[english] Basic of Wireless Networks (summary)

Basic of Wireless Networks

IMTS (Improved Mobile Telephone Service) was the first commercially available radio and telephone system was put into service in 1946. To use IMTS, a tall transmitter  tower was erected near the center of a metropolitan area. Several assigned channel were then transmitted and received from the antenna atop this tower and any vehicle within range given these constrictions, the number of channels available didn't come close to satisfying the damand. 

The solution of this problem was cellular radio. Two important characteristics of cellular system contribut to their usefullness. The first is their controlled handoff. Second, system were designed to locate particular subscribers by paging them in each of the cells.

The initial transmission technology used between vehicles and the cell site was analog in nature and known as AMPS; the analog scheme used was called FDMA. Digital transmission was later developed, resulting in TDMA. In Europe called GSM, now known as Global System for Mobile Communications. 

A few years later, a third group of companies developed spread-spectrum technology called CDMA. The continuing growth of cellular communication led government and industry in US. The development of Personal Communication Service (PCS) industry led to search for additional ways to satisfy the obvious need.

Additional frequency bands were allocated for their use, the FCC auctioned them off. Unfortunately, after acquiring the spectrum, many of the new potential operators went bankrupt and never actually had a chance to use it.