Normally, the first generation of communication was made of independant systems. Private oragnizations, such as TACS (Total Access Communication System) and NMT (Nordic Mobile Telephone) used in Europe or AMPS (Analogue Mobile Phone System) used in America, have started developing their own systems with the same key idea of deviding geographical areas into cells, where each BTS ( Base Station) served a cell to implement the frequency reuse.
despite supporting five to ten times more users, this indepency of systems made the roaming service impossible, besides others weaknesses like the low security on air interface and the full ana log mode of communication. What pushed these organizations to finally work together under the European Telecommunications Standards Institute (ETSI) and develop the 2nd generation system.