IEEE Transactions on Vehicular Technology

HSST is an acronym for high-speed surface transport and is the trade name of the vehicle levitated by the attractive electromagnets and propelled by the linear induction motor (LIM) developed by Japan Air Lines. Two test vehicles have been designed, manufactured, and flight-tested. The first test vehicle, HSST-01, marked a maximum speed of 307.8 km/h on a 1300-m long test track in February, 1978, whereas the second test vehicle, HSST-02, has demonstrated boarding test flights successfully to an aggregated total of abut 1500 passengers since April, 1978, onward. The HSST-01 weighs one ton, is 4 m long, designed for high-speed testing, and incorporates eight electromagnets and a LIM with a maximum thrust of 300 kg. The levitating power supply is taken from the batteries carried on board the vehicle, and the three-phase VVVF power for the LIM propulsion is supplied from the wayside power lines through the power collector. The nine-seated HSST-02 has a loaded weight of 2.3 tons. Major items of additional functions realized in the HSST-02 include: 1) the electromagnets are fitted to the flexible chassis for better riding comfort by incorporating mechanical suspension between the chassis and the body, and 2) with the continuous levitation, the power for the LIM is rectified and supplied to the electromagnets jointly serving with the batteries carried on board. In light of the test results obtained so far, it is shown that the predicted performances of the levitation magnets, LIM, and the power collector system have been satisfactorily established, and that there would be no major technical problems in the course of our future development for implementation of the HSST system toward commercial services. The design of a preoperational test vehicle is now underway, and its test flight is scheduled to he initiated in 1980. This 80-seated preoperational test vehicle will have test flights on a 15-km test tract at a target crusing speed of 300 km/h.

Operation of long stator Maglev transport systems requires instrumentation for remote control of the propulsion and for monitoring the actual operating conditions of the vehicle subsystems as well as of the propulsion itself. An additional control system is needed to provide data on instantaneous vehicle position and speed. To fulfill safety requirements, a self-contained unit has to monitor the limit values of vehicle velocity. A control system has been designed and manufactured for the TR 05 to perform these operations. It includes a slotted waveguide for wide-band transmission (0.8 GHz), a noncontact counting system which detects the teeth and slots of the stator, and inductive sensors working against trackside marks for the purpose of safe speed limit control. The system is described in detail.

For the design of indoor radio communication or a portable radio telephone system, 1.2 GHz band radio wave propagation characteristics are investigated in a concrete building. Penetration loss through a window, local median variations, and cumulative distributions of received signal levels in a room, reflection coefficient or equivalent dielectric constant and transmission loss of a wall/floor are discussed.

Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented

The practical space and frequency diversity performance achievable inside a building at 1.75 GHz under fading conditions due to the motion of a portable terminal and due to the movement of people are investigated. Data are collected using a four-branch dual-frequency envelope receiver positioned throughout one floor of a university building of common construction type. The measurement environment is characterized for large-scale path loss and wall transmission loss. Envelope cross correlations are calculated, and performance of diversity is measured for various frequency separations and antenna spacings which would be applicable given the physical size of portable telephones and data terminals. Two-branch space diversity is directly compared to two-branch frequency diversity and to four-branch hybrid diversity based on simultaneous measurements of each using selection combining. The distributions of correlations and diversity gain at different locations are also investigated. Results indicate that two- and four-branch diversity can be a very effective way to combat signal fading for portable terminals in an indoor radio environment

This paper presents the results of measurements performed at 1.8 GHz in a microcellular environment in a city center (Athens, Greece). Studies have shown that the microcellular environment is dissimilar to the conventional macrocell area, therefore, accurate knowledge of propagation characteristics is essential. The aim of the measurement campaign is to provide a clear understanding of the propagation parameters affecting the design of a personal communication system (PCS) in a city center. Theoretical predictions developed using ray tracing techniques and measurement-based models are plotted versus distance for alternative configurations. The measurement procedure, data analysis, and comparison between theoretical and experimental results are given

An accurate propagation channel model is crucial for evaluating the performance of a communication system. A propagation channel can be described by a Markov model with a finite number of states, each of which is considered to be quasi-stationary over a short period. This work proposes a two-layer multistate Markov model. Instead of a large Markov transition matrix used in a conventional single-layer Markov model, two small Markov transition matrices are employed by a two-layer Markov model to reduce the computational complexity of the model without increasing the memory requirements. The proposed approach characterizes the multiplicative processes of a propagation channel as shadowing and fast fading. Each type of fading is considered as several channel states and each of the states corresponds to a specific mixed Rayleigh-lognormal distribution. Numerical results reveal that the statistical properties of the simulated data are quite close to those obtained from the measurements; indeed, the proposed two-layer Markov model is more accurate and less complex, and requires less memory than the single-layer Markov model. Furthermore, the proposed two-layer Markov model enables the fading statistics and error probability performance of a quadrature phase-shift keying modulation scheme in a typical urban Taipei environment to be more accurately predicted. Besides, it can easily be applied to similar environmental scenarios.

