What is High Speed Downlink Packet Access (HSDPA) or 3.5G and what is the Difference between HSDPA and 3G?

By | July 21, 2011

High-Speed Downlink Packet Access (HSDPA) also known as 3.5G (3.5 generation of wireless telecommunication technology) is new protocol for data transmission through mobile phones. HSDPA (High Speed Downlink Packet Access) as the name indicates it improves the speed and Quality of downlink data transmission on the networks based on Universal Mobile Telecommunications System (UMTS) .Ideally HSDPA uses a packet based data transfer in W-CDMA which provides the downlink with speed ranging from 8-10 Mbps over the bandwidth of 5 MHz. HSDPA supported mobile phone can attain a download speed same as an ADSL (Asymmetric Digital Subscriber Line) line assuming phone is working at optimal speed. HSDPA consist of Multiple-Input Multiple-Output (MIMO), Hybrid Automatic Request (HARQ), Adaptive Modulation and Coding (AMC), advanced receiver design and fast cell search. High-Speed Downlink Shared Channel (HS-DSCH) is the new channel for HSDPA that has been added to UMTS. High-Speed Downlink Shared Channel (HS-DSCH) uses HS-SCCH (High Speed-Shared Control Channel), HS-DPCCH (High Speed-Dedicated Physical Control Channel) and HS-PDSCH (High Speed-Physical Downlink Shared Channel) channels for attaining faster downlink speed. All users using channel dependent scheduling shares HS-DSCH channel to make optimal uses of radio signals for faster downloads. HSDPA also provides a higher uplink speed of 384 kbit/s which is much more than 3g (uplink speed 128kbit/s).

What is the difference between HSDPA and 3G?

  • HSDPA is just an advancement of 3G in terms of Speed and Quality of Transmission. It does not provide any other new feature to 3G.
  • Ideally HSDPA provides the speed ranging from 8-10 Mbps downlink which is much more than 3G.
  • HSDPA has less¬†¬†latency as compared to 3G.
  • HSDPA is cheap because it only has to be upgraded from 3G.

What is Latency?

Latency is the time difference between the time at which request was sent and time in which reply was received. Higher latency does not cause much difference for the users who are just browsing web sites, but it noticeable for users using video calls as higher latency causes dropped packets or lag in the voice signal which directly weakens the call quality.