HB Blog 118: Cell Broadcast - The Mobile Technology For Mass Message Broadcast.

Cell Broadcast (CB) is a mobile technology that allows messages (currently of up to 15 pages of up to 93 characters) to be broadcast to all mobile handsets and similar devices within a designated geographical area. The broadcast range can be varied, from a single cell to the entire network.
This technology is used in deploying location-based subscriber services, such as regional auctions, local weather, traffic conditions and 'nearest' services (like requesting the nearest service station or restaurant).
It is designed for simultaneous delivery of messages to multiple users in a specified area. Whereas the Short Message Service (SMS) is a one-to-one and one-to-a-few service, It is one-to-many geographically focused service.
It enables messages to be communicated to multiple mobile phone customers who are located within a given part of its network coverage area at the time the message is broadcast. Cell Broadcast is more akin to other mass distribution media such as teletext or Radio Data System (RDS).
It  is a technology that allows a text or binary message to be defined and distributed to all mobile terminals connected to a set of cells. Whereas SMS messages are sent point-to-point, Cell Broadcast (SMS-CB) messages are sent point-to-area. This means that one SMS-CB message can reach a huge number of terminals at once. In other words, SMS-CB messages are directed to radio cells, rather than to a specific terminal. SMS-CB is an unconfirmed push service, meaning that the originator of the message does not know who has received the message, allowing for services based on anonymity.

A Cell Broadcast Entity (CBE) is a multi-user front-end that allows the definition and control of SMS-CB messages. A CBE can be located at the site of a content provider. At the site of the operator a so-called Cell Broadcast Centre (CBC) is located. The CBC is the heart of the Cell Broadcast System and acts as a server for all CBE clients. It takes care of the administration of all SMS-CB messages it receives from the CBEs and does the communication towards the GSM network. The GSM network itself takes care of delivering the SMS-CB messages to the mobile terminals.
Cell Broadcast can be used for a number of different services and has been de-ployed by several network operators.

Early Warning System (EWS) for citizen alert
Cell Broadcast on mobile telephones can be used for Early Warning Systems (EWS) by Governments. A few countries in the world have already adopted this technique, in addition to older and already existing forms of communication like siren, or radio and TV. The advantage of this system is that it allows sending messages without having to know the phone numbers of the users in the region. Instead of sending a message to a specific known mobile phone you can send a text to all mobile phones in a specific zone. Mass communication, very fast, in case it really matters.

Advertising
Retail outlets in certain areas would be interested in sending customers and potential customers information about special offers and attractions such as sales, special offers, extended opening times and so on. Shopping centers, exhibition halls, airports and sports stadiums are the kinds of location that could be targeted for Cell Broadcast based services.

Information Services
Cell Broadcast is ideal for delivering local or regional information which is suited to all the people in that area, rather than just one or a few people. Examples include hazard warnings, cinema programs, local weather, flight or bus delays, tourist information, parking and traffic information. Cell Broadcast can also be used for managing and communicating with a remote but local team such as emergency services or airport staff. The emergency services could send an encrypted message out to all officers or other staff in a certain area to respond to an incident. This is particularly useful for standby workers who only need to be called in and present in a certain place when certain events occur.

