Showing papers in "IEEE Transactions on Vehicular Technology in 1996"
TL;DR: Four suboptimum detection techniques based on zero forcing and minimum mean-square-error equalization with and without decision feedback (DF) are presented and compared and it is shown that the performance of the MMSE equalizers is better than that of the corresponding ZF equalizers.
Abstract: In code-division multiple-access (CDMA) systems transmitting over time-varying multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) arise. The conventional suboptimum receiver consisting of a bank of matched filters is often inefficient because interference is treated as noise. The optimum multiuser detector is too complex to be implemented at present. Four suboptimum detection techniques based on zero forcing (ZF) and minimum mean-square-error (MMSE) equalization with and without decision feedback (DF) are presented and compared. They combat both ISI and MAI. The computational complexity of all four equalizers is essentially the same. All four equalizers are independent of the size of the data symbol alphabet. It is shown that the performance of the MMSE equalizers is better than that of the corresponding ZF equalizers. Furthermore, the performance of the equalizers with DF is better than that of the corresponding equalizers without DF. The impairing effect of error propagation on the equalizers with DF is reduced by channel sorting.
581 citations
TL;DR: The experimental measurements confirm the usefulness of the first-order Markovian assumption and show that given the information corresponding to the previous symbol, the amount of uncertainty remaining in the current symbol should be negligible.
Abstract: The use of received signal-to-noise ratio (SNR) as the side information in communication systems has been widely accepted especially when the channel quality is time varying. On many occasions, this side information is treated as the received SNR of the current channel symbol or that of previous symbols. In particular, the first-order Markov channel provides a mathematically tractable model for time-varying channels and uses only the received SNR of the symbol immediately preceding the current one. With the first-order Markovian assumption, given the information of the symbol immediately preceding the current one, any other previous symbol should be independent of the current one. Although the experimental measurements confirm the usefulness of the first-order Markovian assumption, one may argue that second or higher-order Markov processes should provide a more accurate model. We answer this question by showing that given the information corresponding to the previous symbol, the amount of uncertainty remaining in the current symbol should be negligible.
542 citations
TL;DR: The present authors have extended this analysis by including an additional criterion based on absolute signal strength in the handoff decision algorithm, which is proved to be sufficiently accurate by comparison with simulation.
Abstract: An analytic model has been previously developed for evaluating the performance of handoff algorithms based on relative signal strength measurements, i.e., the difference of signal strength from two base stations (BSs). The present authors have extended this analysis by including an additional criterion based on absolute signal strength in the handoff decision algorithm. The absolute signal strength is the averaged value of the received signal level from the current serving BS measured by the mobile unit. This value has to be below a fixed threshold to initiate a handoff (a necessary, not sufficient condition). In this way, the mobile unit should be assigned to a new BS if the absolute signal strength from the old BS drops below the threshold and the relative signal strength between the new and old BS reaches the hysteresis level. The model is proved to be sufficiently accurate by comparison with simulation. The effect of adding absolute signal strength is illustrated.
253 citations
TL;DR: The probability of erroneous assignment of a mobile to a microcell or macrocell is shown to be significantly lower than previous approaches, and a systematic way for finding an optimal partition of frequency spectrum between microcells and macrocells is proposed.
Abstract: In this paper, we study spectrum management in a two-tier microcell/macrocell cellular system. Two issues are studied: micro-macro cell selection and frequency spectrum partitioning between microcells and macrocells. To keep the handoff rate in a two-tier cellular system at an acceptable level, low mobility users (with speed /spl upsi/ V/sub 0/) should undergo handoffs at macrocell boundaries. The mobile determines user mobility from microcell sojourn times and uses it for channel assignment at call origination and handoff. The probability of erroneous assignment of a mobile to a microcell or macrocell is shown to be significantly lower than previous approaches. We investigate the optimal velocity threshold, V/sub 0/, and propose that it may be dynamically adjusted according to traffic load. Finally, we propose a systematic way for finding an optimal partition of frequency spectrum between microcells and macrocells. This partitioning is based on the traffic load and velocity distribution of mobiles in the system.
