Floating point: Let's hear it for voice
01 June 2001
Why do people buy mobiles? To talk. The latest mobile phones might look great but voice quality is not. The sound is tinny, calls are dropped, and echo can be a real nuisance. Once upon a time third generation networks looked like the answer. Now they're not, argues Bob Emmerson.
It is ironic that all the wireless talk is now about data. The reason we have mobile phones is to talk. The number of gsm subscribers continues to rise with the Gsm Association claiming they have just gone over 500 million. And if you take sms out of the equation then voice accounts for over 95 per cent of the traffic on most networks.
So by now we would expect operators to be delivering high-quality speech services. After all, this is the cash cow they've been milking for years.
But as every subscriber knows, call quality can be dreadful and is usually at its worst in the US. We accept it because there is no alternative.
Calls still get dropped far too often and at times echo makes communication almost impossible.
While there are various technical explanations, for example signals bouncing off buildings in urban areas causing significant variations in signal strength, the real reason is commercial. Quality is inversely proportional to capacity and capacity has been the name of the wireless operators' game. Thus, instead of improving, things have actually been getting worse.
Data compression is used to increase cell capacity and when there's a problem echo is introduced. The message "no network coverage" means the cell is running at maximum capacity. So move into one of these cells while talking and your call will be dropped.
This drive by operators to get more and more subscribers has resulted in call quality being driven down to unacceptable levels, but accept them we must until something better comes along. Theoretically third generation should have been that something better. After all, the service was conceived in order to increase capacity, and on that front it does a great job.
The boost is about two orders of magnitude, which helps explain the high prices operators were prepared to pay for a spectrum licence. In theory having a 100 per cent digital service should enable cd-quality speech.
It used to be part of the pitch for why introducing third generation networks was such a good idea.
But nobody talks about it any more, because there are some serious technical problems that have to be resolved and one tricky commercial issue that will hit some networks very soon, gprs.
This packet-switched service uses spare capacity so that if a channel is free it will be used for data transmission. Pauses in conversations can also be employed. It means gprs is a very efficient service, but what happens if there is no spare capacity? Gprs data services would then be an expensive flop and even more data disillusion will result.
The industry can't afford for that to happen so it's more than likely that operators will take one of the eight voice channels and turn it over to data. Good news for the data service, but bad news for the cash cow.
Voice capacity goes down so fewer urban calls can be made, less cash will be generated, and more calls will be dropped. Potentially a wicked Catch 22 scenario.
Voice in a third generation network has further challenges. The problems of transmitting voice over ip networks are well documented. For example, small delays in the delivery of data packets is not an issue, but voice is a real-time medium and a cumulative delay of more than around 300 milliseconds is not acceptable. Thus, third generation voice traffic will have to reserve bandwidth in advance, set up calls in a similar way to atm, or use intelligence to recognise voice traffic and give it priority.
This is not easy in a fixed, wireline environment, but maintaining the requisite bandwidth during hand-off of a voice call from one cell to another is going to be very tricky and expensive.
BT was hoping to introduce the world's first commercial third generation service in the Isle of Man but announced a delay for this very reason, as did Docomo. The stated reason was software problems in the phones.
So, no cd-quality talk for a while and no use of all that extra capacity for voice, despite the fact that this was the very raison d'etre for third generation.
totaltele.com
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"..what happens if there is no spare capacity? Gprs data services would then be an expensive flop and even more data disillusion will result.The industry can't afford for that to happen so it's more than likely that operators will take one of the eight voice channels and turn it over to data.."
I thought GPRS was going to master multiple cells for data - 2, 4, 6. or even 8.... 1 single cell for data? Sounds like <10kbs speeds ....
Seems like that's the good news, because..
"..Voice capacity goes down so fewer urban calls can be made, less cash will be generated, and more calls will be dropped..."
OOPs!
"..Potentially a wicked Catch 22 scenario.."
Yep. |
