Showing papers in "IEEE Transactions on Vehicular Technology in 1989"
TL;DR: In this article, two novel channel assignment strategies are proposed: the locally optimized dynamic assignment (LODA) strategy and the borrowing with directional channel-locking (BDCL) strategy.
Abstract: Two novel channel-assignment strategies are proposed: the locally optimized dynamic assignment (LODA) strategy and the borrowing with directional channel-locking (BDCL) strategy. Their performance is compared with the fixed-assignment (FA) strategy (currently used on certain systems) and the borrowing with channel ordering (BCO) strategy (the strategy that has given the lowest blocking probability in previous research). Computer simulations on a 49-cell network for both uniform and nonuniform traffic showed that the average call-blocking probability of the BDCL strategy is always the lowest. The LODA performance is comparable with that of BCO under nonuniform traffic conditions but is inferior under uniform traffic conditions. >
401 citations
TL;DR: In this paper, a robust submodel is formulated for the dynamics of the IC engine, where-in the engine is viewed as a system with input given by cylinder pressure and output corresponding to crankshaft angular acceleration and crankshft torque.
Abstract: A contribution is made to the task of constructing a global model for the IC (internal combustion) engine. A robust submodel is formulated for the dynamics of the IC engine, where-in the engine is viewed as a system with input given by cylinder pressure and output corresponding to crankshaft angular acceleration and crankshaft torque. The formulation is well suited to closed-loop engine control and transmission control applications. In the model, cylinder pressure is deterministically related to net engine torque through the geometry and dynamics of the reciprocating assembly. The relationship between net engine torque and crankshaft angular acceleration is explain in terms of a passive second-order electrical circuit model with constant parameters. Experimental results confirm the validity of the model over a wide range of engine operating conditions, including transient conditions. It is concluded that the model provides a powerful tool for estimating average and instantaneous net engine torque based on an inexpensive noncontacting measurement of crankshaft acceleration, thus providing access to one of the primary engine performance variables. >
162 citations
TL;DR: It is shown that splitting analog channels does not increase the spectrum efficiency in cellular radio systems, but that using digital cellular channels does, and a simple evaluation method for judging Spectrum efficiency in different digital systems is introduced.
Abstract: The spectrum efficiency in cellular radio systems can be measured by a parameter that is called radio capacity. Using radio capacity, it is shown that splitting analog channels does not increase the spectrum efficiency in cellular radio systems, but that using digital cellular channels does. A simple evaluation method for judging spectrum efficiency in different digital systems is introduced. Also, several new concepts of spectrum efficiency in cellular radio systems are described. >
161 citations
TL;DR: In this article, a power-saving electromagnetic suspension system was developed in which electromagnets with permanent magnets were used to suspend the vehicle and the electromagnetic coil current required to keep a vehicle levitating was extremely small, ideally zero.
Abstract: A power-saving electromagnetic suspension system has been developed in which electromagnets with permanent magnets are used to suspend the vehicle. The electromagnets are controlled to maintain air gap length so that the attractive force by the permanent magnet always balances the total weight of the vehicle and its loads, based on modern control theory. This technology realizes a significantly power-saving system in which the electromagnetic coil current required to keep a vehicle levitating was extremely small, ideally zero. The 8-kg weight test vehicle with 4-kg load could be levitated continuously over 8 h, without recharging the on-board 1300-mAh batteries. This technology realized a completely contact-free material transportation system when combined with a contact-free driving system using linear motors. The attractive force characteristics of a permanent magnet with control electromagnets and the newly developed electromagnet control system that can eliminate power collecting devices from the electromagnetic suspension system are described. >
158 citations
TL;DR: An experimental position-measuring system has been built and tested, and it demonstrated the ability of this technique to function as a key element in a navigation system for autonomous vehicles.
Abstract: A method for navigating autonomous vehicles is presented. Based on the three-point problem from land surveying, this navigational technique makes use of angular measurements between fixed beacon pairs. Extremely accurate position information can be obtained over a large area with simple trigonometric or analytic geometry calculations. Typical worst-case errors are of the order of 10 cm throughout a 2500 m/sup 2/ workspace. An experimental position-measuring system has been built and tested, and it demonstrated the ability of this technique to function as a key element in a navigation system for autonomous vehicles. >
130 citations
TL;DR: A mathematical model of the dynamics of Rayleigh fading is used to explore the optimum duration of data packets, and the optimum packets are considerably shorter than the 125-B packets customarily used in terrestrial and satellite systems.
