為了提高無線電頻譜的使用率，因而促生了感知無線電的概念。感知無線電的發明，使得非授權使用者可以動態地利用閒置頻道互相通訊。這些閒置頻道原先是分配給授權使用者但卻在某時段閒置無用的。感知無線電網路由這些動態使用者以不同裝置、不同頻率感知能力所組成，可廣泛地被應用在多種情境。而要讓一對感知無線電開始通訊，有兩個重要步驟：頻道相遇與資料頻道之協調。
頻道相遇指得是兩個感知無線電在同一時間調頻到同一頻道。在寬頻或動態使用者所組成之感知無線電網路上，可被使用的候選頻道數非常大，使得現有的跳頻相遇方法遭遇巨大的相遇延遲。此延遲對絕大多數的應用情境來說皆無法接受。另一方面，在使用者眾多的場所，現有跳頻相遇方法亦會造成使用之頻道壅塞。
資料頻道之協調發生在頻道相遇之後，指得是兩個感知無線電協調並同意使用一或多個共同閒置頻道作為傳輸資料之資料頻道。而傳輸的資料在同一應用情境亦可小可大，如災情緊急訊息可為文字(小資料)或影音(大資料) 。但不同的資料頻道協調方法，及其在不同大小之資料上的效能並未有人研究過。此外，在實際運用上，感知無線電尚需處理傳輸角色變換、無法對時等難題。
針對上述問題，此論文提出了快速達成頻道相遇的演算法，大幅縮減相遇時間，與此同時，也提出了將動態使用者之通訊分散在不同頻道上避免頻道壅塞的方法。另一方面，不同的資料頻道協調方法也被完盡地驗證其效能，並以其為基礎，提出了一套資料頻道篩選演算法，可使感知無線電間的資料傳輸更加穩定。廣泛的實驗結果顯示，我們提出的頻道相遇及資料頻道篩選演算法可達到快速低延遲、低頻道壅塞並減少了傳輸中斷之可能性。

The Cognitive Radios (CRs) are proposed aiming to increase the usage of radio spectrum. Cognitive Radios allow the Secondary Users (SUs) to opportunistically utilize the avail- able channels, i.e., channels that have been allocated to the Primary Users (PUs, or called licensed users) but are idle currently, to communicate with each other. Cognitive Radio Networks (CRNs) are formed by stranger devices are useful or necessary for many appli- cations and are likely to contain heterogeneous devices with different sensing capabilities. There are two known steps for a pair of CRs to start communication: the rendezvous and data-channel negotiation.

By rendezvous we mean that two CRs will tune into some common available channels at the same time. In wideband CRNs or stranger CRNs where the number of potential channels, n, is large, existing CH sequence construction schemes incur a long delay to ren- dezvous (proportional to O(n2)) that are unlikely to be acceptable in many applications. Also, rendezvous schemes may fail due to congestion with multiple CRs in those crowded places, like cities.

For data-channel negotiation after rendezvous, two CRs need to agree on one or more common available channels and use these channels as the data-channels for data transmis- sion. The data size may be either small (e.g., when transmitting text) or large (e.g, when transmitting multimedia) in the same application scenario. But the impact of different data-channel negotiation schemes on the data transmission performance, both for small and large data size, remains unclear. Moreover, some practical issues in such wideband and stranger CRNs, such as role-agile and async clocks, should be coped with.

This thesis provides fast rendezvous schemes that shorten the rendezvous time, and at the same time, balance the communication loading over different channels. Also, the effec- tiveness of different data-channel negotiation schemes have been thoughtfully investigated and a new data-channel selection algorithm is proposed to ensure a stable data transmis- sion between CRs. The extensive simulation results show that the proposed schemes gives acceptable delay and low loading and reduces interruptions during transmissions.

