Implementation of a High-Performance Assignment Scheme for Orthogonal Variable-Spreading-Factor Codes in WCDMA Networks

[[abstract]]In WCDMA, channelization is achieved by assigning OVSF codes to different users. The codes in a Node-B are valuable and limited. Much research has been devoted to devising OVSF code-assignment strategies to support as many users as possible. A number of the strategies suffer from a “code-set fragmentation” problem, which increases the call blocking probability (CBP) on the Node-B. In order to resolve this issue some strategies have applied code-exchange and reassignment policies but increased the corresponding complexity. This paper proposes a Best-fit Least Recently Used (BLRU) code-assignment scheme without reassignment to approach an optimal method. Furthermore, we devise a revised version, Queue-assist BLRU (QBLRU), to improve system utilization and to obtain an even lower CBP than the optimal method does. Consequently, code-assignment simulation results present a QBLRU scheme that has a low CBP and the highest utilization, which is a high performance OVSF code-assignment scheme which should be useful for WCDMA networks

Contribution to resource management in cellular access networks with limited backhaul capacity

La interfaz radio de los sistemas de comunicaciones móviles es normalmente considerada como la única limitación de capacidad en la red de acceso radio. Sin embargo, a medida que se van desplegando nuevas y más eficientes interfaces radio, y de que el tráfico de datos y multimedia va en aumento, existe la creciente preocupación de que la infraestructura de transporte (backhaul) de la red celular pueda convertirse en el cuello de botella en algunos escenarios. En este contexto, la tesis se centra en el desarrollo de técnicas de gestión de recursos que consideran de manera conjunta la gestión de recursos en la interfaz radio y el backhaul. Esto conduce a un nuevo paradigma donde los recursos del backhaul se consideran no sólo en la etapa de dimensionamiento, sino que además son incluidos en la problemática de gestión de recursos. Sobre esta base, el primer objetivo de la tesis consiste en evaluar los requerimientos de capacidad en las redes de acceso radio que usan IP como tecnología de transporte, de acuerdo a las recientes tendencias de la arquitectura de red. En particular, se analiza el impacto que tiene una solución de transporte basada en IP sobre la capacidad de transporte necesaria para satisfacer los requisitos de calidad de servicio en la red de acceso. La evaluación se realiza en el contexto de la red de acceso radio de UMTS, donde se proporciona una caracterización detallada de la interfaz Iub. El análisis de requerimientos de capacidad se lleva a cabo para dos diferentes escenarios: canales dedicados y canales de alta velocidad. Posteriormente, con el objetivo de aprovechar totalmente los recursos disponibles en el acceso radio y el backhaul, esta tesis propone un marco de gestión conjunta de recursos donde la idea principal consiste en incorporar las métricas de la red de transporte dentro del problema de gestión de recursos. A fin de evaluar los beneficios del marco de gestión de recursos propuesto, esta tesis se centra en la evaluación del problema de asignación de base, como estrategia para distribuir el tráfico entre las estaciones base en función de los niveles de carga tanto en la interfaz radio como en el backhaul. Este problema se analiza inicialmente considerando una red de acceso radio genérica, mediante la definición de un modelo analítico basado en cadenas de Markov. Dicho modelo permite calcular la ganancia de capacidad que puede alcanzar la estrategia de asignación de base propuesta. Posteriormente, el análisis de la estrategia propuesta se extiende considerando tecnologías específicas de acceso radio. En particular, en el contexto de redes WCDMA se desarrolla un algoritmo de asignación de base basado en simulatedannealing cuyo objetivo es maximizar una función de utilidad que refleja el grado de satisfacción de las asignaciones respecto los recursos radio y transporte. Finalmente, esta tesis aborda el diseño y evaluación de un algoritmo de asignación de base para los futuros sistemas de banda ancha basados en OFDMA. En este caso, el problema de asignación de base se modela como un problema de optimización mediante el uso de un marco de funciones de utilidad y funciones de coste de recursos. El problema planteado, que considera que existen restricciones de recursos tanto en la interfaz radio como en el backhaul, es mapeado a un problema de optimización conocido como Multiple-Choice Multidimensional Knapsack Problem (MMKP). Posteriormente, se desarrolla un algoritmo de asignación de base heurístico, el cual es evaluado y comparado con esquemas de asignación basados exclusivamente en criterios radio. El algoritmo concebido se basa en el uso de los multiplicadores de Lagrange y está diseñado para aprovechar de manera simultánea el balanceo de carga en la intefaz radio y el backhaul.Postprint (published version

