ellis@uunet.uu.net (John T Ellis) (02/17/91)
A few days ago, I posted the following article to this list: > Digital cellular will increase capacity in the following manner. The > first method under development (and actually being tested) is TDM - > Time Division Multiplexing. The capacity increase on paper is 3:1 (3 > times more than current analog). The other method being looked at is > CDM - Code Division Multiplexing. On paper it is said to provide an > increase of 20:1. > The biggest problem with these new technologies is the size of the > phone needed to implement them. Currently the phone designs call for > some huge ie. garbage can, phone with an unbelievable power source. > So ... digital cellular is a ways off. [text deleted] In my haste to appear knowledgable and make a contribution to this list, I gave you information that was not based on research. Rather, it was based on rumors and distorted facts. I would like to apologize to the list for my unprofessionalism. I am not in any way affiliated with Motorola's work on digitial cellular since I am an analog switch engineer. However, I wanted to share with you what little I knew and in my haste, failed to verify my information. Again, I would like to apologize and assure you that it will not happen again. Following is information I obtained from an engineer who, for a period of time, worked on the Motorola USDC project. 1. I can assure you that the digital mobile is NOT the size of a garbage can. In fact, the full-function mobile is enclosed in a Motorola FM Transciever case, about two feet by one foot by four inches. And that is only the first cut at it. I guarantee they will get smaller. The aim is a digital luggable or largish handheld. 2. TDMA = Time Division Multiple Access CDMA = Code Division Multiple Access (not multiplexing as I originally wrote) 3. The capacity increase of 3:1 is not on paper; we have shown the TDMA capability to Pactel with a working demo system. The 20:1 increase that is proposed for CDMA (Code Division Multiple Access, a form of spread sprectrum transmission) is only on paper; nobody has built a working example. 4. The biggest problems with TDMA technology is the degradation of speech quality with channel errors, and the fact that a POCKET-SIZED digital mobile is several years away. Also the great difficulty in expanding the speech compression to the final 6:1; that is the theoretical limit for this application. It was brought to my attention that my original posting gave some bad impressions of Motorola's committment to digital cellular. I would like to iterate that Motorola DOES officially support US Digitial Cellular. Finally, the information and views expressed above, in my original posting and in all future postings are my own and are not necessarily those of Motorola's. Thanks. John T. Ellis 708-632-7857 Motorola Cellular motcid!ellis@chg.mcd.mot.com