Mohammed Hassan, profile picture
Uploaded byMohammed Hassan
PPTX, PDF537 views

Gsm (4)

The document discusses Global System for Mobile Communication (GSM) technology. It covers various radio problems in wireless communication like fading and time dispersion. It explains how GSM solves these problems using techniques like increasing fading margin, antenna diversity, frequency hopping, and increasing carrier-to-reflection ratio. It also describes the GSM transmission process which includes speech coding, channel coding, interleaving, encryption, analog-to-digital conversion, burst formatting, and modulation for digital transmission of voice calls over the cellular network.

Embed presentation

Downloaded 56 times
GSM Global System for Mobile Communication By: Mohammed Hassan E-mail:
Radio problems & Digital Information
Chapter Objectives By the End of this Chapter you will: • Know the Fading Problem and how it is Solved • Know the Time Dispersion Problem and how it is Solved • Know the Time Delay Problem and how it is Solved • Know how the Digital information is coded Radio problems & Digital Information
The reason for shadowing is the presence of obstacles like large hills or buildings in the path between the site and the mobile. The signal strength received fluctuates around a mean value while changing the mobile position resulting in undesirable beats in the speech signal. 2. Rayleigh Fading (Multi-path Fading) The received signal is coming from different paths due to a series of reflection on many obstacles. The difference in paths leads to a difference in paths of the received components. 1. Shadowing (Normal fading): Fading Problems Radio problems & Digital Information
Fading Problems Radio problems & Digital Information
Fading Problems Solutions time Fading Margin Receiver Sensitivity db 1. Increase the fading Margin Radio problems & Digital Information
Fading Problems Solutions The cell transceiver will use two receiving antennas instead of one. They will be separated by a distance of about 5 meters, and they will receive radio signals independently, so they will be affected differently by the fading dips and the better signal received will then be selected. 3. Frequency hopping (frequency Diversity) 2. Antenna diversity (Space Diversity) 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 t F f3 f2 f1 Radio problems & Digital Information
Frame Rate = 270.8 Kb/s One BIT Duration = 3.7  sec Bit stream is moving with the velocity of light which equals 3 x 10 5 Km/sec Then, when bit 2 is transmitted, bit one will cut a distance = 3.7 x 10 -6 x 3 x 10 5 = 1.1 km 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 270.8 Kb/s Time dispersion problem 270.8 Kb/s 270.8 Kb/s Radio problems & Digital Information
Time dispersion problem There would be an interference between the a bit in the reflected ray and 1 bit later in the direct way . Radio problems & Digital Information
The C/R ratio is defined as the difference in signal strength between the signal received from the RBS and the strongest reflected signal . C/R  Relative position to the BTS Result Planner should choose the proper position of the site to make the C/R maximum everywhere in the coverage area of the site. Time dispersion problem Solution Increase the Carrier to reflection ratio Radio problems & Digital Information
If a mobile subscriber is located far from the site, then its transmitted bursts will arrive at the cell transceiver with a significant delay that may lead to overlapping with the bursts sent on the next time slot. Solution to time delay problem The site will send a “Timing Advance” value to the mobile station that is moving away, telling it to send its bursts with a certain amount of time a head of the synchronization time. The timing advance has values from 0 to 63 depending on how far the mobiles located. The size of a cell is limited by this parameter to a maximum radius of 35 Km. Time Delay problem Radio problems & Digital Information
GSM Transmission Process Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Analog to Digital Conversion Analog to digital conversion takes place in 3 steps: 1. Sampling 2. Quantization 3. Coding 1. Sampling Telecommunication systems use Sampling rate = 8 Kbit/s Radio problems & Digital Information
2. Quantization Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Analog to Digital Conversion Within common telephony, 256 levels are used while in GSM 8192 levels are used. Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Analog to Digital Conversion Coding involves converting the quantized values into binary. Every value is represented by a binary code of 13 bits (2 13 = 8192). 1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10 The output rate of the A/D Conversion process is: 8000 Samples/Sec x 13 bits/Sample = 104 Kb/s If one frequency will be used for 8 calls, then the bit rate will be 8 x 104 kb/s = 832 kb/s this will not fit in the 200 KHz channel allocated for one frequency. Coding should be used to reduce the rate. 3. Coding Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation 1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10 160 sample in 20 ms = 1 Segment 1 2 3 4 . . . . . . . . . . . . . . . 160 Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission GSM Speech Coding Instead of using 13 bits per sample as in A/D conversion, GSM speech coding uses 260 bits to encode one segment. This calculates as 260 bits / 20 ms = 13 kb/s. This provides a speech quality which is acceptable for mobile telephony and comparable with wire line PSTN phones. Many types of speech coders are available. Some offer better speech quality, at the expense of a higher bit rate (waveform coders). Others use lower bit rates, at the expense of lower speech quality (vocoders). The hybrid coder used by GSM provides good speech quality with a low bit rate, at the expense of speech coder complexity. Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Channel Coding speech coding does not consider the problems which may be encountered on the radio transmission path. The next stages in the transmission process, channel coding and interleaving, help to overcome these problems. Inputis260bitsrepresenting1segment Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Interleaving 1. First Level Interleaving 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 57Bits 8 Groups Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Interleaving 2. Second Level Interleaving 1 A T 5 D 2 A T 6 D 3 A T 7 D 4 A T 8 D 1 B T 5 A 2 B T 6 A 3 B T 7 A 4 B T 8 A 1 C T 5 B 2 C T 6 B 3 C T 7 B 4 C T 8 B 1 D T 5 C 2 D T 6 C 3 D T 7 C 4 D T 8 C 1 2 3 4 5 6 7 8 20 ms Block A 1 2 3 4 5 6 7 8 20 ms Block A 1 2 3 4 5 6 7 8 20 ms Block D 1 2 3 4 5 6 7 8 20 ms Block D 1 2 3 4 5 6 7 8 20 ms Block c 1 2 3 4 5 6 7 8 20 ms Block c 1 2 3 4 5 6 7 8 20 ms Block B 1 2 3 4 5 6 7 8 20 ms Block B Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Ciphering and Encryption The purpose of ciphering is to encode the burst so that it cannot be interpreted by any other device than the intended receiver. The ciphering algorithm in GSM is called the A5 algorithm. It does not add bits to the burst, meaning that the input and output to the ciphering process is the same as the input: 456 bits per 20 ms. Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Burst Formatting Every transmission from an MS/BTS must include some extra information such as the training sequence. The process of burst formatting is to add these bits (along with some others such as tail bits) to the basic speech/data being sent. In GSM, the input to burst formatting is the 456 bits received from ciphering. Burst formatting adds a total of 136 bits per block of 20 ms, bringing the overall total to 592. Now, the 592 bits will be sent on 4 bursts, each containing 2 x 57 bits + 136 / 4 = 148 bits. However, each time slot on a TDMA frame is 0.577 ms long. This provides enough time for 156.25 bits to be transmitted (each bit takes 3.7 us), The rest of the space, 8.25 bit times, is empty and is called the Guard Period Radio problems & Digital Information
Ramp up means to get power from the battery/power supply for transmission. Ramping down is performed after each transmission to ensure that the MS is not transmitting during time slots allocated to other MSs. The output of burst formatting is a burst of 156.25 bits or 625 bits per 20 ms. When it is considered that there are 8 subscriber per TDMA frame, the overall bit rate for GSM can be calculated to be 270.9 kbits/s. Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Burst Formatting Guard Period Tail Bits Encrypted Bits Training Sequence Encrypted Bits Tail Bits 8.253571261573 TDMA Frame 76543210 156.25 bits in 577 u Sec Radio problems & Digital Information
Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Modulation and Transmission Radio problems & Digital Information
Traffic Cases Communicate Anywhere
Chapter Objectives By the End of this Chapter you will:  Know How the Mobile Terminating call is done  Know how the PLMN Coverage area is divided ( MSC Coverage Areas & Location Areas )  Know the different types of Location Updates  Know the different types of Handover Procedures  Know How the Mobile Originating call is done  Know the different Traffic Cases a Roamer can have Traffic Cases
Why do we need to update our location data ? Actually, the location update process is invited in aim to exactly identify your location within the network so that any incoming call goes directly to the called subscriber.To fulfill this aim, one can say that we may update the system with the cell ID each time the subscriber changes his serving cell. The MSC/VLR will now know the exact cell you are roaming in. This will result in a huge amount of location update messages. An extreme is never to make a location update and to be paged in all the network. This will cause huge amount of paging messages. Do you have a compromising solution ? Location Update Traffic Cases
Location area is a part of the MSC/VLR coverage area. Each group of adjacent cells is assigned a universal unique location area identity. The mobile subscriber is only required to update the network with its new location every time it changes its Location Area. Introducing the concept of Location area enables us to make an approximate estimation of your location. Location Area Traffic Cases
LA 1 LA 2 MSC LA 3 LA4 MSC Coverage Area Traffic Cases
Location Area Identity (LAI) MCC : Mobile Country Code MNC : Mobile Network Code LAC : Location Area Code Vodafone Egypt LAI 602 MCC 02 MNC 1607 LAC Traffic Cases
Cell Global Identity (CGI) MCC : Mobile Country Code MNC : Mobile Network Code LAC : Location Area Code CID : Cell ID Vodafone Egypt CGI 602 MCC 02 MNC 1607 LAC 781 CID Traffic Cases
1. Normal Location update within same MSC/VLR service area 2. Normal Location update between 2 different MSC/VLR service areas 3. IMSI attach/detach 4. Periodic Location Update Types of Location Update Traffic Cases Location Update
Normal Location within the same MSC/VLR Service area BSC 1. The Mobile sends an allocation request message to the BTS 2. The BTS responds with the allocation message 3. The mobile sends a location update request message with its IMSI to the MSC/VLR 4 4. The MSC/VLR updates the location information and sends a Location Update confirmation message MSC/VLR Updates LA Record Traffic Cases Location Update
Old MSC/VLR New MSC/VLR NEW BSCOld BSC LA 1 LA 2 1. The mobile sends a location update request to the MSC. 2. The new MSC/VLR receives the IMSI . IMSI to MGT translation 3. The MSC/VLR sends a subscriber information request with the IMSI to the proper HLR 4. The HLR stores the address of the new MSC/VLR VLR Address = Old MSC VLR Address = New MSC 5. The HLR sends the data to the new MSC/VLR and it is kept there 6. The HLR sends a location cancellation message to the old MSC/VLR to remove the data HLR 7. The new MSC/VLR sends a location updating confirmation message to the mobile Normal Location Update between 2 different MSC/VLR service areas Traffic Cases Location Update
1. At power off, the MS asks for a signaling channel. 2. The MS uses this signaling channel to send the IMSI detach message to the MSC/VLR. 3. In the VLR, an IMSI detach flag is set for the subscriber. This is used to reject incoming calls to the MS. IMSI Detach Traffic Cases Location Update
IMSI attach is a complement to the IMSI detach procedure. It is used by the mobile subscriber to inform the network that it has re-entered an active state and is still in the same location area. If the MS changes location area while being switched off, a normal location update takes place. 1. The MS requests a signaling channel. 2. The MSC/VLR receives the IMSI attach message from the MS. 3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready for normal call handling. 4. The VLR returns an acknowledgment to the MS. MSC/VLRBSC 1 2 3 4 IMSI Attach Traffic Cases Location Update
