IEEE 802.11 MAC protocol uses two techniques to avoid interference ¡V physical carrier sensing and RTS/CTS handshake (virtual carrier sensing). Ideally, these two techniques can solve most of interference problem. But in normal situation a host cannot receive packet successfully unless the power of receiving signal is much higher than that of interference signal. This fact leads that other host can interfere the reception in farther distance than the distance between the transmitter and the receiver. When the distance between the transmitter and the receiver is larger than certain value, some hosts that are out of the range covered by RTS/CTS packet may still interfere the receiver. This problem can be solved by using a very large physical carrier sensing range, which is limited by antenna and will reduce the network throughput. So it¡¦s not suitable to avoid large interference problem. So far some schemes were proposed to solve or improve this problem, but most of them cause power waste at the same time. In this thesis, we will propose a scheme to look after both interference and power consumption. Simulation results verify that our scheme can solve most interference caused by large interference range with less power consumption.

In the present day, Ad Hoc wireless networks are quite convenient in a local area. But hidden terminal problems and exposed terminal problems exits in Ad Hoc networks. So how to avoid these problems and add channel bandwidth utilization efficiently in MAC (Medium Access Control) layer is a very critical topic. A number of MAC protocols have been presented to overcome these drawbacks, such as RTS / CTS ¡V based and busy tone ¡V based protocol. In this paper, we proposed a dynamic power control scheme, Adjustable Power Control Protocol (APC). APC is based on the concept of power level with broadcasted message. The basic idea is sender should not interfere with other hosts¡¦ going transmissions. Sender would use a suitable power level to send its data so as to overcome above problems. Our simulations show that the channel utilizations of APC is indeed increased in the same time.

Ad hoc wireless networks are constructed by several mobile hosts and have a property that its topology is changed as mobile hosts moved. There is no stationary infrastructure or based station to coordinate packets transmissions and advertise the information of network topology or something important. The special networks are used in temporal wireless networks, such as battlefield, disease rescue place, and so on. So without any stationary infrastructure supported, mobile hosts can communicate with others immediately or indirectly. Because topology is often changed while mobile hosts moving, mobile hosts must exchange information to deal with the changed conditions. Mobile hosts often utilize broadcasting to exchange information with their neighbor hosts, but there is high bit error ratio in wireless networks, packet corruption occurs frequently, so that mobile host might lost some important information sent from its neighboring host. In 802.11 standard, lack of acknowledgement, broadcasting is an unreliable transmission, because sender host do not know whether all of it neighboring hosts received broadcasting packets correctly or no. Many proposed papers of reliable broadcast assumed that links between mobile hosts are bidirectional links, but bidirectional link is an ideal assumption. In real environment, links are unidirectional, so host A could send packets to host B immediately, but host B could not because of their transmission range are different. In this paper, we propose a new reliable broadcast scheme, Highly Reliable Broadcast Scheme with Directional Antennas (HRBSDA). HRBSDA can reduce the influence of unidirectional links and reach for highly reliable broadcasting. HRBSDA uses directional antennas and concept of Time Division Multiple Access (TDMA)-like. HRBSDA divide DCF Inter-Frame Space (DIFS) into several minislots, and mobile hosts use these minislots to ask sender for retransmission of lost packets. By the way, HRBSDA can not only reach for highly reliable broadcasting, but also reduce Packet Loss Recovery Time, and avoid causing extra overhead. Using directional antennas HRBSDA can reduce collision, so that improving throughput and channel utilization.

The standard IEEE 802.11 MAC protocol assumes that each mobile host uses maximum transmission power for the transmission of each packet. However, energy is very valuable resources for mobile host in ad hoc wireless network. In the past, several researches about power control were proposed. These power control schemes use different power levels and one more separate power control channel in order to save energy, avoid occurrence of collision, and increase network channel utilization. But various power levels lead to each mobile host having different transmission power ranges, and cause the additional hidden terminal problem, namely heterogeneous power terminal problem. Therefore, in this paper, we propose a simple and efficient power control protocol that used dynamic adjustment transmission power ranges to reduce power consumption, avoid collision, increase the network channel utilization, and ease heterogeneous power terminal problem as well.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: This thesis involves research on wildlife telemetry tracking for the Cape Leopard Trust (CLT). The CLT needed a network to transfer GPS data and single frame photos from remote locations in the Cederberg to a researcher's base station. The proposed solution is an ad hoc wireless network, where nodes perform polling of leopard collars and send information via the multi-hop network to the researcher's base once it is downloaded from a collar. The literature study involved medium access control - and routing protocols for e ectively transferring information. The solution was implemented in hardware and range tests were done in the Cederberg to determine feasible locations for nodes in this network for covering most of the CLT study area. Link budgets for this area was determined with Radio Mobile to compare with actual ranges as measured. The simulation of protocols was done in OMNET++ which could be compared with actual results from the physical network. / AFRIKAANSE OPSOMMING: Hierdie tesis handel oor navorsing wat gedoen is vir die Kaapse Luipaard Trust (CLT) vir die opsporing van luipaarde. Die CLT het 'n netwerk nodig gehad wat GPS data en enkel raam fotos van afgeleë gebiede in die Cederberge na 'n navorser se basis stuur. Die voorgestelde oplossing is 'n ad hoc draadlose netwerk, waar nodisse luipaard nekbande oproep om data af te laai en dan te stuur deur die multi-hop netwerk na die navorser se basis. Die literatuurstudie handel oor medium toegangs beheer - en roete verkryging protokolle vir die effektiewe oordrag van informasie. Die oplossing is in hardeware geïmplimenteer en radio-afstand-toetse is gedoen in die Cederberge om goedgeleë posisies vir nodisse te bepaal om die grootste gedeelte van die CLT studie area te dek. Radio Mobile is gebruik om voorspellings te maak rakende die afstande verkrygbaar tussen radios om te vergelyk met die fisiese metings in die veld. Die simulasie van protokolle is gedoen in OMNET++ en vergelyk met prestasie metings op die fisiese netwerk.