Rf optimization

Physical channelPhysical channel - Each timeslot on a carrier is referred to as a physical
channel. Per carrier there are 8 physical channels.
Logical channelLogical 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
CHANNELSCHANNELS

GSM Traffic ChannelsGSM Traffic Channels
Traffic Channels
TCH/F
Full rate 22.8kbits/s
TCH/H
Half rate 11.4 kbits/s

GSM Control ChannelsGSM 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

BCH ChannelsBCH Channels
BCCH( Broadcast Control Channel )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 )SCH( Synchronisation Channel )
• Downlink only
• Carries information for frame synchronisation. Contains TDMA
frame number and BSIC.
FCCH( Frequency Correction Channel )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.

CCCH ChannelsCCCH Channels
RACH( Random Access Channel )RACH( Random Access Channel )
• Uplink only
• Used by the MS to access the Network.
AGCH( Access Grant Channel )AGCH( Access Grant Channel )
• Downlink only
• Used by the network to assign a signalling channel upon
successfull decoding of access bursts.
PCH( Paging Channel )PCH( Paging Channel )
• Downlink only.
• Used by the Network to contact the MS.

DCCH ChannelsDCCH Channels
SDCCH( Standalone Dedicated Control Channel )SDCCH( Standalone Dedicated Control Channel )
• Uplink and Downlink
• Used for call setup, location update and SMS.
SACCH( Slow Associated Control Channel )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 )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.

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
00 11 22 33 44 55 66 77 00 11 22 33 44 55 66 77 00 11 22 33 44 55 66 77
120 msec
4.615 msec
2626 FRAME MULTIFRAME STRUCTUREFRAME MULTIFRAME STRUCTURE
• MS on dedicated mode on a TCH uses a 26-frame multiframe
structure.
• Frame 0-11 and 13-24 used to carry traffic.
• Frame 12 used as SACCH to carry control information from and to MS
to BTS.
• Frame 25 is idle and is used by mobile to decode the BSIC of neighbor
cells.

BCCH
CCCH
BCCH
CCCH
BCCH
CCCH
BCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
0
10
20
30
40
50 50
40
30
20
10
0
IDLE
CCCH BLOCK
BCCH BLOCK
SCH BLOCK
FCCH BLOCK
BCCH/CCCH NON-COMBINED MULTIFRAMEBCCH/CCCH NON-COMBINED MULTIFRAME
RACH BLOCK
DownlinkDownlink UplinkUplink

0
10
20
30
40
50 50
40
30
20
10
0
IDLE
CCCH BLOCK
BCCH BLOCK
SCH BLOCK
FCCH BLOCK
BCCH/CCCH COMBINED MULTIFRAMEBCCH/CCCH COMBINED MULTIFRAME
51
101 101
51
BCCH
CCCH
BCCH
CCCH
CCCH
BCCH
CCCH
CCCH
CCCH
SACCH
SACCH
CCCH
CCCH
CCCH
CCCHSDCCH
SDCCH
SDCCH
SDCCH
BCCH
CCCH
BCCH
CCCH
CCCH
BCCH
CCCH
CCCH
CCCH
SACCH
SACCH
CCCH
CCCH
CCCH
CCCHSDCCH
SDCCH
SDCCH
SDCCH
BCCHCCCHSDCCH
CCCHSACCH
CCCHSACCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH
BCCHCCCHSDCCH
CCCHSACCH
CCCHSACCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCHRACH BLOCK
SDCCH/4
SACCH/4

0
10
20
30
40
50 50
40
30
20
10
0
IDLE
DCCH/8 MULTIFRAMEDCCH/8 MULTIFRAME
51
101 101
51
SDCCH/8
SACCH/C8
BCCH
CCCH
A2
A3
BCCH
CCCH
A0
A1
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0
BCCH
CCCH
A6
A7
BCCH
CCCH
A4
A5
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0
BCCHA0
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0
BCCH
CCCH
A6
A7
CCCHA5
BCCHA4
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0
BCCH
CCCH
A2
A3
CCCHA1

00 11
00 11 22 20452045 20462046 20472047
1 Hyperframe = 2048 superframes = 2,715,648 TDMA frames3h 28min 53s 760ms
1 Superframe = 1326 TDMAframes = 51(26 fr) 0r 26(51 fr) multiframes
11 2 33 494847 50
00 11 2424 2525
00 11 22 2323 2424 2525 00 484811 22 4949 5050
22 33 44 55 66 77
6.12s
0
235.38ms120ms
Control 51 - Frame MultiframeTraffic 26 - Frame Multiframe
4.615ms
TDMA Frame
HYPERFRAME AND SUPERFRAME STRUCTUREHYPERFRAME AND SUPERFRAME STRUCTURE

Mobile originated callMobile 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 ]
TCH Seizure
S
D
C
C
H
T
C
H

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
T
C
H TCH Seizure
Mobile terminated callMobile terminated call

PROPAGATION MECHANISMSPROPAGATION MECHANISMS
Reflection
• Occurs when a wave impinges upon a smooth surface.
• Dimensions of the surface are large relative to λ.
• 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 λ 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 λ or less, causing the reflected energy to spread out or“scatter”
in many directions.

MultipathMultipath
• Multiple Waves Create “Multipath”
• Due to propagation mechanisms, multiple waves arrive at the
receiver
• Sometimes this includes a direct Line-of-Sight
(LOS) signal

Multipath PropagationMultipath 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 thingsMultipath 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.

FadingFading
• 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.

