1. System Requirements:
Data Rate and Modulation: Clearly define the required data rate and modulation scheme (256QAM/2048QAM) to accurately calculate signal power and receiver sensitivity
Distance and Frequency: Specify the transmission distance and operating frequency, which impact path loss and antenna gain calculations.
Availability: Determine the desired link availability (percentage of time the system must be operational) to guide decisions on fade margin and redundancy measures
Regulatory Compliance: Ensure adherence to relevant regulatory requirements for frequency usage, emission power levels, and interference mitigation.
2. Link Budget Components:
Transmitter Power: Select a transmitter with sufficient power output to overcome path loss, accounting for antenna gain, feeder loss, and atmospheric attenuation.
Antenna Gain: Choose antennas with suitable gain characteristics for the required transmission and reception directions, taking into account antenna size, beamwidth, and polarization. Consider diversity techniques (e.g., spatial, polarization) to improve signal strength and mitigate fading.
Path Loss: Calculate the signal attenuation due to free space propagation and atmospheric effects using appropriate models (e.g., ITU-R P.525, COST 235) based on frequency, distance, and terrain characteristics. Include any additional losses due to obstacles or vegetation.
Feeder Loss: Factor in the signal loss in cables or waveguides connecting the transmitter and antenna, using manufacturer data or empirical formulas.
Receiver Sensitivity: Select a receiver with sensitivity matching the expected signal level after accounting for all losses. Consider noise figure and receiver dynamic range requirements.
Fade Margin: Add a fade margin to the link budget to account for signal degradation due to weather, multipath propagation, or other impairments.
3. Link Budget Calculations:
Friis Transmission Formula: Use the Friis transmission formula or its variants to calculate the received signal power based on transmitter power, antenna gains, path loss, and frequency.
Link Margin: Calculate the link margin by subtracting the received signal power from the receiver sensitivity.
Signal-to-Noise Ratio (SNR): If feasible, estimate the SNR at the receiver to assess the link’s performance in terms of bit error rate (BER) or data quality.
4. Optimization and Design Trade-offs:
Cost-Effectiveness: Balance performance requirements with cost considerations by evaluating trade-offs between transmitter power, antenna size, and path loss.
Reliability: Incorporate redundancy measures (e.g., standby equipment, path diversity) if high availability is critical, but weigh the cost and complexity implications.
5. Additional:
Environmental Factors: Account for potential environmental impacts like temperature extremes, wind, or precipitation that might affect antenna performance or signal propagation.
