Design issues relevant to developing an integrated voice/datamobile radio system

The various design issues related to developing an integrated voice/data mobile radio system, including high speed digital radio frequency modulation in a mobile environment, statistics for the talkspurt/silence gap composition of speech, switching schemes for voice/data integration, encoding techniques, and voice and data traffic statistics are discussed. A performance analysis is conducted for a typical design, showing that a voice-only mobile radio system can be upgraded to an integrated voice/data system capable of carrying the full voice and data loads without requiring additional radio channels and without compromising voice performance. Data traffic is only minimally delayed (46.2 ms mean delay) for a fully loaded system     

Probability of error analysis of digital partial responsecontinuous phase modulation with two-bit differential detection andoffset receiver diversity in fast Rayleigh fading channels

The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems     

Joint detection with coherent receiver antenna diversity in CDMAmobile radio systems

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

Equalization and space diversity techniques in mobile environments

The development of high-quality digital mobile radio systems has become a major goal in the field of digital communications. The possibility of providing speech and data services free of wire constrictions in different environments is a very attractive proposition, supported by means of the personal communications network (PCN) concept. The aim of the present article is to analyze the behavior of different receiver structures for such systems in order to obtain some clues to be used in designing the next generation of mobile systems. These systems have to provide both low- and high-data-rate services (up to 1 Mb/s) and be efficient in environments where a high density of traffic is generated. Moreover, as the carrier frequencies will range between 1 and 4 GHz, and the vehicle speed can be as high as 400 km/hr (e.g., high-speed trains), large Doppler frequency values must be coped with. Under certain conditions, diversity techniques perform better than equalization techniques in typical mobile radio environments     

GMSK Modulation for Digital Mobile Radio Telephony

This paper is concerned with digital modulation for future mobile radio telephone services. First, the specific requirements on the digital modulation for mobile radio use are described. Then, premodulation Gaussian filtered minimum shift keying (GMSK) with coherent detection is proposed as an effective digital modulation for the present purpose, and its fundamental properties are clarified with the aid of machine computation. The constitution of modulator and demodulator is then discussed from the viewpoints of mobile radio applications. The superiority of this modulation is supported by some experimental test results.     

A reduced-state Viterbi receiver with prefiltering for the mobile radio channel

This paper presents a possible receiver structure for high bit rate transmission on the mobile radio channel. The receiver is based on a reduced-state Viterbi algorithm combined with decision feedback, known as Decision Feedback Sequence Estimation. A tdma concept using a training sequence for channel estimation and continuous phase modulation is assumed. For channel estimation a least squares method is studied, and an adaptive prefilter is used to improve the receiver performance on minimum phase channels. Estimates on the computational complexity of the receiver and simulation results showing the performance on a typical urban (tu) channel are presented. The results show that the prefilter improves the performance of the receiver significantly when a small number of states is used in the Viterbi algorithm. However, the computational complexity for 2 Mbit/s continuous transmission is very high.     

Bit error performance evaluation of double-differential QPSK infaded channels characterized by Gaussian plus impulsive noise andDoppler effects

A Fourier-Bessel series-based analysis that allows real-time symbol-to-symbol error performance evaluation for mobile radio direct-sequence code division multiple-access (DS-CDMA) systems is described. The technique analyzes mobile radio communication aeronautic links and generates average bit error rate (BER) and bit-to-bit patterns. Various communication systems parameters (e.g., modulation scheme, data rate, signal-to-noise ratio, and receive speed) as well as multiaccess interference (MAI) environments (i.e., Rayleigh-faded channels with Doppler frequency shift) may be specified and permit performance comparison. Additive white Gaussian (AWG) and impulsive ϵ-mixture type of noise are also considered to be present for the asynchronous and quasi-synchronous DS-CDMA configurations, with both schemes characterized by the incorporation of double-differential QPSK (DDQPSK) modulation. The obtained results demonstrate that the proposed combination in terms of multiplexing and digital modulation may be a suitable alternative solution for air-to-air and/or air-to-ground aeronautic communications for optimized BER versus signal-to-noise ratio system performance and, hence, for “best” channel capacity versus receiver complexity     

