3. Physical channel - Each timeslot on a carrier is referred to as a physical
channel. Per carrier there are 8 physical channels.
Logical channel - Variety of information is transmitted between the MS and
BTS. There are different logical channels depending on the information
sent. The logical channels are of two types
• Traffic channel
• Control channel
Downlink
Uplink
CHANNELS
5. GSM Control Channels
BCH ( Broadcast channels )
Downlink only
Control Channels
DCCH(Dedicated Channels)
Downlink & Uplink
CCCH(Common Control Chan)
Downlink & Uplink
Synch.
Channels
RACH
Random
Access Channel
CBCH
Cell Broadcast
Channel
SDCCH
Standalone
dedicated
control channel
ACCH
Associated
Control Channels
SACCH
Slow associated
Control Channel
FACCH
Fast Associated
Control Channel
PCH/
AGCH
Paging/Access grant
FCCH
Frequency
Correction channel
SCH
Synchronisation
channel
BCCH
Broadcast
control channel
6. BCH Channels
BCCH( Broadcast Control Channel )
• Downlink only
• Broadcasts general information of the serving cell called System
Information
• BCCH is transmitted on timeslot zero of BCCH carrier
• Read only by idle mobile at least once every 30 secs.
SCH( Synchronisation Channel )
• Downlink only
• Carries information for frame synchronisation. Contains TDMA
frame number and BSIC.
FCCH( Frequency Correction Channel )
• Downlink only.
• Enables MS to synchronise to the frequency.
• Also helps mobiles of the ncells to locate TS 0 of BCCH carrier.
7. CCCH Channels
RACH( Random Access Channel )
• Uplink only
• Used by the MS to access the Network.
AGCH( Access Grant Channel )
• Downlink only
• Used by the network to assign a signalling channel upon
successfull decoding of access bursts.
PCH( Paging Channel )
• Downlink only.
• Used by the Network to contact the MS.
8. DCCH Channels
SDCCH( Standalone Dedicated Control Channel )
• Uplink and Downlink
• Used for call setup, location update and SMS.
SACCH( Slow Associated Control Channel )
• Used on Uplink and Downlink only in dedicated mode.
• Uplink SACCH messages - Measurement reports.
• Downlink SACCH messages - control info.
FACCH( Fast Associated Control Channel )
• Uplink and Downlink.
• Associated with TCH only.
• Is used to send fast messages like handover messages.
• Works by stealing traffic bursts.
15. Mobile originated call
MS
Channel Request (RACH)
BSS MSC
SDCCH Seizure
Immediate Assignment [ Reject ] (AGCH)
CM Service Request + Connection Request < CMSREQ >
Connection [ Confirmed / Refused ]
Link Establishment
Authentication Request
Authentication Response
DT1 <CICMD>
Ciphering Mode Command
Ciphering Mode Complete
DT1 <CICMP>
Identity Request
Identity Response
Setup
Call Proceeding
Connection Management
Assignment Request
Assignment Request [ Failed ]
Assignment Command
Assignment [ Complete / Failure ]
Assignment [ Complete / Failure ]
TCH Seizure
S
D
C
C
H
T
C
H
16. MS BSS MSC
Paging
SDCCH Seizure
Link Establishment
Paging Request (PCH)
UDT < PAGIN >
Paging
Channel Request (RACH)
Immediate Assignment [ Reject ] (AGCH)
Paging Response + Connection Request < PAGRES >
Connection [ Confirmed / Refused ]
Authentication Request
Authentication Response
S
D
C
C
H
Ciphering Mode Command
Ciphering Mode Complete
DT1 <CICMD>
DT1 <CICMP>
Identity Request
Identity Response
Setup
Call Confirmed
Connection Management
Assignment Request
Assignment Request [ Failed ]
Assignment Command
Assignment [ Complete / Failure ]
T
C
H TCH Seizure
Assignment [ Complete / Failure ]
Mobile terminated call
17. PROPAGATION MECHANISMS
Reflection
• Occurs when a wave impinges upon a smooth surface.
• Dimensions of the surface are large relative to .
• Reflections occur from the surface of the earth & from buildings & walls.
Diffraction (Shadowing)
• Occurs when the path is blocked by an object with large dimensions
relative to and sharp irregularities (edges).
• Secondary “wavelets” propagate into the shadowed region.
• Diffraction gives rise to bending of waves around the obstacle.
Scattering
• Occurs when a wave impinges upon an object with dimensions on the
order of or less, causing the reflected energy to spread out or“scatter”
in many directions.
18. Multipath
• Multiple Waves Create “Multipath”
• Due to propagation mechanisms, multiple waves arrive at the
receiver
• Sometimes this includes a direct Line-of-Sight
(LOS) signal
19. Multipath Propagation
• Multipath propagation causes large and rapid fluctuations in a signal
• These fluctuations are not the same as the propagation path loss.
Multipath causes three major things
• Rapid changes in signal strength over a short distance or time.
• Random frequency modulation due to Doppler Shifts on different
multipath signals.
• Time dispersion caused by multipath delays
• These are called “fading effects
• Multipath propagation results in small-scale fading.
20. Fading
• The communication between the base station and mobile station in
mobile systems is mostly non-LOS.
• The LOS path between the transmitter and the receiver is affected by
terrain and obstructed by buildings and other objects.
• The mobile station is also moving in different directions at different
speeds.
• The RF signal from the transmitter is scattered by reflection and
diffraction and reaches the receiver through many non-LOS paths.
• This non-LOS path causes long-term and short term fluctuations in
the form of log-normal fading and rayleigh and rician fading, which
degrades the performance of the RF channel.
22. Long Term Fading
• Terrain configuration & man made environment causes long-term
fading.
• Due to various shadowing and terrain effects the signal level
measured on a circle around base station shows some random
fluctuations around the mean value of received signal strength.
• The long-term fades in signal strength, r, caused by the terrain
configuration and man made environments form a log-normal
distribution, i.e the mean received signal strength, r, varies log-
normally in dB if the signal strength is measured over a distance of
at least 40.
• Experimentally it has been determined that the standard deviation, ,
of the mean received signal strength, r, lies between 8 to 12 dB with
the higher generally found in large urban areas.
23. Rayleigh Fading
• This phenomenon is due to multipath propagation of the signal.
• The Rayleigh fading is applicable to obstructed propagation paths.
• All the signals are NLOS signals and there is no dominant direct path.
• Signals from all paths have comparable signal strengths.
• The instantaneous received power seen by a moving antenna becomes
a random variable depending on the location of the antenna.
24. Ricean Fading
• This phenomenon is due to multipath propagation of the signal.
• In this case there is a partially scattered field.
• One dominant signal.
• Others are weaker.
26. Antennas
• Antennas form a essential part of any radio communication system.
• Antenna is that part of a transmitting or receiving system which is
designed to radiate or to receive electromagnetic waves.
• An antenna can also be viewed as a transitional structure between
free-space and a transmission line (such as a coaxial line).
• An important property of an antenna is the ability to focus and shape
the radiated power in space e.g.: it enhances the power in some
wanted directions and suppresses the power in other directions.
• Many different types and mechanical forms of antennas exist.
• Each type is specifically designed for special purposes.
27. Antenna Types
• In mobile communications two main categories of antennas used are
– Omni directional antenna
• These antennas are mostly used in rural areas.
• In all horizontal direction these antennas radiate with
equal power.
• In the vertical plane these antennas radiate uniformly
across all azimuth angles and have a main beam with
upper and lower side lobes.
28. – Directional antenna
• These antennas are mostly used in mobile cellular systems to
get higher gain compared to omnidirectional antenna and to
minimise interference effects in the network.
• In the vertical plane these antennas radiate uniformly across all
azimuth angles and have a main beam with upper and lower
side lobes.
• In these type of antennas, the radiation is directed at a specific
angle instead of uniformly across all azimuth angles in case of
omni antennas.
29. Radiation Pattern
• The main characteristics of antenna is the radiation pattern.
• The antenna pattern is a graphical representation in three dimensions of
the radiation of the antenna as a function of angular direction.
• Antenna radiation performance is usually measured and recorded in two
orthogonal principal planes (E-Plane and H-plane or vertical and
horizontal planes).
• The pattern of most base station antennas contains a main lobe and
several minor lobes, termed side lobes.
• A side lobe occurring in space in the direction opposite to the main lobe is
called back lobe.
