Showing papers in "IEEE Transactions on Vehicular Technology in 1992"
TL;DR: In order to derive upper performance bounds for transmitter power control schemes, algorithms that are optimum in the sense that the interference probability is minimized are suggested.
Abstract: Most cellular radio systems provide for the use of transmitter power control to reduce cochannel interference for a given channel allocation. Efficient interference management aims at achieving acceptable carrier-to-interference ratios in all active communication links in the system. Such schemes for the control of cochannel interference are investigated. The effect of adjacent channel interference is neglected. As a performance measure, the interference (outage) probability is used, i.e., the probability that a randomly chosen link is subject to excessive interference. In order to derive upper performance bounds for transmitter power control schemes, algorithms that are optimum in the sense that the interference probability is minimized are suggested. Numerical results indicate that these upper bounds exceed the performance of conventional systems by an order of magnitude regarding interference suppression and by a factor of 3 to 4 regarding the system capacity. The structure of the optimum algorithm shows that efficient power control and dynamic channel assignment algorithms are closely related. >
1,256 citations
TL;DR: An algorithm that successfully approximates the behavior of the best known algorithms is proposed, which involves a novel distributed C/I-balancing scheme and shows that the balancing procedure is very robust to measurement noise.
Abstract: Distributed power control algorithms that use only the carrier-to-interference ratios (C/I ratios) in those links actually in use are investigated. An algorithm that successfully approximates the behavior of the best known algorithms is proposed. The algorithm involves a novel distributed C/I-balancing scheme. Numerical results show that capacity gains on the order of 3-4 times can be reached also with these distributed schemes. Further, the effects of imperfect C/I estimates due to noise vehicle mobility, and fast multipath fading are considered. Results show that the balancing procedure is very robust to measurement noise, in particular if C/I requirements are low or moderate. However, for required high C/I levels or for a rapidly changing path loss matrix, convergence may be too slow to achieve substantial capacity improvements. >
812 citations
TL;DR: The computation of the tap gains of the discrete-time representation of a slowly time-varying multipath channel is investigated and a known Monte Carlo based method approximating the given scattering function is extended by including filtering and sampling.
Abstract: The computation of the tap gains of the discrete-time representation of a slowly time-varying multipath channel is investigated. Assuming the channel is wide-sense stationary with uncorrelated scattering (WSSUS), a known Monte Carlo based method approximating the given scattering function (which fully determines the WSSUS channel) is extended by including filtering and sampling. The result is a closed-form solution for the tap gains. This allows the efficient simulation of the continuous-time channel with, e.g., only one sample per symbol, and without explicit digital filtering. >
626 citations
TL;DR: In this article, the energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations and all computations are performed and validated applying the three-dimensional multiple multipole software package.
Abstract: The energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations. All computations are performed and validated applying the three-dimensional multiple multipole software package. The numerical model of the plane phantom is additionally checked by accurate as possible experimental measurements. For the plane phantom, the interaction mechanism can be described well by H-field induced surface currents. The spatial peak specific absorption rate can be approximated within 3 dB by a formula given here based on the incident H-field or antenna current and on the conductivity and permittivity of the tissue. These findings can be generalized to heterogeneous tissues and larger biological bodies of arbitrary shape for frequencies above 300 MHz. The specific absorption rate is mainly proportional to the square of the incident H-field, which implies that in the close near field, the spatial peak specific absorption rate is related to the antenna current and not to the input power. >
321 citations
TL;DR: The proposed parallel algorithm is based on an artificial neural network composed of nm processing elements for an n-cell-m-frequency problem and found better solutions than the existing algorithm in one out of eight problems.
Abstract: The channel assignment problem involves not only assigning channels or frequencies to each radio cell. but also satisfying frequency constraints given by a compatibility matrix. The proposed parallel algorithm is based on an artificial neural network composed of nm processing elements for an n-cell-m-frequency problem. The algorithm runs not only on a sequential machine but also on a parallel machine with up to a maximum of nm processors. The algorithm was tested by solving eight benchmark problems where the total number of frequencies varied from 100 to 533. The algorithm found the solutions in nearly constant time with nm processors. The simulation results showed that the algorithm found better solutions than the existing algorithm in one out of eight problems. >
264 citations
TL;DR: The authors explore features of office buildings of modern construction that influence propagation between transmitter and receiver located on the same floor and evaluates the sector average signal.
