Land mobile radio (LMR) systems are used for communication by public safety and other government and commercial organizations. LMR systems offer mission-critical or even life-critical service in the day-to-day activities of such organizations. Traditionally, a variety of different LMR systems have been deployed by different organizations, leading to a lack of radio interoperability. A voice application that connects LMR systems via a packet-switched network is called an LMR Voice over IP (LMRVoIP) system and is a potential solution to the interoperability problem. LMRVoIP systems are time critical, i.e., are delay and jitter sensitive. Transmission of LMRVoIP traffic in a congested packet-switched network with no quality of service (QoS) or priority mechanisms in place could lead to high delays and extreme variations in delay, i.e., high jitter, thus resulting in poor application performance. LMRVoIP systems may also have performance issues with the use of virtual private networks (VPNs). To the best of our knowledge, there has been no prior thorough investigation of the performance of an LMRVoIP system with different queuing schemes for QoS and with the use of VPN. In this thesis, we investigate the performance of an LMRVoIP system with different queuing schemes and with the use of VPN. An experimental test bed was created to evaluate four QoS queuing schemes: first-in first-out queuing (FIFO), priority queuing (PQ), weighted fair queuing (WFQ), and class-based weighted fair queuing (CBWFQ). Quantitative results were obtained for voice application throughput, delay, jitter, and signaling overhead. Results show that, compared to a baseline case with no background traffic, LMRVoIP traffic suffers when carried over links with heavy contention from other traffic sources when FIFO queuing is used. There is significant packet loss for voice and control traffic and jitter increases. FIFO queuing provides no QoS and, therefore, should not be used for critical applications where the network may be congested. The situation can be greatly improved by using one of the other queuing schemes, PQ, WFQ, or CBWFQ, which perform almost equally well with one voice flow. Although PQ has the best overall performance, it tends to starve the background traffic. CBWFQ was found to have some performance benefits over WFQ in most cases and, thus, is a good candidate for deployment. The LMRVoIP application was also tested using a VPN, which led to a modest increase in latency and bandwidth utilization, but was found to perform well. / Master of Science

Modern Land Mobile Radio has the potential for large growth in the near future. Current regulations have set the stage for a required transition to more spectrally efficient technologies. While several organizations are working to ease this transition, there still remain many details and feature sets which the end user must decide amongst and often there is no clear dividing line between these choices. This thesis provides a high-level view of the distinguishing components in modern LMR systems. Discussions related to trunked channel allocation, coverage, costs, security, and other capabilities are given. The application to and effect on everyday users is also considered. Several quantitative examples are provided to assist the end-user in determining when a solution is viable. The discussion and analysis included reaffirm that LMR design is complex and wide-ranging. Ultimately, the designer must evaluate needs and technologies to provide a course of action which is optimum and justifiable. / Master of Science

