Is the GPRS honeymoon over?
by Brian Jepson
The industry accepted standard raw data rate for each timeslot is 11.4 kbps, however the actual data payload will be between 9.6 and 10 kbps per timeslot ... For the AT&T Wireless GPRS network, devices will be able to transmit over a maximum of 5 timeslots either 4 and 1 or 3 and 2.
So, depending on your device, the best you can hope for is 40kbps, even though the theoretical maximum is 115kbps. There are channel coding schemes (CS-4) where you can get 21.4kbps per timeslot, so you could get up to 85.6kbps if your cellular provider supports it.
That's GPRS. Lots of folks call it 2.5G because it's not quite as fast as the promised 3G speeds (384kbps is what I'm hoping for). It's OK for some things: I don't mind using it for email and some web surfing, but it's still 40kbps, and that's slower than dialup. CDMA2000 is a 3G network that's being rolled out in stages. Stage 1 is called 1xRTT; Verizon and Sprint both offer unlimited usage on the network for $80 a month, and it is about twice as fast as GPRS.
I did some tests recently, downloading a 70k http download (a PNG graphic)--keep in mind that there's network overhead when comparing this to the overall data rates. I performed the download with a 1xRTT modem 17 times in 4 different locations, getting an average speed of 6.3 KB/s (kilobytes per second), about 50kbps. With GPRS, I did 18 different downloads in four locations, and got an average speed of 2.42 KB/s (about 20kbps, in line with what AT&T's page suggests is likely for average web browser speeds on a loaded network).
As of July 1, things could be getting a little faster. As has been reported in a a few places, Cingular is rolling out limited EDGE service (Indianapolis only for now, with buildout to occur later in the year) They are promising speeds of up to 170kbps, with 75-135kbps more likely (go back to the AT&T 3G Technology Center and look at the speeds they are promising for EDGE). I don't know what the pricing is like, but it's certainly worth watching.
I was excited when GPRS became available here in the US, and it's still better than nothing (although if a hotspot is available, I'll pay $7 or so a day to use it). But in its current incarnation, it's a bridge technology; CDPD was too slow to meet most users' needs except for people who are total freaks about connectivity. 2.5G GPRS is there for early adopters and to keep folks happy while we wait for the faster stuff to roll out. EDGE will be better, but CDMA2000 1xRTT is here now, and I like it. It's fast enough that I could get serious work done with it. But, I'm in a contract with AT&T, and I really do like being able to use my T68i with my Mac over Bluetooth. SmithMicro has solutions for tethering a Mac to phones from various providers, including Sprint and Verizon. So it is a little tempting to consider what life would be like at twice the speed.
What about you? How are you keeping connected on the road?
But CDMA is US-only
While I agree with your assessment of the relative speed merits of GSM/GPRS vs. CDMA deployments in the U.S., the fact remains that CDMA is a (mostly) US-only deal.
But CDMA is US-only
Really good point, thanks. There are plenty of people who can't live without GSM's global capabilities.