Periodic location update is a routine task performed by the network if the MS doesn’t make any location update ( any of the previous 4 types) during a predefined period. If the MS doesn’t respond to this periodic location update, it will be marked as implicitly detached. ( Temporarily out of service ) Periodic Location Update Traffic Cases Location Update
 Handover is to keep continuity of the call when the subscriber is roaming along the network moving from one cell to another and moving between different nodes in the network.  During call, the MS is continuously measuring transmission quality of neighboring cells and reports this results to the BSC through the BTS.  The BSC, being responsible on supervising the cells, is responsible of handover initiation.  Good neighbor relations between cells is an important factor in keeping the network performance in the accepted level. Handover Traffic Cases
1. Intra BSC Handover: When the cell to which the call will be handed over belongs to the same BSC of the serving cell. 2. Inter BSC / Intra MSC Handover: When the cell to which the call will be handed over belongs to the different BSCs but to the same serving MSC. 3. Inter MSC When the cell to which the call will be handed over belongs to the different BSC and different MSC. Types of Handover Traffic Cases Handover
BSC Serving Cell New Cell 1. The BSC decides from the power measurement reports that the call must be handed over to another cell 2 2. The BSC checks for an vacant TCH in the new cell and orders this cell to activate the TCH 3 3. The BSC orders the serving cell to send a message to the MS telling the information of new TCH 4. The MS tunes to the new frequency and Sends handover access burst 4 5. The new cell detects the handover burst and sends information about the suitable timing advance to the MS 5 6. The MS sends a HO complete message to the new cell 6 7. The new cell sends a message to the BSC that the handover is successful 7 8. The BSC orders the old Cell to release the TCH 8 Intra BSC Handover Traffic Cases Handover
Inter BSC /Intra MSC Handover Traffic Cases Handover 1. The serving (old) BSC sends a Handover Required message to the MSC containing the identity of the target cell. 2. The MSC knows which BSC controls this cell and sends a Handover Request to this BSC. 3. The new BSC orders the target RBS to activate a TCH. 4. The new BSC sends a message to the MS via the MSC and the old RBS. 5. MS tunes to the new frequency and transmits handover access bursts in the correct time slot. 6. When the new RBS sends information about TA. 7. MS sends a Handover Complete message to MSC via new BSC. 8. MSC sends the old BSC an order to release the old TCH. 9. The old BSC tells the old RBS to release the TCH.
Inter MSC Handover Traffic Cases Handover 1. The serving (old) BSC sends a Handover Required message to the serving MSC (MSC–A), with the identity of the target cell. 2. MSC–A identifies that this cell belongs to another MSC, (MSC–B), and requests help. 3. MSC–B allocates a handover number to reroute the call. A Handover Request is then sent to the new BSC. 4. The new BSC orders the target RBS to activate a TCH. 5. MSC–B receives the information, and passes it on to MSC–A together with the handover number. 6. A link is set up to MSC–B, possibly via PSTN. 7. MSC–A sends a handover command to the MS, via the old BSC.
Inter MSC Handover Traffic Cases Handover 8. The MS tunes to the new frequency and transmits handover access bursts in the correct time slot 9. When the new RBS detects the handover bursts it sends information about TA. 10. The MS sends Handover Complete message to the old MSC via the new BSC and the new MSC/VLR. 11. A new path in the group switch in MSC–A is established,and the call is switched through. 12. The old TCH is deactivated by the old BSC (not shown in the picture).
1. The mobile sends a call request along with its IMSI to its serving MSC/VLR which will mark the mobile as busy. 2. Authentication is performed by the MSC to verify the mobile access to the network, and then ciphering is initiated in order to protect the mobile call on the radio path. 3. The mobile sends a call setup message to the MSC with information about the call type, services required and the dialed number. 4. MSC checks the categories of the mobile subscriber to verify that he is authorized to use the required services, and then a link is established between the MSC and BSC. 5. BSC checks the mobile serving BTS for an idle traffic channel and then orders that BTS to seize this channel for a call. 6. The BSC informs the MSC when the traffic channel assignment is complete, and then the MSC/VLR starts to analyze the dialed number and sets up a connection to the called subscriber. PSTN Mobile Originated Call BSC MSC Traffic Cases
Mobile Terminating call Traffic Cases 1. The PSTN subscriber keys in the MS’s telephone number (MSISDN). The MSISDN is analyzed in the PSTN, which identifies that this is a call to a mobile network subscriber. A connection is established to the MS’s home GMSC. 2. The GMSC analyzes the MSISDN to find out which HLR the MS is registered in, and queries the HLR for information about how to route the call to the serving MSC/VLR. 3. The HLR translates MSISDN into IMSI, and determines which MSC/VLR is currently serving the MS. The HLR also checks if the service, “Call forwarding to C–number” is activated, if so, the call is rerouted by the GMSC to that number.
Traffic Cases 7. The MSC/VLR knows which LA the MS is located in. A paging message is sent to the BSC’s controlling the LA. 8. The BSC’s distribute the paging message to the RBS's in the desired LA. The RBS’s transmit the message over the air interface using PCH. To page the MS, the network uses an IMSI or TMSI valid only in the current MSC/VLR service area. 9. When the MS detects the paging message, it sends a request on RACH for a SDCCH. 10. The BSC provides a SDCCH, using AGCH. 11. SDCCH is used for the call set-up procedures. Over SDCCH all signaling preceding a call takes place. This includes: • Marking the MS as “active” in the VLR • The authentication procedure • Start ciphering • Equipment identification 12. The MSC/VLR instructs the BSC/TRC to allocate an Mobile Terminating call

