Complete Tutorial 3G Rf-Optimization & Log-File Analysis

Rf-Optimization & Log-File Analysis

Before Starting

This document was prepared with TEMS screen shots from live examples of previous
experiences to guide RF Engineers on how to define/analyze problems or cases and optimize

network. After each case/problem demonstration, specific step to be taken will be defined and

appropriate recommendation will be given.
The document will be focusing on Drive Testing part of the Optimization Process and give
definitions on basic GSM principals, features and parameters when needed.
The readers of this document are considered to have basic knowledge of cell planning and TEMS
Investigation usage. Only little information will be given just to remember TEMS interface.

DRIVE TESTING

Drive testing is the most common and maybe the best way to analyze Network performance by
means of coverage evaluation, system availability, network capacity, network retainibility and
call quality. Although it gives idea only on downlink side of the process, it provides huge
perspective to the service provider about what’s happening with a subscriber point of view.
The drive testing is basically collecting measurement data with a TEMS phone, but the main
concern is the analysis and evaluation part that is done after completition of the test. Remember
that you are always asked to perform a drive test for not only showing the problems, but also
explaining them and providing useful recommendations to correct them. Please note that a
successful analysis should be supported by handling of network statistics from a statistics tool
(Metrica/NetDoc–NMS/SRP–OSS, etc..) and careful evaluation of coverage predictions from a
cell planning tool (Planet, DB–Planner, TEMs Cell Planner, etc..). Please see Figure for a usual view from TEMS.

TEMS Information

The information provided by TEMS is displayed in status windows. This information includes
cell identity, base station identity code, BCCH carrier ARFCN, mobile country code, mobile
network code and the location area code of the serving cell.
There is also information about RxLev, BSIC and ARFCN for up to six neighboring cells;
channel number(s), timeslot number, channel type and TDMA offset; channel mode, sub channel
number, hopping channel indication, mobile allocation index offset and hopping sequence
number of the dedicated channel; and RxLev, RxQual, FER, DTX down link, TEMS Speech
Quality Index (SQI), timing advance (TA), TX Power, radio link timeout counter and C/A
parameters for the radio environment.
The signal strength, RxQual, C/A, TA, TX Power, TEMS SQI and FER of the serving cell and
signal strength for two of the neighboring cells can also be displayed graphically in a window.

Layer 2 and 3 messages and SMS cell broadcast messages are displayed in separate scrollable

windows as can be seen in Figure 2. If desired, specific Layer 3 messages can be displayed.
By connecting an additional TEMS phone to a vacant serial port of the PC, data from two
networks can be monitored and logged at the same time. In this case, the data from the second
mobile phone is serving cell and neighboring cell data and radio environment parameters.
TEMS Investigation also can perform frequency scanning of all significant carrier frequencies.
The information presented is ARFCN, RxLev and, if successfully decoded, BSIC.

Basic Counters of Network Performance

Accessibility
Accessibility counter is one of the most important statistics and it is the
performance expression of the network at the first glance. Accessibility is
calculated by multiplying SDDCH serviceability by TCH accessibility.
Accessibility = SDCCH Serviceability * TCH Accessibility
For accessibility performance of the network, repeated short call set–ups
must be performed by drive tests.
Retainability
Retainability is the clue to network continuity and targets TCH Call
Success rate of the network. It takes all type of drops into consideration.
Retainability = TCH Call Access Rate = 1 – TCH Call Drop Rate
TCH Call Drop rate is calculated by dividing total number of drop calls to
number of total TCH seizures and attempts. Total number of drop calls
contains all types of TCH drops including any radio related, user activated,
network activated, ABIS fail, A interface, LAPD, BTS failure or BSCU
reset drops. Please note that any TCH re–establishment should be
subtracted from TCH call drop rate as call is somehow able to continue.
Total number of TCH attempts and seizures will include any TCH seizures
for new calls and TCH to TCH attempts during Handover and number of
intracell handovers as well.
Retainability is wanted to be as near as to 100 percent. For measuring
retainability and integrity of a network, long continuous calls must be
performed by drive tests.
Access Fails
Access failures are the total number of unsuccessful TCH attempts which
is calculated by subtracting number of assigned TCH seizures from
number of TCH attempts – including the ones during handovers.

Idle Mode Behavior

A powered on mobile station (MS) that does not have a dedicated channel allocated is defined as
being in idle mode (see Figure 3). While in idle mode it is important that the mobile is both able
to access and be reached by the system. The idle mode behavior is managed by the MS. It can be
controlled by parameters which the MS receives from the base station on the Broadcast Control
Channel (BCCH). All of the main controlling parameters for idle mode behavior are transmitted
on the BCCH carrier in each cell. These parameters can be controlled on a per cell basis.
Moreover, to be able to access the system from anywhere in the network, regardless of where the
MS was powered on/off, it has to be able to select a specific GSM base station, tune to its
frequency and listen to the system information messages transmitted in that cell. It must also be
able to register its current location to the network so that the network knows where to route
incoming calls.

Location Update

The MS listens to the system information, compares the Location Area Identity (LAI) to the one
stored in the MS and detects whether it has entered a new location area or is still in the same
location area. If the broadcast LAI differs from the one stored in the MS, the MS must perform a
location update, type normal. The MS sends a channel request message including the reason for
the access. Reasons other than location updating can be for example, answering a page or
emergency call.
The message received by the BTS is forwarded to the BSC. The BSC allocates a signaling
channel (SDCCH), if there is one idle, and tells the BTS to activate it. The MS is now told to tune
to the SDCCH. The outcome of the procedure is that a radio resource connection is dedicated to
the MS. The procedure is therefore called RR connection establishment.
The MS sends a location updating request message which contains the identity of the MS, the
identity of the old location area and the type of updating. The authentication parameter is sent to
MS. In this case the MS is already registered in this MSC/VLR and the authentication parameter
used is stored in the VLR. If the MS is not already registered in this MSC/VLR the appropriate
HLR or the previously used MSC/VLR must be contacted to retrieve MS subscriber data and
authentication parameters. MS sends an answer calculated using the received authentication
parameter.
If the authentication is successful, the VLR is updated. If needed, the old HLR and old VLR are
also updated. The MS receives an acceptance of the location updating. The BTS is told to release
the SDCCH. The MS is told to release the SDCCH and switches to idle mode.
If the MS is moving in a border area between location areas, it might repeatedly change between
cells of different location areas. Each change of location area would require a location updating
to be performed, which would cause a heavy signaling load and thereby also increasing the risk
of paging messages being lost.
Cells bordering a different location area may have lots of location updating, and cells on a
highway probably have many handovers. In order to calculate the need for SDCCHs the number
of attempts for every procedure that uses the SDCCH as well as the time that each procedure
holds the SDCCH must be taken into account. The procedures are; location updating, periodic
registrations, IMSI attach/detach, call setup, SMS, facsimile and supplementary services.
Next step will be analyzing Call Set–up process. Being the start point and direct factor to
accessibility of the network, call set–up has great importance in GSM performance. Some basic
information on the procedure will be given. As Layer 3 messages will be our reference point
when defining problems during log files analysis, they will also be explained with their
appearance order during and after call set–up.