243 citations
TL;DR: This work investigates how an evolutionary inspired computing technique known as genetic algorithms (GAs) may be used for global optimization techniques that avoid many of the shortcomings exhibited by local search techniques on difficult search spaces.
Abstract: The problem of assigning appropriate channels to the individual members of a cellular network is an important challenge facing network designers. Heuristics may be used to solve this problem, although in recent years parallel distributed methods have also been suggested. We investigate how an evolutionary inspired computing technique known as genetic algorithms (GAs) may be used. These global optimization techniques avoid many of the shortcomings exhibited by local search techniques on difficult search spaces. The new approach is tested on several problems of different sizes and complexity. The critical aspects of this technique and additional improvements are also discussed.
187 citations
TL;DR: A novel computer simulation model for a land mobile radio channel based on an efficient approximation of filtered white Gaussian noise processes by finite sums of properly weighted sinusoids with uniformly distributed phases that can be interpreted as a deterministic model that approximates stochastic processes.
Abstract: We present a novel computer simulation model for a land mobile radio channel. The underlying channel model takes for granted non-frequency-selective fading but considers the effects caused by shadowing. For such a channel model we design a simulation model that is based on an efficient approximation of filtered white Gaussian noise processes by finite sums of properly weighted sinusoids with uniformly distributed phases. In all, four completely different methods for the computation of the coefficients of the simulation model are introduced. Furthermore, the performance of each procedure is investigated on the basis of two quality criteria. All the presented methods have in common the fact that the resulting simulation model has a completely determined fading behavior for all time. Therefore, the simulation model can be interpreted as a deterministic model that approximates stochastic processes such as Rayleigh, log-normal, and Suzuki (1977) processes.
164 citations
TL;DR: Analytical models and simulations investigating the traffic impacts are presented, as are the results that show that even in the highest offered load considered a 3-min conversation in the busy hour experiences less than half a second of sub-rated conversation on average.
Abstract: A new personal communications services (PCS) hand-off scheme is proposed. This scheme provides for hand-off to radio ports on which there is no free channel by "sub-rating" an existing connection. With sub-rating, an occupied full-rate channel is temporarily divided into two half-rate channels: one to serve the existing call and the other to serve the hand-off request. The blocking probabilities (combined forced terminations of existing calls and blocking of new call attempts) of this new scheme compare favorably with the standard scheme (nonprioritizing) and the previously proposed prioritizing schemes. The costs for this scheme are presented and discussed, as well as the additional procedural complexity of implementing on-the-fly sub-rating and the impact of continuing the conversation on a lower rate channel (which may lower speech quality of increase battery drain). Analytical models and simulations investigating the traffic impacts are presented, as are the results that show that even in the highest offered load considered a 3-min conversation in the busy hour experiences less than half a second of sub-rated conversation on average and only about 3% of the calls experience more than 5.12 s of sub-rated conversation. This scheme can increase capacity by 8-35% for systems with 1% call incompletion probability.
157 citations
TL;DR: In this paper, a deterministic approach to model the radio propagation channels in tunnels with and without traffic is proposed, which applies the modified shooting and bouncing ray (SBR) method to find equivalent sources (images) in each launched ray tube and sums the receiving complex amplitude contributed by all images coherently.
Abstract: We propose a deterministic approach to model the radio propagation channels in tunnels with and without traffic. This technique applies the modified shooting and bouncing ray (SBR) method to find equivalent sources (images) in each launched ray tube and sums the receiving complex amplitude contributed by all images coherently. In addition, the vector effective antenna height (VEH) is introduced to consider the polarization-coupling effect resulting from the shape of the tunnels. We verify this approach by comparing the numerical results in two canonical examples where closed-form solutions exist. The good agreement indicates that our method can provide a good approximation of high-frequency radio propagation inside tunnels where reflection is dominant. We show that the propagation loss in tunnels can vary considerably according to the tunnel shapes and the traffic inside them. From the results we also find a "focusing" effect, which makes the power received in an arched tunnel higher than that in a rectangular tunnel. Besides, the deep fading that appears in a rectangular tunnel is absent in an arched tunnel. The major effect of the traffic is observed to be the fast fading due to the reflection/obstruction of vehicles. Additional considerations, such as time delay, wall roughness, and wedge diffraction of radio wave propagation in tunnels are left for future studies.