by Wong Chun Kau, Jolly. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 84-88). / ABSTRACT --- p.1 / ACKNOWLEDGEMENT --- p.3 / Chapter 1. --- INTRODUCTION --- p.7 / Chapter 1.1 --- Land Mobile Radio (LMR) Communications / Chapter 1.2 --- Paramilitary Communications Security / Chapter 1.3 --- Voice Scrambling Methods / Chapter 1.4 --- Digital Voice Encryption / Chapter 1.5 --- Digital Secure LMR / Chapter 2. --- DESIGN GOALS --- p.20 / Chapter 2.1 --- System Concept and Configuration / Chapter 2.2 --- Operational Requirements / Chapter 2.2.1 --- Operating conditions / Chapter 2.2.2 --- Intelligibility and speech quality / Chapter 2.2.3 --- Field coverage and transmission delay / Chapter 2.2.4 --- Reliability and maintenance / Chapter 2.3 --- Functional Requirements / Chapter 2.3.1 --- Major system features / Chapter 2.3.2 --- Cryptographic features / Chapter 2.3.3 --- Phone patch facility / Chapter 2.3.4 --- Mobile data capability / Chapter 2.4 --- Bandwidth Requirements / Chapter 2.5 --- Bit Error Rate Requirements / Chapter 3. --- VOICE CODERS --- p.38 / Chapter 3.1 --- Digital Speech Coding Methods / Chapter 3.1.1 --- Waveform coding / Chapter 3.1.2 --- Linear predictive coding / Chapter 3.1.3 --- Sub-band coding / Chapter 3.1.4 --- Vocoders / Chapter 3.2 --- Performance Evaluation / Chapter 4. --- CRYPTOGRAPHIC CONCERNS --- p.52 / Chapter 4.1 --- Basic Concepts and Cryptoanalysis / Chapter 4.2 --- Digital Encryption Techniques / Chapter 4.3 --- Crypto Synchronization / Chapter 4.3.1 --- Auto synchronization / Chapter 4.3.2 --- Initial synchronization / Chapter 4.3.3 --- Continuous synchronization / Chapter 4.3.4 --- Hybrid synchronization / Chapter 5. --- DIGITAL MODULATION --- p.63 / Chapter 5.1 --- Narrowband Channel Requirements / Chapter 5.2 --- Narrowband Digital FM / Chapter 5.3 --- Performance Evaluation / Chapter 6. --- SYSTEM IMPLEMENTATION --- p.71 / Chapter 6.1 --- Potential EMC Problems / Chapter 6.2 --- Frequency Planning / Chapter 6.3 --- Key Management / Chapter 6.4 --- Potential Electromagnetic Compatibility (EMC) Problems / Chapter 7. --- CONCLUSION --- p.80 / LIST OF ILLUSTRATIONS --- p.81 / REFERENCES --- p.82 / APPENDICES --- p.89 / Chapter I. --- Path Propagation Loss(L) Vs Distance (d) / Chapter II. --- Speech Quality Assessment Tests performed / by Special Duties Unit (SDU)

[pt] Este trabalho apresenta os resultados da investigação da utilização da Técnica de Sondagem em Frequência na estimação de dispersividade Espaço-Temporal do Canal Rádio Móvel. Modifcações na técnica clássica de varredura em frequência foram implementadas: um conjunto de antenas denominado array foi construído e calibrado e um algoritmo de pós-processamento do sinal medido foi testado. Foi realizada uma campanha de medidas em três ambientes diferentes para averiguar a aplicabilidade do conjunto. Foram obtidos bons resultados, demonstrando a efciência da metodologia de medidas aplicada. / [en] This work presents the results of an investigation of the use of the Frequency Sounding technique in Mobile Radio Channel`s Space-Time Dispersion characterization. Hence, some changes in the classical Frequency Sounding Technique were employed: a set of antennas was built and calibrated and an algorithm for signal pos processing was tested. A measurement campaign was carried out on three different environments to test the applicability of the set as a whole. Very good results showed the efficiency of the measurements methodology applied.

<p>Prediction of the rapidly fading envelope of a mobile radio channel enables a number of capacity improving techniques like fast resource allocation and fast link adaptation. This thesis deals with linear prediction of the complex impulse response of a channel and unbiased quadratic prediction of the power. The design and performance of these predictors depend heavily on the correlation properties of the channel. Models for a channelwhere the multipath is caused by clusters of scatterers are studied. The correlation for the contribution from a cluster can be approximated as a damped complex sinusoid. A suitable model for the dynamics of the channel is an ARMA-process. This motivates the use of linear predictors.</p><p>A limiting factor in the prediction are the estimation errors on the observed channels. This estimation error, caused by measurement noise and time variation, is analyzed for a block based least squares algorithm which operates on a Jakes channel model. Efficient noise reduction on the estimated channel impulse responses can be obtained with Wienersmoothers that are based on simple models for the dynamics of the channel combined with estimates of the variance of the estimation error.</p><p>Power prediction that is based on the squared magnitude of linear prediction of the taps will be biased. Hence, a bias compensated power predictor is proposed and the optimal prediction coefficients are derived for the Rayleigh fading channel. The corresponding probability density functions for the predicted power are also derived. A performance evaluation of the prediction algorithm is carried out on measured broadband mobile radio channels. The performance is highly dependent on the variance of the estimation error and the dynamics of the individual taps.</p>