More Related Content

PPTX
Gsm (3)
byMohammed Hassan
 
PPTX
Gsm (2)
byMohammed Hassan
 
PPT
Overview Of Gsm Cellular Network & Operations
byDeepak Sharma
 
PPT
Gsm VS cdma
byGhanshyam Dusane
 
PDF
Ch1 gsm “ global system for mobile communication
byMohamed Shaaban
 
PPTX
Gsm
byTempus Telcosys
 
DOC
Wireless networks gsm cdma
byRavindranath Tagore
 
PPTX
Gsm (1)
byMohammed Hassan
 
Gsm (3)
byMohammed Hassan
 
Gsm (2)
byMohammed Hassan
 
Overview Of Gsm Cellular Network & Operations
byDeepak Sharma
 
Gsm VS cdma
byGhanshyam Dusane
 
Ch1 gsm “ global system for mobile communication
byMohamed Shaaban
 
Gsm
byTempus Telcosys
 
Wireless networks gsm cdma
byRavindranath Tagore
 
Gsm (1)
byMohammed Hassan
 

What's hot

PPT
Full gsm overview (modified)
byAdvanced group of Institutions
 
PPTX
Cdma : mobile
byAzlin lolin
 
PPT
Cdma system
bytrimba
 
PPT
CDMA 2000 Principle Issue4.0
byTempus Telcosys
 
PDF
3g cdma-qualcom
byTempus Telcosys
 
PDF
Digital cellular networks GSM
byRAVIKIRAN ANANDE
 
PPTX
GSM Network
bynareshkingster
 
PPTX
GSM Network - Distributed Service Model
byReni Sagayaraj
 
PPT
Gsm Network
byObject-Frontier Software Pvt. Ltd
 
PPT
Cdma Anjan V1
byDr Anjan Krishnamurthy
 
PPTX
IS-95 Cdma
byyogesh singh
 
PDF
03 Wireless Concept
byTempus Telcosys
 
PPT
Gsm basics
byRishi Mahajan
 
PPTX
Basic of teleom gsm
byKartik Kalpande Patil
 
PPTX
GSM Base transceiver station
byNaveen Jakhar, I.T.S
 
PPT
Lecture 8 9
byJoe Christensen
 
PPT
Is95 System Engineering
byPengpeng Song
 
PPT
My PptIntroduction to 3G, GSM, GPRS, EDGE Network
byARVIND SARDAR
 
PPT
Ai Cdma
byDeepak Sharma
 
PDF
Cdma
byAbed Sam
 
Full gsm overview (modified)
byAdvanced group of Institutions
 
Cdma : mobile
byAzlin lolin
 
Cdma system
bytrimba
 
CDMA 2000 Principle Issue4.0
byTempus Telcosys
 
3g cdma-qualcom
byTempus Telcosys
 
Digital cellular networks GSM
byRAVIKIRAN ANANDE
 
GSM Network
bynareshkingster
 
GSM Network - Distributed Service Model
byReni Sagayaraj
 
Gsm Network
byObject-Frontier Software Pvt. Ltd
 
Cdma Anjan V1
byDr Anjan Krishnamurthy
 
IS-95 Cdma
byyogesh singh
 
03 Wireless Concept
byTempus Telcosys
 
Gsm basics
byRishi Mahajan
 
Basic of teleom gsm
byKartik Kalpande Patil
 
GSM Base transceiver station
byNaveen Jakhar, I.T.S
 
Lecture 8 9
byJoe Christensen
 
Is95 System Engineering
byPengpeng Song
 
My PptIntroduction to 3G, GSM, GPRS, EDGE Network
byARVIND SARDAR
 
Ai Cdma
byDeepak Sharma
 
Cdma
byAbed Sam
 

Similar to Gsm (4)

PPT
GSM+Transmission+Process (1).ppt
bywafahop
 
PPTX
GSM lectures_1, giving details about architecture.pptx
byatul397017
 
PDF
Gsm rf interview questions
byradira03
 
PPT
GSM concepts_Slide with frame strucutre.ppt
byATULJOSHI721117
 
PPT
GSM concepts_Slide with frame structure.ppt
byATULJOSHI721117
 
PDF
GSM Air Interface
byNaveen Jakhar, I.T.S
 
PPTX
Phase Modulation , Error, Hamming Distance , GSM -Data Communication
byMd Sadequl Islam
 
PDF
Mobile network structure
byAhmed Hussien Ali Gomaa Bebars
 
PPT
Properties of radio path
byDeepak Joshi
 
DOCX
Gsm security and encryption
byjyothsnapaidi
 
PDF
Answers to questions
byOgundiran Joseph
 
PDF
Gsmrfinterviewquestions 120421043611-phpapp01
byanil parmar
 
PDF
Q nd a on rf
byashwani srivastava
 
PDF
Gsm inteview question
byNaeem Ullah
 
PPT
Lecture 7n
byJoe Christensen
 
PPTX
Ons training day 1
bymohammad ali amini
 
PDF
Access And Radio Theory
bySokunth Che
 
PDF
Gsm rf interview q&a
byGurpreet Singh
 
PDF
2g 3g blogspot RF-knowledge
byatbarawi
 
PDF
Chapter 1
byFawad Masood
 
GSM+Transmission+Process (1).ppt
bywafahop
 
GSM lectures_1, giving details about architecture.pptx
byatul397017
 
Gsm rf interview questions
byradira03
 
GSM concepts_Slide with frame strucutre.ppt
byATULJOSHI721117
 
GSM concepts_Slide with frame structure.ppt
byATULJOSHI721117
 
GSM Air Interface
byNaveen Jakhar, I.T.S
 
Phase Modulation , Error, Hamming Distance , GSM -Data Communication
byMd Sadequl Islam
 