31. Antenna Gain
• Antenna gain is a measure for antennas efficiency.
• Gain is the ratio of the maximum radiation in a given direction to that of a
reference antenna for equal input power.
• Generally the reference antenna is a isotropic antenna.
• Gain is measured generally in “decibels above isotropic(dBi)” or “decibels
above a dipole(dBd).
• An isotropic radiator is an ideal antenna which radiates power with unit
gain uniformly in all directions. dBi = dBd + 2.15
• Antenna gain depends on the mechanical size, the effective aperature
area, the frequency band and the antenna configuration.
• Antennas for GSM1800 can achieve some 5 to 6 dB more gain than
antennas for GSM900 while maintaining the same mechanical size.
33. Front-to-back ratio
• It is the ratio of the maximum directivity of an antenna to its directivity in a
specified rearward direction.
• Generally antenna with a high front-to-back ratio should be used.
First Null Beamwidth
• The first null beamwidth (FNBW) is the angular span between the first
pattern nulls adjacent to the main lobe.
• This term describes the angular coverage of the downtilted cells.
34. Antenna Lobes
• Main lobe is the radiation lobe containing the direction of maximum
radiation.
• Side lobes
Half-power beamwidth
• The half power beamwidth (HPBW) is the angle between the points on
the main lobe that are 3dB lower in gain compared to the maximum.
• Narrow angles mean good focusing of radiated power.
Polarisation
• Polarisation is the propagation of the electric field vector .
• Antennas used in cellular communications are usually vertically polarised
or cross polarised.
35. Frequency bandwidth
• It is the range of frequencies within which the performance of the
antenna, with respect to some characteristics, conforms to a specified
standard.
• VSWR of an antenna is the main bandwidth limiting factor.
Antenna impedance
• Maximum power coupling into the antennas can be achieved when the
antenna impedance matches the cables impedance.
• Typical value is 50 ohms.
Mechanical size
• Mechanical size is related to achievable antenna gain.
• Large antennas provide higher gains but also need care in deployment
and apply high torque to the antenna mast.
36. • Antenna radiation pattern will become superimposed when the distance
between the antennas becomes too small.
• This means the other antenna will mutually influence the individual
antenna patterns.
• Generally 5 to 10 horizontal separation provides sufficient decoupling of
antenna patterns.
• The vertical distance needed for decoupling is usually much smaller as
the vertical beamwidth is generally less.
• A 1 separation in the vertical direction is sufficient in most cases.
37. • Antenna installation configurations depend on the operators preferences.
• It is important to keep sufficient decoupling distances between antennas.
• If TX and RX direction use separated antennas, it is advisable to keep a
horizontal separation between the antennas in order to reduce the TX
signal power at the RX input stages.
38. Antenna downtilt introduction
• Network planners often have the problem that the base station antenna
provides an overcoverage.
• If the overlapping area between two cells is too large, increased switching
between the base station (handover) occurs.
• There may even be interference of a neighbouring cell with the same
frequency.
• If hopping is used in the network, then limiting the overlap is required to
reduce the overall hit rate.
• In general, the vertical pattern of an antenna radiates the main energy
towards the horizon.
• Only that part of the energy which is radiated below the horizon can be
used for the coverage of the sector.
• Downtilting the antenna limits the range by reducing the field strength in
the horizon.
39. Antenna downtilting
• Antenna downtilting is the downward tilt of the vertical pattern towards the
ground by a fixed angle measured w.r.t the horizon.
• Downtilting of the antenna changes the position of the half-power
beamwidth and the first null relative to the horizon.
• Normally the maximum gain is at 0• (parallel to the horizon) and never
intersects the horizon.
• A small downtilt places the beams maximum at the cell edge
• With appropriate downtilt, the received signal strength within the cell
improves due to the placement of the main lobe within the cell radius and
falls off in regions approaching the cell boundary and towards the reuse
cell.
• There are two methods of downtilting
– Mechanical downtilting
– Electrical downtilting.
40. Mechanical Downtilt
• Mechanical downtilting consists of physically rotating an antenna
downward about an axis from its vertical position.
• In a mechanical downtilt as the front lobe moves downward the back lobe
moves upwards.
• This is one of the potential drawback as compared to the electrical
downtilt because coverage behind the antenna can be negatively affected
as the back lobe rises above the horizon.
• Additionally , mechanical downtilt does not change the gain of the
antenna at +/- 90deg from antenna horizon.
• As the antenna is given downtilt, the footprint starts changing with a notch
being formed in the fron’t while it spreads on the sides.
• After 10 degrees downtilt the notch effect is quiet visible and the spread
on the sides are high. This may lead to inteference on the sides.
43. Vertical antenna pattern at 0
Vertical antenna pattern at 15 downtilt
Backlobe shoots over the horizon
Mechanical Downtilt
44. Electrical downtilt
• Electrical downtilt uses a phase taper in the antenna array to angle the
pattern downwards.
• This allows the the antenna to be mounted vertically.
• Electrical downtilt is the only practical way to achieve pattern
downtilting with omnidirectional antennas.
• Electrical downtilt affects both front and back lobes.
• If the front lobe is downtilted the back lobe is also downtilted by equal
amount.
• Electrical downtilting also reduces the gain equally at all angles on the
horizon. The that adjusted downtilt angle is constant over the whole
azimuth range.
• Variable electrical downtilt antennas are very costly.
47. Obstacle requirement
• Nearby obstacles are those reflecting or shadowing materials that can
obstruct the radio beam both in horizontal and vertical planes.
• When mounting the antenna on a roof top, the dominating obstacle in
the vertical plane is the roof edge itself and in the horizontal plane,
obstacles further away like surrounding buildings, can act as reflecting
or shadowing material.
• The antenna beam will be distorted if the antenna is too close to the
roof. Hence the antenna must be mounted at a minimum height above
the rooftop or other obstacles.
• If antennas are wall mounted, a safety margin of 15 degrees between
the reflecting surface and the 3-dB lobe should be kept.
49. Optimal Downtilt
• Although the use of downtilt can be a effective tool for controlling
interference, there is a optimum amount by which the antenna can be
downtilted whereby both the coverage losses and the interference at
the reuse cell can be kept at a minimum.
downtilt angle (D)
3 dB Beamwidth
Main lobe
Height (H)
Cellmax
50. • The figure shows a cells coverage area.
• The primary illumination area is the area on the ground that receives the
signal contained within the 3dB vertical beamwidth of the antenna.
• The distance from the base station to the outer limit of the illumination
area is denoted by Cellmax.
• It should be noted that the cellmax can be different from the cell
boundary area which is customer defined.
• Ideally in a well planned network Cellmax should always be less than
the co-channel reuse distance to minimise interference.
• We now derive the relation between height (H), downtilt angle (D), 3dB
vertical beamwidth and Cellmax.
• As shown in the schematic is the angle between the upper limit of the
3dB beamwidth and the horizon.
Optimal Downtilt
51. • tan ( ) = Cellmax / H
= D - 0.5 * 3dB vertical beamwidth
Cellmax = H * tan (D - 0.5 * 3dB vertical beamwidth)
• For the Cellmax to be a positive quantity , downtilt angle must be more
than half of the 3dB vertical beamwidth.
• When the downtilt angle is less than half of the 3dB beamwidth, part of
the signal from the main beam shoots over the horizon .
• The signal directed towards or above the horizon can potentially cause
interference at the reuse sites.
Optimal Downtilt
53. WHAT IS INTERFERNCE ?
• Interference is the sum of all signal contributions that are neither noise
not the wanted signal.
54. EFFECTS OF INTERFERNCE
• Interference is a major limiting factor in the performance of cellular
systems.
• It causes degradation of signal quality.
• It introduces bit errors in the received signal.
• Bit errors are partly recoverable by means of channel coding and error
correction mechanisms.
• The interference situation is not reciprocal in the uplink and downlink
direction.
• Mobile stations and base stations are exposed to different interference
situation.
55. SOURCES OF INTERFERNCE
• Another mobile in the same cell.
• A call in progress in the neighboring cell.
• Other base stations operating on the same frequency.
• Any non-cellular system which leaks energy into the cellular frequency
band.
56. TYPES OF INTERFERNCE
• There are two types of system generated interference
– Co-channel interference
– Adjacent channel interference
Co-Channel Interference
• This type of interference is the due to frequency reuse , i.e. several
cells use the same set of frequency.
