sported on the same fiber that transmits traffic from landline carriers. Cell Site Power Requirements Regardless of the generation, every cell site needs local power for equipment at the site. Maintaining service during electrical outages is a critical issue and loss of power at cell sites is one of the reasons that mobile phones might not operate during disas- ters. However, not all carriers have adequate backup. Some have battery backup for momentary power glitches and short outages lasting only a few hours. Deployment of generators that operate for a few days is uneven. The Streamlined Infrastructure of Long-Term Evolution Architecture The Functions of Radios and Modems in Mobile Networks Every wireless device contains a radio. Radios in mobile networks extract radiofre- quency signals from the air and convert them into small bits of frequency compatible with the devices. The radios then hand off slices of bits of data to modems within devices. At the transmitting end, radios convert signals to the frequencies used in the cellular network, and then transmit these wireless signals over the air. At the receiving end, modems remove noise caused by interference and decode the radiofrequency data signals into those compatible with the landline network. If the amount of noise is SO great that the signal can't be decoded, the modem requests that the base station retransmit the signals. Removing the noise from signals is the most complex function in modems. At the transmitting end, modems encode (modulate) the signals to make them compatible with the radiofrequency wireless network. Modems also add encryption at the transmission end for protection from eavesdroppers. Software-Defined Radios Software-Defined Radios (SDRs) have air interfaces based on software rather than hardware. The term "software-defined radio" was coined by the military and used in Europe and the United States throughout the 1990s. As it is used in mobile networks, the term is actually misleading because the radios are in fact based on hardware; on