CS718 Solved Mid Term Exam Papers By Muhammad Sadaqat Ali

QoS Profile for GPRS Bearers
Ø  4 Parameters
o   Service precedence
§  3 Classes
o   Reliability parameter
§  3 Classes
o   Delay parameters
§  4 Classes
o   Through parameter
§  Maximum and mean bit rates
Ø  QoS profile is included in Packet Data Protocol (PDP) context
Ø  Negotiation managed through PDP procedures (activation, modification and deactivation)

HSCSD: (High Speed Circuit Switched Data)
Ø  Works in circuit switch mode.
Ø  Speed increased by allowing single user to use consecutive time slots in GSM standard
Ø  Relaxes error control coding algorithms specified in GSM increasing data rate from 9.600 to 14.400 Kbps
Ø  By using 4 slots, raw data rate of up to 57.6 kbps to individual user.
Ø  Ideal for dedicated streaming or real-time interactive web sessions.

EDGE: (Enhanced Data rates for GSM Evolution) (2.75 G)
Ø  More advanced upgrade to 2G that requires addition of new hardware and software
Ø  Developed as a path to become eventual 3G high speed data access
Ø  New  modulation 8-PSK in addition to GSM standard GMSK.
Ø  Allows nine different formats known as Multiple modulation and Coding Scheme(MCS)
Ø  Each state may either use GMSK (low rate) or 8-PSK (high rate).
Ø  family of MCS for each GSM slot and users can adaptively determine best MCS setting
Ø  User start first with max error protection and max data  rate until the link has unacceptable outage or delay
Ø  By combining different channels (multi-carrier trans), EDGE provides upto several megabits per second data throughput.

IS-95 Reverse Link:
Ø  Consists of upto 94 logical channels each occupying same bandwidth of 1228 KHz.
Ø  It supports 32 access channels and 62 traffic channels
Ø  Access channel is used to initiate a call, to respond to paging channel and for location update.
Ø  In reverse, convolutional encoder has a rate of 1/3, thus tripling the effective rate to a max of 28.8 kbps
Near –far Problem:
Ø  Signals closer to the receiver are received with less attenuation than signals farther away
Identifiers in the GSM Network:
Ø  GSM uses several identifiers for
o   The routing of calls
o   Identifying subscribers (e.g. for charging)
o   Locating the HLR, identifying equipment, etc.
Ø  International Mobile Subscriber Identity (IMSI)
o   It is embedded on the SIM card and is used to identify a subscriber.
Ø  International Mobile Equipment identifier
o   IMEI is used to identify the ME
Ø  Mobile Station Roaming Number
o   MSRN is used in the GSM network for routing a call to a MS.
Ø  Mobile Station Integrated Services Digital Network Number (MSISDN Number)
o   The MSISDN is used to identify the subscriber when, among other things, establishing a call to that subscriber or sending an SMS to that subscriber.



Absolute bandwidth:
Ø  Width of the spectrum of a signal
Effective bandwidth:
Ø  Narrow band of frequencies that most of the signal’s energy is contained in

Logical Channels:
Ø  Mapped by the MAC to physical channels
Ø  Control channels for control, synchronization and signaling
o   Common
o   Broadcast
o   Dedicated
Ø  Packet Traffic channels
o   Encoded speech
o   Encoded data
Reservation ALOHA:
Ø  Adv:
o   Higher throughput under heavy loads
o   Max throughput upto 80% of channel capacity
Ø  Dis-Adv:
o   More demanding on users as they have to obtain / keep ‘reservation list’ up-to-date.


BCH Codes:
Ø  BCH à Discoverer: Bose, Chaudhuri and Hocquenghem
Ø  Multiple error correcting codes
Ø  Generalization of Hamming Code
Ø  Flexibility in choice of parameters
o   Block length, code rate
Ø  Working:
o   For positive pair of integers m and t,
§  a(n, k)
o   BCH code has parameters
§  Block length: n= 2m-1
§  Number of check bits: n-k <=mt
§  Minimum distance: dmin>=2t+1
o   Correct combinations of t or fewer errors
o   The generator polynomial can be constructed from the factors of (X2m-1+1)
Call Routing in GSM:
A/Gb mode:
Ø  Class A: MS can operate simultaneous packet switched and circuit switched services
Ø  Class B: MS can operate either one at one time
o   Most common for handsets today
Ø  Classs C: MS can operate only packet switched services
o   E.g. expansion cards for laptops
               
Cell Splitting: -
Ø  Achieve ‘capacity improvement’ by decreasing R and keeping D/R (cell reuse ratio) unchanged
Ø  Divide the congested cells into smaller cells
o   Smaller cells are called micro cells
Ø  If radius of cell is cut to half, approximately four cells would be required
o   Increased number of cells would increase the number of clusters, which in turn increase the capacity
Ø  Allows a system to grow by replacing larger cells with smaller cells without upsetting the allocation scheme
Sectoring:
Ø  Keep cell radius unchanged and decrease D/R
Ø  Increases SIR so that cluster size may be reduced
o   SIR is improved using directional antennas
o   Hence increasing frequency reuse without changing transmission power
Ø  Cell is partitioned into 3 120o sectors or 6 60o sectors
Cluster:
Ø  N cells, which collectively use the complete set of available frequencies
Ø  If a cluster is replicated M times in the system, the number of duplex channels C as a measure of capacity is C= MkN= MS
Ø  So capacity is directly proportional to the replication factor in a fixed area.
Ø  Clusters are inversely proportion to N

o   Capacity is directly proportional to  ClustersQoS Profile for GPRS Bearers
Ø  4 Parameters
o   Service precedence
§  3 Classes
o   Reliability parameter
§  3 Classes
o   Delay parameters
§  4 Classes
o   Through parameter
§  Maximum and mean bit rates
Ø  QoS profile is included in Packet Data Protocol (PDP) context
Ø  Negotiation managed through PDP procedures (activation, modification and deactivation)

