Modelling and Optimisation of GSM and UMTS Radio Access Networks

The size and complexity of mobile communication networks have increased in the last years making network management a very complicated task. GSM/EDGE Radio Access Network (GERAN) systems are in a mature state now. Thus, non-optimal performance does not come from typical network start-up problems, but, more likely, from the mismatching between traffic, network or propagation models used for network planning, and their real counterparts. Such differences cause network congestion problems both in signalling and data channels. With the aim of maximising the financial benefits on their mature networks, operators do not solve anymore congestion problems by adding new radio resources, as they usually did. Alternatively, two main strategies can be adopted, a) a better assignment of radio resources through a re-planning approach, and/or b) the automatic configuration (optimisation, in a wide sense) of network parameters. Both techniques aim to adapt the network to the actual traffic and propagation conditions. Moreover, a new heterogenous scenario, where several services and Radio Access Technologies (RATs) coexist in the same area, is now common, causing new unbalanced traffic scenarios and congestion problems. In this thesis, several optimisation and modelling methods are proposed to solve congestion problems in data and signalling channels for single- and multi-RAT scenarios

The Racial Origins of Modern Criminal Procedure

The constitutional law of state criminal procedure was born between the First and Second World Wars. Prior to 1920, the Supreme Court had upset the results of the state criminal justice system in just a handful of cases, all involving race discrimination in jury selection. By 1940, however, the Court had interpreted the Due Process Clause of the Fourteenth Amendment to invalidate state criminal convictions in a wide variety of settings: mob-dominated trials, violation of the right to counsel, coerced confessions, financially-biased judges, and knowingly perjured testimony by prosecution witnesses. In addition, the Court had broadened its earlier decisions forbidding race discrimination in jury selection in ways that made it practically as well as theoretically possible to establish equal protection violations in that context. Altogether, the Supreme Court decided six landmark state criminal procedure cases during the interwar period. Four of these cases involved black defendants from southern states. This Article contends that the linkage between the birth of modern criminal procedure and southern black defendants is no fortuity. For the Court to assume the function of superintending the state criminal process required a departure from a century and a half of tradition and legal precedent, both grounded in federalism concerns. The Justices were not prepared to embark on such a novel enterprise in cases of marginal unfairness - where the police had interrogated a suspect a bit too vigorously or permitted defense counsel a little less time than optimal for preparing a case. On the contrary, the Court was willing to take this leap only when confronted with cases in which defendants were brutally tortured into confessing or the appointment of defense counsel in a capital case was a complete sham. Such flagrant injustices were not frequent occurrences in the United States during the 1920s and 1930s - except in the South, in cases involving black defendants charged with serious interracial crimes, usually rape or murder

Quality of Service Differentiation in Heterogeneous CDMA Networks : A Mathematical Modelling Approach

Next-generation cellular networks are expected to enable the coexistence of macro and small cells, and to support differentiated quality-of-service (QoS) of mobile applications. Under such conditions in the cell, due to a wide range of supported services and high dependencies on efficient vertical and horizontal handovers, appropriate management of handover traffic is very crucial. Furthermore, new emerging technologies, such as cloud radio access networks (C-RAN) and self-organizing networks (SON), provide good implementation and deployment opportunities for novel functions and services. We design a multi-threshold teletraffic model for heterogeneous code division multiple access (CDMA) networks that enable QoS differentiation of handover traffic when elastic and adaptive services are present. Facilitated by this model, it is possible to calculate important performance metrics for handover and new calls, such as call blocking probabilities, throughput, and radio resource utilization. This can be achieved by modelling the cellular CDMA system as a continuous-time Markov chain. After that, the determination of state probabilities in the cellular system can be performed via a recursive and efficient formula. We present the applicability framework for our proposed approach, that takes into account advances in C-RAN and SON technologies. We also evaluate the accuracy of our model using simulations and find it very satisfactory. Furthermore, experiments on commodity hardware show algorithm running times in the order of few hundreds of milliseconds, which makes it highly applicable for accurate cellular network dimensioning and radio resource management

Call Center Experience Optimization: A Case for a Virtual Predictive Queue

The evolution of the call center into contact centers and the growth of their use in providing customer-facing service by many companies has brought considerable capabilities in maintaining customer relationships but it also has brought challenges in providing quality service when call volumes are high. Limited in their ability to provide service at all times to all customers, companies are forced to balance the costs associated with hiring more customer service representatives and the quality of service provided by a fewer number. A primary challenge when there are not enough customer service representatives to engage the volume of callers in a timely manner is the significant wait times that can be experienced by many customers. Normally, callers are handled in accordance with a first-come, first-served policy with exceptions being skill-based routing to those customer service representatives with specialized skills. A proposed call center infrastructure framework called a Virtual Predictive Queue (VPQ) can allow some customers to benefit from a shorter call queue wait time. This proposed system can be implemented within a call center’s Automatic Call Distribution (ACD) device associated with computer telephony integration (CTI) and theoretically will not violate a first-come, first served policy

Investigating the mean response time in finite-source retrial queues using the algorithm by Gaver, Jacobs, and Latouche

In this paper, we discuss the maximum of the mean response time that appears in finite-source retrial queues with orbital search when the arrival rate is varied. We show that explicit closed-form equations of the mean response time can be derived by exploiting the block-structure of the finite Markov chain underlying the model and using an efficient computational algorithm proposed by Gaver, Jacobs, and Latouche. However, we also show that already for the discussed relatively simple model, the resulting equation is rather complex which hampers further evaluation