• These cells are called co-channel cells.
• Co-channel interference cannot be combated by increasing the power
of the transmitter. This is because an increase in carrier transmit power
increases the interference to neighboring co-channel cells.
• To reduce co-channel interference, co-channel cells must be physically
separated by a minimum distance to provide sufficient isolation due to
propagation or reduce the footprint of the cell.
57. Co-Channel Interference
• Some factors other then reuse distance that influence co-channel
interference are antenna type, directionality, height, site position etc,
• GSM specifies C/I > 9dB.
Carrier f1 Interferer f1
dB
Distance
C
I
58. Co-Channel Interference
• In a cellular system, when the size of each cell is approximately the
same, co-channel interference is independent of the transmitted power
and becomes a function of cell radius(R) and the distance to the centre
of the nearest co-channel cell (D).
C1
C2
C3
C1
C2
C3
D
59. Co-Channel Interference
• Q = D / R = 3N
• By increasing the ratio of D/R, the spatial seperation between the co-
channel cells relative to the coverage distance of a cell is increased. In
this way interference is reduced from improved isolation of RF energy
from the co-channel cell.
• The parameter Q , called the co-channel reuse ratio, is related to the
cluster size.
• A small value of Q provides larger capacity since the cluster size N is
small whereas a large value of Q improves the transmission quality.
60. Adjacent-Channel Interference
• Interference resulting from signals which are adjacent in frequency to
the desired signal is called adjacent channel interference.
• Adjacent channel interference results from imperfect receiver filters
which allow nearby frequencies to leak into the passband.
• Adjacent channel interference can be minimized through careful
filtering and channel assignments.
• By keeping the frequency separation between each channel in a given
cell as large as possible , the adjacent interference may be reduced
considerably.
62. POWER CONTROL
• RF power control is employed to minimise the transmit power required
by MS or BS while maintaining the quality of the radio links.
• By minimising the transmit power levels, interference to co-channel
users is reduced.
• Power control is implemented in the MS as well as the BSS.
• Power control on the Uplink also helps to increase the battery life.
• Power received by the MS is continously sent in the measurement
report.
• Similarly uplink power received from the MS by the BTS is measured
by the BTS.
• Complex algorithm evaluate this measurements and take a decision
subsequently reducing or increasing the power in the Uplink or the
downlink.
63. SECTORIZATION
• For 120 degrees sectored site as compared to an omni site almost
1/3rd interference is received in the uplink.
• The more selective and directional is the antenna, the smaller is the
interference.
• Reduction in interference results in higher capacity in both links.
66. NEED OF DIVERSITY
• In a typical cellular radio environment, the communication between the
cell site and mobile is not by a direct radio path but via many paths.
• The direct path between the transmitter and the receiver is obstructed
by buildings and other objects.
• Hence the signal that arrives at the receiver is either by reflection from
the flat sides of buildings or by diffraction around man made or natural
obstructions.
• When various incoming radiowaves arrive at the receiver antenna,
they combine constructively or destructively, which leads to a rapid
variation in signal strength.
• The signal fluctuations are known as ‘multipath fading’.
67. Multipath Propagation
• Multipath propagation causes large and rapid fluctuations in a signal
• These fluctuations are not the same as the propagation path loss.
Multipath causes three major things
• Rapid changes in signal strength over a short distance or time.
• Random frequency modulation due to Doppler Shifts on different
multipath signals.
• Time dispersion caused by multipath delays
• These are called “fading effects
• Multipath propagation results in small-scale fading.
68. DIVERSITY TECHNIQUE
• Diversity techniques have been recognised as an effective means
which enhances the immunity of the communication system to the
multipath fading. GSM therefore extensively adopts diversity
techniques that include
Diversity techniques
Interleaving
In time domain
Frequency Hopping
In Frequency domain
Spatial diversity
In spatial domain
Polarisation diversity
In polarisation domain
69. CONCEPT OF DIVERSITY ANTENNA SYSTEMS
• Spatial and polarisation diversity techniques are realised through
antenna systems.
• A diversity antenna system provides a number of receiving branches
or ports from which the diversified signals are derived and fed to a
receiver. The receiver then combines the incoming signals from the
branches to produce a combined signal with improved quality in
terms of signal strength or signal-to-noise ratio (S/N).
• The performance of a diversity antenna system primarily relies on
the branch correlation and signal level difference between branches.
71. SPATIAL DIVERSITY ANTENNA SYSTEMS
• The spatial diversity antenna system is constructed by physically
separating two receiving base station antennas.
• Once they are separated far enough, both antennas receive
independent fading signals. As a result, the signals captured by the
antennas are most likely uncorrelated.
• The further apart are the antennas, the more likely that the signals
are uncorrelated.
• The types of the configuration used in GSM networks are:
horizontal separation
vertical separation
75. POLARISATION DIVERSITY ANTENNA SYSTEMS
• A single (say vertical) polarised electromagnetic wave is converted to
a wave with two orthogonal polarised fields while it is propagating
through scattering environment.
• It has also been found that the two fields exhibit some extent of
decorrelation.
76. DUAL POLARISED ANTENNAS
• A dual-polarisation antenna consists of two sets of radiating elements
which radiate or, in reciprocal, receive two orthogonal polarised
fields.
• The antenna has two input connectors which separately connects to
each set of the elements.
• The antenna has therefore the ability to simultaneously transmit and
receive two orthogonally polarised fields.
H / V Slant 45
77. ADVANTAGES OF DUAL POLARISED ANTENNAS
• The best advantage of using the dual polarisation antenna is the
reduction in the number of antennas per sector.
• Reduced size of the headframe of the supporting structure
• Reduced windload and weight.
• Reduced difficulty in site acquisition and installation.
• Cost saving
– Requiring slim tower
– Requiring less installation time.
– Cost of one dual polarisation antenna is generally lower than that
of two
– Single polarised antennas
78. DUAL POLARISED ANTENNA CONFIGURATIONS
DUAL
POLE
ANTENNA
T R
TX RX RX
DUAL
POLE
ANTENNA
SINGLE
POLE
ANTENNA
RX RX
TX
DUAL
POLE
ANTENNA
T T
R R
TX RX TX RX
80. BROADCAST MESSAGES
• System information is data about the network which the MS
needs to be able to communicate with the network in a
appropriate manner.
• System information messages are sent on the BCCH and
SACCH.
• There are six different types of system information messages.
• System information messages 1 to 4 are broadcast on the BCCH
and are read by the MS in idle mode.
• System information message 5 and 6 are sent on the SACCH to
the MS in dedicated mode.
• System information messages 1 to 4 are broadcast on the BCCH
in a cyclic mode over 8 BCCH multiframes, i.e. 8 * 51 frames.
• Every message is sent at least after every 1.8 sec.
81. What is sent is optional on BCCH Multiframe 4 and 5
• System information 5 and 6 are sent on the SACCH immediately
after HO or whenever nothing else is being sent.
• Downlink SACCH is used for system information messages while
Uplink SACCH is used for measurement reports.
BROADCAST MESSAGES
System
Information
BCCH
Multiframe
1 0
2 1
3 2 and 6
4 3 and 7
82. SYSTEM INFORMATION 1
When frequency hopping is used in cell MS needs to know which
frequency band to use and what frequency within the band it should
use in hopping algorithm.
Cell Channel Description
Cell allocation number :- Informs the band number of the
frequency channels used.
00 - Band 0 ( Current GSM band )
Cell allocation ARFCN :- ARFCN’s used for hopping. It is coded
in a bitmap of 124 bits.
124 123 122 121
016 015 014 013 012 011 010 009
008 007 006 005 004 003 002 001
83. SYSTEM INFORMATION 1
RACH Control Parameters
Access Control Class :- Bitmap with 16 bits. All MS spread out on
class 0 - 9. Priority groups use class 11-15. A bit set to 1 barres
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 :-
0 - Yes
1 - No
84. RACH Control Parameters
Re-establishment allowed :-
0 – Yes
1 - No
max_retransmissions :- Number of times the MS attempts to
access the Network [ 1,2,4 or 7 ].
tx_integer :- Number of slots to spread access retransmissions
when a MS attempts to access the system.
Emergency Call Allowed :- Yes / No
SYSTEM INFORMATION 1
85. • Contains list of BCCH frequencies used in neighbor cells.
• MS uses this list to measures the signal strength of the neighbors.
