| Summary: | 碩士 === 朝陽科技大學 === 資訊工程系碩士班 === 94 === In mobile ad-hoc networks (MANETs), the DCF protocol is commonly used to prevent collisions between nodes, each node has to wait for a random time period, called the backoff time, before it sends a handshaking signal to another node. However, when the number of nodes increases, the mean time of the random backoff time has to increase in order to reduce the probability of collisions. A performance degradation problem arises because a longer backoff time results in lower bandwidth utilization. A dynamically adjustable backoff time is proposed to improve bandwidth utilization. However, statistics of the network traffic for a period of time need to be determined in order to decide the backoff time dynamically; that is, collisions or low bandwidth utilization may occur before a proper mean value for the backoff time is set. In this paper, we address the problem of wasting bandwidth resources due to waiting for the backoff time and propose using multiple channels to achieve the goal of a high performance MAC design. In our design, a control channel and a data channel are used to improve bandwidth utilization. When the control channel waits for the backoff time, the data channel may transfer data. As a result, bandwidth utilization can be improved.
The IEEE 802.11 DCF protocol is commonly used for the medium access control layer (MAC) protocol to reduce the number of the collisions and contentions. mobile nodes have to wait for data transmission to be completed before they send data to anothers. As a result, performance degradation results from such limitations in the DCF mechanism. In this paper, we propose an overlapping data sub-channel method. The overlapping data sub-channel method can use a data sub-channel when the sender and receiver is currently using the same data sub-channel. In order to make the overlapping data sub-channel method work, we use the multiple channel technique to solve the interference problem. Although the overlapping data sub-channel method can increase the throughput, how to allocate the bandwidth of the control and data sub-channels to maximize bandwidth utilization is an important issue. we further propose a bandwidth allocation method to make the control signals and data signals in continuous frames be sent or received in a pipeline fashion.
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