Call Setup

The cell selection algorithm tries to find the most suitable cell of the selected PLMN according to
various requirements. If no suitable cell is found and all available and permitted PLMNs have
been tried, the MS will try to camp on a cell irrespective of PLMN identity and enter a limited
service state. In this state the MS will be able to make emergency calls only. If the MS loses
coverage it will return to the PLMN selection state and select another PLMN.
After a cell has been successfully selected, the MS will start the cell reselection tasks. It will
continuously make measurements on its neighboring cells to initiate cell reselection if necessary.
For multiband MSs the strongest non–serving carriers may belong to different frequency bands.
The MS continuously monitors all neighboring BCCH carriers, as indicated by the BA list, in
addition to the BCCH carrier of the serving cell, to detect if it is more suitable to camp on another
cell. At least five received signal level measurement samples are required for each defined
neighboring cell. A running average of the received signal level will be maintained for each
carrier in the BA list. Provided that the MS is listening to the system information in the cell and
that it is registered in the MSC/VLR handling this cell, the MS can attempt to make a call.
First, radio connection between MS and network is established. Then MS indicates that it wants
to set up a call. The identity of the MS, IMSI, is analyzed and the MS is marked as busy in the
VLR. Authentication is performed as described for location updating. Then ciphering is initiated.
MSC receives a setup message from the MS. This information includes what kind of service the
MS wants and the number (called the B number) dialed by the mobile subscriber. MSC checks
that the MS does not have services like barring of outgoing calls activated. Barring can be
activated either by the subscriber or by the operator. If the MS is not barred, the setup of the call
proceeds. Between the MSC and the BSC a link is established and a PCM TS is seized. The MSC

sends a request to the BSC to assign a traffic channel (TCH). The BSC checks if there is an idle

TCH, assigns it to the call and tells the BTS to activate the channel. The BTS sends an

acknowledgment when the activation is complete and then the BSC orders the MS to transfer to
the TCH. The BSC informs the MSC when the assignment is complete. The traffic control
subsystem analyzes the digits and sets up the connection to the called subscriber. The call is
connected through in the group switch. An alert message is sent to the MS indicating that a
ringing tone has been generated on the other side. The ringing tone generated in the exchange on
the B subscriber side is sent to the MS via the group switch in MSC. The ringing tone is sent over
the air on the traffic channel.
When the B subscriber answers, the network sends a connect message to the MS indicating that
the call is accepted. The MS returns a connect acknowledgment, which completes the call set–up.
Please see Figure for the Call Set–up process.

Call Set–up Process in Layer 3 Messages

Call Set–up procedure starts with Channel Request Command and MS passes to Dedicated Mode
with this command. This channel request message is sent in random mode on the RACH
( Random access channel –Uplink only, used to request allocation of a SDCCH ) and the most
important part of the message is Establishment cause. The cause for channel request could be;
–Answer to paging
–Emergency call
–Call re–establishment
–Other services requested by the mobile user (originating call, supplementary service short
message)
–All Other cases
Below window dump in Figure  showing a channel request from TEMS is an example to an
originating call.

The Channel request command is followed by Paging request message (Figure ) which is sent

on the CCCH (Common Control Channel) by the network to up to two mobile stations to trigger
channel access by these.

System Information Type 13 (Figure ) message is sent to determine GPRS options of the cell

with the given ARFCN.

Immediate Assignment message in Figure  is sent on the CCCH by the network to the mobile

station in idle mode to change the channel configuration to a dedicated configuration while
staying in the same cell

CM Service Request message in Figure is sent by the mobile station to the network to request

a service for the connection management sub layer entities, e.g. circuit switched connection
establishment, supplementary services activation, short message transfer.

System Information Type 5 (Figure ) is sent by the network to mobile stations within the cell

giving information on the BCCH allocation in the neighbor cells. When received, this

information must be used as the list of neighboring cells to be reported on. Any change in the

neighbor cells description must overwrite any old data held by the MS. The MS must analyze all

correctly received system information type 5 messages.

Class mark Change message in Figure  is sent on the main DCCH by the mobile station to the

network to indicate a class mark change.

GPRS Suspension Request in Figure  asks system to suspend GPRS.

Ciphering Mode Command message (Figure 14) is sent on the main DCCH from the network to

the mobile station to indicate that the network has started deciphering and that enciphering and

deciphering shall be started in the mobile station, or to indicate that ciphering will not be

performed. This message is followed by a Ciphering Mode complete message (Figure)

Call Set–up message (Figure ) is sent, from either the mobile station or the network, to initiate

call establishment. It consists of below information elements;

–Protocol discriminator

–Transaction identifier

–Message type

–Repeat indicator: The repeat indicator information element is included immediately before the

first bearer capability information element when the in–call modification procedure is used.

–Bearer capabilities: In the mobile station to network direction, at least one bearer capability

information element must always be present. In the network to mobile station direction, the

bearer capability information element may be omitted in the case where the mobile subscriber is

allocated only one directory number for all services.

–Mobile identity: May be included by the calling mobile station to identify the calling mobile

station.

–Facility: May be included for functional operation of supplementary services.

–Progress indicator: Included in the event of interworking or in connection with the provision of

in–band information/patterns.

–Signal: Included if the network optionally provides additional information describing tones.

–Calling party BCD number: May be included by the network to identify the calling user.

–Calling party sub–address: Included in the Mobile Station–to–network direction when the

calling user wants to indicate its sub address to the called user. Included in the network–to–

Mobile Station direction if the calling user includes a calling party sub–address information

element in the SETUP message.

–Called party BCD number: The called party BCD number information element is included by

the network when called party number information is conveyed to the mobile station. The called

party BCD number shall always be included in the mobile station to network direction.

–Called party sub– address: Included in the Mobile Station–to–Network direction when the

calling user wants to indicate the called party sub address. Included in the Network–to Mobile

Station direction if the calling user includes a called party sub address information element in the

SETUP message.

–Repeat indicator: The repeat indicator information element is included when the in–call

modification procedure is used and two low layer compatibility information elements are

included in the message.

–Low layer compatibility: Included in the MS–to–network direction when the calling MS wants

to pass low layer compatibility information to the called user. Included in the network–to–mobile

station direction if the calling user included a low layer compatibility information element in the

SETUP message.

–Repeat indicator: The repeat indicator information element is included when the in–call

modification procedure is used and two high layer compatibility information elements are

included in the message. The repeat indicator information element is not included when the

optional high layer compatibility information elements are omitted.