148 citations
TL;DR: An efficient two-phase adaptive local-search algorithm for the channel-assignment problem is described, which has been applied to several existing benchmark problems with encouraging results and outperforms the existing algorithms in the quality of the solution obtained.
Abstract: The channel-assignment problem (CAP) for cellular radio networks is an NP-complete problem. Previous techniques for solving this problem have used graph-coloring algorithms, neural networks, simulated annealing, and pattern-based optimization procedures. We describe an efficient two-phase adaptive local-search algorithm for the channel-assignment problem. This algorithm has been applied to several existing benchmark problems with encouraging results. In many cases it outperforms the existing algorithms in the quality of the solution obtained. When used in conjunction with structured preprocessing, the algorithm can be applied to large networks. It is thus a practical tool for the planning of cellular radio networks.
115 citations
TL;DR: In this article, the authors measured the amplitude variation for individual pulses, in addition to the path loss, mean excess delay, root mean square (RMS) delay spread, and the coherence bandwidth of the indoor channel.
Abstract: The growing use of unlicensed wireless systems has spurred interest in the 2.4-GHz ISM band. In order to facilitate the design of such systems, measurements of the pulse response characteristics have been made inside commercial buildings. From the measured pulse response, the statistical properties of the amplitude variation for individual pulses was determined, in addition to the path loss, mean excess delay, root mean square (RMS) delay spread, and the coherence bandwidth of the indoor channel.
110 citations
TL;DR: The loss in capacity of a Rayleigh fading channel with respect to the additive white Gaussian noise (AWGN) channel turns out to be negligible for all values of the signal-to-noise ratio that are of interest.
Abstract: Lee (see ibid., vol.39, p.187, no.8, 1990) proposed a very simple and elegant model for estimating the capacity of slowly fading channels. A small error in his paper, however, has led to an inexact picture. We correct that inaccuracy. As a consequence, the loss in capacity of a Rayleigh fading channel with respect to the additive white Gaussian noise (AWGN) channel turns out to be negligible for all values of the signal-to-noise ratio that are of interest. Furthermore, we extend the analytical results to the situation with M-branch diversity and Ricean fading channels. The lower moments of the associated distributions, i.e., of the /spl chi//sup 2/-distribution (Nakagami with integer m-parameter) and Rice distribution agree when the parameters of the distribution are suitably chosen. With that choice of parameters, the capacities of the M-branch diversity and of the Ricean fading channel become almost identical.
TL;DR: It is demonstrated that the controlled active vision framework can be utilized to provide a visual tracking modality to a traffic advisory system in order to increase the overall safety margin in a variety of common traffic situations.
Abstract: The complexity and congestion of current transportation systems often produce traffic situations that jeopardize the safety of the people involved. These situations vary from maintaining a safe distance behind a leading vehicle to safely allowing a pedestrian to cross a busy street. Environmental sensing plays a critical role in virtually all of these situations. Of the sensors available, vision sensors provide information that is richer and more complete than other sensors, making them a logical choice for a multisensor transportation system. We propose robust detection and tracking techniques for intelligent vehicle-highway applications where computer vision plays a crucial role. In particular, we demonstrate that the controlled active vision framework can be utilized to provide a visual tracking modality to a traffic advisory system in order to increase the overall safety margin in a variety of common traffic situations. We have selected two application examples, vehicle tracking and pedestrian tracking, to demonstrate that the framework can provide precisely the type of information required to effectively manage the given traffic situation.
TL;DR: A new technique is presented, which allows the Nakagami distributions for both signal and interferers to be arbitrary, and exact formulas for probability of outage with and without a constraint on minimum signal power are derived.