Neighbor Cell Description
BA Indicator :- Allows to differentiate measurement results related
to different list of BCCH frequencies sent to the MS.
BCCH Allocation number :- Band 0 is used.
BCCH ARFCN number :- Bitmap 1 -124
1 = Set
0 = Not set
PLMN permitted
RACH Control Parameters
SYSTEM INFORMATION 2
86. SYSTEM INFORMATION 3
Location Area Identity
Cell Identity
8 7 6 5 4 3 2 1
Octet A
1 1 1 1 Octet B BCD
Octet C
Octet D
Octet E
MCC DIG 1
MCC DIG 2
MCC DIG 3
MNC DIG 1
MNC DIG 2
LAC
LAC
Binary
8 7 6 5 4 3 2 1
Octet F
Octet G
CI
CI
Binary
87. SYSTEM INFORMATION 3
Control Channel Description
Attach / Detach
0 = Allowed
1 = Not allowed
cch_conf :- Defines multiframe struture
bs_agblk :- Number of block reserved for AGCH [ 0-7 ].
Ba_pmfrms :- Number of 51 frame multiframes between
transmisiion of paging messages to MS of the same group.
T3212 :- Periodic location update timer [ 1-255 deci hours].
cch_conf Physical Channels Combined No of CCH
0 1 timeslot (0) NO 9
1 1 timeslot (0) YES 3
2 2 timeslots (0, 2) NO 18
4 3 timeslots (0, 2, 4) NO 27
6 4 timeslots (0, 2, 4, 6) NO 36
88. SYSTEM INFORMATION 3
Cell Options
dtx
pwrc :- Power control on the downlink.
0 = Not used
1 = Used
Radio link timeout :- Sets the timer T100 in the MS.
Cell Selection Parameters
Rxlev_access_min :- Minimum received signal level at the MS for
which it is permitted to access the system.
0-63 = -110 dBm to -47dBm
mx_txpwr_cch :- Maximum power the MS will use when accessing
the system.
Cell_reselect_hysteresis :- Used for cell reselection.
RACH Control Parameters
89. SYSTEM INFORMATION 4
Location Area Identification
Cell Selection Parameters
Rxlev_access_min
mx_txpwr_cch
Cell_reselect_hysteresis
RACH Control Parameters
max_retransmissions
tx_integer
Cell barred for access
Re-establishment allowed
Emergency Call Allowed
Access Control Class
90. SYSTEM INFORMATION 4
Channel Description
Channel type :- Indi. channel type SDCCH or CBCH( SDCCH/8).
Subchannel number :- Indicates the subchannel.
Timeslot number :- Indicates the timeslot for CBCH [0 - 7].
Training Sequence Code :- The BCC part of BSIC[0 - 7 ].
Hopping Channel(H) :- Informs if CBCH channel is hopping or
single. 0 - Single RF Channel 1 - RF hopping channel
ARFCN :- If H = 0
MAIO :- If H = 1 , informs the MS where to start hopping. Values [0
- 63].
HSN :- If H = 1 , informs the MS in what order in what order the
hopping should take place. Values [ 0 - 63]. HSN = 0 Cyclic
Hopping.
MA :- Indicates which RF Channels are used for hopping. ARFCN
numbers coded in bitmap.
91. SYSTEM INFORMATION 5
Sent on the SACCH on the downlink to the MS in dedicated mode.
Neighbour Cell Description
BA-IND :- Used by the Network to discriminate measurements
results related to different lists of BCCH carriers sent by the MS(
Type 2 or 5).
Values 0 or 1 ( different from type 2).
BCCH Allocation number :- 00 - Band 0 (Current GSM band).
BCCH ARFCN :- Neighboring cells ARFCN’s. Sent as a bitmap.
0 = ARFCN not used
1 = ARFCN used
124 123 122 121
016 015 014 013 012 011 010 009
008 007 006 005 004 003 002 001
92. SYSTEM INFORMATION 6
• MS in dedicated mode needs to know if the LA has changed.
• MS may change between cells with different Radio link timeout
and DTX.
Cell Identity
Location Area Identification
Cell Options
dtx
pwrc
Radio link timeout
PLMN permitted
93. PAGING
• Whenever the Network wants to contact the MS, it sends
messages on the paging channel.
• Paging is sent on the PCH and it occupies 4 bursts.
• MS has to monitor the paging channel to receive paging
messages.
• MS does not monitor all paging channel but only specific paging
channels.
• There are three types of paging messages
Paging
Type
No of MS
using IMSI
No of MS
using TMSI
Total no of
MS
1 2 - 2
2 1 2 3
3 - 4 4
94. CALCULATION OF PAGING GROUP
Following factors are used for calculation of paging group
• CCCH_group
– cch_conf in System Information 3 defines the number of
CCCH used in the cell.
– CCCH can be allocated only TN 0, 2, 4, 6.
– Each CCCH carries its own paging group of MS.
– MS will listen to paging messages of its specific group.
• bs_pa_mfrms
• bs_ag_blk_res
95. CALCULATION OF PAGING GROUP
Total number of paging groups on 1 CCCH_GROUP(N)
No of paging groups N = Paging blocks * Repitition of paging blocks
= [ CCCH - bs_ag_blk_res ] * bs_pa_mfrms
Range of Paging Groups on 1 CCCH_Group
Minimum available Paging Groups = Min pag blocks * min bs_pa_mfrms
= 2 * 2
= 4
Maximum available Paging Groups = Max pag blocks * max bs_pa_mfrms
= 9 * 9
= 81
96. AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUP
Maximum AGCH reservation for non-combined multiframe = 7
Available paging blocks = 2
Maximum AGCH reservation for combined multiframe = 1
Available paging blocks = 2
Minimum AGCH reservation for non-combined multiframe = 0
Available paging blocks = 9
Minimum AGCH reservation for combined multiframe = 0
Available paging blocks = 3
No of paging blocks will have a range of 2 - 9
97. CALCULATION OF CCCH AND PAGING GROUP NO
CCCH_GROUP = [ ( IMSI mod 1000) mod (BS_CC_CHANS * N ) ]
div N
Paging group no = [ ( IMSI mod 1000) mod (BS_CC_CHANS * N )
] mod N
99. • The GSM handover process uses a mobile assisted technique for
accurate and fast handovers, in order to:
– Maintain the user connection link quality.
– Manage traffic distribution
• The overall handover process is implemented in the MS,BSS &
MSC.
• Measurement of radio subsystem downlink performance and signal
strengths received from surrounding cells, is made in the MS.
• These measurements are sent to the BSS for assessment.
• The BSS measures the uplink performance for the MS being served
and also assesses the signal strength of interference on its idle
traffic channels.
• Initial assessment of the measurements in conjunction with defined
thresholds and handover strategy may be performed in the BSS.
Assessment requiring measurement results from other BSS or other
information resident in the MSC, may be perform. in the MSC.
HANDOVER
100. • The MS assists the handover decision process by performing
certain measurements.
• When the MS is engaged in a speech conversation, a portion of the
TDMA frame is idle while the rest of the frame is used for uplink
(BTS receive) and downlink (BTS transmit) timeslots.
• During the idle time period of the frame, the MS changes radio
channel frequency and monitors and measures the signal level of
the six best neighbor cells.
• Measurements which feed the handover decision algorithm are
made at both ends of the radio link.
HANDOVER (Cont)
101. • At the MS end, measurements are continuously signalled, via the
associated control channel, to the BSS where the decision for
handover is ultimately made.
• MS measurements include:
–Serving cell downlink quality (bit error rate (BER) estimate).
–Serving cell downlink received signal level, and six best neighbor
cells downlink received signal level.
• The MS also decodes the Base Station ID Code (BSIC) from the
six best neighbor cells, and reports the BSICs and the
measurement information to the BSS.
MS END
102. • The BTS measures the uplink link quality, received signal level,
and MS to BTS site distance.
• The MS RF transmit output power budget is also considered in
the handover decision.
• If the MS can be served by a neighbor cell at a lower power, the
handover is recommended.
• From a system perspective, handover may be considered due to
loading or congestion conditions. In this case, the MSC or BSC
tries to balance channel usage among cells.
BTS END
103. • During the conversation, the MS only transmits and receives for one
eighth of the time, that is during one timeslot in each frame.
• During its idle time (the remaining seven timeslots), the MS switches
to the BCCH of the surrounding cells and measures its signal
strength.
