The performance of an "imbedded" Aloha protocol in wireless networks

We propose a protocol "imbedding" technique whereby a secondary, slotted Aloha protocol is imbedded within the idle slots of an existing primary, slotted-time, multiple access scheme via "idle sensing", a form of carrier sense multiple access. We consider two applications: mixed-priority data transmission in multistation networks and integrated voice/data operation in cellular systems. For mixed-priority data transmission, we propose a two-level, imbedded, slotted Aloha protocol which consists of a primary and secondary level protocol. The secondary's operation is imbedded within the idle slots of the primary. Higher priority traffic is given to the primary protocol and lower priority traffic is given to the secondary. Since the performance of the primary slotted Aloha protocol (which operates independently of the secondary) is well known, we focus on the performance of the secondary protocol and analyze its throughput and delay. The protocol's operation is studied in both single cell and multicell settings where, in the latter, intercell interference is modeled as feedback errors. We present a novel approximation method for analyzing the secondary protocol's performance based on the notion that the non-empty slots of the primary protocol can also be viewed as the "feedback error interference" at the secondary protocol. This reduces the order of the underlying Markov chain from two dimensions to one with almost no loss of accuracy. Using these same methods, we also study the usage of this imbedding technique for data transmission in a voice-only, cellular TDMA system.