Abstract: Because of the potential implementation of indoor wireless local area networks (LANs) and personal communication networks (PCNs) it is important to understand propagation of signals in the UHF band inside buildings. The authors explore features of office buildings of modern construction that influence propagation between transmitter and receiver located on the same floor. One feature is the clear space between ceiling and furnishings or floor that results in excess attenuation of the signal. A second feature is reflection and transmission at interior and exterior walls. Diffraction at corners and propagation along the exterior wall are also shown to be a significant means for radiation to reach the receivers. The influences of the first two features are combined into a computer program that evaluates the sector average signal, which is then compared with measurements. >
252 citations
TL;DR: In this article, a microcell interference model termed the Nakagami m/sub x/m/sub y/ model is introduced, in which the desired signal and the cochannel interferers are assumed to have Nakagi statistics but with different amounts of fading.
Abstract: A microcell interference model termed the Nakagami m/sub x//m/sub y/ model is introduced. The desired signal and the cochannel interferers are assumed to have Nakagami statistics but with different amounts of fading. A special case of this model is obtained when the desired signal has Nakagami statistics while the cochannel interferers are subject to Rayleigh fading. The probability density function of the signal-to-interference ratio in the Nakagami model is derived. This model is also compared with a Rician/Rayleigh microcellular model. Expressions for the outage probabilities in microcell systems are derived. Numerical results show that, compared to medium/large cell systems, the microcellular systems have a lower outage probability. The impact of diversity on the microcellular system is also studied. An improvement of the outage probability due to diversity is observed. >
216 citations
TL;DR: A novel transmitter diversity scheme that generates forced fading to improve the performance of channel coding is proposed and investigated and it is shown that excessively long interleaving is not required by the use of transmitter diversity.
Abstract: A novel transmitter diversity scheme that generates forced fading to improve the performance of channel coding is proposed and investigated. Since the required phase sweeping frequency is much smaller than the transmission bit rate, bandwidth expansion is negligible. A sinusoidal phase sweeping function Delta Theta sin(2 pi f/sub H/t) is employed in laboratory experiments using 32 kbit/s quarternary differential phase shift keying (QDPSK) with differential detection and BCH(23,12) code. It is shown that Delta Theta =200 degrees and f/sub H/=67 Hz can be used when m (interleaving depth)=10 b. Hence, excessively long interleaving is not required by the use of transmitter diversity. Under very slow Rayleigh fading (f/sub D/=1 Hz), a measured improvement of 4.8 dB is obtained at a word error rate of 10/sup -2/ without receiver diversity. Applications include paging systems that require very simple receivers. >
192 citations
TL;DR: The authors present an analog static predistortion linearization circuit that uses the envelope of the baseband signal to generate the nonlinear functional used in predistorting the input signal.
Abstract: A slowly adapting predistorter is presented. The approach is to minimize the transmitter output power in spectral regions occupied only by intermodulation (IM) products. In this way, only a spot power measurement is required. This technique relies on the principle that the power amplifier's characteristics vary slowly with time. By monitoring the out-of-band power one can obtain an estimate for the distortion introduced by the power amplifier. Adaptation is accomplished by iterative adjustment of the predistorter parameters to minimize the IM power. For a polynomial predistorter, the authors analytically demonstrate that the IM power is a quadratic function of the coefficients. A variety of algorithms therefore apply. The authors present an analog static predistortion linearization circuit that uses the envelope of the baseband signal to generate the nonlinear functional used in predistorting the input signal. The improvement obtained with an amplitude-modulated input signal was 15 dB in the third- and 5 dB in the fifth-order intermodulation products. The IM improvement could be maintained with the use of a robust direct search algorithm. >
165 citations
TL;DR: Experimental results demonstrate that a reduction in out-of-band spectra in excess of 20 dB may be achieved by employing digital feedback and a complex gain predistorter to linearize a nonlinear power amplifier.
