TCP protocol has been widely used on the internet.TCP responds to the channel condition and the traffic of the network dynamically, adjust the data rate injected to the network effectively and provides a reliable connection. The characteristics of TCP render for its wide spread usage in many applications and encourages the use of this protocol in wireless Ad Hoc networks. TCP protocol has many challenges in Ad Hoc networks as it was originally designed for wired networks. Every time that a packet is lost, TCP concludes that there is congestion in the network which is not always correct in Ad Hoc networks. In Ad Hoc networks reasons like lossy channel, contention in wireless medium and link breakage due to node mobility cause packet loss. Every time a packet is lost due to one of these reasons, TCP slows down and reduces size of congestion window which leads to throughput degradation although the reason for packet loss is not congestion. In this thesis the goal is to reduce the number of acknowledgement generated by the receiver in order to reduce contention between data packets and Acks. So collisions will be reduced and throughput is increased. This idea aims to mitigate the hidden terminal problem in the networks which are based on IEEE 802.11 protocol like Ad Hoc networks. In order to reduce number of Acks at the receiver, four techniques will be evaluated and simulated using NS2 network simulator. All techniques are implemented in two different scenarios: 1- SANET 2- MANET. In MANET scenario throughput is calculated for different speeds and in SANET scenario throughput is calculated for chains of hops of different length. Also in SANET scenario number of TCP connections between sender and receiver are changed. Then performance of all techniques is compared with original TCP algorithm. A new technique for delaying and reducing ACKs at the receiver will be proposed which estimates channel condition and changes the rate of ACKs accordingly. In the proposed technique, ACK rate is changed in an efficient way and TCP congestion window can increase faster to obtain better throughput. The new technique will be also simulated using NS2, compared with the other four techniques and the improvement will be shown.