Mobile network structure
byAhmed Hussien Ali Gomaa Bebars
 
Properties of radio path
byDeepak Joshi
 
Gsm security and encryption
byjyothsnapaidi
 
Answers to questions
byOgundiran Joseph
 
Gsmrfinterviewquestions 120421043611-phpapp01
byanil parmar
 
Q nd a on rf
byashwani srivastava
 
Gsm inteview question
byNaeem Ullah
 
Lecture 7n
byJoe Christensen
 
Ons training day 1
bymohammad ali amini
 
Access And Radio Theory
bySokunth Che
 
Gsm rf interview q&a
byGurpreet Singh
 
2g 3g blogspot RF-knowledge
byatbarawi
 
Chapter 1
byFawad Masood
 

Recently uploaded

PPT
Network model of data communication subject
byhackyourdailylife
 
PPT
01 Transistor Scaling in semiconductor applications
byPradeep Dixit
 
PPTX
Unit-1_Introduction to Microcontroller.pptx
bysidhantkulkarni1
 
PPTX
PQ CHP-2 is about passive pq problems and
bySureshEtukuriE1
 
PPTX
UNIT-1.pptx...................................
byRavinderKaur647214
 
PPT
CHAPTER 09 - Digital signatures cryptography note
bySherin Wilson
 
PPT
introduction to supply chain management.ppt
byrutujawawre
 
PDF
I am sharing 'AI in power station ' with you - Hari A K.pdf
bypugalaiml123
 
PPTX
Semiconductor diodes ppt and also characteristics
bynivishnasece
 
PPTX
PEMET 413 COMPOSITE MATERIALS MOD1 LECTURE 3.pptx
byVINAY B
 
PPTX
Lecture note on the engineering economics
byMuhammed936900
 
PPT
Lecture Note on Forming processes for MME 213 2025-2026 Academic session.ppt...
byOcheriCyril2
 
PPTX
Basics of internal combustio nengines, vapor compression cycle
byPrashantPatunkar1
 
PPTX
GROUND BASED SENSOR it in agriculture system
bycmuthupriya
 
PDF
Layer 1 Blockchain Ecosystem — Executive Brief (Jan 2026)
byGarima Singh
 
PPTX
22PEOIT4C Session 16 Backtracking CSP.pptx
byGuru Nanak Technical Institutions
 
PPT
DECISION MAKING SYSTEMS Modelling and Support
byAnu S S
 
PPT
plumbing design considerations for Federal High Court Sanitary PP.ppt
byMiku87
 
PPTX
SIMPLE HERMONIC OSCILLATORS pptx
byAnkit Bera
 
PPTX
AI-Module1..pptx module 1 Introduction to Ai
bydeekshithkumark66
 
Network model of data communication subject
byhackyourdailylife
 
01 Transistor Scaling in semiconductor applications
byPradeep Dixit
 
Unit-1_Introduction to Microcontroller.pptx
bysidhantkulkarni1
 
PQ CHP-2 is about passive pq problems and
bySureshEtukuriE1
 
UNIT-1.pptx...................................
byRavinderKaur647214
 
CHAPTER 09 - Digital signatures cryptography note
bySherin Wilson
 
introduction to supply chain management.ppt
byrutujawawre
 
I am sharing 'AI in power station ' with you - Hari A K.pdf
bypugalaiml123
 
Semiconductor diodes ppt and also characteristics
bynivishnasece
 
PEMET 413 COMPOSITE MATERIALS MOD1 LECTURE 3.pptx
byVINAY B
 
Lecture note on the engineering economics
byMuhammed936900
 
Lecture Note on Forming processes for MME 213 2025-2026 Academic session.ppt...
byOcheriCyril2
 
Basics of internal combustio nengines, vapor compression cycle
byPrashantPatunkar1
 
GROUND BASED SENSOR it in agriculture system
bycmuthupriya
 
Layer 1 Blockchain Ecosystem — Executive Brief (Jan 2026)
byGarima Singh
 
22PEOIT4C Session 16 Backtracking CSP.pptx
byGuru Nanak Technical Institutions
 
DECISION MAKING SYSTEMS Modelling and Support
byAnu S S
 
plumbing design considerations for Federal High Court Sanitary PP.ppt
byMiku87
 
SIMPLE HERMONIC OSCILLATORS pptx
byAnkit Bera
 
AI-Module1..pptx module 1 Introduction to Ai
bydeekshithkumark66
 

Gsm (4)

