An adaptive, high performance mac for long-distance multihop wireless networks

Abstract

We consider the problem of efficient MAC design for long-distance WiFi-based mesh networks. In such networks it is common to see long propagation delays, the use of directional antennas, and the presence of inter-link interference. Prior work has shown that these characteristics make traditional CSMA-based MACs a poor choice for long-distance mesh networks, prompting several recent research efforts exploring the use of TDMA-based approaches to media access. In this paper we first identify, and then address, several shortcomings of current TDMA-based proposals, which exhibit inefficienct throughput and delay charactersistics as they use fixedlength transmission slots that cannot adapt to dynamic variations in traffic load. We show that throughput achieved by existing solutions falls far short of the optimal achievable network throughput. Current TDMA-based solutions also only apply to bipartitie network topologies due to interference scheduling contraints.In this paper, we present JazzyMac, a simple, practical and efficient MAC protocol that addresses the above limitations. JazzyMac achieves efficiency by enabling variable-length link transmissions slots; each node can adapt the length of their transmission slots in accordance with changing traffic demands. JazzyMac is practical as it can be applied to arbitrary network topologies, and each node can use purely local information for slot adaptation. Finally, the use of dynamic slot lengths allows JazzyMac to achieve better tradeoffs between throughput and delay.We evaluate JazzyMac using detailed simulation over a range of traffic patterns and realistic topologies. Our results show that JazzyMac improves throughput in all considered scenarios. This improvement is often substantial (e.g.,in 50% of our scenarios, throughput improves by over 40%) and is particularly pronounced for the common case of asymmetric traffic (e.g.,leading to almost 100% improvements). Furthermore, JazzyMac can achieve much better average delay for the same throughput.

A QoS-aware dynamic bandwidth allocation scheme for multi-hop WiFi-based long distance networks

“…In the literature of WiLD networks, MAC protocols like 2P [3], WiLDNet [4], JazzyMAC [6], JaldiMAC [12], and Lit MAC [13,14] have literally changed the face of WiLD networks. Most of these protocols focus on overall network performance enhancement.…”

“…In such situation, end-to-end QoS provisioning becomes more challenging. MAC protocols proposed for WiLD networks in [3,4,6] do not address this issue, rather they focus on maximizing slot reuse among various neighboring links and thereby improving overall network performance. Although the purpose of multi-hop WiLD and sensor networks are different, they resemble in many aspects particularly in their architectures.…”

TDMA MAC Protocols for WiFi-based Long Distance Networks: A Survey

“…While designing low cost WiLD networks by using off-the-shelf WiFi hardware, the existing CSMA/CA MAC protocol shows detrimental performance [5,11,14]. The expected performance parameters of such networks in supporting various applications including real-time applications such as e-learning, tele-medicine, etc., cannot be delivered by the existing MAC protocols unless redesigned or tuned properly.…”

“…As it was not designed for long distance operation, real WiLD links show abysmal end-to-end performance [5,11,2]. The key reasons for this detrimental performance are highlighted by Patra et al [14] as (1) high probability of packet loss, (2) inefficient acknowledgement mechanism, and (3) possible interference.…”

“…JazzyMAC [11] provisions variable length transmission slots by which each node can adapt the length of their transmission slots in accordance with their changing traffic demands. The protocol is specifically designed to allow neighbor nodes to proceed with parallel independent transmissions which contribute to enhanced throughput.…”