Narrow-band propagation measurements were conducted at two floors of a multi-storied building at 1.9 GHz to study the behavior of the Rice factor and local mean power. To evaluate the influence of the Rice factor on a pico-cellular system, the outage probability is calculated for two different cases: (i) Rician fading for the desired and interfering signals with different Rice factors; (ii) desired signal with Rician fading and interfering signals with Rayleigh fading with a different local mean power for each interfering signal. Finally, a pico-cellular structure is determined as an illustration

There is an explosive growth in the market of wireless communications services in urban areas. New regulatory environments as well as competition in the communications industry require that these systems be deployed quickly and at low cost. Computer-based radio propagation prediction tools are strong candidates for this goal. We introduce an outdoor radio propagation prediction tool using a ray tracing technique in two dimensions (2-D) and three dimensions (3-D). We have compared the predicted and measured results in various propagation environments. Comparisons indicate that 2-D is adequate for a low transmitter while 3-D is recommended for a high transmitter whose height is comparable with or higher than surrounding buildings. In most locations, the computer tool predicts the correct propagation loss with a mean error of less than 7 dB and a standard deviation of less than 8 dB

The blockage effect of a large box truck passing through the line-of-sight path in a typical 11-GHz microcellular mobile communications link was measured. The results show that attenuation and diffraction effects can be significant when the truck is close to the relatively low antenna on the mobile unit. At a distance of 13 ft, this attenuation can be as much as 35 dB, depending on the type of mobile antenna. As the distance between the truck and the mobile increases, the attenuation decreases. At a distance of 140 ft, the attenuation is insignificant. It is shown that attenuations calculated for this path using the unified theory of diffraction agree very well with measured data. On the basis of this agreement, the theory is used to estimate the attenuation caused by truck blockage, as a function of truck distance to the mobile unit, for frequencies between 1 and 40 GHz

An analytical method is presented for the error probability evaluation that can be used in many cases to reduce significantly the computation time with respect to that required by simulation techniques. The method can take into account thermal noise, intersymbol interference caused by intermediate frequency (IF) and baseband (BB) filterings, multipath propagation with typical delay spreads, Rayleigh fading, and random FM noise. A number of results are presented relevant to multipath fading channels with different vehicle speeds, several modulation techniques belonging to the 12PM3 class with frequency discriminator detection and different IF and BB filters

We estimate link reliabilities for IS-54/136 digital cellular handsets operating with or without an equalizer in urban, suburban, rural, and mountainous environments. We define the reliability of a user's receiver as the probability that the bit error rate (BER) is less than some specified value. The probability is taken over all mobile positions in a cell area and the BER is averaged over multipath fading. Using a range of tools for modeling and simulation of the digital cellular link (transmitter, channel, and receiver), we present an extensive set of results showing the influence of: (1) receiver structures (differential detection with no equalizer, differential detection with selection diversity, or coherent detection with a medium-complexity equalizer); (2) joint distribution of the channel's RMS delay spread and average signal-to-noise ratio (SNR) (this distribution is based on an environment-specific model reported previously); and (3) vehicle speed (0-200 km/h). In all simulations, we assumed a two-path Rayleigh fading channel characterized by: (1) the delay between paths and (2) the ratio of power received from the first path to that from the second path (the RMS delay spread relates to these two parameters). For typical cell sizes, we find that imposing an equalization requirement in IS-54/136 handsets is overly stringent in all environments, except mountainous areas. For these environments, achieving high reliability requires either equalization or other measures, such as smaller cells, directional base-station antennas, or dual-diversity handsets