Abstract: Since in mobile radio Rayleigh fading poses the main threat to accurate data transmission, a mathematical model of the dynamics of Rayleigh fading is used to explore the optimum duration of data packets. The performance criterion is the rate of information transfer through the mobile radio channel. In addition to packet size, the information rate depends on: the speed of the mobile terminal, the channel bit rate, the size of the packet header, and the fade margin of the modulation and coding techniques. In particular, attention is focused on line rates of 16 kb/s and 256 kb/s (which are representative of the rates proposed for digital mobile radio systems in North America and Europe, respectively). At 16 kb/s, the optimum packet size is approximately 17 B (8.5-ms duration). At 256 kb/s, maximum throughput occurs when the packet contains about 48 B (1.5-ms duration). The precise optimum depends on vehicle speed, header size, and fade margin. The optimum packets are considerably shorter than the 125-B packets customarily used in terrestrial and satellite systems. >
93 citations
TL;DR: It is shown that the WADS vehicle detection algorithm becomes more reliable if the vehicle detection threshold includes a term depending on actual road intensity, and an algorithm that would permit vehicle tracking for distances up to 120 m using available charge-coupled-device (CCD) cameras is proposed.
Abstract: Research efforts have been made or are in progress on the application of machine vision to traffic monitoring and control. Of all the proposed systems, the wide-area detection system (WADS) appears to be the most reliable. However, limited field tests indicate that some malfunctions exist. Among these are false vehicle detection caused by sudden changes in road illumination and also by shadows or glare on the road produced by automobiles in adjacent lanes. After a brief review of WADS characteristics and problems, algorithm improvements to alleviate these problems are proposed. It is shown that the WADS vehicle detection algorithm becomes more reliable if the vehicle detection threshold includes a term depending on actual road intensity. Finally, an algorithm that would permit vehicle tracking for distances up to 120 m using available charge-coupled-device (CCD) cameras is proposed. >
72 citations
TL;DR: An electromagnetic suspension system has been developed that cuts off electric power-collecting devices from a magnetically levitated vehicle as mentioned in this paper, which makes it possible to transport materials with no mechanical contact at all between the vehicle and ground facilities.
Abstract: An electromagnetic suspension system has been developed that cuts off electric power-collecting devices from a magnetically levitated vehicle. This system makes it possible to transport materials with no mechanical contact at all between the vehicle and ground facilities. A control system for linear induction motors used in the magnetically levitated carrier system is described. The system was developed to transport materials in an environment which must be kept free from even microscopic dust motes and trivial noise. The linear induction motor control method used for positioning a vehicle at the station is described along with several kinds of switches without any mechanical motion in the ground facilities. A supervisory control system for the magnetically levitated carrier system is also discussed. >
41 citations
TL;DR: An approximate analysis of the stability of a slotted ALOHA system with capture effect is developed using catastrophe theory in which the effects of system and user parameters on the stability are characterized by the cusp catastrophe.
Abstract: The stability of a slotted ALOHA system with capture effect is investigated under a general communication environment where terminals are divided into two groups (low-power and high-power) and the capture effect is modeled by capture probabilities. An approximate analysis is developed using catastrophe theory in which the effects of system and user parameters on the stability are characterized by the cusp catastrophe. In particular, the authors focus on the low-power group, since it must bear the strain under the capture effect. The stability conditions of the two groups are given explicitly by bifurcation sets. >
37 citations
TL;DR: In this paper, computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel, and it is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel.
Abstract: Computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel. Unfiltered 2-, 4-, and 8-PSK and 16-QAM with a rectangular signaling pulse are compared first, followed by 4- and 16-QAM with a raised-cosine Nyquist pulse. The bit error rate performances averaged over fading samples under the influence of the intersymbol interference caused by delay spread are compared for modulations of different levels. It is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel. Both the spectral and the power efficiencies can be enhanced using Nyquist signaling pulses. >
32 citations
TL;DR: In this article, a stochastic model for the cylinder pressure process and the dynamics of the internal combustion engine is proposed, and the deterministic model and the stochastastic representation are tied together in a Kalman filter model.