Abstract: Amplification of linear modulation schemes, (which exhibit fluctuating envelopes), by high power amplifiers invariably leads to the generation of distortion and intermodulation products. Recent theoretical work has suggested that a complex gain predistorter may be employed to linearize a nonlinear power amplifier. The authors present experimental results demonstrating that a reduction in out-of-band spectra in excess of 20 dB may be achieved by employing digital feedback and a complex gain predistorter. >
159 citations
TL;DR: In this paper, a simple analytical model is developed for the neighboring-cell interference experienced by users as a function of distance from their home base station, which leads to the shape of the optimum radial distance dependent power-control law that will provide uniform service to all the users.
Abstract: The forward-link (base to mobile) power-control problem in code division multiple access (CDMA) cellular systems is studied. For a better understanding of the problem, a simple analytical model is developed for the neighboring-cell interference experienced by users as a function of distance from their home base station. Using this model, the recently proposed nth-power-of-distance power-control laws are investigated, especially with regard to the possibility of creation of a service hole. The investigation leads to the shape of the optimum radial distance dependent power-control law that will provide uniform service to all the users. >
TL;DR: Analytical, closed-form expressions for cellular outage probabilities in generalized Nakagami fading are derived for three practical diversity combining schemes, and the results for the Rayleigh fading channel are obtained and presented as a special case.
Abstract: Analytical, closed-form expressions for cellular outage probabilities in generalized Nakagami fading are derived for three practical diversity combining schemes. The outage is defined as the probability that the signal-to-interference power ratio (SIR) is less than a power protection ratio. The analysis considers L-branch equal gain (EG), selection (SC), and switched (SW) diversity combining schemes. The analyses are not limited to a single interferer, but rather assume the presence of multiple independent cochannel interferers. Previous results have used some approximations to study the performance of the EG combiner. A precise method is used to analyze the performance of an L-branch EG combiner. Selection diversity combining using the total power algorithm, the desired power algorithm, and the signal-to-interference power algorithm is analyzed. The effects of diversity on the reuse factor and on the spectrum efficiency of cellular mobile radio systems are considered in detail. The results for the Rayleigh fading channel are obtained and presented as a special case of the generalized Nakagami fading model. >
TL;DR: In this article, the impact of propagation path loss and user distribution on the frequency reuse efficiency of CDMA systems is analyzed. But, the authors do not consider the effect of path loss on the user distribution.
Abstract: Analysis techniques for quantitatively describing the impact of propagation path loss and user distribution on wireless direct-sequence code-division multiple-access (DS-CDMA) spread spectrum systems are presented. Conventional terrestrial propagation models which assume a d/sup 4/ path loss law are shown to describe modern cellular and personal communication system channels, poorly. A two-ray propagation model and path loss model derived from field measurements are used to analyze the impact of path loss on the frequency reuse efficiency of DS-CDMA cellular radio systems. The analysis shows that the frequency reuse efficiency (F) of the reverse channel with a single ring of adjacent cells can vary from a maximum of 71% in d/sup 4/ channels with a favorable distribution of users, to a minimum of 33% in d/sup 2/ channels with a worst-case user distribution. For three rings of adjacent users, F drops to 58% and 16%, respectively. Using the two-ray model, it is shown that F can vary over a wide range of values due to the fine structure of propagation path loss. >
TL;DR: Vehicle positions in multipath environments are estimated from the angle of arrival of waves received by multibeam antennas installed at two base stations by measuring angle-of-arrival by using time series data and averaging.
Abstract: Vehicle positions in multipath environments are estimated from the angle of arrival of waves received by multibeam antennas installed at two base stations. The estimated root mean square (RMS) position error is about 350 m. This can be reduced to about 200 m by using two kinds of processes: the averaging of time series data and the averaging of two sets of data. The position estimate error is caused by reflection from buildings near the vehicles, and a large error exceeding 500 m is caused by reflections from high buildings located some distance from the vehicle. Precise estimation of vehicle position in multipath environments by measuring angle-of-arrival is difficult because of building reflection. >
TL;DR: By employing the technique known as the matched filter bound, the authors derive analytical expressions for the distribution and average of the bit-error-rate in an ideal space diversity mobile radio receiver, giving insight into the relative benefits of antenna diversity and wideband transmission over the mobile radio channel.
