Telecom Giga: Concepts of High Speed Downlink Packet Access(HSDPA)

Monday, June 11, 2012

Concepts of High Speed Downlink Packet Access(HSDPA)

Release 5 of the 3GPP W-CDMA specification adds HSDPA in an effort to make the system more efficient for packet data applications by increasing peak data rates and reducing packet latency. Although the theoretical peak data rate for HSDPA is approximately 14 Mb/s, the actual rates achieved will be much lower than that. The performance of HSDPA depends largely on the cell size. In macro cell applications, HSDPA may improve on W-CDMA data capacity only by perhaps 30 percent, with sustainable peak data rates for one user of maybe 1 Mb/s. But in micro and pico cell deployments where co-channel interference is minimal, HSDPA is capable of delivering much higher performance over basic W-CDMA. The exact improvement is very hard to predict since it depends on actual channel conditions and the real-time capabilities of the BTS–neither of which are standardized. However, some credible estimates for Release 5 suggest a cell capacity of up to 3 Mb/s rising to 5 Mb/s in Release 6, which includes a more advanced UE receiver and improved BTS packet scheduling. Peak user data rates might reach 3.6 Mb/s for short periods of time but are unlikely to be sustainable.

The result of adding HSDPA to W-CDMA is similar to that of adding E-GPRS to GSM: that is, the improvement in peak data rates and the overall increase in system capacity,particularly in small cells. Network operators are pushing for quick adoption of HSDPA, which means that design and test engineers require suitable test equipment to enable them to develop and test new HSDPA features in the BTS and UE.

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