The Role of Error Correlations in the Design of Protocols for Packet Switched Services Michele Zorzi and Ramesh R. Rao Center for Wireless Communications, University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093-0407 e-mail: zorzi,rao @ece.ucsd.edu 35th Annual Allerton Conference on Communications, Control and Computing Allerton House, Monticello, IL, Sept. 29 – Oct. 1, 1997 Abstract In this paper we show that correlated errors can be potentially beneficial in packet com- munications. We present results that confirm this at the MAC level by focusing on packet scheduling and documenting the extent to which knowledge of the channel correlations can help improve efficiency of channel utilization. We then summarize some recent find- ings at other levels of the protocol stack, and discuss some implications to protocol design for the wireless channel. 1 Introduction Fading impacts every layer of a protocol stack, regardless of the number and nature of func- tions assigned to the various layers. In this paper, we focus on the effect of error correlation introduced by fading, and in particular on its impact at the media access control (MAC) layer and the transport layer. The traditional role of MAC protocols is to enable a group of uncoordinated users to share a common channel. In the development of MAC protocols for the wireless environment, one detects a certain convergence of thinking on the structure of such protocols. There is typically a segment of the protocol that deals with the initial signaling between the multiple users and the base station or central controller. Then there is a segment of the protocol that allocates the available resource, be it time slots, frequency channels or codes, to the users that have already signaled their needs. The allocation process is sometimes hard wired, as in the PRMA protocol [1] which specifies exactly how to allocate the slots. Other proposal, such as the DQRUMA protocol [2] or the CDPA architecture [3], are more flexible and allow for various types of allo- cation strategies to be implemented. In any event, nearly all recently proposed MAC protocols focus on the need to develop explicit or implicit scheduling algorithms for accommodating heterogeneous users but many of them ignore the capriciousness of the wireless channel that results from fading and mobility. 1