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In mobile radio systems, especially in urban mobile service, one fixed transmitting station is located at the center part of the area, while several fixed receiving stations are installed at different location. In such systems the receiving station with the highest signal-to-noise ratio should be selected at all times. This paper presents two methods to select the best receiving station. One is an analog processed switching system. The other is a digital processed system. The design objectives, circuit diagrams and characteristics are described in detail. The performance of these two systems were compared in a field test. It became clear that there were no essential differences in the performance. The analog system was adopted in the actual mobile system taking into consideration the advantage in cost.

Radio equipment and systems designers face an alarming complexity of considerations, when they attempt to calculate probable interference rates. Only a computer is able to handle all of these variables and predict system performance to a meaningful degree of probability. Therefore, this paper describes a computer simulation approach which has been used to: (1) Explore the relation between interference rates and equipment characteristics; (2) Determine the manner in which channel loading affects the various types of interference; and (3) Analyze multi-system configurations of both the concentrated and the geographically spread types.

This paper describes the original VHF mobile radio system in the Indiana and Michigan Electric (I&ME) Company and how it operated with standard squelch. It points out some of the problems which were encountered at the relatively low operating frequency in the 37-MHz region and goes on to show the solution for most of these problems by converting the entire system of 19 base stations and 300 mobile units from standard squelch to a tone coded squelch. The entire changeover was done in an economical manner and without disrupting operation of the original system while the conversion was being made. The benefits ensuing from this conversion are covered in detail.

A signal-to-interference ratio for the transmission of scanned images and digital data in the dynamic multipath environment was derived in an earlier paper. The dynamic case depends upon a Doppler environment-signal parameter ratio, while the static result is independent of the signal structure. The dynamic case is asymptotic to, but always worse than, the static one. For a Doppler-signal ratio of less than 10 percent the dynamic signal-to-noise ratio is essentially equal to the static one. Most real systems today fall in this region. This indicates why certain simple multipath analyses in use today have been successful. The method of designing a signal to fall below the 10-percent value is indicated. Signal-to-noise ratio curves are provided for system design purposes. These results permit system analysis and tradeoff studies to be based on earth reflection coefficient distributions and aircraft or satellite operation envelopes.

Many agencies, both governmental and private, in the highway transportation field need a system which would automatically identify motor vehicles. The basic concept of such a system requires a vehicle-mounted coded device, a transponder, that uniquely identifies that vehicle. As this vehicle comes within the range of a system interrogator installed along or on the highway, the code is read by this interrogator and the identification of the vehicle is obtained. The ideal transponder is passive and requires no power; has no effect on, and is not affected by the vehicle; does not require physical contact with the interrogator, and requires no action by the vehicle operator. Sensing at a distance (noncontact) involves the detection of some type of energy; either radiated or reflected from the object being monitored. Many different sensing techniques, including magnetic, infrared, optical, sonic, radioactive, radio frequency (RF) transmission, microwaves, have been surveyed, investigated, and analyzed to determine their applicability for an automatic vehicle identification (AVI) system. This analysis has concluded that a low-frequency induction system is presently the most appropriate method for use on the highway environment, Several diverse systems differing in design details have been constructed and tested, utilizing this basic technique. This paper describes the design of these systems as well as the methods that have been proposed and/or developed using the other sensing technologies.

Electronic clocks are rapidly becoming practical for automotive applications. These digital clocks promise not only superior timekeeping in automotive clocks, but they also could be used for a myriad of timing functions throughout the car. These range from turn signal flashers to top-speed limiting and safety-monitoring checks. Integrated circuits utilizing complementary metal oxide semiconductor devices (CMOS and silicon gate CMOS) make several system approaches feasible. This paper outlines some possible system approaches and summarizes considerations for CMOS IC's, quartz crystals, and electronic readout devices.

This paper describes in detail the criteria for the design of a mobile laboratory for the characterization and measurement of man-made electromagnetic noise in the urban, suburban, and rural environment. A significant difference from previous similar measurements is the bandwidth of the receiving system, which is here of the order of 1 MHz. A simple model is proposed to describe the impulsive noise together with a series of experiments to validate the model and determine the significant necessary parameters. The detailed requirements for each of the subsystems of the mobile laboratory are discussed and some typical results obtained in trial runs are presented.

