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GSM TRAINING Presentation Transcript
1.GSM INTRODUCTION
2. The global system for mobile communications (GSM) is a set of recommendations and specifications for a digital cellular telephone network (known as a Public Land Mobile Network, or PLMN). These recommendations ensure the compatibility of equipment from different GSM manufacturers, and interconnectivity between different administrations, including operations across international boundaries.
3.THE GSM NETWORK
4.THE GSM NETWORK - CONTINUED
5.DIGITAL NETWORKSGSM networks are digital and can cater for high system capacities. They are consistent with the world wide digitization of the telephone network, and are an extension of the Integrated Services Digital Network (ISDN), using a digital radio interface between the cellular network and the mobile subscriber equipment.
6.INCREASED CAPACITY
7.CGI : CELL GLOBAL IDENTITY
8.MSISDN
9.MSISDN
10.IMSI
11.IMEI
12.SUBSCRIBER IDENTIFICATION
13.SUBSCRIBER IDENTIFICATION MODULE (SIM)
14.EQUIPMENT IDENTITY NUMBER
15.Frequency Bands
16.GSM Network Architecture
17.MS – Mobile Station
18.MS
19.Mobile Station Output Power
20.Mobile Station Identities
21.IMSI (International Mobile Subscriber Identity)
22.IMEI (International Mobile Equipment Identity)
23.SIM ( Subscriber Identity Module)
24.Contents of SIM 25.SIM Security
26.BTS (Base Transceiver Station)
27.BTS
28.BSC – Base Station Controller
29.BSC
30.TRAU – Transcoder Rate Adaptation Unit
31.The MSC is based on ISDN switching. The Fixed Network is also ISDN based. ISDN has speech rate of 64 kbps. Mobile communicates at 13 kbps. TRAU converts the data rates between 13kbps GSM rate to 64kbps Standard ISDN rate TRAU can be collocated with the BTS, BSC or MSC or it can be a separate unit.
32.Location of Transcoder
33.MSC – Mobile Switching Centre
34.Exchange where calls are established, maintained and released Database for all subscribers and their associated features. Communicates with the BSCs on the A interface and with PSTN on fixed line. MSC is weighted on the number of subscribers it can support. E.g. an MSC of 1 lac subscribers means one MSC is enough till subscriber base increases upto 1 lac, beyond which another MSC is required.
35.Multiple MSCs
36.HLR – Home Location Register
37.VLR – Visiting Location Register
38.VLR 39.AUC – Authentication Centre
40.EIR (Equipment Identity Register)
41.Classification of IMEIs
42.Billing Centre (BC)
43.Billing Centre (BC)
44.OMC – Operations and Maintenance Centre
45.Also called the NOC (Network Operations centre) It is the central monitoring and remote maintenance centre for all network elements OMC has links to BSCs and MSCs
46.OMC
47.GSM Channels
48.Physical Channel One time slot on one carrier is called physical channel. Logical Channel Information carried by physical channels is called logical Channels. Logical channels are mapped on physical channels.
49.Logical Channels
50.Traffic Channels(TCH)
51.Control Channels(CCH)
52.BCH(Broadcast Channels)
53.BCH(Broadcast Channels)
54.FCCH(Frequency Correction Channels) Downlink Only. Enable MS to synchronies to the frequency.
55.CCCH(Common Control Channel)
56.AGCH(Assess Grant Channel) Downlink only. Used for acknowledgement of the access attempt sent on RACH. Used by the network to assign a signaling cannel upon successful decoding of access bursts.
57.PCH(Paging Channel) Downlink only. The network will page the MS ,if there is a incoming call or a short Message. It contains the MS identity number, the IMSI or TMSI.
58.SDCCH (Stand-alone Dedicated Control Channel) Uplink and Downlink. Used for call setup, authentication, ciphering location update and SMS.
59.SACCH(Slow Associated Control Channel) Downlink and Uplink. Used to transfer signal while MS have ongoing conversation on traffic or while SDCCH is being used. On the forward link, the SACCH is used to send slow but regularly changing control information to each mobile on that ARFCN, such as power control instructions and specific timing advance instructions
60.SACCH(Slow Associated Control Channel) cont’d The reverse SACCH carries information about the received signal strength and quality of the TCH, as well as BCH measurement results from neighboring cells.
