It is a 3GPP standard deployed on the 3G existing network infrastructure providing high-speed downlink data rates.
• It improves the spectral efficiency for the data services with the help of adaptive and higher order modulation, quick scheduling, hybrid ARQ retransmission method for shared downlink packet data channel.
• It provides twice an increase in the air interface capacity and five times increase in data speed on downlink reducing downlink transmission delay variance.
The main features of HSDPA are as follows:
1. HSDPA systems provide high rates upto 20 Mbps compatible to WCDMA.
2. HSDPA provides download speeds on a mobile phone equivalant to to an ADSL.
3. It provides improved user end quality.
4. With higher layer protocols it provides improved efficiency.
5. It can be deployed in in FDD and TDD both the modes.
6. It provides faster downstream throughput .
7. It uses adaptive coding and modulation to offer high data rates.
8. It uses shared channel transmission that efficiently use the code and the power resources.
9. HSDPA provides Link adaptation, that maximizes the channel usage and allows the base station to operate at power close to maximum cell power.
10. 16QAM and 64QAM can be used in HSDPA to obtain hgh bit-rates.
11. Fast hybrid Automatic Repeat Request (ARQ)
HSDPA introduced three new channel types as follows:
1. The user data is sent on High Speed Downlink Shared Channel (HS-DSCH).
2. The control information is sent on High Speed Common Control Channel (HS-SCCH). HS-SCCH is sent two slots prior to HS-DSH, for informing the scheduled User Equipment about incoming transmission on HS-DSCH.It has fixed rate of 960 kbps.
3. High Speed Dedicated Physical Control Channel(HS-DPCCH) that carries Channel Quality Indicators(CQIs) & used to carry the acknowledgment signals to Node.
Advantages of HSDPA:
1. The network can use data schedulers that provide a higher priority torea time applications.
2. It is well suited for applications with highly variable bandwidth requirements.
3. HSDPA provides small delays, allowing new applications like interactive networked games.
4. HSDPA provides uses shorter frame length, thus it accelerates scheduled packet transmission.