Multi-hop OFDM Research

Orthogonal frequency division multiplexing (OFDM) is a practical broadband signaling technique for use in multipath fading channels. Incorporated with MIMO, OFDM is promising technology for higher capacity multi-hop networks. One of the main challenges of incorporating OFDM into multi-hop networking is distributed subcarrier allocation among multiple users. Because of the independence in the fading channel states between different users, there is an opportunity to take advantage of frequency selectivity and perform channel aware scheduling and resource allocation.

Select Results Thus Far

Recently, we propose a multichannel feedback protocol to enable local scheduling with channel state information for wireless multi-hop networks with orthogonal frequency division multiplexing (OFDM). In our proposed protocol, the frequency subcarrier domain is shared by multiple control channels, on which request to- send (RTS) and clear-to-send (CTS) are exchanged. These control channels are created using random spreading signatures. Channel state information of the simultaneous transmissions, which defines the gains of these channels, is exchanged on these control channels and channel state information tables that contain the channel information of both the desired link and the interfering links are created at the transmit nodes, then scheduling decisions are made based on the channel information tables.

Future Research

We are investigating improved protocols for exploiting multi-user diversity in OFDM multi-hop networks as well as extensions to MIMO-OFDM.

  • Design of enhanced multi-hop multi-nodes friendly OFDM scheduler
  • Development of efficient algorithms for stream control and sub-carrier scheduling

Relevant Publications

T. Tang, K.Mandke, C. B. Chae, R. W. Heath, Jr., and S. Nettles, “Multichannel Feedback in OFDM Ad Hoc Networks” to appear in theĀ Proc. of the International Workshop on Wireless Ad-hoc Networks, New York, NY, June 28 – 30, 2006.

Sponsors

National Science Foundation under grant CNS-626797, Office of Naval Research (ONR) under grant number N00014-05-1-0169, and the DARPA IT-MANET program, Grant W911NF-07-1-0028. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the aforementioned sponsors.

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