We've discussed, at least in passing, five different cellular radio systems. We looked in particular at AMPS, the mostly analog, original cellular radio scheme. That's because three digital schemes default to AMPS, so it's important to understand this basic operating system.We also looked at IS-54, the first digital service, which followed AMPS and is now folded into IS-136. This AT&T offering, the newest of the TDMA services, still retains an AMPS operating mode. IS-54 and now IS-136 co-exist with AMPS service, that is, a carrier can mix and match these digital and analog services on whatever channel sets they choose. IS-95 is a different kind of service, a CDMA, spread spectrum offering that while not an evolution of the TDMA schemes, still defaults to advanced mobile phone service where a IS-95 signal cannot be detected.
Confused by all these names and abbreviations? Consider how many different operating systems computers use: Unix, Linux, Windows, NT, DOS, the Macintosh OS, and so on. They do the same things in different ways but they are all computers. Cellular radio is like that, different ways to communicate but all having in common a distributed network of cell sites, the principle of frequency-reuse, handoffs, and so on.
If an American carrier uses these words or phrases, then you have one of these technologies:
If your phone has a "SIM or smart card" or memory chip it is using GSM
If your phone uses CDMA the technology is IS-95
If the carrier doesn't mention either word above, or if it says it uses TDMA, then you are using IS-136
And iDEN is, well, iDEN, a proprietary operating system built by Motorola (external link) that, among others, NEXTEL uses.
PCS1900, although not a real trade name, usually refers to an IS-95 system operating at 1900MHz. Usually. If you see a reference to PCS1900 as a GSM service then it is a TDMA based system, not a CDMA technology. PCS1900 in CDMA is not compatible with other services, but it has a mode which lets the phone choose AMPS service if PCS1900 isn't available. Want more confusion? Many carriers that offer IS-136 and GSM, like Cingular, refer to IS-136 as simply TDMA. This is deceptive since GSM is also TDMA. Whatever. And since we are reviewing, let's make sure we understand what transmission technologies are involved.
Different transmission techniques enable the different cellular radio systems. These technologies are the infrastructure of radio. In frequency division multiple access, we separate radio channels or calls by frequency, like the way broadcast radio stations are separated by frequency. One call per channel. In time division multiple access we separate calls by time, one after another. Since calls are separated by time TDMA can put several calls on one channel. In code division multiple access we separate calls by code, putting all the calls this time on a single channel. Unique codes assigned to every bit of every conversation keeps them separate. Now, back to CDMA, specifically IS-95. (Make sure to download the .pdf files to the left.)
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[What is this?] Article Index I. Introduction II. Cellular History III. Cell Sector Terminology IV. Basic Theory and Operation IX. Code Division Multiple Access: IS-95 A. B. Back to the CDMA Discussion C. Summary of CDMA D. A different way to share a channel E. Synchronization F. What Every Radio System Must Consider G. CDMA Benefits H. Call Processing: A Few Details V. Cellular frequency and channel discussion VI. Channel Names and Functions VII. AMPS Call Processing A. Registration B. Pages: Getting a call C. The SAT, Dial Tone, and Blank and Burst D. Origination: Making a call E. Precall Validation VIII. AMPS and Digital Systems compared X. Appendix A. AMPS Call Processing Diagram B. Land Mobile or IMTS C. Early Bell System Overview of Amps D. Link to Professor R.C. Levine's article XI. Additional Assistance A. Q&A: Cell Tower Capacity Recent Posts What Every Radio System Must Consider CDMA Benefits Call Processing: A Few Details Appendix AMPS Call Processing Land Mobile or IMTS Early Bell System Overview of Amps Link to Professor R.C. Levine's article Cell Tower Lease Expert Q&A: Cell Tower Capacity Powered by
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