Abstract .......................... i
Acknowledgements .......................... iii
1 Introduction .......................... 1
2 Related Literature .......................... 7
2.1 Channel-Availability Models .......................... 7
2.2 Rendezvous Schemes .............................. 8
2.2.1 Centralized Schemes .......................... 8
2.2.2 Channel Hopping (CH) Schemes.................... 9
2.2.3 Short-Cycle CH schemes ........................ 10
2.3 Data-Channel Negotiation ........................... 11
2.3.1 Data-Channel Negotiation Schemes .................. 11
2.3.2 Channel Stability Model ........................ 13
3 Fast Pairwise Rendezvous Scheme for Heterogeneous CRs .......................... 14
3.1 Overview..................................... 15
3.2 Existing CH Techniques and Remaining Challenges . . . . . . . . . . . . . 19
3.2.1 Techniques for Guaranteeing Rendezvous . . . . . . . . . . . . . . . 22
3.2.2 Techniques for Coping with Asynchronous Timers . . . . . . . . . . 22
3.2.3 Challenges and Requirements for Heterogeneous Model . . . . . . . 23
3.3 Principles of Heterogeneous Hopping ..................... 25
3.3.1 The Fixed-Short-Cycle Technique................... 26
3.3.2 Parity-Alignment ............................ 27
3.4 Design of Heterogeneous Hopping ....................... 30
3.4.1 Rounding for Asynchronous Timers.................. 32
3.4.2 Guarantee of Rendezvous and MTTR................. 33
3.5 Advanced Heterogeneous Hopping....................... 34
3.5.1 Supporting Misaligned Cycle Boundaries of Rotating Sequences . . 34
3.5.2 Supporting Discontinuous Capability ................. 35
3.6 Role-agile Heterogeneous Hopping....................... 36
3.6.1 Design of RHH ............................. 38
3.6.2 Guarantee of Rendezvous ....................... 40
3.7 Performance Evaluation ............................ 41
3.7.1 Simulation Setup ............................ 41
3.7.2 Verifying the Guarantee of Rendezvous . . . . . . . . . . . . . . . . 44
3.7.3 Time To Rendezvous.......................... 44
3.7.4 Degree of Congestion.......................... 45
3.7.5 Role-agile Heterogeneous Hopping................... 47
4 Fast & Load-balancing Rendezvous Scheme for Mixture Networks of Homogeneous & Heterogeneous CRs .......................... 48
4.1 Overview..................................... 49
4.2 Multi-Layer Design Principle for Cross-Type CH Schemes . . . . . . . . . . 54
4.2.1 Problem Definition ........................... 54
4.2.2 Single-Layer CH Schemes ....................... 56
4.2.3 The Multi-layer Principle........................ 58
4.2.4 The Two-Layer CH Scheme for Heterogeneous CRs - HH . . . . . . 61
4.3 The Three-Layer Cross-Type CH Scheme - ICH . . . . . . . . . . . . . . . 64
4.3.1 Mutually exclusive weaknesses..................... 65
4.3.2 Interlocking Channel Hopping Scheme . . . . . . . . . . . . . . . . 67
4.4 TTR Analysis.................................. 70
4.5 Congestion Analysis .............................. 73
4.6 Experimental Analysis ............................. 75
4.6.1 Heterogeneous Environment ...................... 76
4.6.2 Homogeneous Environment ...................... 82
4.6.3 Cross-type Network........................... 86
5 Data-Channel Negotiation Toward Stable Data Transmission for CRs .......................... 89
5.1 Overview..................................... 90
5.2 Preliminaries .................................. 93
5.2.1 The CR Environment.......................... 94
5.2.2 CH Schemes for Rendezvous...................... 94
5.2.3 Data-Channel Negotiation after Rendezvous . . . . . . . . . . . . . 96
5.3 Self-Channel Selection ............................. 98
5.3.1 Communication Procedure....................... 98
5.3.2 Experimental Observations.......................100
5.3.3 The Need for Self-Channel Selection..................105
5.4 The RSSD Selection Scheme..........................107
5.4.1 Algorithm................................107
5.4.2 Analysis.................................109
5.5 Practical Adaptations..............................114
5.5.1 Leveraging the Synchronous Clocks ..................114
5.5.2 Leveraging the Known Roles......................115
5.6 Performance Evaluation ............................116
6 Discussion & Future Work.......................... 123
6.1 HH: Fast Pairwise Rendezvous Scheme for Heterogeneous CRs . . . . . . . 123
6.2 ICH: Fast & Load-balancing Rendezvous Scheme for Multi-User Mixture
CRN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
6.3 RSSD:Data-ChannelNegotiationAlgorithm . . . . . . . . . . . . . . . . . 124
6.4 FutureWork...................................125
Bibliography.......................... 125

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