• The signal strength measurements of the surrounding cells, and the
signal strength and quality measurements of the serving cell, are
reported back to the serving cell via the SACCH once in every
SACCH multiframe.
• This information is evaluated by the BSS for use in deciding when
the MS should be handed over to another traffic channel.
• This reporting is the basis for MS assisted handovers.
MS IDLE TIME REPORTING
104. MEASUREMENT IN ACTIVE MODE
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2
Frame 24 Frame 25 Idle Frame Frame 0
Frame 24 Frame 25 Idle Frame Frame 0
1 2 3 1 2 1 2
1. MS receives and measures signal strength on serving cell(TS2).
2. MS transmits
3. MS measures signsl strength for at least one neighbor cell.
4. MS reads BSIC on SCH for one of the 6 strongest neighbor.
4
Downlink
Uplink
105. • Maximum 32 averaging of RSS takes place.
• Practically a cell neighbors can be equipped for a cell.
• If high numbers of neighbors are equipped, then the accuracy of
RSS is decreased as should have 8 to 10 neighbors.
T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
NUMBER OF NEIGHBORS
106. NUMBER OF NEIGHBORS
• In one SACCH multiframe there are 104 TDMA frames.
• Out of this 104 frames 4 frames are idle and are used to decode the
BSIC.
• Remaining 100 TDMA frames are used to measure RSS( Received
Signal Strength) of the neighbor.
• If 25 neigbors are equipped, then in one SACCH multiframe each
neigbor is measured 100/25 = 4 times and averaged out. This
produces a less accurate value.
• If 10 neigbors are equipped, then in one SACCH multiframe each
neigbor is measured 100/10 = 10 times and averaged out. This
produces a more accurate value.
107. • GSM causes its own time interference.
• The MS has a omni-directional antenna. Much of the MS power goes
to the server but a lot is interfering with surrounding cells using the
same channel.
• The TDMA frames of adjacent cell are not aligned since they are not
synchronised. Hence the uplink in the surrounding cell suffers from
interference.
INTERFERENCE ON IDLE CHANNEL
Channel 10
Cell 1
Channel 10
Cell 2
108. • The BSS keeps on measuring the interference on the idle timeslots.
• Ambient noise is measured and recorded 104 times in one SACCH
multiframe.
• These measurements are averaged out to produce one figure.
• The BSS then distributes the idle timeslots into band 0 to band 5.
• Since the BSS knows the interference level on idle timeslots, it uses
this data to allocate the best channel first and the worst last.
INTERFERENCE ON IDLE CHANNEL
0 1 2 3 4 5 6 7
Inteference on idle channel measured on Idle Timeslot by BSS
109. The following measurements is be continuously processed in the BSS :
i) Measurements reported by MS on SACCH
- Down link RXLEV
- Down link RXQUAL
- Down link neighbor cell RXLEV
ii) Measurements performed in BSS
- Uplink RXLEV
- Uplink RXQUAL
- MS-BS distance
- Interference level in unallocated time slots
Every SACCH multiframe (480 ms) a new processed value for each of
the measurements is calculated..
HANDOVER
110. Handover is done on five conditions
– Interference
– RXQUAL
– RXLEV
– Distance or Timing Advance
– Power Budget
Interference - If signal level is high and still there is RXQUAL problem,
then the RXQUAL problem is because of interference.
RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being the best
and 7 the worst
RXLEV - It is the receive level. It varies from -47dBm to -110dBm.
Timing Advance - Ranges from 0 to 63.
Power budget - It is used to save the power of the MS.
HANDOVER CONDITIONS
111. • Handover takes place in the same cell from one timeslot to another
timeslot of the same carrier or different carriers( but the same cell).
• Intra-cell handover is triggered only if the cause is interference.
• Intra-cell handover can be enabled or disabled in a cell.
HANDOVER TYPES
Intra-Cell Handover
BSC
BTS
Call is handed
from timeslot 3 to timeslot 5
0 1 2 3 4 5 6 7
112. • Handover takes place between different cell which are controlled by
the same BSC.
HANDOVER TYPES
Intra-BSC Handover
BSC1
BTS1
Call is handed from timeslot 3
of cell1 to timeslot 1 of cell2 .
Both the cells are controlled
by the same BSC.
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
113. • Handover takes place between different cell which are controlled by
the different BSC.
HANDOVER TYPES
Inter-BSC Handover
BSS1
BTS1
Call is handed from timeslot
of cell1 to timeslot 1 of cell2
Both the cells are controlled
by the different BSC.
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
BSS2
MSC
BTS2
114. • Handover takes place between different cell which are controlled by
the different BSC and each BSC is controlled by different MSC.
HANDOVER TYPES
Inter-MSC Handover
BSS1
BTS1
Call is handed from timeslot 3
of cell1 to timeslot 1 of cell2 .
Both the cells are controlled
by the different BSC, each BSC
being controlled by different MSC
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
BSS2
MSC1
BTS2
MSC2
115. • Measurement reports are sent to the BSS on the downlink every
480ms.
• Similarly the BSS measures the uplink level and quality.
• These reports are averaged out according to setting of factors
hreqave and hreqt.
• Each averaged value is called a N.
MEASUREMENT REPORT PROCESSING
Measurement report sent every 480ms
1st
MR
2nd
MR
3rd
MR
4th
MR
5th
MR
6th
MR
Average
Average
Average
Average
116. • Power control by BSS is based on the measurement report sent by
the MS.
• Averaging mechanism is used to produce N. The number of
measurement reports to be averaged depends on the values
hreqave.
POWER CONTROL BSS
-110 dBm
-100 dBm
-90 dBm
-80 dBm
-70 dBm
-47 dBm
-85 dBm
-75 dBm
0
10
20
30
40
63
l_rxlev_dl_p = 25
u_rxlev_dl_p = 35
• N and P values as well as
hreqave has to be set by the
operator.
• P out of N averages must
exceed thershold.
• N1 & P1 values are used for
power increase and N2 &
P2 values for power
decrease .
• A window has to be created
by setting the upper level
117. Lower level threshold = 25
Upper level threshold = 35
Power increase N1 = 5
P1 = 3
Power decrease N2 = 4
P2 = 3
POWER CONTROL BSS
Only 2 N above threshold
So no increase of power
3 N below threshold
So power is decreased by
the BSS
-110 dBm
-47 dBm
-85 dBm
-75 dBm
0
63
l_rxlev_dl_p = 25
u_rxlev_dl_p = 35
Increase Power
Decrease Power
Do nothing
-60 dBm
N considered for power increase
N considered for power decrease
118. bts_P_Con_INTERVAL : Minimum interval between changes in the RF
power level. Range 0 - 30 steps, size 0.96s.
Pow_Incr_Step_Size : Range 2, 4 or 6 dB.
Pow_Red_Step_Size : Range 2 or 4 dB.
BS_TXPWR_MAX : Maximum TXPWR used by the BSS.
POWER CONTROL BSS
119. • Power control by MS is based on the measurements taken by the
BSS.
• Averaging mechanism is used to produce N. The number of
measurement reports to be averaged depends on the values
hreqave.
POWER CONTROL MS
• N1 & P1 and N2 and P2
values that are used by BSS
for power control are also
applicable to the MS.
• P out of N averages must
exceed threshold.
• A window has to be created
by setting the upper level
and lower level thresholds
u_rxlev_ul_p and
l_rxlev_ul_p.
-110 dBm
-90 dBm
-80 dBm
-47 dBm
-85 dBm
0
63
l_rxlev_ul_p = 20
u_rxlev_ul_p = 30
P1 out of N1
Increase Power
P2 out of N2
Decrease Power
120. Lower level threshold = 20
Upper level threshold = 30
Power increase N1 = 5
P1 = 3
Power decrease N 2= 4
P2 = 3
POWER CONTROL MS
3 N above threshold
So Power is increased
by the MS
Only 2 N below threshold
So no power is decreased
the MS
-110 dBm
-47 dBm
-90 dBm
-80 dBm
0
63
l_rxlev_ul_p = 20
u_rxlev_ul_p = 30
Increase Power
Decrease Power
Do nothing
-60 dBm
N considered for power increase
N considered for power decrease
121. ms_P_Con_INTERVAL : Minimum interval between changes in the RF
power level. Range 0 - 30 steps, size 0.96s.
