High Speed Downlink Packet Access (HSDPA)

High Speed Downlink Packet Access (HSDPA):

High Speed Downlink Packet Access (HSDPA)
 High Speed Downlink Packet Access (HSDPA)

It is a 3GPP standard deployed on the 3G existing network infrastructure providing high-speed downlink data rates at low deployment cost.

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 reasons mobile operators prefer to use HSDPA are as follows:

1. HSDPA has radio capacity trunking gain.

 2. Downlink has the highest data load.

3. Shorter frame length accelerates packet scheduling for transmission.

4. Existing 3G/UMTS networks can be used for deploying HSDPA

5. HSDPA with indoor coverage systems provide high rates upto 14.4 Mbps on downlink.

6. Like WiFi HSDPA does not require access points (APs).

7. HSDPA provides more spectrum efficiency in comparison to the UMTS and EDGE systems. Also, more data per Hz is available.

8.  The production cost is low per Mb. 

9. It can be easily compared with Wi-Fi systems.

Must Read>> HSPA (High Speed Packet Access)

The main features of HSDPA are as follows:

1. HSDPA with indoor coverage systems provide high rates up to 14.4 Mbps on downlink.

2. HSUPA is used for uplink data transmission from mobile. To provide high-quality data service an active DAS (distributed antenna system) is used.

3. In HSDPA there is no soft handover. Hence, overlapping of picocells in the same building creates "self-interference". 

4. It is a downlink data service providing cost-effective, high bandwidth. packet-oriented, low delay service within UMTS. 

5. It reduces the link latency and increases the capacity and data transfer rates of the network. 

6. HSDPA provides download speeds on a mobile phone equivalent to an ADSL.

7. It provides improved user end quality.

8. With higher layer protocols it provides improved efficiency.

9. It can be deployed in FDD and TDD both the modes.

10. It provides faster downstream throughput. 

11. It uses adaptive coding and modulation to offer high data rates.

12. It uses shared channel transmission that efficiently uses the code and the power resources.

13. A shorter Transmission Time Interval (TTI) , decreases the round trip time and improves the tracking of fast channel variations.

14. HSDPA provides Link adaptation, that maximizes the channel usage and allows the base station to operate at power close to maximum cell power.

15. Fast scheduling in HSDPA provides users with the most suitable channel conditions. Fast retransmission and soft-combining, increase the capacity.

16. 16QAM and 64QAM can be used in HSDPA to obtain high bit rates. 

17. Fast hybrid Automatic Repeat Request (ARQ).

18. Shorter frame length accelerates packet scheduling for transmission.

HSDPA channels:

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-DSCH ,for informing the scheduled User Equipment about incoming transmission on HS-DSCH.

3. High Speed Dedicated Physical Control Channel (HS-DPCCH) that carries Channel Quality Indicators (CQIS).

Advantages of HSDPA:

1. The network can use data schedulers that provide a higher priority to real-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 uses a shorter frame length, thus it accelerates scheduled packet transmission.

Disadvantages of HSDPA:

HSDPA is not preferred for applications with low bandwidth requirements like voice.

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