Distributed Cooperative Synchronization for Large-Scale 4G Wireless Sensor Networks Using CAZAC Sequences

Clock synchronization is an important requirement of wireless sensor networks (WSNs). Synchronization is crucial to maintain data consistency, coordination, and perform fundamental operations. Many application scenarios exist where external clock synchronization may be required because WSN itself may not consist of an infrastructure for distributing the clock reference. In distributed systems the clock of a reference node is synchronized with GPS time tag or UTC as conventional external clock sources. The rest of the nodes estimate the offset and drift based on a synchronization protocol. For vast WSN, where the topology introduces propagation delay and fast drift rate of clock over sampling periods, synchronizing the WSN nodes and maintaining the synchronization is difficult. To maintain an accurate synchronization across the WSN, the authors propose a cooperative synchronization method, which uses Constant Amplitude Zero Auto Correlation (CAZAC) sequences for OFDM symbols. The proposed method is part of a class of distributed methods known as Gossip or Consensus. These protocols are robust and self-correcting to topology changes and link failure. In this paper, the authors introduce a specific type of power-law topology called scale-free and compare the synchronization performance of the proposed method in random and scale-free topologies. DOI: 10.4018/jitn.2012010104 International Journal of Interdisciplinary Telecommunications and Networking, 4(1), 56-71, January-March 2012 57 Copyright © 2012, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. the nodes operate in a coordinated and synchronized fashion. In all of these applications, all the nodes of the network need to refer to a common notion of time. Wireless sensor nodes have not improved considerably since 802.15.4 standard was introduced. As new complicated applications come, the need for coordinating wireless sensor nodes in a cooperative manner within a network becomes more prominent. This implies the need for better quality in sensor nodes functionality both individually and cooperatively which necessitates more advanced communication capabilities. Our proposed system is based on 4G standard with IP-based infrastructure and is bandwidth scalable, OFDMA broadband modulated that offers optional MIMO and iterative decoding methods (Ghash, Ratasuk, Classon, Nangia, Love, Schwent, & Wilson, 2007). Ad Hoc Sensor Networks are characterized by multi-hop forwarding issues such as forwarding delay in nodes that act as routers, mobility challenges, limited energy (potentially mitigated by fuel cell breakthroughs) and bandwidth, large routing tables, and bandwidth overhead. The use of 4G, i.e., 3GPP-LTE resource management and physical layer technology, leads to new protocols, optimizations and other communication capabilities.