Modems for emerging digital cellular-mobile radio system

Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. In particular, theoretical performance, experimental results, principles of operation. and various architectures of π/4-QPSK (π/4-shifted coherent or differential QPSK) modems for second-generation US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the π/4-QPSK modems (emerging American and Japanese digital cellular standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot-aided (digital channel sounding) techniques are also considered for π/4-QPSK and other digital modems. More spectrally efficient modem trends for future cellular mobile (land mobile) and satellite communication system applications are also highlighted     

Decision feedback sequence estimation for continuous phasemodulation on a linear multipath channel

An approach to reduced-complexity detection of partial response continuous phase modulation (CPM) on a linear multipath channel is presented. The method, referred to as decision feedback sequence estimation (DFSE), is based on a conventional Viterbi algorithm (VA) using a reduced-state trellis combined with decision feedback (DF). By varying the number of states in the VA, the receiver structure can be changed gradually from a DF receiver to the optimal maximum-likelihood sequence estimator (MLSE). In this way different tradeoffs between performance and complexity can be obtained. Results on the receiver performance, based on minimum distance calculations and bit error rate simulations, are given for Gaussian minimum-shift keying modulation on typical mobile radio channels. It is shown that for channels with a long memory, a significant complexity reduction can be achieved at the cost of a moderate degradation in performance     

Performance evaluation of a novel M-detector for coherent receiverantenna diversity in a GSM-type mobile radio system

Powerful adaptive detectors such as the maximum-likelihood (ML) detector based on the Viterbi algorithm (VA) are required at the receivers for GSM type mobile radio systems in order to combat the effect of frequency-selective fading radio channels. The use of diversity techniques like receiver antenna diversity leads to a further improvement of the receiver performance. Hence, ML detectors for coherent receiver antenna diversity (CRAD) have attracted the attention of many authors. However, the complexity of the defector for CRAD can be considerably decreased when the VA is replaced with the M-algorithm, which is a suboptimum tree search algorithm. In the course of this paper, the M-detector is extended to CRAD in the case of maximal-ratio combining (MRC), equal-gain combining (EGC), and selection combining (SC), and its performance in GSM type mobile radio systems is studied by simulations using the radio channel models rural area (RA), typical urban (TU), and bad urban (BU) specified by COST 207. It is demonstrated that this novel M-detector for CRAD can perform similarly to the ML detector for CRAD thus being a favorable alternative     

On Multicarrier Detection and Coherent CDMA Mobile Receiver Radio Systems with Joint Antenna Diversity

The combination of code division multiple access(CDMA) and multicarrier (MC) transmission techniques,termed MC-CDMA, is considered a promising alternative toconventional DS (direct sequence)-CDMA. For this reason, recent research activities haveconcentrated on the application of MC-CDMA to mobileradio systems. In this paper an MC-CDMA concept which iswell suited for mobile radio applications is described. The described MC-CDMA concept overcomesdisadvantages of previously proposed concepts. InMC-CDMA mobile radio systems, signal reception isimpaired by time-varying multipath propagation. Theimpairments can be reduced by applying diversitytechniques. Coherent receiver antenna diversity (CRAD)is especially attractive because only the signalprocessing at the receivers must be modified. In thiscommunication, the application of CRAD in combination withjoint detection (JD) techniques to the more criticaluplink of MC-CDMA mobile radio systems is investigated.It is explained that the deployment of JD techniques for CRAD is an effective countermeasure againstthe influence of the mobile radio channel on the systemperformance. Four JD techniques for CRAD which areapplicable to MC-CDMA are presented. Their performances are studied in bad urban, typical urban, andtypical macrocellular environments. It is shown thatMC-CDMA allows a favorable performance compared to otherCDMA concepts.     

