In the previous post we had compared the path loss of LTE at 728 MHz and 1805 MHz in a free space line of sight channel. This is a very simplistic channel model which tells us that ratio of the received signal strengths at these frequencies can be simply found as:
That is the received signal strength at 728 MHz is 6.15 times higher than the received signal strength at 1805 MHz.
Now let us consider a more realistic channel model known as the COST-231 model. According to this model the path loss (difference between the transmit power and receive power) is given as:
f=frequency in MHz (0.1500 MHz – 2000 MHz)
ht=base station antenna height in m (30 m – 200 m)
hr=mobile station antenna height in m (1 m – 10 m)
d=transmit receive separation in km (1 km – 20 km)
C=3 dB for metropolitan centres
and mobile station antenna correction factor is given as:
Using the above equations with ht=30 m, hr=1 m and d=1 km the path loss at 728 MHz and 1805 MHz is found out to be 100.63 dB and 114.00 dB respectively i.e. there is a gain of 13.37 dB when using the lower frequency. In simpler terms the received signal at 728 MHz would be 21.72 times stronger than the signal at 1805 MHz.
Such a remarkable improvement in signal strength or in signal to noise ratio (SNR) has the potential of increasing the throughput four folds. For example at an SNR of 1.5 dB QPSK 1/2 would give a throughput of 6.00Mbps whereas at an SNR of 14.7 dB a modulation coding scheme (MCS) of 64QAM 2/3 would result in a throughput of 24.01 Mbps.
Author: John (YA)
John has over 15 years of Research and Development experience in the field of Wireless Communications. He has worked for a number of companies around the world including Qualcomm Inc. USA. He has an MS in Electrical Engineering from Virginia Tech USA and has published his work in international journals and conferences.