GPRS (General Packet Radio Service) and EDGE (Enhanced Data for Global Evolution) are two packet-based mobile data technologies that were introduced in second-generation GSM networks. GPRS could provide peak download speeds of up to 171.2 kbps. EDGE followed GPRS and increased the maximum download speed to 384 kbps.
When the original GSM (Global System for Mobile Communications) networks were launched in the early 1990s, they only had the circuit-switched (CS) capability. CS requires the use of dedicated circuits for any user sessions such as voice calls or data. The original GSM networks mainly supported voice calls but around a year later, the short-messaging-service (SMS) was introduced to help customers send and receive text messages. In GSM, each transceiver (radio unit) is assigned one frequency channel (ARFCN) that creates one cell. Each cell has eight (8) time-slots to accommodate multiple calls or text messages.
Circuit-Switched Data with CSD and HSCSD
The original GSM networks employed a technology called CSD (Circuit-Switched-Data) that was able to utilise time-slots of the radio units for providing mobile data. CSD allowed a maximum download speed of up to 9.6 kbps by using a single time-slot. High-Speed Circuit Switched Data (HSCSD) was an enhancement that could improve the data speeds of CSD by up to 6 times. HSCSD used better error-coding techniques to increase the maximum data rate of a single time-slot from 9.6 kbps to 14.4 kbps. It also had the capability to use multiple time-slots (maximum limit of 4) for a single data session. As a result, HSCSD was able to achieve a maximum download speed of up to 57.6 kbps which is six (6) times higher than the maximum speed of CSD.
Packet Switched Data with GPRS and EDGE
While HSCSD was a choice for some mobile operators, it wasn’t widely adopted in Europe. Even though mobile operators could use circuit-switched technology for mobile data, it wasn’t the most efficient. Mobile operators, therefore, needed a different solution which came in the form of GPRS that was based on the packet-switched technology. With the packet-switched method, mobile data is sent and received in the form of packets of data bursts at different time intervals by sharing the available capacity with multiple users. So rather than dedicating the entire capacity to one session, the capacity is shared between multiple users to facilitate multiple sessions. In this way, when a certain user in a certain session isn’t sending/receiving any data-bursts, other users in other sessions can utilise the same capacity. GPRS can enable peak download speeds of up to 171.2 kbps which may not seem a lot today but it was a considerable improvement at the time. GPRS was a big achievement as it paved the way for the evolution of packet-based mobile data. The mobile networks today also use packet-switched techniques for offering mobile data services.
GPRS was followed by EDGE or Enhanced Data for Global Evolution which was another enhancement to improve mobile data speeds even further. EDGE can offer peak downlink speeds of up to 384 kbps for downloads, which is more than double of what GPRS can offer. Even though 384 kbps can theoretically support basic mobile internet tasks, we don’t get peak speeds in real life. Generally, depending on how many people are on the network and how far you are from the base station, you may only get to enjoy a small portion of this 384 kbps. EDGE also uses the packet-switched methodology to send and receive mobile data just like GPRS. With EDGE, the capacity available on the packet-switched part of the network is shared between multiple users. The packets of data bursts are sent at different intervals for different users which makes the overall process much more efficient. GPRS and EDGE are often referred to as 2.5G and 2.75G respectively. Check out this post to learn more about the different upload and download speeds achievable through various mobile network technologies.