Some may say that peak data rate for LTE is 300mbps.
How did they arrive at this number? In this chapter we shall make it clear.
1 frame = 10 subframe = 10ms
1 subframe = 2 slots = 0.5ms
1 slot = 12 sub carriers & 7 symbols
1 slot = Resource Block
Hence, 1RB = 12 x 7 = 84 Resource Elements
Bandwidth of 1 Resource Block = 180 Khz
Bandwidth of 1 Sub Carrier = 15 Khz (spacing)
WKT LTE will work on below bandwidths and has the resource blocks:
Channel bandwidth Resource BLocks: 1.4 MHz 6 3 MHz 15 5 MHz 25 10 MHz 50 15 MHz 75 20 MHz 100
So in LTE uses OFDM in downlink and SC-FDMA in uplink.
In OFDMA it is possible to have below 3 modulation techniques.
QPSK 2 bits per symbol
16QAM 4 bits per symbol
64QAM 6 bits per symbol
Some of the parameters to be considered while calculating bandwidth are:
Some Parameters to be considered:
1. Cyclic prefix
2. Available Resource
3. Modulation and coding scheme
So in our example let us assume below parameters:
20 Mhz channel bandwidth, normal CP & 4×4 MIMO
Step 1: Calculate the number of RE in each subframe of 20Mh
12 subcarriers x 7 symbols x 100 RB x 2 slots (each subframe has 2 slots) = 16800 RE’s per subframe.
Step 2: Assume 64QAM modulation & no coding, 1 modulation symbol will carry 6bits.
so 16800 modulation symbols x 6bits/modulation symbol = 100800bits = 100.8Mbps is the data rate
Step 3: With 4×4 MIMO, peak data rate = 4×100.8 = 403Mbps
Step 4: Estimating 25% is for signaling such as PDCCH, reference signal, sync signal, PBCH & some coding we get,
= 403Mbps x 0.75 = 302Mbps