After many research I found that HSPA share the UMTS 5 Mhz band. However, I have not understood how can these two thechnology share it and why don't operator use only HSPA technology if it can offer the best performance than UMTS?

Can user use the two network in the same time and how? How can user choose between HSPA and UMTS to send his data? What the difference in code plan?


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You can think of HSPA as an upgraded version of UMTS which gives you the ability to use higher data speeds. HSPA is like a feature of the 3G network which improves data speeds by giving you a channel with higher capacity. It has own transport layer channel and 3 physical layer channels.

HSPA uses better modulations in good radio conditions to deliver higher speeds.

HSPA is part of the UMTS and it and it is only for data.

UMTS uses for data the lower speed R99 data channel but it ca also carry channel switched voice and video.

Operator offer both UMTS data and HSPA data for backward compatibility, not all handsets support HSPA.

A user cannot choose which technology to use. The user equipment (the handset) automatically selects which technology to use according to the radio conditions and the network settings. You can only choose between 2G and 3G or automatic, this is the only setting I have seen.


This is correct, and in addition, the choice of the technology used depends also on the QoS allowed to the subscriber by the operator.

When a subscriber buy a simcard, this simcard has some uplink bit rate and some downlink bitrate.

So, if the Qos data subscription of the simcard is very low, let's say the customer bought only 256Kbps for uplink rate, it would be difficult for him to reach HSPA, maybe he will camp on HSDPA depending on the threshold in the network configuration.

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