The number of users who can be serviced depends on the location of the users-how many of them are within a given cell and what signal-to-noise ratio the service provider deems acceptable. Spread spectrum allows for two compression ratios for digitized voice, and they vary according to the channel quality: 13Kbps, which is used to provide near-land-line voice qualities (e.g., in support of something like wireless local Chapter 13 Wireless Communications Basics loop), and 8Kbps, which is used to maximize the use of the spectrum and extend battery life. It is important to realize that spread spectrum requires complex power control schemes, and power control is very important in spread spectrum. Power Control Schemes in TDMA and Spread Spectrum The classic example that instructors give their students when talking about wireless is the following: You walk into a TDMA cocktail party, and a group of people stands in a circle. Each person takes a turn at making a comment or answering a question. You can sepa- rate the conversations by the moment in time when each individual is speaking. You walk into a spread spectrum party and you feel as though you've walked into the United Nations. There's German in the left-hand corner, Japanese in the right-hand corner, and English in the center. Somebody says a word in your language that you rec- ognize, and you immediately focus your attention there. You're able to filter out the extraneous conversation as noise because you've tuned in on a code that's understand- able to you. You can continue to filter out the extraneous conversation unless another 200 delegates walk in and add their conversations to the overall mix, making it impossi- ble for you to distinguish between the conversations. On spread spectrum networks, channels can be reused in adjacent cells without creating co-channel interference because different pseudorandom number (PN) codes are used in each cell site. Spread spectrum was developed by the military to be secure. The wide spreading of the signal makes if diffic