GSM Time Division Multiple Access (TDMA)

Students learning Cell Site Analysis (CSA) are eventually faced with having to communicate to other non-technical people various technical aspects of the transmission technology that is the subject of the student's work. Sometimes this means finding visual ways to present a technical statement. Below are some visual suggestions that may help.



GSM mobile telephones transmit and receive information in bursts (conversation split into parts) of data, and sent over a physical channel (carrier). By spreading the conversations in *bursts and sent in allocated time slots, over the radio carrier, this is called Time Division Multiplexing.

The benefit GSM gains from using TDMA over the cellular radio network air interface means theoretically eight (8) mobile phone conversations maybe carried over a single carrier; theoretically this could also be stated as eight (8) mobile telephones sharing one carrier (a particular radio frequency.)



Simply exemplifying the benefits of TDMA is not enough and the student should also consider where multiple handsets are active in a particular radio area what impact that would have on a particular mast (BTS base transceiver station) and how the network handles that? Remember, handover may be possible but this is an effect, not the cause. A possible cause is the important factor needed to be known, at first instance.

* A brief discussion and visual about a GSM burst can be found here: 
GSM Normal Burst Power/Time Template - http://cellsiteanalysis.blogspot.co.uk/2014/06/gsm-normal-burst-powertime-template.html

GSM Normal Burst Power/Time Template

The image (below) is of the power/time template to illustrate a GSM Normal Burst (GSM05.01/05.02). A single burst when transmitted may contain up to 114-bits of useful speech data. Given the speed at which GSM radio signals traverse the ether calculated in micro-seconds to be received at a destination handset and processed by that handset in milli-seconds and converted into audible speech within one or seconds opens possibilities for examiners to demonstrate the power of mobile communications.

For instance, an attacker communicating a single 'provocative' word consisting of 80-bits in a normal burst to an accomplice could be:

D               E              T              O              N             A              T               E
01000100 01000101 01010100 01001111 01001110 01000001 01010100 01000101

The entire timing of this event may last no longer that 2 seconds. When you get time try a simple test to see how many clearly audible words you can speak within 2 seconds and what messages can be communicated in that time. Moreover, the clock for recording call records can be operated in 1000-ths of a second separated into 5 x 200-ths of a second. Whilst it is possible to see a call detail record showing a 0-second call duration and it is generally accepted there is no meaningful communication taking place, what about call that lasts 1, 2 or 3 seconds?

The knowledge tool to demonstrate the GSM Normal Burst power/time template, the power output of MS and BTS etc can be found in 3GPP TS 05.05 V8.20.00 (2005-11) Release 99.

GSM Normal Burst Power/Time Template

The image (below) is of the power/time template to illustrate a GSM Normal Burst (GSM05.01/05.02). A single burst when transmitted may contain up to 114-bits of useful speech data. Given the speed at which GSM radio signals traverse the ether calculated in micro-seconds to be received at a destination handset and processed by that handset in milli-seconds and converted into audible speech within one or seconds opens possibilities for examiners to demonstrate the power of mobile communications.

For instance, an attacker communicating a single 'provocative' word consisting of 80-bits in a normal burst to an accomplice could be:

D               E              T              O              N             A              T               E
01000100 01000101 01010100 01001111 01001110 01000001 01010100 01000101

The entire timing of this event may last no longer that 2 seconds. When you get time try a simple test to see how many clearly audible words you can speak within 2 seconds and what messages can be communicated in that time. Moreover, the clock for recording call records can be operated in 1000-ths of a second separated into 5 x 200-ths of a second. Whilst it is possible to see a call detail record showing a 0-second call duration and it is generally accepted there is no meaningful communication taking place, what about call that lasts 1, 2 or 3 seconds?

The knowledge tool to demonstrate the GSM Normal Burst power/time template, the power output of MS and BTS etc can be found in 3GPP TS 05.05 V8.20.00 (2005-11) Release 99.

D-Day 6th June

On the 6th June 2011 I wrote about D-Day at this blog. I did so because much of history was being forgotten by the younger generation. When I posted the thread below the blog received nearly 3000 hits in a few days. In 2014, we are now seeing a substantial increase, reported in the papers and on television, raising awareness about this day and other important historical dates that allow the young generation to re-connect with their heritage. It is so important to keep this knowledge flowing from generation to generation if the mistakes of the past are not to be forgotten but, worse still, to be repeated.

Today, this day, is remembrance of those men and women who fought, and so many gave their lives, to bring hope that we could enjoy our sunny days of freedom. 

This photo reminds me of how appropriate it is to use the words real heros.  


D-Day 6th June

I mentioned today's important date to a number of people. Quite a few had forgotten the date and mainly the younger generation didn't know about events that took place on this date back in 1944.

For anyone who may have missed it or might want to know more, here are some links providing the historical background.

NORMANDY LANDINGS
British Legion Remembrance d-day-65
Wikipedia Normandy Landings
Britannica DDay
Remembrance D-Day.html
Lifeformation D-Day


SCHOOL CHILDREN (CBBC)
BBC/CBBC D-Day