[joedeluco (OP)]

Joe De Luco asked the Naked Scientists:
   
Hi Guys,
 
I have a question about cell phones.  I am always baffled by the numerous plans, costs and options that are offered.

I recently stopped the email service on my account when I saw how much it cost, especially when emailing photos with my cell phone camera.
 
I was wondering if technically there is that much a  difference between my cell phone usage versus transmitting text and emails that merits the high charges they apply?
 
Thanks so much

Joe De Luco

What do you think?

[graham.d]

There area lot of "bits" of data in a picture and this takes up bandwidth and, ultimately, it is this that you pay for. Actually text takes up very little bandwidth but they charge a relatively very high amount. But that is just an example of the difference between price and cost when weighted by what people are prepared to pay.

Voice is encoded to around 12kb/sec. Modern vocoders can do a lot better than this without much loss in fidelity - typically down to 2.4kb/s - but these are not used on a GSM network. So a 1 minute call can involve about 700kbits of data.

A typical text is probably only around 1kbit.

A photo (even on a phone) is around 3Mpixels. Each pixel is 3 colours with at least 8 bits of brightness (often more) for each colour. So 3000k x 24 bits = 72000kbits. However useing compression algorithms (like jpeg formats) reduces this to a few hundred kbits, but it is still quite high and comparable with a voice call.

[syhprum]

I am fascinated by the video snippets that are broadcast by the BBC etc from far away places such as Afghanistan that I presume have come via the Iridium satellite network.
Can you give me any technical details such as the bandwidth, type of compression or even the cost per second.