the assignments do not have to stay fixed at all. It makes alot more sense to utilize the airwaves in the most efficent manner, and the mixing of voice and data is lower capacity.
When you have voice, you have certain parameters in terms of delay, availability, and coverage (error rate) that must be adhered to. this forces a lower bit rate and a higher amount of redundant information being sent. Sending data onthis channel, while being convienent, is not the most efficient.
What is efficient is using the best coding for the job, which means having a set of channels dedicated to 1x voice only and a set of them dedicated to a higher coding scheme with the ability to have errors and do data only.
first from a mixing of them point of view, if the BTS has the newest CSM chip in it, it can do either 1x or DO in the same chipset and the radio and transmission part of the channel does not know if it is 1x or DO. So the carrier can map by the minute how many channels they want of 1x and of DO, as long as the DO fits into a single 1.25 MHz slot. for instance, VZ can program 10 Mhz of their allocation to voice and 2.5 Mhz to DO during peak voice hours and then remix it to 10 Mhz DO and 2.5 MHz voice during hours from 7 PM to 2 AM. And they can do this in 1.25 Mhz slots at any time they want. the only difference in teh backhaul is if the data coming across the channel goes to a voice codec or to a router.
As far as the error rate and using data more efficiently, in voice, you cannot drop more than so many bits in a row or loose so many packets in a row before you have degraded voice service. You must maintin the "real timeness" of hte link. If you mix data in there, the data must follow pretty much the same rules.
In DO, you can burst a high amount of data in a short time to a single user and you can montior if that user has high error rate or low error rate and allocate them data bursts as needed. You can also send alot of data and have the channel miss the data and not have a problem with latency, where you would have that problem on voice and data channels. Also if you sending data only, you can change the coding scheme to send data about 50x faster than voice channels. Again, it has to do wiht the time division multiplexing that is available on the DO system versus the voice and data system.
All you really get is mixing of data and voice in the D+V system....quite true. |
