Given below are the key differences between the two generations:

• Digital traffic channels: The most notable difference between the two genera- tions is that first-generation systems are almost purely analog, whereas second- generation systems are digital. In particular, the first-generation systems are designed to support voice channels using FM digital traffic is supported only by the use of a modem that converts the digital data into analog form. Second generation systems provide digital traffic channels. These readily support digital data; voice traffic is first encoded in digital form before transmitting. Of course, for second-generation systems, the user traffic (data or digitized voice) must be converted to an analog signal for transmission between the mobile unit and the base station.

• Encryption: Because all of the user traffic, as well as control traffic, is digitized in second-generation systems, it is a relatively simple matter to encrypt all of the traffic to prevent eavesdropping. All second-generation systems provide this capability, whereas first-generation systems send user traffic in the clear, providing no security.

• Error detection and correction: The digital traffic stream ofs econd-generation systems also lends itself to the use of error detection and correction techniques. The result can be very clear voice reception.

• Channel access: In first-generation systems, each cell supports a number of channels. At any given time a channel is allocated to only one user. Second- generation systems also provide multiple channels per cell, but each channel is dynamically shared by a number of users using time division multiple access (TDMA) or code division multiple access (CDMA).