Equalization of microwave digital radio channels with a hybridacousto-optic and digital processor

Digital radio transmission systems use complex modulation schemes that require powerful signal processing techniques to correct channel distortions and to minimize bit-error rates (BERs). Combined analog and digital processors are investigated for minimizing the mean square error (MSE) of the radio receiver. The analog filters are implemented using acousto-optic (AO) processing since rapidly adaptable, inverse channel filters can be produced for either minimum or nonminimum phase channels. A specific architecture is identified and a laboratory system is tested to verify the ability of the processor to track and correct time-varying channels. Computer simulations are used to show that hybrid analog and digital equalization allows an increase in the modulation capacity of radio, relative to all digital equalization, while maintaining similar equipment signatures     

Quasi-synchronous digital trunked TETRA performance

In some private mobile radio/public access mobile radio (PMR/PAMR) applications, there is a stringent need for high-coverage locations probabilities. A spectrally efficient approach in this case is the use of several radio transmitters operating in a simulcast mode. There have been several analog mobile radio systems working in this way up to now, but less is known about the performance of digital trunked radio systems operating in simulcast mode. In this paper, predicted digital Trans-European Trunk RAdio (TETRA) system performance results operating in a quasi-synchronous mode are presented. These results were obtained by simulation of such a system under a wide range of operational conditions. A comparison is also presented with the European analog standard MPT 1327 currently in operation. It has been concluded that quasi-synchronous techniques well known in analog PMR/PAMR can also be successfully used in digital PMR/PAMR applications     

Performance of the π/4-DQPSK, GMSK, and QAM modulation schemesin mobile radio with multipath fading and nonlinearities

As mobile communications have become so indispensable, every possible effort should be spent to achieve the optimum operating conditions. In addition to the normal impairments associated with wireless communications, in general, the mobile channel suffers from particular limitations that confine the performance of a mobile radio system. Among those impairments are the bandwidth limitation, interference, and multipath fading. With the strong motivation toward portable radio and personal communication systems, power limitation has manifest itself in the picture, and, consequently, nonlinear operation of the amplifiers involved (hence, the channel) will have to be dealt with. Constant envelope modulation schemes have been used in digital mobile radio systems recently installed. The Gaussian minimum shift keying (GMSK) is employed in the Global System for Mobile (GSM) communications installed in Europe, while in the North American IS-54 system, the modulation scheme used is the π/4-DQPSK. As the quest for higher data rates has kept on increasing, multilevel modulation schemes have been proposed with their performance over nonlinear channels having been overlooked. The paper provides a comparative study, based on simulation, and tests the performance of various modulation schemes operating over a wide variety of mobile radio channel conditions. The effective throughput of all systems is also considered     

Digitized speech transmission at VHF using existing FM mobile radios

An extensive study of digitized speech transmission over existing VHF FM mobile radio sets is presented. Objective criteria expressed in terms of bit error rate (BER) are determined for the performance evaluation of analog FM radios when transmitting digital voice. These criteria are used to define the technical characteristics such as the receiver sensitivity, co-channel rejection, and adjacent channel selectivity in the case of digital FM transmission. The concept of performance measurements of existing sets in the digital mode of operation is suggested. The results of performance measurements reported here include the following: 1) radiated FM spectra, 2) bit error rate curves, 3) receiver sensitivity, 4) BER performance in the presence of analog or digital FM interference on the same or adjacent channel, 5) signal plus noise plus distortion to noise plus distortion ratio (SINAD) performance in the presence of co-channel or adjacent channel interference for both types of interfering signals, 6) co-channel rejection and adjacent channel selectivity for various combinations of the wanted and interfering signals, 7) receiver selectivity for both modes of operation, and 8) adjacent-signal selectivity for various combinations of the desired and undesired signals. Optimum values of design parameters of digital voice radio system are deduced from the obtained results. Finally, the implications of digitized speech transmission on the technical characteristics, operating range, channel reuse distance, and adjacent channel interference performance of analog FM radios are discussed.     

