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Selected Areas in Communications, IEEE Journal on

Issue 5 • Date June 1987

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Displaying Results 1 - 21 of 21
  • [Back cover]

    Page(s): 0
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    Freely Available from IEEE
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Guest Editorial: Portable and Mobile Communications

    Page(s): 761 - 763
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    Freely Available from IEEE
  • Perfect-Capture ALOHA for Local Radio Communications

    Page(s): 806 - 814
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    We consider a set of uncoordinated users employing an ALOHA protocol to transmit packets to a central base station in a local radio environment, e.g., in an urban area or within a building. Because of the different distances between the various users and the base station, the signals received from different users have substantially different power levels. This near/far phenomenon gives rise to a capture effect at the receiver such that when several packets are transmitted simultaneously, the receiver has a good chance of accurately detecting the packet arriving with the highest energy. Moreover, capture can be made near perfect in this environment through the use of properly design spread-spectrum signaling technique that enables the receiver to differentiate among the arriving packets based on both power differences and differing arrival times. We investigate variations to the conventional ALOHA protocols that take advantage of perfect capture to reduce the delays and increase the throughputs of all users, including the furthest one. Three protocols are introduced and compared, which we call "persistent ALOHA with capture" (PAC), "gated ALOHA with capture" (GAC), and "gated ALOHA with capture/exhausted" (GAC/E). Two goals are considered in the comparison: an equatable delay profile among the users, and a small expected number of simultaneously transmitted packets. The latter is quite relevant for the practical implementation of a perfect-capture receiver. We conclude that the GAC/E protocol is most desirable from the twin points of view of delay profile and receiver implementation. View full abstract»

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  • Cellular Efficiency with Slow Frequency Hopping: Analysis of the Digital SFH900 Mobile System

    Page(s): 835 - 848
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    The new digital cellular SFH900 mobile system, based on "mixed" slow frequency hopping (SFH) combined with time division, is described in detail. The system includes Viterbi quasi-coherent demodulation of GMSK for which performance measurements in multipath conditions are presented. A concatenated coding scheme that takes full benefit of built-in frequency diversity and interference diversity is introduced. A model for SFH cellular performance evaluation is presented and the quality-versus-capacity tradeoff for SFH900 is given for various frequency reuse patterns. With advanced 16 kbit/s speech coding techniques, and including a 25 percent overhead for management and signaling, the spectrum efficiency of a many-celled SFH900 network is around 3.5 users/cell/MHz, a significant increase in comparison to conventional analog systems. SFH provides intrinsic adaptability to varying traffic conditions and enhanced flexibility for multiservice operation. The SFH900 principles, which have been recently validated through field tests, are very promising for second generation cellular systems. View full abstract»

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  • Cell Boundary Detection in the German Cellular Mobile Radio: System C

    Page(s): 849 - 854
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    The efficiency of frequency utilization in mobile radio strongly depends on the performance of handoffs. Criteria for handoffs are usually derived from measured carrier-to-interference ratios (C/I). However, in mobile radio signal levels vary so rapidly that channel allocation cannot be performed in real time for optimum C/I. On the other hand, too many handoffs reduce frequency efficiency. The determination of cell boundaries, which are not only governed by C/I, but allocated to geographical lines in the terrain avoid unnecessary handoffs. In addition to C/I auxilary data are measured in the German system C and processed to detect the cell boundaries. The improvements gained from this procedure are demonstrated by measured results. View full abstract»

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  • Universal Digital Portable Communications: A System Perspective

    Page(s): 764 - 773
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    In our highly mobile society, the provision of voice and data communications to a person away from his/her wireline telephone has become a major communications frontier. The early penetration of this frontier has been based on very limited portable communications approaches, e.g., cordless telephones, mobile radio telephones, and radio paging. Each of these approaches only partially satisfies portable communications needs. This paper describes an approach to providing universal digital portable communications integrated into telephone networks. A system configuration employing time-division multiple-access radio link architecture and frequency reuse is described. Issues affecting radio link transmission rates and radio system coverage are discussed. Characteristics and parameters of a possible system to supplement the wire (or fiber) loop are indicated. View full abstract»

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  • A Comparison of Digital Speech Coding Methods for Mobile Radio Systems

