Free-space optical (FSO) communication system group

自由空间光学（FSO）通信是指通过调制可见光或红外（IR）光波段发射穿过大气的信息传输。FSO对于最后一英里宽带连接尤其有趣，因为它可以以相对较低的成本将高速光纤骨干网扩展到用户的住宅。这种类型的连接有很大的需求，例如，美国大约75%的商业建筑距离主要光纤干线不到1公里，但只有5%的商业建筑连接到该干线。然而，FSO也很好地应用于光纤备份，在城域网和空间通信中。与更传统的RF无线链路相比，FSO可以实现更高的数据速率，不受共信道或相邻信道干扰的影响，并且由于光束的高指向性而提供固有的安全性。此外，FSO系统重量轻，可快速部署，不需要昂贵的频谱许可，与光纤或射频系统相比价格低廉。尽管有这些优势，而且工业界和学术界对这项技术的兴趣越来越大，但FSO的广泛部署面临三个主要挑战：(1)为了实现可靠的通信，FSO发射机必须直接照亮FSO接收器。发射器和接收器之间的不对准导致接收信号强度的大波动。(2)大气湍流导致FSO链路衰落。这导致了信号强度在空间和时间上的波动。(3)大雾、暴雨、大雪等恶劣天气条件会严重削弱FSO链路。拟议研究项目的总体目标是开发新的智能信号处理技术，以克服这些挑战，促进FSO技术的广泛部署。这需要对以下方面进行基础研究：(a)城市FSO信道的建模，(b) FSO系统的编码和调制，(c)多输入多输出（MIMO） FSO系统，以及(d)混合FSO- rf系统的信号设计。

Free-space optical (FSO) communication refers to the transmission of information via modulated visible or infrared (IR) optical band emissions through the atmosphere. FSO is particularly interesting for last-mile broadband connectivity as it can virtually extend the high speed fiber backbone network to the subscriber's premises at comparatively low cost. There is a large demand for this type of connectivity since, for example, approximately 75% of commercial buildings in the US are within 1 km of a major fiber trunk, but only 5% of these are connected to that trunk. However, FSO is also favorably applied as fiber back up, in meteropolitan area networks, and in space communications. When compared to more conventional RF wireless links, FSO enables significantly higher data rates, is not affected by co- or adjacent-channel interference, and offers inherent security due to the high directivity of the light beam. Furthermore, FSO systems are lightweight and rapidly deployable, do not require expensive spectrum licensing, and are inexpensive compared to fiber or RF systems. Despite these advantages and a growing interest in this technology from both industry and academia, widespread deployment of FSO faces three primary challenges: (1) For reliable communication the FSO transmitter has to directly illuminate the FSO receiver. Misalignment between transmitter and receiver leads to large fluctuations in the received signal intensity. (2) Atmospheric turbulence causes fading in FSO links. This leads to signal intensity fluctuations in both space and time. (3) Adverse weather conditions such as fog, heavy rain, and heavy snow can severely attenuate FSO links. The overall goal of the proposed research project is to develop new intelligent signal processing techniques that can overcome these challenges and facilitate the widespread deployment of FSO technology. This requires fundamental research on (a) the modeling of urban FSO channels, (b) coding and modulation for FSO systems, (c) multiple-input multiple-output (MIMO) FSO systems, and (d) signal design for hybrid FSO-RF systems.