–High layer compatibility: Included in the MS–to–network direction when the calling MS wants

to pass high layer compatibility information to the called user. Included in the network–to–

mobile station direction if the calling user included a high layer compatibility information

element in the SETUP message. This information element may be repeated if the in–call

modification procedure is used. Bearer capability, low layer compatibility, and high layer

compatibility information elements may be used to describe a CCITT telecommunication service,

if appropriate.

–User–user: Included in the calling mobile station to network direction when the calling mobile

station wants to pass user information to the called remote user. Included in the network to called

mobile station direction when the calling remote user included a user–user information element in

the SETUP message.

System Information Type 6 (Figure ) is sent on the SACCH by the network to mobile stations

within the cell giving information of location area identification, of cell identity and various other

information.

SACCH –Slow Associated Control Channel is used to transmit system information or

measurement reports. One SACCH period corresponds to 0.48 second. The free time slots on

TCH are used as SACCH when needed.

SACCH DL transmits system information messages to MS during calls. SACCH UL is used to

transmit measurement reports from MS to BTS. SACCH is also used for Mobile originated

(Connection initiated by the MS) or Mobile terminated (Connection initiated by the network

towards MS) SMS when a call is simultaneously on.

FACCH –Fast Associated Control Channel is used to transmit Handover commands, last

messages of call setup and call clearing messages. These messages are sent on TCH by using the

TCH in signaling mode. No speech or data is transmitted while the TCH is used as FACCH.

Measurement Report message (Figure ) is sent on the SACCH by the mobile station to the

network to report measurement results about the dedicated channel and about neighbor cells. This

message is repeated for every new measurement report to generate neighbor lists and is the basis

for handover command.

Call Proceeding message (Figure ) is sent by the network to the calling mobile station to

indicate that the requested call establishment information has been received, and no more

call establishment information will be accepted.

Assignment Command message (Figure 1) is sent on the main DCCH by the network to the

mobile station to change the channel configuration to another independent dedicated channel

configuration. Below are some definitions of information given in this message.

–Channel mode information element appears if the channel mode is changed for the channel

defined in the mandatory part of the message.

–Channel description information element appears in the case of a so–called intracell handover or

an assignment occurring after a call reestablishment if the MS carries two connections (on two

dedicated channels).The connection using the channel previously defined in the mandatory part

of an ASSIGNMENT COMMAND or HANDOVER COMMAND message shall use the channel

defined in the mandatory part of the ASSIGNMENT COMMAND message defining the new

configuration.The first indicated channel carries the main DCCH. The SACCH used is the one

associated with that channel.

–Channel mode 2 information element appears if the channel mode is changed for the channel

defined in the optional channel description information element.

–Mobile allocation information element appears in the case of frequency hopping. It applies to all

assigned channels.

–Starting time information element appears in particular if a frequency change is in progress.

After this command comes Assignment Complete (Figure 2 ) message.

ANALYSIS of LOG FILES

Coverage Problems

Low signal level is one of the biggest problems in a Network. The coverage that a network

operator can offer to customers mostly depends on efficiency of network design and investment

plans. This problem usually pops up when building a new Network or as the number of

subscribers increases by the time resulting in new coverage demands.

Low signal level can result in unwanted situations that could directly lower the network

performance. Poor coverage problems are such problems that are really hard to solve, because it

is impossible to increase coverage by optimizing network parameters. Any hardware

configuration changes might improve the coverage a little.

Let’s have a look at some different cases to poor coverage related problems.

Get paid to share your links!

Solutions to Low Level Problems

Possible solution ways can be listed as below:

–New Site Proposal

–Sector Addition

–Repeater

–Site Configuration Change (Antenna Type, height, azimuth, tilt changes)

–Loss or Attenuation Check ( Feeders, Connectors, Jumpers, etc..)

The best thing to do in case of low signal strength could be recommending new site additions. A

prediction tool with correct and detailed height and clutter data supported with a reasonable

propagation model could be used to identify the best locations to put new sites. If client is not

eager to put new sites because of high costs to the budget or finds it unnecessary because of low

demand on traffic, then appropriate repeaters could be used to repeat signals and improve the

coverage. Adding repeaters always needs extra attention because they can bring extra interference

load to the network. The received level in the repeater should be above –80dBm (or desired

limits) so that it can be amplified and transmitted again. The mobile should not receive both the

original and the repeated signals at the same area, cause signal from the repeater is always

delayed and it will interfere with the original signal. A repeater should not amplify frequencies

outside the wanted band.

If none of the above recommendations are accepted by the client, then cheaper and easier ways

should be followed. First things to be checked would be possible attenuation on the cells. Faulty

feeders–jumpers–connectors or other faulty equipment, high combiner loss, reduced EIRP,

decreased output power, the orientations and types of antennas, unnecessary downtilts, existence

of diversity and height of the site should be deeply investigated. Putting higher gain antennas,

increasing output power, removing attenuations, changing antenna orientations towards desired

area, reducing downtilts, replacing faulty equipment or usage of diversity gain could improve the

coverage.

Please note, amplifiers (TMA or MHA) could be used to improve uplink or compensate the loss

caused by long feeder. Be careful, because they will also amplify interfering signals and they will

be received at higher level.

Quality Problems

Indicators collected from the network which give information about the speech quality are:

– Dropped calls due to bad quality

– Call releases due to bad quality

– Handover failures

– Handover, quality controlled

– Intra–cell handover, quality controlled

– RXQUAL distribution

– FER measurements/distributions

BER and FER

Let’s remember BER– Bit error Rate and FER– Frame Erasure Rate

expressions:

The speech quality is degraded by high BER for the air interface. The BER

and frame erasure ratio (FER) are dependent on a number of factors such

as fading and interference. Therefore a good cell planning is needed to

avoid co–channel interference, adjacent–channel interference, time

dispersion and other types of radio interference. The BER and FER

caused by the radio network is the most important speech quality degradation

factor. The degradation can be minimized by using the radio network

features DTX, Power control and Frequency hopping. The handovers while

moving from cell to cell will also introduce a speech quality disturbance.

Bad Quality due to Signal Strength – FER is Bad (Figure )

SQI

SQI, Speech Quality Index is another expression when Quality is

concerned:

The need for speech quality estimates in cellular networks have been

recognized already in the GSM standard, and the RxQual measure was

designed to give an indication of the quality.

However, the RxQual measure is based on a simple transformation of the

estimated average bit error rate, and two calls having the same RxQual

ratings can be perceived as having quite different speech quality. One of

the reasons for this is that there are other parameters than the bit error rate

that affects the perceived speech quality. Another reason is that knowing

the average bit error rate is not enough to make it possible to accurately

estimate the speech quality. A short, very deep fading dip has a different

effect on the speech than a constant low bit error level, even if the average

rate is the same.