Pow_Incr_Step_Size : Range 2, 4 or 6 dB.
Pow_Red_Step_Size : Range 2 or 4 dB.
MS_TXPWR_MAX : Maximum TXPWR a MS may use in the serving
cell. Range (13, 43 dBm); step size 2 dB.
POWER CONTROL MS
122. • The MS and BSS also measure the downlink and uplink quality
respectively.
• The RXQUAL measurements are averaged and compared against
upper and lower thresholds set in the database.
POWER CONTROL -RXQUAL
• N and P voting mechanism
is used to determine if
power increase or decrease
is required on not.
• HO on RXQUAL is done
only if the MS or BSS is at
full power.
0.14%
0
u_rxqual_ul_p
u_rxqual_dl_p
2
3
4
6
7
0.57%
2.26%
9.05%
18.10%
1.13%
l_rxqual_ul_p
l_rxqual_dl_p
P4 out of N4
decrease Power
P3 out of N3
Increase Power
123. • If an MS is moving out of a cells coverage area then RXLEV and
RXQUAL measurements will cause the BSS and MS to increase
their power output.
• This process continues till the MS reaches its maximum permitted
output power and then handover is required.
HANDOVER - RXLEV
• N5 and P5 values are used
in voting mechanism for
RXLEV handover.
• P out of N averages must
exceed thershold.
• l_rxlev_ul_h, l_rxlev_dl_h,
are the thresholds set in the
database by the operator.
-110 dBm
-100 dBm
-90 dBm
-80 dBm
-70 dBm
-47 dBm
-85 dBm
-75 dBm
0
10
20
30
40
63
l_rxlev_ul_p
l_rxlev_dl_p
u_rxlev_ul_p
u_rxlev_dl_p
l_rxlev_ul_h
l_rxlev_dl_h
124. • If an MS is moving out of a cells coverage area then RXLEV &
RXQUAL measurements will cause the BSS & MS to increase their
power output.
• This process continues till the MS reaches its maximum permitted
O/P power and then handover is required.
HANDOVER - RXQUAL
• N6 and P6 values are used
in voting mechanism for
RXQUA; handover.
• P out of N averages must
exceed thershold.
• l_rxqual_ul_h, l_rxqual_dl_h,
are the thresholds set in the
database by the operator.
0.14%
0
u_rxqual_ul_p
u_rxqual_dl_p
2
4
6
7
0.57%
2.26%
9.05%
18.10%
l_rxqual_ul_p
l_rxqual_dl_p
l_rxqual_ul_h
l_rxqual_dl_h
2.26%
Adjust Power
125. • If the RXQUAL of either the U/L or D/L reaches the threshold that
would normally cause a HO but the RXLEV is at a value higher than
the threshold requiring a power increase then a HO may be initiated
due to interference. This type of handover is always intra_call
Handover.
• N7 and P7 are set for the voting mechanism.
HANDOVER - INTERFERENCE
0.14%
0
u_rxqual_ul_p
u_rxqual_dl_p
2
4
6
7
0.57%
2.26%
9.05%
18.10%
l_rxqual_ul_p
l_rxqual_dl_p
l_rxqual_ul_h
l_rxqual_dl_h
2.26%
Adjust Power
-110 dBm
-100 dBm
-90 dBm
-70 dBm
-47 dBm
0
10
20
30
40
63
l_rxlev_ul_ih
l_rxlev_dl_ih
Quality
Interference
126. • As the MS moves away from BSS, the BSS calculates the timing
advance and instructs the MS to transmit earlier to compensate for
the propagation delay.
• The maximum timing advance is upto 63 bits.
• The MS_RANGE_MAX field can be set to any one of these 63 values
thus determining the cell radius.
• As soon as the MS exceeds the MS_RANGE_MAX, a “handover
recognised” message is generated.
• The interval between timing advance changes is determined by the
timing_advance_period field. It has a range of 0-31, each step being a
SACCH multiframe.
• N8 and P8 are used in the voting mechanism.
HANDOVER - MS DISTANCE
127. POWER BUDGET
• This assessment process is employed by the network as a criterion in the
hand-over process, by setting a flag in the BSS by O&M command.
• If the process is employed, every 480 ms, for every connection and for
each of allowable 16 adjacent cells, the BSS evaluates the following
expression :
PBGT(n) = (Min(MS_TXPWR_MAX,P) - RXLEV_DL - PWR_C_D)
- (Min(MS_TXPWR_MAX(n),P) - RXLEV_NCELL(n))
Where the values of RXLEV_NCELL(n) and RXLEV_DL are obtained
with the averaging processes defined above.
PWR_C_D is the diff between the max D/L RF power permitted in the cell
& the actual D/L power due to the BS power control.
MS_TXPWR_MAX is the maximum RF TXPWR an MS is permitted to
use on a traffic channel in the serving cell.
MS_TXPWR_MAX (n) is the maximum RF TXPWR an MS is permitted to
use on a traffic channel in adjacent cell n.
P is the maximum TXPWR capability of the MS.
128. • The network initiates the hand-over procedure by sending an HAND-
OVER COMMAND message to the Mobile Station on the main DCCH.
• The NETWORK then starts timer T3103.
• T3103 guards against the receipt of either the unsuccessful message
from the source cell or successful message from the target cell. The
receipt of either message stops this timer.
• If this timer expires then a CLEAR REQUEST will be sent to the MSC in
a bid to clear the connection.
• The HANDOVER COMMAND contains all the data related to the target
cell like BCCH ARFCN, NCC, BCC, Timeslot Number, Training
sequence code, Power level to be used, Handover reference number
etc.
• The MS sends HANDOVER ACCESS burst with the same referance
number and starts timer T3124.
• The MS sends Handover access bursts and waits for a PHYSICAL
INFORMATION from the Network.
HANDOVER PROCEDURE
129. • When the Network sends the PHYSICAL INFORMATION message
timer T3105 is started by the network.
• If T3105 expires before the correct response from the MS has been
received, T3105 is reset and the PHYSICAL INFORMATION
message is repeated.
• This process is repeated a number of times until either the MS
correctly responds or the maximum number of repititions(NY1) is
reached.
• If the maximum number of repetitions is reached the newly allocated
channels are release and the handover abandoned.
• On the MS side if the timer T3124 expires, then the MS deactivates
the new channel, reactivates the old channel and if it is successful
sends a HANDOVER FAILURE message on the old channel and the
call continues.
• The value of T3124 is set to 320ms. (It must be lower than Ny1 times
T3105 for proper functions.)
HANDOVER PROCEDURE
130. • The timer T3105 can be set from 20 - 60 ms.
• If timer T3103 expires before either the HAND-OVER COMPLETE
message is received on the new channels, or a HAND-OVER
FAILURE message is received on the old channels, or the MS has
re-established the call, the old channel is released.
HANDOVER PROCEDURE
HANDOVER COMMAND
HANDOVER FAILURE
START TIMER T3103
STOP TIMER T3103
MS NETWORK
SOURCE CELL
INITIATE HANDOVER
UNSUCCESSFUL HANDOVER
HANDOVER COMPLETE
HANDOVER SUCCESSFUL
TARGET CELL
STOP TIMER T3103
EXPIRED
EXPIRED
TIMER T3103
131. HANDOVER PROCEDURE
TIMER T3105
HANDOVER COMMAND
START TIMER T3105
MS TARGET CELL
SOURCE CELL
HANDOVER ACCESS
PHYSICAL INFORMATION
HANDOVER COMPLETE
IF HO COMPLETE MSG
STOP TIMER T3105
EXPIRED
EXPIRED
HANDOVER ACCESS
PHYSICAL INFORMATION
IF NO HO COMPLETE MSG
AND T3105 EXPIRES
SEND PHYSICAL INFO AND
START TIMER T3105
NY1 TIMES
HANDOVER FAILURE TO BSC
If NY1 = 0
132. HANDOVER COMMAND
Sent by the source cell to the MS
• Cell Description
NCC
BCC
BCCH ARFCN
• Channel Description
Channel Type - TCH/F + ACCH
Timeslot Number
TSC
Hopping Channel - Single RF Channel
ARFCN
• Handover Reference Number
• Power level
133. HANDOVER ACCESS
Sent by the MS to the target cell on FACCH
Handover Reference Number
Sent by the Target cell to the MS
Timing Advance Value
PHYSICAL INFORMATION
135. • Optimisation is an invaluable element of service required to maintain
and improve the quality and capacity of a network.
