Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!netsys!vector!telecom-gateway From: euatdt@euas11g.ericsson.se (Torsten Dahlkvist) Newsgroups: comp.dcom.telecom Subject: Re: More on Cellular Overseas Message-ID: Date: 26 Jun 89 13:34:32 GMT Sender: news@vector.Dallas.TX.US Reply-To: Torsten Dahlkvist Organization: Ellemtel Utvecklings AB, Stockholm, Sweden Lines: 40 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 215, message 7 of 8 In article John Wheeler writes: >Curious as to how "cellular" can be operated at 450 MHz. At frequencies that >"low" the cells would spill all over the place. 400-500 MHz is in fact >"famous" for its abilities to get into nooks and crannies everywhere, >bouncing off every building and hill within sight. That's largely the idea. The tranceivers are built into the (nation-wide) net of FM-repeaters covering the country. Because of the size of the cells, the NMT-450 rapidly out-grew its' capacity (nobody had even dreamed it would get that popular) and nowadays NMT-900 is recommended unless you absolutely MUST have nation-wide access. A friend just bought a cellular phone and he said if you wanted a 450 subscription there was a waiting-line of several months while a 900 one you can get overnight. Apparently the Telco is restricting the numbers of 450 users and diverting as much of the traffic as possible to 900. Even in a 900 MHz-system, there's always some overlap between two adjoining cells and a certain "spill" is bound to occur. Due to this, adjoining cells never share the same channels and the net-phone protocol handles the supervision necessary to detect when a phone has moved into a new cell and a switch is indicated. Since 900-cells are smaller, there are never as many phones in any one cell at the same time as there can be in the 450-system, so even with the same number of channels, 900 would have higher throughput. As it is, I believe 900 also has more channels than 450, so capacity is MUCH higher. However, 900 does not work if you get too far away from the urban areas and/or high up into the mountains. I have for a fact used a NMT-450 in the border mountains between Sweden and Norway. The Swedish carrier reached well into Norwegian territory and vice-versa. A rough estimate is that the overlap was at least 6 miles (10 km). NMT phones have a "Nation Select" key where you can switch between the different carriers. This is to prevent the phone from suddenly locking onto the "wrong" cell and causing your calls to be charged extra for "international". This also makes it possible to see how far into Norwegian territory the Swedish carrier reaches. /Torsten Torsten Dahlkvist ! "I am not now, nor have I ever ELLEMTEL Telecommunication Laboratories ! been, intimately related to P.O. Box 1505, S-125 25 ALVSJO, SWEDEN ! Dweezil Zappa!" Tel: +46 8 727 3788 ! - "Wierd" Al Yankowitz