Abstract: By employing the technique known as the matched filter bound, the authors derive analytical expressions for the distribution and average of the bit-error-rate in an ideal space diversity mobile radio receiver. Each diversity branch receives from a frequency-selective Rayleigh fading channel of arbitrary delay profile, and is subjected to additive Gaussian noise of arbitrary spectral shape. Numerical results calculated from the analytical expressions give insight into the relative benefits of antenna diversity and wideband transmission over the mobile radio channel. >
TL;DR: In this paper, an adaptive predistorter for linearizing a power amplifier in a mobile transmitter is studied, and the analytical, simulation, and measured results are presented, and a complex convolution method for measuring the out-of-band power that requires no additional local oscillator or phase reference is provided.
Abstract: An adaptive predistorter for linearizing a power amplifier in a mobile transmitter is studied, and the analytical, simulation, and measured results are presented. This predistorter does not have the problems of loop delay or phase shifting in its feedback path. The feedback is used only periodically to update the predistorter parameters so that it adapts to changes in the amplifier characteristics. An adaptation method for predistorters of the polynomial type is described. Its complexity is significantly lower than that of the previously described methods and its convergence speed, though low, is more than sufficient to track amplifier drift. Analytical verification that the measurement of out-of-band power is sufficient to drive the adaptation, a complex convolution method for measuring the out-of-band power that requires no additional local oscillator or phase reference, and a demonstration of the system performance utilizing a 16-QAM signal in a 25-kHz bandwidth, centered at 850 MHz, are provided. >
TL;DR: In this paper, an ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed and its performance is studied in a highway microcellular radio environment, where channels are assigned in an ordered basis in conjunction with a minimax algorithm under cochannel interference constraints, to provide high capacity and to alleviate worst case channel congestion in each microcell.
Abstract: An ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed, and its performance is studied in a highway microcellular radio environment. Channels are assigned in an ordered basis in conjunction with a minimax algorithm under cochannel interference constraints, to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure, at the expense of an increase in complexity and call switching requirements. >
TL;DR: The authors study the degradation in receiver performance caused by actual interblock channel variation, and offer a measure of the rate of channel time-variations, and give guidelines for deciding when those variations can be considered slow.
Abstract: In the design of block-oriented digital communication systems that must operate over time-dispersive channels, it is usually assumed that the channel is constant over the duration of a data block, even if the channel fades. The authors study the degradation in receiver performance caused by actual interblock channel variation. For tractability, attention is restricted to the case in which the channel variations are not tracked using decision-directed adaptation. The results suggest that unless the system parameters are carefully chosen, the constant-channel assumption is far from accurate. The quantitative results also offer a measure of the rate of channel time-variations, and give guidelines for deciding when those variations can be considered slow. These guidelines can be used as first-order evaluators of important system design decisions, such as total block size, training overhead, and data rate, for particular channel conditions. >
TL;DR: It is demonstrated that it is possible to achieve higher spectrum efficiency by reducing the cluster size in a sectorized system without lowering the S/I ratio below the minimum requirement.
Abstract: The effects of sectorization on the spectrum efficiency of a cellular system at different values of cell radius are studied. For a given cluster size, sectorization provides a higher signal-to-interference (S/I) ratio but reduces the spectrum efficiency of the system. It is demonstrated that it is possible to achieve higher spectrum efficiency by reducing the cluster size in a sectorized system without lowering the S/I ratio below the minimum requirement. In this respect, under both shadowing and nonshadowing conditions, there is an increase of spectrum efficiency of the sectorized systems over the omnidirectional system. The consistent gain in efficiency occurs when the cell radius exceeds a certain value depending on the traffic density in the cell. >
TL;DR: This analytical framework is used to evaluate the performance of the Reed-Solomon/hybrid-ARQ protocol (RS/HARQ) over fading channels with feedback to provide excellent reliability performance at the expense of a reduction in throughput.
