05-09-2012, 05:13 PM
Wireless Communications
1G,2G,3G.ppt (Size: 524.5 KB / Downloads: 29)
Circuit and Packet Switching
Circuit-switched
A physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Ordinary voice phone service is circuit-switched. The phone company reserves a specific physical path to the number being called for the duration of the call. During that time, no one else can use the physical lines involved.
Packet-switched
Small units of data called packets are routed through a network based on the destination address contained within each packet. The same data path can be used by many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching. The Internet is basically a connectionless network.
CDMA and TDMA
CDMA (Code-Division Multiple Access) a digital cellular technology that uses spread-spectrum techniques. Unlike systems that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence.
TDMA (Time Division Multiple Access) a technology for delivering digital wireless service using time division multiplexing. TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels. TDMA is used by the GSM digital cellular system.
Making a Call
Scan Control Channels: Your cell phone needs to use the "closest" base station because that's the one with the strongest signal and the one that will give the best connection. To find the closest base station, your phone checks all control channels and determines which has the strongest signal.
Choose Strongest: Your cell phone chooses the strongest signal and decides to use that one for placing the call.
Send Origination Message: Your cell phone now transmits a very short message (about 1/4 second) that contains the MIN (Mobile Identification Number, aka your cell phone number), its ESN (Electronic Serial Number), and the number you just dialed.
Get Channel Assignment: After the cellular service provider verifies that you are a valid, paying customer (based on the MIN and ESN your phone sent), the base station sends a Channel Assignment message to your phone (also a short 1/4-second burst). This message tells your phone where (that is, on which channel) the conversation will take place.
Begin Conversation
Roaming
A wireless roaming network has five components that make it work:
A database for storing customer profile information such as features, dialing capabilities, and the home serving area identification. This is called the home location register (HLR).
A database of mobile numbers used by each switch on the network.
A signaling network for transmitting data messages between switches.
Routing specifications that direct the data messages to the appropriate destination.
Public long-distance connections for call delivery
Hand-over
During a call, the base station would monitor the signal level from the mobile phone. When the mobile phone is moving into a new cell, the signal level will fall to a critical value causing the base station to inform the Mobile Switching Center(MSC) about this event. The MSC would instruct all the surrounding base stations to measure the mobile phone's signal level and transfer control to the base station receiving the strongest signal level. This is known as hand-over and occurs within 400ms, so the phone user is hardly aware of a break.
Registration is done again with the new base station. Location information stored in the MSC about this mobile telephone is updated. If the mobile telephone is moved into a cell belonging to a different cluster it would also have to register with the new MSC.
1G (Analog)
AMPS (Advanced Mobile Phone System) is the analog cellular phone system used in North and South America. AMPS uses FDMA and operates at 800 MHz band. AMPS was introduced in the USA in 1983.
TACS (Total Access Communication System) was developed in Britain using the 900 MHz band. TACS was based on the AMPS system and was adopted in other countries such as Hong Kong and Japan.
ETACS (Extended Total Access Communication System) was developed in the UK and is available in Europe and Asia.
1G,2G,3G.ppt (Size: 524.5 KB / Downloads: 29)
Circuit and Packet Switching
Circuit-switched
A physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Ordinary voice phone service is circuit-switched. The phone company reserves a specific physical path to the number being called for the duration of the call. During that time, no one else can use the physical lines involved.
Packet-switched
Small units of data called packets are routed through a network based on the destination address contained within each packet. The same data path can be used by many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching. The Internet is basically a connectionless network.
CDMA and TDMA
CDMA (Code-Division Multiple Access) a digital cellular technology that uses spread-spectrum techniques. Unlike systems that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence.
TDMA (Time Division Multiple Access) a technology for delivering digital wireless service using time division multiplexing. TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels. TDMA is used by the GSM digital cellular system.
Making a Call
Scan Control Channels: Your cell phone needs to use the "closest" base station because that's the one with the strongest signal and the one that will give the best connection. To find the closest base station, your phone checks all control channels and determines which has the strongest signal.
Choose Strongest: Your cell phone chooses the strongest signal and decides to use that one for placing the call.
Send Origination Message: Your cell phone now transmits a very short message (about 1/4 second) that contains the MIN (Mobile Identification Number, aka your cell phone number), its ESN (Electronic Serial Number), and the number you just dialed.
Get Channel Assignment: After the cellular service provider verifies that you are a valid, paying customer (based on the MIN and ESN your phone sent), the base station sends a Channel Assignment message to your phone (also a short 1/4-second burst). This message tells your phone where (that is, on which channel) the conversation will take place.
Begin Conversation
Roaming
A wireless roaming network has five components that make it work:
A database for storing customer profile information such as features, dialing capabilities, and the home serving area identification. This is called the home location register (HLR).
A database of mobile numbers used by each switch on the network.
A signaling network for transmitting data messages between switches.
Routing specifications that direct the data messages to the appropriate destination.
Public long-distance connections for call delivery
Hand-over
During a call, the base station would monitor the signal level from the mobile phone. When the mobile phone is moving into a new cell, the signal level will fall to a critical value causing the base station to inform the Mobile Switching Center(MSC) about this event. The MSC would instruct all the surrounding base stations to measure the mobile phone's signal level and transfer control to the base station receiving the strongest signal level. This is known as hand-over and occurs within 400ms, so the phone user is hardly aware of a break.
Registration is done again with the new base station. Location information stored in the MSC about this mobile telephone is updated. If the mobile telephone is moved into a cell belonging to a different cluster it would also have to register with the new MSC.
1G (Analog)
AMPS (Advanced Mobile Phone System) is the analog cellular phone system used in North and South America. AMPS uses FDMA and operates at 800 MHz band. AMPS was introduced in the USA in 1983.
TACS (Total Access Communication System) was developed in Britain using the 900 MHz band. TACS was based on the AMPS system and was adopted in other countries such as Hong Kong and Japan.
ETACS (Extended Total Access Communication System) was developed in the UK and is available in Europe and Asia.