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Wireless: LTE Data Throughput, how to choose TB Size to get maximum data throughput? What's the relationship between TB Size and throughput?

Environment/Versions

8100 LTE RA v4.80/CS8 IT v1.80

Answer

TB Size(transport block size) defines how many bits MAC layer transfers to Physical layer per TTI (Transmission Time Interval, defined as 1ms). Note: TM1/TM2 can carry 1 TB Size per TTI, TM3/TM4 can carry 2 TB Size per TTI (two code word).

Theoretically speaking, data throughput is TB Size/TTI(1ms) for TM1/TM2, 2*TB Size/TTI for TM3/TM4. To get maximum rate, we need choose maximum TB Size. TB Size is affected by bandwidth, modulation and allocated RB, and we can figure out maximum TB Size on CS8 IT GUI.

e.g. we want to figure out the maximum data throughput for 5MHz bandwidth.

  • First, we need figure out the maximum TB Size. On CS8 IT GUI PHY Tab, set MIB to 5MHz, on Scheduler Tab, set DL Static Modulation to 64QAM, DL Static Num RB to 25, then we can see all the available DL Static TB Size, the maximum one is 18336.
  • Then we know the maximum rate is 18336/1ms, around 18Mbps for TM1/TM2 (36Mbps for TM3/TM4). But TB Size includes some overhead information, thus maximum rate in lab is smaller than this value.

Note:

15MHz and 20MHz bandwidth throughput is not verified on CS8 IT v1.80. They will be officially supported from next commercial CS8 IT release (v2.0 or higher).

Product : Data throughput,Wireless,LTE,eAirAccess,LTE Test System