3G HSPA benefits
The UMTS cellular system as defined under the 3GPP Release 99 standard was orientated more towards switched circuit operation and was not well suited to packet operation. Additionally greater speeds were required by users than could be provided with the original UMTS networks. Accordingly the changes required for HSPA were incorporated into many UMTS networks to enable them to operate more in the manner required for current applications.
HSPA provides a number of significant benefits that enable the new service to provide a far better performance for the user. While 3G UMTS HSPA offers higher data transfer rates, this is not the only benefit, as the system offers many other improvements as well:
1. Use of higher order modulation: 16QAM is used in the downlink instead of QPSK to enable data to be transmitted at a higher rate. This provides for maximum data rates of 14 Mbps in the downlink. QPSK is still used in the uplink where data rates of up to 5.8 Mbps are achieved. The data rates quoted are for raw data rates and do not include reductions in actual payload data resulting from the protocol overheads.
2. Shorter Transmission Time Interval (TTI): The use of a shorter TTI reduces the round trip time and enables improvements in adapting to fast channel variations and provides for reductions in latency.
3. Use of shared channel transmission: Sharing the resources enables greater levels of efficiency to be achieved and integrates with IP and packet data concepts.
4. Use of link adaptation: By adapting the link it is possible to maximize the channel usage.
5. Fast Node B scheduling: The use of fast scheduling with adaptive coding and modulation (only downlink) enables the system to respond to the varying radio channel and interference conditions and to accommodate data traffic which tends to be "bursty" in nature.
6. Node B based Hybrid ARQ: This enables 3G HSPA to provide reduced retransmission round trip times and it adds robustness to the system by allowing soft combining of retransmissions.
For the network operator, the introduction of 3G HSPA technology brings a cost reduction per bit carried as well as an increase in system capacity. With the increase in data traffic, and operators looking to bring in increased revenue from data transmission, this is a particularly attractive proposition. A further advantage of the introduction of 3G HSPA is that it can often be rolled out by incorporating a software update into the system. This means its use brings significant benefits to user and operator alike.