GSM Evolution and the RF Technology changes

Ever wondered why the GSM mobile standards community keeps changing the RF technology with each evolution? The original GSM standard is based on TDMA RF technology. When GSM evolved to UMTS (3G), the RF technology was changed to spread spectrum (WCDMA). The RF technology once again changed with LTE, the 4G evolution of the standard, to OFDMA.


TDMA (Time Division Multiple Access) was chosen for the original GSM standard back in the late 1980s/1990 to make more efficient use of the radio spectrum by enabling higher capacity to be supported in a given radio spectrum (bandwidth) when compared to the previous 1G analog RF technology (FDMA). In GSM, the 200Khz carrier frequencies are time division multiplexed between different users, with each user using the carrier frequency for 1/8th of the time (0.577ms).


WCDMA (Wideband Code Division Multiple Access) was chosen for UMTS to meet the requirement for higher data rates, for higher capacity and to perform well in dense areas (city centers, etc). Carrier frequencies were allocated in chunks of 5MHz. TDMA technology could not meet the performance and data rate requirements specified for UMTS.


LTE, the 4G evolution of the GSM technology, uses OFDM (Orthogonal Frequency Division Multiple Access) for the downlink and Single Carrier FDMA for the uplink. OFDMA was chosen for multiple reasons:

• Flexibility in spectrum allocation. OFDMA can be deployed in spectrum ranging from 1.5 MHz to 20MHz. WCDMA, on the other hand, required spectrum in multiples of 5 MHz.
• Requirement for higher bandwidth and data rates. In UMTS, 5 MHz spectrum allocation limits the maximum achievable data rate.
• Lower latency with OFDMA.
• Better tolerance to multipath fading and interference.

What will the RF technology be when the GSM technology evolves to 5G in several years? We’ll just have to wait and see …