Abstract Efficient management of rather limited resources, including radio spectrum and mobile-terminal battery power, has been the fundamental design challenge of wireless networks and one of the most widespread research problems over the years. MAC (Medium Access Control) for packet access and CAC (Call Admission Control) for connection-oriented service domains are commonly used as effective tools to manage radio resources, capacity and performance of wireless networks while providing adequate QoS (Quality of Service) to mobile users. Hence, analysis and synthesis of efficient MAC and CAC schemes for advanced wireless networks have significant academic and practical values. This dissertation addresses that topic and presents seven separate contributions of the author: four on adaptive MAC schemes for centralized PRN (Packet Radio Networks), referred to as SPA (Smart Packet Access) and three on CAC schemes for cellular networks, referred to as SCA (Smart Call Admission). These contributions are published in eighteen original papers by the author, which are listed and referred to as Papers I–XVIII in this thesis. In SPA, the first contribution, reported in Papers II and IV, studies implementation losses of adaptive feedback-control MAC schemes for the uplink of DS-CDMA (Direct-Sequence Code Division Multiple Access) PRN in the presence of various system imperfections. The second contribution, reported in Papers XI, XII, XV and XVI, proposes a bit-rate adaptive MAC scheme for DS-CDMA PRN, referred to as SPR (Smart Packet Rate). The third contribution, reported in Papers III, XIII and XIV, develops two alternative MAC schemes with adaptive packet-length over correlated fading channels in DS-CDMA PRN, referred to as SPL (Smart Packet Length). The fourth contribution, reported in Papers XVII and XVIII, develops alternative adaptive MAC schemes for optimal trade-offs between throughput and energy consumption of TCP (Transmission Control Protocol) applications in advanced cellular networks. These include a so-called SPD (Smart Packet Dispatching) for HSPA (High Speed Packet Access) and, again, SPL for LSPA (Low Speed Packet Access). Moving on to SCA, the first contribution, reported in Papers V and VII, provides a simple and accurate analytical method for performance evaluation of a class of fixed-assignment CAC schemes with generic guard-channel policy and queuing priority handoffs in cellular networks. The second contribution, reported in Papers VI, IX and X, proposes a simple and effective SCAC (Soft-decision CAC) scheme for CDMA cellular networks. This is evaluated against fixed-assignment and measurement-based CAC schemes with a simple and reliable method provided as a part of the contribution. The third contribution, reported in Papers I and VIII, incorporates alternative QoS differentiation paradigms and resource partitioning into CAC, defines GoS (Grade of Service) for multimedia cellular networks, and provides an in-hand tool for efficient capacity and GoS management.

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The next generation wireless system (NGWS) has been conceived as a ubiquitous wireless environment. It integrates existing heterogeneous access networks, as well as future networks, and will offer high speed data, real-time applications (e.g. Voice over IP, videoconference ) and real-time multimedia (e.g. real-time audio and video) support with a certain Quality of Service (QoS) level to mobile users. It is required that the mobile nodes have the capability of selecting services that are offered by each provider and determining the best path through the various networks. Efficient radio resource management (RRM) is one of the key issues required to support global roaming of the mobile users among different network architectures of the NGWS and a precise call admission control (CAC) scheme satisfies the requirements of high network utilization, cost reduction, minimum handover latency and high-level QoS of all the connections. This thesis is going to describe an adaptive class-based CAC algorithm, which is expected to prioritize the arriving channel resource requests, based on user¿s classification and channel allocation policy. The proposed CAC algorithm couples with Fuzzy Logic (FL) and Pre-emptive Resume (PR) theories to manage and improve the performance of the integrated wireless network system. The novel algorithm is assessed using a mathematical analytic method to measure the performance by evaluating the handover dropping probability and the system utilization.

In IEEE 802.11 WLANs, Link Adaptation mechanisms, which choose the transmission rate of each node, provoke unexpected and random variations on the effective channel capacity. When these changes are towards lower bitrates, inelastic flows, such as VoIP, can suffer from sudden congestion, which results on higher packet delays and losses. In this thesis, a VoIP codec adaptation algorithm is proposed as a solution, based on a cross-layer feedback from RTCP packets and the MAC layer, which can adapt the codecs of active calls to adjust them to the multirate scenario. A combination of this algorithm with a call admission control mechanism is also studied. The results show an important improvement in terms of the QoS of the already active flows as also in the total hotspot's capacity. Additionally, by defining a new Grade of Service related parameter, the Q-Factor, which captures the trade-off between dropping and blocking ratio and perceived speech quality, the codec adaptation algorithm can be tuned to achieve maximum capacity without severely penalizing any of those variables, and hence satisfying both technical and user quality requirements. Finally, a new QoS-enabled AP, which implements these enhancements is designed. / En las redes inalámbricas del estándar IEEE 802.11, los mecanismos de adaptación de enlace que eligen la tasa de transmisión de cada nodo, pueden provocar variaciones aleatorias e inesperadas en la capacidad efectiva del canal. Cuando estos cambios son hacia tasas de transmisión mas bajas, los flujos inelásticos, tales como los de VoIP, pueden de repente sufrir congestión, lo que se traduce en aumento de retrasos y pérdidas de paquetes. En esa tesis, se propone un algoritmo de adaptación de codificadores de voz como solución, basado en técnicas multinivel (cross-layer) que combinan el uso de información de diferentes capas, como los paquetes RTCP y la capa MAC, y que puede adaptar los codecs de las llamadas activas para ajustarlos al escenario "multi-rate". Adicionalmente, la combinación de este algoritmo con un mecanismo de control de admisión de llamadas (CAC) se ha estudiado. Los resultados muestran una importante mejora en términos de QoS de los flujos activos como también en la capacidad total del hotspot. Además, mediante la definición de un nuevo factor, el Q-Factor, que puede captar la compensación entre la tasa de corte y de bloqueo de llamadas y de la calidad percibida por esas, el algoritmo de adaptación de codecs se puede ajustar para lograr la máxima capacidad sin penalizar severamente ninguna de esas variables y así satisfacer los requisitos técnicos de calidad y los usuarios. Por último, un nuevo punto de acceso (AP) habilitado para ofrecer calidad de servicio, ha sido diseñado que lleva a cabo estas mejoras.