), receiver sensitivity (PRX), free-space loss (LFS) and other losses combined in the fade margin (LFM), together Table 4-19: Balancing factors in the link budget Reducing required PTX Increasing required PTX Lower receiver sensitivity (bigger negative) PRX Higher free space loss LFS Higher transmitter antenna gain GTX Higher fade margin LFM Higher transmitter antenna gain GRX Radio Communication Basics define the link budget that is available to bring the data signal successfully from transmission to detection (Table 4-19). It is convenient to express the link budget in terms of the transmitter power (PTX) required to deliver a signal to the receiver at its sensitivity limit (PRX). Expressed in dBm, this is: PTX = - - dBm (4.11) For example, a system comprising a directional transmitting antenna with a gain of 14 dBi, a patch receiving antenna (6 dBi), and a receiver with a sensitivity of -90 dBm, operating over 100 metres at 2.4 GHz (LFS = 80 dB) with a 36 dB fade margin (LFM) results in a required transmitter power of: PTX = -90 dBm - 14 dBi - -6 dBi + 80 dB + 36 dBm = +6 dBm To ensure that the signal at the receiving antenna is above the receiver sensitivity, the required transmitter power is therefore +6 dBm (4 mW), as shown graphically in Figure 4-33. This configuration would be comfortably achieved with a 100 mW (20 dBm) transmitter, with an extra 14 dB link margin for unaccounted losses or noise. Required PTx Free space Fade margin Antenna Receiver gain Rx sensitivity Antenna gain Tx Figure 4-33: Link Budget Expressed as Required Transmitter Power Chapter Four Ambient Noise Environment As well as the receiver noise floor, which defines the limit of receiver sensitivity, other sources of external RF noise will also have an impact on the reliability of RF signal detection and data decoding. The total RF noise entering a radio antenna at any particular location is termed the ambient noise environment and is made up of two components: Ambient noise floor - the aggregate background noise from distant sources s