針對無線感知網路下多頻帶傳輸機制的設計與分析

Abstract

近幾年來，基於跳頻選擇機制的資源擷取控制通訊協定 (channel-hopping based medium access control (MAC) protocols) 被提出來增進分散式多頻帶無線感知網路 (cognitive radio (CR) networks) 下的通道容量而不需使用額外的控制通道，在其中，每個感知使用者必須隨機去跟隨初始的跳頻序列 (channel-hopping sequence) 去進行通道的偵測以及資料傳輸。在本論文中，無線隨意感知網路基於跳頻選擇機制的資源擷取控制通訊協定在配對傳輸以及廣義傳輸的模式底下，考慮現實感知網路中的不完美通道檢測以及同步，利用排隊理論模型 (queueing theory) 提出感知網路下的通道吞吐量分析以及主要使用網路 (primary networks) 所能提供的通道空閒資源和其所受感知使用者影響所產生的封包延遲。接著，根據此分析模型，基於動態規畫 (dynamic programming) 的技巧，在主要使用者的封包延遲限制之下提出最佳的跳頻選擇機制 (OCS)，藉著開發最佳的資源分配機制去平衡通道空閒資源和通道使用率，此方法可以找出此網路底下最佳的通道吞吐量，同時降低對主要使用者的干擾。除此之外，在廣義的傳輸模式底下存在著所謂的邏輯分割問題 (logical partition problem)，由於感知網路中感知使用者溝通成功率的下降，它會造成網路中吞吐量嚴重的減少，由其是在比較雍塞的感知網路底下，因此，在此論文中，兩個演算法被提出來減緩此問題的發生，它們分別是喚醒連續競爭機制 (WSC) 以及喚醒計數器重設連續競爭機制 (WCSC)，藉由解決不完美通道檢測所產生的盲點，造成感知使用者被阻擋在通道外面，此兩種方法可以增加感知使用者間溝通的次數，更而增加網路中的吞吐量。從模擬的結果中可以看出所提出的最佳的跳頻選擇機制、喚醒連續競爭機制、喚醒計數器重設連續競爭機制的確和其它傳統的跳頻機制相比可以大幅提升網路的吞吐量，並且確保主要使用網路的封包延遲限制。

In recent years, channel-hopping based medium access control (MAC) protocols are proposed to improve the capacity in a decentralized multi-channel cognitive radio (CR) networks without extra usage of a control channel. Each CR user has to stochastically follow a default channel-hopping sequence in order to sense a channel and to conduct its frame transmission. In this thesis, based on the channel-hopping protocol in both the paired and generalized CR network, an analysis is conducted on both the probability of channel availability and the average frame delay for the primary queueing networks. Analytical model is proposed by considering the impact caused by the imperfect sensing of the CR users and the imperfect synchronization between the primary and CR networks. According to the proposed model with realistic considerations, an optimal channel-hopping sequence (OCS) approach is designed for the CR users based on dynamic programming technique. It is designed by exploiting the optimal load balance between both the channel availability and channel utilization within the delay constraints of primary users (PUs). By adopting the OCS approach, the maximum aggregate throughput of CR users and the quality of service (QoS) requirement of PUs can both be achieved. Moreover, in addition to the paired CR networks, the logical partition problem that occurs in the generalized CR network will also be addressed. The problem can severely degrade the aggregate throughput due to the decreasing probability in connectivity between the CR users, especially under CR network with heavy traffic. Therefore, both the wake-up successive contention (WSC) and the wake-up counter-reset successive contention (WCSC) algorithms are proposed to increase the number of negotiations by exploring a blind spot in imperfect sensing and amending the contention mechanisms between the CR users. Numerical results illustrate that the proposed OCS, OCS-WSC, and OCS-WCSC schemes can e®ectively maximize the aggregate throughput compared to the conventional channel-hopping sequences, and as well guarantee the QoS requirement of the PUs.