By Topic

Selected Areas in Communications, IEEE Journal on

Issue 7 • Date Sep 1993

Filter Results

Displaying Results 1 - 15 of 15
  • A soft-output bidirectional decision feedback equalization technique for TDMA cellular ratio

    Page(s): 1034 - 1045
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB)  

    Issues encountered in the design of reliable narrowband time-division multiple access (TDMA) digital cellular mobile communication systems are considered. In particular, the problem of compensating for the harsh multipath fading environment in systems whose transmission bandwidth is commensurate with the coherence bandwidth of the fading channel is considered. A TDMA channel characterization parameter, the slot-normalized fade rate, is introduced, and an adaptive bidirectional equalization technique, which estimates the location of a deep fade within a time slot, is proposed. The simulation results show that the carrier-to-noise ratio requirement is only 15.5 dB when this equalization technique is used. This is achieved without diversity, and with low complexity. An equivalent equalized land mobile radio channel model and the analytical solution for the optimal bit likelihood calculation for π/4-shift quadrature differential phase-shift keying (QDPSK) modulation are also derived under certain channel conditions. The results are used as soft decisions for the convolutional decoder View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Irreducible error performance of a digital portable communication system in a controlled time-dispersion indoor channel

    Page(s): 1024 - 1033
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    The authors investigated experimentally, analytically, and by simulation the irreducible errors such as error floor for high signal-to-noise ratio that are introduced by time dispersion in a slowly fading Rayleigh channel. A multipath indoor propagation environment with controlled delay spread was created to validate this approach. The system is close to the Digital European Cordless Telecommunications (DECT) standard with 1 Mb/s GMSK-modulated signals being transmitted in FDM/TDMA/TDD format and received by a differential direct-conversion receiver. The measured and simulated error probability floor is Pe≈5×10-3 as a consequence of delay spread that is 10% of the bit length. This value is approximated by a closed-form analytical description of phase jitter due to large group delay bursts. Simulation results obtained previously by others for comparable cases are partially corroborated and partially disproved View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurements and models of radio frequency impulsive noise for indoor wireless communications

    Page(s): 991 - 1001
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (988 KB)  

    The authors present the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3-dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulse noise in office and retail environments View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impulse response modeling of indoor radio propagation channels

    Page(s): 967 - 978
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1080 KB)  

    If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming of the channel's transfer functions. It is shown that the number of multipath components in each impulse response estimate is a normally-distributed random variable with a mean value that increases with increasing antenna separations; a modified Poisson distribution shows a good fit to the arrival time of the multipath components; amplitudes are lognormally distributed over both local and global areas, with a log-mean value that decreases almost linearly with increasing excess delay; for small displacements of the receiving antenna, the amplitude of the multipath components are correlated; the amplitudes of adjacent multipath components of the same impulse response function show negligible correlations; and the RMS delay spread over large areas is normally distributed with mean values that increase with increasing antenna separation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Concepts and results for 3D digital terrain-based wave propagation models: an overview

    Page(s): 1002 - 1012
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1256 KB)  

    Mobile communication links are severely influenced by propagation effects. Wave propagation in the VHF/UHF frequency range over natural and man-made terrain is strongly dependent on topography and morphography. Propagation modeling is based on a ray-optical approach. Wave interactions, like diffraction and scattering, over the propagation path are described by the uniform theory of diffraction (UTD) and physical optics (PO). Propagation models for rural and urban areas are presented for 2-D and 3-D ray tracing. Near-range models apply to the corresponding areas in forest and urban sites. The field-strength delay spectrum describes ray contributions with deterministic amplitudes but statistical phases are used to derive time-and frequency-domain channel characteristics. Comparisons between measured and predicted data are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of an all-digital BPSK direct-sequence spread-spectrum IF receiver architecture

    Page(s): 1096 - 1107
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (932 KB)  

