Calculation for Body Loss and Feeder Loss for LTE
When we RF Planning in LTE then Losses are one of most important factor to take in calculation for predication coverage. Below you find how Body loss and Feeder loss calculation for LTE.
Body Loss :
Body loss indicates the loss generated due to signal blocking and absorption when a terminal antenna is close to the body. This affects handsets in particular. Body loss depends on the position of the terminal. For fixed service, normally USB dongle is used. Terminals, such as indoor and outdoor CPEs, are often mounted on roofs, windows, or desks.
An eNodeB antenna is mounted at a height of tens of meters, in which case body loss can be ignored as the body loss value is 0 dB. For mobile applications, especially PDA-based VoIP services, body loss must be considered and in this instance, the body loss is about 3 dB.
Feeder Loss :
Feeder loss indicates the signal loss caused by various devices that are located on the path of the antenna to the receiver. Any device using an external antenna for service provision at either the base station side or terminal side must consider feeder loss. If a USB dongle, an indoor CPE, or an outdoor CPE integrated with an antenna is used, feeder loss can be ignored at the terminal side, but not at the base station side.
In the actual link budget, you must calculate feeder loss according to feeder type and length and connector type. Figure below shows the typical connections of the antenna feeder system in an indoor base station.
The formula for calculating the feeder loss according to the feeder type and length is as follows:
Feeder loss (dB) = Feeder loss per 100 m (dB/100 m) × feeder length (m)/100
The feeder loss per 100 meters is related to the frequency band. Table below lists typical feeder losses.
Typical feeder losses Table :
If a base station is mounted indoors, the link budget must include the losses of all devices from the RF port of the base station to the antenna interface, including the indoor jumper, connector, main transmission feeder, combiners, splitters and the outdoor jumper.
If the RRU of a distributed base station is mounted on the tower top, you need to consider only the loss of the outdoor 1/2″ jumper. In this case, the total cable loss can be greatly reduced to approximately 0.5dB.
Background Noise :
The background noise of the LTE system is the same as that of other communication systems. The calculation formula is as follows:
Nth = KTB. K indicates the Boltzmann constant.
The value is as follows: 1.38 x 10 ^ (- 23) J/K. T indicates absolute temperature at a value of 290K. The result of KT is the density of the heat noise power spectrum and the value is -174dBm/Hz. B indicates channel bandwidth and in LTE, it can be 1.4MHz/3MHz/5 MHz/10 MHz/15 MHz/20 MHz