In this paper, we investigate spatial-temporal equalization for IS-136 time-division multiple-access (TDMA) cellular/PCS systems to suppress intersymbol interference and cochannel interference and improve communication quality. This research emphasizes channels with large Doppler frequency (up to 184 Hz), delay dispersion under one symbol duration, and strong cochannel interference. We first present the structure of the optimum spatial-temporal decision-feedback equalizer (DFE) and linear equalizer and derive closed-form expressions for the equalizer parameters and mean-square error (MSE) for the case of known channel parameters. Since the channel can change within an IS-136 time slot, the spatial-temporal equalizer requires parameter tracking techniques. Therefore, we present three parameter tracking algorithms: the diagonal loading minimum MSE algorithm, which uses diagonal loading to improve tracking ability, the two-stage tracking algorithm, which uses diagonal loading in combination with a reduced complexity architecture, and the simplified two-stage tracking algorithm, which further reduces complexity to one M×M and one 3×3 matrix inversion for weight calculation with M antennas. For a four-antenna system, the simplified two-stage tracking algorithm can attain a 10^-2 bit error rate (BER) when the channel delay spread is half of the symbol duration and the signal-to-interference ratio (SIR) of the system is as low as 5 dB, making it a computationally feasible technique to enhance system performance for IS-136 TDMA systems

In digital mobile communication systems, intersymbol interference is one of the main causes of degrading system performance. Decision feedback equalization (DFE) is the commonly used remedy for this problem. Since the channel is fast-varying, an adaptive algorithm possessing a fast convergence property is then required. The least mean square (LMS) algorithm is well known for its simplicity and robustness; however, its convergence is slow. As a consequence, the LMS algorithm is rarely considered in this application. In this paper, we consider an LMS-based DFE for the North American IS-136 system. We propose an extended multiple-training LMS algorithm accelerating the convergence process. The convergence properties of the multiple-training LMS algorithm are also analyzed. We prove that the multiple-training LMS algorithm can converge regardless of its initial value and derive closed-form expressions for the weight error vector power. We further take advantage of the IS-136 downlink slot format and divide a slot into two subslots. Bidirectional processing is then applied to each individual subslot. The proposed LMS-based DFE has a low computational complexity and is suitable for real-world implementation. Simulations with a 900-MHz carrier show that our algorithm can meet the 3% bit error rate requirement for mobile speeds up to 100 km/hr

The train communication network standard was approved in 1999 by the International Electrotechnical Commission (IEC) and the IEEE to warrant train and equipment interoperability. However, we have not found any published work presenting a top-down device design that is compliant with this standard. None of the found publications deals with the real-time protocols of the design nor resolves the many open points left in it. The link-layer design that is presented here implements the full set of specifications of the IEC 61375-1 standard (also named the IEEE 1473-T standard) that is related to the slave devices for the multifunction vehicle bus (MVB), including all of its real-time protocols, procedures, and free options. It is the first step to obtaining a true system-on-chip, including all the layers of any MVB device, as stated by the standard. Our proposal is based on a concurrent, easily parameterized and reconfigurable, top-down design procedure that is implemented in a single field-programmable gate array plus a very simple embedded application processor. The performance of our design is only limited by the standard constraints themselves, which is restricted neither by its proposed implementation nor by our design criteria.

Portable radio antenna performance on the human body was measured for several different radio models in the 150, 450, 800, and 900 MHz. bands. In-vehicle measurements were made at an outdoor antenna range equipped with a vehicle turntable. All other measurements were made in an anechoic chamber. Tests were made at the head level, at the side-level swivel-type carry case, at the side-level belt-loop type carry case, and at the shoulder level with a speaker microphone antenna. A statistical analysis was made of the data for use in coverage propagation predictions, and system designs. The results of the statistical analysis are presented

Transmission on mobile radio circuits is often affected by standlng-wave breakup" resulting from spatial variations in rf signal amplitude, which to the moving mobile unit appear as rapid fades. Measurements made in the 150 mHz band confirm previous reports that within any small area such signal variations tend to follow the Rayleigh distribution. Statistical distributions have also been determined for the depths and widths of fades, in several different environments where fading was severe; rural, suburban and urban situations were found to produce rather similar results in-these respects. Some information is also given on the relation between median signal and circuit quality for speech, under fading conditions.

The propagation loss into ten medium-sized buildings in Schaumburg, IL, has been measured. At 900 MHz, the mean penetration loss in the lower enclosed floors at or near ground level was found to be 10.8 dB with a standard deviation of 5.8 dB. At 1500 MHz, penetration loss was found to be 10.2 dB, and the standard deviation was 5.6 dB. Data was also taken up to 12 floors (with a higher concentration of data on the first five floors) to show higher elevation trends in the penetration loss. The measured building penetration loss was combined with data from other references, and the slope of a best fit curve as a function of frequency is found to be -7.9 dB per decade