• It is essential if an operator wants to implement changes to the
network to maintain the high quality of service levels expected by
subscribers in networks.
• Without optimisation the network will degrade from the commissioned
state, due to the network changing radically as the traffic on the
system grows, and snapshot optimisation will not keep pace with
these changes.
• Without optimisation the system will suffer poor call quality, many
dropped calls due to interference and inaccurate parameters resulting
in poor handover performance.
• These together with other problems, have the same result, Subscriber
Dissatisfaction.
NEED FOR OPTIMISATION
136. Drive testing
INPUTS TOOLS Output
Alarms and events
Analysis from OMC
Customer complaint
Analysis
Drive test kit(TEMS) and
optimization tool( PLANET)
OMC-R or Traffic
Analysis Tool(Metrica)
OMC-R
Customer Care
Centre Database
Database
Parameters
1) Frequency
2) BCCH changes
3) BSIC changes
4) Antenna downtilt
5) Azimuth changes
6) Antenna type
changes
7) Database
parameters changes
8) Handover
algorithm tunings
Quality Of
Service Metrics
RF Design
Parameters
137. • The following inputs are considered for optimisation:
– QOS Parameters
– RF Design Parameters
– OMC alarms
– Routine Drive Testing
– Customer feedback
– Database Parameters
• Using the above inputs we can determine the optimization requirement
and the the area which needs to be optimized.
INPUTS
138. • QOS Parameters are the quality indicators of the Network.
• Call Success rate, Call Drop Rate, Handover success rate, Call
Congestion are some of the QOS parameters.
• These parameters have to be continually monitored on cell, site , BSC
and Network basis.
• If any abnormality is observed or if any deterioration is seen in any of
the parameters optimization process has to be initiated.
• When a Network is designed benchmarking is done for Network
quality, capacity, failure and congestion parameters.
• Whenever the Network is unable to comply with any of the RF design
parameters, optimization process needs to be initiated.
QOS PARAMETERS
RF DESIGN PARAMETERS
139. • Any problem in the Network results in a alarm at the OMC.
• Whenever a alarm is observed at the OMC it must be carefully
analyzed to determine if there is a network problem and if it is
required to initiate optimization process.
• The alarm can be due to faulty hardware which can create problems
in the network.
OMC ALARMS
140. • Drive testing is done continually to monitor the health of the network.
• It is a normal procedure to define drive test routes and have them drive
tested daily to monitor the network.
• All sites and sectors should be tested within the drive test routes at
least once.
• Following care should be taken while defining the routes
– All major roads and highways should be tested at least twice per
week within the agreed routes.
– All cells should be tested for handout and hand-in within the routes
if possible.
– The routes should be approximately 2 - 3 hours in duration. This is
required to manage the data collected for analysis, routes longer
than this can be difficult to analyze and transfer from P.C to P.C
due to the files being too large.
– Routes of major importance should be identified prior to starting
and should be driven first. i.e. Airports to the city centre.
DRIVE TESTING
141. • A procedure to feed back customer information on the
performance and coverage of the network can be extremely
useful.
• The received information is used to target areas requiring
optimisation and to verify coverage against the RF design.
• The information fed back is also used in assessing the growth of
the network by identifying areas of high traffic volumes.
CUSTOMER FEEDBACK
143. • Once the optimization needs have been identified the optimization
process is started to analyze the problem and then provide
possible solutions.
• Optimization process involves studying and analyzing the problems
using the following steps
– Statistical Analysis
– Drive testing
– OMC tools
– Site visits
OPTIMIZATION PROCESS
144. • The quality of the network can be measured through the statistics
generated from the network.
• These are available through the OMC (Operations and Maintenance
Center) and are used to generate key metrics.
• This operational metrics will then be measured against the required
metrics as agreed between the operator and vendor, from this
comparison an optimization plan will be generated.
• Drive test statistics represent a small sample of the total calls on the
network and can provide a useful indication of network quality.
• In order to provide a precise information of user traffic, the statistics
obtained from the whole network through the OMC are a more
accurate assessment of the quality of the network.
STATISTICAL ANALYSIS
145. The following metrics can be used to measure the performance of
the network.
• Dropped Call Rate
• Handover Success Rate
• Overall RF Loss Rate - TCH & SDCCH RF loss combined
• TCH Assignment Success Rate
• Call Success rate
• TCH Blocking Rate
• SDCCH Blocking
KEY QUALITY METRICS
146. • It is important for a good optimization engineer to have good
knowledge of various statistics available from performance
management.
• Any change in the network whether good or bad is definitely reflected
in the statistics.
• By studying and analyzing the statistics we can not only detect the
problems in the network but in some cases even provide the solution
for the problem.
• Statistical Analysis can be divided into two categories
– Trend Analysis
– Daily Analysis
IMPORTANCE OF STATISTICAL ANALYSIS
STATISTICAL ANALYSIS TYPES
147. • Analysis which is carried out using statistical data over a period of
time is called trend analysis.
• The longer the period better the analysis and accurate the results.
• Trend analysis helps us in understanding the performance of the
Network over a period of time.
• It is important in generating Network Performance report and helps
us to understand the progress of the network.
• It also helps us in Network expansion planning.
• It is expected that the operator maintain at least six months of data.
TREND ANALYSIS
149. • Key statistics are analyzed on a daily basis for the Network, BSC’s
and cells.
• If any problem is observed (e.g. RF losses for a particular cell has
gone up drastically) the concerned statistics are analyzed in detail
to determine the problem and then to initiate appropriate action.
• Daily performance analysis helps us check and solve problems at
the initial stage itself and thus help us to maintain the quality of the
Network.
DAILY ANALYSIS
151. • Analyze key statistics for cell wise data.
• Note down the problems and prioritize them.
• Evaluate the concerned statistics in detail to pinpoint the possible
cause for the problems.
• Initiate appropriate action to determine the solution.
• Apply the solution.
• Check statistics for improvement.
• If no or little improvement repeat steps 3,4,5 and 6.
• Same process can be applied for BSC wise and Network data.
STATISTICS EVALUATION PROCESS
152. • SDCCH and TCH congestion
• This statistics tell you if your TCH and SDCCH were congested
• To check if it is required to add a new carrier we must look at these
statistics but should also look at time congestion statistics.
• These statistics tell you the amount of time for which the cell was
congested during the day.
• Also it is important to study the trend for the above statistics before
the action to be taken is decided.
STATISTICS EVALUATION PROCESS(Eg)
155. General
• Drive testing involves driving in a vehicle and collecting network data
by making a lot of calls.
• The data collected includes data for serving cell as well as the
neighbors.
• This data collected helps us to find and analyze the problems in the
network.
• These data can also be loaded on the planning and optimization
tools like Pegasos, Planet etc. and usefull plots can be generated
such as serving cells coverage plots, Quality plots etc.
• Equipment Necessary for Drivetesting.
– Vehicle
– Drive test mobile phone (e.g.Ericcson TEMS)
– External vehicle mounted GPS
– Laptop with drive test software and GPS connection capability.
156. Drive test Outputs
• Using the drive test equipment we can monitor the following
– Status Information
– Error reports
– Mode reports
– Layer 2 messages
– Layer 3 messages
157. Status Information
• In status information we get the following information
– General Information: This includes the Latitude ,longitude data,
server call name, Marker ,data, time , log file name etc.
– Serving cell: This includes Cell Identity, BSIC, ARFCN ,MCC,
MNC, LAC.
– Serving + Neighbor cell data: This includes CI, BSIC, ARFCN,
Rxlev, C1 and C2 for the serving and the best 6 neighbors.
– Dedicated channel: This includes data such as Channel
number, Timeslot number, Channel type and TDMA
offset,hopping information and channel mode.
– Radio Environment: This includes serving cell,lat , long, rxlev,
rxqual, TA, DTX and RL Timeout counter information.
158. Error reports
• If any errors are reported during the call they can be analyzed
from this report.
Mode reports
• These are the channel mode reports.
Layer 2 messages
• All the layer 2 messages can be analyzed.
Layer 3 messages
• All the layer 3 messages can be analyzed.
159. Drive test types:
• Drive test can be categorized in three types
– Routine drive test
– Problem specific drive test
– Cell coverage analysis drive test
160. Routine drive test
• As we have discussed earlier optimization is a ongoing process
and the network needs to be monitored on a daily basis.