The TEMS Speech Quality Index, which is an estimate of the perceived

speech quality as experienced by the mobile user, is based on handover

events and on the bit error and frame erasure distributions. The quality of

speech on the network is affected by several factors including what type of

mobile the subscriber is using, background noise, echo problems, and radio

channel disturbances. Extensive listening tests on real GSM networks have

been made to identify what type of error situations cause poor speech

quality. By using the results from the listening tests and the full

information about the errors and their distributions, it is possible to

produce the TEMS Speech Quality Index. The Speech Quality Index is

available every 0.5 second in TEMS and predicts the instant speech quality

in a phone call/radio–link in real–time.

Collusion of MA List Causing Low C/I (Figure )

C/I Aspect

Co–channel interference is the term used for interference in a cell caused

By carriers with the same frequency present in other cells.The GSM

specification states that the signal strength ratio, C/I, between the carrier,

C, and the interferer, I, must be larger than 9 dB. However it is generally

recommended to use C/I >12 dB as a planning criterion. If frequency

hopping is implemented, it adds extra diversity to the system corresponding

to a margin of approximately 3 dB.

One must remember that interference does not only appear on the down–

link, but also on the uplink. If interference on the downlink is experienced

in one cell, there is a risk that you would have this problem on the uplink as

well. Not in the same cell, but in the interfering cell. However, downlink

interference is normally a larger problem than uplink interference.

C/I > 12 dB (without frequency hopping)

C/I > 9 dB (with frequency hopping)

C/A Aspect

The distance between adjacent frequencies on the uplink or the downlink is

called channel separation. The channel separation is 200 kHz, regardless of

the standard chosen from the ones mentioned above. This separation is

needed to reduce interference from one carrier to another neighboring

frequency.

Adjacent carrier frequencies (i.e., frequencies shifted ±200 kHz) with

respect to the carrier cannot be allowed to have too strong a signal strength

either. Even though they are at different frequencies, part of the signal can

interfere with the wanted carrier’s signal and cause quality problems.

Adjacent frequencies must be avoided in the same cell and preferably in

neighboring cells as well.

The GSM specification states that the signal strength ratio, C/A, between

the carrier and the adjacent frequency interferer, A, must be larger than –9

dB. However, adjacent channel interference also degrades the sensitivity as

well as the C/I performance. During cell planning the aim should be to

have C/A higher than 3 dB.

C/A > 3 dB

C/A Interference (Figure )

Time Dispersion

Time dispersion may cause problems in environments with, e.g.,

mountains, lakes with steep or densely built shores, hilly cities, and high

metal–covered buildings. The interferer, R, is a time delayed reflection of

the wanted carrier. According to GSM specifications, the signal strength

ratio C/R must be larger than 9 dB (compared to the C/I–criterion).

However, if the time delay is smaller than 15 ms (i.e., 4 bits or

approximately 4.4 km), the equalizer can solve the problem. If there are

quality problems, time dispersion measurements must be taken to verify

that time dispersion is actually causing the poor quality.

By using all or most of the received power, instead of only the direct

signal, there is a larger probability to decode the information. This may be

considered as a type of time diversity.

There are couples of things to remember when dealing with time dispersion

problems:

• Not all reflections are harmful, only low attenuated reflections that are

delayed more than the equalizer can handle.

• The further away the objects are, the weaker the reflections are. Hence,

Get paid to share your links!

objects just outside the ellipse are the ones most likely to cause the

majority of problems.

• For problems to occur, there will, in most cases, be a line of sight from

both mobile and base station to the reflector. Small cells in an urban

environment are not likely to encounter any time dispersion problems.

The distances (time delays) are short, and the buildings will shield

from, and also scatter the reflections.

Reflections are a function of the location of the site and mobile. Therefore

none of the radio network features are of much help in combating

reflections. Frequency hopping does not improve on BER that is due to

reflections (C/R).

The most radical solution is to move a site. A site could be placed near the

reflecting object to prevent time dispersion. Easier and sometimes just as

efficient is to modify the antenna arrangement, either in azimuth

(horizontally) or by tilt (vertically). Those measures may also be used to

improve C/I. For down–tilt to be efficient, antennas with narrow vertical

lobes would be needed to avoid illuminating the reflector.

Bad Quality due to Time Dispersion (Figure )

Inter–system Interference

Sometimes the planning is restricted by interference from external sources,

such as other cellular systems in the same area operating on adjacent

frequencies, or old microwave links or military equipment operating on

certain frequencies within or close to the band.

This type of interference is often very difficult to control (avoid), and must

thus be considered in the frequency planning. One possible countermeasure

is to avoid disturbed frequencies on a certain site, or sites in a certain

region.

If interference from external sources are anticipated or suspected,

measurements are normally performed in order to get a clear picture of the

situation. RFI measurements, utilizing a spectrum analyzer, is a common

approach.

Propagation Behavior

Propagation properties are different across the frequency spectrum. Many

factors including absorption, refraction, reflection, diffraction, and

scattering affect the wave propagation.

The fast fading signal (peak–to–peak distance ≈ l/2) is usually present

during radio communication due to the fact that the mobile antenna is

lower than the surrounding structures such as trees and buildings. These act

as reflectors. The resulting signal

consists of several waves with various amplitudes and phases. Sometimes

these almost completely cancel out each other. This can lead to a signal

level below the receiver sensitivity. In open fields where a direct wave is

dominating, this type of fading is

less noticeable.

Short–term fading is Rayleigh distributed with respect to the signal voltage.

Therefore, it is often called Rayleigh fading. This type of fading affects the

signal quality, and as a result some measures must be taken to counter it.

The first and most simple solution is to use more power at the

transmitter(s), thus providing a fading margin. Another way to reduce the

harm done by Rayleigh fading is to use space diversity, which reduces the

number of deep fading dips.

Handover

Mobiles in communication with the network will continuously perform measurements on serving

and neighboring cells. The measurement results are sent to the BSC and used in the locating

procedure to make decisions about handover. There are different types of handovers:

· Intra BSC handover: The new and old cells both belong to the same BSC. The BSC can handle

the handover on its own.

· Inter BSC handover: The new and old cells belong to different BSC but the same MSC/VLR. In

this case the MSC/VLR must help the BSC to carry out the handover.

· Inter MSC handover: The new and old cells belong to different MSC/VLR. The serving

MSC/VLR must get help from the new MSC/VLR to carry out the handover.

· Intra cell handover: No change of cell but of connection within the cell.

During a call, the serving BSC decides that a handover is necessary. The handover procedure

happens in this way:

• The serving BSC sends Handover Required, including the identity of the target cell, to the

MSC.

• The old MSC asks the new MSC for help.

• The new MSC allocates a handover number (ordinary telephone number) in order to reroute

the call. A handover request is sent to the new BSC.