Abstract: Some of the research problems pertaining to cyclic combustion variability are reformulated from a perspective markedly different from the fluid dynamic and thermodynamic models which traditionally characterize this research: a system viewpoint is embraced to construct a stochastic model for the cylinder pressure process and the dynamics of the internal combustion engine. A deterministic model for the dynamics of the engine is briefly described, and a stochastic model is proposed for the cylinder pressure process. The deterministic model and the stochastic representation are tied together in a Kalman filter model. Experimental results that validate the models are discussed. >
TL;DR: Symmetric DPSK outperforms conventional DPSK in most cases and was particularly noted when the time delay between the specular and diffused signal components was taken into account.
Abstract: An expression is derived for the error probability of M-ary offset differential phase-shift keying (DPSK) with the differential phase detector and narrowband receiver filter in the satellite mobile (Rician) channel, which includes as special cases the Gaussian and land mobile (Rayleigh) channels. The error probability is computed as a function of various system parameters for M=2, 4, and 8 symbols and third-order Butterworth receiver filter. Both symmetric and conventional DPSK systems are considered. The optimal normalized bandwidth is close to 1.0. Symmetric and conventional DPSK differ significantly in error probability only for M=2 and in the lower range filter bandwidth. In most cases, symmetric DPSK outperforms conventional DPSK. This was particularly noted when the time delay between the specular and diffused signal components was taken into account. >
TL;DR: Results indicate that the system designer can trade off spectral efficiency by using a double-error-correction code with channel interleaving and SFH to make the SFH/BC system perform as well as a system using two-branch antenna diversity.
Abstract: The authors compare the performance of a TDMA (time-division multiple-access) system plan using two-branch antenna diversity to other TDMA system plans using channel and time slot interleaving and slow frequency hopping/burst error correction (SFH/BC). Results indicate that the system designer can trade off spectral efficiency by using a double-error-correction code with channel interleaving and SFH to make the SFH/BC system perform as well as a system using two-branch antenna diversity. For a system with interleaving and SFH, the number of hopping frequencies required depends on the code used and on the design of the demodulator (i.e. hard versus soft decisions). As long as the code is chosen such that the system can handle the complete failure of one of the hopping frequencies, it can achieve about the same outage probability or speech block dropping rate as a system using antenna diversity. However, this equality is exacted at the price of spectral efficiency. In this instance, the decrease in required signal-to-interference ratio (S/I) is not enough to offset the decrease in the number of available channel sets caused by the wider bandwidth required to transmit the lower rate code. Other coding plans must be evaluated for relative spectral efficiency. >
TL;DR: Repetition code, diversity and single error correcting codes are examined for use with binary modulation techniques over the faded mobile channel and optimum repetitions are found.
Abstract: Repetition, diversity, and single-error-correcting codes are examined for use with binary modulation techniques over a mobile communication fading channel. Both bit-error performance and bandwidth efficiency are considered for phase-shift keyed, differential phase-shift keyed, and frequency-shift keyed modulations. The error-correction capability of repetition coding is considered, and optimum repetition is found. M-tuple diversity with maximum-ratio-combining is then compared with repetition coding both with a single-error-correcting code and without coding. It is found that a minimum of a 10 dB signal-to-noise power ratio is required for an improved performance with repetition code or diversity. The repetition code is about 3 dB inferior to optimal diversity. An optimized design of moderate complexity and bandwidth expansion can be reached with twofold diversity and three repetitions as an inner layer of coding concatenated with an outer single-error-correcting code. >
TL;DR: The effects on performance of magnetostrictive torque sensors due to nonlinear properties of magnetic materials are analyzed and a solution for the nonlinear problem is described.
Abstract: The effects on performance of magnetostrictive torque sensors due to nonlinear properties of magnetic materials are analyzed. A solution for the nonlinear problem is described. For constant magnetomotive force (constant current) excitation, nonlinear effects dramatically reduce the predicted output signal of the sensor from that computed using linear models. Saturation and the subsequent fall-off of a sensor signal as excitation current is increased are predicted and agree well with experimental results. The sensor signal continually increases with the increase of excitation frequency. As is shown, this gain must be balanced against growing problems of sensor signal-to-noise ratio, surface-localized noise, and requirements for higher-power/higher-voltage excitation sources. >
TL;DR: In this paper, a new extremely low-loss SAW filter (loss of as low as 1.2-2.0 dB at 600 MHz) has been developed for a SAW antenna duplexer.
