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Selected Areas in Communications, IEEE Journal on

Issue 8 • Date Oct 1992

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Displaying Results 1 - 16 of 16
  • Performance and jitter analysis of quadrature partial response/trellis coded modulation (QPR-TCM) signals in the presence of intersymbol interference and colored noise

    Publication Year: 1992 , Page(s): 1264 - 1270
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    To improve both bandwidth efficiency and error performance, partial response signaling and trellis coded modulation are considered together for QAM. A new receiver for a data transmission system employing combined partial response/trellis coded modulation (QPR-TCM) is investigated. Combined 6QPR-TCM and 42QPR-TCM systems are introduced. Simulation studies in the ISI environment are done. In a colored noise environment, the error probability of 6QPR-TCM is analytically lower bounded and compared to the classical 4QAM-TCM. An optimal (QPR-TCM) scheme is proposed which improves both jitter and error response in a colored noise environment View full abstract»

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  • Trellis coding of quadrature frequency/phase modulated signals

    Publication Year: 1992 , Page(s): 1254 - 1263
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    The authors explore the trellis coding of continuous-phase quadrature frequency/phase modulated (CPQFPM) signal sets and continuous-phase FPM (CPFPM) signal sets, which are embodiments of the quadrature biorthogonal modulation (QBOM) technique. Conventional TCM and multiple TCM schemes with these modulation formats are examined using both the AWGN channel and the Rician fading channel design. Asymptotic coding gains in d2(free) are tabulated for trellis-coded rate 3/4, 5/6, and 6/7 QFPM schemes, in comparison with uncoded modulations (8AMPM, 32AMPM) and other trellis-coded modulations [TCM (2FSK/4PSK 16QAM, 64QAM), MTCM (2FSK/8PSK)] of equivalent throughput rate. Performance gains on the Rician fading channel are demonstrated by increased values of the design parameters for this channel, namely symbol diversity Lmin and branch distance product P View full abstract»

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  • Protocol design for mobile radio group communications over satellite

    Publication Year: 1992 , Page(s): 1351 - 1361
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    A protocol design for a mobile radio service supporting half-duplex push-to-talk voice communications over mobile satellite systems is presented. The service enables a closed group of mobile radio users to communicate among themselves, so that a transmission from any user is received by all. A key issue is the efficient utilization of satellite channels. Demand-assignment multiple access (DAMA) is employed to allocate channels only to those user groups in active sessions of conversations. Owing to the unique characteristics of the half-duplex point-to-multipoint group communications, a new DAMA protocol is proposed for this service. Within a channel assigned to a user group, access contentions exacerbated by very long round-trip delay can occur. A signaling protocol is devised to arbitrate access contentions so as to improve the utilization of the assigned channel. The proposed access control protocol offers 65% or 18% improvement in throughput capacity compared to manual carrier-sensed access without and with collision detection, respectively View full abstract»

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  • DSD (double soft decision) concatenated FEC scheme in mobile satellite communication systems

    Publication Year: 1992 , Page(s): 1271 - 1277
    Cited by:  Papers (5)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    In order to realize a higher-code-gain forward error correction scheme in mobile satellite communication systems, a novel concatenated coding scheme employing soft decision decoding for not only inner codes but also outer codes (double soft decision, or DSD, concatenated forward error correction scheme) is proposed. Soft-decision outer decoding can improve the bit error probability of inner decoded data. In this scheme, likelihood information from an inner Viterbi decoder is used in the decoding of outer codes. A technique using the path memory circuit status 1.0 ratio for likelihood information is proposed, and is shown to be the most reliable even though it requires the simplest hardware among the alternative methods. A computer simulation clarifies that the DSD scheme improves Pe performance to one-third of that of the conventional hard-decision outer decoding. Moreover, to reduce the interleaving delay time in fading channels or inner decoded data of concatenated codes, a parallel forward error correction scheme is proposed View full abstract»

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  • Statistical observations of data transmission over land mobile satellite channels

    Publication Year: 1992 , Page(s): 1227 - 1235
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    It is shown how Rician fading limits the performance of the HDLC protocol. It is observed that for accurate reception, a packet must be transmitted entirely during an interfade interval. This means that packets ought to be sufficiently short so that most of them fall in the interfade time intervals. This leads to a high transmission efficiency. Consequently, the HDLC protocol is more efficient with shorter packets. However, a smaller packet size increases the overhead fraction of the packet and thereby reduces the effective throughput. In addition, the HDLC peak efficiency and optimum packet size increase with increasing fade margin and decrease with increasing vehicle velocity. Among other effects, the bit rate of the land-mobile satellite system channel is the most critical for optimum packet size and HDLC efficiency. Thus, a low bit rate implies long packet duration for a moderate packet size in bytes View full abstract»

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  • Symbol-aided plus decision-directed reception for PSK/TCM modulation on shadowed mobile satellite fading channels

