20-12-2009, 06:15 PM
High-Speed Downlink Packet Access (HSDPA) (Sometimes known as High-Speed Downlink Protocol Access) is a 3G mobile telephony protocol in the HSPA family, which provides a roadmap for UMTS-based networks to increase their data transfer speeds and capacity. Current HSDPA deployments now support 1.8 Mbit/s, 3.6 Mbit/s, 7.2 Mbit/s and 14.4 Mbit/s in downlink.
Further speed grades are planned for the near future. The networks are then to be upgraded to HSPA Evolved, which provides speeds of 42 Mbit downlink in its first release.
In addition to supporting high data speeds, HSDPA greatly increases the capacity of the network. Current HSDPA networks have the capacity to provide each customer with 30 gigabytes of data per month in addition to 1000 minutes of voice and 300 minutes of mobile TV.HSDPA stands for High Speed Downlink Packet Access. As the name suggests, this is a piece of UMTS functionality designed to deliver downlink packet data at very high data rates. It is a release 5 feature. It achieves its aim by using the following techniques:
¢ Use of shared channel concept Rather than constantly allocating and deallocating dedicated channels to individual users, users share a high bandwidth channel “ the HS-DSCH (High Speed Downlink Shared Channel). This allows the system to operate with a fat pipe. An analogous situation in queuing theory is that an M/M/1 queuing system is more efficient than an M/M/n system.
¢ Use of Hybrid ARQ/Incremental Redundancy
¢ Use of multicode transmission
¢ Availability of high level modulation (QAM)
¢ Link Adaptation
¢ Fast scheduling, facilitated by a short TTI.
