Cell Broadcasting Technical Primer

The Cell Broadcast’ Functionality, of 2nd Generation digital wireless networks specifically addresses several inherent shortcomings of standard Short Messaging Service. 

For example, the standard recognizes that as a ‘multi-cast’ feature, requiring network registration, SMS is not able to deliver identical messages to a large number of terminals in a short timeframe.  Additionally, as a true broadcast feature, Cell Broadcast, would have the unique advantage of providing geographic message and data delivery.

Sighting its obvious benefit in providing geo-targeted mass notification applications such as emergency information dissemination, Cell Broadcast is defined by GSM Standard  03.41 and 03.49.

The GSM committee, the body responsible for the development of the GSM standard, was formed under the auspices of the European Telecommunications Standards Institute (ETSI) based in Sofia Antipolis, France.

Originally proposed as a ‘Pan European Digital’ standard, it soon became a global standard, which by now is adopted all over

the world, and has become arguably the leading digital standard, at least from the point of view of deployment.

The GSM committee is run under a Memorandum of Understanding (MoU) arrangement, with network operators and governmental regulators having the greatest influence in development. Accordingly the standard is more driven by the need of network operators to offer more features to their customers, than by strictly technocratic technology for its own sake.

Notwithstanding, the standard has been highly dynamic over the years, and will in the future progress through the General Packet Radio Service (GPRS) and the Enhanced Data Rates for GSM Evolution (EDGE) developments, to provide third generation bearers into the future.

Following the set up of the WCDMA based UMTS technology, it was clear that many operators who were running second generation GSM networks, would also be offering 3rd generation UMTS networks. Clearly it was in the interests of the network owners to have a seamlessly integrated approach to the deployment of GSM and UMTS as one network. For example, a user could be switched from GSM to UMTS and vice versa in order to optimize the best abilities of both, and make the most efficient use of the bandwidth available to both.

Accordingly the 3GPP organization was formed, with a UMTS branch and a GSM branch working closely together. It is the stated position of this umbrella organization that, as far as technologically possible, each should inherit the bearer functionality of the other. This is so that a user may be handed over from one to the other without any loss of functionality.

The GSM committee is always looking to make the standard yet more flexible, in order to better meet customer expectations. One case in point was the creation of the ‘Cell Broadcast’ function, as described in standard 03.41 and 03.49. It was clear that SMS, while an important feature, had many shortcomings, which it was possible to resolve. For example that SMS is not geo specific, and that it is not an efficient way of transmitting a large number of identical messages to terminals in real time.

The GSM committee approved and implemented the Cell Broadcast function, citing as one example of its application, ‘emergency’ messages. The 3GPP group has also incorporated this feature into the UMTS system as 23.41 and 23.49.  Since the IS95 CDMA and CDMA 2000 group are now all part of the 3GPP enterprise, CDMA also has the feature (known as SMS-CB).

We believe that the Japanese PDP system has the feature, and we suspect that FOMA may also have it.

The critical change was that the cell transmits the message as a broadcast, from a logical channel reserved for this purpose. All mobiles which are in the idle state, and which have the feature switched on by the users, will check the cell broadcast barer channel. If any message bears the logical channel number corresponding to one that the terminal has enabled, then the message is picked up and either displayed, or passed to the SIM card for further processing. All of this means that;

1.         It is geo specific; you can select which cells to transmit,

2.         It uses reserved capacity, so it works during disasters where other services are prevented because of over load conditions,

3.         There is no limit to how many terminals can receive the message in 20 seconds or so, because there is no load on the mobility management system.