Land Mobile Communication Systems Research Articles

1. Activities on Enhanced Availability of 5G/B5G Land Mobile Communication Systems

1. Activities on Enhanced Availability of 5G/B5G Land Mobile Communication Systems

An iALM-ICA-Based Antijamming DS-CDMA Receiver for LMS Systems

We consider a land mobile satellite communication system using spread spectrum techniques where the uplink is exposed to multitone jamming attacks, and the downlink is corrupted by multipath fading channels. We propose an antijamming receiver, which exploits inherent low-dimensionality of the received signal model, by formulating a robust principal component analysis-based recovery problem. Simulation results verify that the proposed receiver outperforms the conventional receiver for a reasonable rank of the jamming signal.

Adaptive coding and modulation scheme for satellite-UMTS TDD systems based on a photogrammetric channel estimation method

The conventional wireless communication systems are designed to overcome the worst-case channel, using the huge amount of redundant bits to assure communications performance and quality of services. Those systems cannot achieve the optimum spectrum and power efficiency. This paper presents an adaptive coding and modulation scheme used in the user terminals of the third-generation satellite communication system. A three-state photogrammetric channel estimation method is introduced for tracing the variations of large-scale environments. The mobile user terminal dynamically switches the suitable coding and modulation schemes according to the result of photogrammetric channel estimator in order to maximize the power efficiency and data throughput. The real measurement data were used to validate our proposed method. The results show that the proposed method not only reduces the system complexity, but also mitigates the power control requirements and increases the data throughput for the land mobile satellite personal communication systems. Copyright © 2006 John Wiley & Sons, Ltd.

Web traffic capacity of multi-beam GEO and MEO mobile satellite systems

An investigation into the downlink web traffic capacity of W-CDMA land mobile satellite communication systems for Geostationary (GEO) and Medium Earth Orbit (MEO) constellations is presented. It is shown that the effect of power control errors on the web traffic capacity severely degrades the performance of mobile satellite systems. It is also shown that the use of the proposed macrodiversity system is to mitigate the effect of power control errors, and consequently increases the web traffic capacity of multi-beam GEO and MEO mobile satellite systems.

A Study on Signal Parameters Estimation via Nonlinear Minimization

The problem for parameters estimation of the received signals impinging on array sensors has long been of great research Interest in a great variety of applications, such as radar, sonar, and land mobile communications systems. Conventional subspace-based algorithms, such as MUSIC and ESPRIT, require an extensive computation of inverse matrix and eigen-decomposition In this paper, we propose a new parameters estimation algorithm via nonlinear minimization, which is simplified computationally and estimates signal parameters simultaneously.

A circular planar inverted‐L antenna with a vertical ground plane

AbstractA new broadband planar inverted‐L antenna (PILA) with a vertical ground plane (VGN) is experimentally presented. With the electromagnetic coupling between the radiator and VGN, the 2:1 VSWR impedance bandwidth of > 45% has been attained. The radiation patterns similar to those of conventional planar inverted‐ L or F antennas are applicable for land mobile communication systems. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 315–317, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10594

Performance comparison and improvement in adaptive arrays based on time‐ and frequency‐domain signal processing

AbstractIt has been known that an adaptive array antenna is effective for reducing frequency‐depending selective fading, which is a problem in wide‐band land‐mobile communication systems. In an environment in which many delayed signals arrive, it is desirable to improve their SN ratio by using co‐phase synthesis. There have been two types of adaptive array antenna for this purpose: an antenna based on time‐domain signal processing using a TDL (tapped delay line), and an antenna based on frequency‐domain signal processing using a fully reconfigurable filter. The latter has variations in its configuration, and is useful for making practical apparatus. However, its convergence process and behavior in a fading environment have not been clearly understood. In this paper, the performance and the advantages and disadvantages of adaptive array antennas based on various configurations with time‐ and frequency‐domain signal processing are compared. It is found that combinations of some configurations improve their performance. The improvement in performance is also described. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(9): 35–42, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1117 Copyright © 2002 Scripta Technica

Broadband planar inverted-L antennas

A new feeding arrangement applied to a broadband planar inverted-L antenna (PILA) is experimentally presented. The proposed feeding structure comprises a narrow strip excited by a coaxial probe and a grounded wall, which are etched onto a vertical finite-size dielectric slab. The measurements on the proposed square PILAs with the new feeding structures are executed. 50% impedance bandwidths for VSWR = 2:1 have been obtained and the radiation patterns similar to those of conventional planar inverted-L or -F antennas are suitable for land mobile communication systems.