  • 1.
    GSM Global System forMobile Communication By: Mohammed Hassan E-mail:
  • 2.
    Radio problems &Digital Information
  • 3.
    Chapter Objectives By theEnd of this Chapter you will: • Know the Fading Problem and how it is Solved • Know the Time Dispersion Problem and how it is Solved • Know the Time Delay Problem and how it is Solved • Know how the Digital information is coded Radio problems & Digital Information
  • 4.
    The reason forshadowing is the presence of obstacles like large hills or buildings in the path between the site and the mobile. The signal strength received fluctuates around a mean value while changing the mobile position resulting in undesirable beats in the speech signal. 2. Rayleigh Fading (Multi-path Fading) The received signal is coming from different paths due to a series of reflection on many obstacles. The difference in paths leads to a difference in paths of the received components. 1. Shadowing (Normal fading): Fading Problems Radio problems & Digital Information
  • 5.
    Fading Problems Radio problems& Digital Information
  • 6.
    Fading Problems Solutions time FadingMargin Receiver Sensitivity db 1. Increase the fading Margin Radio problems & Digital Information
  • 7.
    Fading Problems Solutions Thecell transceiver will use two receiving antennas instead of one. They will be separated by a distance of about 5 meters, and they will receive radio signals independently, so they will be affected differently by the fading dips and the better signal received will then be selected. 3. Frequency hopping (frequency Diversity) 2. Antenna diversity (Space Diversity) 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 t F f3 f2 f1 Radio problems & Digital Information
  • 8.
    Frame Rate =270.8 Kb/s One BIT Duration = 3.7  sec Bit stream is moving with the velocity of light which equals 3 x 10 5 Km/sec Then, when bit 2 is transmitted, bit one will cut a distance = 3.7 x 10 -6 x 3 x 10 5 = 1.1 km 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 270.8 Kb/s Time dispersion problem 270.8 Kb/s 270.8 Kb/s Radio problems & Digital Information
  • 9.
    Time dispersion problem Therewould be an interference between the a bit in the reflected ray and 1 bit later in the direct way . Radio problems & Digital Information
  • 10.
    The C/R ratiois defined as the difference in signal strength between the signal received from the RBS and the strongest reflected signal . C/R  Relative position to the BTS Result Planner should choose the proper position of the site to make the C/R maximum everywhere in the coverage area of the site. Time dispersion problem Solution Increase the Carrier to reflection ratio Radio problems & Digital Information
  • 11.
    If a mobilesubscriber is located far from the site, then its transmitted bursts will arrive at the cell transceiver with a significant delay that may lead to overlapping with the bursts sent on the next time slot. Solution to time delay problem The site will send a “Timing Advance” value to the mobile station that is moving away, telling it to send its bursts with a certain amount of time a head of the synchronization time. The timing advance has values from 0 to 63 depending on how far the mobiles located. The size of a cell is limited by this parameter to a maximum radius of 35 Km. Time Delay problem Radio problems & Digital Information
  • 12.
    GSM Transmission Process Segmentation SpeechCoding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Radio problems & Digital Information
  • 13.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Analog to Digital Conversion Analog to digital conversion takes place in 3 steps: 1. Sampling 2. Quantization 3. Coding 1. Sampling Telecommunication systems use Sampling rate = 8 Kbit/s Radio problems & Digital Information
  • 14.
    2. Quantization Segmentation Speech Coding ChannelCoding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Analog to Digital Conversion Within common telephony, 256 levels are used while in GSM 8192 levels are used. Radio problems & Digital Information
  • 15.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Analog to Digital Conversion Coding involves converting the quantized values into binary. Every value is represented by a binary code of 13 bits (2 13 = 8192). 1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10 The output rate of the A/D Conversion process is: 8000 Samples/Sec x 13 bits/Sample = 104 Kb/s If one frequency will be used for 8 calls, then the bit rate will be 8 x 104 kb/s = 832 kb/s this will not fit in the 200 KHz channel allocated for one frequency. Coding should be used to reduce the rate. 3. Coding Radio problems & Digital Information
  • 16.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation 1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10 160 sample in 20 ms = 1 Segment 1 2 3 4 . . . . . . . . . . . . . . . 160 Radio problems & Digital Information
  • 17.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission GSM Speech Coding Instead of using 13 bits per sample as in A/D conversion, GSM speech coding uses 260 bits to encode one segment. This calculates as 260 bits / 20 ms = 13 kb/s. This provides a speech quality which is acceptable for mobile telephony and comparable with wire line PSTN phones. Many types of speech coders are available. Some offer better speech quality, at the expense of a higher bit rate (waveform coders). Others use lower bit rates, at the expense of lower speech quality (vocoders). The hybrid coder used by GSM provides good speech quality with a low bit rate, at the expense of speech coder complexity. Radio problems & Digital Information
  • 18.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Channel Coding speech coding does not consider the problems which may be encountered on the radio transmission path. The next stages in the transmission process, channel coding and interleaving, help to overcome these problems. Inputis260bitsrepresenting1segment Radio problems & Digital Information
  • 19.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Interleaving 1. First Level Interleaving 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 57Bits 8 Groups Radio problems & Digital Information
  • 20.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Interleaving 2. Second Level Interleaving 1 A T 5 D 2 A T 6 D 3 A T 7 D 4 A T 8 D 1 B T 5 A 2 B T 6 A 3 B T 7 A 4 B T 8 A 1 C T 5 B 2 C T 6 B 3 C T 7 B 4 C T 8 B 1 D T 5 C 2 D T 6 C 3 D T 7 C 4 D T 8 C 1 2 3 4 5 6 7 8 20 ms Block A 1 2 3 4 5 6 7 8 20 ms Block A 1 2 3 4 5 6 7 8 20 ms Block D 1 2 3 4 5 6 7 8 20 ms Block D 1 2 3 4 5 6 7 8 20 ms Block c 1 2 3 4 5 6 7 8 20 ms Block c 1 2 3 4 5 6 7 8 20 ms Block B 1 2 3 4 5 6 7 8 20 ms Block B Radio problems & Digital Information