Analytically tractable statistical-physical models of man-made noise environments have been constructed [1]-[3]. These permit quantitative description of the various types of electromagnetic interference appearing in typical radio receivers and, in particular here, for the communication links employed in mobile transportation systems and urban environments generally. This paper presents a summary of some of the principal analytical results obtained to date [1], [4], and includes some suggested next steps for joint theoretical and experimental study of these increasingly important phenomena. First-order probability density functions (pdf's) and probability distributions (pd's) are obtained explicitly; (higher order pdf's and pd's may also be found by similar methods) [2]. These models are based on a Poisson distribution of sources in space. The approach is canonical, in that the results are, in form, independent of particular emitted waveforms, propagation conditions, source distributions, beam patterns, and specific system parameters, as long as the interference is narrow-band following (at least) the aperture and/or the RF stages of a typical receiver. Considered here only are the cases of communication interference, where source and receiver bandwidths are comparable. The paper concludes with a short discussion of some features of suggested future interaction between theory and experiment.

In those radio communications applications where area coverage is not desired, a series of repeaters, each operating at low power, can be used to extend the radio over long distances. Microwave relay systems operate on this principle with each node representing a point of potential local distribution. Where it is desirable to have the nodes closely spaced, such as along a highway, it becomes desirable to utilize a single frequency for all transmissions in one direction in the interest of conserving spectrum. This paper covers such a system operating in the 935-MHz band. The system described provides both the "backbone" communications system which employs single-frequency repeaters and the "roadside" communications from the repeater node points to users in their vehicles. The functioning of the repeaters is described, and the relationship between signal levels, isolation, external noise levels, and thresholds is presented. Both analog and digital modulations are employed, and it is shown how each repeater is remotely switched between "backbone" and "roadside" communications modes. Extensions from current single-channel to multiple-channel operation is described in terms of the application to a variety of highway-related uses. The results of propagation experiments both along the "backbone" and on the "roadside" are described and related to theoretical models. From these data, conclusions can be drawn about the relationship between repeater spacing, height, and power level, as well as their relationship to user antenna height, output power, and receiver sensitivity.

Advances in the design, development, and fabrication of key microwave components along with those in electronics have resulted in growing optimism about the application of radar technology to solving the automotive highway collision problem. However, before an automotive radar system can be fully realized, a major effort will be required to define the environment in which the system must operate, and to obtain a fundamental understanding of the influence of these RF parameters. One such parameter which will have a considerable effect on the design of automobile radars is that due to the presence of natural and man-made surfaces within the beamwidth of the antenna. Generally, the presence of such a surface will result in incident RF energy being reflected off the surface in a forward direction and some portion being scattered in a backward direction. This paper presents the results of a program which was designed to measure this type of reflectivity characteristic for common road surfaces. Measured data are presented along with a theoretical study demonstrating the influence that this phenomenon can have on highway collision radar systems.

This paper begins with a discussion of multipath interference. The spatial description of the field impinging upon a mobile radio antenna is derived and the power spectrum and other properties of the signal envelope are considered. Next, large scale variations of the average signal are discussed. Measurements of observed attenuation on mobile paths over both smooth and irregular terrain are summarized. The paper concludes with a discussion of methods of predicting the area of coverage from a base station.

The design of a mobile or portable radio communications system requires the consideration of a number of unique engineering factors which do not necessarily apply to the design of a fixed, or point-to-point system. The design procedure is a combination of theoretical and empirical methods, which when taken with measured data, produce a system design meeting the required specifications. This paper will treat that portion of the system design pertaining to radio frequency propagation and system coverage. It stresses a realistic measurement program which will provide coverage data in support of the system design.

In this paper, both simulations and measurements are used to explore the propagation properties of ultrahigh-frequency (UHF) waves traveling through building structures and, in particular, windows. The propagation influence of several features of a typical window structure is examined, including the electrical properties of the surrounding wall, the homogeneity and roughness of this wall, and the incidence angle of the UHF wave. In these studies, ray tracing is benchmarked against both narrow-band measurements and the results of a full-wave moment method technique. Some of the inherent limitations of ray tracing are assessed and corrective methods are proposed in order to improve its accuracy.