Prediction of the rapidly fading envelope of a mobile radio channel enables a number of capacity improving techniques like fast resource allocation and fast link adaptation. This thesis deals with linear prediction of the complex impulse response of a channel and unbiased quadratic prediction of the power. The design and performance of these predictors depend heavily on the correlation properties of the channel. Models for a channelwhere the multipath is caused by clusters of scatterers are studied. The correlation for the contribution from a cluster can be approximated as a damped complex sinusoid. A suitable model for the dynamics of the channel is an ARMA-process. This motivates the use of linear predictors. A limiting factor in the prediction are the estimation errors on the observed channels. This estimation error, caused by measurement noise and time variation, is analyzed for a block based least squares algorithm which operates on a Jakes channel model. Efficient noise reduction on the estimated channel impulse responses can be obtained with Wienersmoothers that are based on simple models for the dynamics of the channel combined with estimates of the variance of the estimation error. Power prediction that is based on the squared magnitude of linear prediction of the taps will be biased. Hence, a bias compensated power predictor is proposed and the optimal prediction coefficients are derived for the Rayleigh fading channel. The corresponding probability density functions for the predicted power are also derived. A performance evaluation of the prediction algorithm is carried out on measured broadband mobile radio channels. The performance is highly dependent on the variance of the estimation error and the dynamics of the individual taps.

The goal of software-defined radio (SDR) is to move the processing of radio signals from the analog domain to the digital domain — to use digital microchips instead of analog circuit components. Until faster, higher-precision analog-to-digital (ADCs) and digital-to-analog converters (DACs) become affordable, however, some analog signal processing will be necessary. We still need to convert high-radio frequency (RF) signals that we receive to low intermediate-frequency (IF) or baseband (centered on zero Hz) signals in order for ADCs to sample them and feed them into microchips for processing. The reverse is true when we transmit. Amplification is also needed on the receive side to fully utilize the dynamic range of the ADC and power amplification is needed on the transmit side to increase the power output from the DAC for transmission. Analog filtering is also needed to avoid saturating the ADC or to filter out interference when receiving and to avoid transmitting spurs. The analog frequency conversion, amplification and filtering section of a radio is called the RF front end. This thesis describes work on a new RF front end daughterboard for the Universal Software Radio Peripheral, or USRP. The USRP is a software-radio hardware platform designed to be used with the GNU Radio software radio software package. Using the Motorola RFIC4 chip, the new daughterboard receives RF signals, converts them to baseband and does analog filtering and amplification before feeding the signal into the USRP for processing. The chip also takes transmit signals from the USRP, converts them from baseband to RF and amplifies and filters them. The board was designed and laid out by Randall Nealy. I wrote the software driver for GNU Radio. The driver defines the interface between the USRP and the RFIC chip, controls the physical settings, and calculates and sets the hundreds of variables necessary to operate this extremely complex chip correctly. It allows plug-and-play compatibility with the current USRP daughterboards and supplies additional functions not available in any other daughterboard. / Master of Science

In this thesis a new approach for characterisation of digital mobile radio channels is investigated. The new approach is based on recognition of the fact that while the fading which is characteristic of the mobile radio channel is very rapid, the processes underlying this fading may vary much more slowly. The comparative stability of these underlying processes has not been exploited in system designs to date. Channel models are proposed which take account of the stability of the channel. Estimators for the parameters of the models are proposed, and their performance is analysed theoretically and by simulation and measurement. Bounds are derived for the extent to which the mobile channel can be predicted, and the critical factors which define these bounds are identified. Two main applications arise for these channel models. The first is the possibility of prediction of the overall system performance. This may be used to avoid channel fading (for instance by change of frequency), or compensate for it (by change of the signal rate or by power control). The second application is in channel equalisation. An equaliser based on a model which has parameters varying only very slowly can offer improved performance especially in the case of channels which appear to be varying so rapidly that the convergence rate of an equaliser based on the conventional model is not adequate. The first of these applications is explored, and a relationship is derived between the channel impulse response and the performance of a broadband system.

