The original wireless data was based on CSD (Circuit Switched Data) connections: using the connection that would normally carry a voice to transport data. The problem with CSD, apart from its lamentable lack of speed, is that the amount of bandwidth used remains the same even if no data is being transmitted. Early Wap sessions were commonly billed by the minute like phone calls.
From 2001, the 8390: Nokia's first GPRS phone
That changed with GPRS (General Packet Radio Service), which did at least use a digital connection and one that slipped packets into unused voice slots rather than converting data into audible tones. But the speed was still poor and mobile data only expanded from the specialist to the geek - still far from the mobile internet promised in the adverts.
The slots available to GPRS exist because while GSM is an FDD (Frequency Division Duplex) technology it's also TDMA (Time Division Multiple Access). The first term means that one frequency is used for sending and another, simultaneously, for receiving. That's in contrast, incidentally, to TDD (Time Division Duplex) where the same frequency flips between send and receive many times a second.
TDMA means that where more than one user is on the same frequency they are allocated time slots in rotation, up to eight of them in GSM, later upgraded to 16. If fewer than eight people are on the same frequency then GPRS can drop data into those unused time slots.
Handsets have even got quite good at using more several slots. Up to four are commonly used giving a speed something in the region of 53.6Kb/s with a following wind, if the empty slots are available - voice still takes precedence every time. That's a huge improvement, but users still proved obstinately slow to embrace mobile data.
3GPP GSM/GPRS/Edge Timeline
Then we were told that Edge (Enhanced Data rates for GSM Evolution) would deliver what we had been promised. Edge uses better encoding than GPRS to squeeze three times the data into the same slot, usually with a basestation and handset software upgrade as everything but the data encoding remains the same.
COMMENTS
OFDM
In the process of trying to make OFDM more palatable to a non-comms audience, you seem to have missed the real advantage of the technique. The real beauty of OFDM is the flexibility given by so many orthogonal low-bandwidth sub-carriers: you can avoid the problem of frequency-selective fading for one user (mitigating their bad channel) by moving their allocation in the spectrum. This leads to much more efficient usage of spectrum, and better channels for all. It is excellent at adapting to nasty channel conditions in slowly-changing channels*.
I'm not really sure what you're getting at with regards to "solving" the problem of "timing". If you're referring to inter-symbol interference, which is indeed a concern, then OFDM doesn't directly solve this by "putting [chunks] in different frequencies" - but what it does do is ensure that the symbol rate on each individual component frequency is low enough that ISI can be mitigated easily. But if you're referring to interleaving, which does indeed spread "chunks" of data amongst frequencies, then that helps solve a different problem: the issue of losing bursts of data in frequency-specific fades.
On the down side, OFDM really isn't good in channels with a great deal of doppler shift (since it breaks the orthogonality between the sub-carriers) - making it non-ideal for use in fast-moving vehicles, for instance, without specific counter-measures.
8390? shouldnt that be 8310?
Good article, but as this article seems to have a UK slant to it.. the 8310 should have been the phone that was mentioned as being the first with GPRS in the UK. The 8390 was not even the first phone in the US with GPRS, a motorola timeport was, if i remember correctly.
Jobs - because the iPhone wasnt a world first in any area.
"mobile data is all about ..."
That's the 64billion dollar question, isn't it.
Is it about seeing the same internet as at home (or in the office), when you're on the move (nb on the move, *not* just away from base but stationary at a WiFi hotspot).
Or is it about the mobile web, about some selection of significant websites recognising that there are going to be as many folk viewing them on "mobile internet devices" (phones, PDAs, maybe netbooks) as there are on PCs, and that their website designs should reflect that (eg no Flash).
It isn't about "m-commerce" yet, or about "location dependent services", and folks have been trying that for a decade or so. Mind you, Google has recently changed the market rules, as it sometimes does, with Google Maps for Mobile and the things you can do with that.
Yahoo nearly works on my S60 mobile in Opera Mini. BBC news has a "low graphics" version too. Google Maps for Mobile is fantastic, though without a GPS it sometimes gets confused (but that's probably not Google's fault).
But not everyone does so well. Obviously anyone designing in Flash has wasted their time even more than usual. Some sites that you would imagine might be of particular interest to those out and about are so full of big-screen rubbish and scripts and so on that they are useless on a small screen device, mobile or otherwise. Classic examples would include weather forecasts from the Met Office and traffic reports from the Highways Agency.
http://www.metoffice.gov.uk/weather/uk/se/reading_forecast_weather.html
http://www.trafficengland.com
Madness.
So, what exactly is the killer app for mobile broadband? How is it going to make money for the cellcos, so they can pay for all that extra bandwidth to all those new cells?
I know, we could do location-dependent downloaded-on-demand high-definition video ringtone subscription service. Yeah, that'd work. Where's the Dragon's Den number.
Well? You got any better ideas?
Handset or PC?
To me the main reason that data on 2G/3G etc. has not really taken off is that most content is not suitable for a phone handset.
When WAP first came out, most web content was too complex and there were attempts to produce WAP portals which would offer cut down content suitable for the handsets.
At that point most web content would have displayed well on my EEE PC (if it had existed then).
Now content is so rich and so loaded with fancy video and special effects that I struggle on my EEE PC and my older portable to view the website in the way that the cutting edge design intended.
Nice on my new 1440 * 900 Dell portable, though :-)
Not much good on a phone handset :-(
For me, mobile data is all about freeing portable PCs from fixed ADSL/cable connections.
You can get the rich content you have come to expect when you are away from your cosy nest.
Now if only the coverage, reliability, bandwidth etc. etc. wasn't totally crap. (Speaking as a Virgin customer).
If I want to talk to someone or send a text message I use my phone.
For getting serious data off t'Internet I use a PC.
Then again, I am from the keyboard generation and can't think through my thumbs.
Cheers
Dave R