Abstract: Outage probability provides a fundamental performance measure of the grade of service for cellular mobile radio systems. Determination of the outage probability in a Nakagami (1960) mobile environment is particularly important since Nakagami fading is, as shown by various empirical measurements, the most appropriate model in many practical applications. Effective techniques have been developed recently to determine outage probability in the presence of multiple Nakagami interferers by assuming that the fading parameters of both signal and co-channel interferences are integer-valued. However, the general problem with arbitrary Nakagami signal and interferers remains unsolved. A new technique is presented, which allows the Nakagami distributions for both signal and interferers to be arbitrary. Exact formulas for probability of outage with and without a constraint on minimum signal power are derived, and computer results are also presented to illustrate the theory.
TL;DR: The quantization effects in different parts of a table based complex gain predistortion linearizer based on the knowledge of the RF amplifier gain characteristic, the probability density function for the modulation scheme and the maximum allowable adjacent channel interference level are investigated.
Abstract: Significant improvements in terms of reduced power consumption and increased bandwidth are obtained if a digital predistortion linearizer is implemented with an application specific digital signal processor. This paper investigates the quantization effects in different parts of a table based complex gain predistortion linearizer. The analysis can be used to optimize the predistortion linearizer with respect to word length based on the knowledge of the RF amplifier gain characteristic, the probability density function for the modulation scheme and the maximum allowable adjacent channel interference level. A predistorter chip is described that has been designed using the analysis. The chip has been fabricated and tested. Compared with a standard digital signal processing (DSP) solution it provides seven times higher bandwidth but consumes only 10% of the power.
TL;DR: Comparisons with a classical fixed allocation technique (FCA) and a different DCA technique are shown to highlight the better performance of the proposedDCA technique.
Abstract: The interest in global spectrum allocation techniques is growing with the always increasing spectrum demand for (cellular) mobile communications. However, the best algorithms suffer from high computational times that reduce the possibility of a practical implementation. This paper deals with a dynamic channel allocation (DCA) technique based on an energy function whose minimization gives the optimal allocation. Due to the particular formulation of such an energy function, the minimization can be performed by a Hopfield neural network for which a fast hardware implementation has been recently proposed in the literature. The performance of the proposed DCA technique is derived by computer simulations. Comparisons with a classical fixed allocation technique (FCA) and a different DCA technique are shown to highlight the better performance of the proposed DCA technique.
TL;DR: A fuzzy proportional-plus-integral (PI) control is introduced to determine each user's transmitting power in order to maintain simultaneously all users' signal power received at the base station nearly equal and to achieve better system stability and control performance.
Abstract: Introduces a new application of fuzzy-logic control (FLC) to power control in a DS/CDMA cellular system over mobile fading radio channels. The conventional feedback power control algorithms allow the base station to send a power command to raise/lower each user transmitting signal power level by a fixed power step and then keep the received powers almost equal. The fixed-step approach is actually an integral control whose power increment is determined according to the bang-bang-like control policy. However, this control scheme suffers from several disadvantages. To tackle these difficulties, a fuzzy proportional-plus-integral (PI) control, whose input variables are the received power error and error change, is introduced to determine each user's transmitting power in order to maintain simultaneously all users' signal power received at the base station nearly equal and to achieve better system stability and control performance. The derivation of the fuzzy PI control has been carried out by analyzing both the closed-loop steady state behavior and transient response of the system with a priori knowledge of the dynamics of the CDMA mobile fading channels. In fuzzy control, linguistic descriptions of actions in controlling a process are represented as fuzzy rules. This fuzzy-rule base is used by an inference mechanism in conjunction with some knowledge of the states of process in order to determine control actions. These actions would lead to the fast rise time, minimum overshoot, and small root-mean-squared (rms) tracking error. Additional advantages of fuzzy PI control over conventional control theories are discussed.
TL;DR: This paper investigates multiuser receivers that combine explicit antenna diversity, RAKE multipath diversity, and multipath decorrelating detection, and demonstrates a significant increase in up-link capacity over the conventional RAKE receiver, at the expense of complexity.