In preparing or revising an RF channel plan for a group of mobile radio nets operating in the same region, the order in which the nets are assigned channels can be crucial to success. One well-known principle for selecting such an assignment sequence is to rank the channel requirements of the various nets in descending order of "assignment difficulty." This paper describes an easily automated heuristic assignment technique in which the channel requirements that prove themselves to be "difficult," through repeated failures to be assigned channels, rise rapidly toward the top of the list of requirements. The heuristic technique is useful in solving complex frequency-assignment problems that involve cochannel, adjacent-channel, spurious and intermodulation interference; nonrepetitive zone structures; fixed pre-existing frequency assignments; and frequency-resource lists that contain gaps and vary from zone to zone.

Results are presented of UHF propagation measurements conducted at 820 MHz in urban Philadelphia. The Philadelphia tests departed from previous path-loss measurements in that emphasis was placed on transmission from relatively low land-site antennas at heights of 40-70 feet above local ground level. Composite path-loss statistics have been derived for transmissions from five separate locations covering local environments considered typical of an urban area. This paper describes the measurement configuration, summarizes the data processing techniques, and presents results of the analysis.

Multiple-antenna receiving-diversity was shown previously to be effective in mitigating the effects of random angular orientation and multipath radio propagation for portable radiotelephones. This paper shows that time-division adaptive retransmission used with appropriate antenna configurations can also mitigate these effects. The retransmission configurations require fewer antennas than the receiving diversity configurations for a given improvement in relative signal-to-noise ratio (S/N). Cumulative distributions of S/N were determined for adaptive retransmission and diversity using random orientation and multipath propagation models. Distributions of S/N for systems with two antennas at the portable set and two appropriately polarized antennas at the Portable Radiotelephone Terminal (PORT) are similar to distributions for two branch selection diversity in the fixed-oriented mobile radio environment. Systems with one portable antenna and two PORT antennas have distributions with slopes similar to two branch mobile radio distributions but the distributions for the portables range from 3 to 7 dB worse.

This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maximize the output signal-to-interference-plus-noise ratio. Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical cellular mobile radio systems show that optimum combining increases the output signal-to-interference ratio at the receiver by several decibels. Thus, systems can require fewer base station antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays.

Densensitization, or the blocking of the receiver portion of the communications system, is one of the principal causes limiting receiver operation, especially in mobile networks under cositing situations. A clear understanding of this nonlinear effect is thus essential when attempting to improve the reliability of mobile radio communication systems so as to prevent severe interferences. A thorough qualitative analysis of desensitization effects on receiver parameters is provided and semi-empirical and statistical relationships useful for performing quantitative computations are developed. The developed analysis initially treats the computation of desensitization effects on radio communication system scenarios for both a single interfering transmitter and several simultaneous interfering transmitters. The results of this qualitative analysis then allow us to compute quantitatively the desensitization effects of a typical mobile radio system which are presented in a second paper.

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.

Design and performance of a single-chip minimum shift keying (MSK) coherent demodulator fabricated by complementary metal oxide semiconductor-integrated circuit (CMOS-IC) technology is described. The demodulator consists of a phase detection circuit, carrier recovery circuit, data recovery circuit, and timing-clock recovery circuit. For the carrier recovery circuit, three types of Costas-loop are reviewed from the viewpoint that MSK modulation format has a close relationship to binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). Among these loops, a loop of center-frequency locking scheme modified from a BPSK Costas-loop, termed MSK Costas-loop in this paper, is adopted for IC implementation. Digital IC design techniques are next described. Utilizing the sample-and-hold operation of the digital devices, a divided-frequency locking scheme of the quadrature coherent demodulation is proposed. Finally, IC demodulator performance is experimentally shown in the static and Rayleigh fading environments. The bit error rate performance and error-burst characteristic are measured. It is concluded that the single-chip coherent demodulator is suitable for digital mobile radio application.