Improved selective repeat ARQ scheme for mobile multimedia communications

This paper suggests a NAK-based selective repeat (SR) scheme for reliable data transmission in the future land-mobile communications systems supporting multimedia services. The proposed scheme is an improved version of the automatic repeat request defined in IS-707. We analyze the proposed SR under the assumption of a two-states Markov channel. The numerical results show that drastic performance improvement can be achieved at the cost of minor increase in complexity.

Path diversity using an adaptive array with circularly arranged directional antenna elements

This paper proposes a new path diversity method using an adaptive array antenna in order to improve the quality and capacity for high-data-rate land mobile communication systems. In the proposed scheme, some elements from circularly arranged directional antenna arrays are selected based on estimated delay profiles, and some outputs of the adaptive array are combined for each delayed wave. Therefore, interference waves can be suppressed by this space-time processing approach with low computational complexity. Computer simulations show that the performance of the proposed scheme can be improved drastically by the path diversity combining method which minimizes mean square errors, even if delayed waves are incident from the same directions as a direct wave. © 2000 Scripta Technica, Electron Comm Jpn Pt 3, 83(12): 9–18, 2000

Internetworking ATM with wireless land mobile (WLM) communication systems

Internetworking ATM with wireless land mobile (WLM) communication systems

Signal fading in land-mobile satellite communication systems: Statistical characteristics of data measured in Japan using ETS-VI

The space–earth links in land-mobile satellite communications are frequently cut off as a result of the shadowing and blockage, due to roadside trees, buildings, utility poles, and other artificial obstacles. Knowledge about the fade statistics is therefore important in designing cost-effective land-mobile satellite communication systems. Using a 15.5 dBi-gain satellite-tracking antenna, an S-band (2.1 GHz) unmodulated continuous-wave signal transmitted from the elliptically orbiting ETS-VI satellite was measured, while the vehicle the antenna was mounted on was driven around a city in Okinawa. The investigation reports on fade statistics and fade and nonfade-duration (interfade-duration) statistics for elevation angles ranging from 57.9° to 66.5° and for several thresholds of fade state (fade margins from 3 to 15 dB).

Physical–statistical prediction of performance for land mobile satellite communication systems

A performance analysis of land mobile satellite systems is presented. A physical–statistical model is applied to infer narrowband channel parameters, such as fade distribution, level-crossing rate or bit error ratio. The physical–statistical approach combines a ray-tracing tool with the statistical distribution of the parameters describing the environment. Simulation results are successfully compared with measurements at the L-band. The model is then used to predict the performance of a typical LMS system, with a new point of view, which differentiates temporal availability and spatial coverage. The physical nature of the method highlights the role of relevant parameters.

Transmission modelling of ENCAP-OQPSK radio links

Offset quaternary PSK-type (OQPSK) digital modulation schemes are strongly recommended for radio transmission within land mobile and/or satellite communication systems requiring good power/bandwidth tradeoffs and low-cost, power-efficient implementations. The ENCAP-OQPSK design method (encoded-amplitude-and-phase) previously proposed by the authors was shown to provide a wide class of OQPSK-type schemes of practical interest; a flexible, digital transmitter implementation can be directly based on the encoding rules of this design method. The paper deals with the transmission modelling of radio links where ENCAP-OQPSK modulators are employed. In spite of the apparent complexity of the encoding rules, it was possible to define an appropriate signal model, both accurate and user-friendly. In fact, the nonlinearly modulated ENCAP-OQPSK signals can always be exactly represented as a sum of linear OQPSK-type components. Similar representations, also exact, can be adopted for any signal obtained by filtering and/or nonlinear amplification of the signals. This modelling approach simplifies spectral computations and performance evaluations, and is quite accurate, in general, when the sum of the two main linear components is used to approximate the transmitted signals.

Analysis of a 16-ary Quadrature Amplitude Modulation for Land Mobile Satellite Data Communication

The paper is concerned with evaluating the performance of a 16-ary quadrature amplitude modulation (QAM) signaling when transmitted through a land mobile satellite channel. The channel exhibits fading and shadowing as well as additive white Gaussian noise. Fading and shadowing cause both envelope and phase variations of the received signal. The paper derives upper bounds of the probability of error due to each one of these variations. An expression of the irreducible probability of error is also derived. The derived expressions are useful for the design of land mobile satellite data communication systems.

