Land Mobile Channel Research Articles

Interactive Multiple Model Filter for Land-Mobile Satellite Communications at Ka-Band

In this paper, an Interactive Multiple Model filter design is proposed to improve signal shadowing detection performance on land-mobile channels during rain fading for a downlink operating at Ka-band through a geostationary satellite. A robust solution for on-line determination of the filter measurement error covariance is provided. Analyses are performed for a combination of channels under different atmospheric conditions, clear sky and rain, and different scenarios, suburban and rural. Using International telecommunications union-based synthesized attenuation time-series, the proposed filter achieved a reduction in the incorrect detection duration of 32% for the scenario with a mobile terminal experiencing rain, and by 60% for the scenario with a fixed terminal experiencing rain.

Geometry-Based Statistical Model for the Temporal, Spectral, and Spatial Characteristics of the Land Mobile Channel

The main drawback of channel models presented in the literature is the lack of physically justified integration of all basic phenomena such as fluctuations, channel dispersion, and selective fading that occur in the actual radio channels. Based on physical premises, presented in this paper, the developed channel model reproduces all basic phenomena that affect the temporal, correlational–spectral, and spatial characteristics of the modelled radio channels. This effect is achieved by the structure of the model, which includes both the geometric channel model and statistical models of the received signal parameters. The geometry used in the model is based on the Parsons–Bajwa multi-elliptical model and the relationship, which describes the Doppler frequency as a function of the spatial position of object. Therefore, this model is called the Doppler multi-elliptical channel model (DMCM). The source of input data that define the geometric and statistical parameters of the model is the power delay profile or the power delay spectrum. This makes sure that DMCM characteristics depend on the properties of the modelled propagation environment. A comparative analysis of the simulation results and the measurements that DMCM can correctly capture the actual transmission properties of real channels.

Wave scattering from rough building surfaces in a virtual city model for the land mobile satellite propagation channel

The diffuse multipath component is studied in land mobile satellite (LMS) built-up propagation scenarios. The method of physical optics (PO) was implemented to model scattering from rough building facades. The results in terms of received power time-series are used to obtain the average multipath power level relative to free space for several roughness levels and various elevations and azimuths toward the transmitter. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2310–2314, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26237

Review of generative models for the narrowband land mobile satellite propagation channel

AbstractThe land mobile satellite (LMS) propagation channel is frequently described using statistical models. These models usually make different assumptions regarding the behavior of the direct signal, the diffuse multipath component and the shadowing effects. This paper analyzes the theoretical formulation and implementation of time‐series synthesizers based on three typical statistical models: Loo, Corazza–Vatalaro and Suzuki, describing their similarities and differences. The discussion is not limited to the amplitude of the complex envelope but also to the phase variations and Doppler spectra. Finally, guidelines are also provided for comparing model parameters supplied by different authors. Copyright © 2008 John Wiley & Sons, Ltd.

BCH Coding Performance Evaluation on a Land Mobile Channel Based OFDM System

BCH Coding Performance Evaluation on a Land Mobile Channel Based OFDM System

Limiter discriminator detection of narrow‐band duobinary FSK in a land mobile channel

AbstractError rates (BER) for narrow‐band duobinary FM with discriminator detection and integrate and dump (LDI) post‐detection filtering in land mobile channel characterized by fading and Doppler frequency shift are obtained. The fading process is assumed to be much slower than data rate, allowing the fading process to be analysed in a quasistatic manner as it passes through the narrow‐band filter. A simulation model was constructed using the signal processing simulator, and the simulated error rate results are shown to agree well with the calculated error rate results. Copyright © 2004 John Wiley & Sons, Ltd.

Combining PSA fading estimation techniques for TCM and diversity reception in Rician fading channels

AbstractIn this paper, a novel pilot‐symbol‐aided (PSA) technique is proposed for fading estimation in the land mobile satellite fading channels. The proposed technique combines the fading estimates obtained from a bandwidth‐efficient technique and a conventional technique according to the signal‐to‐noise ratios (SNRs) of the fading estimates. To enhance the transmission quality, trellis‐coded modulation (TCM) and diversity reception are employed in the system, and the combined estimates are subsequently used to correct the channel fading effects, to weight the signals from different diversity branches, and to provide channel state information to the Viterbi decoder. Monte Carlo computer simulation has been used to study the bit‐error‐rate (BER) performance of the proposed technique on trellis‐coded 16‐ary quadrature amplitude modulation in the frequency non‐selective Rician fading channels. Results have shown that the proposed PSA technique requires a very low bandwidth redundancy to provide satisfactory BER performance at low SNRs, and thus is suitable for use with TCM and diversity reception to achieve both bandwidth and power‐efficient transmission. Copyright © 2002 John Wiley & Sons, Ltd.

