01-03-2011, 04:47 PM
PRESENTED BY:
T.VENKATA MAHESH REDDY.
A.RAJESH KUMAR REDDY
[attachment=9309]
ABSTRACT
• The most modern telephone is the cellular telephone, or commonly Called a cell phone. A cellular telephone is designed to give the user maximum freedom of movement while using a telephone.
• Mobile communications is a hot topic. The number of mobile communication devices users is growing very fast. The number of mobiles (cellular phones) is now exceeding the number of fixed lines in many countries (Finland, Japan etc.).
• Cellular/mobile phones are everywhere and their utility is growing. A cell phone is a radio telephone, that may be used wherever "cell" coverage is provided. The role of cellular phones has risen with improvement in services, reduction in service costs and the ever increasing services available through cell phones.
• This paper covers the basic architecture of Cellular Communications and concentrates mainly on GSM.
What is GSM ?
• Global System for Mobile (GSM) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation
• GSM Network Architecture
• Mobile Equipment(ME)
• SIM
(SUBSCRIBER INDENTITY MODULE)
• Allows users to send and receive calls and receive other subscribed services
• It is a best database used in GSM network.
• It is a small memory devices.
• BTS
• Encodes ,encrypts, multiplexes, modulates, and feeds the RF signals to the antenna.
• Frequency Hopping.
• Communicates Mobile station and the Bsc.
• Consists of Transceiver units.
• BSC
MANAGING HANDOVERS
• Handoff occurs when the mobile network automatically transfers a call from aradio channel in one base station to another radio channel in an adjacent base station asthe subscriber crosses into the adjacent base stations cells area.
• As the subscriber approaches the cell border, the call signal drops to a minimum threshold, at which point the mobile informs the network of this fact.
• The network then must find an unused channel on the appropriate adjoining base station
and sends the mobile the details to switch to the new channel (channel number ect).
• The mobile phone then switches to the new channel, without the subscriber even noticing.
However, some problems still occur:
• When the mobile needs to handoff and the adjoining basestation is at full capacity, there
are no free channels to switch to, so the call is dropped.
• The call is sometimes lost between handoff as the adjoining base station doesn’t lock into the call before the first base station hands it off.To reduce these problems, other handoff procedures were implemented:
• Mobile Assisted Handoff (MAHO)
• Soft Handoff
• MSC (Mobile Switching Centre)
• HLR(HOME LOCATION REGISTER)
• Management of mobile subscribers.
• Permanent database about mobile subscribers in a large service area.
• Data base contain Prepaid\postpaid roaming restrictions supplementary services.
VLR(VISITOR LOCATION REGISTER)
- Temporary database which updates whenever new MS enters its area, by HLR database.
- Controls those mobiles roaming in its area .
- Reduces number of queries to HLR.
Authentication Center (AUC)
- Maintains authentication keys and algorithms and provides security triplets .
- Generally associated with HLR
- It can code the information between MS and BTS.
- Verifies the SIM cards.
Equipment Identity Register (EIR)
- Database that is used to track handsets using the IMEI (International Mobile Equipment Identity)
- Made up of three sub-classes: The White List, The Black List and the Gray List.
GSM Specifications
Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM.
•frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station).
•duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.
•channel separation—The separation between adjacent carrier frequencies. In GSM, this is 200 kHz.
•modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK).
•transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps.
•access method—GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different callsmay share the same carrier. Each call is assigned a particular time slot.
•speech coder—GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract.
• FDMA AND TDMA IN GSM
• GSM is a combination of FDMA & TDMA.The total No. of channels are 124 and each channel is 200kHz.Both 935-960MHz uplink and 890-915 downlink have allocated 25MHz for a total of 50MHz and 45 for duplex. In TDMA with in a 200kHz, 8 time slots of 4.615ms frame duration and burst duration of 0.557ms .
• FDMA
• TDMA
• FDM and TDM
• IS CDMA BETTER THAN GSM
• CDMA TECHNICAL ADVANTAGES OVER GSM:
CDMA provides increased security over the air interface than GSM.
Subscriber capacity is 5 to 6 times the GSM Capacity for the same frequency spectrum.
Call dropping is very less as CDMA uses soft handoff(GSM uses hard handoff).
CDMA provides better sound quality and reach than GSM.
CDMA PRACTICAL ADVANTAGES OVER CDMA:
CDMA provides clear voice but there is some delay associated with it.
CDMA mobility is limited and GSM mobility is unlimited.
Unlike GSM CDMA , subscriber cannot change handset without change in existing number.
Conclusions:
• The cellular & mobile beyond any doubt, has emerged as the most powerful medium effecting our lives in many way no other medium has ever. It has brought the world and its people closer than imagined before. But what makes it an indispensable part of our lives is the enormous potential that it provides for growth and success in our fields.
• Now cellular with advanced concepts like picture messages and internet access are to give a roaming net, there by increasing our knowledge, be it a fun, education or employment internet with cellular could change our lives and enhance our performance in what ever duties we have been given to handle.