    Page(s): 915 - 920
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    Subjective quality measurements on three digital speech coders, simulated with mobile radio channel transmission, were performed using the "mean opinion score (MOS)" method. The three speech coding methods tested were: continuously variable slope deltamodulation (CVSD) coding, adaptive predictive coding (APC), and residually excited linear predictive (RELP) coding. Several versions of each coder, with transmission rates in the range of 7.3 to 16.1 kbits/s, were simulated. Five different channel conditions, including three derived from land mobile radio field experiments, were applied to the speech coders' encoded output to study the effects. The results show that of the three coders, the CVSD coder is the most robust to channel errors, but produces reconstructed output speech of unacceptable quality. The 14.4 kbit/s RELP coder produces relatively good Output speech quality, exhibits a mild degree of robustness to mobile radio channel errors, and is slightly less complex than the APC coder. Of the three digital speech coders tested, the RELP coder appears the most suitable for use with land mobile radio. However none of the three coders was able to produce speech of telephone toll quality in a mobile radio environment. View full abstract»

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  • Highly Efficient Digital Mobile Communications with a Linear Modulation Method

    Page(s): 890 - 895
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    Although linear modulation methods can achieve high spectrum efficiency, very little attention has been directed to their use in mobile radio systems. This is mainly due to the fact that the nonlinearity of the transmitter power amplifier tends to spread the spectrum and thus eliminate any spectrum efficiency advantage gained through the use of linear modulation methods. In this paper, a linear modulation system is proposed, which solves the above difficulty and which gives higher spectrum efficiency than conventional digital FM. The modulation/demodulation method ispi /4shift QPSK and phase-shift detection with a limiter-discriminator and an integrate-and-dump filter. By introducing a cartesian coordinate negative feedback control, 35 percent power efficiency at 10 W output power and - 60 dB relative out-of-band radiation are simultaneously achieved with a class "AB" amplifier, owing to the 29 dB feedback gain. The receiver configuration is easy to realize and gives immunity against fast fading through the use of noncoherent detection with limiter-discriminator. By using a novel decision method, bit error rate performances under both nonfading and fading condition are comparable to those obtained by digital FM. These results make it possible for linear modulation methods to achieve higher spectrum efficiency than is possible with conventional digital FM methods in mobile radio communications. View full abstract»

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  • Performance Analysis of a Built-In Planar Inverted F Antenna for 800 MHz Band Portable Radio Units

    Page(s): 921 - 929
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    The pattern averaging gain (PAG) method to estimate the average gain of mobile antennas in a multipath propagation environment is proposed. By using this method and a wire-grid model, the radiation characteristics of the planar invertedFantenna (PIFA) mounted on a portable radio case is analyzed. In particular, the variation of the antenna gain with the radio case dimensions and inclination angle of the radio case during operation is clarified. Also, the effect on antenna patterns of the operator holding the portable radio is experimentally investigated. Based on this analysis, the antenna configuration with the PIFA element mounted on the lateral side of the radio case is found to be most suitable for portable radio units. In addition, an appropriate selection of the radio case dimensions is found to result in further improvements in the antenna bandwidth. View full abstract»

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  • On the Capacity of Radio Communication Systems with Diversity in a Rayleigh Fading Environment

    Page(s): 871 - 878
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    In this paper, we study the fundamental limits on the data rate of multiple antenna systems in a Rayleigh fading environment. WithMtransmit andMreceive antennas, up toMindependent channels can be established in the same bandwidth. We study the distribution of the maximum data rate at a given error rate in the channels between up toMtransmit antennas andMreceive antennas and determine the outage probability for systems that use various signal processing techniques. We analyze the performance of the optimum linear and nonlinear receiver processor and the optimum linear transmitter/receiver processor pair, and the capacity of these channels. Results show that with optimum linear processing at the receiver, up toM/2channels can be established with approximately the same maximum data rate as a single channel. With either nonlinear processing at the receiver or optimum linear transmitter/receiver processing, up toMchannels can be established with approximately the same maximum data rate as a single channel. Results show the potential for large capacity in systems with limited bandwidth. View full abstract»

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  • Features and Performance of 12PM3 Modulation Methods for Digital Land Mobile Radio

