The Link Budget
The link budget (LB) is the fundamental calculation for planning of any RF link between a transmitter (Tx) and a receiver (Rx). In two-way calculations we actually have two LB calculations, one for the DL and one for the UL.
The result of the link budget calculations is the maximum allowable path loss (APL) from the base station to the mobile in the downlink and the maximum allowable link loss on the reverse link, from the mobile to the base station the uplink. You need to include all the attenuation and gains of the end-to-end signal path from the Tx to the Rx, the attenuation due to the distance, adding the clutter loss of the environment, cable attenuation and antenna gains. You will also need to include a safety margin to provide a given probability of the desired signal, accounting for fading margins and body losses.
Depending on the type of distribution system you design, there are various parameters to take into account when calculating the link budget. Based on these parameters for the DAS, the radio service requirement, and the impact of noise from existing signal sources operating on the same frequency or channel, you must calculate the link budget for both links, the uplink and the downlink, to determine the service range of the system in both directions. The link budget for the particular radio service range can be either UL- or DL-limited; this will depend on the parameters affecting the links. One cell can be downlink-limited for one type ...