SMS versus Cell Broadcast: -

Short Message Service (SMS)	Characteristic	Cell Broadcast (CELL BROADCAST)
Messages sent point-to-point	Transmission type	Messages sent point-to-area
Required. Requires specific phone numbers to be known	Mobile Number dependency	Independent. Does not require phone numbers to be known
No. Only pre-registered numbers will be notified; message will be received regardless of actual location	Location based targeting	Yes. All phones within a targeted geographical area (cells) will be notified.
Static messages will be sent to pre-registered numbers.	Message type	Location specific. Tailored messages can be sent to different areas.
Direct. Users can receive messages and respond directly to the sender via SMS.	Bi-directionality	Indirect. The message should contain a URL or number to reply.
Subject to network congestion. Delivery is queued. Congestion can occur	Congestion and delay	CELL BROADCAST is always available.
140-160 characters. Longer 'concatenated' messages are supported.	Message length	93 characters. Longer 'multiple page’ messages are supported.
Poor authenticity. The source of the message cannot be verified.	Security	Good security. Only the mobile operator can broadcast messages.
No barring.	Service barring	Yes. Users can turn off CELL BROADCAST reception or a specific channel.
By default. When phone is turned on messages can be received.	Reception	Requires action. CELL BROADCAST needs to be turned on in order to receive messages.
Yes. Senders can request delivery confirmation.	Delivery confirmation	No. Confirmation of delivery to the handset is not available, however actual broadcast in the network is.
No repetition rate.	Repetition rate	Yes. Can be repeated between 2 seconds and 32 minutes.
No. Identical to all receivers.	Language selection	Yes. Messages can be broadcasted in subscriber’s preferred language
Yes.	Message storage	Handset dependant.

HB Blog 72: Inside The Cell Phone Jamming Device.

A mobile phone jammer is an instrument used to prevent cellular phones from receiving signals from base stations. When used, the jammer effectively disables cellular phones. These devices can be used in practically any location, but are found primarily in places where a phone call would be particularly disruptive because silence is expected. A jamming device transmits on the same radio frequencies as the cell phone, disrupting the communication between the phone and the cell-phone base station in the tower. It's a called a denial-of-service attack. The jammer denies service of the radio spectrum to the cell-phone users within range of the jamming device.

Cell Phone Jamming Device 
Jamming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out. Cell phones are designed to add power if they experience low-level interference, so the jammer must recognize and match the power increase from the phone. Cell phones are full-duplex devices, which means they use two separate frequencies, one for talking and one for listening simultaneously. Some jammers block only one of the frequencies used by cell phones, which has the effect of blocking both. The phone is tricked into thinking there is no service because it can receive only one of the frequencies. Less complex devices block only one group of frequencies, while sophisticated jammers can block several types of networks at once to head off dual-mode or tri-mode phones that automatically switch among different network types to find an open signal. Some of the high-end devices block all frequencies at once, and others can be tuned to specific frequencies. To jam a cell phone, all you need is a device that broadcasts on the correct frequencies. Although different cellular systems process signals differently, all cell-phone networks use radio signals that can be interrupted. GSM, used in digital cellular and PCS-based systems, operates in the 900-MHz and 1800-MHz bands in Europe and Asia and in the 1900-MHz (sometimes referred to as 1.9-GHz) band in the United States. Jammers can broadcast on any frequency and are effective against AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems. Old-fashioned analog cell phones and today's digital devices are equally susceptible to jamming. The actual range of the jammer depends on its power and the local environment, which may include hills or walls of a building that block the jamming signal. Low-powered jammers block calls in a range of about 30 feet (9 m). Higher-powered units create a cell-free zone as large as a football field. Units used by law enforcement can shut down service up to 1 mile (1.6 km) from the device.

Inside Cell Phone Jammers

 Electronically speaking, cell-phone jammers are very basic devices. The simplest just have an on/off switch and a light that indicates it's on. More complex devices have switches to activate jamming at different frequencies. Components of a jammer include:
Antenna
Every jamming device has an antenna to send the signal. Some are contained within an electrical cabinet. On stronger devices, antennas are external to provide longer range and may be tuned for individual frequencies.
Circuitry

The main electronic components of a jammer are:

• Voltage-controlled oscillator - Generates the radio signal that will interfere with the cell phone signal
• Tuning circuit - Controls the frequency at which the jammer broadcasts its signal by sending a particular voltage to the oscillator
• Noise generator - Produces random electronic output in a specified frequency range to jam the cell-phone network signal (part of the tuning circuit)
• RF amplification (gain stage) - Boosts the power of the radio frequency output to high enough levels to jam a signal
  

Power supply
Smaller jamming devices are battery operated. Some look like cell phone and use cell-phone batteries. Stronger devices can be plugged into a standard outlet or wired into a vehicle's electrical system.