Hi, I feel like I have forgotten the basics already.
How many symbols are there in one PRB in LTE (let’s say normal CP)? 7 or 84 ?
My understanding is that, one PRB spans 1 slot (0.5 ms) and 12 subcarriers (each with 15 KHz BW). So, one PRB is 0.5 ms in time domain and 180 KHz in frequency domain. And 1 slot in time domain has 7 symbols (normal CP). So, there should be 84 RE in one PRB. And thus, 84 symbols in one PRB. (That was my understanding, each RE contains one symbol, so 1 PRB = 84 RE = 84 symbols )
But after googling, I came to see that each PRB has 7 symbols. So, what is it? Seven symbols in one PRB or 84 symbols in one PRB?
If it is indeed 7 symbols in one PRB, does it mean that each symbol spans the whole 12 subcarriers (15 KHz x 12 = 180 KHz) ? I thought each symbol only spans only one subcarrier !
1 PRB = 84 REs
RE is a 2-D unit of resources spanning 1 subcarrier in the frequency domain and 1 OFDM symbol in the time domain
Each RE carriers 2,4,6 or 8 bits of information based on the modulation scheme used
The unit of scheduling is in terms of PRBs in a TTI (1ms=1SF). As we know, 1SF=14 OFDM symbols. This should mean that one OFDM symbol carries the information contained in 12REs (12 subcarriers) X No. of PRBs. scheduled in a TTI.
Please clarify if you find this incorrect.
1 PRB = 12 subscarrier x 7 symbols = 84 Resource Elements.
Since the minimum required transmission time interval (TTI) is 1 ms in LTE, allocations are done in pairs of PRB. Two PRBs form a subframe with minimum bandwidth of 180 kHz and minimum TTI of 1 ms.
1 RE = 1 symbol x 1 subscarrier, each symbol does NOT spans the whole 12 subscarriers.