無線隨意網路上以迴歸補救方式運行的無信標繞徑

Abstract

在無線隨意網路中，Beaconless geographic routing(BLR)能讓節點不必知道他們鄰居點座標位置下執行greedy forwarding，節點依靠RTS/CTS機制讓鄰居點從RTS封包有足夠的資訊執行MAC contention，最先回應CTS封包的鄰居點視為下個中繼點。如果當節點已無法從鄰居點得到回應時，表示當下封包所在節點離目的節點是最近的，greedy forwarding失敗後換成補救方法rotation sweep algorithm，鄰居點依幾何圖形(如Reuleaux triangle)運作機制決定MAC conten-tion競爭回傳時間，確保封包正確的繞徑路線和減少所傳的節點數。著名的BLR研究成果都假設在節點具有相同的傳輸範圍，這在真實網路中是不可能成立的，以致於先前可信任的方法難以實際應用。 在真實網路中，節點間連接是不完美的，我們修改greedy forwarding流程，在MAC conten-tion的設計納入距離和角度因素，在補救方法方面，主要將cooperation rotational sweep 網路第三層繞徑方式調整到MAC和Routing的跨層運作方式，目的是利用cooperation rotational sweep犧牲封包標頭的空間來記錄歷史節點的位置資訊，讓各個鄰居點能利用歷史節點來解決傳送過程中存在的隱藏節點問題。 將所提出的方法模擬實驗結果呈現封包抵達率、路徑延展和CTS封包碰撞次數都會隨著封包標頭所記錄的歷史節點個數成正向成長。

Beaconless geographic routing(BLR) allows nodes to perform greedy forwarding without the knowledge of the neighborhood in wireless Ad Hoc network. The node relies on the RTS/CTS mechanism to offer neigh-bors enough information from the RTS packet to implement MAC contention. The neighbor node that first successfully responds with a CTS packet is chosen as the next relay. If the node doesn’t get a CTS response from neighbors, it is implicitly located locally closest to the destination node. Rotation sweep algorithm is then applied after the greedy forwarding fails. Neighbors rely on a sweep of curve with some geometry (such as Reuleaux triangle) to decide the response time of sending a CTS response in MAC contention. Recovery approach adjusts the routing path of sending a packet so as to improve routing success rate. The well-known BLR research assumes that all node have the same transmission range. The assumption is not true in reality, and therefore their methods are difficult to apply practically. In this work, the range of connection between nodes is not fixed. We modify the greedy forwarding pro-cess to include the variables of distance and angle into the design of MAC contention latency. For recovery mode operation, we adopt the technique of cooperative rotational sweep scheme for use in the cross-layer operation involving MAC contention and routing decision here. This is essentially at the cost of packet head-er overhead to record the positions of historical visited nodes, so that each neighbor can solve the hidden node problem existing in a network topology. Simulation results show that the packet arrival ratio, path sketch and CTS packet collisions increase with the number of historical nodes memorized in packet header.