SpecEES: Unified System Architecture for Energy Efficient Cognitive Radios

尽管长期以来的设想是大幅提高频谱利用率，并在不干扰许可用户的情况下安全地共享多个频段，但构建和部署具有动态频谱接入的节能认知无线电已被证明是一项具有挑战性的任务。该项目提出了一种节能的认知无线电系统，该系统解决了许多实际挑战，包括在多个频段运行的低功耗宽带无线电，以及在通信无证用户之间无缝有效地协调操作频段的方法。提出的工作提供了一个完整的集成解决方案，包括无线电实现，信号处理算法开发和网络连接。这些不同的抽象层已被联合优化，以实现低功耗和健壮的认知无线电系统。本文提出的节能认知无线电（CR）系统在电路层、信号处理层和网络层进行了联合优化，其工作原理如下：1)辅助用户（SU）采用一种基于混频器谐波实现的多相序列的新型压缩采样接收器，同时感知整个感兴趣的频率范围。2)由于单个单元之间的通信频带是未知的，因此通过在整个感兴趣的频率范围内以低功率水平发送相同的信号来传输数据，同时在主要用户（PU）频带中消除能量。为此，提出了一种新型的亚奈奎斯特发射机，它可以看作是压缩感知接收机的对应物。3)接收SU使用相同的压缩采样接收器用于感知pu接收SU信号。这是通过将接收到的信号投射到PU的零空间来实现的，在传感期间估计其频率位置。通过适当选择模拟前端设置的基函数，可以相干地增加接收到的大部分能量。4)由于SU能量分布在整个感兴趣的频率范围内，因此产生的信道脉冲响应（CIR）是丰富的散射。因此，CIR本身可以作为用户的签名来实现多址通信。此外，利用多用户检测理论的技术，可以实现高频谱效率。

Although long envisioned to dramatically improve spectrum utilization and to safely share multiple frequency bands without interfering with licensed users, building and deploying energy efficient cognitive radios with dynamic spectrum access have proven to be a challenging task. This project proposes an energy-efficient cognitive radio system that addresses its many practical challenges including a low-power wideband radio that operates in multiple frequency bands and a means to seamlessly and efficiently coordinate the operating bands between communicating unlicensed users. The proposed work presents a complete integrated solution, ranging from radio implementation, signal processing algorithm development, and network connectivity. These different layers of abstraction have been jointly optimized to enable a low-power and robust cognitive radio system.The proposed energy-efficient cognitive radio (CR) system, which is jointly optimized at the circuit, signal processing, and network layers, operates as follows: 1) A secondary user (SU) employs a novel compressed sampling receiver based on polyphase sequences implemented via mixer harmonics to sense concurrently the entire frequency span of interest. 2) Since the communicating band between SUs is unknown, data is transmitted by sending the same signal at low power levels across the entire frequency span of interest while nulling energy in the primary user (PU) bands. A novel sub-Nyquist transmitter, which can be viewed as a dual of the compressed sensing receiver, is proposed for this purpose. 3) The receiving SU uses the same compressed sampling receiver for sensing PUs to receive the SU signals. This is achieved by projecting the received signals to PU's null space, whose frequency locations were estimated during sensing. By appropriately selecting the basis functions set in the analog front-end, most of the received energy can be added coherently. 4) As SU energy is spread across the entire frequency span of interest, the resulting channel impulse response (CIR) is richly scattered. The CIR itself, therefore, can be used as users' signatures for achieving multiple-access communications. Furthermore, by leveraging on techniques from multiuser detection theory, high spectral efficiency can be achieved.