61.FACCH(Fast Associated Control Channel) Downlink and uplink. Associate with TCH only. It is used to send fast message like hand over message. Work by stealing traffic bursts.
62.The Logical channels are mapped on the physical channels. The TDMA frames are grouped together into multi-frame. 26 TDMA multi-frame for Traffic. 51 TDMA multi-frame for control signal.
63.Combined All the controlling signals are in the time slot 0 of the Multi-frame. Non Combined Dedicated controlling signals are in time slot 1 of the Multi-frame.
64.Cell with single carrier. Timeslot 0 :BCCH+CCCH+SDCCH. Timeslot 1-7 :TCH/FACCH+SACCH.
65.Cell with Two carrier Timeslot 0 (of carrier 1) BCCH+CCCH. Timeslot 1 (of carrier1) SDCCH+SACCH. Timeslot 2-7 & 0-7(of both carriers) TCH/FACCH+SACCH.
66.SYSTEM INFORMATION
67.SYSTEM INFORMATION 1
68.SYTEM INFORMATION 1
69.RACH Control Parameters Access Control Class(ACC) :-Bitmap with 16 bits. All MS spread out on class 0 –9 . Priority groups use class 11-15. A bit set to 1 barred access for that class. Bit 10 is used to tell the MS if emergency call is allowed or not. 0 – All MS can make emergency call. 1 - MS with class 11-15 only can make emergency calls. Cell barred for access(CB):- 0- Yes 1- No
70.RACH Control Parameters
71.System Information Type 2 message consists of the Double BA list which defines the BCCH frequencies used in the neighboring cells. The Double BA list provides the MS with different frequencies on which to measure, depending on whether the MS is in idle or active mode. In active mode, the MS should measure on a reduced number of frequencies in order to improve the accuracy of measurements.
72.In Idle mode,the MS should measure on larger number of frequencies, so that the time required for the MS to access the network after power on is reduced. The MS is also informed which PLMN’s it may use. As well as System Information Type 2,it is also possible to have System Information Type 2 Bis and System information Type 2 Ater, depending on the size of the BA List. System Information Type 2 Bis/Ter are optional.
73.Neighbor Cell Description:- BA Indicator(BA IND):- Allows to differentiate measurement results related to different list of BCCH frequencies sent to MS. BCCH Allocation number(BANO):- Band 0 is used. PLMN Permitted(NCCPERM):-This the PLMN color codes permitted and tells the MS which network color codes(NCC) on the BCCH carriers it is allowed to monitor when it is in this cell.
74.RACH Control Parameters
75.SYSTEM INFORMATION 2
76.BCCH ARFCN Number(BAIND):- ARFCN’s used for in a Bitmap of 124 bits
77.The System Information Type 3 contains information on the identity of the current LA and cell identity, because a change means that the MS must update the network. System Information 3 also as Control Channel Description parameters used to calculate the Paging group. When the MS is in idle mode it decides which cells to lock to. Information needed by the MS for cell selection is also broadcast in the Type 3 information.
78.SYSTEM INFORMATION 3
79.Control Channel Description
80.SYSTEM INFORMATION 3
81.Cell options
82.Cell Selection Parameters
83.Location Area Identification.
84.RACH Control Parameters
85.CBCH Description(Optional) :
86.Hopping Channel(H):-Informs if CBCH Channel is hopping or single.
87.Sent on the SACCH on the downlink to the MS in dedicated mode.
88.Neighbor Cell Description:-
89.BCCH ARFCN:-Neighboring cells ARFCN’s. Sent as a bitmap. 0-Not used 1-Used.
90.Ms in dedicated mode needs to know if the LA has changed.If so, it must perform location updating when the call is released.
91.Cell options:
92.System Information Types 7 and 8 contain Cell Reselect parameters. Their function is to supplement System Information Type 4.
93.GSM Interfaces
94.The interfaces between MSC and MS is called A, Abis and Um interfaces. On these interfaces only three layers are defined.They are not corresponding to the OSI (Open System Interconnection) model.