Theoretical and experimental studies are made on radiation patterns of mobile antennas within the frequency range from 300 to 900 MHz. In order to calculate vertical plane patterns of quarter wavelength monopole and a half-wavelength dipole located on an automobile's roof, a theoretical model of an automobile body is developed, in conjunction with the geometrical theory of diffraction (GTD). The theoretical model consists of three-perfectly conducting plates. It is ascertained from a comparison between calculated and measured results for the feed point impedance and the radiation pattern that the effect of the body and the earth can be well examined with the theoretical model. The results of pattern calculation for the above two antennas show that the radiation patterns depend largely on the configuration of the automobile body and the earth condition. The technique described in this paper can be used as a design tool to estimate radiation performance of mobile antennas.

This paper studies adaptive equalization for time-dispersive communication channels whose impulse responses have unknown lengths. This problem is important, because an adaptive equalizer designed for an incorrect channel length is suboptimal; it often estimates an unnecessarily large number of parameters. Some solutions to this problem exist (e.g., attempting to estimate the "channel length" and then switching between different equalizers); however, these are suboptimal owing to the difficulty of correctly identifying the channel length and the risk associated with an incorrect estimation of this length. Indeed, to determine the channel length is effectively a model order selection problem, for which no optimal solution is known. We propose a novel systematic approach to the problem under study, which circumvents the estimation of the channel length. The key idea is to model the channel impulse response via a mixture Gaussian model, which has one component for each possible channel length. The parameters of the mixture model are estimated from a received pilot sequence. We derive the optimal receiver associated with this mixture model, along with some computationally efficient approximations of it. We also devise a receiver, consisting of a bank of soft-output Viterbi algorithms, which can deliver soft decisions. Via numerical simulations, we show that our new method can outperform conventional adaptive Viterbi equalizers that use a fixed or an estimated channel length.

Pilot symbol assisted modulation (PSAM) has been shown to give good performance in Rayleigh fading and additive noise. In cellular systems, though, it is cochannel interference, more than noise, that limits the system. The paper is the first analytical investigation of the performance of PSAM in fading, interference, and noise. The investigation yields both an exact solution and an accurate but much more computationally efficient approximation. >

This paper considers the performance of automatic link transfer(ALT) in a frequency-reuse portable radio system using time-division multiple-access (TDMA) for portable-to-base transmission. It is assumed that customers undergo small-scale movement that would be typical of an office environment, where customers may be walking around in their office, changing posture, etc. Without line-of-sight transmission paths from the bases to the portable radio, signals undergo multipath fading. In this environment, the decision by the portable to initiate an ALT is sensitive to wavelength, customer speed, measurement acquisition time, number of signal samples averaged, hysteresis, and average signal power. Results pertaining to these factors are presented, including the effect of delay of the call switch and intentional blind ALT limiting. Implications to system design and equipment topology are discussed. It is shown that ALT in a narrow-band frequency channelized portable radio system could be a significant contributing factor to overhead in the fixed radio infrastructure when the customer does not have line-of-sight to nearby base stations. The radio measurement process, trigger conditions, and channel selection method depend on whether a local, fast, dedicated controller is used, or whether the call transfer is made in the fabric of a remote general purpose switch, such as those used in the local exchange. This paper is targeted towards understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks. >

This paper describes a centralized power control scheme for cellular mobile radio systems. The power for the mobiles in the proposed scheme is computed based on signal strength measurements. All the mobiles using the same channel in this scheme will attain a common carrier-to-interference ratio. The proposed scheme is analyzed and shown to have an optimal solution. >

This paper describes the performance of an adaptive array as a countermeasure to multipath fading for a 256 kbps Gaussian-filtered minimum shift keying (GMSK) mobile communication system operating in the 1.5 GHz band. An adaptive array having four antenna elements is implemented using the digital beam forming concept. The constant modulus algorithm (CMA) is employed for the adaptation process to ease the implementation. Measurements in central Tokyo of the bit error rate (BER) performance and an array pattern arising in the multipath environment are presented. Analysis of the array pattern confirms that the array succeeds in directing nulls to the delayed signals. BER performance shows an improvement in E/sub b//N/sub 0/, compared with that of a single antenna system, of 17.5 to 22 dB at a BER of 1.0*10/sup -2/ in a frequency-selective fading channel. >

