A Utility-based Framework for Assessing Fairness Schemes in Ad-Hoc Networks

Fairness in multihop ad hoc networks has received considerable attention in the literature. A plethora of protocols have been proposed, which compute the ``optimal'' bit rates of the transmitting mobile nodes over short time-scales so that a certain fairness criterion is met. However, there has been limited research on the impact of the varying short-term allocations of these protocols due to nodes mobility on the user-perceived QoS (and social welfare) for services of long duration. In this paper, we introduce a utility-based framework, based on {\em QoS-aware history-dependent} utility functions. These functions quantify the satisfaction that the users of the MANETs obtain from the way their long-lived service sessions are allocated bandwidth, due to the behavior of the fairness protocols proposed for ad hoc networks. Finally, we demonstrate the framework's usefulness, by performing a comparative assessment of the fairness protocol of our previous work with the standard IEEE 802.11

Opportunistic transmission scheduling for next generation wireless communication systems with multimedia services

The explosive growth of the Internet and the continued dramatic increase for all wireless services are fueling the demand for increased capacity, data rates, and support of different quality of service (QoS) requirements for different classes of services. Since in the current and future wireless communication infrastructures, the performances of the various services are strongly correlated, as the resources are shared among them, dynamic resource allocation methods should be employed. With the demand for high data rate and support of multiple QoS, the transmission scheduling plays a key role in the efficient resource allocation process in wireless systems. The fundamental problem of scheduling the users\u27 transmissions and allocating the available resources in a realistic CDMA wireless system that supports multi-rate multimedia services, with efficiency and fairness, is investigated and analyzed in this dissertation. Our proposed approach adopts the use of dynamically assigned data rates that match the channel capacity in order to improve the system throughput and overcome the problems associated with the location-dependent and time-dependent errors and channel conditions, the variable system capacity and the transmission power limitation. We first introduce and describe two new scheduling algorithms, namely the Channel Adaptive Rate Scheduling (CARS) and Fair Channel Adaptive Rate Scheduling (FCARS). CARS exploits the channel variations to reach high throughput, by adjusting the transmission rates according to the varying channel conditions and by performing an iterative procedure to determine the power index that a user can accept by its current channel condition and transmission power. Based on the assignment of CARS and to overcome potential unfair service allocation, FCARS implements a compensation algorithm, in which the lagging users can receive compensation service when the corresponding channel conditions improve, in order to achieve asymptotic throughput fairness, while still maintaining all the constraints imposed by the system. Furthermore the problem of opportunistic fair scheduling in the uplink transmission of CDMA systems, with the objective of maximizing the uplink system throughput, while satisfying the users\u27 QoS requirements and maintaining the long-term fairness among the various users despite their different varying channel conditions, is rigorously formulated, and a throughput optimal fair scheduling policy is obtained. The corresponding problem is expressed as a weighted throughput maximization problem, under certain power and QoS constraints, where the weights are the control parameters that reflect the fairness constraints. With the introduction of the power index capacity it is shown that this optimization problem can be converted into a binary knapsack problem, where all the corresponding constraints are replaced by the users\u27 power index capacities at some certain system power index. It is then argued that the optimal solution can be obtained as a global search within a certain range, while a stochastic approximation method is presented in order to effectively identify the required control parameters. Finally, since some real-time services may demand certain amount of service within specific short span of time in order to avoid service delays, the problem of designing policies that can achieve high throughput while at the same time maintain short term fairness, is also considered and investigated. To this end a new Credit-based Short-term Fairness Scheduling (CSFS) algorithm, which achieves to provide short-term fairness to the delay-sensitive users while still schedules opportunistically the non-delay-sensitive users to obtain high system throughput, is proposed and evaluated

Sobre la justicia en las redes IEEE 802.11e: desincronización de su mecanismo de acceso al medio

Since the advent of the first IEEE 802.11 standard, several papers have proposed means of providing QoS to IEEE 802.11 networks and evaluate various traffic-prioritization mechanisms. Nevertheless, studies on the assignment of AIFS times defined in IEEE 802.11e reveal that the various priority levels work in a synchronized manner. The studies show that, under large loads of high-priority traffic, EDCA starves low-priority frames, which is undesirable. We argue that QoS traffic needs to be prioritized, but users sending best-effort frames should also obtain the expected service. High-priority traffic can also suffer performance degradation when using EDCA because of heavy loads of low-priority frames. Thus, we have proposed a mechanism based on desynchronizing the IEEE 802.11e working procedure. It prevents stations that belong to different priority classes from attempting simultaneous transmission, prioritizes independent collision groups and achieves better short-term and long-term channel access fairness. We have evaluated the proposal based on extensive analytical and simulation results. It prevents the strangulation of low-priority traffic, and, moreover, reduces the degradation of high-priority traffic with the increased presence of low-priority frames.Peer Reviewe

