Post on 17-Jan-2016
How to Calculate LTE Peak Capacity Rate during Trail for All LTE BANDS
Date: 28/10/2012
Case Name: How to Calculate LTE Peak Capacity Rate during Trail for All LTE BANDS
Description: In A Country LTE Trial Project: While Conducting the trial process ,the Customer Would
like to focus on LTE capacity and present what can realistically be obtained. I have
seen wild figures, mainly pushed by system vendors and consumed by many operators,
journalist and writers who like to wow readers of the promise of new technologies. For
network operators, referring on capacity expectations has negative consequences as
capacity fundamentally impact the cost of the network both on the access side and the
backhaul side. Inflated capacity figures would lead to under-dimensioning on the access
side and over-dimensioning on the backhaul side. So, for example, if we think LTE cell
will provide 100 Mbps of throughput while in reality can only do 50 Mbps, the operator
will be short by 50% of capacity in the access network resulting in poor user experience
(e.g. slow download, blocking, etc.) and will be 50% over the required capacity for
backhaul in which case it’s investment in capacity that’s sitting idle. This is why it is
important to get capacity expectations right
Alarm: NULL
Handling Process In a A country LTE Trail Project, the Customer main focus will look at the peak capacity
of LTE. This is the maximum possible capacity which in reality can only be achieved in
lab conditions. To understand the calculations below, one needs to be familiar with the
technology (I will provide references at the end). But for now, let’s assume a 2×5 MHz
LTE system. We first calculate the number of resource elements (RE) in a subframe (a
subframe is 1 msec):
12 Subcarriers x 7 OFDMA Symbols x 25 Resource Blocks x 2 slots = 4,200 REs
Then we calculate the data rate assuming 64 QAM with no coding (64QAM is the
highest modulation for downlink LTE):
6 bits per 64QAM symbol x 4,200 Res / 1 msec = 25.2 Mbps
The MIMO data rate is then 2 x 25.2 = 50.4 Mbps. We now have to subtract the
overhead related to control signaling such as PDCCH and PBCH channels, reference &
synchronization signals, and coding. These are estimated as follows:
PDCCH channel can take 1 to 3 symbols out of 14 in a subframe. Assuming that on
average it is 2.5 symbols, the amount of overhead due to PDCCH becomes 2.5/14 =
17.86 %.
Downlink RS signal uses 4 symbols in every third subcarrier resulting in 16/336 =
4.76% overhead for 2×2 MIMO configuration
The other channels (PSS, SSS, PBCH, PCFICH, PHICH) added together amount to
2023-4-21
How to Calculate LTE Peak Capacity Rate during Trail for All LTE BANDS
Date: 28/10/2012
~2.6% of overhead
The total approximate overhead for the 5 MHz channel is 17.86% + 4.76% + 2.6% =
25.22%.
The peak data rate is then 0.75 x 50.4 Mbps = 37.8 Mbps.
Note that the uplink would have lower throughput because the modulation scheme for
most device classes is 16QAM in SISO mode only.
There is another technique to calculate the peak capacity which I include here as well
for a 2×20 MHz LTE system with 4×4 MIMO configuration and 64QAM code rate 1:
Downlink data rate:
Pilot overhead (4 Tx antennas) = 14.29%
Common channel overhead (adequate to serve 1 UE/subframe) = 10%
CP overhead = 6.66%
Guard band overhead = 10%
Downlink data rate = 4 x 6 bps/Hz x 20 MHz x (1-14.29%) x (1-10%) x (1-6.66%) x (1-
10%) = 298 Mbps.
Uplink data rate:
1 Tx antenna (no MIMO), 64 QAM code rate 1 (Note that typical UEs can support only
16QAM)
Pilot overhead = 14.3%
Random access overhead = 0.625%
CP overhead = 6.66%
Guard band overhead = 10%
Uplink data rate = 1 * 6 bps/Hz x 20 MHz x (1-14.29%) x (1-0.625%) x (1-6.66%) x (1-
10%) = 82 Mbps.
2023-4-21
How to Calculate LTE Peak Capacity Rate during Trail for All LTE BANDS
Date: 28/10/2012
Fig 1:Peak Downlink rates in LTE
Fig 2: Peak Uplink Rates in LTE.
Suggestion: So Conducting a trial for LTE we have To conclude, the LTE capacity depends on the
following:
1. 1)Channel bandwidth
2. 2)Network loading: number of subscribers in a cell which impacts the overhead
3. 3)The configuration & capability of the system: whether it’s 2×2 MIMO, SISO, and the
MCS scheme.
attachment:
2023-4-21
How to Calculate LTE Peak Capacity Rate during Trail for All LTE BANDS
Date: 28/10/2012
2023-4-21