Technical challenges and trends in broadband wireless access at frequencies between 2 and 11 GHz

Broadband wireless access (BWA) is a promising technology for new operators without an existing infrastructure to reach the end users. There is a wide spectrum for BWA at millimeter-wave frequencies (above 20 GHz), but the technology is not mature enough to make these systems cost-effective for residential applications. Therefore, there is currently a strong interest in BWA at microwave frequencies between 2 and 11 GHz. BWA systems in these frequency bands are not strictly line-of-sight (LOS) and they are subjected to strong multipath propagation leading to large channel dispersions. For this reason, recent technical specifications by the IEEE 802.16 and the ETSI BRAN Groups have been based on orthogonal frequency-division multiplexing (OFDM), orthogonal frequency-division multiple access (OFDMA), and single-carrier transmission with frequency-domain equalization (SC/FDE), three technologies which can cope with long channel dispersions. This tutorial discusses the technical challenges of BWA at frequencies between 2 and 11 GHz and describes the basic technologies used in the recently-developed IEEE and ETSI standards. We also discuss some other potential transmission and multiple access techniques for this application.