HSPA improves the end-user experience by increasing peak data rates up to 14 Mbit/s in the downlink and 5.8 Mbit/s in the uplink. It also reduces latency and provides up to five times more system capacity in the downlink and up to twice as much system capacity in the uplink, reducing the production cost per bit compared to original WCDMA protocols. HSPA increases peak data rates and capacity in several ways:

Shared-channel transmission, which results in efficient use of available code and power resources in WCDMA
A shorter Transmission Time Interval (TTI), which reduces round-trip time and improves the tracking of fast channel variations
Link adaptation, which maximizes channel usage and enables the base station to operate close to maximum cell power
Fast scheduling, which prioritizes users with the most favorable channel conditions
Fast retransmission and soft-combining, which further increase capacity
16QAM (Quadrature Amplitude Modulation), which yields higher bit-rates ...more