Maximally Flexible Assignment of Orthogonal Variable Spreading Factor Codes for Multi-Rate Traffic

In universal terrestrial radio access (UTRA) systems, orthogonal variable spreading factor (OVSF) codes are used to support different transmission rates for different users. In this paper, we first define the flexibility index to measure the capability of an assignable code set in supporting multirate traffic classes. Based on this index, two single-code assignment schemes, nonrearrangeable and rearrangeable compact assignments, are proposed. Both schemes can offer maximal flexibility for the resulting code tree after each code assignment. We then present an analytical model and derive the call blocking probability, system throughput and fairness index. Analytical and simulation results show that the proposed schemes are efficient, stable and fair

An Algorithmic View on OVSF Code Assignment

Orthogonal Variable Spreading Factor (OVSF) codes are used in UMTS to share the radio spectrum among several connections of possibly different bandwidth requirements. The combinatorial core of the OVSF code assignment problem is to assign some nodes of a complete binary tree of height h (the code tree) to n simultaneous connections, such that no two assigned nodes (codes) are on the same root-to-leaf path. A connection that uses a 2-d fraction of the total bandwidth requires some code at depth d in the tree, but this code assignment is allowed to change over time. Requests for connections that would exceed the total available bandwidth are rejected. We consider the one-step code assignment problem: Given an assignment, move the minimum number of codes to serve a new request. Minn and Siu propose the so-called DCA algorithm to solve the problem optimally. In contrast, we show that DCA does not always return an optimal solution, and that the problem is NP-hard. We give an exact nO(h)-time algorithm, and a polynomial-time greedy algorithm that achieves approximation ratio Θ(h). A more practically relevant version is the online code assignment problem, where future requests are not known in advance. Our objective is to minimize the overall number of code reassignments. We present a Θ(h)-competitive online algorithm, and show that no deterministic online algorithm can achieve a competitive ratio better than 1.5. We show that the greedy strategy (minimizing the number of reassignments in every step) is not better than Ω(h) competitive. We give a 2-resource augmented online algorithm that achieves an amortized constant number of (re-)assignments. Finally, we show that the problem is fixed-parameter tractabl

Cooperative control of relay based cellular networks

PhDThe increasing popularity of wireless communications and the higher data requirements of new types of service lead to higher demands on wireless networks. Relay based cellular networks have been seen as an effective way to meet users’ increased data rate requirements while still retaining the benefits of a cellular structure. However, maximizing the probability of providing service and spectrum efficiency are still major challenges for network operators and engineers because of the heterogeneous traffic demands, hard-to-predict user movements and complex traffic models. In a mobile network, load balancing is recognised as an efficient way to increase the utilization of limited frequency spectrum at reasonable costs. Cooperative control based on geographic load balancing is employed to provide flexibility for relay based cellular networks and to respond to changes in the environment. According to the potential capability of existing antenna systems, adaptive radio frequency domain control in the physical layer is explored to provide coverage at the right place at the right time. This thesis proposes several effective and efficient approaches to improve spectrum efficiency using network wide optimization to coordinate the coverage offered by different network components according to the antenna models and relay station capability. The approaches include tilting of antenna sectors, changing the power of omni-directional antennas, and changing the assignment of relay stations to different base stations. Experiments show that the proposed approaches offer significant improvements and robustness in heterogeneous traffic scenarios and when the propagation environment changes. The issue of predicting the consequence of cooperative decisions regarding antenna configurations when applied in a realistic environment is described, and a coverage prediction model is proposed. The consequences of applying changes to the antenna configuration on handovers are analysed in detail. The performance evaluations are based on a system level simulator in the context of Mobile WiMAX technology, but the concepts apply more generally