This paper presents an extensive computer simulation of the influence of the human body on a circular-loop-wire antenna to simulate the pager antenna. The coupled integral equations (CIEs) approach and the method of moments (MoM) are employed for numerical simulation of this antenna-body-coupling problem. The magnetic frill source is used to model the antenna-feeding structure. A realistically shaped full-scale human-body model (1.7 m) is constructed. A small loop antenna (loop radius b=1.7 cm and wire radius a=0.072 cm) of x, y, and z orientation, in free space or proximate to the human body at the top pocket (chest position) or belt level (waist position), is considered. Numerical results of the antenna characteristics and body absorption at 152, 280, and 400 MHz are presented and discussed for radio-paging applications. At 280 MHz, it is found that the real part of the impedance increases about five to ten times, and, hence, the antenna ohmic-loss radiation efficiency increases from 17% (in free space) to 69%, 44.3%, and 58.4%, respectively, for the x-, y-, and z-oriented loops when proximate to the body. The radiation efficiencies, reduced by the body-absorption effect, are 5%, 61%, and 25% for the x-, y-, and z-oriented loops, respectively. For the y-oriented loop, which is found to be the most suitable for paging communications, the antenna efficiencies are almost the same at the two location levels for all frequencies considered. The computed antenna characteristics influenced by the human body; including the input impedance, antenna patterns, cross-polarization field level, radiation efficiencies, and maximum and minimum power gains, are important for the antenna/RF design and the link-budget consideration

In this paper, the validity of recommendation ITU-R P.1546 in a short-range terrestrial environment is analyzed. Its three versions (P.1546, P.1546-1, and P.1546-2) are compared against simple models and evaluated using measurement results that were obtained by utilizing the pilot signal of a commercial code-division multiple-access mobile telephone network. Measurement results show that P.1546-2, on average, underestimates the field strength by more than 10 dB for typical Australian rural areas. However, it improves the error standard deviation compared to previous versions. The causes of these effects and the suggestions for further development of the Recommendation are discussed and evaluated.

Mobile radio systems require highly bandwidth efficient digital modulation schemes because of the limited resources of the available radio spectrum. A theoretical analysis of bit error rate (BER) is presented for the differential detection of differentially encoded 16-level amplitude/phase shift keying (16DAPSK) under Rician fading in the presence of Rayleigh faded co-channel interference (CCI) and additive white Gaussian noise (AWGN). Differential detection comprises eight-level differential phase detection (DPD) and two-level amplitude ratio detection (ARD). Exact expressions for probability distributions of differential phase noise and amplitude ratio are derived for the BER calculation. The calculated BER performance of 16DAPSK is presented for various values of Rician fading K factor, Doppler spread of diffused component, and Doppler shift of the specular component, and is compared with that of 4-16DPSK. It is shown that 16DAPSK is superior to 16DPSK and requires 1.7 (1.6) dB less E_b/N₀ (SIR) at BER=10^-3 in Rician channels with K=5 dB

In this paper 16 kbit/s digital voice transmission with conventional channel spacing of 25 kHz, employing a 16 kbit/s adaptive delta modulation (ADM) coder-decoder (CODEC) is evaluated. The main characteristics of narrow-band digital FM modulation schemes, such as tamed FM, Gaussian filtered minimum shift keying (GMSK), four-level FM and phase locked loop-quaternary phase shift keying (PLL-QPSK), are compared by laboratory tests. Digitized voice quality in a digital channel incorporating a 16 kbit/s ADM CODEC and GMSK coherent detection was compared with voice quality of a conventional analog FM channel. Bit error ratio (BER) performance is shown to depend primarily on demodulation schemes. Digital voice quality is inferior to that of analog voice with an opinion score difference of about 0.5 in fading environments. This kind of digital voice transmission will be applicable for those systems that require high security at an expense of speech quality.

The bit-error rate (BER) performance of differential 16 STAR-QAM in frequency-selective Rician fading channels with diversity reception is theoretically analyzed for three different types of delay profiles: double-spike, one-sided exponential, and Gaussian profiles as well as two kinds of pulse-shaping filtering: a raised cosine (RC) Nyquist signaling pulse and the rectangular pulse. The effect of time delay between line-of-sight (LOS) and multipath components is also included in the analysis and shown to degrade the system performance significantly

In this paper, the performance of fully digital synchronization techniques for time-division multiple-access (TDMA) differentially encoded 16-QAM signal transmission, over cellular mobile radio channels, is considered. The preamble-less feedforward nondecision-aided (FF-NDA) synchronization techniques used for symbol timing recovery, carrier phase recovery and amplitude gain control to overcome Rayleigh fading channel impairments, are described. Novel techniques for digital amplitude gain estimation are presented. The performance of the synchronization parameters' estimators at the receiver is evaluated by computer simulation over additive white Gaussian noise (AWGN) and slow Rayleigh fading environment. Statistical properties of the algorithms developed are evaluated in terms of the bias and variance of the estimated errors and are compared to the Cramer-Rao lower bound

