Praise for Fundamentals of WiMAX

20 Chapter 1 • Introduction to Broadband WirelessNextel, and Clearwire. Regulatory changes may be required in many countries to make this bandmore available and attractive, particularly for mobile WiMAX.Licensed 2.3GHz: This band, called the WCS band in the United States, is also available inmany other countries such as Australia, South Korea, and New Zealand. In fact, the WiBro servicesbeing deployed in South Korea uses this band. In the United States, this band includes twopaired 5MHz bands and two unpaired 5MHz bands in the 2.305GHz to 2.320GHz and2.345GHz to 2.360GHz range. A major constraint in this spectrum is the tight out-of-band emissionrequirements enforced by the FCC to protect the adjacent DARS (digital audio radio services)band (2.320GHz to 2.345GHz). This makes broadband services, particularly mobileservices, difficult in the sections of this band closest to the DARS band.Licensed 3.5GHz: This is the primary band allocated for fixed wireless broadband accessin several countries across the globe, with the notable exception of the United States. In theUnited States, the FCC has recently allocated 50MHz of spectrum in the 3.65GHz to 3.70GHzband for high-power unlicensed use with restrictions on transmission protocols that precludesWiMAX. Internationally, the allocated band is in the general vicinity of 3.4GHz to 3.6GHz, withsome newer allocation in 3.3GHz to 3.4GHz and 3.6GHz to 3.8GHz as well. The available bandwidthvaries from country to country, but it is generally around 200MHz. The available band isusually split into many individual licenses, varying from 2 × 5MHz to 2 × 56MHz. Spectrumaggregation rules also vary from country to country. While some countries only allow FDDoperations, others allow either FDD or TDD. In most countries, the current rules in this band donot allow for nomadic and mobile broadband applications. It is hoped that the regulations in thisband will, over time, become more flexible, and the WiMAX Forum has committed to workingwith regulatory authorities around the world to achieve this flexibility. The heavier radio propagationlosses at 3.5GHz, however, is likely to make it more difficult to provide nomadic andmobile services in this band.License-exempt 5GHz: The license-exempt frequency band 5.25GHz to 5.85GHz is ofinterest to WiMAX. This band is generally available worldwide. In the United States, it is part ofthe unlicensed national information infrastructure (U-NII) band and has 200MHz of spectrumfor outdoor use. An additional 255MHz of spectrum in this band has been identified by the FCCfor future unlicensed use. Being free for anyone to use, this band could enable grassrootsdeployments of WiMAX, particularly in underserved, low-population-density rural and remotemarkets. The large bandwidth available may enable operators to coordinate frequencies and mitigatethe interference concerns surrounding the use of license-exempt bands, particularly inunderserved markets. The relatively high frequency, coupled with the power restrictions in thisband, will, however, make it extremely difficult to provide nomadic or mobile services. Evenfixed applications will, in most cases, require installing external antennas at the subscriberpremise. Within the 5GHz band, it is the upper 5.725GHz–5.850GHz band that is most attractiveto WiMAX. Many countries allow higher power output—4 W EIRP (effective isotropic radiatedpower)—in this band compared to an EIRP of 1W or less in the lower 5GHz bands. In theUnited States, the FCC is considering proposals to further increase power output—perhaps to