De nombreuses applications de communication numériques font face à des canaux de transmission sélectifs en temps et en fréquence que nous pouvons assimiler à des systèmes linéaires variants dans le temps. À travers ces travaux de thèse, nous montrons que les modulations multiporteuses suréchantillonnées constituent une technique de transmission adaptée à ce type d'environnement. Cependant, la complexité algorithmique des émetteurs-récepteurs présentent un frein majeur à leur adoption. Fort de ce constat, nous nous intéressons à la sous-famille des modulations multiporteuses suréchantillonnées à filtres courts (WCP-OFDM), dont la complexité algorithmique est comparable à celle de l'OFDM avec préfixe cyclique. Après avoir exprimé les conditions de reconstructions parfaites, nous développons des égaliseurs de faible complexité et étudions la problématique du rapport de puissance crête sur puissance moyenne du signal en sortie d'émetteur. Enfin, nous analysons les performances de ces modulations à travers plusieurs scénarios de propagation radiomobiles. Les résultats de simulation confirment l'intérêt du WCP-OFDM, associé à des filtres prototypes bien localisés en temps et en fréquence pour faire face aux canaux doublement sélectifs. / Many digital communication applications are facing time and frequency selective channels that can be modelled by linear time-variant systems. Through this thesis work, we show that oversampled multicarrier modulations provide a suitable transmission technique for such an environment. However, the complexity of the transmitter-receiver remains a major obstacle for their adoption. Based on this observation, we focus on the sub-family of oversampled multicarrier modulation with short filters (WCP-OFDM), whose complexity is similar to cylic prefix OFDM. After introducing the perfect reconstruction conditions, we develop low-complexity equalizers and we study the peak-to-average power ratio issue at the output of the transmitter. Finally, we evaluate the performances of these moduations over several mobile radio propagation scenarios. Simulation results confirm the benefits of WCP-OFDM, with time-frequency localized prototypes filters, over doubly selective channels.

[pt] Este trabalho apresenta os resultados de uma sondagem em frequencia do canal indoor de faixa larga em 1,8GHz, onde foram testados alguns ambientes na tentativa de simular a mobilidade de um usuário. A técnica de sondagem é baseada na técnica clássica de varredura em frequencia, onde foi implementado um link óptico ao invés de cabos coaxiais, para permitir um maior range de medidas. A completa análise de dispersão temporal em pequena e larga escala foi extraída de medidas da resposta impulsiva, como retardo médio, espalhamento rms de retardos, banda de coerência e suas variações com a mobilidade. Do conjunto de análises efetuadas dois resultados obtiveram destaque: perfis de potência de retardo com a distância , resultando em uma boa representação dos principais espalhadores do ambiente; e a validação de um limitante teórico da relação entre a banda de coerência e o espalhamento rms de retardos, recentemente proposto por outro autor. Este trabalho apresenta os resultados de uma sondagem em frequencia do canal indoor de faixa larga em 1,8GHz, onde foram testados alguns ambientes na tentativa de simular a mobilidade de um usuário. A técnica de sondagem é baseada na técnica clássica de varredura em frequencia, onde foi implementado um link óptico ao invés de cabos coaxiais, para permitir um maior range de medidas. A completa análise de dispersão temporal em pequena e larga escala foi extraída de medidas da resposta impulsiva, como retardo médio, espalhamento rms de retardos, banda de coerência e suas variações com a mobilidade. Do conjunto de análises efetuadas dois resultados obtiveram destaque: perfis de potência de retardo com a distância , resultando em uma boa representação dos principais espalhadores do ambiente; e a validação de um limitante teórico da relação entre a banda de coerência e o espalhamento rms de retardos, recentemente proposto por outro autor. / [en] The results of a 1.8 GHz indoor wide-band channel souding survey at some typical environments, trying to account for pedestrian subscriber mobility, are presented. The sounding technique has been based on the classical frequency domain one, with an optic link instead of coaxial cables provinding an extended path range. Complete small and large- scale time dispersionanalysis have been derived from the impulse responses measured, like mean delay, rms delay spread, coherence bandwidth and its variations with mobility. From the whole analysis carried out, two main results are worth remarking: the power delay profile variation with distance providing a pictorial representation of the main scattering mechanisms of the environment; and the validation of a lower bound relation between the coherence bandwidth and rms delay spread recently proposed by another author.