UMTS - Success and Limitations
The success story of GSM (2G) is exceptional. To facilitate data communication, some extensions were made in existing GSM, but the success was limited. GPRS was introduced for mobile users for packet data, basic data rate went up to 172 Kb/s in theory, but hardly allocated the maximum 8 logical channels for a user. GPRS has the concept of a 2 stage access to IP connectivity.
First step is to connect to and register with the network. For this the transmission of user data requires the establishment of PDP (Packet Data Protocol) environment. At this point only the IP address is assigned. GPRS is also known as 2.5G network.
For both GSM/CS (Circuit Switching) and GPRS/PS (Packet Switching), continuous efforts for optimizations were made on the basis of higher modulation efficiency under EDGE (Enhanced Data Rates for GSM Evolution), but nothing was changed fundamentally.
The next 3G generation of mobile networks (UMTS) built on a new radio technology known as WCDMS (Wideband CDMA) and it ensured two things −
- More bandwidth due to new radio spectrum;
- Higher peak data rates for the end user.
UMTS network architecture was designed keeping both CS and PS in parallel. Later on, a completely different service layer was created in form of the Internet and Multimedia Subsystem (IMS). UMTS was latter on improved for higher data rates by HSPA and HSPA+. This was divided into downlink/HSDPA and uplink/HSUPA. 3GPP Rel 5 has standardized for HSDPA and Rel 6 has standardized for HSUPA. HSPA+ comes under Rel. 7 standard of 3GPP.
Continuous improvement was achieved already within the legacy PS technology by Direct Tunnel approach. However, it was clear that more changes in architecture are required to achieve this goal. Another aspect of improvement in the legacy technology can be identified with supernatural efficiency, the effective number of bits deliverable per radio frequency unit and time unit. Even though new radio spectrum has been made available for mobile communication, the pressure for cost reduction and competitiveness required further gain.