FADINGFADING
SignalPower(dBm)
Large scale fading component
Small scale fading
component

Long Term FadingLong 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 40λ.
• Experimentally it has been determined that the standard deviation,
σ, of the mean received signal strength, r, lies between 8 to 12 dB
with the higher σ generally found in large urban areas.

Rayleigh FadingRayleigh 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.

Ricean FadingRicean 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.

AntennasAntennas
• 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.

Antenna TypesAntenna Types
• In mobile communications two main categories of antennas used are
– Omni directional antennaOmni 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.

– Directional antennaDirectional 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.

Radiation PatternRadiation 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.

Radiation PatternRadiation Pattern

Antenna GainAntenna 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.

Main Lobe Axis
½ Power Beamwidth
Side Lobe
Back Lobe
First Null

Front-to-back ratioFront-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 BeamwidthFirst 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.

Antenna LobesAntenna Lobes
• Main lobe is the radiation lobe containing the direction of maximum
radiation.
• Side lobes
Half-power beamwidthHalf-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.
PolarisationPolarisation
• Polarisation is the propagation of the electric field vector .
• Antennas used in cellular communications are usually vertically polarised
or cross polarised.

Frequency bandwidthFrequency 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 impedanceAntenna impedance
• Maximum power coupling into the antennas can be achieved when the
antenna impedance matches the cables impedance.
• Typical value is 50 ohms.
Mechanical sizeMechanical 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.

• 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 10λ 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 1λ separation in the vertical direction is sufficient in most cases.

• 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.

Antenna downtilt introductionAntenna 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.

Antenna downtiltingAntenna 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.

Mechanical DowntiltMechanical 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.

Vertical antenna pattern at 0°
Vertical antenna pattern at 15° downtilt
Backlobe shoots over the horizon

Electrical downtiltElectrical 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.

Electrical downtiltElectrical downtilt

Obstacle requirementObstacle 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.

Main Radiation
Direction
Half Power
Beamwidth
Safety Margin
15 Degrees
Building
Obstacle requirementObstacle requirement

Optimal DowntiltOptimal 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
Φ
Φ

• 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 φ is the angle between the upper limit of the
3dB beamwidth and the horizon.

• tan (Φ ) = Cellmax / H
Φ = 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.

WHAT IS INTERFERNCE ?WHAT IS INTERFERNCE ?
• Interference is the sum of all signal contributions that are neither noise
not the wanted signal.

EFFECTS OF INTERFERNCEEFFECTS 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.

SOURCES OF INTERFERNCESOURCES 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.

TYPES OF INTERFERNCETYPES OF INTERFERNCE
• There are two types of system generated interference
– Co-channel interference
– Adjacent channel interference
Co-Channel InterferenceCo-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.

• 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

• 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

• 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.

Adjacent-Channel InterferenceAdjacent-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.

Adjacent-Channel InterferenceAdjacent-Channel Interference
Carrier f1 Interferer f2
dB
A
C
Distance

POWER CONTROLPOWER 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.

SECTORIZATIONSECTORIZATION
• 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.

DIVERSITY ANTENNADIVERSITY ANTENNA
SYSTEMSSYSTEMS

NEED OF DIVERSITY
Building
Building
Building

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’.

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

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.

Transmission
media 1
Transmission
Tmedia 2
Peak
Fade
ReceiverInformation
CONCEPT OF DIVERSITY ANTENNA SYSTEMS

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

TYPICAL SPATIAL ANTENNA DIVERSITY CONFIGURATIONS
Horizontal Separation Vertical Separation

THREE ANTENNA SPATIAL CONFIGURATION
10λ Separation
Receive 1 Transmit Receive 2

TWO ANTENNA SPATIAL CONFIGURATION
10λ Separation
Receive 2
Tx Rx
Transmit Receive 1
Duplexer

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.

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°

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

DUAL POLARISED ANTENNA CONFIGURATIONS
DUALPOLEANTENNA
T R
TX RX RX
DUALPOLEANTENNASINGLEPOLEA
RX RX
TX
DUALPOLEANTENNA
T TR R
TX RX TX RX

SYSTEM INFORMATIONSYSTEM INFORMATION
MESSAGESMESSAGES

BROADCAST MESSAGESBROADCAST 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.

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 MESSAGESBROADCAST MESSAGES
System
Information
BCCH
Multiframe
1 0
2 1
3 2 and 6
4 3 and 7

SYSTEM INFORMATION 1SYSTEM 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

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

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

• 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
SYSTEM INFORMATIONSYSTEM INFORMATION 22

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 1MCC DIG 2
MCC DIG 3
MNC DIG 1MNC DIG 2
LAC
LAC
Binary
8 7 6 5 4 3 2 1
Octet F
Octet G
CI
CI
Binary

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

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.

Location Area Identification
Cell Selection Parameters
Rxlev_access_min
mx_txpwr_cch
Cell_reselect_hysteresis
max_retransmissions
tx_integer
Cell barred for access
Re-establishment allowed
Emergency Call Allowed
Access Control Class

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.

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

• 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

PAGINGPAGING
• 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

CALCULATION OF PAGING GROUPCALCULATION 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

CALCULATION OF PAGING GROUPCALCULATION 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

AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUPAVAILABLE 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
Minimum AGCH reservation for non-combined multiframe = 0
Minimum AGCH reservation for combined multiframe = 0
No of paging blocks will have a range of 2 - 9

CALCULATION OF CCCH AND PAGING GROUP NOCALCULATION 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

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