Data Compression

To get more use out of available bandwidth, you can make sure that the data takes less time to travel to its destination, thus freeing the bandwidth sooner for other transmissions. Since the mid-80s, the algorithms for compression have dramatically improved due to better design and better processing hardware.

Another means of conserving bandwidth is to channel the frequencies so that more than one subscriber can use them at once. There are a number of different methods of doing this, but here we'll restrict the discussion to two that you're likely to encounter: time-division multiple access (TDMA) and code-division multiple access (CDMA). Although these channeling technologies function differently from each other, they have the same purpose: to let more than one signal use the same frequency in the same place at the same time.

TDMA uses the same multiplexing techniques that time-division multiplexing does. Bandwidth is split into a number of logical channels, and each signal gets one of the channels. For example, six devices can transmit data at 330MHz in the same place at the same time. The process actually involves extraordinarily rapid switching of the channel among its various "simultaneous" users so that each of them has the apparent sole use of the channel but is in fact sharing that channel with all its other users, occupying it for specific segments of time. Think of it as shuffling the users in and out of the channel at predefined intervals but doing the shuffling so quickly that it is transparent to them.

CDMA, also called spread-spectrum technology, works a little differently. Rather than dividing the frequency into perhaps six channels, as TDMA would, it mixes the six transmissions and sends them all as a heap. Each transmission has a unique digital code assigned to it that permits the recipient to sort out its own data from the other transmissions. CDMA works like a packet-switching network. This sounds confusing, but it's not that complicated. Think of a mailbox in an office building. If each office in the building has its own mailbox and must pay rent on it, that can get expensive and is unnecessary for those who don't constantly send mail much more efficient to have one big mailbox in the office building that everyone shares rent on. To keep everyone's mail from getting mixed up, each office color-codes its envelopes: Rutger's Insurance uses blue envelopes, Wilson Industries pink, and so forth. Thus, all of the offices can share transmission bandwidth (the mailbox) and jumble their signals together to get the most use out of the available bandwidth, but the data (that is, the mail) doesn't get confused because each piece is coded for the recipient).

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