (CCSDS), the nominal return link margins of Rosetta are 1.5 dB, too low even with a state-of-the-art 34-m Earth station antenna. Similar problems are also expected from Mars Express and SMART-1. Currently undergoing feasibility studies. For this (as well as other) reasons, ESA, together with NASA, has started investigating if the previously introduced turbo codes could outperform the CCSDS standard concatenated code by at least 1.5 dB on frame error rate. This paper describes the methodology through which a number of moderate complexity turbo codes with improvement on frame error rate as high as 2.8 dB has been found View full abstract»

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  • Averaging methods for blind multiuser detection in DS/CDMA systems

    Page(s): 3566 - 3571 vol.6
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    We present a blind adaptive code-aided algorithm for suppression of multiuser interference (MAI) and narrow-band interference (NBI) in DS/CDMA systems. The algorithm -which we call the BAG algorithm-is based on the concept of accelerating the convergence of stochastic gradient methods by averaging. This ingenious concept of averaging was invented by Polyak-our paper examines its application to interference suppression in DS/CDMA systems. We prove that our averaged gradient algorithm has the same asymptotic rate of convergence as RLS, but at a order of magnitude lower computational cost View full abstract»

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  • Application of frequency-shift filtering to the removal of adjacent channel interference in VLF communications

    Page(s): 3515 - 3520 vol.6
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    The use of frequency-shift (FRESH) filtering for the rejection of adjacent channel interference (ACI) in GMSK modulated VLF communications is investigated. A range of scenarios based on a high powered interferer (up to 40 dB greater than the signal of interest (SOI)) in an adjacent channel to the SOI are tested, and the use of a FRESH filter for rejection of the interference is investigated. It is shown that a major improvement in BER performance over a fractionally spaced equaliser (FSE) is possible, and that only one interferer related frequency shift is required. This demonstrates that FRESH filters can be highly effective in ACI removal, with only a moderate increase in complexity over an FSE View full abstract»

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  • Robust event correlation scheme for fault identification in communications network

    Page(s): 3745 - 3750 vol.6
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    The complexity of communications network and the amount of information transferred in these networks have made the management of such networks increasingly difficult. Since faults are inevitable, quick detection, identification, and recovery are crucial to make the systems more robust and their operation more reliable. This paper proposes a novel event correlation scheme for fault identification in communications network. This scheme is based on the algebraic operations of sets. The causality graph model is used to describe the cause-and-effect relationships between network events. For each problem, and each symptom, a unique prime number is assigned. The use of the greatest common devisor (GCD) makes the correlation process simple and fast. A simulation model is developed to verify the effectiveness and efficiency of the proposed scheme. From simulation results, we notice that this scheme not only identifies multiple problems at one time but also is insensitive to noise alarms. The time complexity of the correlation process is close to a function of n, where n is the number of observed symptoms, with order O(n2); therefore, the on-line fault identification is easy to achieve View full abstract»

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  • Throughput analysis and design of fixed and adaptive ARQ/diversity systems for slow fading channels

    Page(s): 3686 - 3691 vol.6
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    We study the performance of a fixed diversity (FD) ARQ system in which no error correction coding is used, and only second order transmitter diversity is used. In the system two spatially separated antennas are used to transmit the same information signal in a staggered fashion. In an FD system with two transmitting antennas, due to the staggered nature of transmission, the information rate of the FD system is 1/2, and we compare this system with the block-coded hybrid ARQ system of rate 1/2 used by Sayeed (see International Journal of Wireless Information Networks, 1997, Doctoral Disseration, University of Pennsylvania, 1996), and by Weerackody (1993). Due to the lower information rate of the transmitter diversity system, we do not wish to diversify at all times, but only when diversity is required. Thus we propose an adaptive ARQ/diversity (AD) system, in which the transmitter adaptively switches between the single antenna and dual antenna mode using the implicit channel state information contained in the number of consecutive ACKs and NACKs. Using analytical techniques we show that the performance of the adaptive diversity system equals the performance of adaptive ARQ/FEC techniques that have been used by Kallel (1994), by Sayeed and Weerackody (see Proceedings of Conference on Information Sciences and Systems, CISS '96, 1996), and by Deng and Lin (see IEEE Transactions on Communications, vol.-43, no.2/3/4, p.733-7, 1995) which uses the uncoded and a rate half maximum distance separable code (MDS) View full abstract»