An evaluation of a number of equalizers for frequency selective fading channels has appeared recently. Linear and decision feedback equalizers have been considered. IS-54 digital cellular channels based on TDM concepts have delay spreads that result in at most one data symbol of overlap. Using a standard fading model, the authors find that a 16-state sequence estimator, following a receive filter matched to the transmitter filter, provides excellent performance for delay spreads from zero to one symbol interval. It is superior to both linear and decision feedback equalizers in this application. Herein is assumed perfect channel state information to establish ultimate performance. In practical application, at most three complex samples of the overall impulse that includes the receiver filter must be estimated. The frequency selective channel is a two-path model with time variation following standard Doppler variations for IS-54 channels. Cochannel interference is included and results are presented for both root-raised-cosine filtered π/4-DQPSK and QPSK modulation formats

A combined subband speech coding (SBC), Bose-Chaudhuri-Hocquenghem (BCH) error-correction coding, and 16-level quadrature amplitude modulation (16-QAM) scheme with switched diversity and speech postenhancement is proposed. The system's performance is dramatically improved by deploying some degree of fade tracking capability over fading channels. Further quality enhancement accrues by using appropriate mapping between the SBC speech codec and the Gray coded QAM words. Various BCH codes are utilized to adequately match the error-correcting power to the perceptual importance of the SBC bits. One of the proposed systems operates at 7 kBd and yields good communications-quality speech for channel signal-to-noise ratios (SNRs) in excess of 20 dB and encounters a maximum overall system delay of 55.125 ms. A more complex arrangement uses second-order switched diversity to reduce the channel SNR required to around 16 dB and the transmission rate to 5 kBd when the vehicular speed is 30 mph while the system delay is unchanged at 55.125 ms

We propose a multichannel joint detector which eliminates other user, multipath, and intercarrier interference through a decorrelating process in a multicarrier 16-QAM direct-sequence code-division multiple-access system. The performance of the proposed detector under a frequency-selective fading channel is analytically derived and compared to that of a conventional single-user detector. The symbol error ratio curve of the proposed detector does not show the error floor that is seen in the conventional detector, and the resultant performance is close to that of a multicarrier 16-QAM system without any interference.

Computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel. Unfiltered 2-, 4-, and 8-PSK and 16-QAM with a rectangular signaling pulse are compared first, followed by 4- and 16-QAM with a raised-cosine Nyquist pulse. The bit error rate performances averaged over fading samples under the influence of the intersymbol interference caused by delay spread are compared for modulations of different levels. It is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel. Both the spectral and the power efficiencies can be enhanced using Nyquist signaling pulses

An expression for the bit-error rate (BER) of 16 STAR-quadrature amplitude modulation (QAM) with differential encoding and detection in a Rician fading channel with diversity reception is obtained. Two types of intermediate frequency (IF) filters are considered in the analysis: the intersymbol interference (ISI)-free matched and nonISI-free Gaussian filters. BER curves for various ratios of the line-of-sight (LOS) power to the multipath power, Doppler spread frequencies, and orders of diversity are presented. It is shown that 16 STAR-QAM outperforms 16 DPSK under the same power-limited condition. For the Gaussian receive filter, a filter bandwidth of about 1.2 times the symbol rate is found to lead to a minimum error probability prior to the appearance of error-rate floors

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.

The design of the codec for the ATCS radio data link is considered. The code is defined. The encoding algorithm, the decoding algorithm, and Galois field arithmetic are discussed. Implementation of the Reed-Solomon codec as a stand-alone system in order to provide a possibility of real-time bit-rate measurement is discussed. The implementation of this codec using three different 8-b and 16-b microprocessors/microcomputers is described. Their complexity and throughput are discussed

Trellis-coded 16QAM/TDMA systems are proposed that have a high spectral efficiency and high transmission quality and that can support a wide variety of services. A digital pilot-symbol-aided channel sounding scheme, as well as diversity reception with maximal ratio combining, are used to compensate for fading. To further improve transmission quality, symbol interleaving and two-frequency hopping are used in the trellis-coded 16QAM/TDMA system. Computer simulation demonstrates that the bit error rate (BER) performance and the spectral efficiency of the trellis-coded 16QAM/TDMA cellular system are superior to those of π/4-QPSK/TDMA used in the American and Japanese digital cellular standards. It is also demonstrated that the trellis-coded 16QAM/TDMA with diversity, symbol interleaving, and frequency hopping can achieve a BER of about 10^-4 if the delay spread is 0.1 T_s

