基于802.11ac标准的射频前端非理想性对系统性能影响的研究

发布时间：2018-03-18 05:30

本文选题：802.11ac　切入点：EVM　出处：《杭州电子科技大学》2014年硕士论文　论文类型：学位论文

【摘要】：现代无线通信技术的发展是为了满足人们对高速通信的要求，使得各种新的应用场景不再受到物理层通信速率的限制。这就要求无线通信系统不断改进其物理层和MAC层协议。具体到WLAN标准，经过十多年的发展，其标准从最初的802.11b不断演进出802.11a/g/n,以及最新802.11ac标准。 802.11ac标准之所以能大幅度提高系统通信速率有赖于其更宽的信道带宽，更高阶的调制星座图密度，以及多用户多入多出技术（MU-MIMO）。不考虑MU-MIMO技术的影响，高带宽高阶QAM-OFDM技术能大大提高系统的频谱效率，这是因为相对于单载波调制，OFDM技术利用子载波间的正交性，消除了保护频带，从而能大大提高系统的频谱效率，同时，，更高阶星座图使得每个子载波上的符号能携带更多的比特位。但是这样的代价是：首先OFDM系统对系统的相位噪声非常敏感，对本振信号的相位噪声提出了很高要求，同时OFDM结合高阶的QAM调制产生了具有极高峰均比的时域信号，这对系统的线性度提出了很高的要求，由于线性度往往和功耗之间存在折衷，这给功率放大器的设计带来挑战。当前射频集成电路对于集成度以及成本和功耗的考虑，使得直接变频收发机成为收发机结构的主流，然而直接变频结构对IQ两路的失配非常敏感，而OFDM系统同样对IQ失配非常敏感。IQ失配的来源，不仅包括由于本振信号通路上IQ失配引起的，还包括IQ两路频率选择性电路引起的频率选择性失配，通常这部分失配是由IQ两路的低通滤波器失配引起的，这种失配随着信号带宽的更加越来越明显。因此，可以看到由于OFDM和M-QAM调制技术对系统的线性度和相位噪声提出了较高的要求，同时直接变频收发机对系统的匹配度有很高的要求，这给相应的收发机射频前端设计带来极大的挑战。因此，本文针对802.11ac标准搭建了射频基带联合仿真的系统级仿真平台，并结合系统EVM指标对系统的一些关键射频电路模块指标提出设计参考。此项工作的意义在于作为射频和基带的桥梁，给射频前端电路设计师从系统级的高度提供有益的设计指导。
[Abstract]:The development of modern wireless communication technology is to meet the requirements of high-speed communication. All kinds of new application scenarios are no longer restricted by physical layer communication rate, which requires wireless communication system to improve its physical layer and MAC layer protocol continuously. Specific to WLAN standard, after more than ten years' development, Its standards have evolved from the original 802.11b to 802.11a / g / n and the latest 802.11ac standard. The reason why the 802.11ac standard can greatly improve the system communication rate depends on its wider channel bandwidth, higher modulation constellation density, and MU-MIMOO, a multi-user multi-input and multi-output technology. High-order QAM-OFDM technology with high bandwidth can greatly improve the spectral efficiency of the system. This is because compared with the single-carrier modulation QAM-OFDM technology, the orthogonality between sub-carriers is used to eliminate the protected frequency band, which can greatly improve the spectral efficiency of the system, at the same time, The higher-order constellation makes the symbols on each subcarrier carry more bits. But the cost is: first, the OFDM system is very sensitive to the phase noise of the system, and the phase noise of the local oscillator signal is very demanding. At the same time, OFDM combined with high-order QAM modulation produces time-domain signals with PAPR, which requires high linearity of the system, because there is a tradeoff between linearity and power consumption. This brings challenges to the design of power amplifiers. Due to the consideration of integration, cost and power consumption in RF integrated circuits, direct frequency conversion transceivers become the mainstream of transceiver architecture. However, direct frequency conversion structure is very sensitive to IQ mismatch, and OFDM system is also very sensitive to IQ mismatch. The source of IQ mismatch is not only caused by IQ mismatch in local oscillator signal pathway. It also includes frequency selective mismatch caused by IQ two-channel frequency selective circuit, which is usually caused by IQ two-channel low-pass filter mismatch, which becomes more and more obvious with the increase of signal bandwidth. Therefore, it can be seen that OFDM and M-QAM modulation technology put forward higher requirements for system linearity and phase noise, and direct frequency conversion transceivers have high requirements for system matching. This brings a great challenge to the RF front-end design of the transceiver. Therefore, a system-level simulation platform of RF baseband joint simulation is built for 802.11ac standard. Combined with the EVM index of the system, the design reference of some key RF circuit modules is put forward. The significance of this work is to serve as a bridge between RF and baseband. To RF front-end circuit designers from the system level to provide useful design guidance.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN92

【共引文献】