What is High Speed Downlink Packet Access (HSDPA)?

With the constant evolution of the mobile communications industry, a vast number of technologies and terminologies have become part of our daily lives. We already have access to the 5G networks in some geographical locations as long as we use compatible mobile phones. However, 5G is still very new in most countries and it will take some time before it is widely available. Until then, we will still need to rely on earlier technologies supported by the more widespread mobile networks like 4G and 3G. HSDPA is one such technology that was introduced as an enhancement in the 3G era to provide high-speed internet services through mobile networks. Let’s have a quick look at HSDPA and the data rates it enables in the 3G UMTS networks.

HSDPA or High Speed Downlink Packet Access is a technology that provides high-speed internet services through mobile phones and mobile data cards. It was part of the 3G evolution for mobile networks that followed the GSM/UMTS track. The word ‘downlink’ in HSDPA means that the high-speed data is available in downlink only.

The downlink in mobile cellular communications is the link that sends data from the mobile base station to the mobile phone. In simple terms, the downlink is the link that enables the downloads and the uplink is the link that enables the uploads. So, the higher the speed you get through HSDPA, the better the chances of you being able to download things more quickly through the mobile network.

Now you might be wondering what happens when you are trying to upload something heavy e.g. sending an email with a large attachment or uploading lots of photos or videos. Well, 3G mobile networks also have something called HSUPA or ‘High-Speed Uplink Packet Access’ for that. HSUPA is the counterpart of HSDPA in the uplink direction. These two technologies are collectively known simply as High-Speed Packet Access or HSPA. When your mobile phone shows the ‘H’ symbol, it means that you are being served by HSPA, so both HSDPA and HSUPA.

What speeds do you get with HSDPA?

If we talk about peak speeds, then you will find the HSDPA and HSUPA speeds decent enough for most things we do. But as you may know, we don’t usually get peak speeds on our mobile devices because the mobile networks are serving many users simultaneously and the network coverage (signal quality) also impacts the speeds we get.

HSDPA can enable peak downlink speeds of up to 14.4 Mbps, while HSUPA can allow peak uplink speeds of up to 5.76 Mbps. HSPA is also often referred to as 3.5G and is usually shown on a mobile phone as ‘H’ or ‘3G+’ symbols. There is also a more enhanced version of HSPA called HSPA+, which stands for Evolved High-Speed Packet Access. HSPA+ is a technology upgrade to HSPA which maximises the data speeds you get from 3G UMTS networks. HSPA+ can offer peak data speeds of up to 42 Mbps in the downlink for downloads and 11.5 Mbps in the uplink for uploads.

The equivalent of HSPA in the CDMA-based 3G network CDMA2000 is the EVDO technology which stands for EVolution Data Optimized. EVDO can offer peak downlink speeds of up to 14.7 Mbps and maximum uplink speeds of up to 5.4 Mbps. 

How does it work?

HSDPA adds new capabilities to the UMTS network by introducing a new high-speed downlink channel which is shared among multiple users. It uses a much shorter transmission duration of just 2 milliseconds as compared to over 10 ms in UMTS Release 99. As a result, it is much quicker at switching users and responding to the changing radio network conditions. It also uses faster data traffic scheduling which allows it to allocate most of the available cell capacity to one user so that he/she receives high-speed data in a short space of time. It uses superior modulation and coding techniques, and faster retransmission of erroneous packets.

Due to these improvements, mobile users can get higher data rates with HSDPA. HSUPA, on the other hand, adds a new radio interface for uplink communication. Unlike HSDPA, HSUPA uses a dedicated channel and not a shared one. HSUPA also uses a fast retransmission technique just like HSDPA.

As a mobile user, if you live in a country or region where mobile operators use UMTS-based 3G networks, then you don’t have to do anything unusual to be able to use HSPA (HSDPA & HSUPA). You just need a 3G/HSPA capable phone (smartphone or feature phone) in order to get access to HSPA. To be clear, if you use a basic 2G/GSM phone, then you may only get 2G data services i.e. GPRS and EDGE. If you want to use HSPA as an internet source for other non-mobile devices like your laptop, then you need 3G/HSPA data cards that come in the form of USB dongles and Mi-Fi devices.

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