8 research outputs found
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An Adaptive Tree Algorithm to Approach Collision-Free Transmission in Slo ed ALOHA
KALOHA: ike i ke ALOHA
A new family of channel-access schemes called KALOHA (for ``Knowledge in ALOHA") is introduced. KALOHA consists of modifying the pure ALOHA protocol by endowing nodes with knowledge regarding the local times when packets and acknowledgments are received, and sharing estimates of channel utilization at the medium access control (MAC) layer. The only physical-layer feedback needed in KALOHA is the reception of correct data packets and their ACKs. A simple Markov-chain model is used to compare the throughput of KALOHA with ALOHA and slotted ALOHA. The analysis takes into account the amount of knowledge that nodes have and the effect of acknowledgments and turnaround latencies. The results demonstrate the benefits derived from using and sharing knowledge of channel utilization at the MAC layer. KALOHA is more stable than ALOHA and attains more than double the throughput of ALOHA, without the need for carrier sensing, requiring time slotting at the physical layer, or using other physical-layer mechanisms
Hybrid channel access scheduling in Ad Hoc networks
We present the hybrid activation multiple access (HAMA) protocol for ad hoc networks. Unlike previous channel access scheduling protocols that activate either nodes or links only, HAMA is a node-activation channel access protocol that also maximizes the chance of link activations using time- and code-division schemes. HAMA only requires identifiers of the neighbors within two hops from each node to schedule channel access. Using this neighborhood information, each node determines whether to transmit in the current time slot on a dynamically assigned spreading code. A neighbor protocol supplements HAMA with up-to-date two-hop neighborhood information by reliably propagating the one-hop neighbor updates through a novel random access technique. The throughput and delay characteristics of HAMA in randomly-generated multihop wireless networks are studied by analyses and simulations. The results of the analyses show that HAMA achieves higher channel utilization in ad hoc networks than a distributed scheduling scheme based on node activation, similar throughout as a well-known scheduling algorithm based on complete topology information, and much higher throughout than the ideal CSMA and CSMA/CA protocols.