• Routine drive test forms a integral part of this process.
• Drive test routes are decided by the Network operator and these
routes are regularly drive tested and any problems found are
reported.
• These problems are then further analyzed and solved.
• Hence it is important that these drive test routes are selected
carefully.
• Drive test routes should include all the major road, important
location, airports etc.
• Also they should be able to cover most of the cells.
• Each drive test route should be typically 2 - 3 hours long.
161. Typical Optimization Process using routine drive testing
• The drive test routes must be decided by the operator and a priority
set on the routes for testing.
• The drive test routes are usually 2 - 3 hours in duration in order to
ensure that the data generated is of a manageable size.
• The drive test teams use the Test Mobile equipment (e.g.TEMS) to
make test calls to the MSC test number on the network of 2 minute
duration with a 15 second break.
• All data is logged on the computer, location information is also
taken using a GPS receiver.
• During or after completion of the drive test route, analysis of the
data collected is performed to identify areas of dropped or noisy
calls.
• This will be done using FICS or other similar software.
162. • Should the analysis of the route indicate problems of either
dropped or noisy calls then with the aid of the RF design and
Database parameters, an assessment is made to identify the
possible source of interference causing the noisy or dropped call.
• If a call is dropped and no interference is present a retest is made
in the same area, if the scenario of the dropped call can be
repeated, the identity of the problem cell will be obtained and
corrective action taken.
• To assist in confirming possible sources of interference there may
be a requirement to remove the suspected interfering channel.
• This would be done by the optimisation engineers.
• The suspected interfering carrier would be removed temporarily
from service and test calls made again in the problem area, this
would show if the interference had been removed.
• The process for temporarily removing carriers would have to be
agreed with the operator, this usually varies as to the importance
of the cell as to what time of day it can be taken out of service.
163. • After conformation as to what is causing the problem with the drive
test route, the drive test engineer will attempt to find a solution to the
problem.
• This can be one of a number of possibilities i.e. Power Change to
BTS, Frequency Plan change, Neighbor addition required, etc.
• Once a possible solution to the problem has been found it may be
possible in some circumstances to immediately attempt the solution
via the OMC, this usually relates to minor database changes and
adding neighbors.
• The solution is implemented and proven immediately.
• If the problem is rectified the change remains in place and a change
request is raised for the solution for the purpose of keeping records
of all changes in the network.
• If the solution requires a major database change or antenna work a
change request must be raised via the Optimization Control
Engineers.
• After the solution is implemented a retest of the problem area is
carried out to confirm the problem has been solved
164. Problem drive testing
• Any problem reported by statistical analysis, routine drive testing,
customer care centre , alarms need to be analyzed in detail to find a
solution.
• Problem specific drive testing is a important tool which helps us do it.
• Here we make a list of problematic cell and drive test them
thoroughly to analyze the problem.
• There may be many different methods which a optimization engineer
may employ for the analysis.
• As an example, if a particular cell is being interfered the frequency of
the cell may be changed temporarily to identify the interferer.
• Also the levels and TA at which the cell is being interfered may be
analyzed.
• Here the data collection and analysis are done simultaneously.
165. Cell Coverage Analysis Drive Test
• It has been found that normally that the coverage and server area
of the cells differ from the planned area.
• Hence it is often found that new cells that come on air serve far
more or much less area than initially planned and same could be
the case with the coverage.
• This could lead to two problems. If the server area is less than
planned it could lead to coverage holes or poor cover areas. If the
coverage area is more than planned it may cause interference in
the network.
• Hence it is important that once new cells come on air they must be
thoroughly drive tested to determine their server and coverage
areas.
• If any major deviation from the initially planned design is found the
cell sites should be optimized.
166. Scanning
• This is a important feature of the drive test software.
• It enables us to lock onto a particular frequency during the drive test
which is helpful in determining the server area of a cell.
• Also we scan a set of frequencies and have a graphical display of
the same or can also be stored for further analysis.
• This is helpful in finding interfering frequencies and also in finding
clear frequency.
167. Optional Features
• Some drive test equipment provide supplementary features which
help during drive test.
• Map displaying the drive tested area showing the major roads,
location, cell sites is provided ,this helps us to be always aware as to
where we are in the network.
• Also some vendors provide spectrum analyzer which helps in finding
the interfering frequencies and to find clear frequencies.
180. General
• Many vendors provide advanced tools which help in optimization of
the Network.
• Some vendors provide Network Health reports which provide you
list of bad performing sites with poor sites and possible causes for
the problems.
• However one powerful tool provided by all operators is the call trace
tool.
• The degree to which this feature has been developed varies from
vendor to vendor.
• This is perhaps the most important tool in optimization. We will be
having a look at this feature in detail.
181. Call Trace Feature
• This feature enables us to put a trace on a call and collect all data
related to the call.
• The call trace can be put on a cell basis, BTS wise, over the BSC or
over the entire Network.
• Call trace can be put on a IMSI, IMEI ,TMSI or on every nth call being
made in the cell, BTS, BSC or the Network.
• Call trace gives you all the information that you get in the drive test
plus it also give you uplink Rxlev and Rxqual information.
• Also drive testing can be done only on the roads hence it becomes
difficult to locate and solve indoor problems.
• Since in call trace we can accumulate data for call being made
throughout the cell it includes the indoor calls also and hence gives us
the the correct picture regarding the performance of the cell.
182. Protocol Analyzer :
• Protocol analyzer may be used to analyze the C7 signaling
messages between the MSC and the BSC .
• These are used to analyze problems which may originate either
in the Radio part or the MSC e.g. paging problems.
184. General
• When we visit the problematic site for optimizing we must ask three
simple questions which will help us in optimizing
1. Why was this site put up?
2. Will this site serve that purpose ?
3. What are the problems that I see at this site and how can I
solve them ?
• Let us now look at each of those questions individually.
185. Why was this site put up ?
• We must know if the site was installed for capacity or coverage.
• If it was for capacity we should know if it should offload the
traffic of some existing sites and if it should generate traffic of its
own.
• Also if the site in question is a hotspot or not. If the site was
installed for coverage we should know exactly the area it is
supposed to cover and if there is some existing coverage in that
area.
186. Will this selected site serve that purpose ?
• Once we are clear about the objective of installing the site we
must analyze if the site in question serves that purpose or not.
• It is important that the selected site serves its objective.
What are the problems and how can I solve them
• Some of the common problems could be as follows
– The neighboring sites cause interference to the proposed
site.
– The site is a cause of interference to some existing sites.
– If there is a possibility of a backlobe or sidelobe problem.
– There could be some near end obstruction
188. General
• Once the problem has been analyzed a solution has to be
provided. Common solution to problems are
– Database Parameters Changes
– Antenna Optimization
– Frequency changes
– Neighbor addition and deletion
– Formation of new location areas
– Addition of new cellsites
189. Database Parameter Changes
• Many problems can be solved by changing some database
parameters.
• Some of the common changes are
– Handover parameters and thresholds
– Maximum transmit power of BTS
– Paging parameters
– SDCCH Parameters
190. Antenna Optimization
• This includes changing of antenna tilts, orientations, positions.
Sometimes the antenna may also be changed.
Frequency Changes
• Frequency changes help us to control the interference in the
network.
• However one should be careful when doing these changes so that
this changes do not affect the other sites adversely.
• If there are a lot of changes it is advisable to change the whole
frequency plan.
• A careful study of cell coverage area and server area helps in
making those changes.
191. Neighbor Addition And Deletion
• Many problems arise due to wrong neighbor definitions or missing
neighbors.
• Neighbor definitions must be reviewed on a regular basis.
Statistics and drive tests provide good inputs for this purpose.
Formation Of New Location Areas
• Sometimes to solve paging load problems it might be required to
for new location areas.
Addition of new cell sites
• Sometimes to solve coverage hole problems we need to add more
site (normally micro or pico cells)
192. Path Balance
• Many problems also may arise due to poor path balance. Hence it
is important that we make a mention about it.
• Path balance data can be collected from the statistics.
• As we use different frequencies for uplink and downlink, we have
different footprints for the uplink and the downlink .
• It is imperative that the footprints match.
• If the downlink is stronger it implies that the mobiles at the
boundaries of the serving area are not able to reach the BTS and
there is a uplink problem.
• Similarly if the uplink is stronger it implies a downlink problem.
