Introduction

Wireless communication is, by any measure, the fastest growing segment of the communication industry. As such, it has captured the attention of the media and the imagination of the public. Cellular systems have experienced exponential growth over the last decade and there are currently around two billion users worldwide. Indeed cellular phones have become a critical business tool and part of everyday life in most developed countries .In addition, wireless local area networks currently supplement or replace wired networks in many homes, business, and campuses. Many new applications, including wireless sensor networks ,automated highways and factories, smart homes and appliances, and remote telemedicine, are emerging from research ideas to concrete systems. The explosive growth of wireless systems coupled with the proliferation of laptop and palmtop computers indicate a bright future for wireless network .

History of Wireless Communications:
The first wireless networks were developed in the pre-industrial age. These systems transmitted information over line-of-sight distance using smoke signals, torch signaling, flashing mirrors, signal flares, or semaphore flags. An elaborate set of signal combinations was developed to convey complex messages with these rudimentary signals. Observation stations were built on hilltops and along roads to relay these messages over large distances. These early communication networks were replaced first by the telegraph network and later by the telephone. In 1895 , a few decades after the telephone was invented ,Marconi demonstrated the first radio transmission ,and radio communications was born. Radio technology advanced rapidly to enable transmissions over larger distances with better quality, less power, and smaller ,cheaper devices, thereby enabling public and private radio communications ,television, and wireless networking.
Early radio systems transmitted analog signals. Today most radio systems transmit digital signals composed of binary bits, where the bits are obtained directly from a data signal or by digitizing an analog signal. A digital radio transmit a continuous bit stream or it can group the bits into packets. The latter type of radio is called a Packet radio and is characterized by bursty transmissions. The U.S.military was extremely interested in the combination of packet data and broadcast radio inherent to ALOHANET.These networks continue to be developed for military use. Packet radio networks also found commercial application in supporting wide area wireless data services. These services ,first introduced in the early 1990’s,enable wireless data access at fairly low speeds ,on the order of 20Kbps.A strong market for these wide-area wireless data services never really materialized, due mainly to their low data rates ,high cost, and lack of “killer applications”.
The introduction of wired Ethernet technology in the 1970’s steered many commercial companies away from radio-based networking. Ethernet’s 10Mbps data rate far exceeded anything available using radio, and companies did not mind running cables within and between their facilities to take advantages of these high rates. In 1985 the Federal Communications Commission’s(FCC) enabled the commercial development of wireless LANs by authorizing the public use of the Industrial, scientific, and medical(ISM) frequency bands for wireless LAN products.
By far the most successful application of wireless networking has been the cellular telephone system. The roots of this system began in 1915.In 1946 public mobile telephone service was introduced in United States. These initial systems used a central transmitter to cover an entire metropolitan area. This inefficient use of the radio spectrum coupled with the state of radio technology at the time severely limited the system capacity.
The second generation of cellular systems, first deployed in the early 1990’s,were based on digital communications. The shift from analog to digital was driven by its higher capacity and the improved cost, speed and power efficiency of digital hardware. It initially provide mainly voice services, these systems gradually evolved to support data services such as e-mail, Internet access and short messaging.

References:
Wireless communication
By
Andrea Goldsmith

Stanford University

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