Department of Electrical and Computer Engineering
M.S. Thesis Abstract
Spread Spectrum Interference Issues In The 900 MHz ISM Band
In this thesis we investigate the use of the 902-928 MHz unlicensed band for wireless communications. This band has been allocated by the FCC (Federal Communications Commission) for industrial, scientific and medical (ISM) applications. Although a license is not required to operate in this band, one does need to comply with a minimum set of rules laid down by the FCC.
Due to the high cost of licensing of radio spectrum, the unlicensed band offers a free and attractive alternative to service providers. As a consequence, this band is witnessing a rapid growth in both the number of systems as well as the diverse technologies being used by them. However, this latitude comes at a price in the form of susceptibility to excessive mutual interference. Since the systems operate independently and do not cooperate with each other, it becomes necessary for them to be able to sustain the mutual interference.
Among the various products operating in the ISM band, this thesis will focus on a particular class of products designated by the FCC as the 15.247 Devices. Part 15.247 devices include wireless LANs, cordless phones and automatic meter readers (AMRs). These devices have proliferated the ISM band and their numbers continue to rise. Since the FCC requires that all 15.247 devices use spread spectrum communications, the systems use either DS-SS (Direct Sequence Spread Spectrum) or FH-SS (Frequency Hopping Spread Spectrum). Due to the difference between these communication technologies, the mutual interference experienced has different characteristics as well.
In this thesis, we evaluate the performance of DS-SS and FH-SS systems under the in uence of mutual interference. We have developed simple yet general models that represent some of the DS and FH systems operating in this spectrum. Through the models, we achieve an understanding of the problems encountered by these systems due to their susceptibility to excessive mutual interference.
Thesis Director: Professor Roy Yates