The average bit error rate (BER) performances of coherently detected 2PSK, 4PSK, and 16QAM in frequency-selective slow Rayleigh fading are analyzed. Decision feedback channel estimation (DFCE) is considered, in which the past L-received signal samples are remodulated to remove the modulation phase by feeding back the detected symbol sequence and then averaged. Analytical expressions for the conditional BER for the given transmitted symbol sequence are derived, and the average BER performances are evaluated by Monte Carlo simulation. It is shown that as L increases, the BER performance improves and approaches that of ideal coherent detection (with perfect channel estimation), and the loss in E_b/N₀ required for BER=0.1% relative to ideal coherent detection becomes as small as 0.4 dB when L=10. It is found that while the best performance is achieved by 2PSK and 4PSK when additive white Gaussian noise (AWGN) is the predominant cause of error (i.e., low E_b/N₀ regions), 16QAM modulation can achieve almost the same performance as 4PSK when the delay spread is the predominant cause of error (i.e., large E_b/N₀ regions), and the worst performance in this case is by 2PSK. The effects of power delay profile shape (double-spike, exponential, and Gaussian profiles assumed), rolloff factors of the Nyquist transmit/receive filters, and the transmitted symbol sequence pattern on the average BER performance are discussed

Star 16QAM is a modulation method that transmits 4 bits per symbol and has the advantage that it may be differentially encoded and detected. It is very robust to fast multiplicative Rayleigh fading and is suitable for mobile telephone systems and personal communication networks. The main contribution of this paper is the derivation and bit error probability simulation of the maximum likelihood differential detector using phase differences and amplitude ratios from L diversity branches for bit decisions. As a comparison, much simpler previously known post detection combining techniques are generalized for star 16QAM and optimized. The bit error probability is simulated for both diversity detectors on a multiplicative Rayleigh fading channel with additive white Gaussian noise. It is found that the bit error probability of the ML detector may also be obtained by the simple combining detector. This is also true for the error floor due to the maximum Doppler frequency. The diversity gain is almost 8 dB, measured in signal to noise ratio per diversity branch, at a bit error probability of 1 percent. The diversity detector can sustain an almost 3 times larger Doppler frequency again at a bit error probability of 1 percent. We also show that star 16QAM offers, at most, 3 subchannels with different bit error probabilities

Pilot symbol-assisted modulation (PSAM) has been proposed to overcome the Rayleigh fading. However, as the fading rate becomes more rapid, it is difficult to provide an exact interpolation with conventional PSAM. To compensate for the fast Rayleigh fading, a PSAM which calculates in the frequency domain rather than the time domain as in conventional PSAM is proposed. Although this PSAM scheme only needs the zero interpolation for fading estimation, it provides a very accurate estimate even in relatively fast Rayleigh fading environments. We introduce this PSAM using fast Fourier transform (FFT) and apply it to 16QAM and then show some results of computer simulations

This paper proposes a complexity-reduced decision feedback equalizer (DFE) for 16-ary quadrature amplitude modulation (16QAM) using tap gain interpolation, bi-directional equalizing (BDE) and space diversity combining (SDC) to achieve high spectral efficiency and high quality data transmission over frequency-selective fading channels in land mobile communications. To reduce the amount of computation required for BDE and SDC, we propose a tap gain interpolation scheme and pre-decision schemes for both processes. Computer simulation of a (16QAM/TDMA system) confirms that the proposed scheme improves frequency-selective fading compensation performance by 6 dB or more while using only 27% of the computation of conventional single branch DFE receivers

Determines the mean signal level and envelope cross-correlation of 1800 MHz base station signals received in two-branch spatial and polarization diversity schemes. Measurements have been conducted with the experimental base site located in (i) two urban sites, (ii) a residential area, (iii) a rural area, and (iv) near a motorway. In each location, the effect of the random orientation of a typical mobile radio telephone handset has been studied by examining the characteristics of signals received from a mobile collinear antenna inclined at angles of 0°, 30°, 45°, 60°, and 90° to the vertical. Furthermore, the diversity gain at 90% signal reliability has been evaluated for each diversity scheme by simulating selection, equal-gain and maximal-ratio combining techniques using the recorded signals as inputs. Results have shown that 20λ separation in the horizontal plane or 15λ in the vertical plane is sufficient to obtain a cross-correlation of less than 0.7 for most of the time at 1800 MHz. Similar cross-correlation results were obtained for polarization diversity. When the antenna is inclined at 45°, a 6 dB degradation in signal level was recorded for space diversity schemes. However, the diversify gain is unaffected by tilt and remains unchanged at 5-6 dB for horizontal and 3.5-4.5 dB for vertical separation. For polarization diversity, only a little degradation is experienced because most of the energy lost on the vertical branch is recovered on the horizontal branch. The diversity gain is between 1-2 dB at 0° tilt and increases to 3-5.2 dB at 45°

