Cross-layer opportunistic adaptation for voice over ad hoc networks
Computer Networks: The International Journal of Computer and Telecommunications Networking
| Hi-index | 0.00 |
Recent years have witnessed fast growth in Voice over IP (VoIP) applications. With the rate at which wireless access points are spreading, VoIP over wireless is becoming increasingly important. The all-IP architecture refers to inter-operability of different networks within an IP framework. Supporting VoIP over ad hoc networks is part of realizing this all-IP goal. Voice has many applications over ad hoc networks whether these networks serve as extensions to infrastructure-based wireless networks or in stand-alone configurations. The wireless channel introduces many challenges due to its broadcast nature and temporal response variability. Ad hoc networks also suffer from resource scarcity, making support for real-time applications over ad hoc networks a formidable task. Adaptation to varying channel conditions is essential to support applications in ad hoc networks. In addition, cross-layer design allows interactions among protocol parameters to be exploited to improve performance. This research tackles the problem of supporting VoIP over wireless ad hoc networks by proposing opportunistic adaptation within a cross-layer framework. Starting with the requirements of voice, parameters whose adaptation appears important to provide acceptable quality are identified. The significance of the selected parameters is verified in two ways: through extensive simulations of adaptation over wireless links, and through statistical analysis. The insight gained about the parameters is integrated into an opportunistic cross-layer protocol with the goal of maximizing the multiplexing gain without compromising the quality achieved. To limit the overhead and complexity of the protocol, hop-to-hop-only adaptation is considered first. Then, end-to-end adaptation is incorporated in the protocol design, which works at a different time scale and has a broader view of network conditions. The performance of the refined protocol is studied using actual audio traces in the simulation. The resulting output stream is compared with the original stream using objective audio metrics which are mapped into subjective measure scores when possible. The results indicate the critical role compression, packet-size, and modulation play in supporting voice over ad hoc networks. Header compression contributes to achieving acceptable to good voice quality over long routes, under reasonably high load conditions and in the presence of mobility.