Opportunistic scheduling algorithms in downlink centralized wireless networks.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.As wireless spectrum efficiency is becoming increasingly important with the growing demands for wideband wireless service scheduling algorithm plays an important role in the design of advanced wireless networks. Opportunistic scheduling algorithms for wireless communication networks under different QoS constraints have gained popularity in recent years since they have potentials of achieving higher system performance. In this dissertation firstly we formulate the framework of opportunistic scheduling algorithms. Then we propose three new opportunistic scheduling schemes under different QoS criteria and situations (single channel or multiple channel). 1. Temporal fairness opportunistic scheduling algorithm in the short term. We replicate the temporal fairness opportunistic scheduling algorithm in the long term. From simulation results we find that this algorithm improves the system performance and complies with the temporal fairness constraint in the long term. However, the disadvantage of this algorithm is that it is unfair from the beginning of simulation to 10000 time slot on system resource (time slots) allocation - we say it is unfair in the short term. With such a scheme, it is possible that some users with bad channel conditions would starve for a long time (more than a few seconds) , which is undesirable to certain users (say, real-time users). So we propose the new scheme called temporal fairness opportunistic scheduling algorithm in the short term to satisfy users ' requirements of system resource in both short term and long term. Our simulation results show that the new scheme performs well with respect to both temporal fairness constraint and system performance improvement. 2. Delay-concerned opportunistic scheduling algorithm. While most work has been done on opportunistic scheduling algorithm under fairness constraints on user level, we consider users' packet delay in opportunistic scheduling. Firstly we examine the packet delay performance under the long term temporal fairness opportunistic scheduling (TFOL) algorithm. We also simulate the earliest deadline-first (EDF) scheduling algorithm in the wireless environment. We find that the disadvantage of opportunistic scheduling algorithm is that it is unfair in packet delay distribution because it results in a bias for users with good channel conditions in packet delay to improve system performance. Under EDF algorithm, packet delay of users with different channel conditions is almost the same but the problem is that it is worse than the opportunistic scheduling algorithm. So we propose another new scheme which considers both users' channel conditions and packet delay. Simulation results show that the new scheme works well with respect to both system performance improvement and the balance of packet delay distribution. 3. Utilitarian fairness scheduling algorithm in multiple wireless channel networks. Existing studies have so far focused on the design of scheduling algorithm in the single wireless communication network under the fairness constraint. A common assumption of existing designs is that only a single user can access the channel at a given time slot. However, spread spectrum techniques are increasingly being deployed to allow multiple data users to transmit simultaneously on a relatively small number of separate high-rate channels. Not much work has been done on the scheduling algorithm in the multiple wireless channel networks. Furthermore in wire-line network, when a certain amount of resource is assigned to a user, it guarantees that the user gets some amount of performance, but in wireless network this point is different because channel conditions are different among users. Hence, in wireless channel the user's performance does not directly depend on its allocation of system resource. Finally the opportunistic scheduling mechanism for wireless communication networks is gaining popularity because it utilizes the "multi-user diversity" to maximize the system performance. So, considering these three points in the fourth section, we propose utilitarian fairness scheduling algorithm in multiple wireless channel networks. Utilitarian fairness is to guarantee that every user can get its performance requirement which is pre-defined. The proposed criterion fits in with wireless networks. We also use the opportunistic scheduling mechanism to maximize system performance under the utilitarian fairness constraint. Simulation results show that the new scheme works well in both utilitarian fairness and utilitarian efficiency of system resource in the multiple wireless channel situation

Practical Resource Allocation Algorithms for QoS in OFDMA-based Wireless Systems

In this work we propose an efficient resource allocation algorithm for OFDMA based wireless systems supporting heterogeneous traffic. The proposed algorithm provides proportionally fairness to data users and short term rate guarantees to real-time users. Based on the QoS requirements, buffer occupancy and channel conditions, we propose a scheme for rate requirement determination for delay constrained sessions. Then we formulate and solve the proportional fair rate allocation problem subject to those rate requirements and power/bandwidth constraints. Simulations results show that the proposed algorithm provides significant improvement with respect to the benchmark algorithm.Comment: To be presented at 2nd IEEE International Broadband Wireless Access Workshop. Las Vegas, Nevada USA Jan 12 200

Joint Dynamic Radio Resource Allocation and Mobility Load Balancing in 3GPP LTE Multi-Cell Network

Load imbalance, together with inefficient utilization of system resource, constitute major factors responsible for poor overall performance in Long Term Evolution (LTE) network. In this paper, a novel scheme of joint dynamic resource allocation and load balancing is proposed to achieve a balanced performance improvement in 3rd Generation Partnership Project (3GPP) LTE Self-Organizing Networks (SON). The new method which aims at maximizing network resource efficiency subject to inter-cell interference and intra-cell resource constraints is implemented in two steps. In the first step, an efficient resource allocation, including user scheduling and power assignment, is conducted in a distributed manner to serve as many users in the whole network as possible. In the second step, based on the resource allocation scheme, the optimization objective namely network resource efficiency can be calculated and load balancing is implemented by switching the user that can maximize the objective function. Lagrange Multipliers method and heuristic algorithm are used to resolve the formulated optimization problem. Simulation results show that our algorithm achieves better performance in terms of user throughput, fairness, load balancing index and unsatisfied user number compared with the traditional approach which takes resource allocation and load balancing into account, respectively

Downlink Video Streaming for Users Non-Equidistant from Base Station

We consider multiuser video transmission for users that are non-equidistantly positioned from base station. We propose a greedy algorithm for video streaming in a wireless system with capacity achieving channel coding, that implements the cross-layer principle by partially separating the physical and the application layer. In such a system the parameters at the physical layer are dependent on the packet length and the conditions in the wireless channel and the parameters at the application layer are dependent on the reduction of the expected distortion assuming no packet errors in the system. We also address the fairness in the multiuser video system with non-equidistantly positioned users. Our fairness algorithm is based on modified opportunistic round robin scheduling. We evaluate the performance of the proposed algorithms by simulating the transmission of H.264/AVC video signals in a TDMA wireless system