    A VLSI architecture for an all-digital binary phase shift keying (BPSK) direct-sequence (DS) spread spectrum (SS) intermediate frequency (IF) receiver is presented, and an in-depth performance analysis is given. The all-digital architecture incorporates a Costas loop for carrier recovery and a delay-locked loop for clock recovery. For the pseudorandom noise (PN) acquisition block, a robust energy detection scheme is proposed to reduce false PN locks over a broad range of signal-to-noise ratios. The proposed architecture is intended for use in the 902-928 MHz unlicensed spread spectrum radio band. A 100 kbs information rate and a 12.7 Mchips/second PN code rate are assumed. The IF center frequency is 12.7 MHz and the IF sampling rate is 50.8 Msamples/second, which is the Nyquist rate for the 25.4 MHz bandwidth signal. Finite wordlength effects have been simulated to optimize the architecture, thereby minimizing the chip area, and results of the finite wordlength simulations demonstrate that the chip architecture achieves a bit error rate performance within 1 dB of theory in an additive white Gaussian noise channel View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical fiber feeder for microcellular mobile communication systems (H-O15)

    Page(s): 1118 - 1126
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The authors investigate the feasibility of using an optical fiber feeder for microcellular mobile communication systems. The optical feeder enables compact and low-cost base stations, easy radio channel control, and flexible mobile communication systems. Basic transmission characteristics were investigated through optical transmission experiments. Using these results, it is estimated that the optical feeder can transmit 880 telephone channels for digital TDM systems and 2000 channels for analog FDM systems through 20 km of optical fiber. Furthermore, two kinds of novel techniques that enlarge dynamic range of the optical feeder are reported View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A spread-spectrum multiaccess system with cochannel interference cancellation for multipath fading channels

    Page(s): 1067 - 1075
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    The authors propose and analyze a direct-sequence spread-spectrum multiaccess (DS/SSMA) receiver that employs a cascade of cochannel interference (CCl) cancellers for communication over multipath fading channels. The receiver first coherently demodulates and despreads the received signal to produce correlator outputs and initial data estimates. Based on these estimates, the cancellation scheme essentially creates replicas of the contributions of the CCl embedded in the correlator outputs and removes them for a second improved hard data decision. By repeating this operation over and over, a cascade of CCl cancellers is derived. Through theoretical analysis and simulation, the authors investigate the canceller's bit error rate (BER) performance in both the absence and presence of errors in the amplitude and phase estimates of each user's received signal. Numerical results show the considerably large improvement in performance that can be attained by the cancellation scheme, even under partially degraded estimates View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Antenna systems for base station diversity in urban small and micro cells

    Page(s): 1046 - 1057
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    The authors describe cross-correlation properties for compact urban base station antenna configurations, nearly all of which result in very low envelope cross-correlation coefficients of about 0.1 to 0.3. Specifically, polarization diversity systems are examined for their potential in improving link quality when hand-held terminals are involved. An expression is given for the correlation function of compound space and polarization diversity systems. Dispersion and envelope dynamic statistics are presented for the measured environments. For microcell applications, it is found that systems such as GSM having a bandwidth of 200 kHz or less can use narrowband cross-correlation analysis directly View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Direct sequence CDMA power control, interleaving, and coding

    Page(s): 1085 - 1095
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    The authors develop and analyze models of power control that consider other aspects of code-division multiple access (CDMA) systems, such as interleaving and coding on the land mobile radio channel. The orientation is that a power control scheme keeps the received powers at the base station almost equal, and the performance degradation incurred if the powers are not exactly equal will be quantified. In doing so, the authors consider the performance implications of control latency and a maximum speech delay constraint. Because of positive correlations between the fading channel amplitudes, the effectiveness of the combination of interleaving and coding in combating the effects of power variations due to slow Rayleigh fading is reduced. It is shown that power control and interleaving/coding are most effective in complementary parameter regions, thus providing a degree of robustness for both fast and slow Rayleigh fading View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fiber-optic microcell radio systems with a spectrum delivery scheme