Handsfree speaker input of mobile telephones is most desirable today in order to enable safe operation in cars. This is also a prerequisite for voice control of car devices. This paper presents an "on the road" evaluation of the performance of an adaptive microphone array for speech enhancement in cars. The results show a signal-to-noise ratio (SNR) improvement in the range of 10-15 dB over the telephone frequency range with a slight favour for higher frequencies when driving at normal speeds. >

In a multiple-track railroad, the conductors form mutually-coupled ground return circuits. Accurate electrical circuit analysis, required for signaling, traction, and electromagnetic compatibility analysis, is difficult to achieve because of the variability in the equivalent electrical components from their material properties and environmental conditions. The paper describes an application of the finite element method to the electromagnetic analysis of rail track. After validation by benchmark tests using single rail, single- and three-rail track, the technique is used to predict crosstalk between adjacent tracks of a two-track electric railroad. >

The current interest in linear modulation and multilevel signals has resulted in an emphasis on DSP implementations to achieve precision signal manipulation. However, most transceivers, and direct conversion designs in particular, rely on analog implementations of the quadrature modulator and demodulator, thereby sacrificing much of the precision gained through DSP. The present paper focuses on the three principal impairments of analog quadrature modulators and demodulators: gain imbalance, phase imbalance, and DC offset. The paper contains three main contributions. First is an analysis and quantitative assessment of the losses-primarily a degraded BER and out-of-band power in the transmitted signal-due to imbalances and offsets. The second contribution is an adaptive compensation technique for the quadrature modulator at the transmitter, and the third is a compensation technique for the quadrature demodulator at the receiver. Both compensation methods converge quickly and present only a modest computational load. >

Direct sequence spread spectrum, with its inherent resistance to multipath interference, has become a commercial reality for indoor wireless communications and has been proposed for personal communication networks. To allow multiple users within the limited bandwidths allocated by the FCC, code-division multiple-access (CDMA) is needed. This paper analyzes the performance of CDMA systems using random orthogonal codes over fading multipath indoor radio channels using channel measurements from five different buildings. The effect of RAKE receiver structure is studied, as is the effect of average power control. The average probability of error as a function of signal-to-noise ratio is used as the performance criteria. Results are compared with models for Rayleigh fading channels. >

In TDMA system each channel may have more than one time slot to serve more than one user. Techniques for the assignment of time slots to users while minimizing co-channel interference are important. The paper presents six time slot assignment techniques. A discrete event stochastic simulation study was performed on 120/spl deg/ and 60/spl deg/ sectored systems. The simulation employs the "blocked calls cleared" traffic model and a log-linear path loss propagation model. Only the down link is considered. The results compare the performance of the six techniques and investigates the effect of the number of time slots per frame and the maximum acceptable interference level. >

In a combination tutorial and research paper, propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored. The tutorial section of the paper presents basic principles of propagation at IR, a comparison with indoor radio propagation, and the derivation of the channel's baseband model. The research aspect of the paper reports on the results of recent frequency response measurements at eight different sites in a university building. A major result shows that the indoor wireless optical channel is very dynamic, with great variations in the channel's characteristics for data collected in different rooms, in different locations within the same room, and for different orientations of the optical receiver at the same location of the same room. Numerical values of the channel's relative path loss and 3 dB bandwidth, along with frequency response plots covering a wide range of conditions, are presented and discussed. Finally, on the basis of the results of measurements, schemes for improving the performance of future wireless in-building optical transceivers are proposed. >

In this paper, interference caused by multiple uncoordinated low-power wireless access system transmitters to fixed point-to-point microwave receivers is analyzed. The analysis shows that the density of wireless access system users that can share spectrum with point-to-point microwave systems depends critically on the propagation relation, the threshold of detecting energy from point-to-point transmitters, and the allowable interference into point-to-point receivers. We also show that, for reasonable assumptions of point-to-point link, wireless access system, and propagation parameters, a wireless access system employing measurement-based interference avoidance must detect energy of point-to-point transmissions far below the thermal noise floor of the wireless access system receivers. Meeting this requirement could increase the complexity of wireless access systems. This work is targeted towards understanding the implications for local exchange networks of wireless system alternatives that could provide access to those networks. >

