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Link Distance – Wireless Video Selection Criteria

The total distance that can be covered between endpoints in a wireless link is affected by a combination of factors including frequency, antenna geometry, interference, and obstructions. These factors make precise distance calculations extremely dependent on local environments. However, some general rules can be defined to help guide technology selection.

Rule 1) Lower frequency bands support greater transmission distances, and are less sensitive to signal path obstructions. But low frequency bands are more likely to be restricted by the FCC (or other national authorities) to narrow channel bandwidths and hence limited bit rates.

Rule 2) More complex modulation schemes (such as 16QAM as compared to QPSK) that deliver more bits in a given channel bandwidth require greater signal to noise ratios to deliver an acceptable error rate. Other things being equal, shorter usable link distance limits will apply for more complex modulation.

Rule 3) Narrow-beam antennas produce higher gains than wide-beam ones, thereby permitting longer link distances to be used.  Omnidirectional antennas having much shorter ranges than either panel or parabolic antennas.

Rule 4) Greater levels of interfering signals will reduce usable link distances due to a reduction in signal to noise ratio. Interference can come from many sources, including other equipment occupying the same frequencies nearby and consumer devices such as microwave ovens that emit RF energy. In general, heavily populated areas have much more ambient interference than rural environments.

Rule 5) Path obstructions, including buildings, power lines and trees or other vegetation will attenuate wireless signals and reduce usable range. High frequency signals tend to suffer greater attenuation than low frequency signals for a given obstacle. Extremely high frequency signals may only work if there is a clear line of sight from the transmitter to the receiver.

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