Broadcast communications is critically important in vehicular networks. Many safety applications need safety warning messages to be broadcast to all vehicles present in an area. In this thesis, we propose a novel repetition-based broadcast protocol based on ``optical orthogonal codes.'' Optical orthogonal codes are used because of their ability to reduce the possibility of collision. We present a detailed mathematical analysis for obtaining the probability of success and the average delay. Furthermore, we propose to use coding to increase network throughput, and ``adaptive elimination'' of potentially colliding transmissions to further increase reliability. We show, by analysis and simulations, that the proposed protocol outperforms existing repetition-based ones and provides reliable broadcast communications and can reliably deliver safety messages under load conditions deemed to be common in vehicular environments. We also show that the proposed protocol is able to provide different levels of quality of service.

Broadcast communications is critically important in vehicular networks. Many safety applications need safety warning messages to be broadcast to all vehicles present in an area. In this thesis, we propose a novel repetition-based broadcast protocol based on ``optical orthogonal codes.'' Optical orthogonal codes are used because of their ability to reduce the possibility of collision. We present a detailed mathematical analysis for obtaining the probability of success and the average delay. Furthermore, we propose to use coding to increase network throughput, and ``adaptive elimination'' of potentially colliding transmissions to further increase reliability. We show, by analysis and simulations, that the proposed protocol outperforms existing repetition-based ones and provides reliable broadcast communications and can reliably deliver safety messages under load conditions deemed to be common in vehicular environments. We also show that the proposed protocol is able to provide different levels of quality of service.

Ad hoc networks are becoming an interesting research area, as they inher-ently support unique network applications for the wireless communications in a rug-ged environment, which requires rapid deployment and is difficult to be provided by an infrastructure network. Many issues need to be addressed for the ad hoc networks. In this dissertation, we propose an efficient distributed coordination function, a dynamic rate adaptation and fragmentation scheme, and a simultaneous frame transmission scheme on the media access control protocol to enhance the power conservation of mobile hosts and to im-prove the network throughput of an ad hoc network. Extensive simulations are studied to evaluate the improvement of the proposed schemes. The results of the simulations exhibit significant improvement to the stan-dard access control protocol. Not only the improvement of the throughput of the ad hoc networks, but also the conservation of the battery power of the mobile hosts were achieved with our schemes.

In this thesis, we proposed a delay limited routing scheme in wireless ad hoc networks. When nodes transmit packets in wireless ad hoc networks, most people think the one-hop way is better than the multi-hop way in reducing the delay time. Since most cases in wireless ad hoc networks are not single sources, we should consider at least two sources transmitting packets at the same time and then use the multi-hop way in order to reduce the energy consumption. We want to maximize the throughput with limited delay. Our contribution is to transform the optimal scheduling problem in wireless ad hoc networks to the classic maximum flow problem. The maximum flow approach does maximize the throughput and can get the optimal solution.

In this thesis, we consider how to reduce the communication cost of the key exchange procedures as many as possible, while the secure group communication can still be achieved. Due to the energy consumption is usually proportional to the distance, we use the shortest paths algorithm to find the shortest communication paths between any pair of the secure group members. We first propose a straightforward heuristic named Minimum-Energy First-Selected ( MEFS ). MEFS tries to select the pair of group members which has less communication cost than all other pairs have at every time. Though MEFS performs better than random selecting, it still has some weakness in solving the energy-aware key management problem. So we use the concept of the minimum cost flow problem, and by appropriate transformation, then we get the optimal solution of the energy-aware key management problem under some constraints. At last, the simulation results proves that the minimum cost flow approach actually works better than MEFS does.

In recent years, there has been a growing interest in wireless ad hoc network. One of the major issues in wireless network is developing efficient routing protocol. Based on the concept of designing protocol model such as OSI model, the designers distilled the process of transmitting data to its most fundamental elements and identified which networking functions had related uses and collected those functions into discrete groups that became the layers. It is not suitable to design wireless ad hoc routing protocol based on OSI model conception because the OSI model is developed from the view point of wired network and there are many different characteristics between wired and wireless environment. The main different characteristics between wired and wireless are the mobility of mobile host and the transmission medium. Such differences have great effect on network performance. Due to the differences between wired and wireless characteristics, we present a comprehensive conception of designing wireless ad hoc routing protocol. In this context, we provide a wireless ad hoc routing protocol based on physical layer characteristics, ex: bit error rate, robust link. Our routing protocol will find out a route in good transmission environment and it is efficient to improve network throughput. Furthermore, our routing protocol will decrease the number of route request packets, the amount of retransmissions, link breakage rate, and increase throughput.