95.A Interface A interface between the BSC and the MSC The A interface provides two distinct types of information, signalling and traffic, between the MSC and the BSC. The speech is transcoded in the TRC and the SS7 (Signalling system) signalling is transparently connected through the TRC or on a separate link to the BSC.
96.Abis Interface
97.(Um) Air Interface 98.This interface is the radio interface between the mobile station and the network and uses layer Three messages. On Layer three messages we have the division of message types into CM (communication Management), MM (Mobility Management), and RR (Radio Resource Management).
99.Connection Management
100.Mobility Management
101.Radio Resource Management
102.B Interface
103.C Interface
104.D Interface
105.E Interface
106.F Interface
107.G Interface
108.Encoding and Interleaving of Information Signal in GSM
109.Topics for discussion
110.Speech Encoding
111.Speech Encoding ckt
112.Speech Encoding ckt
113.Voice Encoding ckt
114.Channel coding
115.Channel Coding for speech
116.Channel coding for Speech
117.Class 1b - 132 bits are not parity checked but are fed into the convolutional coder along with 4 tail bits which are used to set the registers in the receiver to a known state for decoding purpose. Class 2- 78 bits, these are not so important and are not protected but are combined with the output of the convolution coder.
118.Control Channel Coding
119.The control information is received in blocks of 184 bits. These bits are first protected with a cyclic code called as Fire code, which is useful in correction and detection of burst errors. 40 Parity bits are added, along with 4 tail bits. These 228 bits are given to the CC whose output is again 456 bits at a bitrate of 22.8Kbps. The control channels include the RACH, PCH, AGCH etc.
120.Data Channel Coding
121.The data bits are received in blocks of 240 bits. These are directly convolution coded after adding 4 tail bits. The output of the CC is now 488 bits, which actually increases the bitrate to 24.4 Kbps. To keep the bitrate constant on the air interface we need to puncture the output of the CC. Hence, we have a final bitrate of 22.8 Kbps again .
122.The above explanation was given keeping in view a full rate Traffic, Control, or Data channel. For Half rate or Lesser rates the same principle of channel coding holds good, with slight differences in the encoding process.
123.Interleaving
124.The following interleaving depths are used : Speech – 8 blocks Control – 4 blocks Data – 22 blocks The interleaving process for a speech block is shown wherein which a 456 bit speech block is divided into 8 blocks of 57 bits each and each of these odd and even 57 bit blocks are interleaved diagonally on to alternate bursts on the TDMA frame.
125.Speech Interleaving
126.Control Data Interleaving
127.Data Interleaving
128.Here the data block of 456 bits is divided into 4 blocks of 114 bits each. The first 6 bits from each of the 114 bit blocks is inserted in to each frame, the second 6 bits from each of the 114 bits into the next frame and so on spreading each 114 block over 19 TDMA bursts while the entire 456 bits is spread over 22 TDMA bursts. Thus the data interleaving is said to have a depth of 22 bursts.
129.The reason why data is spread over such along period of time is that if data burst is corrupted or lost, only a small part of it is lost which can be reproduced at the receiver. This wide interleaving depth does produce a time delay during transmission but that is acceptable since it does not affect the data signal quality at the receiver, unlike speech where delay could result in bad quality of signal to the subscriber. *Note – The interleaving used in data is diagonal interleaving.
130.Interleaving Advantage
131.Air Interface Bitrate
132.The Kc is the ciphering key and A5 algorithm are applied to the information(speech or data) which increases the bitrate to a final rate of 33.8 Kbps from/to each mobile. If we assume all 8 timeslots of the cell to be occupied then the bitrate of the Air interface comes to 33.8 * 8= 270.4 Kbps/channel.
133.Air Interface Bitrate cont’d
134.Air Interface Bitrate
135.Decoding and Deinterleaving at the Receiver
136.Channelization
137.Channelization methods
138.FDMA
139.TDMA
140.CDMA
141.Duplex Access Methods
142.Time Division Duplex
143.GSM Air Interface
144.GSM Air interface
145.The GSM Burst
146.Speech Coder
147.Error Correction
148.Diagonal Interleaving
149.Convolutional Coding and Interleaving
150.Speech Coding Process
151.TRAU frame
152.Midamble or Training Bits
153.Downlink and Uplink
154.Measurements made by MS and BTS
155.Mobile Power Control
156.Timing Advance
157.Concepts of Channels in GSM
158.Frames and Multiframes
159.GSM Operations
160.Mobile Turn On
161.Location Area
162.Location Area Identity
163.Importance of Location Area
164.What is Location Update?