Abstract: Various applications of surface-acoustic-wave (SAW) technologies are investigated in which the use of SAW devices would result in reduced volume and weight for VHF/UHF radio communication transceivers. Attention is given to improved insertion loss and power requirements reported for SAW filters. In particular, by analyzing the loss mechanisms of a previously developed high-performance SAW filter for mobile telephones, a new extremely low-loss SAW filter (loss of as low as 1.2-2.0 dB at 600 MHz) has been developed. The results of fundamental experiments for a SAW antenna duplexer using this new SAW filter as the transmitter filter with a semicoaxial filter as the receiver filter at 800 MHz are presented. >
TL;DR: Formulas are derived for the error probability of M-ary frequency shift keying (FSK) with differential phase detection in a satellite mobile channel that is composed of a specular signal, a diffuse signal, and white Gaussian noise.
Abstract: Formulas are derived for the error probability of M-ary frequency shift keying (FSK) with differential phase detection in a satellite mobile channel. The received signal in this channel is composed of a specular signal, a diffuse signal, and white Gaussian noise; hence, the composite signal is fading and has a Rician envelope. The error probability is shown to depend on the following system parameters: (1) the signal-to-noise ratio; (2) the ratio of powers in the specular and diffuse signal components; (3) the normalized frequency deviation; (4) the normalized Doppler frequency; (5) the maximum normalized Doppler frequency; (6) the correlation function of the diffuse component, which depends on the normalized Doppler frequency and the type of the antenna; (7) the number of symbols; and (8) the normalized time delay between the specular and diffuse component (t/sub d//T) where 1/T is the symbol rate. Except for T/sub d//T, all normalized parameters are the ratios of the parameter value and symbol rate. The Doppler frequency depends on the velocity of the vehicle and the carrier frequency. The error probability is computed as a function of the various parameters. The bit error probability is plotted as a function of signal-to-noise ratio per bit and other system parameters. >
TL;DR: An analysis of noncoherent detection of constant-envelope digital partial-response continuous-phase modulation in fast Rayleigh fading that characterizes land mobile radio channels finds closed-form expressions for the probability of error are derived for limiter discriminator detection, and both 1- and 2-bit differential detection.
Abstract: An analysis is presented of noncoherent detection of constant-envelope digital partial-response continuous-phase modulation (PRCPM) in fast Rayleigh fading that characterizes land mobile radio channels. Closed-form expressions for the probability of error are derived for limiter discriminator detection, and both 1- and 2-bit differential detection. Numerical results are presented for cases of practical interest to researchers and designers of land mobile radio systems. The expressions derived for the probability of error are general and can be used for all PRCPM schemes. >
TL;DR: An efficient method of sensor diagnosis in electronically controlled IC engines is demonstrated and the resulting diagnostic systems can be implemented in on-board digital computers of passenger vehicles using a pair of failure-sensitive filters.
Abstract: An efficient method of sensor diagnosis in electronically controlled IC engines is demonstrated. The approach taken is based on the failure detection and isolation (FDI) theory, and the resulting diagnostic systems can be implemented in on-board digital computers of passenger vehicles. The proposed diagnostic system, referred to as the binary phase detection filter (BPDF), uses a pair of failure-sensitive filters. Based on the reference model of an internal combustion engine, BPDF not only isolates the failed sensor, but also estimates the associated amount of failure. A wide variety of sensor failures, including soft partial types (e.g. calibration or bias drift), can be detected using BPDF. >
TL;DR: In this paper, a novel DAMA design is presented that ameliorates this problem by using the block-calls-queued service discipline, batched processing of several calls by the network dispatcher, and pipelined messaging for channel setup verification.
Abstract: Conventional DAMA (demand-assignment multiple access) designs process mobile radio calls in much the same way as mobile telephone calls. In mobile radio dispatch networks, where the dispatcher is often the resource bottleneck, these designs result in the inefficient use of satellite channels. A novel DAMA design is presented that ameliorates this problem by using the block-calls-queued service discipline, batched processing of several calls by the network dispatcher, and pipelined messaging for channel setup verification. Analysis shows that the proposed design offers advantages in satellite channel utilization and DAMA signaling overhead compared to previous designs. As space segment resources are expected to be very expensive in the mobile satellite systems networks under development, the proposed procedures could result in significant cost savings. >
TL;DR: A method for selecting a forward error correcting (FEC) code for the Advanced Train Control System (ATCS) radio data link and the application of the ATCS and the performance issues involved in selecting a code are detailed.
Abstract: A method for selecting a forward error correcting (FEC) code for the Advanced Train Control System (ATCS) radio data link is described. The application of the ATCS and the performance issues involved in selecting a code are detailed. On the basis of the data, the ATCS Communications Component Specification Drafting Committee chose the Reed-Solomon 2 code as the FEC code for ATCS. This choice was based on best overall performance in providing throughput and good performance relative to other codes on other metrics. >
TL;DR: It is concluded that this digital simulator for an automotive multiplexing system is a useful design/development tool due to its flexibility in testing alternative design strategies.