  • 21.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Ciphering and Encryption The purpose of ciphering is to encode the burst so that it cannot be interpreted by any other device than the intended receiver. The ciphering algorithm in GSM is called the A5 algorithm. It does not add bits to the burst, meaning that the input and output to the ciphering process is the same as the input: 456 bits per 20 ms. Radio problems & Digital Information
  • 22.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Burst Formatting Every transmission from an MS/BTS must include some extra information such as the training sequence. The process of burst formatting is to add these bits (along with some others such as tail bits) to the basic speech/data being sent. In GSM, the input to burst formatting is the 456 bits received from ciphering. Burst formatting adds a total of 136 bits per block of 20 ms, bringing the overall total to 592. Now, the 592 bits will be sent on 4 bursts, each containing 2 x 57 bits + 136 / 4 = 148 bits. However, each time slot on a TDMA frame is 0.577 ms long. This provides enough time for 156.25 bits to be transmitted (each bit takes 3.7 us), The rest of the space, 8.25 bit times, is empty and is called the Guard Period Radio problems & Digital Information
  • 23.
    Ramp up meansto get power from the battery/power supply for transmission. Ramping down is performed after each transmission to ensure that the MS is not transmitting during time slots allocated to other MSs. The output of burst formatting is a burst of 156.25 bits or 625 bits per 20 ms. When it is considered that there are 8 subscriber per TDMA frame, the overall bit rate for GSM can be calculated to be 270.9 kbits/s. Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Burst Formatting Guard Period Tail Bits Encrypted Bits Training Sequence Encrypted Bits Tail Bits 8.253571261573 TDMA Frame 76543210 156.25 bits in 577 u Sec Radio problems & Digital Information
  • 24.
    Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/DConversion Burst Formatting Modulation and Transmission Segmentation Speech Coding Channel Coding Interleaving Ciphering/Encryption A/D Conversion Burst Formatting Modulation and Transmission Modulation and Transmission Radio problems & Digital Information
  • 25.
  • 26.
    Chapter Objectives By theEnd of this Chapter you will:  Know How the Mobile Terminating call is done  Know how the PLMN Coverage area is divided ( MSC Coverage Areas & Location Areas )  Know the different types of Location Updates  Know the different types of Handover Procedures  Know How the Mobile Originating call is done  Know the different Traffic Cases a Roamer can have Traffic Cases
  • 27.
    Why do weneed to update our location data ? Actually, the location update process is invited in aim to exactly identify your location within the network so that any incoming call goes directly to the called subscriber.To fulfill this aim, one can say that we may update the system with the cell ID each time the subscriber changes his serving cell. The MSC/VLR will now know the exact cell you are roaming in. This will result in a huge amount of location update messages. An extreme is never to make a location update and to be paged in all the network. This will cause huge amount of paging messages. Do you have a compromising solution ? Location Update Traffic Cases
  • 28.
    Location area isa part of the MSC/VLR coverage area. Each group of adjacent cells is assigned a universal unique location area identity. The mobile subscriber is only required to update the network with its new location every time it changes its Location Area. Introducing the concept of Location area enables us to make an approximate estimation of your location. Location Area Traffic Cases
  • 29.
    LA 1 LA 2 MSC LA3 LA4 MSC Coverage Area Traffic Cases
  • 30.
    Location Area Identity(LAI) MCC : Mobile Country Code MNC : Mobile Network Code LAC : Location Area Code Vodafone Egypt LAI 602 MCC 02 MNC 1607 LAC Traffic Cases
  • 31.
    Cell Global Identity(CGI) MCC : Mobile Country Code MNC : Mobile Network Code LAC : Location Area Code CID : Cell ID Vodafone Egypt CGI 602 MCC 02 MNC 1607 LAC 781 CID Traffic Cases
  • 32.
    1. Normal Locationupdate within same MSC/VLR service area 2. Normal Location update between 2 different MSC/VLR service areas 3. IMSI attach/detach 4. Periodic Location Update Types of Location Update Traffic Cases Location Update
  • 33.
    Normal Location withinthe same MSC/VLR Service area BSC 1. The Mobile sends an allocation request message to the BTS 2. The BTS responds with the allocation message 3. The mobile sends a location update request message with its IMSI to the MSC/VLR 4 4. The MSC/VLR updates the location information and sends a Location Update confirmation message MSC/VLR Updates LA Record Traffic Cases Location Update
  • 34.
    Old MSC/VLR NewMSC/VLR NEW BSCOld BSC LA 1 LA 2 1. The mobile sends a location update request to the MSC. 2. The new MSC/VLR receives the IMSI . IMSI to MGT translation 3. The MSC/VLR sends a subscriber information request with the IMSI to the proper HLR 4. The HLR stores the address of the new MSC/VLR VLR Address = Old MSC VLR Address = New MSC 5. The HLR sends the data to the new MSC/VLR and it is kept there 6. The HLR sends a location cancellation message to the old MSC/VLR to remove the data HLR 7. The new MSC/VLR sends a location updating confirmation message to the mobile Normal Location Update between 2 different MSC/VLR service areas Traffic Cases Location Update
  • 35.
    1. At poweroff, the MS asks for a signaling channel. 2. The MS uses this signaling channel to send the IMSI detach message to the MSC/VLR. 3. In the VLR, an IMSI detach flag is set for the subscriber. This is used to reject incoming calls to the MS. IMSI Detach Traffic Cases Location Update
  • 36.
    IMSI attach isa complement to the IMSI detach procedure. It is used by the mobile subscriber to inform the network that it has re-entered an active state and is still in the same location area. If the MS changes location area while being switched off, a normal location update takes place. 1. The MS requests a signaling channel. 2. The MSC/VLR receives the IMSI attach message from the MS. 3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready for normal call handling. 4. The VLR returns an acknowledgment to the MS. MSC/VLRBSC 1 2 3 4 IMSI Attach Traffic Cases Location Update
