Biologically Inspired Intercellular Slot Synchronization
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Research Article Biologically Inspired Intercellular Slot Synchronization Alexander Tyrrell1, 2 and Gunther Auer1 1 DOCOMO 2 Institute
Euro-Labs, 80687 Munich, Germany of Networked and Embedded Systems, University of Klagenfurt, 9020 Klagenfurt, Austria
Correspondence should be addressed to Alexander Tyrrell, [email protected] Received 30 June 2008; Revised 3 November 2008; Accepted 21 January 2009 Recommended by Erchin Serpedin The present article develops a decentralized interbase station slot synchronization algorithm suitable for cellular mobile communication systems. The proposed cellular firefly synchronization (CelFSync) algorithm is derived from the theory of pulse-coupled oscillators, common to describe synchronization phenomena in biological systems, such as the spontaneous synchronization of fireflies. In order to maintain synchronization among base stations (BSs), even when there is no direct link between adjacent BSs, some selected user terminals (UTs) participate in the network synchronization process. Synchronization emerges by exchanging two distinct synchronization words, one transmitted by BSs and the other by active UTs, without any a priori assumption on the initial timing misalignments of BSs and UTs. In large-scale networks with inter-BS site distances up to a few kilometers, propagation delays severely affect the attainable timing accuracy of CelFSync. We show that by an appropriate combination of CelFSync with the timing advance procedure, which aligns uplink transmission of UTs to arrive simultaneously at the BS, a timing accuracy within a fraction of the inter-BS propagation delay is retained. Copyright © 2009 A. Tyrrell and G. Auer. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction Slot synchronization is an enabling component for cellular systems. It is a prerequisite for advanced intercellular cooperation schemes, such as interference suppression between neighboring cells, as well as multicast and broadcasting services. The problem of intercell slot synchronization is to align the internal timing references of all nodes, so that base stations (BSs) and user terminals (UTs) agree on a common reference instant that marks the start of a transmission slot. In the context of cellular systems a slot is composed of a number of successive uplink and downlink frames, referred to as superframe. Network synchronization in cellular systems is commonly performed in a master-slave manner: BSs synchronize to an external timing reference, known as the primary reference clock, and transfer this timing to UTs. This reference clock can be acquired through the global positioning system (GPS) or through the backbone connection. The first method requires the installation of a GPS receiver at each BS, which increases costs and, more importantly, does not work in environments where GPS signals cannot be received.
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