State of the Art - General Information
Radio Network
A radio network is a network system which distributes programming to multiple stations simultaneously, or slightly delayed, for the purpose of extending total coverage beyond the limits of a single broadcast signal. The resulting expanded audience for programming essentially applies the benefits of mass-production to the broadcasting enterprise. A radio network has two sales departments, one to package and sell programs to radio stations, and one to sell the audience of those programs to advertisers.
Most radio networks also produce much of their programming. Originally, radio networks owned some or all of the radio stations that broadcast the network's programming. Presently however, there are many networks that do not own any stations and only produce and/or distribute programming. Similarly station ownership does not always indicate network affiliation. A company might own stations in several different markets and purchase programming from a variety of networks.
Radio networks rose rapidly with the growth of regular broadcasting of radio to home listeners in the 1920s. This growth took various paths in different places. In Britain the BBC was developed with public funding, in the form of a broadcast receiving license, and a broadcasting monopoly in its early decades. In contrast, in the United States of America various competing commercial networks arose funded by advertising revenue. In that instance, the same corporation that owned or operated the network often manufactured and marketed the listener’s radio.
Major technical challenges to be overcome when distributing programs over long distances are maintaining signal quality and managing the number of switching/relay points in the signal chain. Early on, programs were sent to remote stations (either owned or affiliated) by various methods, including leased telephone lines, pre-recorded gramophone records and audio tape. The world's first all-radio, non-wireline network was claimed to be the Rural Radio Network, a group of six upstate New York FM stations that began operation in June 1948. Terrestrial microwave relay, a technology later introduced to link stations, has been largely supplanted by coaxial cable, fiber, and satellite, which usually offer superior cost-benefit ratios.
Many early radio networks evolved into Television networks.
Mobile Network
A public land mobile network (PLMN) is any wireless communications system intended for use by terrestrial subscribers in vehicles or on foot. Such a system can stand alone, but often it is interconnected with a fixed system such as the public switched telephone network (PSTN). The most familiar example of a PLMN end user is a person with a cell phone. However, mobile and portable Internet use is also becoming common.
The ideal PLMN provides mobile and portable users with a level of service comparable to that of subscribers in a fixed network. This can be a special challenge in regions where the terrain is irregular, where base station sites are hard to find and maintain, and in urban environments where there are numerous obstructions such as buildings, and myriad sources of radio-frequency (RF) radiation that can cause noise and interference. Most systems today use digital technology rather than the older analog methods. This transition has resulted in improved communications coverage and reliability, but as anyone who regularly uses a cellular telephone knows, perfection has yet to be achieved.
A PLMN requires special security measures because a wireless system is inherently more susceptible to eavesdropping and unauthorized use than a hard-wired system. Smart cards containing user data, encryption/decryption, and biometric verification schemes can minimize this problem.
GSM (Global System for Mobile communication) is a digital mobile telephony system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephony technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band.
Mobile services based on GSM technology were first launched in Finland in 1991. Today, more than 690 mobile networks provide GSM services across 213 countries and GSM represents 82.4% of all global mobile connections. According to GSM World, there are now more than 2 billion GSM mobile phone users worldwide. GSM World references China as "the largest single GSM market, with more than 370 million users, followed by Russia with 145 million, India with 83 million and the USA with 78 million users."
Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries. SIM cards (Subscriber Identity Module) holding home network access configurations may be switched to those will metered local access, significantly reducing roaming costs while experiencing no reductions in service.
GSM, together with other technologies, is part of the evolution of wireless mobile telemmunications that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS).