Free-space optical (FSO) communication system group

自由空间光通信(FSO)是指通过大气中调制的可见光或红外(IR)光波段发射来传输信息。FSO对于最后一英里的宽带连接特别有趣，因为它可以以相对较低的成本将高速光纤主干网络虚拟地扩展到用户驻地。例如，美国大约75%的商业建筑位于主干光纤干线1公里范围内，因此对这种连接的需求很大，但只有5%的商业建筑连接到该干线。然而，FSO也被有利地用作光纤备份，用于城域网络和空间通信。与更传统的射频无线链路相比，FSO能够实现显著更高的数据速率，不受同频道或相邻频道干扰的影响，并由于光束的高方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，而且与光纤或射频系统相比价格低廉。尽管有这些优点，工业界和学术界对这项技术的兴趣也越来越大，但FSO的广泛部署面临着三个主要挑战：(1)为了实现可靠的通信，FSO发射机必须直接照射FSO接收器。发射机和接收机之间的不对准导致接收信号强度的巨大波动。(2)大气湍流引起FSO链路衰落。这导致了信号强度在空间和时间上的波动。(3)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，并促进自由空间光通信技术的广泛部署。这就需要对(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系统的信号设计进行基础研究。

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.