We can devide this system into two: radiofrequency systems and infrared systems. Subdivision of radiofrequency system is possible-to NSS(non spread spectrum) and SS(spread spectrum). SS system is unlicensed and it requires 50-75 hopping frequency at 910 MHz and 2.5 GHz respectively. Infrared system is used to download data among computers and cell phones. But this is limited to distances under 15m. A typical infrared system can have a range 1-2m with a data rate 4 Mbps. IR system downloads faster with a feeble interference.
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