Dual-Space Diversity over Land Mobile Satellite Channels Operating in the L and K Frequency Bands

Land mobile satellite communication systems at Ka/K band (30/20 GHz) are attracting more and more attention to researchers because of its frequency band availability and the possibility of using small earth stations and satellite antennas for the systems. However, the Ka/K-band communications also give significant challenges in the system design due to severe channel impairments expected from the satellite links. In this paper, K-band channel characteristics are studied and compared with those at L band. The channel is modeled as Rayleigh multipath fading with the line-of-sight (LOS) component following a lognormal distribution. The first and second-order statistics of the fading channel are studied. Dual-space diversity reception is investigated to combat the flat channel fading. The bit error rate performance of coherent binary phase shift keying (BPSK) with ideal bit and carrier phase synchronization over the fading channel at K band is evaluated theoretically and verified by computer simulations in the case with and without diversity reception.

A coherent detection system with a suppressed pilot channel for ds/cdma systems

AbstractThis paper proposes a coherent detection system using a suppressed pilot channel to achieve coherent RAKE diversity combining for DS/CDMA up‐link in land mobile communication systems. At the receiver, delay profile is measured using the suppressed pilot channel and simultaneously chip timing is detected by using block demodulation and maximum likelihood estimation, and measured the complex delay profile. The performance of proposed adaptive RAKE diversity is evaluated by computer simulation for quadriphase‐shift keying (QPSK) system. The results show that the performance of the proposed scheme is superior to that of the conventional DPSK/PDI, and it is almost the same as the theoretical performance for the coherent RAKE diversity receivers.

SER Analysis of QAM with Space Diversity in Rayleigh Fading Channels

This paper derives the symbol error probability for quadrature amplitude modulation(QAM) with L-fold space diversity in Rayleigh fading channels. Two combining techniques, maximal ratio combining(MRC) and selection combining(SC), are considered. The formula for MRC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an additive white Gaussian noise(AWGN) channel over a chi-square distribution with 2L degrees of freedom. The obtained formula overcomes the limitations of the earlier work, which has been limited only to deriving the symbol error rate(SER) of QAM with two branch MRC space diversity. The formula for SC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an AWGN channel over the distribution of the maximum signal-to-noise ratio among all of the diversity channels for SC space diversity. No analysis for QAM with SC space diversity has been reported yet. Analytical results show that the probability of error decreases with the order of diversity. We can also see that the incremental diversity gain per additional branch decreases as the number of branches becomes larger. On the other hand, the performance of 16 QAM with MRC becomes much better than that of SC as the number of branches becomes larger. By giving the order of diversity, L, and the number of signal points, M, we have been able to obtain the SER performance of QAM with general space diversity. These results can be used to determine the order of diversity to achieve the desired SER in land mobile communication system employing QAM modulation.

Orthogonal multicarrier frequency hopping‐code division multiple access scheme for frequency‐selective fading

AbstractTo improve frequency efficiency or user capacity in land mobile communication systems, orthogonal multi‐carrier frequency hopping‐code division multiple access (FH‐CDMA) is introduced and investigated. Such improvement is achieved by combining orthogonal frequency division multiplexing (OFDM) with FH‐CDMA. the theoretical analysis includes bit error rate (BER), required S/N, and maximum bit rate.A modified scheme allowing transmission power to be controlled according to the number of simultaneously accessing users also is discussed. This scheme improves BER performance for frequency‐selective fading when the number of simultaneously accessing users in a cellular zone is small.

Square-QAM adaptive modulation/TDMA/TDDsystems using modulation level estimationwith Walsh function

The authors propose a square-QAM adaptive modulation/time division multiple access/time division duplex (TDMA/TDD) system for land mobile communications to achieve high quality and high bit rate transmission in both flat and frequency selective fading environments. To further improve performance, a new modulation level estimation scheme using the Walsh function and maximum likelihood (MS) estimation is also proposed. Computer simulation confirms that the proposed system gives 8 dB better performance and four times larger delay spread immunity than that of conventional QPSK systems at BER = 10-3.