||The most studies on ad hoc network mainly focus on TCP (Transmission Control Protocol) of transport layer, the routing of network layer, multi-hop of Data-link layer, and the integration of WWAN and WLAN to increase the load balancing, coverage, and power savings. Nevertheless, in this dissertation, the system performances of four schemes proposed are improved with respect to data-link and network layers.|
One purpose of the data link layer is to perform error correction or detection. The other is responsible for the way in which different users share the transmission medium. The Medium Access Control (MAC) sublayer is responsible for allowing frames to be sent over the shared media without undue interference with other users. This aspect is referred to as multi-access communications. In the first and third schemes, the FDMA (Frequently-division multiple access) is employed to improve system performance, while in the fourth scheme the CDMA (Code-division multiple access) is used to enhance performance.
Network layer has several functions, first is to determine the routing information. A second function is to determine the quality of service. A third function is flow control to avoid network to become congested. In the third scheme, the data-link and network layers have been used to increase system performance. Furthermore, the second scheme mainly concentrates on power savings under wireless sensor network.
In ad hoc wireless networks, most data delivery is accomplished through multi-hop routing (hop by hop). This approach may leads to long delay and routing overhead regardless of which routing protocol is used. To overcome this inherent characteristic, this work presents a novel idea adopting dual-card-mode and performing self-organization process with specific IP naming and channel assignment to form a hierarchical star-graph ad hoc network (HSG-ad hoc) which can not only expedite the data transmission but also eliminate the route discovery procedure during data transmission. Therefore, the overall network reliability and stability can be significantly improved. Simulation results show that the proposed approach achieves substantial improvements in terms of average end-to-end delay, throughput, and packet delivery ratio.
In a large-scale wireless sensor network, a topology is needed to gather state-based data from sensor network and efficiently aggregate the data given the requirements of balanced load, minimal energy consumption and prolonged network lifetime. In this study, we proposed a ring-based hierarchical clustering scheme (RHC) consisting of four phases: pre-deployment, parent-child relationship building, deployment, and member join phases. Two node types are distributed throughout the network: cluster head nodes (type 1 node) and general sensor nodes (type 2 node). The type 1 node has better battery life, software capability and hardware features than the type 2 node does; therefore, the type 1 node is a better cluster head than type 2 node.
Most routing protocols focus mainly on obtaining a workable route without considering network traffic conditions for a mobile ad hoc network. Consequently, real time and multimedia applications do not achieve adequate quality of service (QoS). To support QoS, this work proposes a QoS-aware routing protocol, i.e. QUality of service with Admission control RouTing (QUART), that incorporates an admission control scheme into route discovery and route setup procedures. One variant of QUART, called, QUART-DD, adopts a dual-card dual-signal mechanism to increase system performance. Simulation results indicate that QUART-DD can significantly improve packet delivery ratio and throughput, while having a lower average end-to-end delay than routing protocols without QoS support.
The performance of ad hoc wireless network suffers from problems in multi-hop transmission. This study adopts code division to modulate the frame header and the frame payload separately. A common spreading code modulates the frame header, and a special spreading code is negotiated and to modulate the frame payload. A field in the frame header indicates the spreading code used to modulate the successive frame payload. The modulated frame is transparent for every node, enabling many frames to be transmitted simultaneously. To allow the special spreading code negotiation, the RTS/CTS command is modified as ERTS/ECTS, and a spreading code table (SCT) is maintained in every node. Due to the space reuse, the proposed scheme has superior performance in latency and bandwidth utilization, as revealed by the simulation results.