| 摘要: | 近年來，由於無線網路使用者日益增加，開發多頻道利用率已受到學者們的重視，而會面問題與多頻道隱藏節點問題是Multi-Channel中首要解決的兩大挑戰，如何發展一好的協定以克服其兩大挑戰，已成為一熱門的研究議題。此外，由於Cognitive Radio Networks (CRNs)環境，皆為多頻道之網路環境，因此，亦必須克服會面問題與多頻道隱藏節點問題，且現存之次級使用者(Secondary Users，SUs)如何能達到不影響優先使用者(Primary Users，PUs)傳輸的前提下，尋找並使用其頻道傳輸，亦為一重要的研究議題。因此，本論文針對CRNs環境與一般多頻道網路環境研發出三種不同的MAC Protocol，分別為SMC-CR-MAC、QM-MAC與HM-MAC，其中SMC-CR-MAC作用於CRNs中，QM-MAC與HM-MAC則作用於一般的多頻道網路環境中。SMC-CR-MAC，將解決SUs會面與頻寬資源浪費的問題，使各個SUs能夠在不影響PUs的情況下進行資料傳輸，提高頻寬利用率以及降低SUs的資料傳輸延遲時間。透過QM-MAC，能夠提高網路效能，HM-MAC則針對QM-MAC所產生的公平性問題進行修改，進一步達到網路平衡。
Recently, developing the Medium Access Control (MAC) protocol has been considered in such a way for improving the utilization of wireless spectrum. However, to develop the multi-channel MAC protocol, there are two challenges need to be considered, the Rendezvous Problem and Multi-Channel Hidden Terminal Problem. To handle the rendezvous problem, some literatures can be classified into the control-channel based (CCB) channel model. In this channel model, all node stay on the control channel to reserve the proper data channel for data exchange. Nevertheless, the channel model will introduced the multi-channel hidden terminal problem. Herein, to overcome the above-mentioned problems, other previous studies can fall into the class of control-period based channel model (CPB) channel model. In this channel model, all nodes stay on the ATIM window of the predefined channel to exchange control packets to reserve the data window. However, since all nodes should switch to the default channel for participating in the ATIM windows, the ATIM windows of all channels other than the default channel will not be used, resulting in poor network performance.
This thesis firstly proposed two multi-channel MAC protocols which aim at improving the channel utilization without rendezvous and multi-channel hidden terminal problems. The first MAC protocol, named QM-MAC, employs the concept of the Quorum system. By applying the Quorum system, the node only equips with one transceiver can resolve the rendezvous and multi-channel hidden terminal problems. Moreover, the network throughput can be obviously improved. On the other hand, in the second multi-channel MAC protocol, called HM-MAC, applies the Hadamard matrix to increase the network performance in terms of the utilization of control window, traffic load-balanced, and network throughput.
As a result, the wireless spectrum can be fully utilized, however, the wireless spectrum demand has greatly increased in the last few decades because that the rapid deployment of new wireless devices and applications. Cognitive Radio (CR) is a novel and promising spectrum management technique proposed recently, which is able to alleviate the inefficient spectrum utilization and spectrum scarcity problems by opportunistically employing portions of the licensed bands.
To ensure that the operation of licensed users will not be adversely affected, this paper proposes a stepwise multi-channel MAC protocol, called SMC-CR-MAC. By applying the proposed SMC-CR-MAC protocol, the spectrum utilization can be maximized, hence increasing the network throughput. In addition, two types of the detection situations are considered. According to the detection situation, several problems might occur, resulting in the failure data exchange. To successfully exchange data between sender and receiver, the proposed SMC-CR-MAC applies Contiguous Channel Swap and Sender-Receiver Channel Swap approaches. By applying above two approaches, the rendezvous, packet collision and the channel congestion problems can be overcome. Simulation results show that the proposed QM-MAC, HM-MAC and SMC-CR-MAC protocols can obviously improve the network performance in terms of utilization of wireless spectrum, traffic load-balanced, and network throughput. |