• The new BSC, in cases where there is an idle TCH in the target cell, tells the new BTS to

activate a TCH.

• The new MSC receives the information about the new TCH and handover reference.

• The TCH description and handover reference is passed on to the old MSC together with the

handover number.

• A link is set up from the old MSC to the new MSC.

• A Handover Command message is sent on a signaling channel (FACCH) to the MS with

information about which frequency and time slot to use in the new cell and what handover

reference to use in the HO access burst.

• The MS tunes to the new frequency and sends HO access bursts on the FACCH. When the

new BTS detects the HO access burst it sends physical information containing timing advance

to the MS on the FACCH.

• The old MSC is informed (via, the new BSC and the new MSC) about the detection of HO

bursts. The new path through the group switch in the old MSC is set–up.

• A handover complete message is sent from the MS. The new BSC and MSC inform the old

MSC. The old MSC informs the old BSC and the old TCH is released.

The originating MSC retains the main control of the call until it is cleared. This MSC is called the

anchor MSC. Because the call entered a new LA the MS is required to perform a location

updating when the call is released. During the location updating, the HLR is updated and sends a

Cancel Location message to the old VLR telling it to delete all stored

information about the subscriber.

Handover decision is given following order of priority :

– RXQUAL

– RXLEV

– DISTANCE

– PBGT

Handover in Layer 3 Messages (Figure)

s

Let’s have a look at Layer 3 messages to understand better about the Handover process.

Synchronization Channel Information (Figure ) message is sent on the SCH, which is one of

the broadcast channels. Its purpose is to support the synchronization of a MS to a BSS and is

repeated for many times during the call.

Synchronization between BSS and MS is controlled by collecting Synchronization Channel

Information for each channel. Synchronization Channel Information message continuously

appears in Layer 3 messages display window. This message is sent on the SCH, which is one of

the broadcasts. Its purpose is to support the synchronization of a MS to a BSS. This measurement

is performed on downlink and contains carrier, BSIC and TDMA frame number information.

System Information Type 5 message (Figure ) is sent on the SACCH by the network to mobile

stations within the cell giving information on the BCCH allocation in the neighbor cells. This

downlink information will later form neighbor lists. When received this information must be used

as the list of neighboring cells to be reported on. Any change in the neighbor cells description

must overwrite any old data held by the MS. The MS must analyze all correctly received system

information type 5 messages.

Meanwhile MS performs consecutive measurements to create neighbor lists. Measurement

Report message (Figure ) is sent on the SACCH by the mobile station to the network to report

measurement results about the dedicated channel and about neighbor cells. It contains RXLEV

and RXQUAL information of the serving carrier and list of best neighbors sorted by best RXLEV

value. BCCH and BSIC information of the neighbor cell are also in this message. Consecutive

neighbor measurement reports are performed during the process to update neighbor lists.

Handover decision process continues with System Information Type 6 message (Figure )

which is sent on the SACCH by the network to mobile stations within the cell giving information

of location area identification, of cell identity and various other information.

Handover command message (Figure ) is sent on the main DCCH by the network to the

mobile station to change the dedicated channel configuration. The message contains Cell

description, Channel description, Handover reference, Power command, Synchronization

indication, Cell channel description, Channel mode, Channel description, Channel mode 2,

Frequency channel sequence, Mobile allocation and starting time information.

Cell channel description information element appears if frequency hopping is used on the new

cell. Channel mode element appears if the channel mode is changed for the channel defined in the

mandatory part of the message. Channel description information element appears if the MS

carries two connections (on two dedicated channels). The connection using the channel

previously defined in the mandatory part of an assignment command or handover command

message shall use the channel defined in the mandatory part of the handover command message

defining the new configuration.The first indicated channel (i.e. in the mandatory part) carries the

main DCCH. The SACCH used is the one associated with that channel.

Channel mode 2 element appears if the channel mode is changed for the channel defined in the

optional channel description information element. Frequency channel sequence element is a

combination of mobile allocation element and cell channel description element. It is designed to

allow the sending of the handover command in one signaling block for systems using frequency

hopping. If this element is present, then the cell channel description and mobile allocation

information elements are not required. Mobile allocation information element appears if

frequency hopping is used on the new cell. If it appears, it applies to all assigned channels. This

information element cannot appear if the cell channel description information element is not

present. Starting time information element appears if a frequency change is in progress. It refers

to the new cell time.

Handover Access message (Figure ) is sent in random mode on the main DCCH during a

handover procedure.

Handover Complete message (Figure ) is sent on the main DCCH from the mobile station to

the network to indicate that the mobile station has established the main signaling link

successfully.

If handover is not successful for some reason, then comes a Handover Failure message. This

message is sent on the main DCCH on the old channel from the mobile station to the network to

indicate that the mobile station has failed to seize the new channel.

Types of Handover

Power Budget Handover (Figure )

When signal strength difference between serving cell and neighbor cell

exceeds Power Budget Handover margin which is set in Handover

parameters, the call is handed over to the neighboring cell. This margin is

usually set to 3 to 6 dB. Power Budget HO feature should be enabled for

this type of Handover.

In case of ping–pong handovers between the same two cells, power budget

handover margin between the two could be increased to reduce number of

handovers. Margin should be decreased if faster handover decision is

wanted.

Please keep in mind that adjusting power budget handover margin between

two neighbors is something you have to pay extra attention. If it is not set

correctly, there is high risk of interference. The strongest cell will not serve

in the cell border area resulting C/I (Carrier to Interference ratio) to get

bad.

Another risk will be stepping stone effect. Let’s investigate this effect with

an example:

Assume we have below power budget handover margins between three

neighbors.

A to B HO Margin PBGT = 0

A to C HO Margin PBGT = +10

B to C HO Margin PBGT = 0

In an area where signal strength of cell A is the weakest and signal strength

of cell C is strongest, the HO attempt might happen in such an order that

cell A will first hand the call to B and cell B will immediately hand it to

cell C. In this case, cell B will be used as a stepping stone to make a

handover to the strong cell C. You will observe ping–pong or unnecessary

handovers.

Ericsson uses KOFFSET and LOFFSET parameters to set this margin

between the neighboring cells depending on the selected handover

algorithm. KOFFSET stands for handover decision based on signal strength

while LOFFSET does on path loss.

Level Handover

If downlink level is worse then HO Thresholds Lev DL parameter, then an

immediate level handover takes place. This parameter is set to –95dBm as

default.

If uplink level is worse then HO Thresholds Lev UL parameter, then an

immediate level handover takes place. This parameter is set to –105dBm as

default.

Quality Handover (Figure )

If downlink quality is worse then HO Thresholds Qual DL parameter, then

an immediate quality handover takes place. This parameter is generally set

to 3.2%–6.4%. If uplink quality is worse then HO Thresholds Qual UL

parameter, then an immediate quality handover takes place. This parameter

is generally set to 3.2%–6.4%.

