Vidyut

Global synchronization across time and frequency domains significantly benefits wireless communications. Multi-Cell (Network) MIMO, interference alignment solutions, opportunistic routing techniques in ad-hoc networks, OFDMA etc. all necessitate synchronization in either time or frequency domain or both. This paper presents sysname, a system that exploits the easily accessible and ubiquitous power line infrastructure to achieve synchronization in time and frequency domains across nodes distributed beyond a single-collision domain. sysname uses the power lines to transmit a reference frequency tone to which each node locks its frequency. sysname exploits the steady periodicity of delivered power signal itself to synchronize distributed nodes in time. We validate the extent of sysname's synchronization and evaluate its effectiveness. We verify sysname's suitability for wireless applications such as OFDMA and multi-cell MIMO by validating the benefits of global synchronization in an enterprise wireless network. Our experiments show a throughput gain of 8.2x over MegaMIMO, 7x over NemoX and 2.5x over OFDMA systems. Enterprise wireless networks are supported by an Ethernet backbone. Researchers have been exploring techniques over the backbone to enable and assist in improving the performance of the wireless networks. Recent work also showed the benefit of sharing information in the air between the nodes to enable higher performance of the network. Even sharing information as little as synchronization information has been demonstrated to open new avenues (such as MU-MIMO, Physical Network Coding, Opportunistic routing, etc.) for the wireless networks to enhance its performance. However, another medium shared by majority of the nodes in the enterprise network - the power line infrastructure - has been largely left untapped to assist the wireless network. While the power lines are noisy and have a frequency selective transmission characteristic, its uniqueness is that its range can extend beyond that over air while it is unburdened by switching and other responsibilities of the Ethernet backbone. This paper poses the following question: How best to exploit the opportunity presented by the power lines to further enhance enterprise wireless networks? The key contributions of this paper are the following: Identify and demonstrate the feasibility of utilizing power lines as a medium to achieve synchronization (in time and frequency domains) between nodes in the network; Demonstrate the scalability of this technique by achieving synchronization between nodes beyond the transmission range of any of the individual nodes. The paper presents empirical results pertaining to the accuracy of synchronization and the benefit of the proposed synchronization method to existing distributed wireless techniques by virtue of extension across multiple collision domains.