An All Digital Implementation of Constant Envelope: Bandwidth Efficient GMSK Modem using Advanced Digital Signal Processing Techniques

Gaussian Minimum Shift Keying (GMSK) has been the most common modulation format belonging to the class of partial response Continuous Phase Modulation (CPM) scheme. It is primarily adopted in the GSM standards (B=0.3) for land mobile radio communication systems because of its high bandwidth efficiency and constant envelope modulation characteristics. The focus of this paper is the design of the demodulator wherein we demonstrate an all digital implementation of sub-optimal synchronization techniques for a GMSK modem based on two Laurent Amplitude modulation pulse (AMP) streams approximation representing the matched filter. In this all digital implementation, we perform a joint estimation of the symbol timing and carrier offset wherein the symbol timing is performed using interpolation techniques.     

Impact of the power delay profile shape on the bit error rate inmobile radio systems

Typical power delay profiles (PDPs) are simulated using different digital modulation schemes in order to study the influence of the PDP shape on the bit error rate (BER) performance of terrestrial mobile radio communication systems. Therefore, a multitap channel model with Rayleigh and lognormal fading is proposed, which is used for a software simulation. The simulation is focused on the investigation of typical details of the PDP as peaks, slope, attenuation, and distance of a second group of waves. This yields information about the properties, which have essential effects on the BER. Two of the most frequently applied types of modulation schemes, 0.3 GMSK (coherent detection) and π/4 DQPSK, are considered     

The effect of sample timing on bit error rate performance in a multipath fading channel

Digital mobile radio often suffers from fatal effects caused by frequency-selective fading, resulting in severe bit error rate (BER) degradation. The feasibility of digital mobile radio largely depends on the multipath-distortion tolerant capability of modulation technique. The BER performance is compared among four digital modulation techniques in a frequency selective fading channel with large multipath delay spread. In particular, taking the timing fluctuation of eye patterns due to delay distortion of a fading channel into account, the effect of sample timing on BER is analyzed. The analyses have revealed that BER performance markedly depends on the choice of sample timing, and also an interesting fact that BPSK is outstanding in the multipath-distortion tolerance, if coupled with adaptive sampling, and its BER curves remain almost the same as that of frequency-flat fading as long as multipath delay difference is less than a bit interval.     

Performance evaluation of COFDM for digital audio broadcasting. I.Parametric study

This paper describes the performance of COFDM (coded orthogonal frequency division multiplexing) for digital audio broadcasting (DAB) over various multipath mobile radio channels. COFDM is a channel coding and modulation scheme which mitigates the adverse effects of fading by using wideband multicarrier modulation combined with time interleaving and a convolutional error correcting code. A guard interval is inserted at the transition between successive symbols to absorb the intersymbol interference created by the time domain spread of the mobile radio channel. The decoding process is performed using differential demodulation in conjunction with a soft decision Viterbi decoder. The COFDM evaluation is done by means of computer simulations. A parametric study of the proposed COFDM system is done in this first of a series of papers to determine the optimal system parameter values for operation at a radio frequency of 1.5 GHz. The results show that the parameter values proposed in the standard are indeed well suited for operation at 1.5 GHz. Using the set of optimal parameter values found, the COFDM performance is then evaluated in mobile radio channels typical of different geographical environments. Simulation results confirm the benefit that the system gains from frequency diversity found in the urban and hilly terrain areas     

Results on turbo-codes for speech transmission in a joint detectionCDMA mobile radio system with coherent receiver antenna diversity

Turbo-codes which are applicable to speech transmission in digital mobile radio systems are treated. Three turbo-codes of different complexity are presented. The proposed turbo-codes are suitable for the application to speech transmission in the joint detection code-division multiple access (JD-CDMA) mobile radio system with coherent receiver antenna diversity (CRAD) which are described concisely. The performance of the designed turbo-codes in terms of bit and frame error rates are shown in the case of additive white Gaussian noise (AWGN) channels, flat Rayleigh fading channels, and in the uplink of the aforementioned JD-CDMA mobile radio system