Interference Handover

Any quality problem when downlink signal level is higher then HO Thr

Interference DL causes a handover. This level is generally set to –80dBm.

Any quality problem when uplink signal level is higher then HO Thr

Interference UL causes a handover. This level is usually set to –80dBm.

Umbrella Handover

Macro site which is defined as umbrella will shift all the TCH traffic to

small sites until signal level of small site becomes worse then HO Level

Umbrella RX Level parameter. This parameter could be set from –80 to –

90dBm. HO Margin PBGT parameter should be set to 63 maximum to

prevent any power budget handover.

Umbrella HO feature should be enabled for this type of Handover.

MS Distance Handover

MS Distance HO Threshold parameter MS Range Max should be set to

desired value with the required Px–Nx Sampling values. This parameter is

set to max 63 as default which corresponds to maximum Time advance

value.

If an overshooting site is needed to hand its traffic after some distance from

its origin, MS Range Max value could be adjusted to limit the serving area

of the site.

MS Distance Process feature should be enabled for this type of Handover.

Intra–cell Handover (Full Rate to Half Rate) (Figure )

The Intra–cell Handover feature aims to maintain good quality of a

connection by performing a handover to a new channel within the same cell

when bad quality is detected. If the signal strength is very high, the

interference is probably lower on another channel within the same cell.

Intra–cell Handover aims at improving the carrier–to–interference ratio,

C/I, for a connection when the bit error rate estimation, RXQUAL, has

indicated poor quality, and the received signal strength at the same time is

high. This is done by changing the channel within the cell, a so called

intra–cell handover. The intra–cell handover can be triggered from bad

quality in the uplink, as well as the downlink.

Intra–cell handover decision is given when serving cell is the best cell and

quality is worse then 4 and signal strength is lower then –85dBm.

Intra–cell handover can solve temporary co– and adjacent channel

interference as well as intermodulation problems, but permanent

interference and time dispersion cannot be solved. Intracell Handover

feature should be enabled for this type of Handover.

Rapid Field Handover

In some cases, UL RX Level suddenly decreases because of the terrain –

generally in tunnels. This sudden level drop happens so fast that it is

usually too late to give a handover decision for the BSC and call drops.

This type of drop is called Rapid Field Drop.

There is still a way to save the call and hand it to one definite neighbor that

is known to be the best handover candidate in such cases. This is done by

handing the call to a chained cell whenever a threshold is reached in Uplink

direction. The handover candidate has to be defined as Chained Adjacent

Cell to the target cell to take the call regardless of any other neighbors in

the area. This threshold is set with the parameter HO Thr Rapid Lev UL. Its

value is –110dBm by default.

Rapid Field handover decision could be given faster by adjusting Px

sampling speed value if needed.

Directed Retry Handover

When no TCH is available in the serving cell, TCH can be allocated in an

adjacent cell regardless of mobile originated or mobile terminated call. It is

basically handover from SDCCH to TCH. Handover candidates are ranked

based on radio properties.

SDCCH handover should be enabled to have use of this type of handover.

Handover Problems

Always keep in mind that all power related parameters need to be correctly

set. Otherwise the handover (HO) attempts will be done in a wrong place.

There will always be risk of a handover loop if handover parameters

between two neighbors are not correctly set.

Late Handover (Figure )

There will be such cases that you will notice handover process taking place

a little late. There could be couple of reasons to that. First thing to check

will be handover margins between the neighbors. If margins for level,

quality or power budget handovers are not set correctly, handover will not

take place at the right time. If margins are too much, handover will happen

late, vice versa.

If umbrella handover is enabled between two neighbors, you will notice

that the small site will still keep the traffic although the level of umbrella

cell id too much higher. This is due to HO Level Umbrella RX Level which

is set to some definite level.

Power Control Effect (Figure )

Power Control feature also misleads planners sometimes. Looking to their

RX Levels on TEMs Line charts, you might think that handover is

happening too late between two neighbors. HO margins look fine and

umbrella HO is disabled. Remember that power balance is possible only on

traffic channels, but not in broadcasting channels. You will sometimes

notice that the call you are continuing is on a timeslot that belongs to TCH

TRX. In this case, power control feature will try to reduce output power as

much as possible until a quality problem occurs. That’s why you will see

your serving cell signal level is less than neighbor’s level. It looks less but

in reality, the signal level on BCCH TRX is still higher than neighbors

broadcasting level.

Ping–Pong Handover (Figure )

If measurement analysis shows an inconsistency in the parameter setting,

hysteresis and offset parameters can be tuned to improve network quality.

A hysteresis is used to prevent the ping–pong effect i.e., several

consecutive handovers between two cells. The ping–pong effect can be

caused by fading, the MS moving in a zigzag pattern between the cells, or

by non–linearities in the receiver.

Incorrect handover margins will cause ping–pong handovers. You will

have to adjust these margins in such a way that handover will happen at the

right time, not earlier or late.

Remember, lack of dominant server in an area or too many overlapping

coverage can also cause ping–pong effect.

Ping–Pong Handover due to Lack of Dominant Server

Unnecessary Handover (Figure )

Just like ping–pong handover effect, incorrect margins can cause

unnecessary handovers that will directly affect network performance. The

more number of handovers, higher the risk of facing quality problems or

even drop calls.

Unnecessary handovers or ping–pong handovers will decrease the

efficiency of data networks.

Unnecessary Handover – Adjust Power Budget Handover

Missing Neighbor Relation (Figure )

If a handoff is not performed to a neighbor cell that seems to be best server,

there is a possibility of a missing neighbor relation. This will happen with

sudden appearance of strong cell in the neighbor list just after a handover.

Fake Neighbor (Figure )

Sometimes you will see a good handover candidate in the neighbor list but

handover will not take place and call will drop. Although that neighboring

cell with a very good signal level appears to be a neighbor, in reality it is

not. Just because the serving cell has another neighbor with the same

BCCH, this cell appears in the list

Get paid to share your links!

BCCH Missing from Serving Cells MBCCH list

There will be cases you will notice handover is not taking place although

two cells are defined as neighbors to each other. If neighbors BCCHNO is

missing from serving cells MBCCHNO list, MS will not monitor or report

the neighbors BCCH frequency. This will prevent HO attempt to the

neighbor.

NCC Missing from Serving Cells NCCPERM List

If neighbors NCC (Network Color Code – first number in BSIC) is missing

from serving cells NCCPERM list, then MS will not be allowed to include

the neighbor in the measurement report, because its NCC is not permitted.

This will result HO attempt not to happen.

The Same BCCH&BSIC Combination

During calls the MS reports the BCCH, BSIC and Signal strength of the six

strongest neighbors to the BSC. BSC has to map the neighbors

BCCHNO&BSIC combination to neighbors CGI (Cell Global Identity –

combination of MCC–MNC–LAC and CI). Therefore all neighbors of

same cell shall have a unique BCCHNO&BSIC combination.

