12Personal WirelessCommunications Systems
Historical Note
As discussed in previous chapters, the radio frequency spectrum is generally allocated by a national body to provide specific telecommunications services to end-users. Governments further design policies to ensure the spectrum is licensed to those organisations which can efficiently provide these services.
The discovery of dielectric heating at microwave frequencies for medical usage (such as in physiotherapy) and industrial use (such as microwave ovens, pictured [1])1 in the 1940s necessitated frequency allocations for non-telecommunications applications. However, these devices emitted substantial electromagnetic energy which potentially could interfere with nearby telecommunications equipment operating using the same frequency band. To ensure zero mutual interference a number of frequencies were set-aside worldwide for industrial, scientific and medical (ISM) applications ...
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