SSCH switches each radio across multiple channels so that multiple flows within interfering range of each other can simultaneously occur on orthogonal channels. This results in significantly increased network capacity when the network traffic pattern consists of such flows.
SSCH is a distributed protocol, suitable for deployment in a multi-hop wireless network. It does not require synchronization or leader election. Nodes do attempt to synchronize, but lack of synchronization results in at most a mild reduction in throughput.
SSCH defines a slot to be the time spent on a single channel. We choose a slot duration of 10 ms to amortize the overhead of channel switching. At 54 Mbps (the maximum data rate in IEEE 802.11a), 10 ms is equivalent to 35 maximum-length packet transmissions. A longer slot duration would have further decreased the overhead of channel switching, but would have increased the delay that packets encounter during some forwarding operations. The channel schedule is the list of channels that the node plans to switch to in subsequent slots and the time at which it plans to make each switch. Each node maintains a list of the channel schedules for all other nodes it is aware of - this information is allowed to be out-of-date, but the common case will be that it is accurate. The good performance exhibited by SSCH (Section 4) validates this claim.
We develop the SSCH protocol by first describing its assumptions about the underlying hardware and Medium Access Control (MAC) protocol (Section 3.1). We then describe the packet transmission attempts that are made by each node within a slot, and we refer to this as the packet schedule (Section 3.2). We then define the policy for updating the channel schedule and for propagating the channel schedule to other nodes (Section 3.3). We then describe the mathematical properties that guided SSCH's design (Section 3.4). Finally, we discuss implementation considerations for SSCH (Section 3.5).