Noncontiguous orthogonal frequency division multiplexing (NC‐OFDM)‐based cognitive radio (CR) systems achieve highly efficient spectrum utilization by transmitting unlicensed users' data on subcarriers of licensed users’ data when they are free. However, there are two disadvantages to the NC‐OFDM system: out‐of‐band power (OBP) and a high peak‐to‐average power ratio (PAPR). OBP arises due to side lobes of an NC‐OFDM signal in the frequency domain, and it interferes with the spectrum for unlicensed users. A high PAPR occurs due to the inverse fast Fourier transform (IFFT) block used in an NC‐OFDM system, and it induces nonlinear effects in power amplifiers. In this study, we propose an algorithm called “Alternative Projections onto Convex and Non‐Convex Sets” that reduces the OBP and PAPR simultaneously. The alternate projections are performed onto these sets to form an iteration, and it converges to the specified limits of in‐band‐power, peak amplitude, and OBP. Furthermore, simulations show that the bit error rate performance is not degraded while reducing OBP and PAPR.

中文翻译：

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同时降低基于NC‐OFDM的认知无线电系统中的PAPR和带外功率的优化技术

基于非连续正交频分复用（NC-OFDM）的认知无线电（CR）系统通过在许可用户数据空闲时在许可用户数据的子载波上传输非许可用户数据来实现高效频谱利用率。但是，NC-OFDM系统有两个缺点：带外功率（OBP）和峰均功率比（PAPR）高。OBP是由于频域中NC-OFDM信号的旁瓣而产生的，它会干扰无执照用户的频谱。由于在NC-OFDM系统中使用了快速傅里叶逆变换（IFFT）块，因此发生了很高的PAPR，并在功率放大器中引起了非线性效应。在这项研究中，我们提出了一种称为“凸集和非凸集的交替投影”的算法，该算法可同时降低OBP和PAPR。对这些集合执行备用投影以形成迭代，并且收敛到带内功率，峰值幅度和OBP的指定限制。此外，仿真表明，在降低OBP和PAPR的同时，不会降低误码率性能。