We have concluded that the spectrum efficiency can be achieved in wireless PCS systems by applying the intelligent cell concept. The intelligent cell can either reduce interference by intelligently delivering the signal to the mobile unit, or can tolerate a great deal of interference while receiving with it. The former isolates the signal with multiple zones. In the latter, the signal resides with the interference but retains its processing gain. This paper presents the philosophy of achieving spectrum efficiency by applying the intelligent cell concept in wireless PCS systems. >

Examines the performance enhancements that can be achieved by employing spatial filtering in code division multiple access (CDMA) cellular radio systems. The goal is to estimate what improvements are possible using narrow-beam adaptive antenna techniques, assuming that adaptive algorithms and the associated hardware to implement these systems can be realized. Simulations and analytical results are presented which demonstrate that steerable direction antennas at the base station can dramatically improve the reverse channel performance of multicell mobile radio systems, and new analytical techniques for characterizing mobile radio systems which employ frequency reuse are described using the wedge-cell geometry of Rappaport and Milstein (1992). The authors also discuss the effects of using directional antennas at the portable unit. Throughout the paper the authors use phased arrays and steerable, fixed pattern antennas to approximate the performance of adaptive antennas in multipath-free environments. >

The paper presents a method of automatic vehicle location (AVL). Signals are transmitted from base stations in a cellular communications system. A device is embedded into a cellular phone installed in a vehicle. When this vehicle is traveling through a cellular territory, the device receives those signals and calculates the attenuation of those signals to locate the current vehicle position. A preliminary study by using computer simulation shows that the error between the exact position and the estimated position is in the range from 0 to 575 m. This result is based on the assumptions that the base stations are separated from each other by 5 km and the point-to-area terrain configuration has a 3 dB standard deviation of a normal signal strength distribution. A further modification by employing fuzzy logic is under development. The goal is to keep the location accuracy within 200 m. >

This paper examines the outage probabilities of BPSK and BPSK/DFE radio modems with omnidirectional and six-sector antennas. The effects of room size, data rate, transmitted power and sector antenna patterns on the performance of the systems are analyzed. A 2-D ray tracing algorithm is used to model the radio propagation in a typical indoor environment used for wireless LAN applications. The parameters of the radio propagation model are adjusted to fit the results of simulations to the results of empirical measurements with omnidirectional antenna. It is shown that in a line-of-sight (LOS) environment, a six-sector antenna is more effective than a DFE with an omnidirectional antenna at eliminating the effects of multipath. For an obstructed-line-of-sight (OLOS) environment where at least one wall exists between the transmitter and the receiver, the DFE is more effective than the six-sector antenna. It is shown that a BPSK/DFE modem with a six-sector antenna can support data rates close to 20 Mbps. >

Channel borrowing without locking (CBWL) is a family of channel sharing schemes for cellular communication systems. They allow real-time borrowing of channels from adjacent cells without the need for channel locking in cochannel cells. In this paper, an analysis of cochannel interference for CBWL schemes in sectorized cellular systems is presented. Two typical configurations are analyzed. One has 120/spl deg/ directional antennas and a reuse factor of seven. The other has 60/spl deg/ directional antennas and a reuse factor of four. The analysis shows that CBWL can significantly enhance the traffic capacity of sectorized cellular systems at the cost of a slight increase of cochannel interference in comparison with the corresponding sectorized scheme and no borrowing. >

The purpose of this paper is to conduct performance analysis for a frequency-hopped spread spectrum multiaccess network which is subject to the threat of multipath interference. Baseband modulation is done through frequency shift keying and signal detection is accomplished by a noncoherent type receiver. The quality of a signal is affected by the channel noise, multiuser interference, and multipath interference. Performance analysis is conducted on the basis of bit error rate. Due to the sophistication of the system exact analysis is not feasible. The accuracy of approximation is checked against simulations. One major discovery Is that when signal-to-noise ratio is low, multipath interference on the contrary may help to enhance the quality of the signal. Another discovery is that when signal-to-noise ratio is high enough, multipath/multiuser interference becomes the bottleneck of performance. The effect of channel noise can be eliminated by maintaining a large signal-to-noise ratio while spread spectrum technique is employed to reduce the effect of multipath/multiuser interference. >