165.Types of Location Updates
166.IMSI Attach
167.Normal Location Update
168.Periodic Location Update
169.What happens at Location Update?
170.MSC starts Authentication If successful, Updates the new Location area for the Mobile in the VLR Sends a confirmation to the Mobile Mobile leaves SDCCH, and comes to idle mode
171.Mobile Originated Call
172.Mobile Terminated Call
173.Security Features
174.Security Features (TMSI Reallocation)
175.Security Features (Identity Check)
176.Handover
177.Criteria for Handover
178.Handover Decision
179.Handover Decision
180.Types of Handovers
181.INTRA-CELL HANDOVER
182.Inter-cell Handover
183.Inter-cell Handover
184.INTRA-BSC Handover
185.Inter BSC Handover
186.Inter MSC Handover
187.Cell Barring
188.Every mobile has an access class The access class is stored in the SIM Classes 0-9 are termed normal calsses Classes 11-15 are emergency classes 188.What is DTX?
189.VAD (Voice Activity Detector)
190.Evaluation of Background Noise
191.Emergency Calls
192.Cell (Re)selection
193.The following parameters are used to calculate the C1 criterion
194.C1 = A - Max(B,0)
195.Cell Reselect Hysteresis
196.Cellular concept
197.Why to use the cellular concept ?
198.A portion of the total channels available is allocated to each base station. Neighboring base stations are assigned different groups channels, in order to minimize interference.
199.Cell shape
200.1-Omni-directional cell-site (Omni-directional antenna). 2-Rhombus-shaped sectors (Directive antenna). 3-Hexagonal shaped sectors (Directive antenna).
201.Cell size
202.Types of cells
203.What is a cluster ?
204.Cluster size
205.Types of clusters
206.Channel assignment strategies
207.2) Dynamic : Channels are not allocated to different cells permanently. Each new call BTS requests new channel from MSC. MSC allocate a channel, by using an algorithm that takes into account: 1- Frequency is not already in use. 2- Min. reuse distance to avoid co-channel interference.
208.Adv. of dynamic assignment strategy : 1) Increase channel utilization ( Increase trunking efficiency ). 2) Decrease probability of a blocked call.
209.Frequency reuse Concept
210.Reuse cluster
211.Co-channel Reuse ratio (Q) :
212.Handover
213.Definition : procedure that allows MS to change the cell or time-slot to keep as good link as possible during all the call.
214.Types of handover
215.Measurements before handover
216.Basic handover algorithms
217.Handover priority
218.Interference
219.Sources of interference include:
220.Interference effects
221.Main types of interference :
222.Co-channel interference
223.Another form : C/I = 10 log {(1/n)(D/R)*m} Where : m = propagation constant (dep’s on nature of environment) n = number of co-channel interferers. Can be minimized by : Choosing minimum reuse distance = (2.5….3)(2R).
224.Adjacent channel interference
225.General rule
226.Traffic engineering theory
227.Why do we need to know traffic?
228.Traffic intensity (E)
229.Typical traffic profile
230.Traffic tables
231.Erlang – B table
232.Trunking
233.Trunking efficiency in presence of one operator :
234.System capacity
235.total duplex channels available for use = k*N
236.Improving system capacity
237.Cell splitting
238.Sectoring
239.What does sectoring mean?
240.Directional frequency reuse
241.Comparison between various types of clusters
242.N = 7 omni frequency plan :
243.N = 7 trapezoidal frequency plan
244.Trunking efficiency : 312 one direction voice channels N = 7 ? 312 / 7 = 44.57 ~ 44 ch./cell. From Erlang-B table @ GOS = 2% T = 35 E. nT = 35 / 44 = 79.55 %.
245.N = 9 omni frequency plan
246.Trunking efficiency :
247.4 / 12 cell pattern
248.3 / 9 cell pattern
249.120 degree cell sectoring
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