Abstract: Code division multiple-access (CDMA) techniques using interference cancellation are being explored for the capacity increase in third-generation universal mobile telecommunications systems. However, multipath fading is a major constraint on the performance of wireless CDMA systems, with multipath propagation worsening the effects of multiple-access interference, and fading on propagation paths leading to the near far problem. Multiuser detection, exploiting the knowledge of other users to cancel multiple-access interference, has the capability of eliminating the near far problem and providing a significant capacity increase in CDMA systems. On the other hand, diversity techniques effectively combat the fading effects of the channel. This paper investigates multiuser receivers that combine explicit antenna diversity, RAKE multipath diversity, and multipath decorrelating detection. Both coherent reception with maximal-ratio combining and differentially coherent reception with equal-gain combining are analyzed. The results demonstrate a significant increase in up-link capacity over the conventional RAKE receiver, at the expense of complexity. In the case of limited receiver complexity, where the number of correlators is less than the number of resolvable paths at the RAKE front-end, antenna diversity is shown to be effective in reducing residual multiple-access interference.
TL;DR: This work identifies a suitable state characterization and framework for a performance analysis that enables numerical computation of theoretical performance results and shows carried traffic, blocking probability, and forced termination probability for each platform type and for each call type.
Abstract: The proliferation of mobile, portable, and personal communication systems will bring a variety of offered services. Practical systems that are envisioned must support different types of calls. These may include voice only, mixed voice and data, high-speed data, low-speed data, image transmission, and an array of intelligent network services. In addition there may be a mixture of platforms (such as persons, autos, buses, trains, boats, and planes) having a range of mobility characteristics. In such environments, the bandwidth and/or resources needed for different call sessions will not be identical. As a result, calls will generally encounter different blocking and hand-off constraints. These effects are in addition to differences in blocking and forced (call) termination probabilities that are attributable to differing platform mobilities and (resource) channel quotas. Cellular systems with mixed platforms that support calls with differing resource requirements are considered. Loss-type systems and hybrid delay-loss systems are treated. In each case, priority access to resources for hand-off calls is allowable. We identify a suitable state characterization and framework for a performance analysis that enables numerical computation of theoretical performance results. Example performance characteristics are obtained. These show carried traffic, blocking probability, and forced termination probability for each platform type and for each call type.
TL;DR: This paper analyzes the effect of quantization in a digital signal component separator (SCS) for linear amplification with nonlinear components (LINC) transmitters.
Abstract: Spectrally efficient modulation schemes have been chosen for the second generation of cellular systems in the United States and Japan, as well as for private mobile radio (PMR) systems This paper analyzes the effect of quantization in a digital signal component separator (SCS) for linear amplification with nonlinear components (LINC) transmitters The analysis relies on the fact that the two signal components can be obtained as the source signal plus/minus a signal in quadrature to the source signal The equations derived are vital because they allow the designer to optimize digital signal processor (DSP) power consumption and bandwidth The word lengths that are required for the source signal and the quadrature signal can be calculated from the amplifier gain characteristic, the probability density function for the modulation scheme, and the specified adjacent channel interference (ACI) The validity of the analysis has been verified by means of simulations
TL;DR: An analytical approach for analyzing the mean packet delay and mean queue length at the transmitting terminal in wireless packet networks using the selective repeat (SR) automatic repeat request (ARQ) scheme to control the errors introduced by the nonstationary transmission channel is presented.
Abstract: This paper presents an analytical approach for analyzing the mean packet delay and mean queue length at the transmitting terminal in wireless packet networks using the selective repeat (SR) automatic repeat request (ARQ) scheme to control the errors introduced by the nonstationary transmission channel. Each transmitting terminal is modeled as a discrete time queue with an infinite buffer. The nonstationary transmission channel is modeled as a two-state Markov chain. Comparisons of numerical predictions and simulation results are presented to highlight the accuracy of the proposed analytical approach.
TL;DR: The capacity of a slow-frequency-hopped TDMA-based cellular system via calculation of the outage probability is analyzed and the sensitivity to power control error, voice activity factor, and soft capacity of the system is investigated.
