2.4 GHz vs. 900 MHz – range, flexibility and the global marketplace
Range – Propagation and Other Key Factors
For building long-range IoT (Internet of Things) networks, the cost of connectivity is heavily driven by the coverage that can be achieved by each base station deployed in the network. Conventional wisdom says that long-range applications should use 900 MHz due to better propagation. Simply put, a technology with identical technical characteristics (receiver sensitivity, power output, etc.) will cover a wider area implemented in 900 MHz than in 2.4 GHz. Expressed in link budget, this advantage translates into a roughly 9 dB advantage for a 900 MHz system.
What is Link Budget? Link budget, along with assumptions on path loss, is sufficient to give the area covered for a given probability of coverage and a given indoor/underground penetration value. However, for real-world performance, the trade-off is not that simple. The 900 MHz and 2.4 GHz systems have other differences besides propagation loss that are important to performance of the overall system in providing coverage (See Table). Antenna diversity is a well-known technique for improving the effective link budget performance of wireless systems – two antennas with sufficient separation can be governed by independent fade margins. The separation required is directly related to the wavelength in question – providing a distinct advantage to 2.4 GHz systems. The much smaller separation required makes antenna diversity in IoT scale endpoints possible at 2.4 GHz – an option not even available to a technology implemented in 900 MHz spectrum. The improvement in effective link budget from antenna diversity in On-Ramp Wireless’ RPMA system is roughly 8 dB – almost completely offsetting the propagation advantage of a 900 MHz alternative.
What does this mean for the actual coverage of RPMA? Simply put, given the offsetting effects of these two differences, one can simply use link budget to compare the coverage performance of an RPMA system vs. any system implemented in 900 MHz.
2.4 GHZ vs. 900 MHz Comparison
(Stay tuned for the next week’s conclusion of this article)