Optimal Distributed Scheduling for Streaming Traffic in Wireless Networks

Abstract:
Communication and networking have become inseparable components of modern life. Recently, two important properties have emerged as prominent features of current and, most likely, future networking environments: First, streaming traffic typically generated by multimedia podcasts, broadcasts as well as interactive real-time communication applications constitute an increasing fraction of the communication network load. Secondly, there is a significant shift to connections that contain at least one hop delivered over wireless links that are shared by multiple users. The widespread use of multimedia services over wireless networks has started causing stress on the available bandwidth. These networks are currently not properly equipped with appropriate tools to deliver required service quality over limited bandwidth. Ordinary every day users of wireless devices are experiencing vastly varying quality of experience (QoE) levels, especially with streaming multimedia applications. Although QoE is primarily a subjective measure, our past studies indicate that it can be relatively accurately quantified as a function of throughput (bandwidth), mean delay, loss rate, and jitter for both streaming and interactive multimedia flows.

The limited number of existing works on distributed wireless network control dominantly focus on throughput as the only measure of efficiency. These works have been impactful in establishing the throughput maximizing nature of distributed random access schemes with carrier sensing capabilities. However, while important as a first-order metric, throughput is not the only -arguably, not even the crucial- metric for QoE for streaming applications. Recently, several interesting works also studied the delay performance of these throughput-optimal distributed schemes, generally revealing that their delay characteristics are unacceptable for serving streaming type traffic. These findings clearly indicate a need for alternative distributed solutions geared towards the aforementioned QoE metrics associated with streaming traffic.

As a first step in fulfilling this promise, we introduce a distributed cross-layer scheduling algorithm for networks with single-hop transmissions that guarantees finite buffer sizes and meet minimum utility requirements (e.g. throughput guarantees). The proposed algorithm achieves a total utility arbitrarily close to the optimal value with a tradeoff in the buffer sizes. The finite buffer property is not only important from an implementation perspective, but, along with the algorithm, also yields superior delay performance. The algorithm also results in upper-bounds on the average delay that scales inversely with the buffer size. Unlike traditional back-pressure-based optimal algorithms, our proposed algorithm does not need centralized computation and achieves fully local implementation without global message passing. Rigorous numerical and implementation results are presented to illustrate the close-to-optimal throughput and far better delay performance compared to other recent distributed algorithms.

Bio:
Dr. Eylem Ekici has received his BS and MS degrees in Computer Engineering from Bogazici University, Istanbul, Turkey, in 1997 and 1998, respectively. He received his Ph.D. degree in Electrical and Computer Engineering from Georgia Institute of Technology, Atlanta, GA, in 2002. Currently, he is an associate professor in the Department of Electrical and Computer Engineering of The Ohio State University, Columbus, OH. He is an associate editor of IEEE/ACM Transactions on Networking, Computer Networks Journal (Elsevier), and ACM Mobile Computing and Communications Review. Prof. Ekici is the recipient of 2008 Lumley Research Award of the College of Engineering at OSU. Dr. Ekici's current research interests include wireless sensor networks, vehicular communication systems, and next generation wireless systems, with a focus on routing and medium access control protocols, resource management, and analysis of network architectures and protocols. He is a Senior Member of IEEE and a member of ACM.