Abstract: Time-division multiple access (TDMA)-based systems have been adopted as the first generation digital cellular standards in North America, Europe, and Japan. The increasing demand for capacity motivates the study of alternate systems and enhancements to the adopted TDMA standards. In particular, CDMA techniques using direct sequence and slow frequency hopping have been suggested. We analyze the capacity of a slow-frequency-hopped TDMA-based cellular system via calculation of the outage probability. Expressions for the outage probability as a function of voice activity, power control, and antenna diversity are provided for mobile-to-base transmission. These expressions are used to evaluate the system capacity (users/MHz/cell) based on simulating mobile locations within 37 hexagonal cells. The sensitivity to power control error, voice activity factor, and soft capacity of the system is investigated.
TL;DR: A noncoherent hybrid parallel pseudonoise code acquisition scheme for code-division multiple access (CDMA) mobile communication systems is proposed and the effect of multiple access interference (MAI) on the code acquisition performance for Rayleigh and Rician fading channels is analyzed.
Abstract: This paper proposes a noncoherent hybrid parallel pseudonoise (PN) code acquisition scheme for code-division multiple access (CDMA) mobile communication systems and analyzes the effect of multiple access interference (MAI) on the code acquisition performance for Rayleigh and Rician fading channels. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time slightly inferior to that of the total parallel acquisition in the case of severe MAI; on the other hand, it provides the flexibility in the tradeoff between the mean acquisition time and system complexity if no MAI is considered. The closed-form expressions of the detection and false-alarm probabilities and mean acquisition time are derived. Numerical analysis quantifies the severe performance degradation of code acquisition due to both MAI and channel fading, and demonstrates the dependence of the increase of mean acquisition time (due to MAI) on the number of users in the CDMA system, system design parameters, and channel fading statistics.
TL;DR: In this paper, a new Nd-Fe-B permanent magnet synchronous motor (PMSM) drive for electric vehicles is proposed, which possesses high power density and high efficiency, resulting in greater energy and space savings.
Abstract: Availability of high-energy neodymium-iron-boron (Nd-Fe-B) permanent magnet (PM) material has focused attention on the use of the PM synchronous motor (PMSM) drive for electric vehicles (EVs). A new Nd-Fe-B PMSM is proposed for the drive system, which possesses high power density and high efficiency, resulting in greater energy and space savings. The design and optimization of the motor employs finite element analysis and computer graphics. Increasingly, a new PWM inverter algorithm is developed for the drive system, which can handle the nonconstant battery voltage source. An efficiency optimizing control is adopted to further improve the energy utilization of the drive system. Both the control strategy and the PWM generation are implemented in a single-chip microcontroller. As a result, the motor drive achieves high power density, high efficiency, and compactness. A prototype of the 3.2 kW battery-powered drive system has been designed and built for an experimental mini-EV.
TL;DR: The development of a mathematical modular framework based on Petri network (PN) theory to model a traffic network is the subject of this paper and the Petri-net model of a generic traffic junction is presented, with its deadlock avoidance property proven.
Abstract: The development of a mathematical modular framework based on Petri network (PN) theory to model a traffic network is the subject of this paper. Traffic intersections are the primitive elements of a transportation network and are characterized as event-driven and asynchronous systems. Petri networks have been utilized to model these discrete event systems; further analysis of their structure can reveal information relevant to the concurrency, parallelism, synchronization, and deadlock avoidance issues. The Petri-net model of a generic traffic junction is presented, with its deadlock avoidance property proven. These modular networks are effective in synchronizing their components and can be used for modeling of an asynchronous large-scale transportation system. The derived model is suitable for simulations on a multiprocessor computer since its program execution safety is secured. The software pseudocode for simulating a transportation network model on a multiprocessor system is presented.
TL;DR: In this paper, a pulse-code-modulation (PCM) realization of the above two power control mechanisms for the uplink of a direct sequence-code division multiple access (DS-CDMA) cellular mobile radio system is studied.