HSCSD: (High Speed Circuit Switched Data)
Ø  Works in circuit switch mode.
Ø  Speed increased by allowing single user to use consecutive time slots in GSM standard
Ø  Relaxes error control coding algorithms specified in GSM increasing data rate from 9.600 to 14.400 Kbps
Ø  By using 4 slots, raw data rate of up to 57.6 kbps to individual user.
Ø  Ideal for dedicated streaming or real-time interactive web sessions.

EDGE: (Enhanced Data rates for GSM Evolution) (2.75 G)
Ø  More advanced upgrade to 2G that requires addition of new hardware and software
Ø  Developed as a path to become eventual 3G high speed data access
Ø  New  modulation 8-PSK in addition to GSM standard GMSK.
Ø  Allows nine different formats known as Multiple modulation and Coding Scheme(MCS)
Ø  Each state may either use GMSK (low rate) or 8-PSK (high rate).
Ø  family of MCS for each GSM slot and users can adaptively determine best MCS setting
Ø  User start first with max error protection and max data  rate until the link has unacceptable outage or delay
Ø  By combining different channels (multi-carrier trans), EDGE provides upto several megabits per second data throughput.

IS-95 Reverse Link:
Ø  Consists of upto 94 logical channels each occupying same bandwidth of 1228 KHz.
Ø  It supports 32 access channels and 62 traffic channels
Ø  Access channel is used to initiate a call, to respond to paging channel and for location update.
Ø  In reverse, convolutional encoder has a rate of 1/3, thus tripling the effective rate to a max of 28.8 kbps
Near –far Problem:
Ø  Signals closer to the receiver are received with less attenuation than signals farther away
Identifiers in the GSM Network:
Ø  GSM uses several identifiers for
o   The routing of calls
o   Identifying subscribers (e.g. for charging)
o   Locating the HLR, identifying equipment, etc.
Ø  International Mobile Subscriber Identity (IMSI)
o   It is embedded on the SIM card and is used to identify a subscriber.
Ø  International Mobile Equipment identifier
o   IMEI is used to identify the ME
Ø  Mobile Station Roaming Number
o   MSRN is used in the GSM network for routing a call to a MS.
Ø  Mobile Station Integrated Services Digital Network Number (MSISDN Number)
o   The MSISDN is used to identify the subscriber when, among other things, establishing a call to that subscriber or sending an SMS to that subscriber.



Absolute bandwidth:
Ø  Width of the spectrum of a signal
Effective bandwidth:
Ø  Narrow band of frequencies that most of the signal’s energy is contained in

Logical Channels:
Ø  Mapped by the MAC to physical channels
Ø  Control channels for control, synchronization and signaling
o   Common
o   Broadcast
o   Dedicated
Ø  Packet Traffic channels
o   Encoded speech
o   Encoded data
Reservation ALOHA:
Ø  Adv:
o   Higher throughput under heavy loads
o   Max throughput upto 80% of channel capacity
Ø  Dis-Adv:
o   More demanding on users as they have to obtain / keep ‘reservation list’ up-to-date.


BCH Codes:
Ø  BCH à Discoverer: Bose, Chaudhuri and Hocquenghem
Ø  Multiple error correcting codes
Ø  Generalization of Hamming Code
Ø  Flexibility in choice of parameters
o   Block length, code rate
Ø  Working:
o   For positive pair of integers m and t,
§  a(n, k)
o   BCH code has parameters
§  Block length: n= 2m-1
§  Number of check bits: n-k <=mt
§  Minimum distance: dmin>=2t+1
o   Correct combinations of t or fewer errors
o   The generator polynomial can be constructed from the factors of (X2m-1+1)
Call Routing in GSM:
A/Gb mode:
Ø  Class A: MS can operate simultaneous packet switched and circuit switched services
Ø  Class B: MS can operate either one at one time
o   Most common for handsets today
Ø  Classs C: MS can operate only packet switched services
o   E.g. expansion cards for laptops
               
Cell Splitting: -
Ø  Achieve ‘capacity improvement’ by decreasing R and keeping D/R (cell reuse ratio) unchanged
Ø  Divide the congested cells into smaller cells
o   Smaller cells are called micro cells
Ø  If radius of cell is cut to half, approximately four cells would be required
o   Increased number of cells would increase the number of clusters, which in turn increase the capacity
Ø  Allows a system to grow by replacing larger cells with smaller cells without upsetting the allocation scheme
Sectoring:
Ø  Keep cell radius unchanged and decrease D/R
Ø  Increases SIR so that cluster size may be reduced
o   SIR is improved using directional antennas
o   Hence increasing frequency reuse without changing transmission power
Ø  Cell is partitioned into 3 120o sectors or 6 60o sectors
Cluster:
Ø  N cells, which collectively use the complete set of available frequencies
Ø  If a cluster is replicated M times in the system, the number of duplex channels C as a measure of capacity is C= MkN= MS
Ø  So capacity is directly proportional to the replication factor in a fixed area.
Ø  Clusters are inversely proportion to N
o   Capacity is directly proportional to  Clusters

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