Let’s remember what BSIC is;

The MS attempts to decode the BSIC – base station identity code,

parameter for each of the six strongest surrounding cells at least every 30

seconds, to confirm that it is still monitoring the same cells. The BSIC

parameter consists of two parts; NCC, Network Color Code and BCC, Base

Station Color Code. If another BSIC is detected, it will be treated as a new

carrier and the BCCH data for this carrier will be determined.

Otherwise the BSC will start a HO attempt always to the first neighbor will

matching BCCHNO&BSIC combination even though the MS may have

reported another neighbor having the same combination.

Unexpected Coverage Lake

If cell B has a lake of strong coverage inside cell A and cell B is not a

Get paid to share your links!

neighbor and cell C is a neighbor and the BCCHNO&BSIC combination is

the same in cells B and C, then BSC will start a HO attempt to cell C, when

the Ms has monitored/reported the cell B.

One–Way Neighbor Relation

A neighbor relation needs to be defined as mutual. When defining cell A

and Cell B as neighbors to each other, neighbor relation from A to B and

from B to A have to be defined. Otherwise the HO attempt is not possible

in both directions.

Please remember there will be rare cases where planner will need one–way

neighbor relations.

Neighbor Cell in an other BSC

You will always observe handover problems in BSC borders, because

neighbor relations in these cases need extra attention. When the neighbor is

in another BSC, the neighbor needs to be defined as an external cell in

neighboring BSC with correct CGI, BCCHNO, BSIC and power related

parameters. This must also be like this on the other way to have a mutual

neighbor relation.

If the neighboring cell belongs to a different MSC, the cell needs to be

defined as an outer cell in neighboring MSC with correct CGI and MSC

name/address. This must also be like this on the other way to have a mutual

neighbor relation.

Handover not Happening and Dropped Call: The call is not handed to the other cell
although the level of the neighboring cell seems to be good enough. This example looks like fake
neighbor case. After making sure all handover parameters between these two cells are correctly
set, you should look for a neighboring cell to the serving cell with the same BSIC and BCCH
combination. The cell that appears in the neighbor list is not a neighbor to the serving cell in
reality. Just because there is another neighboring cell with the same BCCH, TEMs measures this
BCCH and lists as a neighbor. Handover will not happen because those two are not neighbors in
reality.

Handover Failure

Reasons for handover failure could be unavailable time slots because of

high traffic, congestion, low signal strength or bad quality (Figure ) on

target cell. Handover can be failed because of hardware problems (Figure) in target cells –more likely TRX or time slot problems.

If handover attempt fails, MS tries to return to old channel. If it can not,

call drops. Handover attempt is repeated after a penalty time

Handover Failure: Handover attempt was failed and the call returned back to its all
channel.

Excessive Number of Handover Failure due to Hardware Problem

Drop Calls

If the radio link fails after the mobile sends the Service Connect Complete Message then it is

considered a dropped call. Dropped call analysis can consume a considerable amount of time.

Using good post–processing analysis tools, the root cause of some of the drops can be determined

from mobile data alone. However, there will be cases where the cause cannot be reliably

confirmed unless system data is also used.

Calls often drop when strong neighbors suddenly appear. When the mobile is suddenly

confronted with a strong new signal, or when the signal it is using takes a sudden deep fade, it

will have poor C /I o and high forward FER. The call will drop unless it gets help quickly.

Using a post– processing tool, display a map of the locations of dropped calls that exhibit

symptoms of poor coverage. Verify this type of drop is not occurring in good– coverage areas. If

so, suspect and investigate hardware at the serving site.

Use the prediction tool to help identify other strong signals reaching the drop areas.

Another technique is to examine the dropped call message files and identify the BTS from which

the sync channel message is received immediately after each drop (this will be the cleanest pilot

the handset sees at that time). This could be achieved by analyzing Layer 3 messages in log files

or running traces from NMS/OSS.

Drop calls can be classified by looking to their orientations:

• TCH radio drops are the drops that occurred due to summation of radio and ABIS reasons.

• TCH non–radio drops are the drops that occurred due to summation of network management,

BSCU reset, BTS fail, LAPD failure, user and A interface.

• TCH handover drops are the drops that occurred in handover phase while the call tries back to

old serving channel but fails and drops. These drops may occur due to RF, ABIS and A

interface reasons.

General Reasons for Drop Calls are as follows:

·       Drop Call due to Low Signal Strength

·       Drop Call due to Missing Neighbor

·       Drop Call due to Bad RX Quality

·       Drop Call due to Not–happening Handover

·       Drop Call due to Interference

·       Radio Failures

·       Radio Failures on old Channel in HO

·       Transcoder Failures.

·       Transcoder Failures of old Channel in HO

·       Abis Failures on old Channel in HO

·       Lapd Failures

·       BTS failures

·       Failures due to User Actions

·       Failures due to BCSU Reset

·       Failures due to Radio Network Configuration Action

·       Channel Activation Failures During Call

Dropping Call due to MS Stuck on Overshooting Cell: In this example, MS is stuck
on an overshooting cell which is far away. You may check Time advance value in the Radio
Parameters window. MS can not handover to another cell because this overshooting cell was not
defined as neighbor to the cells nearby as expected. The only way to leave that cell and restart
call on a nearby cell will be possible after the call is dropped.

REPORTS of ANALYSIS

Below are some example recommendation reports those were provided to the clients during

previous optimization projects.

Downtown Seattle Network Performance Recommendations

A Drive Test was performed in Downtown Seattle on 05/21/02 by WFI team. The selected route

starts with AT&T Eastlake Office, includes most of the major and primary roads in the

downtown area and ends with China town in the south. Two MSs were used during the test. One

was acting like an ordinary Mobile phone on dedicated mode and the other was scanning the

1900MHz frequency band. RXQual & RXLev Plots are attached for your reference. The

following recommendations are being given after analyzing the drive test data:

1– Below missing neighbor relations were observed:

1.     Eastlake 179A – DennyWay216B

2.     Olive Street 209A – Blanchard 6th 374C

3.     Olive Street 209A – Waterfront Seattle 186B

4.     Blanchard 6th 374C – Battery Street 191A

5.     Lenora 3rd 426A&B – Waterfront Seattle 186B

6.     Convention Center 185A – Dennyway and Steward 216B

7.     Lenora 3rd 426A – Pike Street 208A

8.     Alaskan Way 211B – Pike Street 208A

9.     2– Below Co–Channels were observed:

10.  Waterfront Seattle 186B – Safeco Field SW 212A (CH589)

11.  Lenora 3rd 426A – Safeco Field NE213A (CH606)

12.  Key Tower 195B – Capitol Hill 180C (CH596)

13.  Blanchard 6th 374C – Convention Center 185A (CH604)

14.  International District 375C – Key Tower 195C (CH599)

15.  Battery Street 191A – Union#2 210A (CH593)

16.  Dexter 206A – Lenora & 3rd 426B (CH597)

17.  Olive Street 209A – First Hill 214B (CH603)

18.  Harrison 173A – Interbay 188A (CH600)

19.  Safeco Field NE213A – Spokane Street 178B (CH606)

20.  3– Below adjacencies were observed:

21.  Olive Street 209A – Blanchard 6th 374C (603–604)

22.  International District 375C – Safeco Field NE 213B (599–600)

23.  Convention Center 185A – Capitol Hill 180B (604–605)

4– Northlake 122B is overshooting and causing interference on Blanchard 6th 374B. They have

the same BCCH (608). Increasing the downtilt on Northlake is recommended.

