||Multi Relay Selection for OFDM-based Cooperative Communication in Cognitive Radio Network
||Institute of Computer & Communication
Orthogonal Frequency Division Multiplexing (OFDM)
在基於正交分頻多工的合作式感知無線電網路中, 訊號源經由不同的正交子載波傳輸訊號到中繼站, 這些中繼站解碼收到的訊號並傳送至終端站。我們的目標是如何選擇這些中繼站作合作式傳輸, 並在干擾限制的條件下最大化訊號源到終端站的等效通道容量。在本研究中, 我們提出了一個基於通道容量增量的演算法, 透過低運算複雜度的選擇多個中繼站達到較高的頻譜效益。其概念是將子載波迭代地分配到候選的中繼站, 同時保持不同跳躍間的通道容量差異最小。
為了評估感知無線電網路之效率, 頻譜轉換率定義為次使用者的通道容量增益與主使用者的通道容量損耗之比值。模擬結果顯示, 選擇多中繼站作傳輸可以達到較高的頻譜轉換率並對主使用者造成較小的干擾。總結而言, 選擇多個中繼站不僅在傳輸功率上較具彈性且在頻譜的使用上更具效率。
In the OFDM-based cooperative cognitive radio (CR) network, the source transmits data to relays over the orthogonal subcarriers. The relays decode and forward the data to the destination. Our aim is to choose the relays for cooperation and maximize the end-to-end capacity under a predefined interference constraint. In this thesis, we propose a capacity increasing based algorithm (CIBA) to achieve higher spectrum efficiency by selecting multiple relays at the cost of lower computational complexity. The concept of CIBA is to iteratively assign the subcarriers to the candidate relays for the purpose of minimizing the capacity difference between the two hops of the cooperative transmission.
To evaluate the CR network from an alternative viewpoint, the transfer ratio (TR) is defined as the proportion of the secondary user’s (SU’s) capacity gain to the primary user’s (PU’s) capacity loss which is caused by the spectrum sharing with SUs. The simulations show that the proposed multi-relay selection scheme can reduce the incurred interference to PU and have higher TR value, which also means the higher spectrum efficiency. In conclusion, the proposed multi-relay selection can not only possess higher flexibility in transmission power allocation but also achieve higher spectrum efficiency.
Chinese Abstract i
English Abstract ii
List of Figures vi
Glossary of Symbols viii
1 Introduction 1
1.1 Problem Formulation and Solution 1
1.2 Thesis Outline 3
2 Background and Literature Survey 4
2.1 Cognitive Radio 4
2.1.1 Dynamic spectrum access for Cognitive Radio 6
2.2 Cooperative Wireless Network 9
2.2.1 Cooperative Model and Protocols 10
2.3 OFDM-based cooperative network 12
2.4 Literature Survey 15
3 System Model and Problem Formulation 16
3.1 Received Signal Expression and Channel Model 19
3.2 Relay Selection Strategy 21
3.2.1 Single Relay Selection 21
3.2.2 Multi Relay Selection 22
3.3 Power Protection and Allocation 24
3.4 Relay Selection Protocol 25
4 Resource Allocation Scheme 27
4.1 Exhaustive Search 28
4.2 Capacity Increasing Based Algorithm 30
4.3 Subcarrier-pair Based Algorithm 35
4.4 Time Complexity Analysis 38
5 Simulation Results 40
5.1 Simulation Setup 40
5.2 Performance of Capacity Increasing Based Algorithm 43
5.3 Comparison of Capacity and Transfer Ratio 45
5.4 Achievable Capacity Against the Interference Temperature 50
5.5 The Probability of the Number of the Assigned Subcarriers for Each Relay 51
6 Conclusions and Future Works 53
6.1 Concluding Remarks 53
6.2 Future Works 54
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