    Page(s): 1108 - 1117
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    The authors examine microcell radio systems that use subcarrier transmission and spectrum delivery switch (SDS) techniques to meet traffic demands for a large number of portable phones. Radio signals are transmitted over fibre between base stations (BS) and a central station (CS). Relationships between blocking probability and offered traffic are described as a parameter of SDS ports. Optical link performances, such as link gain and carrier-to-noise ratio (CNR), are presented. Moreover, it is found that using FM techniques can improve the dynamic range by 20 dB compared to conventional methods for the uplink from BS to CS. The proposed technique can also increase the number of transmittable carriers compared to conventional methods for the downlink from CS to BS. This network strategy results in more flexible transmission View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Combined adaptive RAKE diversity (ARD) and coding for DPSK DS/CDMA mobile radio

    Page(s): 1076 - 1084
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (708 KB)  

    A diversity combining scheme, adaptive RAKE diversity (ARD), is proposed for a differential phase-shift keying (DPSK) direct sequence code division multiple access (DS/CDMA) mobile communications system. The ARD scheme minimizes the mean squared errors in the diversity combiner output. This suppresses the effects of the interference only paths in the time window for path diversity combining. Bit error rate (BER) performances with the proposed ARD and conventional equal gain combining (EGC) schemes are evaluated through laboratory experiments and compared. Block error rate (BKER) performance with the ARD scheme is also evaluated experimentally. Based upon the BKER evaluation results, an error correction scheme is proposed that is suitable for error occurrence characteristics of ARD output View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The dependence of indoor radio channel multipath characteristics of transmit/receiver ranges

    Page(s): 979 - 990
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1036 KB)  

    The authors report experimental and modeling studies that investigate the dependence of indoor radio channel multipath characteristics on a transmit/receive range. Specifically, a simple model for estimation of the complex baseband equivalent impulse response for indoor channels is explained. Using this model, the relationship between RMS delay spread and range on static indoor channels is estimated. Results show that this relationship is nonmonotonic and has a maximum at a range that depends on the building dimensions and the electrical properties of reflecting surfaces. The model is used in infinite, as well as finite, resolution modes to supplement the measurements of impulse response characteristics in different buildings using a limited resolution channel sounder. Experimental and modeling results are combined to derive conclusions that confirm the anticipated nonmonotonic relationship exists in empty buildings. Measurement results demonstrate that furniture has the effect of destroying this relationship, making RMS delay spread almost independent of range View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Linear unbiased data estimation in mobile radio systems applying CDMA

    Page(s): 1058 - 1066
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    Data estimation in the uplink of a synchronous mobile radio system applying code-division multiple access (CDMA) is considered. In mobile radio systems applying CDMA, multipath propagation leads to intersymbol interference (ISI) and together with time variance, to cross interference between the signals of different users regardless of whether the user codes are chosen orthogonal or not. A linear unbiased data estimation algorithm is presented that eliminates both ISI and cross interference perfectly by jointly detecting the different user signals, leading to unbiased estimates of the transmitted data symbols. By theoretical analysis and simulation, the performance of the linear unbiased data estimation algorithm is examined under the assumption that the radio channel impulse responses are known at the receiver. The price to be paid for the interference elimination are SNR degradations, which are calculated for typical mobile radio situations in urban areas. The resulting average uncoded bit error probabilities lead to the conclusion that systems applying the linear unbiased data estimation algorithm are well suited for mobile radio applications View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A measurement-based model for predicting coverage areas of urban microcells

    Page(s): 1013 - 1023
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    The authors have performed data reductions on 900 MHz signal attenuations measured on numerous streets in Manhattan. The database consists of both local spatial averages of signal attenuation and the short-term fluctuations about this average. The former, which is termed the local mean attenuation (LMA), is the primary focus. The database is used to obtain contours of constant LMA for two neighborhoods. It is shown that the contours have the shapes of convex diamonds. The authors propose that squares inscribed within these contours be used as the building blocks of microcellular environments. A theory is developed that explains the contours and predicts, with reasonable accuracy, the sizes of the inscribed squares. It is also shown that the prediction method can be applied without the need for measured data. The short-term fluctuation statistics of the signal attenuation are examined. They are shown to be Rayleigh-like in the non-line-of-sight regions of a microcell and Rice-like in the line-of-sight region. Possible extensions to other frequency bands and other urban environments are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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