The aim of this paper is to evaluate experimentally the relationships between cross-polarization discrimination (XPD), signal cross correlation, and polarization diversity gain with horizontally/vertically (HV) polarized reception at the base-station (BS) end at 1800 MHz. The performance of the horizontal/vertical polarization diversity scheme was also compared with a diversity scheme with ±45° slanted polarizations and horizontal space diversity at 1800 MHz in a personal communication system (PCS) mobile network. A measurement campaign was conducted in small/micro cells in different types of areas, taking into account the influence of mobile antenna inclination. According to the measurements, XPD values for horizontal/vertical polarizations vary between 5-15 dB, depending on the environment. Furthermore, XPD values depend highly on the radio propagation path between the BS and mobile station (MS) due to line-of-sight (LOS) and nonline-of-sight (NLOS) situations. Signal cross correlations of horizontal and vertical polarizations in both LOS and NLOS situations were clearly below 0.7, which is the generally accepted value to have a reasonable improvement at the receiving end with diversity. Finally, the results showed that almost equal diversity gain and system performance in a PCS network at 1800 MHz can be achieved in small/micro cells in different environments with ±45° slanted polarizations at the BS end when comparing results with horizontal space diversity. The performance of horizontal/vertical polarization diversity scheme was approximately 1 dB worse than horizontal space diversity

In a proceeding titled "An Inquiry Relative to the Future Use of the Frequency Band 806-960 MHz," the US Federal Communications Commission (FCC) took steps to open a major segment of the radio spectrum for public safety communication systems and other members of the land mobile radio community. Within the new spectrum allocation the Commission determined to require innovative engineering techniques and methods ofrequency assignments among radio systems as well as to continue some features of established technology and spectrum management systems. The stated purpose of these FCC actions was to devise and implement radio systems and technologies that would use the newly available spectrum with hitherto unacheved efficiency while offering a wide range of choices to eligible spectrum users. In this study the Associated Public-Safety Communications Officers, Inc., (APCO) proposes to evaluate the effect of the policies established by the FCC for the 900-MHz band, including the applicability of the new system and technology contemplated by the FCC for use in that band, on tax-supported public safety radio users. It will evaluate the utility of "trunked" technologies for multichannel systems and the potential of nonprofit and profitmaking suppliers that might be set up to provide these trunked systems. In addition, it will evaluate the practical effect of the decision to abandon block or pool frequency assignments to particular radio services and to remove frequency assignment and coordination from the private radio committees which have been an integral part of public safety radio planning and use.5 As part of this latter point, attention will be given to the staff method of selecting frequencies by "vertical stacking" of systems on each channel in turn and the resulting "first come, first served" licensing apparently without detailed consideration of the systems to be placed on each channel.

Maximum-likelihood sequence-estimation (MLSE) performance on the D-AMPS 1900 channel is evaluated through simulations. A channel-tracking algorithm of least-mean-squares (LMS) complexity is used in conjunction with the MLSE. It is shown that the receiver specification points for D-AMPS 1900 are met and that performance can be further enhanced with fractionally spaced equalization and/or receiver-antenna diversity combining

This paper investigates the correlation properties of shadow fading as a function of the angle between two PCS base stations over urban, light urban, and suburban terrain. Results from this study are relevant to the analysis of interference, handoff gain, and to various frequency planning applications in modern cellular and PCS systems. Using a significantly larger data set than previous experiments, we observed that on the average, the shadow fading components of the signals are not correlated, even at small angles. Our results contradict the conventional wisdom, as expressed in several papers, which says that there is relatively high correlation at small angles. Our results indicate that a mathematically simpler uncorrelated model for the relationship between signals from multiple base stations at small angles can be used in analysis tools. Distance correlation measurements computed by forming the autocorrelation function on a large number of data sets showed that the correlation distance of the shadowing process ranges from about 25 to 100 m

Multihop data delivery through vehicular ad hoc networks is complicated by the fact that vehicular networks are highly mobile and frequently disconnected. To address this issue, we adopt the idea of carry and forward, where a moving vehicle carries a packet until a new vehicle moves into its vicinity and forwards the packet. Being different from existing carry and forward solutions, we make use of predictable vehicle mobility, which is limited by traffic pattern and road layout. Based on the existing traffic pattern, a vehicle can find the next road to forward the packet to reduce the delay. We propose several vehicle-assisted data delivery (VADD) protocols to forward the packet to the best road with the lowest data-delivery delay. Experimental results show that the proposed VADD protocols outperform existing solutions in terms of packet-delivery ratio, data packet delay, and protocol overhead. Among the proposed VADD protocols, the hybrid probe (H-VADD) protocol has a much better performance.