Soft decision differential phase detection with Viterbi decoding in satellite mobile systems

Noncoherent sequence detection is considered with soft decision differential phase detection and Viterbi decoding. The proposed receiver is analyzed with convolutionally encoded binary FSK and DPSK signals over narrowband fading channels. Numerical results presented for a Gaussian, satellite mobile and land mobile channels indicate that the proposed soft decision sequence detection receiver performs significantly better than uncoded signals and hard decision sequence detection. The division of subregions in the soft decision differential phase detector is also analyzed.

Performance analysis and code optimization of low density parity-check codes on Rayleigh fading channels

A numerical method has been presented to determine the noise thresholds of low density parity-check (LDPC) codes that employ the message passing decoding algorithm on the additive white Gaussian noise (AWGN) channel. In this paper, we apply the technique to the uncorrelated flat Rayleigh fading channel. Using a nonlinear code optimization technique, we optimize irregular LDPC codes for such a channel. The thresholds of the optimized irregular LDPC codes are very close to the Shannon limit for this channel. For example, at rate one-half, the optimized irregular LDPC code has a threshold only 0.07 dB away from the capacity of the channel. Furthermore, we compare simulated performance of the optimized irregular LDPC codes and turbo codes on a land mobile channel, and the results indicate that at a block size of 3072, irregular LDPC codes can outperform turbo codes over a wide range of mobile speeds.

Partial response CPM in satellite mobile systems

It is known that Gaussian minimum shift keying (GMSK) is an attractive signaling technique in mobile communications. In this study, it is demonstrated using partial response raised cosine (ZRC) modulation that other partial-response continuous phase modulation (PR-CPM) techniques can perform better than GMSK in a mobile system. ZRC signals are analyzed and compared with GMSK signals in a mobile channel. Differential phase detection (DPD) and limiter discriminator detection (LDD) receivers with decision feedback are separately considered for the detection of the two types of signals. In case of ZRC signals, the delay of the DPD receiver, and the sampling instant of the LDD receiver are selected to minimize the error probability. Numerical results are presented for land mobile, satellite mobile and Gaussian channels at different bandwidths and Doppler shifts. It is shown that ZRC signals can perform better than GMSK signals at the same bandwidth.

On the effect of imperfect interleaving for the Gilbert-Elliott channel

By using the Gilbert-Elliott (1960, 1963) model to study the performance of block-coded transmission over the land mobile channel, a new analytical expression illustrating the effect of various parameters, e,g., mobile speed, delay constraint, and parameters for the error correcting code, is found. Comparisons between the results obtained by this analytical expression and results obtained by computer simulations show that the analytical results are accurate for a broad range of channel parameters. The Gilbert-Elliott model is then used to compare the performance of different binary BCH codes when the delay constraint does not allow the assumption of infinite interleaving. In contrast to the memoryless case, where the performance typically is improved with increased block length, short codes are found to be as good, or even superior, due to the fact that the interleaver works better for shorter codes.

Limiter discriminator-detected GMSK with FM and GMSK interference in a land mobile channel

This paper addresses Gaussian minimum-shift keyed (GMSK) receiver performance analysis for limiter discriminator detection with cochannel interference resulting from a combined cellular voice and packet radio network. A specific example is cellular digital packet data (CDPD), which shares spectrum with cellular voice users; thus, the CDPD receiver will see both narrow-band frequency modulation (NBFM) voice and GMSK data interference. Previous studies investigated the performance of a GMSK receiver with a single GMSK interferer and multipath delay. In this paper, we extend earlier work to multiple Rayleigh fading (Doppler spread) interferers having NBFM (f/sub dm/=12 kHz) analog modulation and/or GMSK modulation. Probability of bit-error expressions are derived for the frequency modulation (FM) and GMSK interferer cases assuming medium-to-high signal-to-noise ratio regions. For scenarios of from one to six NBFM interferers, having the same total power, a corresponding Gaussian approximation is within 1.5 dB. Simulation results are also presented for various combinations of FM and GMSK interference. FM interference is only slightly worse than GMSK interference. Delay spread representing an urban scenario resulted in only a slight increase in the error floor.

Application of turbo codes in satellite mobile systems

Turbo codes are considered in a mobile channel with FSK modulation and LDI detection. Numerical results are presented for narrowband Gaussian, land mobile and satellite mobile channels separately. Numerical results show that turbo codes can significantly improve the performance over uncoded signalling.