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  • Analytical approach for multipath delay spread power distribution

    Page(s): 3680 - 3685 vol.6
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    There is a certain relationship between the delay spread and the received signal strength of multipath waves. This paper describes the geometrical interpretation for spread delay in urban areas. An analytical approach for relative received power as a function of excess delay is discussed. Examples of measured data for power delay profiles are used in comparison with the analytical results. These examples show that the square of the ratio between the shortest time delay and the time delay is sufficient to approximate the power delay profile. This second order equation can also be used to calculate the time dispersive parameters of the channel such as the mean excess delay and RMS delay spread View full abstract»

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  • Costs of upgrading the residential telecommunications infrastructure to broadband

    Page(s): 3153 - 3158 vol.6
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    The paper presents an analysis of the investment costs associated with broadband upgrades in various residential areas in which there is an existing twisted pair infrastructure. Upgrade strategies based on a combination of optical fibre systems and digital subscriber line (DSL) technologies are examined. The analysis highlights the significant differences in investment levels expected in downtown, urban, suburban and rural areas for the ranges of DSL capacities from 2 Mbit/s to 52 Mbit/s. The paper reports work performed in the EURESCOM project P614, “Implementation Strategies for Advanced Access Networks”. The methodology and tool initially developed by the RACE 2087/TITAN project and now under further development in the ACTS 226 OPTIMUM project has been applied in the techno-economic analysis View full abstract»

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  • An ATM-based optical code division multiplexing transport network using coherent ultrashort pulses

    Page(s): 3215 - 3220 vol.6
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    We investigate the feasibility of introducing optical code division multiplexing (OCDM) technique in the path layer and propose an ATM-based OCDM network architecture using ultrashort light pulses. In the proposed network, all the processes of cells in the path layer operate in the optical domain prior to reaching the final destination node. Since each bit can be addressed individually with this technique, the realization of ATM protocols can be easily ensured. Optical technology can be reliably introduced in the path layer and an optical cross-connect (OXC) becomes an important component because it emulates the code conversion as the switching function. The OXC not only provides asynchronous access to each optical code path (OCP) but also has a dynamic bandwidth allocation capability. A lookup table is used in the switching and updated through network management functions. We examine the performance considering different parameters and discuss methods to improve the performance View full abstract»

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  • Performance analysis of the modified circuit reservation multiple access protocol with signalling traffic

    Page(s): 3276 - 3281 vol.6
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    The modified circuit reservation multiple access (CRMA) protocol is a new wireless communication protocol that has been proposed for the use in a cellular environment. The signalling aspect for this protocol is studied and the integration of the signalling traffic within the system is presented and investigated. The operation of the protocol, in which the signalling is embedded, is simulated and the system performance is analysed in terms of throughput and delay View full abstract»

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  • Bit error rate characterisation and modelling for GSM

    Page(s): 3722 - 3727 vol.6
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    This paper presents a method to model the bit error rate in GSM, taking as inputs the carrier to interference ratio and the speed. The procedure is based on a characterisation of the bit error rate second order statistics. Then, a technique which allows matching of both probability distribution and auto-correlation functions is applied in order to obtain replicas of the bit error rate sequence. A method to obtain results for any carrier to interference ratio and speed is then proposed, based on linear interpolation. The results are compared to the output of the full transmission chain simulation, showing that a good degree of accuracy is achieved, while the simulation time is drastically reduced View full abstract»

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