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Selected Areas in Communications, IEEE Journal on

Issue 3 • Date April 1996

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Displaying Results 1 - 20 of 20
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  • Interactive computation of coverage regions for wireless communication in multifloored indoor environments

    Page(s): 420 - 430
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    For indoor wireless communication systems, radio frequency (RF) transceivers need to be placed strategically to achieve optimum communication coverage at the lowest cost. Unfortunately, the coverage region for a transceiver depends heavily on the type of building and on the placement of walls within the building. Traditionally, therefore, transceiver locations have been selected by human experts who rely on experience and heuristics to obtain the optimum (or near-optimum) placement. This paper describes an interactive software system that can be used to assist in transceiver placement. It is intended to be easy to use by individuals who are not experts at wireless communication system design. After the user has selected transceiver locations within a graphical floor plan, the system interprets the floor plan and uses simple path loss models to estimate coverage regions for each transceiver. These regions are highlighted, enabling the user to assess the total coverage. This paper describes the methodology used to compute the coverage regions for multifloored buildings and discusses the effect of interference sources. The resulting system is expected to be useful in the specification of indoor wireless systems View full abstract»

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  • Rapid acquisition algorithms for synchronization of bursty transmissions in CDMA microcellular and personal wireless systems

    Page(s): 570 - 579
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    Two rapid synchronization acquisition algorithms applicable to spread spectrum links of code division multiple access (CDMA) personal communication systems are proposed and evaluated. The algorithms operate within a self-referencing matched filter synchronizer structure, and are particularly useful in reducing synchronization overhead on links designed to carry packet-type services. The main distinguishing characteristic between the two schemes is that one uses hard-decision while the other uses soft-decision detection. The proposed schemes are especially applicable to reverse link transmissions in quasisynchronous CDMA systems in which timing at portable terminals is established via pilot and synchronization signals received on respective code-division channels from the home base. If discontinuous (bursty) transmission is used on reverse links, the acquisition process is required for each transmission burst because of the propagation time uncertainty. Analysis of the algorithms on additive white Gaussian noise (AWGN) and Rayleigh fading channels reveals that their performance depends significantly on the choice of synchronizer parameters and the average despread signal-to-interference ratio (SIR). When this choice is proper, acquisition over a single preamble of relatively short duration can be achieved with high probability. The soft-decision scheme introduces a performance advantage of between 4-9 dB depending on the length of the synchronizing preamble View full abstract»

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  • Performance analysis of a hybrid DS/SFH CDMA system using analytical and measured pico cellular channels

    Page(s): 580 - 588
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    This paper presents the throughput and delay analysis of a packet-switched code division multiple access (CDMA) network based on the hybrid direct sequence (DS)/slow frequency hopping (SFH) spread-spectrum multiple access (SS MA) technique with Q-, B-, and D-PSK modulation using analytical and measured pico cellular channels. The performance of the hybrid DS/SFH, DS, and SFH multiple access techniques have been compared in a pico cellular personal communications network (PCN) environment. Multipath and multiple access interference are considered. The performance is evaluated for a given delay spread and a fixed bandwidth. The effects of forward error correction (FEC) coding and diversity techniques, such as selection diversity and maximal ratio combining on the performance, are also investigated View full abstract»

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  • Spectral efficiency of a power-controlled CDMA mobile personal communication system

    Page(s): 559 - 569
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    The spectral efficiency is determined for a direct-sequence code-division multiple-access (CDMA) communications system that employs rapid closed-loop power control on a channel with doubly selective fading. The sensitivity of the spectral efficiency to the chip rate of the direct-sequence waveform and the number of taps in the RAKE receiver is considered. The effectiveness of the power-control method is also examined for different power-control delays, delay spectra, and Doppler spreads. The implications of the results for the design of personal communication systems are discussed View full abstract»

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  • Effects of antenna directivity and polarization on indoor multipath propagation characteristics at 60 GHz

    Page(s): 441 - 448
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    In millimeter-wave indoor communications systems, the radiation patterns and polarizations of the antennas at base stations and remote terminals have a significant influence on channel characteristics. The work reported in this paper investigated the effects of the radiation patterns of the antennas at remote terminals on multipath propagation characteristics. These effects were investigated by indoor propagation measurements at 60 GHz conducted in a modern office room and by ray-tracing simulations based on geometrical optics. Multipath channel characteristics are compared in terms of impulse responses and their root-mean-square (rms) delay spreads for an omnidirectional antenna and for three directive antennas with different beam widths. From the results of measurements and ray-tracing simulations, the use of a directive antenna at the remote terminal is demonstrated to be an effective method of reducing the effects of multipath propagation. Further reduction in the multipath effects is found to be achieved by the use of circular polarization instead of linear polarization with the directive antennas View full abstract»