Woodlandpark 116A is overshooting in the northern downtown as well. It has the same BCCH

(595) with Alaskan Way 211B and causing low speech quality. Decreasing EIRP on

Woodlandpark 116A by 3dB will prevent it overshooting. Alaskan Way 211B is also interfered

by Spokane Street 178C.

University District 137B is overshooting near Dennyway and interfering with Blanchard 6th 374A

(594). Retune recommended.

5– 4th & Pike 172B is being interfered by Harbor Island 175A (591). Uptilt on Harbor Island

175A is recommended.

Blanchard 374C is being interfered by Woodinville 145A (604).

Union#2 210A is being interfered by White Center 184A (593). White Center should be

sectorized and the antenna facing to downtown should have reduced power.

6– Proposed site Spring&3rd will bring a best server to 3rd & Marion Street and prevent

Waterfront 186B serving there.

7– Other proposal First&Columbia will serve on 2nd Ave and prevent Safeco Field serving out

there. It will as well prevent Ping–Pong handovers between International District 375C / Safeco

Field NE 213A and Key Tower 195B.

8– Increasing EIRP for Pier70 204A by 6dB is recommended. This will pop it up on the area

where 2nd & 3rd Ave starts. It will also prevent Ping–Pong handovers between Harrison 173A and

Pier70 204A. Harrison 173A is interfered by Interbay 188A (600). Retune recommended.

9– Safeco Field and International District are causing many interBSC handovers in the area. If

BSC border could be shifted to south by moving these two sites from BSC5 to BSC2, HO

performance will be improved.

LAKE SAMMAMISH AREA NETWORK PERFORMANCE

RECOMMENDATIONS

A Drive Test was performed on 06/10/02 by WFI team. The selected route covers all around

Lake Sammamish and some part of Bellevue on the west specifically near site Crossroads. Also a

trouble ticket of a customer complaint was taken with and that problematic area was driven. Two

MSs were used during the test. One was on dedicated mode and the other was scanning the

1900MHz frequency band. RXQual & RXLev Plots are attached for your reference. The

following recommendations including site configuration changes proved by before and after plots

are being given after analyzing the drive test data:

1– Sunset Village should be sectorized to have better sector gain and improve coverage. The

proposed sectorization is attached in a plot.

2– Site Issaquah is overshooting and overlapping with West Issaquah and South Sammamish

mostly. Rotating sector A from 50 degrees to 30 degrees with keeping the downtilt but

exchanging antenna type with 7250_05_6deg_1900 that has 6 degrees electrical downtilt. The

possible coverage loss after this modification on southeast cost of Lake Sammamish will be

compensated after appropriate modifications to West Issaquah and South Sammamish sectors

described below.

3– Rotating the antennas in South Sammamish Sector C from 340 to 310 degrees and changing

antenna type with 7250_02_1900 for higher gain is recommended. This will help the coverage on

Southwest coast of Lake Sammamish.

Rotating Sector A antennas from 115 to 80 degrees and exchanging the antenna type to a higher

gain antenna is recommended. This will reduce Ping–Pong handovers between South

Sammamish, Issaquah and West Issaquah and improve the coverage in the area.

4– Rotating West Issaquah Sector C from 355 to 10 degrees will help to have a better coverage

on southeast of the lake.

5– Eastgate should be sectorized to have better coverage on East Side of the Lake Sammamish

where a customer complaint has been reported. In this area drop calls due to poor coverage was

observed. The proposal for the sectorization is given in a plot with the following site data:

*Sector A facing to 20 degrees with 0 degrees downtilt on a 7250_05_6deg_1900 type of

antenna having 50 feet’s height and 50dBm EIRP.

*Sector B facing to 100 degrees with 3 degrees downtilt on a 7250_02_1900 type of

antenna having 54.5 feet’s height and 55dBm EIRP.

*Sector C facing to 210 degrees with 0 degrees downtilt on a 7250_05_6deg_1900 type of

antenna having 50 feet’s height and 50dBm EIRP.

6– We were told not to make any changes on Site Gene Beal, because it is a VIP site. If we could

only be able to increase EIRP on both of the sectors, than we could have a better coverage in the

area. If it could be done with the appropriate hardware configuration, adjacencies of this site

should be rechecked. Currently the level is so poor in the area and even Downtown Redmond is

serving there.

7– Overlake Sector A does not handover to Sector B even with level difference of 7 to 10dB.

This is the same case with Factoria Sector B and C.

8– Lack of coverage and poor quality with Ping–Pong handovers on North–Up Way on East of

156th Ave were observed. Changing the antenna type to type 3 for Overlake Sector A and reduce

its downtilt from 5 to 2 degrees is recommended. Also attenuation reduction to 0 is recommended

on Crossroads (All Sectors).

9– Below missing neighbor relations were observed:

405/520 244A – Crossroads 483A

Crossroads 483A – Bridal Trails 139A

10– Drop call on NE 8th street near 156th Ave was observed. South Sammamish 428C is serving

here and its heavily interfered by Crossroads 483B (BCCH 602). It is strongly recommended to

add Crossroads 483A as neighbor to South Sammamish 428C.

11– Drop call on NE 4th Street on west of 156th Ave NE is observed. It is recommended to add

Crossroads 483B as neighbor to West Issaquah 251C.

12– Lack of coverage and poor quality with Ping–Pong handovers near intersection of 148th Ave

NE and NE 8th Street is observed. It is recommended that Lake Hills which is an Omni site to be

sectorized with the high gain antennas facing this intersection.

CONCLUSION

Optimization is a process that never ends. You can always try improving the quality of the

Network by making site configuration changes or changing parameters or try to understand what

is happening in the network by looking into stats. Everybody knows that there is a lot that could

be done by means of optimization but it is always hard to start. People sometimes get lost in stats,

sometimes struggle with parameters or log files.

Below is a chart (Figure 64) that shows how you could start doing optimization and the steps to

be followed. I am sure you will find vital information on the total process. Hope this works..

Get paid to share your links!