What is the cause of poor LTE data speeds.

 

This question is often heard and experienced by wireless users who see the LTE icon on their phone and expect lightning fast data speeds but rather experience slow downloads or stalled downloads. Or the LTE icon may disappear altogether.

 

Without getting really deep into this topic there are three very basic reasons.

 

#1. Overloaded backhaul to the switching center. All cell sites are connected by a fiber provider which typically install, by request of the wireless carrier, the requested bandwidth to handle the data traffic from the wireless device to the switching center from the cell site. Typically small sites get 50MB and larger traffic carrying cell sites have 100 MB or higher, data traffic from the cell site. This is most unlikely to happen because the backhaul network is always overbuilt. However if the circuits are close to the maximum bandwidth, then data bursts from other customers using the same cell site, will cause slow data speeds or non-responding or stalled data connections. If you are streaming audio or video you will experience stalled data or disconnection from the cell site.

 

#2. Your LTE device acquires a cell site then the cell site hands off your connection to another LTE cell site and your RF signal drops and the data speeds slow way down. Sometimes you may be handed off to another site that does not have LTE present and your LTE icon disappears. The cause of this is that there are not enough user licenses at the LTE cell site that is close to you. The wireless carrier needs to add more user licenses to the LTE cell site so that the LTE customers’ can access the site successfully. If your LTE device is receiving a signal of -98 dB or less, you will have slow data speeds. The better device reception you have, the faster your data will be transferred.

 

#3. One final and the most common issue of LTE cell sites having slow data speeds is that there are too many users. The explanation of this is rather complex. Basically slow data speeds is the result of too many users and not enough bandwidth being transmitted by the cell site. This is commonly referred to as “not enough resource elements.”

In a 5 Mhz bandwidth LTE cell site, there are only 25 Resource Elements” in a “Resource Block.” Those 25 Resource Elements are only 180 KHz in size. If you multiple .180 times 25 you will get 4.5 Mhz. The missing .5 MHz is used for overhead at the cell site. Everyone using LTE at that site are sharing the same Resource Elements. So the more users you have at the site, the slower the LTE data speeds are. The only way to increase it is to add more RF bandwidth. This is done by using more frequencies and their subcarriers, if the wireless provider has them at their disposal.

Remember that the resource elements reside in the resource blocks and those elements are used by everyone accessing that site using LTE.

 

Here is a table that reflects the Bandwidth vs. Resource Blocks.

 

Bandwidth (MHz)

Resource blocks

1.4

6

3

13

5

25

10

50

15

75

20

100

 

Here is a pictorial of the Resource Block and Resource Elements.

 

http://3.bp.blogspot.com/-kwBCtSkMPCo/TuYew3MVDRI/AAAAAAAAEJw/rDTjuESfe-o/s640/a.jpg

 

 

For more explanation of this, please check out this 82 page presentation.

http://www.itu.int/ITU-D/arb/COE/2010/4G/Documents/Doc4-LTE%20Workshop_TUN_Session3_LTE%20Overview.pdf