The performance of HSDPA-HDR in delay constrained applications: closed-form expressions

Scheduling in a Downlink channel based on partial Channel State Information at the Transmitter (CSIT) is carried out through an opportunistic technique. Within a more practical perspective, this paper first presents a transmission strategy where a minimum rate per user is required, which in a wireless fading scenario, can only be guaranteed under a certain system outage constraint. This minimum rate is demanded within a given time interval to satisfy maximum delay restrictions for the user application. Closed form expressions for maximum scheduling delay and maximum jitter are obtained, standing as possible Quality of Service (QoS) indicators for the system behaviour. The derived expressions are then tested via simulations in several transmission scenarios.Postprint (published version

Information Technology

The new millennium has been labeled as the century of the personal communications revolution or more specifically, the digital wireless communications revolution. The introduction of new multimedia services has created higher loads on available radio resources. These services can be presented in different levels of quality of service. Namely, the task of the radio resource manager is to provide these levels. Radio resources are scarce and need to be shared by many users. The sharing has to be carried out in an efficient way avoiding as much as possible any waste of resources. The main contribution focus of this work is on radio resource management in opportunistic systems. In opportunistic communications dynamic rate and power allocation may be performed over the dimensions of time, frequency and space in a wireless system. In this work a number of these allocation schemes are proposed. A downlink scheduler is introduced in this work that controls the activity of the users. The scheduler is a simple integral controller that controls the activity of users, increasing or decreasing it depending on the degree of proximity to a requested quality of service level. The scheduler is designed to be a best effort scheduler; that is, in the event the requested quality of service (QoS) cannot be attained, users are always guaranteed the basic QoS level provided by a proportional fair scheduler. In a proportional fair scheduler, the user with the best rate quality factor is selected. The rate quality here is the instantaneous achievable rate divided by the average throughput Uplink scheduling is more challenging than its downlink counterpart due to signalling restrictions and additional constraints on resource allocations. For instance, in long term evolution systems, single carrier FDMA is to be utilized which requires the frequency domain resource allocation to be done in such a way that a user could only be allocated subsequent bands. We suggest for the uplink a scheduler that follows a heuristic approach in its decision. The scheduler is mainly based on the gradient algorithm that maximizes the gradient of a certain utility. The utility could be a function of any QoS. In addition, an optimal uplink scheduler for the same system is presented. This optimal scheduler is valid in theory only, nevertheless, it provides a considerable benchmark for evaluation of performance for the heuristic scheduler as well as other algorithms of the same system. A study is also made for the feedback information in a multi-carrier system. In a multi-carrier system, reporting the channel state information (CSI) of every subcarrier will result in huge overhead and consequent waste in bandwidth. In this work the subcarriers are grouped into subbands which are in turn grouped into blocks and a study is made to find the minimum amount of information for the adaptive modulation and coding (AMC) of the blocks. The thesis also deals with admission control and proposes an opportunistic admission controller. The controller gradually integrates a new user requesting admission into the system. The system is probed to examine the effect of the new user on existing connections. The user is finally fully admitted if by the end of the probing, the quality of service (QoS) of existing connections did not drop below a certain threshold. It is imperative to mention that the research work of this thesis is mainly focused on non-real time applications.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Packet scheduling algorithms in LTE systems

