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Intelecommunications, particularly inradio frequency engineering,signal strength is thetransmitter power output as received by a reference antenna at a distance from the transmitting antenna.High-powered transmissions, such as those used inbroadcasting, are measured indB-millivolts per metre (dBmV/m). For very low-power systems, such asmobile phones, signal strength is usually expressed indB-microvolts per metre (dBμV/m) or indecibels above a reference level of onemilliwatt (dBm). In broadcasting terminology, 1 mV/m is 1000 μV/m or 60dBμ (often written dBu).

• 100 dBμ or 100 mV/m:blanketing interference may occur on some receivers
• 60 dBμ or 1.0 mV/m: frequently considered the edge of aradio station's protected area in North America
• 40 dBμ or 0.1 mV/m: the minimum strength at which a station can be received with acceptable quality on most receivers

The electricfield 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-wavedipole antenna infree 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

${\displaystyle E_{\theta }(r)=\frac{-j{I}_{\circ }}{2\pi {\epsilon }_{0}cr}\frac{\cos \left(\frac{\pi }{2}\cos \theta \right)}{\sin \theta }{e}^{j\left(\omega t-kr\right)}}$

where${\displaystyle \theta }$ is the angle between the antenna axis and the vector to the observation point,${\displaystyle I_{\circ }}$ is the peak current at the feed-point,${\displaystyle {\epsilon }_0=8.85\times {10}^{-12}F/m}$ is the permittivity of free-space,${\displaystyle c=3\times {10}^{8}m/s}$ is the speed of light in vacuum, and${\displaystyle r}$ is the distance to the antenna in meters. When the antenna is viewed broadside (${\displaystyle \theta =\pi /2}$) the electric field is maximum and given by

${\displaystyle |E_{\pi /2}(r)|=\frac{I_{\circ }}{2\pi {\epsilon }_{0}cr}.}$

Solving this formula for the peak current yields

${\displaystyle I_{\circ }=2\pi {\epsilon }_{0}cr|E_{\pi /2}(r)|.}$

The average power to the antenna is

${\displaystyle P_{avg}=\frac{1}{2}{R}_a{I}_{\circ }^2}$

where${\displaystyle R_a=73.13\mathrm{\Omega }}$ is the center-fed half-wave antenna's radiation resistance. Substituting the formula for${\displaystyle I_{\circ }}$ into the one for${\displaystyle P_{avg}}$ and solving for the maximum electric field yields

${\displaystyle |E_{\pi /2}(r)|=\frac{1}{\pi {\epsilon }_{0}cr}\sqrt{\frac{P_{avg}}{2R_a}}=\frac{9.91}{r}\sqrt{P_{avg}}(L=\lambda /2).}$

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).

For a short dipole (${\displaystyle L\ll \lambda /2}$) the current distribution is nearly triangular. In this case, the electric field and radiation resistance are

${\displaystyle E_{\theta }(r)=\frac{-j{I}_{\circ }\sin (\theta )}{4{\epsilon }_{0}cr}\left(\frac{L}{\lambda }\right)e^{j\left(\omega t-kr\right)},R_a=20{\pi }^2{\left(\frac{L}{\lambda }\right)}^2.}$

Using a procedure similar to that above, the maximum electric field for a center-fed short dipole is

${\displaystyle |E_{\pi /2}(r)|=\frac{1}{\pi {\epsilon }_{0}cr}\sqrt{\frac{P_{avg}}{160}}=\frac{9.48}{r}\sqrt{P_{avg}}(L\ll \lambda /2).}$

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.

Weak signal strength can also be caused bydestructive interference of the signals from local towers in urban areas, or by the construction materials used in some buildings causing significant attenuation of signal strength. Large buildings such as warehouses, hospitals and factories often have no usable signal further than a few metres from the outside walls.

This is particularly true for the networks which operate at higherfrequency since these are attenuated more by intervening obstacles, although they are able to usereflection anddiffraction to circumvent obstacles.

The estimated received signal strength in an activeRFID tag can be estimated as follows:

${\displaystyle \mathrm{d}\mathrm{B}{\mathrm{m}}_{\mathrm{e}}=-43.0-40.0{\log }_{10}\left(\frac{r}{R}\right)}$

In general, you can take thepath loss exponent into account:^[1]

${\displaystyle \mathrm{d}\mathrm{B}{\mathrm{m}}_{\mathrm{e}}=-43.0-10.0\gamma {\log }_{10}\left(\frac{r}{R}\right)}$

The effectivepath loss depends onfrequency,topography, and environmental conditions.

Actually, one could use any knownsignal power dBm₀ at any distance r₀ as a reference:

${\displaystyle \mathrm{d}\mathrm{B}{\mathrm{m}}_{\mathrm{e}}={\mathrm{d}\mathrm{B}\mathrm{m}}_0-10.0\gamma {\log }_{10}\left(\frac{r}{r_0}\right)}$

${\displaystyle {\log }_{10}(R/r)}$ would give an estimate of the number of decades, which coincides with an average path loss of 40 dB/decade.

When we measure cell distancer and received powerdBm_m pairs,we can estimate the mean cell radius as follows:

${\displaystyle R_e=\mathrm{avg}[r{10}^{(\mathrm{d}\mathrm{B}{\mathrm{m}}_{\mathrm{m}}+43.0)/40.0}]}$

Specialized calculation models exist to plan the location of a new cell tower, taking into account local conditions andradio equipment parameters, as well as consideration thatmobile radio signals haveline-of-sight propagation, unless reflection occurs.

• Cellular network
• Mobile phone
• Cellular repeater
• Dropped call
• Dead zone (cell phone)
• Dipole field strength in free space
• Field strength meter
• Received signal strength indicator
• S meter
• Signal
• Mobile phone signal
• Mobile coverage

• Radio electronics
• Mobile technology

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