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  • Transmission of high rate ATM packets over indoor radio channels

    Page(s): 469 - 476
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    The design and performance of a high data rate modem that transmits asynchronous transfer mode (ATM) packets over indoor radio channels is discussed. A discrete Fourier transform (DFT)-based multicarrier modulation technique is used to mitigate intersymbol interface (ISI) caused by a multipath spread of up to 250 ns. A rate one-half channel code is used to combat fading. Computer simulation is performed to investigate the system performance for five different multipath intensity profiles. The system performance is compared using a differentially coherent scheme and a coherent scheme based on channel estimation. The effects of carrier frequency offset and some of the hardware nonlinearities are discussed. Using various channel codes, an signal-to-noise ratio (SNR) of 14-21 dB is required at an average bit error rate (BER) of 10-5 to transmit a total of 155 Mb/s data over a bandwidth of 280 MHz View full abstract»

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  • A characterization of indoor space and frequency diversity by ray-tracing modeling

    Page(s): 411 - 419
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    The performance of space and frequency diversity techniques at 1800 MHz in an indoor environment are investigated. Three linear signal combining techniques are considered: signal selection (SEL), maximal ratio combining (MRC), and equal gain combining (EGC). The computations of received fading envelopes are performed by means of an analytical model, based on a three-dimensional ray-tracing (RT)/uniform theory of diffraction (UTD) technique; the reliability of the adopted approach is confirmed by comparison with some test measurements. The electromagnetic field components are adequately processed to obtain the single branch and combined signal envelope. The results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage for both diversity techniques. Antenna spacings of about 0.75-1λ are nearly sufficient for achieving optimum performance, whereas frequency separation on the order of 10 MHz is needed for sufficiently decorrelated transmission on the two carriers View full abstract»

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  • Effect of correlation in diversity systems with Rayleigh fading, shadowing, and power capture

    Page(s): 449 - 460
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    With the growth of wireless personal communications networks and wireless local area networks (WLAN's), the need for increased reliability of the radio link has become evident. The use of diversity techniques, such as dual receiving antennas, helps mitigate the effect of multipath fading in both the in-building and land mobile radio environments. A significant issue in the design of such systems is the degree to which correlation between the two or more diversity signals can be tolerated. In this paper, we consider the use of diversity techniques in radio systems that are subject to correlation. Rayleigh fading, lognormal shadowing, and the radio capture effect. In the presence of two simultaneously transmitting stations, the throughput, conditioned on the local-mean power, is determined exactly for the case of a dual diversity receiving station. The insight gained from the two-station analysis is used to develop an accurate approximation for cases with more than two stations. The degree to which correlation can be tolerated without significant performance loss relative to the case of independent diversity signals is quantified, as are the effects of different system parameters (i.e., the capture ratio, power roll-off coefficient, and the amount of shadowing). Furthermore, the relationship between the envelope and power correlation coefficients is presented. An application of the capture results to the slotted ALOHA protocol is also included View full abstract»

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  • Space-diversity issues in the context of a B-ISDN-oriented indoor radio environment

    Page(s): 461 - 468
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    A first assessment of the applicability and the tradeoffs involved in a switched (antenna) diversity approach is presented here as seen in the context of a future indoor wireless network operating in the mm-wavelength radio spectrum targeted to provide radio access to asynchronous transfer mode local area networks (ATM LAN's) and broadband integrated services digital networks (B-ISDN). Measurements conducted at 21.6 GHz are used to examine the gain variation of switched-diversity alternatives in terms of cumulative distribution functions. The performance of a two-branch post-detection code diversity combining scheme under Rayleigh fading conditions is also included for purposes of comparison. The results of our work here confirm the hypothesis that the choice of the employed antenna diversity technique in combination with the selected micro-cellular architecture have significant effects on both the throughput and the measured performance of future radio links View full abstract»

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  • Adaptive DFE for GMSK in indoor radio channels