Abstract: The use of nonbinary block error control codes over Rayleigh fading channels with feedback is examined. It is assumed that the fading is slow with respect to the rate of symbol transmission. Expressions are derived for the probabilities of channel symbol error and erasure, which are in turn used to develop expressions for code symbol error and erasure. Two erasure generation mechanisms are considered, one based on the existence of channel amplitude side information, the other not. This analytical framework is used to evaluate the performance of the Reed-Solomon/hybrid-ARQ protocol (RS/HARQ) over fading channels with feedback. The RS/HARQ system uses erasure decoding in a hybrid-ARQ protocol to provide excellent reliability performance at the expense of a reduction in throughput. The RS/HARQ protocol allows for the variation of the erasure threshold and the effective diameter of the decoding operation. >
TL;DR: In this paper, the authors present the model and implementation principles governing the computer simulation of line-of-sight (LOS) microcell wave propagation and demonstrate the advantages of switched transversal antenna diversity.
Abstract: The model and implementation principles governing the computer simulation of line-of-sight (LOS) microcell wave propagation are presented. Multiray propagation above a plane earth constitutes the basic model. For rural microcells, two rays are used while, for urban microcells, 10 rays are used propagating in a dielectric canyon. The model is applied to two relevant problems. In the first, control of electric field falloff with distance, r, is studied. ln the second, the advantages of switched transversal antenna diversity are demonstrated. Power falloff rates of 1/r/sup 4/ and 1/r/sup 6/ were obtained for simple two-element array structures. This may provide an additional interference control tool in the layout and design of microcells. The interference between the various rays propagating in lineal urban microcells results in deep nulls at various locations. The deleterious effects of these nulls can be eliminated by employing simple switched transverse antenna diversity. >
TL;DR: In this paper, the authors derived expressions relating the out-of-band spectra to the misalignments in the quadrature modulator feeding a nonlinear high power amplifier and derived the complex coefficients of the power series describing the amplifier.
Abstract: Misalignments in the quadrature modulator feeding a nonlinear high power amplifier can produce distortion products that lead to spectrum leakage into adjacent channels. Expressions are derived relating the out-of-band spectra to these misalignments and to the complex coefficients of the power series describing the amplifier. For most applications the adjacent channel leakage is proportional to the square of the misalignment error (carrier leak, differential gain, differential phase and level error) except in the case of some higher order products of continuous phase modulations (CPM). A technique for estimating the spectrum for the above situations is described. It involves summing the weighted spectrum of each distortion product. The weighting coefficients can be varied to account for amplifier characteristics, backoff, and misalignment error. The analysis is applicable to linear or continuous phase modulations with or without predistortion. The spectrum estimate is particularly good for continuous phase modulated signals where the error is normally much less than 1 dB. >
TL;DR: In this paper, the authors consider the performance of the compact-spectrum constant-envelope modulation chosen by ETSI/GSM, together with concatenated block and convolutional coding, Viterbi adaptive equalization, and soft-decision decoding to cope with the severe time and frequency-selective distortions caused by propagation phenomena, properly modeled for computer simulation.
Abstract: The introduction of the European Telecommunications Standards Institute/Groupe Special Mobiles (ETSI/GSM) digital land mobile radio system has required the study and application of advanced transmission techniques, necessary to meet the quality objectives in very demanding environments. In particular, the authors consider the performance of the compact-spectrum constant-envelope modulation chosen by ETSI/GSM, together with concatenated block and convolutional coding, Viterbi adaptive equalization, and soft-decision Viterbi decoding to cope with the severe time- and frequency-selective distortions caused by propagation phenomena, properly modeled for computer simulation. Channel coding and adaptive equalization techniques, supported also by frequency hopping and diversity reception, are fundamental to operate the system with the required quality. >
TL;DR: The near-far effect of random access protocols in mobile radio channels with receiver capture is investigated, and various models of receiver capture are compared, namely packet error rates for synchronous detection in slow- and fast-fading channels, and the probability that the signal-to-interference ratio is above a required threshold.
Abstract: The near-far effect of random access protocols in mobile radio channels with receiver capture is investigated. To this end, the probability of successful reception of a packet from a terminal at a known distance from the central receiver is obtained taking into account Rayleigh fading, UHF propagation attenuation, and the statistics of contending packet traffic in radio nets employing slotted ALOHA, carrier sense multiple access (CSMA) or inhibit sense multiple access (ISMA) protocols. Various models of receiver capture are compared, namely packet error rates for synchronous detection in slow- and fast-fading channels, and the probability that the signal-to-interference ratio is above a required threshold. >
TL;DR: In this paper, a phase-locked loop (PLL) frequency synthesizer with high switching speed is proposed, which is composed entirely of digital signal processors except for a voltage-controlled oscillator (VCO).