Efficient admission control schemes in cellular IP networks

The rapid growth of real-time multimedia applications over IP (Internet Protocol) networks has made the Quality of Service (QoS) a critical issue. One important factor affecting the QoS in the overall IP networks is the admission control in the fast expanding wireless IP networks. Due to the limitations of wireless bandwidth, wireless IP networks (cellular IP networks in particular) are generally considered to be the bottlenecks of the global IP networks. Admission control is to maintain the QoS level for the services admitted. It determines whether to admit or reject a new call request in the mobile cell based on the availability of the bandwidth. In this thesis, the term “call” is for general IP services including voice calls (VoIP) and the term “wireless IP” is used interchangeably with “cellular IP”, which means “cellular or mobile networks supporting IP applications”. In the wireless IP networks, apart from new calls, there are handoff (handover) calls which are calls moving from one cell to another. The general admission control includes the new call admission control and handoff call admission control. The desired admission control schemes should have the QoS maintained in specified levels and network resources (i.e. bandwidth in this case) are utilised efficiently. The study conducted in this thesis is on reviewing current admission control schemes and developing new schemes. Threshold Access Sharing (TAS) scheme is one of the existing schemes with good performance on general call admission. Our work started with enhancing TAS. We have proposed an improved Threshold Access Sharing (iTAS) scheme with the simplified ratebased borrowing which is an adaptive mechanism. The iTAS aims to lower handoff call dropping probability and to maximise the resource utilisation. The scheme works at the cell level (i.e. it is applied at the base station), on the basis of reserving a fixed amount of bandwidth for handoff calls. Prioritised calls can be admitted by “borrowing” bandwidth from other ongoing calls. Our simulation has shown that the new scheme has outperformed the original TAS in terms of handoff prioritisation and handling, especially for bandwidth adaptive calls. However, in iTAS, the admission decision is made solely based on bandwidth related criteria. All calls of same class are assumed having similar behaviour. In the real situation, many factors can be referred in decision making of the admission control, especially the handoff call handling. We have proposed a novice scheme, which considered multiple criteria with different weights. The total weights are used to make a decision for a handoff. These criteria are hard to be modelled in the traditional admission models. Our simulated result has demonstrated that this scheme yields better performance in terms of handoff call xiv dropping compared with iTAS. We further expand the coverage of the admission control from a cell level to a system level in the hierarchical networks. A new admission control model was built, aiming to optimise bandwidth utilisation by separating the signalling channels and traffic channels in different tiers. In the new model, handoff calls are also prioritised using call classification and admission levels. Calls belonging to a certain class follow a pre-defined admission rule. The admission levels can be adjusted to suit the traffic situation in the system. Our simulated results show that this model works better than the normal 2-tier hierarchical networks in terms of handoff calls. The model settings are adjustable to reflect real situation. Finally we conclude our research and suggest some possible future work

Improving 3G network throughput by new service and joint design.

Li Ning.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.Includes bibliographical references (leaves 52-55).Abstracts in English and Chinese.Acknowledgments --- p.iiAbstract --- p.iii哲學碩士論文摘要 --- p.ivChapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Research Background --- p.2Chapter 1.2 --- Contributions of the Thesis --- p.5Chapter 1.3 --- Organization of the Thesis --- p.6Chapter Chapter 2 --- Properties of OVSF Codes --- p.7Chapter 2.1 --- Tree-Structured Generation of OVSF Codes --- p.7Chapter 2.2 --- OVSF Codes Assignment --- p.10Chapter Chapter 3 --- Support Delayable Traffic in Wireless Networks --- p.14Chapter 3.1 --- System Model --- p.15Chapter 3.2 --- Scheduling Algorithm with Burst Adaptation --- p.17Chapter 3.3 --- Performance Analysis --- p.22Chapter 3.4 --- Simulation Results --- p.24Chapter Chapter 4 --- Allocate OVSF Codes with Joint Design --- p.30Chapter 4.1 --- Combine Number of Active Users and Error-Control Coding Scheme --- p.31Chapter 4.1.1 --- System Model --- p.31Chapter 4.1.2 --- Scheduling Algorithm Description --- p.33Chapter 4.1.3 --- Simulation Results --- p.35Chapter 4.2 --- Combine Power Adaptation and Error-Control Coding Scheme --- p.39Chapter 4.2.1 --- System Model --- p.39Chapter 4.2.2 --- Scheduling Algorithm Description --- p.41Chapter 4.2.3 --- Simulation Results --- p.44Chapter Chapter 5 --- Conclusion --- p.50Bibliography --- p.5

Bandwidth allocation for wireless multimedia systems.