    Page(s): 492 - 501
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    We simulate the performance of an equalized Gaussian minimum shift keying (GMSK) signal in an indoor radio environment with fading, noise, imperfect carrier recovery, cochannel interference (CCI), and intersymbol interference (ISI). We show that data rates of 20 Mb/s at bit error rates (BER) ⩽10-4 are possible with root mean square (RMS) delay spreads up to 25 ns using a simple limiter-discriminator-integrator (LDI) receiver and a (6, 4) decision feedback equalizer (DFE). In environments with larger RMS delay spreads, coherent detection is required for the same performance. We show that using a decision-directed second-order digital carrier synchronizer with time varying loop filters, frequency offsets up to 200 kHz can be corrected with negligible performance degradation. This paper utilizes a DFE structure which compensates for both modulator and channel ISI, and yet requires no power-intensive multiplication operations in the feedback section. A DFE (8, 8) with two-level switched (selection) diversity is shown to allow 20 Mb/s data transfer at a BER⩽10-4 for RMS delay spreads under 150 ns, with CCI. A light BCH (26, 31) code allows error-free reception of over 90% of packets with RMS delay spreads under 150 ns, and up to 70% of packets with RMS delays of 150 ns View full abstract»

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  • Experimental characterization of EHF multipath indoor radio channels

    Page(s): 431 - 440
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    This paper reports on experimental results and their interpretations for an indoor extremely high frequency (EHF) multipath channel. It is intended to help in establishing design guidelines for indoor wireless communications systems using millimeter waves. It deals with measurements obtained for the narrow and wideband indoor radio channels at 37.2 GHz within a typical concrete building at Laval University. Two kinds of transmission antennas, omnidirectional and directional, are used to investigate the propagation characteristics for the indoor channel. Under line-of-sight (LOS) conditions, the distance-power law exponent is found to be lower than the free space condition with walls playing a major role on the sustaining of high level signals. Large- and smallscale variations extracted from the original data are shown to follow log-normal and Rice distributions, respectively. The observed wideband impulse response has delay spread extending over a range up to 40 ns and a maximum root mean square (rms) value of about 16 ns. Both amplitude and phase behaviors of the signals are available for a better understanding of the various effects View full abstract»

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  • Nonlinear equalization of multipath fading channels with noncoherent demodulation

    Page(s): 512 - 520
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    A nonlinear decision-based adaptive equalizer compatible with differentially coherent phase shift keying (PSK) is proposed for frequency-selective fading channels. This equalization scheme is appropriate whenever conventional equalizers are not capable of tracking phase variations in selective fading channels. The received signal is first converted to a baseband signal and then sent through a differential detector. A nonlinear processor before the equalizer generates the needed nonlinear terms that are weighted and summed in the equalizer. Nonlinear intersymbol interference at the output of the differential detector is dealt with by minimizing an error signal between the output of the equalizer and the detected data. The adaptation algorithm can be any algorithm currently used for conventional equalizers. Our simulation results confirm that for channels with spectral nulls, equalization is achieved successfully with the proposed scheme, whereas, linear equalizers, either with coherent or noncoherent detection, fail View full abstract»

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  • Transmission techniques for radio LAN's-a comparative performance evaluation using ray tracing

    Page(s): 477 - 491
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    This paper uses the results of ray tracing in a typical indoor test area to compare the performance of major radio transmission techniques that are used as the air interface in evolving standards and major wireless local area network (WLAN) products. The performance of direct sequence (DS) and frequency hopping spread spectrum (FHSS) in the test area are compared with the performance of multicarrier modems, as well as modems using decision feedback equalization (DFE) and sectored antenna systems (SAS). The validity of using ray tracing for performance evaluation is examined by comparing the results with the results of performance evaluation obtained from the empirical measurement of the channel characteristics. Based on the maximum achievable data rate and minimum power requirement determined in the test area, operation of all modems in bandlimited and power limited applications are discussed View full abstract»

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  • Statistical analysis of measured impulse response functions of 2.0 GHz indoor radio channels

    Page(s): 405 - 410
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    The measurements of the impulse response of a 2.0 GHz indoor radio channel are reported. A statistical analysis of the characteristics of the amplitude of multipath components is presented. In particular, the spatial correlation of the single multipath components and the cross-correlation between the amplitudes of adjacent multipath components have been determined. Conclusions are drawn with regard to the adequacy of the wide sense uncorrelated scattering model as a consistent model for the indoor radio channel View full abstract»

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  • Comparison of turbo-code decoders applied to short frame transmission systems

    Page(s): 530 - 537
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    A novel class of binary parallel concatenated recursive systematic convolutional codes termed turbo-codes, having amazing error correcting capabilities, has previously been proposed. However, the decoding of turbo-codes relies on the application of soft input/soft output decoders. Such decoders can be realized either using maximum a posteriori (MAP) symbol estimators or MAP sequence estimators, e.g., the a priori soft output Viterbi algorithm (APRI-SOVA). In this paper, the structure of turbo-code encoders as well as of turbo-code decoders is described. In particular, four different decoder structures are illustratively characterized and their error rate performance capabilities compared in both additive white Gaussian noise (AWGN) as well as flat Rayleigh-fading channels based on extensive simulation results for short frames used for speech transmission in the uplink of a digital mobile radio system applying code division multiple access and joint detection. The decoders are investigated as follows: 1) the MAP symbol estimator-based approach used by Berrou et al. [1993], 2) the MAP symbol estimator-based approach used by Robertson [1994], 3) a new reduced complexity MAP symbol estimator-based approach [Jung 1995], and 4) an APRI-SOVA based approach used by Hagenauer et al. [1994] View full abstract»