Abstract: A phase-locked loop (PLL) frequency synthesizer with high switching speed is proposed. Mobile communication networks are evolving towards microcellulars operating in narrowband TDMA and microwave bands to meet the rapidly increasing demands for both voice and data services. Therefore, synthesizers with high switching speed are required for the realization. However, it will be difficult for conventional synthesizers to provide switching times of shorter than 1 ms. The PLL synthesizer proposed is composed entirely of digital signal processors except for a voltage-controlled oscillator (VCO). The VCO control signal is derived by the subtraction of the linear reference phase and the feedback phase; therefore, it does not need the band-limited loop filter which limits the ability of the loop to switch fast. The experimental results show that it can provide switching times as short as 0.1 ms, which is 10/sup 2/ approximately 10/sup 3/ times higher than conventional PLL synthesizers, and spurs of less than -60 dB. >
TL;DR: In this paper, the authors investigate the performance of a scheme in conjunction with convolutional coding and soft-decision Viterbi decoding via a semianalytical technique based on the method of moments.
Abstract: Compound strategies of equalization and space diversity in the form of an optimum baseband combiner are attractive for wideband time division multiple access (TDMA) portable communication radio links in order to combat dispersive fading and cochannel interference. The authors investigate the performance of such a scheme in conjunction with convolutional coding and soft-decision Viterbi decoding via a semianalytical technique based on the method of moments. Such an approach avoids a Gaussian characterization of interference and yields results for both ideal interleaving and no interleaving. With dual space diversity, three taps per forward filter, and a data rate of 10 Mb/s, it is shown that, although a third space diversity branch remains preferable in terms of performance, channel coding can be a viable alternative, particularly in terms of outage rate, to increasing the space diversity order, even in the absence of interleaving, provided the signal-to-interference ratio is sufficiently high. >
TL;DR: Three short-block data detection techniques based on linear, nonlinear decision-directed, and maximum likelihood estimation principles are investigated and performance is presented for BPSK and QPSK type signaling using a Rayleigh fading channel model with severe time-dispersion.
Abstract: The objective is reliable digital communications over fading channels with severe time-dispersion. Three short-block data detection techniques based on linear, nonlinear decision-directed, and maximum likelihood estimation principles are investigated. Short alternating blocks of data and training symbols are used. The training blocks are useful for both channel tracking and data block detection. In contrast to the recursive symbol-to-symbol equalization approaches usually employed, each data block is detected as a unit. Previous restrictions imposed on short-block detection schemes have been removed, resulting in reduced complexity algorithms and higher throughput efficiency. Performance is presented for BPSK and QPSK type signaling using a Rayleigh fading channel model with severe time-dispersion. >
TL;DR: A receiver that utilizes trellis coded continuous phase frequency shift keying (CPFSK) with coherent detection and convolutional interleaving of the coded symbols for data transmission is presented.
Abstract: A receiver that utilizes trellis coded continuous phase frequency shift keying (CPFSK) with coherent detection and convolutional interleaving of the coded symbols for data transmission is presented. An earlier study considered decoding based solely on the code trellis. A new decoding algorithm that copes with the interleaving is presented and uses information from both the modulation trellis and the code trellis. The performance results are obtained by Monte Carlo simulation and are partially verified through analysis. The fading model is Rician, but the line-of-sight (LOS) component is subjected to a log-normal transformation that represents attenuations due to foliage which is referred to as shadowing. The system studied is not suitable for digital speech applications as the required interleaving depths lad to an unacceptable time delay. >
TL;DR: 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.
Abstract: 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. >
TL;DR: In this paper, the average bit error rate (BER) of pi/4-shift QDPSK is theoretically analyzed taking into account additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread; exact diversity gain degradations are calculated.
Abstract: The diversity gain degradations due to fading correlation and unequal average power are investigated for practical, two-branch postdetection selection diversity reception. The average bit error rate (BER) of pi /4-shift QDPSK is theoretically analyzed taking into account additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread; exact diversity gain degradations are calculated. Simple and useful approximate expressions for the gain degradations are also presented. >