Dynamic characteristics of a narrowband land mobile communication channel

Land mobile communication signals are subject to propagation effects that result in variation of the received signal amplitude and phase. The most rapid signal variations are the result of multipath propagation and occur with sufficient severity to make reception difficult. At microwave frequencies, the narrowband (30-kHz) channel is considered nondispersive. It will experience flat amplitude fading and band-limited frequency distortion. An understanding of the dynamic nature of the communication channel is required to design land mobile systems that are tolerant of rapid multipath conditions. A model is presented to characterize the dynamic nature of multipath channels, and a new dynamic measure, fractional power change rate, is introduced. The distribution of the fractional power change rate, power change rate, and phase change rate are predicted by the model and validated by comparison to measured data. The research in this paper is part of an ongoing effort to develop multipath-tolerant demodulation techniques for higher order modulation types. The measures developed are of primary importance for specifying the dynamic requirements for such demodulators.

Source-aided trellis decoding for mobile communication channels

A trellis decoder which incorporates the residual redundancy in low bit rate speech coder parameters is used to decode Reed Solomon (RS) codes. As not all the transmitted speech parameters and bits are equally sensitive to errors, unequal error protection has been employed to enhance speech quality. Subcodes of RS codes, which have been introduced by Shin and Sweeney (1995), are used for this purpose. A trellis decoding method is tailored to combat bursty errors in a mobile communication channel. Simulation results on a land mobile channel show a noticeable increase in performance and computational efficiency of the decoder.

Efficient modeling and evaluation of fiber-fed microcellular networks in a land mobile channel using a GMSK modem scheme

Fiber feeders have been proposed for simplifying the base station in microcells, and thus make feasible the use of the microcellular architecture to overcome the barrier posed by the finite available spectra. We provide an analytical model to evaluate the exact error performance of the system, which accounts for the statistical effects in the mobile channel and the nonlinearity of the laser diode. The nonlinearity of the optical source coupled with the fading nature of the wireless channel mandates a solution based on simulation. However, the computer run time for the simulation is prohibitive, virtually rendering the model useless. We propose a computer-amenable "simplified model" which reduces the computation time immensely and also provides reasonably tight bounds. The BER performance for various channel conditions is evaluated using both models, and comparative studies are made on fiber-optic and non-fiber-optic systems. The tradeoff between the system performance and system capacity is discussed. Results obtained justify the use of fiber-optic feeders for future microcellular systems from a BER-performance point of view.

Satellite-PCS channel simulation in mobile user environments using photogrammetry and Markov chains

In this paper, we present a system that models the land-mobile satellite communication channel with a Markov chain approach supported by images of the mobile Earth station's (MES) environment. Our method employs a video camera with a fish-eye lens capturing image sequences of the user environment from the position of the moving MES, image and signal processing algorithms to recognize propagation path states and extract their duration and transition probabilities, and modeling of the communication channel characteristics using the theory of Markov stochastic processes combined with statistical fade distributions appropriate for given path states. The results demonstrate that the procedure provides a full statistical characterization of the narrow-band land-mobile satellite propagation channel in several environments.

NATIONAL SECURITY/EMERGENCY PREPAREDNESS AND DISASTER RECOVERY COMMUNICATIONS VIA ACTS

During the period from early 1993 to 1994, the U.S. National Communication System (NCS), a government agency, sponsored the development and execution of several fixed and mobile experiments using the advanced communications technology satellite (ACTS). The purpose of these experiments was to evaluate the feasibility of integrating an ACTS-like communications system into national security/emergency preparedness (NS/EP) operational scenarios. These experiments focused on clear and secure voice communications in both the fixed and mobile environment. For the mobile experiments, the focus was on the performance of both clear and secure voice in the land-mobile satellite communications channel. For the fixed experiments, the focus was on the use of a T1 terminal for restoration of communication services in the event of a disaster and for remote user communications. The results of these experiments are described in this paper.

Ring-TCM for fixed and fading channels: land-mobile satellite fading channels with QAM

The authors investigate ring-TCM codes suitable for M-QAM signal sets on nonfrequency-selective fading channels. A new range of nonrotational invariant (NRI) and rotational invariant (RI) fading-optimised ring-TCM codes suitable for rectangular M-QAM schemes is presented. The trade off between the code gain and the decoder complexity of these codes is analysed, and their actual performance under different fading channel conditions is evaluated. In addition, a comparison with the best fading-optimised TCM codes for M-QAM reported in the literature is carried out.

Matlab for Windows Software AID in a Mobile Communications Course

Matlab for windows software aid in a mobile communications course A simple model for the teaching of land mobile communication channel issues has been implemented. The landscapes the mobile terminal traverses are described in terms screens, point scatterers, reflectors, etc. By using simple ray tracing techniques all multipath contributions arriving at the receiver are evaluated and the most relevant channel parameters are computed.