What is High Speed Packet Access (HSPA)?

Have you ever noticed the ‘H’ or ‘H+’ sign on your mobile phone screen when using mobile internet? That is HSPA or High-Speed Packet Access. When you see this sign on your mobile phone, you can expect decent mobile data speeds but keep in mind that HSPA is not 4G.

High Speed Packet Access (HSPA) is an enhancement that was introduced in the 3G UMTS mobile networks for enabling high-speed internet services through your mobile devices. The mobile devices can include your mobile phones, data cards, mobile broadband dongles, MiFi routers, tablets and other similar devices.

The original UMTS networks (Universal Mobile Telecommunications Systems) can provide peak downlink speeds of up to 2 Mbps and peak uplink speeds of up to 128 kbps. HSPA can provide peak downlink speeds of up to 14.4 Mbps and peak uplink speeds of up to 5.76 Mbps.

Breaking down HSPA

HSPA is a combination of two inter-related technologies HSDPA (High-Speed Downlink Packet Access) and HSUPA (High-Speed Uplink Packet Access). The word ‘downlink’ in HSDPA suggests that high-speed data is only available in the downlink. As we know, the downlink is the link that allows a cellular base station to communicate with a mobile phone. So, high-speed in the downlink will allow users to be able to download data such as files, documents, videos, etc. much quicker.

Uplink, on the other hand, is what enables communications from the mobile phone back to the cellular base station. Therefore a high-speed connection in the uplink improves the upload speeds. This is where HSUPA comes in which is the counterpart of HSDPA in the uplink direction. HSDPA delivers peak downlink speeds of up to 14.4 Mbps to help with the downloads and HSUPA enables peak uplink speeds of up to 5.76 Mbps to improve the upload speeds. HSDPA and HSUPA collectively are known as High-Speed Packet Access or HSPA.

On your mobile phone screen, HSPA is shown as the ‘H’ symbol. There is also a more enhanced version of HSPA called Evolved High-Speed Packet Access or HSPA+. HSPA+ is a technology upgrade to HSPA and it can provide peak downlink speeds of up to 42 Mbps and peak uplink speeds of up to 11.5 Mbps. HSPA+ is shown on your mobile phone screen as ‘H+’.

In CDMA2000 networks, a technology called EVolution Data Optimized (EVDO) is used to enable high-speed internet services. EVDO is an equivalent of HSPA in the CDMA networks. Purely for comparison purposes, EVDO can offer peak downlink speeds of up to 14.7 Mbps and peak uplink speeds of up to 5.4 Mbps. More information on EVDO can be found in our post What is EVDO?

How it works

HSDPA and HSUPA use slightly different approaches to enable high-speed data services in the UMTS networks. HSDPA introduces a new high-speed downlink channel which can be shared among multiple mobile users. It uses a transmission duration of only 2 milliseconds as compared to over 10 milliseconds in UMTS (Release 99). With this approach, HSDPA can be really quick when it comes to switching users as it is a shared channel. This short transmission duration also allows HSDPA to respond quickly to the continuously changing radio network conditions. It also uses faster data traffic scheduling in order to allocate most of the available capacity to a single user so that they can receive high-speed data in a very short space of time. HSDPA also uses superior modulation and coding techniques as well as faster re-transmission of erroneous packets.

As a result, mobile users get to enjoy faster download speeds as compared to the original UMTS networks. Unlike HSDPA, HSUPA uses a dedicated channel to add a new radio interface for uplink communication. Just like HSDPA, HSUPA also uses faster re-transmission technique to enable high-speed uploads.

Average data speeds with HSPA/HSPA+

Now you might be wondering why you don’t often get the above speeds when you are on HSPA networks? The above speeds are peak speeds and not the average ones. We don’t usually get peak speeds because the cell within the network serving us also serves many other mobile users simultaneously. The network coverage (signal quality) can also impact the data speeds. Below some examples of randomly selected indoor locations in the UK (Reading) to give you an idea of what average speeds and latency you can expect from HSPA+ (H+). There is also a short video at the end of this article that summarises HSPA.

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