Abstract: Power control (PC) is an important issue in a direct sequence-code division multiple access (DS-CDMA) cellular mobile radio system. Higher link performance and greater system capacity cannot be achieved unless an appropriate PC mechanism is employed. In previous research, a delta-modulation (DM) realization of strength-based and SIR-based PC mechanisms for uplink communication has been studied by simulation. In order to obtain higher PC trackability, we study a pulse-code-modulation (PCM) realization of the above two PC mechanisms for the uplink of a DS-CDMA cellular mobile radio system. The simulation results presented indicate that the PC mechanisms with PCM realization for the uplink can achieve a lower outage probability and thus higher link performance than the PC mechanisms with DM realization. We also obtain optimal design parameters such as the stepsize and the control mode for the two PCM PC mechanisms. In addition, we compare the two PCM PC mechanisms in terms of their outage probability and stability and find that the strength-based mechanism has a higher outage probability but greater stability than the SIR-based mechanism.
TL;DR: Computer simulation results show that the proposed SAW-ARQ protocol can achieve high throughput and reduce the number of retransmission effectively for slow and fast Rayleigh fading/log-normal shadowing conditions.
Abstract: In a noncellular or large cell-size mobile radio communication system, log-normal shadowing as well as Rayleigh fading becomes the predominant source of system degradation. This paper proposes an efficient stop and wait automatic repeat request (SAW-ARQ) protocol with adaptive packet length to provide reliable mobile data packet transmission. The adaptive SAW-ARQ protocol controls the transmitting packet length according to the time-varying channel condition estimated with the number of ACK (acknowledgment packet) and NACK (negative-acknowledgment packet). Computer simulation results show that the proposed protocol can achieve high throughput and reduce the number of retransmission effectively for slow and fast Rayleigh fading/log-normal shadowing conditions.
TL;DR: A dynamic scheme which adaptively updates the size and shape of the LR area is developed by solving the minimization problem and the superiority of the proposed scheme is demonstrated with various computational results.
Abstract: A 0-1 integer programming model is considered to determine the most appropriate dynamic location registration (LR) area of each subscriber in microcellular systems. The minimization model of the LR area updating and paging signal costs is examined. The model is based on the subscriber characteristics, such as the call arrival rate and the velocity, as well as the regional information. The control channel blocking probabilities are considered as constraints to meet the service level of subscribers. A dynamic scheme which adaptively updates the size and shape of the LR area is developed by solving the minimization problem. Paging and location updating procedures are presented based on the dynamic procedure. The superiority of the proposed scheme is demonstrated with various computational results.
TL;DR: In this article, 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 cochannel interference (CCI) and additive white Gaussian noise (AWGN).
Abstract: 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/sub b//N/sub 0/ (SIR) at BER=10/sup -3/ in Rician channels with K=5 dB.
TL;DR: The results further support the notion that high sites together with high gain antennas and suitably selected pattern tilting can result in a significant reduction in path loss and delay spread, as well as reduction in power transmitted from the cell site and reduction in system interference.
Abstract: Results of wideband path loss and delay spread measurements using high gain, high and low antenna heights with pattern tilting are presented. The measurements were done in the frequency range 905-915 MHz, at two existing cellular mobile radio (CMR) sites. Also presented are potential approaches for analyzing data from high gain antennas. It is shown that, to a large extent, existing models can be used to predict path loss for high gain antennas with downtilting. The results further support the notion that high sites together with high gain antennas and suitably selected pattern tilting can result in a significant reduction in path loss and delay spread, as well as reduction in power transmitted from the cell site and reduction in system interference.
TL;DR: The performance of a cellular mobile radio system with frequency reuse is evaluated in terms of outage probability, and it is seen that diversity and power control can improve the system behavior.
Abstract: The performance of a cellular mobile radio system with frequency reuse is evaluated in terms of outage probability. Deterministic path loss, log-normal shadowing, and Ricean fading are accounted for, and the use of diversity and power control is considered in order to enhance system performance. Both hexagonal and lineal cells are considered. Particular attention is given to the sensitivity of the outage probability to the system parameters, especially those related to the propagation model (fading, shadowing, and path loss). It is seen that diversity and power control can improve the system behavior. The performance is sensitive to the fading parameter (i.e., the Rice factor) of the intended user, but is relatively independent of that of the interferers. Also, a significant dependence is observed on the shadowing parameter, whereas a limited dependence is seen on the outage threshold and the channel utilization. Finally, the presence of a dual path loss law degrades the performance, and the outage probability increases as the breakpoint distance gets larger.