    Page(s): 906 - 914
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    A number of continuous-phase modulation methods suitable for digital and mobile radio applications has been grouped in a common class, which has been named 12PM3 (12-state, phase modulation with correlation over three consecutive bits). This paper introduces the definition of this class of modulation schemes, and presents some of its features. With reference to the scheme that gives the best spectral compactness, some effects of typical implementation imperfections of the modulation circuits are discussed. The performance of some 12PM3 modulators associated with a frequency discrimination receiver is then computed with reference to both AWGN (additive white Gaussian noise) channels and the typical propagation conditions envisaged for SCPC/FDMA digital land mobile radio systems in urban environment. The adopted pre and postdiscrimination filters of the receiver are optimized for the best performance. Different decision techniques are considered, namely 2-TH (2-threshold), 4-TH, mixed 2-TH/4-TH and MLSE (maximum-likelihood sequence estimation) techniques. View full abstract»

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  • Design and Experimental Results for a Direct-Sequence Spread-Spectrum Radio Using Differential Phase-Shift Keying Modulation for Indoor, Wireless Communications

    Page(s): 815 - 823
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    We report on our design and measurements that have been made for a direct-sequence spread-spectrum radio using differential phase-shift keying modulation for a wireless PBX. We describe the design and implementation of a transmitter and a receiver using a surface acoustic wave (SAW) filter matching the spread-spectrum code of a user. The receiver performance is within 1 dB of the theoretical performance of a differential phase-shift keying (DPSK) receiver in the presence of additive white Gaussian noise. We also show receiver performance in a multipath fading indoor environment with multipath fade notches of up to 50 dB depth. The indoor channel multipath fading can be overcome by using an equal gain diversity combiner which is suitable when DPSK modulation is used. We confirm that the indoor mean power level attenuation follows the inverse fourth power of the distance. Also, we investigate the multiple-access capability of the system by introducing an interfering transmitter with a different spread-spectrum code sequence. View full abstract»

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  • Advanced Cordless Telecommunications Service

    Page(s): 774 - 782
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    Present analog cordless telephones suffer from lack of privacy, limited facilities and can support only a relatively low density of users. This restricts their benefits and market opportunities. Hence the need for an advanced cordless telecommunications service (ACTS). Consideration is given here to the needs of this service in terms of requirements, demand, system aspects, spectrum needs, propagation, and performance. This leads to a proposed system design for the service which is already under consideration within Europe. It uses 32 kbit/s speech encoding and time-division duplex operation to achieve both-way speech communication on a single 100 KHz-wide radio channel. A pool of radio channels are available to choose from at both base and handset in order to minimize overall interference and maximize system capacity. The addition of another aerial at only the base unit can provide the full spatial diversity improvement to both directions of transmission. The service is due for introduction in the United Kingdom in 1987. View full abstract»

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  • The Effects of Time Delay Spread on Portable Radio Communications Channels with Digital Modulation

    Page(s): 879 - 889
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    Frequency-selective fading caused by multipath time delay spread degrades digital communication channels by causing intersymbol interference, thus resulting in an irreducible BER and imposing a upper limit on the data symbol rate. In this paper, a frequencyselective, slowly fading channel is studied by computer simulation. The unfiltered BPSK, QPSK, OQPSK, and MSK modulations are considered first to illustrate the physical insights and the error mechanisms. Two classes of modulation with spectral-shaping filtering are studied next to assess the tradeoff between spectral occupancy and the performance under the influence of time delay spread. The simulation is very flexible so that different channel parameters can be studied and optimized either individually or collectively. The irreducible BER averaged over fading samples with a given delay profile is used to compare different modulation/detection methods, while the cumulative distribution of short-term BER is employed to show allowable data symbol rates for given values of delay spread. It is found that both GMSK and QPSK with a raised-cosine Nyquist pulse are suitable for a TDM/TDMA digital portable communications channel. View full abstract»

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  • The Hybrid Transmission Scheme of a 900 MHz Digital Land Mobile Radio System

    Page(s): 824 - 834
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    The hybrid transmission scheme of MATS-D uses different transmission principles on both directions of a duplex radio link. Based on the analysis of the radio transmission characteristics and of multiple-access methods, the two directions are designed independently from each other. In the downlink (from base station to mobile station) a combination of TDM and CDM is applied. In the uplink (from mobile station to base station) single channel per carrier FDMA with generalized tamed frequency modulation (GTFM) is employed. Both transmission schemes have been implemented. Measurements with fading generators as well as field tests were carried out. Experimental results are presented for the performance of both transmission schemes, expressed in terms of the bit error rate versus the signal-to-noise ratio and the signal-to-interference ratio. View full abstract»