Chen Chung-Shue.Thesis (M.Phil.)--Chinese University of Hong Kong, 2001.Includes bibliographical references (leaves 100-102).Abstracts in English and Chinese.Chapter 1. --- Introduction --- p.1Chapter 1.1 --- Evolution to 3G Mobile --- p.2Chapter 1.1.1 --- First Generation --- p.2Chapter 1.1.2 --- Second Generation --- p.3Chapter 1.1.3 --- Third Generation --- p.3Chapter 1.2 --- UTRA Framework --- p.5Chapter 1.2.1 --- FDD and TDD --- p.6Chapter 1.2.2 --- Channel Spreading --- p.6Chapter 1.2.3 --- OVSF Code Tree --- p.8Chapter 1.3 --- Cellular Concepts --- p.10Chapter 1.3.1 --- System Capacity --- p.10Chapter 1.3.2 --- Multiple Access --- p.11Chapter 1.3.3 --- Resource Management --- p.15Chapter 1.4 --- Organization of the Thesis --- p.16Chapter 2. --- Analysis on Multi-rate Operations --- p.18Chapter 2.1 --- Related Works in Multi-rate Operations --- p.18Chapter 2.1.1 --- Variable Spreading Factor --- p.19Chapter 2.1.2 --- Data Time-multiplexing --- p.20Chapter 2.1.3 --- Multi-carrier Transmission --- p.21Chapter 2.1.4 --- Hybrid TDMA/CDMA --- p.23Chapter 2.2 --- Problems in Multi-rate Operations --- p.24Chapter 2.2.1 --- Conventional CDMA --- p.24Chapter 2.2.2 --- Data Time-multiplexing --- p.25Chapter 2.2.3 --- MC-CDMA --- p.25Chapter 2.2.4 --- TD-CDMA --- p.27Chapter 2.3 --- Multi-user multi-rate Operations --- p.28Chapter 3. --- Bandwidth Allocation --- p.29Chapter 3.1 --- Most Regular Binary Sequence --- p.30Chapter 3.1.1 --- Properties of MRBS --- p.31Chapter 3.1.2 --- Construction of MRCS --- p.32Chapter 3.1.3 --- Zero-one Sequence under MRBS --- p.33Chapter 3.2 --- MRBS in TD-CDMA --- p.35Chapter 3.2.1 --- Time Slot Optimization --- p.36Chapter 3.2.2 --- Sequence Generator --- p.37Chapter 3.3 --- Most Regular Code Sequence --- p.38Chapter 3.3.1 --- Properties of MRCS --- p.38Chapter 3.2.2 --- Construction of MRCS --- p.41Chapter 3.3.3 --- Fraction-valued Sequence under MRCS --- p.42Chapter 3.3.4 --- LCC and UCC --- p.45Chapter 3.4 --- MRCS in WCDMA --- p.46Chapter 3.4.1 --- Spreading Factor Optimization --- p.46Chapter 3.4.2 --- Code Generator --- p.48Chapter 3.4.3 --- Uplink and Downlink --- p.50Chapter 4. --- Multi-access Control --- p.52Chapter 4.1 --- Conflict and Resolution --- p.53Chapter 4.1.1 --- Conflicts in MRBS and MRCS --- p.53Chapter 4.1.2 --- Resolution with Buffering --- p.55Chapter 4.2 --- MRBS Transmission Scheduling --- p.56Chapter 4.2.1 --- Slot Scheduling on MRBS --- p.56Chapter 4.2.2 --- Properties of Scheduling Algorithm --- p.59Chapter 4.2.3 --- Scheduled MRBS --- p.71Chapter 4.3 --- MRCS Transmission Scheduling --- p.73Chapter 4.3.1 --- Slot Scheduling on MRCS --- p.73Chapter 4.3.2 --- Properties of Scheduling Algorithm --- p.75Chapter 4.3.3 --- Scheduled MRBS --- p.76Chapter 4.4 --- Performance Evaluation --- p.78Chapter 4.4.1 --- Simulation on Algorithm --- p.78Chapter 4.4.2 --- Resource Utilization and Delay Bound --- p.79Chapter 4.4.3 --- Blocking Model and System Capacity --- p.80Chapter 4.4.4 --- Numerical Analysis --- p.86Chapter 5. --- Conclusions and Future works --- p.92Appendix A --- p.94Appendix B --- p.98Bibliography --- p.10