The first generation of the communication system is the analog cellular system, it means that the carrier is analog. we just send waveforms mostly with voice. it is continuous in amplitude and time. the variation of a signal disturbs over long distances. This analog system was introduced in the seventies. NMT, AMPS, TACS, CDPD technologies were used in 1G. It uses the FDMA technique to call a country. All analog systems used circuit-switched technology and were designed only for voice communication and not for data. The cost of system and voice transfer is also high in 1G. The problems with 1G are poor voice quality, shorter battery life, no security, the size of the phone is large and frequent call drops. the second generation is digital cell phone in this it started sending 1s and 0s with the air. It is a circuit-switched and narrowband technology. It is a low-band digital cellular signaling system. Digital is more spectrally efficient and uses technologies such as TDMA, GSM, CDMA, iDEN, PDC, PHS. Uses digital modulation for better audio quality. GSM technology has both FDMA and TDMA techniques. There are now an estimated 248 million users of the GSM system worldwide and it is currently used in 140 countries. In addition to this, TDMA-based PDC (Personal Digital Communication) technology is introduced. After the introduction of this CDMA technology, it divides speech into small segments and encodes to identify calls using spread spectrum. While GSM and TDMA systems are very important in 2G wireless technology, CDMA technology has proven to offer better voice quality, low noise, few call drops, good security and high network capacity. Transmission of data, fax, messages up to 9.6 kbps is possible via 2G, but is not acceptable for multimedia and web browsing applications....half of paper...spectral efficiency modulation schemes that cannot be applied to 3G Infrastructure. The typical speed of 3G is limited to 2 Mbps, while the speed of 4G goes up to 100 Mbps and also eliminates interference caused by the high-speed signal. 4G technology also provides uninterrupted voice, navigation and data services. This speed is achieved using the OFDM modulation technique. Some of the other techniques used are usage planning, power control and adaptive modulation, millimeter and smart wireless antennas. 4G Requirements The advantages of 4G are high speed and also has higher bandwidth, it uses multi hop and Adhoc network and the spectral efficiency of 4G is high, it has service portability and global access, it is a mobile based system on IP with lower costs. We've never seen a 3G phone work on a 4G network. some operators that have both 3G and 4G networks such as Verizon.