SIGNAL PROCESSING SCHEMES FOR BROADBAND FSO-RF HYBRID WIRELESS COMMUNICATION SYSTEMS AND THEIR PERFORMANCE

Open Access
Author:
Lee, Sangwoo
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 17, 2007
Committee Members:
  • Mohsen Kavehrad, Committee Chair
  • Shizhuo Yin, Committee Member
  • Aylin Yener, Committee Member
  • Jesse Louis Barlow, Committee Member
Keywords:
  • hybrid system
  • free-space optical wireless
  • MIMO
  • OFDM
  • space-time codes
  • channel shortening equalization
  • TEQ
  • MIMO-TEQ
Abstract:
In semiconductors, an empirical observation known as Moore¡¯s law states that the number of transistors on an integrated circuit for minimum component cost is doubled every 24 months. In communications, faced with the recent rapid growth of internet, data services, and needs for multimedia services, there have been similar efforts to establish a similar Moore¡¯s law of bandwidth. In cable environments, modem technologies with higher bandwidth can advance rapidly, whereas in wireless environments, due to the highly regulated nature and scarcity of the RF spectrum, it can be harder to see the advent of truly wideband modem technologies in the near future. It is well-known that through clouds or fog, free-space optical (FSO) links suffer from severe attenuation whereas RF links suffer from slight attenuation. On the other hand, in rain, FSO links undergo trivial attenuation while RF links experience high attenuation. Knowing that RF paths and FSO paths are complementary, combining the attributes of a higher data rate but bursty link (FSO) with the attributes of a lower data rate but reliable link (RF) is expected to yield attributes better than either one alone, enabling a high availability link at high data rates. In this thesis, we propose two solutions which can aid existing wireless technologies. First, we propose FSO wireless communications as an attractive alternative to RF wireless communications. Second, as an aid to the weather-dependent FSO links, we propose multi-input-multi-output (MIMO) links with enhanced bandwidth efficiency. Whereas the traditional FSO implementations have been dependent more on truly optical devices, we focus more on FSO by digital signal processing (DSP) technologies in this thesis. As for the MIMO RF link, we study in the context of well-known MIMO-OFDM (orthogonal frequency division multiplexing) links with coding, but we further aim at increasing the spectral efficiency by use of DSP techniques known as channel shortening equalizers. For both the FSO link and the MIMO-OFDM link, the premise in this thesis is that the use of DSP technologies is cost-effective enough to help both the RF and FSO links.