    Publication Year: 1992 , Page(s): 1289 - 1299
    Cited by:  Papers (41)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    The symbol-aided (SA) synchronization concept developed by Moher and Lodge (1989) is applied to the MSAT channel modeled with a shadowed Rician process. Simulation data demonstrate that it can track the severe phase jitter encountered on the fading channel free of the false lock which plagues conventional techniques. The algorithm multiplexes known symbols into the data stream, establishing an absolute reference free of decision errors that is used to estimate the fading phase. An improvement to the SA algorithm which extracts phase information from the data-bearing symbols is proposed. It is found that the new technique is more effective for larger K. The improved algorithm is referred to as symbol-aided plus decision-directed (SADD) phase estimation. A system employing SADD phase estimation, trellis-coded modulation, interleaving, and amplitude weighting within the Viterbi decoder yielded the best BER performance on the shadowed MSAT channel considered View full abstract»

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  • Narrowband channel statistics from multiband propagation measurements applicable to high elevation angle land-mobile satellite systems

    Publication Year: 1992 , Page(s): 1219 - 1226
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB)  

    Results from a multiband propagation experiment for a high elevation angle land-mobile satellite (LMS) channel are presented. A small helicopter was used to fly the transmitter module, transmitting frequencies in the L, S, and Ku bands. A vehicle equipped with the corresponding receivers and data acquisition system was followed by the helicopter on the selected routes. The measurement campaign was undertaken in two phases in September 1991 and in April 1992. The results show considerable decrease in signal attenuation when the path elevation angle is high due to reduced shadowing. In general, the attenuation increases with the increasing radio frequency. Foliage density has also been found to influence the fade levels, especially at higher path elevation angles. The overall analysis of the propagation data indicates that the fading character of the LMS channel is significantly dependent on the surrounding environment View full abstract»

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  • Multifrequency minimum shift keying

    Publication Year: 1992 , Page(s): 1243 - 1253
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    A new modulation scheme that produces a constant envelope continuous phase signal set with a compact power spectrum and power efficiency better than that of MSK is proposed. The scheme can be implemented by quadrature-carrier multiplexing of two frequency/phase modulated signals of the type NFSK/2PSK, both with the same frequency in each transmission interval, and with sinusoidal symbol shapes. The generated signal can be viewed in each transmission interval as an MSK signal at one of the N frequencies and is referred to as multifrequency minimum shift keying (MF MSK). Modulation, demodulation, and synchronization circuits are described, and the spectral properties and power efficiency on the AWGN channel are analyzed. Combining a number of attractive attributes such as constant envelope, excellent spectral properties, high power efficiency, and self-synchronization capability, the proposed modulation format lends itself to a variety of applications, one of them being the digital satellite link View full abstract»

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  • A measurement-based prioritization scheme for handovers in mobile cellular networks

    Publication Year: 1992 , Page(s): 1343 - 1350
    Cited by:  Papers (135)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A method of improving the quality of service in mobile cellular systems based on prioritization of handover requests is presented. The objective is to improve perceived quality of cellular service by minimizing both the probability of forced termination of ongoing calls due to handover failures and the degradation in spectrum utilization. A model based on a multiple-priority nonpreemptive queuing discipline is developed. New calls are blocked if all channels are occupied. Handover requests are queued such that as soon as a channel is available, it is offered to the mobile subscriber with the measurement results closest to the minimum acceptable power level for communication. Service rate is given by channel occupancy time distribution and is assumed to be exponential. The performance of a cellular system employing the proposed handover policy is evaluated analytically and by simulation, and results are compared to those obtained when the cellular system employs nonprioritized call handling and first-in/first-out queuing discipline. This provides lower probability of forced termination and less call blocking, less reduction in traffic, and less delay View full abstract»

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  • Maximum likelihood sequence estimation of quadrature pulse-overlapping modulated signals for portable/mobile satellite communications

    Publication Year: 1992 , Page(s): 1278 - 1288
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB)  

    A maximum-likelihood sequence estimation (MLSE) receiver structure for constant-envelope quadrature pulse-overlapping modulated (QPOM) signals in fading channels is presented. QPOM is first decomposed into a liner encoder followed by a memoryless modulator. The trellis diagram representing this inherent nonredundant coding structure is then used to construct its MLSE receiver. The upper bounds on the average bit error probability in both AWGN and Rayleigh fading channels are derived. Computer simulations are also used to verify the analytical results. In fast-fading shadowed mobile satellite channels the scheme is shown to outperform conventional QPSK techniques. It maintains the low complexity of 4PSK, but its performance is comparable to that of four-state 8PSK TCM schemes. The constant envelope, compact spectrum, superior performance, and low complexity enable QPOM to meet the requirements of low cost, small size, and high power and bandwidth efficiencies for portable/mobile satellite systems View full abstract»

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  • A new carrier recovery circuit for land mobile satellite communication