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  • A multicarrier transmission scheme for wireless local communications

    Page(s): 521 - 529
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    This paper presents a novel multitone transmission scheme that employs a nonlinear binary code to specify multitone signal constellations. The scheme, which can be viewed as a generalization of M-ary frequency shift keying, is amenable to noncoherent demodulation, and it is therefore useful for communication over fading channels. We determine the performance of this modulation scheme when it is used in conjunction with a Reed-Solomon code for error control. Methods for determining and erasing unreliable multitone constellations are presented and their performance is evaluated when they are used in conjunction with errors-and-erasures decoding. The transmission scheme is evaluated with respect to complexity, bandwidth efficiency, and performance in the presence of Gaussian noise and frequency- and time-selective fading View full abstract»

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  • MIMO DFE equalization for multitone DS/SS systems over multipath channels

    Page(s): 502 - 511
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    The combination of multitone modulation with direct sequence spectrum spreading (DS/SS) has been introduced in the past. The performance of a correlation receiver has been evaluated for a multipath channel and in the presence of an additional multiple access interference. We analyze the problem of decision feedback equalization (DFE) for such a system. In order to understand the potential of the system with equalization, we first study the steady-state behavior of the equalizer for a minimum mean square error (MMSE) criterion. The investigation is carried out for a receiver made of a bank of filters matched to both the symbol shape and the channel, and for a two path channel. Assuming transmission of binary phase shift keying (BPSK) symbols, an exact expression of the bit error probability is obtained in the form of an integral. Then adaptive least mean square (LMS) and recursive least square (RLS) structures are derived. The performance of the adaptive RLS algorithm is demonstrated by means of computer simulations View full abstract»

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  • Multiple-subcarrier modulation for nondirected wireless infrared communication

    Page(s): 538 - 546
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    We examine multiple-subcarrier modulation (MSM) schemes for wireless infrared digital communication in the indoor environment. Intensity modulation with direct detection (IM/DD) is employed, which results in equivalent baseband channels with a nonnegativity constraint on the input. The power efficiencies of modulation schemes are compared at 30 Mb/s and 100 Mb/s over an ensemble of experimentally determined multipath channels. Carrier selection and power shaping are examined as methods for improving MSM performance. It is found that MSM schemes can allow operation at higher data rates than single-carrier modulation schemes without equalization. Moreover, MSM schemes can be more bandwidth-efficient and also can provide a simple and flexible method for multiple access to the channel. However, they are not as power efficient as single-carrier schemes, and this will limit their use to applications which are not power limited View full abstract»

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  • Concatenated orthogonal/PN spreading sequences and their application to cellular DS-CDMA systems with integrated traffic

    Page(s): 547 - 558
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    In this paper, we investigate the application of the concatenated orthogonal/PN spreading scheme for a cellular direct sequence code-division multiple access (DS-CDMA) system with integrated traffic. The performance of the system is evaluated in terms of user capacity. In order to incorporate traffic with a wide range of source rates, line rates (adjusted data rates before spreading) have to be selected for transmission. For traffic with source rates higher than the line rate of concern, we propose the use of concatenated orthogonal/PN spreading sequences to subdivide a high rate stream into parallel line rate streams. Therefore, in this paper, we first analyze the properties of the concatenated orthogonal/PN spreading sequences. The results are used to evaluate their performance for homogenous voice traffic in various cellular mobile environments with multipath fading, lognormal shadowing, and path loss. Our results show that the proposed spreading scheme offers a significant improvement in the forward link capacity as compared to using the conventional nonconcatenated long PN sequence, especially if the multipath fading is Rician (e.g., microcellular and indoor picocellular systems). Incorporating the notion of line rate, we then evaluate the performance of a system with integrated voice and video traffic. Special emphasis is placed on the effect of line rate selection on the overall capacity which leads to the optimal selection of line rates View full abstract»

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Aims & Scope

IEEE Journal on Selected Areas in Communications focuses on all telecommunications, including telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation.

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Editor-in-Chief
Muriel Médard
MIT