UMTS: High Speed Packet Access (HSPA) Technology

As of July 31, 2007, there are over 522 million 3G subscribers in the world (source: 3gtoday.com). Out of these 130 million are on UMTS, a growth of almost 100% in one year. Data services are expected to grow significantly within the next few years. Current 2.5 G and 3 G operators are already reporting that a significant proportion of usage is now due to data, implying an increasing demand for high-data-rate, content-rich multimedia services. Although current Release 99 WCDMA systems offer a maximum practical data rate of 384 kbps, the 3rd Generation Partnership Project (3GPP) have included in Release 5 of the specifications a new high-speed, low-delay feature referred to as High Speed Downlink Packet Access (HSDPA). HSDPA also known as Release 5, provides significant enhancements to the Downlink compared to WCDMA Release 99 in terms of peak data rate, cell throughput, and round trip delay. This is achieved through the implementation of a fast channel control and allocation mechanism that employs such features as Adaptive Modulation and Coding and fast Hybrid Automatic Repeat Request (HARQ). Shorter Physical Layer frames are also employed High Speed Uplink Packet Access (HSUPA) (UMTS Release 6) complements the High Speed Downlink Packet Access (HSDPA) technology. As the name suggests the improvement is in the uplink where the theoretical uplink data rate can be up to 5.76 Mbps. Together, HSDPA and HSUPA offer reduced latency and much higher data rates on the downlink and uplink, theoretically as high as 14.