University of Technology Sydney. Faculty of Engineering and Information Technology.There has been a huge increase in demand towards improving the Quality of Service (QoS) of wireless services. Long Term Evolution (LTE) is a development of the Third-Generation Partnership Project (3GPP) with the aim to meet the needs of International Telecommunication Union (ITU). Some of its aspects are highlighted as follows: increase in data rate, scalable bandwidth, reduced latency and increase in coverage and capacity that result in better quality of service in communication. LTE employs Orthogonal Frequency Division Multiple Access (OFDMA) to simultaneously deliver multimedia services at a high speed rate. Packet switching is used by LTE to support different media services. To meet the QoS requirements for LTE networks, packet scheduling has been employed. Packet scheduling decides when and how different packets are delivered to the receiver. It is responsible for smart user packet selection to allocate radio resources appropriately. Therefore, packet scheduling should be cleverly designed to achieve QoS that is similar to fixed line services. eNodeB is a node in LTE network which is responsible for radio resource management that involves packet scheduling. There are two main categories of application in multimedia services: RT (Real Time) and NRT (None Real Time) services. RT services are either delay sensitive (e.g. voice over IP), loss sensitive (e.g. Buffered Video) or both (delay &loss sensitive) for example video conferencing. Best effort users are an example of NRT services that do not have exact requisites and have been allocated to spare resources. Reaching higher throughput has sometimes resulted in unfair allocation to users who are located far from the base station or users who suffer from bad channel conditions. Therefore, a sufficient trade-off between throughput and fairness is essential. The scarce bandwidth, fading radio channels and the QoS requirement of the users, makes resource allocation a demanding issue. Different scheduling approaches have been suggested for different service demands described briefly throughout the thesis. Initially, a comprehensive literature review of existing work on the packet scheduling topic has been accomplished in this thesis to realize the characteristics of packet scheduling and the resource allocation for the wireless network. Many packet scheduling algorithms developed to provide satisfactory QoS for multimedia services in downlink LTE systems. Several algorithms considered in this thesis include time and frequency domain algorithms and their way of approach has been investigated. The next objective of this thesis is to improve the performance of packet scheduling in LTE downlink systems. A new packet scheduling algorithm has been introduced in this thesis. A study on VoLTE (Voice over LTE), video streaming and best effort traffic under three different scheduling algorithms has been conducted. Heterogeneous traffic based on precise modelling of packets has been used in the simulation. The main resource allocation and assignment technique used in this work namely Dynamic Subcarrier Allocation scheme is shown to provide a solution to solve the cross layer optimisation problem. It depends on Channel Quality Information (CQI) and has been broadly investigated for single carrier and multicarrier wireless networks. The problem is based on the maximisation of average utility functions. Different scheduling algorithms in this method consider to be utility functions. The throughput, fairness and Packet Loss Ratio have been considered as the requirements for examining the performance of algorithms. Simulation results show that the proposed algorithm significantly increases the performance of streaming and best effort users in terms of PLR and throughput. Fairness has also been improved with less computational complexity compared to previous algorithms that have been introduced in this thesis

Analytical evaluation of multicast packet delivery and user clustering schemes in high-speed cellular networks

International audienceTransmission on data-oriented radio interfaces of cellular networks has been primarily designed for unicast applications. Nevertheless, unicast may not optimize the resource usage when the same content has to be transmitted to several users in the same cell. In this context, multicast seems to be an efficient means to convey data. In this paper, we develop an analytical model that allows the computation of the mean bitrate for both multicast and multiple-unicast transmission schemes. Furthermore, we propose a multicast transmission scheme called the equal-bitrate (EB) algorithm that allocates bandwidth to mobiles according to their instantaneous channel quality. We compare it to adaptations of the well-known Max-SNR and Round Robin (RR) to multicast. We propose to group users into clusters. The clustering method combines multicast and unicast transmission schemes according to the user’s average channel conditions.We use the analytical model to evaluate the proposed solutions. We compare the resulting performance against pure multicast and multiple-unicast approaches. We show that EB algorithm offers a good trade-off between throughput and fairness. Also, we show that mixed clustering achieves good performance compared to conventional clustering methods

Multipath streaming: fundamental limits and efficient algorithms

We investigate streaming over multiple links. A file is split into small units called chunks that may be requested on the various links according to some policy, and received after some random delay. After a start-up time called pre-buffering time, received chunks are played at a fixed speed. There is starvation if the chunk to be played has not yet arrived. We provide lower bounds (fundamental limits) on the starvation probability of any policy. We further propose simple, order-optimal policies that require no feedback. For general delay distributions, we provide tractable upper bounds for the starvation probability of the proposed policies, allowing to select the pre-buffering time appropriately. We specialize our results to: (i) links that employ CSMA or opportunistic scheduling at the packet level, (ii) links shared with a primary user (iii) links that use fair rate sharing at the flow level. We consider a generic model so that our results give insight into the design and performance of media streaming over (a) wired networks with several paths between the source and destination, (b) wireless networks featuring spectrum aggregation and (c) multi-homed wireless networks.Comment: 24 page

Performance Evaluation of Scalable Congestion Control Schemes for Elastic Traffic in Cellular Networks with Power Control

This paper deals with the performance evaluation of some congestion control schemes for elastic traffic in wireless cellular networks with power allocation/control. These schemes allow us to identify the {\em feasible configurations of instantaneous} up- and downlink {\em bit-rates} of users; i.e., such that {\em can be obtained by allocating respective powers}, taking into account in an exact way the interference created in the whole, multicellular network. We consider the bit-rate configurations identified by these schemes as {\em feasible sets for some classical, maximal fair resource allocation policies}, and study their performance in the long-term evolution of the system. Specifically, we assume Markovian arrivals, departures and mobility of customers, which transmit some given data-volumes, as well as some temporal channel variability (fading), and study the {\em mean throughput} i.e., the mean bit-rates that the policies offer in different parts of a given cell. Explicit formulas are obtained in the case of {\em proportional fair policies}, which may or may-not take advantage of the fading, for {\em null} or {\em infinitely rapid customer mobility}. This approach applies also to a channel shared by the elastic traffic and a strea ing, with predefined customer bit-rates,regulated by the respective admission policy