Signal strength in telecommunications
In telecommunications,[1] particularly in radio frequency engineering, signal strength refers to the transmitter power output as received by a reference antenna at a distance from the transmitting antenna.
For very low-power systems, such as mobile phones, signal strength is usually expressed in dB-microvolts per metre (dBμV/m) or in decibels above a reference level of one milliwatt (dBm).
The electric field strength at a specific point can be determined from the power delivered to the transmitting antenna, its geometry and radiation resistance.
Consider the case of a center-fed half-wave dipole antenna in free space, where the total length L is equal to one half wavelength (λ/2).
If constructed from thin conductors, the current distribution is essentially sinusoidal and the radiating electric field is given by where
) the electric field is maximum and given by Solving this formula for the peak current yields The average power to the antenna is where
and solving for the maximum electric field yields Therefore, if the average power to a half-wave dipole antenna is 1 mW, then the maximum electric field at 313 m (1027 ft) is 1 mV/m (60 dBμ).
In this case, the electric field and radiation resistance are Using a procedure similar to that above, the maximum electric field for a center-fed short dipole is Although there are cell phone base station tower networks across many nations globally, there are still many areas within those nations that do not have good reception.
Some rural areas are unlikely to ever be covered effectively since the cost of erecting a cell tower is too high for only a few customers.
Even in areas with high signal strength, basements and the interiors of large buildings often have poor reception.
Large buildings such as warehouses, hospitals and factories often have no usable signal further than a few metres from the outside walls.
The estimated received signal strength in an active RFID tag can be estimated as follows: In general, you can take the path loss exponent into account:[2] The effective path loss depends on frequency, topography, and environmental conditions.
Actually, one could use any known signal power dBm0 at any distance r0 as a reference: When we measure cell distance r and received power dBmm pairs, we can estimate the mean cell radius as follows: Specialized calculation models exist to plan the location of a new cell tower, taking into account local conditions and radio equipment parameters, as well as consideration that mobile radio signals have line-of-sight propagation, unless reflection occurs.
