A single frequency radio wave does not transmit any information. For information to be transferred, the frequency must vary over time. The range of frequencies that a single channel can occupy is known as bandwidth. To allow multiple calls to be handled by a single base station, multiplexing techniques are used which are ways of combining multiple signals. The four main techniques include: frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and orthogonal frequency division multiplexing (OFDM). FDMA was used in 1G mobile systems (and still used in combination with other techniques today) and assigned a subchannel to each frequency. TDMA was invented in the second generation of cell phones when technology transitioned from analog to digital. In time division multiplexing, the time domain is divided into fixed intervals. These ranges are assigned to each subchannel (connection in the channel). Data for call 1 is assigned to subchannel 1, while data for call 2 is assigned to subchannel 2 until each subchannel is addressed. This information is looped at the sampling rate of the digital signal. This set of subchannels in a loop that includes a synchronization and error correction subchannel is called a frame. TDMA is illustrated in the following figure. In CDMA, a code is assigned to each user and is transmitted with each bit of data sent by the user. This acts as a signature for each signal allowing even more data to be sent in one frequency band. In effect, the bits are distributed over random frequencies in the bandwidth. This makes more noise, but it just means you have to use more energy... middle of paper... move around a 70 lb. briefcase. The 1G speed varied between that of a 28k modem (28kbit/s) and that of a 56k modem (56kbit/s). In terms of overall connection quality, 1G doesn't hold a candle to its 2G digital successors. 1G networks have low capacity, unreliable handoff to towers, poor voice quality, and no security as voice calls were not encrypted and replayed into radio towers, making these calls susceptible to interception. Furthermore, callers could not make offline calls as the different 1G standards (NMT, AMPS, TACS) were not compatible with each other. The range of 1G phones was better than that of its successor thanks to analog signals having a smooth curve unlike a digital signal, which has a jagged corner curve. As the range increases, the quality of the call made from a 1G phone would gradually deteriorate, but a call made from a 2G phone would eventually fail completely.