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  • A Wireless Network for Wide-Band Indoor Communications

    Page(s): 796 - 805
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    We propose and analyze a wide-band indoor communication system that uses radio as the transmission medium either on a stand-alone basis or to supplement a hard-wired network for those situations where complete portability is desired. One principal impairment to such a system is intersymbol interference caused by frequencyselective fading. A novel media-access scheme is proposed which permits the use of resource sharing, wherein a small pool of time slots is effectively shared among all users to provide added protection against channel impairments on an as-needed basis. Our results show that the use of resource sharing and diversity provide excellent protection against intersymbol interference caused by frequency-selective fading with negligible impact on throughput. Furthermore, resource sharing plus diversity can permit significantly higher data rates without large queueing delays. For example, a wireless network with a 10 Mbit/s data rate in a 10 MHz bandwidth using four antennas at the base station has a less than 10-4outage probability at a 10-4BER in buildings with less than 58 ns rms delay spread. A loading of 75 percent is permitted for a queueing delay of less than 20 packet transmission times all but 0.01 percent of the time. View full abstract»

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  • Multipath Time Delay Jitter Measured at 850 MHz in the Portable Radio Environment

    Page(s): 855 - 861
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    Time delay jitter in digital personal communications systems, caused by moving the antenna by a few wavelengths, was studied at two office buildings and two residences at a frequency of 850 MHz. A wide-band pseudonoice code technique was used. The results indicate that peak-to-peak time delay, variations on the order of 375 ns may be encountered. The worst case jitter was not necessarily found when there was a large time delay spread. It was also found that the excess mean delay and the root mean-square (rms) time delay spread of the delay distribution profiles were approximately the same. View full abstract»

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  • Mean-Square Error Optimization of Quadrature Receivers for CPM with Modulation Index 1/2

    Page(s): 896 - 905
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    Detection of continuous phase modulation (CPM) signals can be accomplished using quadrature coherent detectors which include a pair of linear and time-invariant postdetection filters. Performance of the quadrature detectors is highly sensitive to the postdetection filters response. This paper presents a rigorous derivation of an optimum postdetection filter response. The derivation is based on minimizing the mean-square interference subject, to the constraint that the filter noise bandwidth is held constant. The amount of computations involved is fairly small and increases linearly with the receiver observation interval. Performance analysis results for several modulation techniques are presented. View full abstract»

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  • Channel Requirements for a Cordless Telephone Spectrum Allocation

    Page(s): 783 - 795
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    Planning for a permanent cordless telephone spectrum allocation requires that the number of channels necessary to meet the long-term needs of cordless telephones be estimated. To provide the analytical basis for such an estimate, we determine the relationship between the number of channels available to cordless telephones and their performance in a suburban residential environment. Multiple cordless telephones in a community can use the same channel simultaneously, so performance ultimately will be limited by cochannel interference. We therefore develop a mathematical model of the carrier-to-interference ratio. This model accounts for shadowing, polarization, and multipath propagation effects observed in field measurements, as well as the random locations of cordless telephones. A performance measure is developed and evaluated for cordless telephones that can access all available channels and are operating in a suburban residential environment. The results indicate that for carrier frequencies in the low UHF band (300 MHz to 1 GHz), an allocation of 30-40 duplex channels can accommodate universal use of cordless telephones in that environment. For lower carrier frequencies, shadowing is less severe and fewer channels would be necessary. For example, at 50 MHz, 20 duplex channels would suffice. View full abstract»

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  • Macroscopic Diversity in Frequency Reuse Radio Systems

    Page(s): 862 - 870
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    Macroscopic diversity is a technique that can facilitate high quality and ubiquitous communications between low-power portable radiotelephones and data terminals, and radio base stations (ports) that are connected to the local network. It uses radio signals from several base stations to mitigate the effect of shadow fading, a variation of signal strength over space created by the presence of buildings, foliage, and terrain variations. With a path loss exponent of four and a shadow fading standard deviation of 10 dB, four-branch macroscopic diversity results in a 13 dB improvement in signal strength and a 15 dB improvement in signal to cochannel interference ratio for high user capacity interference-limited operation. (Both figures are for 99 percent statistical coverge of the service area.) The improvement in signal to cochannel interference ratio is equivalent to a factor-of-five savings of spectrum. 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.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Muriel Médard
MIT