SpecEES: Unified System Architecture for Energy Efficient Cognitive Radios

虽然长期以来设想显着提高频谱利用率和安全地共享多个频带而不干扰授权用户，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。该项目提出了一种高能效的认知无线电系统，解决了许多实际的挑战，包括低功率宽带无线电，在多个频带和一种手段，无缝和有效地协调通信未授权用户之间的工作频带。拟议的工作提出了一个完整的集成解决方案，从无线电实现，信号处理算法的开发，网络连接。这些不同的抽象层已经被联合优化，以实现低功耗和鲁棒的认知无线电系统。所提出的节能认知无线电（CR）系统，在电路，信号处理和网络层联合优化，操作如下：1）二级用户（SU）采用基于经由混频器谐波实现的多相序列的新颖的压缩采样接收器来同时感测感兴趣的整个频率跨度。2)由于SU之间的通信频带是未知的，因此通过在整个感兴趣的频率跨度上以低功率电平发送相同的信号，同时使主用户（PU）频带中的能量为零来发送数据。为此，提出了一种新型的亚奈奎斯特发射机，它可以被看作是压缩感知接收机的对偶。3)接收SU使用用于感测PU的相同压缩采样接收器来接收SU信号。这是通过将接收到的信号投影到PU的零空间来实现的，PU的零空间的频率位置是在感测期间估计的。通过适当地选择在模拟前端中设置的基函数，可以相干地添加大部分接收到的能量。4)由于SU能量分布在整个感兴趣的频率跨度上，因此产生的信道脉冲响应（CIR）是丰富分散的。因此，CIR本身可以用作实现多址通信的用户签名。此外，通过利用来自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.