On Link-Layer Reliability and Stability for Wireless Communication

A primary focus of popular wireless link-layer protocols is to achieve some level of reliability using ARQ or Hybrid ARQ mechanisms. However, these and other leading link-layer protocols largely ignore the stability aspect of wireless communication, and rely on higher layers to provide stable traffic flow control. This design strategy has led to a great deal of inefficiency in throughput and to other major issues (such as the well-known TCP over-wireless performance degradation phenomenon and the numerous studies in attempt to fix it). In this paper, we propose a paradigm shift where both reliability and stability are targeted using an Automatic Code Embedding (ACE) wireless link-layer protocol. To the best of our knowledge this is the first effort to develop a theoretical framework for analyzing and designing a wireless link-layer protocol that targets system stability in conjunction with reliable communication. We present two distinct analytical frameworks to determine optimal code embedding rates which ensure system reliability and stability for wide range of traffic demand. An important conclusion of our analysis is that various traffic demand can be met using a packet-by-packet code embedding rate constraint that is independent of traffic type. We demonstrate experimentally that ACE provides both rapid and reliable point-to-point wireless data transmission for realtime and non-realtime traffic over real channel traces collected on 802.11b WLAN. We also have conducted extensive TCP simulations in conjunction with ACE; and we demonstrate the high level of efficiency and stability that can be achieved for TCP over ACE, while not making any changes to TCP. Further, the implementation of ACE for real-time video communication shows performance gains of 5-10dB over IEEE ARQ schemes. More importantly, ACE is layer oblivious and requires no changes to higher or lower PHY layers.