Lossless compression is necessary for text, where every character is important, while lossy compression may be acceptable for images or voice (the limitation of the frequency spectrum in telephony being an example of lossy compression).
Compression predates digital technology, having been used in Morse Code, which assigned the shortest codes to the most common characters, and in telephony, which cuts off high frequencies in voice transmission.
A mobile phone antenna's near-field extends to a distance of 5.2 or 2.6 cm, for 900 or 1800 MHz, respectively (most commonly employed carrier frequencies in 2G mobile telephony radiation), according to the relation r = λ/2 π, (r is the distance of near-field far limit from the antenna when the length of the antenna is smaller than the wavelength λ of the emitted radiation) [ 98].
Consequently, femtocellular access points support the same transmission frequency ranges as conventional cellular telephony networks [14].
Elder recently reviewed 36 publications that reported tumorigenicity assays in rodent species, after RF exposure in the frequency range applicable to mobile telephony {Elder JA, personal communication; [these studies are in the WHO EMF Database (WHO 2006a)]}.
Similarly, bandpass filters reject low and high frequencies to pass only frequencies in a middle region, as in telephony, when audio signals are being sent to an ADC.
The emergence of cellular telephony provides important spectrum occupancy at 900 MHz frequency band.
The reason for choosing this set of frequency alternatives is based on the high demand for cellular telephony and the low quality of service presented.
All types of digital mobile telephony radiation, except for their RF carrier signal, employ Extremely Low Frequencies (ELF) necessary for the modulation and for increasing the capacity of transmitted information by pulsing the signal.
This wideband code-division multiple-access frequency-division duplex technology is considered a third-generation wireless telephony system.