Abstract: A digital simulator for an automotive multiplexing system has been developed and tested. The basic architecture and logical flow and block diagrams are described. Some results of the simulation are given. The contention scheme was found to work successfully in the simulator, and the outputs were found to be ordered in the same manner as expected by the requirements of the protocol. The network traffic and its effect on the latency index has also been studied. The simulator has provisions to incorporate alternate message retrial schemes and to test alternative strategies of the tasks. It is flexible enough so that the effects of noise and other nonideal phenomena can be incorporated. It is concluded that this simulator is a useful design/development tool due to its flexibility in testing alternative design strategies. >
TL;DR: In this paper, the application of SPICE to a rail traction network for the simulation of electromagnetic noise emissions and cab signal interference in a DC-fed rail rapid transit system is described.
Abstract: The application of SPICE to a rail traction network for the simulation of electromagnetic noise emissions and cab signal interference in a DC-fed rail rapid transit system is described. The predictions are validated by a laboratory experiment in which real-time signals are generated by computer using a programmable read-only memory (PROM) lookup table. The simulator can be used to study interference in rail rapid transit systems at low and audio frequencies produced by the combined effects of conduction, magnetic induction, and electric induction. Its use permits the influence of such variables as train position, power demand, and traction duty cycle on interference in cab signaling, track circuit, and other critical noise receivers to be determined. The effect of varying simulation parameters-for example, track impedance-can also be evaluated and parameters strongly influencing the degree of interference identified. The method can also be used to evaluate interference characteristics of new propulsion drives. >
TL;DR: In this paper, the issue of reducing the cost of phased array vehicle antennas through the use of a lens feeding arrangement instead of phase shifters at each element is addressed, and a method for reducing the required number of phase shiftters by using an R-KR lens feed network is outlined.
Abstract: The issue of reducing the cost of phased array vehicle antennas through the use of a lens feeding arrangement instead of phase shifters at each element is addressed. In particular, the economic viability of a mobile satellite system (MSAT) is largely dependent on the efficient use of the allocated scarce spectrum and orbit as well as the satellite power. The type of vehicle antenna used will play a critical role in achieving this efficiency. A standard design approach for an electronically steered array uses phase shifters at each element to provide beam steering. A method for reducing the required number of phase shifters by using an R-KR lens feed network is outlined. The authors briefly discuss the phase shifter approach to beam steering, examine various lens feed techniques, and describe the R-KR lens approach. The lens feed network architecture is examined, a computer model for simulation of the array is presented, and the results of analysis of a suggested design for the MSAT application are given. In addition, satellite acquisition and tracking considerations are investigated. >
TL;DR: It is shown that ICMA-DR is suitable for the packet radio multiple-access scheme, especially in the case where fading packet error occurs frequently and ordered traffic is heavy.
Abstract: A population of terminals communicating with a central station over a packet-switched multiple access radio channel is investigated with regard to multiple access control schemes. The authors describe the ICMA-DR, which is an advanced idle-signal casting multiple access (ICMA) scheme characterized by data slot reservation. This improved central controlled multiple-access scheme for packet transmission in terrestrial radio communications is evaluated in terms of throughput traffic, throughput delay characteristics, and handling capacity. It is shown that the throughput characteristics of ICMA-DR are superior than those of ICMA or slotted ALOHA when a packet for data slot reservation is relatively short in comparison to that for upward data. Thus, it is shown that ICMA-DR is suitable for the packet radio multiple-access scheme, especially in the case where fading packet error occurs frequently and ordered traffic is heavy. The ICMA-DR scheme has been utilized for the access control channel of NTT's new 800-MHz-band high-capacity land mobile communication system since the Spring of 1988. >
TL;DR: In this article, the phase statistics of the narrowband mobile channel in an urban environment are measured and compared with theory, and the phase derivative follows closely a student's t-distribution with the Doppler spread as the determining parameter.
