On the performance of slotted ALOHA in a spread spectrum environment

Abstract

We present an extension of the slotted ALOHA protocol for use in a spread spectrum packet radio environment. With spread spectrum, we assume that N distinct codes are available, and that each code can be treated as a separate channel. Running an independent copy of the protocol on each of these channels would be undesirable, since each user would have to select one channel to monitor for packets addressed to it, inducing a logical partitioning of the user population into N groups. To preserve the logical connectivity of the network, we examine the effect of separating packet transmissions into two parts, a short preamble, which is sent over a public channel, and followed by the body,> which is sent over a private channel. We assume that m of the available codes are used as preamble channels, and the remaining N - m codes are used for actual packet transmissions. If m (@@@@) N, then the network can support broadcast and multicast packets, and still make use of all of the available channels.