The modern mobile communication technique starts from 1920s and has experienced 5 periods.

The first period corresponds to 1920s to 1940s, in which specific frequency band has been developed for police work. The carrier frequency is 30-40MHz.

The second period corresponds to 1940s to 1960s, in which mobile communications was spread for public use. The patch is manual and the system capacity is small.

The third period corresponds to 1960s to 1970s. Improved mobile telephone service standard was developed. Automatic 450MHz service was available.

The fourth period corresponds to 1970s to 1980s, in which the cellular mobile communications quickly developed. Advanced mobile phone service trials began in Chicago and Washington. The carrier frequency can reach 900MHz. This is the commonly talked "the first generation".

The fifth period starts from 1980s. The low spectral efficiency and other cons of analog cellular system leads to the development of digital cellular system. And this is just what we talked "the second generation".

Now we'd like to talk about some special techniques used in "the third generation". Also "the fourth generation" is being researched.