This paper describes an adaptive predistortion system to linearize class B and class C radio frequency high power amplifiers. The system, which can handle a 30 dB power control range, uses a digital signal processing microprocessor and memory look-up tables to predistort the baseband drive signals. Low data rate services such as are found in mobile satellite applications ( >

In most applications using the feedforward linearization technique, the overall amplifier efficiency is of significant concern. This paper theoretically analyzes the effect that the insertion loss of the time delay elements has on the overall efficiency of a feedforward amplifier. Practical linearity and efficiency results are given for a feedforward system, using VMOS transistor class C main and error amplifiers, to illustrate the effectiveness of the analysis. >

In the original paper, it was conjectured that the system performance in the up-link and down-link in a cellular radio system under optimum transmitter power control should be statistically similar. In this comment we show that the achievable signal-to-interference ratios in the up- and down-links are, in fact, identical at every instant. >

This paper proposes a single-layer slotted leaky waveguide array antenna for mobile DBS reception. A single-layer feed structure is proposed, where the feed waveguide is in the same layer as the radiating waveguides. This results in the simple fabrication of slotted waveguide arrays, suitable for mass production. Short radiating leaky waveguides are used to get a large beam-tilting angle of about 50/spl deg/ for the horizontal installation of the antenna and a beamwidth broad enough to dispense with mechanical steering in the elevation plane. A prototype antenna sized 30 cm by 21 cm has a maximum of 74% efficiency and more than 69% efficiency within the DBS band. It also has a broad l-dB beamwidth of 7.5/spl deg/ in the elevation plane, which enables clear DBS reception by a picture tube display over about one-third the area of Japan without elevation tracking. >

In this paper, the spectrum and power requirements of an indoor PiCO-Cell radio system at different operating fre- quencies in a building are studied. Based on measurement results obtained in other studies on losses due to walls, floors, etc., a pico- cell radio system with capability is considered for a typical high-rise office building. The amount of spectrum required by the pico-cell system is evaluated based on operating other by a spacing of 2 m. Then, for a given outage probability and the corresponding number of receiver points, we determine the transmitter effective radiated power (ERP) required to provide sufficient signal level to these receiver points. This is done for a one-, two-, three-, and four-cell configuration. The spectrum required for each floor is calculated based on frequency, base station locations and Cell configurations,-verticai reuse distance, outage probabilities, and floor layout, in addition to traffic demand and blocking probability. an assumed traffic level and blocking probability. The overall spectrum for the building can also be obtained Once the vertical reuse distance is known. I. INTRODUCTION T IS WELL-KNOWN that cellular radio systems with small I cells support more traffic than those with larger cells. This concept led to the introduction of micro-cellular systems in the early 1980s. These systems with cell radius in the order of 1 km or less have tremendous traffic carrying capability and have been proposed for outdoor personal communications. In recent years, the requirements of personal communica- tions in the indoor environment are also emerging. Because of the smaller coverage area and a lower power requirement, indoor systems are even smaller in size than micro-cellular systems. Pico-cell systems have cell radius in the order of tens of m and could provide much higher system capacity than cellular radio systems. The purpose of this paper is to study the spectrum and power requirements of such a pico-cell system when implemented in a high-rise office building. These requirements are dependent on a number of factors such as operating frequency, base sta- tion locations and cell configurations, vertical reuse distance, outage probabilities, and floor layout. Since the radio spectrum is scarce, it is necessary to operate the pico-cell system in the most spectrally efficient manner. Furthermore, spectrum at the upper frequency range is relatively more abundant, and hence more attractive for indoor radio applications. It is therefore worthwhile to study the impact of frequency on the spectrum requirement of a pico-cell system. 11. APPROACH In the analysis of the impact of the above factors on the spectrum and power requirements of an indoor radio system, the following approach is taken. First, the floor is represented by a number of receiver points which are separated from each

Feedforward linearization has advantages in bandwidth and generality over other linearization methods. However, it is based on the subtraction of nearly equal quantities, so its major parameters must adapt to changes in environmental or operating conditions. This paper is the first published analysis of adaptation behavior in feedforward amplifier linearizers. As such, it presents an analytical framework and several new results, including convergence time and coefficient jitter, a bias effect that leads to extreme accuracy requirements in one coefficient, the effect of delay mismatch, and the mitigating effects of a filter inserted in one adaptation path.

