Optimum Power Allocation for OFDM Based Cognitive Radio Systems with Arbitrary Input Distributions
Optimum Power Allocation for OFDM Based Cognitive Radio Systems with Arbitrary Input Distributions
复制标题
具有任意输入分布的基于 OFDM 的认知无线电系统的最优功率分配
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
B. Evans
中科院分区：
文献类型：
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作者：
Ahmed Sohail;Mohammed Al;P. Xiao;B. Evans
在文献中，假设高斯输入的最优功率分配已在基于OFDM的认知无线电（CR）系统中进行了评估，以最大限度地提高次用户的容量，同时保持引入到主用户频带的干扰在可容忍的范围内。然而，高斯输入假设是不实际的，并且有限符号字母（FSA）输入分布，即，M-QAM在实际系统中使用。在本文中，我们考虑在实际系统中使用的FSA输入的条件下的功率优化问题，并通过利用互信息和最小均方误差之间的关系推导出一个最优的功率分配策略。所提出的方案被证明可以节省发射功率的CR系统相比，其传统的对应，假设高斯输入。除了额外分配的功率，即，功率浪费，与所提出的方案相比，传统的功率分配方案还导致更多子载波的置零，从而导致传输速率降低。通过仿真，对所提出的最优功率算法进行了评估，并与假设高斯输入的传统算法进行了比较。仿真结果表明，对于BPSK、QPSK和16-QAM输入，当干扰门限值在1 ~ 3 mW时，该算法的发射功率节省分别在55- 75%、42-62%和12- 28%，而速率增益分别在16.8- 12.4%、13 ~ 11.8%和3 ~ 5.8%。
In the literature, optimal power allocation assuming Gaussian input has been evaluated in OFDM based Cognitive Radio (CR) systems to maximize the capacity of the secondary user while keeping the interference introduced to the primary user band within tolerable range. However, the Gaussian input assumption is not practical and Finite Symbol Alphabet (FSA) input distributions, i.e., M-QAM are used in practical systems. In this paper, we consider the power optimization problem under the condition of FSA inputs as used in practical systems, and derive an optimal power allocation strategy by capitalizing on the relationship between mutual information and minimum mean square error. The proposed scheme is shown to save transmit power in a CR system compared to its conventional counterpart, that assumes Gaussian input. In addition to extra allocated power, i.e., power wastage, the conventional power allocation scheme also causes nulling of more subcarriers, leading to reduced transmission rate, compared to the proposed scheme. The proposed optimal power algorithm is evaluated and compared with the conventional algorithm assuming Gaussian input through simulations. Numerical results reveal that for interference threshold values ranging between 1mW to 3mW, the transmit power saving with the proposed algorithm is in the range between 55-75%, 42-62% and 12-28%, whereas the rate gain is in the range between 16.8-12.4%, 13-11.8% and 3-5.8% for BPSK, QPSK and 16-QAM inputs, respectively.