Friday, 4 January 2008

HSPA Data Rates Calculation

People often get lost while calculating the data rates for HSDPA, HSUPA or HSPA+

Note: HSPA+ is better known as eHSPA or HSPAe where e stands for evolution or evolved

Most people are aware that the theoretical maximum for HSDPA is 14.4Mbps, so lets see how we reach 14.4Mbps:

In UMTS, in each slot the maximum number of bits transmitted is 2560. The correct term to use is chips rather than bits. If you want to know where this 2560 comes from or why chips then please refer 3GPP TS 25.211

There are 15 slots per 10ms frame so since the TTI for HSDPA is 2ms, there will be 3 slots. So there will be a total of 7680 chips.

QPSK has 2 bits per symbol = 7680 * 2 chips for 2ms = 15360 chips/2ms = 15360 * 1000 /2 chips per second

Now the SF is fixed at 16
= (15360 * 1000) / (2 * 16)
= 480 Kbps

Terminal that uses 15 QPSK codes will get 480 * 15 = 7.2Mbps

On other hand 16 QAM will have 4 bits per symbol so the rate would be 7.2 * 2 = 14.4Mbps

In HSPA+ we will also have 64QAM which has 6 bits per symbol (2^6 = 64) so the max rate would be 7.2 * 3 = 21.6Mbps.
The figure above is self explanatory and shows the data rate in case of eHSPA.


Anonymous said...

Thanks for the information.

Can we say that 7.2Mbps throughput is possible only if there is just single HSPA user in the network

Zahid Ghadialy said...

Peak rate is for single user in a cell, not the network which would consist of many cells.