T.VENKATA MAHESH REDDY.
A.RAJESH KUMAR REDDY
[attachment=9309]
ABSTRACT
• The most modern telephone is the cellular telephone, or commonly Called a cell phone. A cellular telephone is designed to give the user maximum freedom of movement while using a telephone.
• Mobile communications is a hot topic. The number of mobile communication devices users is growing very fast. The number of mobiles (cellular phones) is now exceeding the number of fixed lines in many countries (Finland, Japan etc.).
• Cellular/mobile phones are everywhere and their utility is growing. A cell phone is a radio telephone, that may be used wherever "cell" coverage is provided. The role of cellular phones has risen with improvement in services, reduction in service costs and the ever increasing services available through cell phones.
• This paper covers the basic architecture of Cellular Communications and concentrates mainly on GSM.
What is GSM ?
• Global System for Mobile (GSM) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation
• GSM Network Architecture
• Mobile Equipment(ME)
• SIM
(SUBSCRIBER INDENTITY MODULE)
• Allows users to send and receive calls and receive other subscribed services
• It is a best database used in GSM network.
• It is a small memory devices.
• BTS
• Encodes ,encrypts, multiplexes, modulates, and feeds the RF signals to the antenna.
• Frequency Hopping.
• Communicates Mobile station and the Bsc.
• Consists of Transceiver units.
• BSC
MANAGING HANDOVERS
• Handoff occurs when the mobile network automatically transfers a call from aradio channel in one base station to another radio channel in an adjacent base station asthe subscriber crosses into the adjacent base stations cells area.
• As the subscriber approaches the cell border, the call signal drops to a minimum threshold, at which point the mobile informs the network of this fact.
• The network then must find an unused channel on the appropriate adjoining base station
and sends the mobile the details to switch to the new channel (channel number ect).
• The mobile phone then switches to the new channel, without the subscriber even noticing.
However, some problems still occur:
• When the mobile needs to handoff and the adjoining basestation is at full capacity, there
are no free channels to switch to, so the call is dropped.
• The call is sometimes lost between handoff as the adjoining base station doesn’t lock into the call before the first base station hands it off.To reduce these problems, other handoff procedures were implemented:
• Mobile Assisted Handoff (MAHO)
• Soft Handoff
• MSC (Mobile Switching Centre)
• HLR(HOME LOCATION REGISTER)
• Management of mobile subscribers.
• Permanent database about mobile subscribers in a large service area.
• Data base contain Prepaid\postpaid roaming restrictions supplementary services.
VLR(VISITOR LOCATION REGISTER)
- Temporary database which updates whenever new MS enters its area, by HLR database.
- Controls those mobiles roaming in its area .
- Reduces number of queries to HLR.
Authentication Center (AUC)
- Maintains authentication keys and algorithms and provides security triplets .
- Generally associated with HLR
- It can code the information between MS and BTS.
- Verifies the SIM cards.
Equipment Identity Register (EIR)
- Database that is used to track handsets using the IMEI (International Mobile Equipment Identity)
- Made up of three sub-classes: The White List, The Black List and the Gray List.
GSM Specifications
Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM.
•frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station).
•duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.
•channel separation—The separation between adjacent carrier frequencies. In GSM, this is 200 kHz.
•modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK).
•transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps.
•access method—GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different callsmay share the same carrier. Each call is assigned a particular time slot.
•speech coder—GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract.
• FDMA AND TDMA IN GSM
• GSM is a combination of FDMA & TDMA.The total No. of channels are 124 and each channel is 200kHz.Both 935-960MHz uplink and 890-915 downlink have allocated 25MHz for a total of 50MHz and 45 for duplex. In TDMA with in a 200kHz, 8 time slots of 4.615ms frame duration and burst duration of 0.557ms .
• FDMA
• TDMA
• FDM and TDM
• IS CDMA BETTER THAN GSM
• CDMA TECHNICAL ADVANTAGES OVER GSM:
CDMA provides increased security over the air interface than GSM.
Subscriber capacity is 5 to 6 times the GSM Capacity for the same frequency spectrum.
Call dropping is very less as CDMA uses soft handoff(GSM uses hard handoff).
CDMA provides better sound quality and reach than GSM.
CDMA PRACTICAL ADVANTAGES OVER CDMA:
CDMA provides clear voice but there is some delay associated with it.
CDMA mobility is limited and GSM mobility is unlimited.
Unlike GSM CDMA , subscriber cannot change handset without change in existing number.
Conclusions:
• The cellular & mobile beyond any doubt, has emerged as the most powerful medium effecting our lives in many way no other medium has ever. It has brought the world and its people closer than imagined before. But what makes it an indispensable part of our lives is the enormous potential that it provides for growth and success in our fields.
• Now cellular with advanced concepts like picture messages and internet access are to give a roaming net, there by increasing our knowledge, be it a fun, education or employment internet with cellular could change our lives and enhance our performance in what ever duties we have been given to handle.
