An evolutionary path towards UMTS

An evolutionary time-division multiple-access scheme is presented, that combines GSM compatibility with high performance and UMTS capabilities. In this evolutionary path higher-order modulation schemes and assignment of multiple carriers to a user enable bit rates up to 2 Mbit per second. GSM already employs spread-spectrum techniques through the use of slow frequency hopping. This spread-spectrum technique provides frequency diversity as well as interference diversity through the interleaving and coding: if a single burst is erased by bad channel conditions, good reception of the other bursts enable the channel coding to recover the data without errors. The addition of multi-carrier modes provides an improved spread-spectrum capability in combination with frequency hopping, as different carriers may fade differently, depending on the coherence bandwidth of the channel and the separation of the carriers. Thus, a large frequency separation of the carriers provides good decoded performance for large coherence bandwidths.