    Publication Year: 1992 , Page(s): 1306 - 1314
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A DCF (dual carrier filter) reverse-modulation-type carrier recovery circuit is proposed to achieve a low carrier skipping rate and satisfactory phase tracking performance for coherent detection of PSK (phase shift keying) signals in fast Rician fading channels. The proposed scheme employs both narrow and wide bandwidth carrier filters simultaneously for the reverse-modulation-type carrier recovery circuit. It is clarified by computer simulation that the Pe performance of a QPSK (quadriphase shift keying) modem employing the proposed scheme shows an improvement of 1.5 dB in required Es/NO at Pe=104 (after Viterbi decoding (R=7/8, K=7), C/M (direct-to-multipath signal power ratio)=10 dB, interleaving size=64×64), compared with conventional coherent detection employing the reverse modulation tank-limiter scheme or the Costas loop scheme View full abstract»

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  • Channel modeling and simulation in satellite mobile communication systems

    Publication Year: 1992 , Page(s): 1209 - 1218
    Cited by:  Papers (61)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    An analog model describing signal amplitude and phase variations on shadowed satellite mobile channels is proposed. A linear combination of log-normal, Rayleigh, and Rice models is used to describe signal variations over an area with constant environment attributes while an M-state Markov chain is applied to represent environment parameter variations. Channel parameters are evaluated from the experimental data and utilized to verify a simulation model. Results, presented in the form of signal waveforms, probability density functions, fade durations, and average bit and block error rates, show close agreement with measurements View full abstract»

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  • On the representation of CPM signals by linear superposition of impulses in the bandpass domain

    Publication Year: 1992 , Page(s): 1236 - 1242
    Cited by:  Papers (7)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    A novel signal generation concept for continuous phase modulations (CPMs) with modulation index 1/2 based on real impulses is presented. With this concept, bandpass CPM signals can be generated directly in one step instead of the two consecutive steps, namely, the generation of the complex envelope and the modulation of the carrier by the complex envelope, which are necessary in conventional signal generators. Mathematical expressions for both the real impulses and the bandpass CPM signals are derived and a simple modulator structure is discussed. Examples for the real impulses are given. Among these are the well-known CPM schemes of minimum shift keying (MSK), sinusoidal frequency shift keying (SFSK), and Gaussian minimum shift keying (GMSK). As an example, the validity of the novel signal generation concept is shown for the latter CPM scheme View full abstract»

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  • A multirate digital multicarrier demodulator: design, implementation, and performance evaluation

    Publication Year: 1992 , Page(s): 1326 - 1342
    Cited by:  Papers (1)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1132 KB)  

    Frequency-division multiple access (FDMA) and single channel per carrier (SCPC) in the uplink and time-division multiplexing (TDM) in the downlink are employed in the system described. To interface FDMA in the uplink and TDM in the downlink, multicarrier demodulation (MCD) is required onboard the satellite. The operation of the onboard MCD is the separation of each individual channel and subsequent demodulation. The results, which concern onboard frequency demultiplexing and demodulation for low-bit-rate carriers, are constrained by the requirement that new-generation payloads could serve the stations already active in the INTELSAT Business System. A digital hardware design that implements an MCD that can process three channels at 4.4 Mb/s or 12 channels at 1.1. Mb/s is described. The test results confirm the MCD feasibility, and further improvements are expected from a semicustom implementation View full abstract»

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  • Multipath reduction using constant modulus conjugate gradient techniques

    Publication Year: 1992 , Page(s): 1300 - 1305
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A conjugate-gradient (CG) constant-modulus adaptive processor is proposed. For the generalized sidelobe canceler (GSC) signal processing configuration, this algorithm, CG-GSC, exhibits improved convergence over previous methods. Theoretical expressions are presented for convergence and weight update of a linearly constrained constant modulus generalized sidelobe canceler. Theoretical expressions are then derived for the conjugate direction vectors. These vectors are used to update the filter weights for a conjugate gradient adaptation rule. A simulation study of the conjugate adaptation rule reveals the increase in convergence rate for the generalized sidelobe canceler. Performance comparisons of the CG-GSC and a first-order gradient GSC for a BPSK signal with multipath and white noise interference indicate that the CG-GSC adaptation rule not only increases convergence by a factor of five compared to the first-order gradient GSC, but in some instances improves the bit error rate of the demodulated BPSK signal View full abstract»

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  • A spectrum- and power-efficient EHF mobile satellite system to be integrated with terrestrial cellular systems

    Publication Year: 1992 , Page(s): 1315 - 1325
    Cited by:  Papers (13)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    An EHF satellite system for land-mobile applications to be integrated with a terrestrial cellular system is described. An approach to evaluate the carrier-to-cochannel interference occurring in multispot satellite coverage adopting frequency reuse is introduced, and results from the analysis are shown. Criteria for spectrum efficiency evaluation are also outlined along with traffic and link budget estimates. Possible options for payload implementation and mobile terminal design are presented 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