Cognitive Radio in Fading Channels: From Gel’fand-Pinsker Coding to Receiver Cooperation
Date Issued
2010
Date
2010
Author(s)
Lin, Pin-Hsun
Abstract
The cognitive radio (CR) is a technology capable of dynamically sensing unused spectrum segments in a target spectrum pool, and communicating via the unused spectrum segments without causing harmful interference to the primary users. The main contribution of this thesis is about improving the CR performances in twofold. First, to accommodate the partial channel state information at the transmitter (CSIT) under Rician fading channels, we propose to use the linear-assignment Gel''fand-Pinsker coding (LA-GPC) to replace the dirty paper coding (DPC) in Jovacic-Viswanath (JV)''s CR model. This replacement can boost the performance of JV''s model. We also provide semi-analytical parameters design for the LA-GPC CR system. However, in Rayleigh fading channels, we find that the LA-GPC based CR cannot mitigate the interference as in Rician fading channels. Thus, our second main contribution is to propose the three-phase unidirectional transmitter cooperation CR and the three-phase unidirectional transmitter receiver cooperation CR. These two new CR models outperform the LA-GPC based and JV''s CR in Rayleigh fading channels.
In the first part of the thesis, we present the design of cognitive radio in the Rician channel with partial CSIT. We replace the dirty paper coding used in JV''s model with full CSIT by the LA-GPC which can achieve better error performance when there is only partial CSIT. Based on the achievable rate derived from the LA-GPC, two optimization problems under the fast and slow fading channels are formulated. We derive semi-analytical solutions to find the relaying ratios and precoding coefficients. We also show that the parameters derived by the proposed methods converge to the optimal full CSIT solutions in the asymptotic cases. This result verifies the correctness of the proposed methods asymptotically. Moreover, a new coding scheme is proposed to implement the LA-GPC in practice. Simulation results show that the proposed semi-analytical solutions perform close to the optimal ones found by brute-force search, and outperform the systems based on naive DPC. Simulation results also show that the proposed practical coding scheme can effectively approach the theoretical rate performance.
In Rayleigh fading channels , we derive that the performance of the LA-GPC based CR is the same as that of treating interference as noise. Thus in the second part of the thesis, we propose two new multi-phase CR transmission schemes by utilizing the relaying from the CR transmitter and receiver under the half-duplex constraints. And the receiver cooperation from the CR is the key to meet the coexistence constraint. Compared to the previous scheme, our multi-phase transmission protocols provide additional “clean” relaying paths without interference from the CR, which have additional diversity. The numerical examples show that the proposed schemes provide significant rate gains over previous scheme with less complexity penalties.
Subjects
cognitive radio
Gelfand Pinsker coding
dirty paper coding
lattice coding
Type
thesis
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