Broadcasting is a fundamental primitive in local area networks (LANs).Operations of many data link protocols, for example, ARP (Address Resolution Protocol) and IGMP (Internet Group Management Protocol), must rely on this LAN primitive. To develop the broadcasting service in mobile ad hoc wireless LANs (WLANs) is a challenge. This is because a mobile ad hoc WLAN is a multi-hop wireless network in which messages may travel along several links from the source to the destination via a certain path. Additionally, there is no fixed network topology because of host moving. Furthermore, the broadcast nature of a radio channel makes a packet be transmitted by a node to be able to reach all neighbors. Therefore, the total number of transmissions (forward nodes) is generally used as the cost criterion for broadcasting. The problem of finding the minimum number of forward nodes in a static radio network is NP-complete. Almost all previous works, therefore, for broadcasting in the WLAN are focusing on finding approximation approaches in a, rather than, environment. In this paper, we propose a novel distributed protocol in WLANs to significantly reduce or eliminate the communication overhead in addition to maintaining positions of neighboring nodes. The important features of our proposed protocol are the adaptability to dynamic network topology change and the utilization of the existing routing protocol. The reduction in communication overhead for broadcasting operation is measured experimentally. From the simulation results, our protocol not only has the similar performance as the approximation approaches in the static network, but also outperforms existing ones in the adaptability to host moving.

With the growth of Internet, the underlying protocols are increasingly challenged by new technologies and applications. The original Internet protocols were, however, not designed for wireless communication, mobility, long disconnection times, and varying bandwidths. In this thesis, we study challenged networking, and how well old and new protocols operate under such constraints. Our study is experimental. We build network testbeds and measure the performance of alternative protocols and architectures. We develop novel methodologies for repeatable experiments that combine emulations, simulations and real world experiments. Based on our results we suggest modifications to existing protocols, and we also develop a new network architecture that matches the constraints of a challenged network, in our case, an opportunistic network. One of our most important contributions is an Ad hoc Protocol Evaluation (APE) testbed. It has been successfully used worldwide. The key to its success is that it significantly lowers the barrier to repeatable experiments involving wireless and mobile computing devices. Using APE, we present side-by-side performance comparisons of IETF MANET routing protocols. A somewhat surprising result is that some ad hoc routing protocols perform a factor 10 worse in the testbed than predicted by a common simulation tool (ns-2). We find that this discrepancy is mainly related to the protocols’ sensing abilities, e.g., how accurately they can infer their neighborhood in a real radio environment. We propose and implement improvements to these protocols based on the results. Our novel network architecture Haggle is another important contribution. It is based on content addressing and searching. Mobile devices in opportunistic networks exchange content whenever they detect each other. We suggest that the exchange should be based on interests and searches, rather than on destination names and addresses. We argue that content binding should be done late in challenged networks, something which our search approach supports well.

Wireless networks are less reliable than wired networks because channels are “exposed” to the surrounding environment that is susceptible to interference and noise. To minimize losses of data due to collisions, wireless networks need a mechanism to regulate the access on the transmission medium. Medium Access Control (MAC) protocols control access to the shared communication medium so that it can be used efficiently. In this thesis, we first describe the collision-controlled Dual Prohibition Multiple Access (DPMA) protocol [45]. The main mechanisms implemented in DPMA, such as binary dual prohibition, power control, interference control, and support for differentiated services (DiffServ), are presented in detail. We conducted a thorough simulation study on DPMA protocol from several aspects. First, we conduct simulations to observe the effects of binary competition number (BCN), unit slot length and safe margin on the performance of DPMA. Secondly, the DiffServ capability of DPMA is demonstrated through simulation results. Finally, we compare the DPMA protocol with the CSMA/CA protocol and find that DPMA with optimal configuration has better performance than CSMA/CA under both low and high network density. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-09-28 16:25:02.515

How much damage can a malicious tiny device cause in a single-hopwireless network? Imagine two players, Alice and Bob, who want toexchange information. Collin, a malicious adversary, wants to preventthem from communicating. By broadcasting at the same time as Alice orBob, Collin can destroy their messages or overwhelm them with his ownmalicious data. Being a tiny device, however, Collin can onlybroadcast up to B times. Given that Alice and Bob do not knowB, and cannot distinguish honest from malicious messages, howlong can Collin prevent them from communicating? We show the answerto be 2B + Theta(lg|V|) communication rounds, where V is theset of values that Alice and Bob may transmit. We prove this resultto be optimal by deriving an algorithm that matches our lowerbound---even in the stronger case where Alice and Bob do not start thegame at the same time.We then argue that this specific 3-player game captures the generalextent to which a malicious adversary can disrupt coordination in asingle-hop wireless network. We support this claim by deriving---via reduction from the 3-player game---round complexity lower boundsfor several classical n-player problems: 2B + Theta(lg|V|) for reliable broadcast,2B + Omega(lg(n/k)) for leader election among k contenders,and 2B + Omega(k*lg(|V|/k)) for static k-selection. We then consider an extension of our adversary model that also includes up to t crash failures. We study binary consensus as the archetypal problem for this environment and show a bound of 2B + Theta(t) rounds. We conclude by providing tight, or nearly tight, upper bounds for all four problems. The new upper and lower bounds in this paper represent the first such results for a wireless network in which the adversary has the ability to disrupt communication.