Abstract: The phase statistics of the narrowband mobile channel in an urban environment are measured and compared with theory. The phase derivative (the random FM frequency) follows closely a student's t-distribution with the Doppler spread as the determining parameter. Moving averages taken over 5-m lengths indicate the nonstationarity of the channel and the gradual shift between groups of reflectors. In a few cases, a two-ray model is effective in explaining the periodicities measured. Correlations between the various parameters are given. >
TL;DR: A forward-looking, relatively inexpensive, onboard automotive radar called cradar, that senses the highway environment of the vehicle is described, that measures the range, range rate, and bearing angle of roadway targets.
Abstract: A forward-looking, relatively inexpensive, onboard automotive radar called cradar, that senses the highway environment of the vehicle is described. The radar measures the range, range rate, and bearing angle of roadway targets. The radar has a proposed angular spread of approximately 17 degrees and a range of 5-100 m. It uses a unique front end, designed to provide maximum information from a single small-aperture antenna. The antenna is time shared between three different driving waveguides modes, modes with quite different radiation patterns. Return signals are separated by mode and continuously parallel processed. Individual mode returns yield target signature characteristics, range, closing speed, and some bearing information. Cross-mode returns yield target bearing and hence transverse speed. It has some multiple and extended-target capability both on straightaways and on curves. Foreseen uses of the system include increasing safety by providing driver information, a smart cruise control for driver convenience, and direct longitudinal control of the vehicle on automated highways. These uses may help to increase the traffic-carrying capacity of existing highways. >
TL;DR: In this paper, a Kalman filter was used to derive a best fit for a particular propagation model to the measured data, which was then corrected with an environmental propagation loss term that takes into account the various environmental effects near the mobile unit.
Abstract: A method is presented to derive a propagation model to predict the received median signal voltage for an 800-MHz mobile radio system. Results are given of an investigation into the performance of a particular model that was derived using this method. The method uses a Kalman filter that uses propagation measurements to derive a best fit for a particular propagation model to the measured data. The model that was derived is based on propagation measurements made in the State of Florida. The new propagation model uses a plane-Earth propagation model that is corrected with an environmental propagation loss term that takes into account the various environmental effects near the mobile unit. The parameters in the environmental propagation loss model were determined using a Kalman filter that computes minimum mean square estimates of the parameters using measured propagation data. The environmental propagation loss term accounts for the effects of Earth diffraction, hills, valleys, urban and suburban areas, bare and grass-covered ground, bushes, trees, swamps, and propagation over fresh and salt water. It was found that, with the 800-MHz propagation model derived with this method, the prediction error for the received median signal voltage had a standard deviation of 5.08 dB. >
TL;DR: A spectrally efficient quadrature amplitude modulation (QAM) scheme with a simple nonlinearly switched filter is shown to provide a signaling waveform that is free from both intersymbol interference and zero-crossing timing jitter in a flat-fading channel.
Abstract: A spectrally efficient quadrature amplitude modulation (QAM) scheme with a simple nonlinearly switched filter is shown to provide a signaling waveform that is free from both intersymbol interference and zero-crossing timing jitter in a flat-fading channel. This modulation with coherent detection is evaluated by a computer simulation in a frequency-selective fading channel. Timing offset between in-phase and quadrature rails is varied. The effects of receiver filter bandwidths are also studied. It is found that this modulation is resistant to delay spread with moderate spectral efficiency and low complexity in a portable radio system, as compared to other spectrally efficient modulations. >
TL;DR: It is shown that the MRC can attain about a 1-dB larger diversity gain than the selection combiner (SC) when two-branch diversity is used, and the degradations of two-BRanch diversity improvement caused by the differences between demodulator sensitivities and between received signal envelope detector gains are evaluated.
Abstract: Postdetection diversity is attractive for narrowband digital FM signal reception because the cophasing function, which may be difficult to realize in a fast Rayleigh fading environment, is not required. The combining scheme evaluated here is to weight each frequency demodulator (FD) output in proportion to the nu th power of the received signal envelope of that branch. Maximum diversity improvement can be obtained with nu =2 (this combiner is referred to as a postdetection maximal ratio chamber (MRC)). Experimental results are presented on postdetection diversity reception in the Gaussian minimum shift keying (GMSK) signal transmission system. Diversity combining and FD-decision algorithms (decision feedback equalizer (DFE) and maximum-likelihood sequence estimator (MLSE)) are performed by software on a computer using the data of the sampled FD output and received signal envelope obtained from a laboratory transmission system. It is shown that the MRC can attain about a 1-dB larger diversity gain than the selection combiner (SC) when two-branch diversity is used. The degradations of two-branch diversity improvement caused by the differences between demodulator sensitivities and between received signal envelope detector gains are evaluated. >