Three of the more common transmission schemes include FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple Access).
To better understand CDMA and how it is different, let's compare the three transmission schemes.
FDMA divides the given spectrum into channels by the frequency domain. Each phone call is allocated one channel for the entire duration of the call. In the figure above, each band represents one call.
Time Division Multiple Access
TDMA enhances FDMA by further dividing the spectrum into channels by the time domain as well. A channel in the frequency domain is divided among multiple users. Each phone call is allocated a spot in the channel for a small amount of time, and "takes turns" being transmitted. In the figure above, each horizontal band represents the channel divided by the frequency domain. Within that is the vertical division in the time domain. Each user then takes turns occupying the channel.
Unlike FDMA and TDMA, CDMA transmission does not work by allocating channels for each phone call. Instead, CDMA utilizes the entire spectrum for transmisson of each call. Each phone call is uniquely encoded and transmitted across the entire spectrum, in a manner known as spread spectrum transmission. In the figure above, each brightly colored pattern represents the encoded phone call being transmitted across the spectrum.
©2001 Kyle Bryson, Alison Chen, and Allen Wan