Designing A High Speed Wireless Data Link
Line of Sight Link Budget Analysis
Several major factors that can impact the performance of a radio system are
- Available/permitted output power,
- Bandwidth,
- Receiver sensitivity,
- Antenna gains
- Environmental conditions
In this case study, the students will be required to calculate the link budget for a LOS Wireless link. Read through the following to understand some of the aspects and elements that need to be considered when calculating a Link Budget.
Received Power
If the estimated/calculated received power is sufficiently large (relative to receiver sensitivity), the link budget is sufficient for sending data.
Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)
Gains(dB)=Transmit Antenna gain+ Receiver Antenna Gain
Receiver sensitivity is the lowest power level at which the receiver can detect an RF signal and demodulate data.
Link Margin/Fade Margin
The amount by which the received power exceeds receiver sensitivity is called the link margin/fade margin.
In wireless systems, multipath propagation results in multiple copies of a signal to arrive at different signal phases at the receiver. If these signals add up destructively, the resulting signal power can be lower by a factor of 100 or 1000 (20 or 30 dB). The signal level relative to the noise declines making signal detection at the receiver more difficult. It is therefore highly recommended to keep a link margin of 30 dB when designing a wireless system.
Link Margin=Received Power-Receiver sensitivity
Losses
In a line-of-sight wireless system, losses are mainly due to free-space path loss (FSPL). Other losses are due to antenna cabling and connectors. Generally, 0.25dB loss per connector and 0.25dB loss for every 3-ft of antenna cable should be included in the link budget calculations. However, for the sake of simplicity, you can neglect these losses for your calculations.