In code division multiple access (CDMA) mobile radio systems, both intersymbol interference and multiple access interference arise which can be combated by using either elaborate optimum or favorable suboptimum joint detection (JD) techniques. Furthermore, the time variation of the radio channels leads to degradations of the receiver performance. These degradations can be reduced by applying diversity techniques. Using coherent receiver antenna diversity (CRAD) is especially attractive because only the signal processing at the receiver must be modified. In the present paper, the application of CRAD to the more critical uplink of CDMA mobile radio systems with suboptimum JD techniques is investigated for maximal-ratio combining. The authors study six different suboptimum JD techniques based on decorrelating matched filtering, Gauss-Markov estimation, and minimum mean square error estimation with and without decision feedback. These six suboptimum JD techniques which are well-known for single antenna receivers are extended for the application to CRAD. A main concern of the paper is the determining of the SNR performance of the presented JD techniques for CRAD and the achievable average uncoded bit error probabilities for the transmission over rural area, typical urban and bad urban mobile radio channels are determined.

The effect of reconstruction filters on direct upconversion is analyzed in a multichannel environment. It is shown that the reconstruction filters cause gain and phase imbalances to be frequency dependent, a significant issue when considering the stringent adjacent channel interference (ACI) requirements for radio communication systems. The paper introduces an adaptive compensation technique as a means of overcoming these frequency dependent imbalances. Additionally the error vector between the mismatched filters is shown to be directly related to the amount of sideband rejection. This analysis is then used to develop a methodology for analysing the performance of the novel compensation technique with respect to the mismatched filters. Analysis of the classical all-pole filter algorithms reveal the sensitivity of direct upconversion in a multichannel environment to filter order, type, percentage mismatch and differing ACI level. >

The reconstruction filters are a major source of error in digital predistortion linearizers for RF power amplifiers. This paper presents a method that enables these filters to be designed for lowest filter complexity and minimum degradation of the linearizer performance. Furthermore, a method to choose an appropriate sampling rate for the predistorter is presented. Different filter approximations and orders are examined for different amplifier configurations by means of simulation. Of the filters tried, low-ripple Chebyshev and Butterworth filters perform best. It is demonstrated that it is possible to account for reasonable filter misalignment with only a small degradation in performance. It is also shown that the effect on the modulation is small with respect to intersymbol interference. >

This paper discusses the system performance degradation resulting from using a non-linear transmit power amplifier (PA) in a North American digital cellular (NADC) portable radio. The NADC portables require a linear power amplifier for the spectrally efficient linear modulation scheme, /spl pi//4-DQPSK. It is well known that these PA's can exhibit non-linear characteristics that degrade system performance. System degradation is measured using bit error rate (BER) as the figure of merit. The PA is modeled by its AM-AM and AM-PM characteristics; the receiver architecture contains the simple, yet robust, differential detector. Simulation results are presented for additive white Gaussian noise (AWGN), Rayleigh fading, and frequency selective fading environments, and compared to results for a truly linear PA. In addition, PA spectral regrowth is discussed as well as the potential use of a linearization technique to compensate for the PA effects. >

The paper introduces a new development of an existing technique for channel sounding waveform generation. The signal is based on an optimized low crest factor signal which is pre-equalized and predistorted to compensate for the linear and nonlinear elements in the transmitter. The generated signal is such that, at the power amplifier's output, the power spectrum over the bandwidth of interest is uniform and such that there are no out-of-band components. In this way best utilisation is made of the available bandwidth and power. No bandpass filters are required. >