  • 37.
    Periodic location updateis a routine task performed by the network if the MS doesn’t make any location update ( any of the previous 4 types) during a predefined period. If the MS doesn’t respond to this periodic location update, it will be marked as implicitly detached. ( Temporarily out of service ) Periodic Location Update Traffic Cases Location Update
  • 38.
     Handover isto keep continuity of the call when the subscriber is roaming along the network moving from one cell to another and moving between different nodes in the network.  During call, the MS is continuously measuring transmission quality of neighboring cells and reports this results to the BSC through the BTS.  The BSC, being responsible on supervising the cells, is responsible of handover initiation.  Good neighbor relations between cells is an important factor in keeping the network performance in the accepted level. Handover Traffic Cases
  • 39.
    1. Intra BSCHandover: When the cell to which the call will be handed over belongs to the same BSC of the serving cell. 2. Inter BSC / Intra MSC Handover: When the cell to which the call will be handed over belongs to the different BSCs but to the same serving MSC. 3. Inter MSC When the cell to which the call will be handed over belongs to the different BSC and different MSC. Types of Handover Traffic Cases Handover
  • 40.
    BSC Serving Cell NewCell 1. The BSC decides from the power measurement reports that the call must be handed over to another cell 2 2. The BSC checks for an vacant TCH in the new cell and orders this cell to activate the TCH 3 3. The BSC orders the serving cell to send a message to the MS telling the information of new TCH 4. The MS tunes to the new frequency and Sends handover access burst 4 5. The new cell detects the handover burst and sends information about the suitable timing advance to the MS 5 6. The MS sends a HO complete message to the new cell 6 7. The new cell sends a message to the BSC that the handover is successful 7 8. The BSC orders the old Cell to release the TCH 8 Intra BSC Handover Traffic Cases Handover
  • 41.
    Inter BSC /IntraMSC Handover Traffic Cases Handover 1. The serving (old) BSC sends a Handover Required message to the MSC containing the identity of the target cell. 2. The MSC knows which BSC controls this cell and sends a Handover Request to this BSC. 3. The new BSC orders the target RBS to activate a TCH. 4. The new BSC sends a message to the MS via the MSC and the old RBS. 5. MS tunes to the new frequency and transmits handover access bursts in the correct time slot. 6. When the new RBS sends information about TA. 7. MS sends a Handover Complete message to MSC via new BSC. 8. MSC sends the old BSC an order to release the old TCH. 9. The old BSC tells the old RBS to release the TCH.
  • 42.
    Inter MSC Handover TrafficCases Handover 1. The serving (old) BSC sends a Handover Required message to the serving MSC (MSC–A), with the identity of the target cell. 2. MSC–A identifies that this cell belongs to another MSC, (MSC–B), and requests help. 3. MSC–B allocates a handover number to reroute the call. A Handover Request is then sent to the new BSC. 4. The new BSC orders the target RBS to activate a TCH. 5. MSC–B receives the information, and passes it on to MSC–A together with the handover number. 6. A link is set up to MSC–B, possibly via PSTN. 7. MSC–A sends a handover command to the MS, via the old BSC.
  • 43.
    Inter MSC Handover TrafficCases Handover 8. The MS tunes to the new frequency and transmits handover access bursts in the correct time slot 9. When the new RBS detects the handover bursts it sends information about TA. 10. The MS sends Handover Complete message to the old MSC via the new BSC and the new MSC/VLR. 11. A new path in the group switch in MSC–A is established,and the call is switched through. 12. The old TCH is deactivated by the old BSC (not shown in the picture).
  • 44.
    1. The mobilesends a call request along with its IMSI to its serving MSC/VLR which will mark the mobile as busy. 2. Authentication is performed by the MSC to verify the mobile access to the network, and then ciphering is initiated in order to protect the mobile call on the radio path. 3. The mobile sends a call setup message to the MSC with information about the call type, services required and the dialed number. 4. MSC checks the categories of the mobile subscriber to verify that he is authorized to use the required services, and then a link is established between the MSC and BSC. 5. BSC checks the mobile serving BTS for an idle traffic channel and then orders that BTS to seize this channel for a call. 6. The BSC informs the MSC when the traffic channel assignment is complete, and then the MSC/VLR starts to analyze the dialed number and sets up a connection to the called subscriber. PSTN Mobile Originated Call BSC MSC Traffic Cases
  • 45.
    Mobile Terminating call Traffic Cases 1.The PSTN subscriber keys in the MS’s telephone number (MSISDN). The MSISDN is analyzed in the PSTN, which identifies that this is a call to a mobile network subscriber. A connection is established to the MS’s home GMSC. 2. The GMSC analyzes the MSISDN to find out which HLR the MS is registered in, and queries the HLR for information about how to route the call to the serving MSC/VLR. 3. The HLR translates MSISDN into IMSI, and determines which MSC/VLR is currently serving the MS. The HLR also checks if the service, “Call forwarding to C–number” is activated, if so, the call is rerouted by the GMSC to that number.
  • 46.
    Traffic Cases 7. TheMSC/VLR knows which LA the MS is located in. A paging message is sent to the BSC’s controlling the LA. 8. The BSC’s distribute the paging message to the RBS's in the desired LA. The RBS’s transmit the message over the air interface using PCH. To page the MS, the network uses an IMSI or TMSI valid only in the current MSC/VLR service area. 9. When the MS detects the paging message, it sends a request on RACH for a SDCCH. 10. The BSC provides a SDCCH, using AGCH. 11. SDCCH is used for the call set-up procedures. Over SDCCH all signaling preceding a call takes place. This includes: • Marking the MS as “active” in the VLR • The authentication procedure • Start ciphering • Equipment identification 12. The MSC/VLR instructs the BSC/TRC to allocate an Mobile Terminating call