Simultaneous four-antenna wide-band mobile channel-sounding measurements were made in two areas at 1920 MHz. The received signal strength and transmission loss were examined. Path-loss exponents for the two sectors were found to be 4.9 and 4.1. Root mean square delay spreads for the two sectors were found to be less than 1.38 and 0.65 μs for 90% of the data and less than 3.14 and 1.35 μs for 99% of the data. Fast fading reduction using antenna diversity and increased channel bandwidth (19.6 kHz, 1.25 MHz, 5.0 MHz, and 10.0 MHz) were examined. Three signal combining methods were considered: selection diversity, equal gain combining, and maximal ratio combining. The measured results show that increasing the number of diversity antennas or the channel bandwidth significantly reduces fading. Maximal ratio combining yields the largest diversity gain, exceeding 11.0 and 17.0 dB at the 90% and 99% fast fade depth probability levels, respectively, for the 19.6-kHz narrow-band signal and 6.7 and 6.9 dB for the 10.0-MHz broad-band signal when all four channels are used

To identify a vehicle uniquely and automatically as it passes on the roadway without requiring any action by the driver, one general approach uses a transponder on the vehicle and an interrogator by the roadside. When the identity is passed from the interrogator to a data system which may have data storage, retrieval, computation, display, and actuation capabilities, various functions such as charging for the use of road or parking facilities, fleet management, and fine grain traffic control become possible. The main purpose is to report recent testing of such systems and consider some probable early applications. At the outset, however, the functional requirements are discussed in more detail, and the background of automatic vehicle identification (AVI) development and testing is briefly reviewed.

In 1977, Cooper and Nettleton proposed a spread spectrum mobile radio system using frequency-hopping multiple access, Hadamard coding for error correction, and differential phase shift keyed (DPSK) modulation, and they claimed higher spectral efficiency than frequency-division (FD) FM systems. Subsequent analyses showed that the DPSK system has a spectral efficiency of 8.4 percent as compared to the efficiency of unity for a FD-FM system with 30-kHz channel spacings. Goodman et al. suggested an alternative modulation scheme in 1980, using multilevel frequency shift keying (MFSK), and a 30 percent efficiency was obtained. The research results in spread spectrum mobile radio are summarized, and the areas requiring further investigation before a commercial system can be implemented are identified.

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The field of emergency medical services (EMS)provides an organizational and operational environment which lacks the geopolitical structure and discipline of other public safety services. The opportunity to rearrange the various service provider elements of EMS into a unified regional agency is not likely in current political and economic circumstances. The new EMS radio communications structure which has evolved from Federal Communications Commission Docket 19880 provides the opportunity for operational order and discipline within the various provider elements of EMS. Despite the opportunity for creating the common system approach to EMS communications, many human elements must be dealt with in breaking down traditional barriers to change.

This paper presents the results of narrow-band and wide-band propagation measurements carried out at 2.0 GHz in an indoor environment using a radiated-mode leaky feeder as the transmitting antenna. The narrow-band measurements were devised to measure attenuation of radio signals and the wide-band techniques to measure multipath impulse responses and their associated root mean square (RMS) delay spread. Analysis of the narrow-band data files shows that the received signal levels in the direction along the feeder generally decay exponentially due to the feeder-specific attenuation. The received signal levels in the direction radial to the feeder decrease slowly, and the distance-power law exponent is found to be smaller than one. The slow and fast variations of the received signal levels are also examined. The results reveal that the slow variations basically follow the log-normal distribution, while the fast variations fit the Rayleigh distribution in the direction parallel to the feeder and the Rician distribution in the direction radial to the feeder, respectively. Analysis of the wide-band data files reveals that the maximum value of the RMS delay spread is 60.6 ns and the RMS delay spread values are less than 42 ns 50% of the time. One therefore can conclude that the indoor channel excited by the radiated-mode leaky feeder has a broad coherent band-width and can support a data rate of up to 3.3 Mb/s without equalization