Minimal CDMA Recoding Strategies in Power-Controlled Ad-Hoc WirelessNetworks
The problem of Code Division Multiple Access (CDMA) code assignment to eliminate primary and hidden collisions in multihop packet radio networks has been widely researched in the past. However, very little work has been done on the very realistic *distributed, dynamic* version of the transmitter-oriented code assignment (TOCA) problem in an ad-hoc network where mobiles use CDMA technology. None of the existing dynamic TOCA CDMA algorithms in literature are efficient, in terms of maximum code index assigned in the network, or number of times a mobile has to change its code. We present a set of local and distributed *recoding* strategies for the TOCA CDMA problem in an ad-hoc network where mobiles can arbitrarily 1) connect and disconnect, 2) move about, and 3) increase or decrease their transmission power - all these may need some mobiles to be recoded, to avoid new collisions. Our strategies, unlike those proposed earlier in literature, guarantee *minimal recoding*, that is, given a current network-wide code assignment and one of the above events, our strategies change the codes of the minimum number of mobiles needed to eliminate all collisions. Minimal recoding can be very important in reducing the effect of frequent code changes on the performance and criticality of distributed applications. Further, among all possible minimal recoding strategies in a class, most of our strategies are also (provably) *optimal* in terms of the maximum code index assigned in the network. Performance results that evaluate our dynamic minimal strategies are also presented.
computer science; technical report
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