What (Theoretical) Maximum Throughput values (Downlink) can you achieve in LTE TDD ?

By Azar

Mostly common deployment of LTE in North American market is FDD based. There have been some operators who made move in TDD deployment.

Previously I discussed LTE throughput that can be achieved in Downlink for  LTE FDD case

Today, we will talk about How much throughput you can achieve (in theory) for LTE Downlink TDD scenario.

PRE-REQUISITE

 

  1. In case if you don’t know the difference between TDD and FDD. This video is for you.
  2. In case if you don’t know the difference between TDD and FDD Radio Frame. There is another video for you.

However, for TDD case, the computation is not as simple as it may sound. This is because of different UL and DL sub-frame configurations and special subframe configurations in TDD Radio

Frame. If you don’t know what I am talking about.  Watch the video of TDD Radio frame once again : )

Depending upon the TDD configurations you consider. TDD radio frame can have different throughput analysis.

 

UL-DL SUBFRAME CONFIGURATIONS

 

Why UL-DL Subframe Configuration 0?

 

 

For this detail below.  The analysis is chosen for subframe configuration 0 because it has the least number of downlink subframes.

Why UL-DL Subframe Configuration 5?

 

 

For this detail below. The analysis is chosen for subframe configuration 5 because it has the most number of downlink subframes.

TDD SPECIAL SUBFRAME CONFIGURATIONS

 

Why Special subframe configuration 0?

 

 

For this analysis, special subframe configuration 0 is selected because it has the least number of OFDM symbols within the DwPTS field of the special subframe

Why Special subframe configuration 4?

 

For this analysis, special subframe configuration 4 is selected because it has the most number of OFDM symbols within the DwPTS field of the special subframe

THEORETICAL MAXIMUM THROUGHPUT

 

The table below presents the maximum throughput (in theory) which can be achieved if all Resource Elements are allocated to the data channel i.e.,  Physical Downlink Shared Channel (PDSCH)

and there are no overheads added. Please remember that these values are not achievable in practical scenarios. However, it gives you an idea to compare realistic throughputs with this maximum expected theoretical throughput.

expected theoretical throughput.

 

Theoretical Throughput in LTE TDD if all Resource Elements are allocated to the PDSCH ( Credits: LTE in Bullets )

 

 

QUICK OBSERVATIONS

 

Few observations from the table above.

  1. The throughput computed above is for normal cyclic prefix only
  2. The throughput can be compared with FDD Downlink throughput values given over here.   Throughput for Uplink-Downlink Subframe configuration 0 is significantly lower than FDD because there are only 2 downlink subframes and 2  special subframes
  3. Uplink-Downlink subframe configuration 5 has 8 downlink subframes and 1 special subframe so the throughputs are closer to the equivalent FDD figures shown here 
  4. TDD throughputs are lower than equivalent FDD throughput because in TDD we use unpaired spectrum (single RF carrier), while FDD has paired spectrum (separate uplink and downlink RF carriers)

CONCLUSION

 

In case of both TDD and FDD, Physical Downlink Shared Channel (PDSCH) is used to transfer application data and throughput.

The throughput achievable depends upon :

  • Number of Resource Elements
  • Modulation scheme
  • Multiple antenna transmission schemes used
  • Physical Layer Processing and redundancy added
  • Modulation scheme
  • Carrier Aggregation
  • Etc.