Historic cell site analysis – Overview of principles and survey

Presented by Xiao MA

Presentation Structure !  Introduction of CDR ! Mobile network brief ! Access service area ! Data interpretation ! Experiments and results

I. INTRODUCTION of CDR ! CDR=Cell Data Records, stored by

network provider ! Different from your photo, video, music

or local data of social network apps ON YOUR PHONE.

! Generally, CDR records relevant data and info about calls and texts the network operator handles.

Information about CDR ! Time and date of the call ! Phone numbers ! Cell ID of the site where the call begins

and ends ! Generally, only answered calls/texts are

recorded. They are meaningful records.

2.Mobile phone networks-brief ! Cell site !  Sector !  Service/range ! Cell selection(important topic)

Cell site !  In brief, a set of physical devices,

deliberately located and operated to serve a particular area.

Theoretic service area

Cell site

Sectors ! Each cell operates as 3 independently

working Sectors. ! The service area of a sector depends on

geographic characteristics

1

2

3

Theoretically Actually

Service and range ! The service area of a cell, generally,

depends on height of antenna, power, location of other cells and geographic features of the land.

! Range varies from 50m~35km(theoretic limitation of GSM)

! Generally less than 20km for rural area, less than 5km in urban area, 2km in city center.

Cell selection ! The following slides introduces: ! How to pick a cell !  Issues when need to move to another cell

How to pick a cell--1 !  In every “cell site”, there are some area, in

which the cell has significant signal advantage over the signal from other cells

! This is the dominant area. ! Handsets in the dominant area of a cell

are most likely to pick this cell. ! Generally, a handset in the DA of a cell

has line sight to the antenna.

How to pick a cell—2 !  In a cell’s non-dominant area, there may

be several cell signals competing each other.

! Handsets may change the cell serving it in non-dominant area frequently. Unnecessary changes are NOT desired in application.

Move to a new cell—1 If a new cell: ! Has significant power advantage to the

current cell ! And this advantage lasts for a period of

time In IDLE MODE, the handset may move itself to the new cell. This approach avoids frequent PingPong.

Move to a new cell—2 ! During a call(DEDICATED MODE), a

handset may still need to move to a new cell for better signal.

!  In this case the network core need to make a decision for this.

! The network may shift the call so that the call is not affected while the handset is moving to a new cell.

Moving to a new cell—3 !  Sometimes a handset need to move to a

new cell because current cell is congested—current cell say NO to handset albeit current cell may have unparalleled signal advantage.

! Direct retry or BA list

Moving to a new cell—3.1 ! Direct retry: handset manually detect

feasible alternative cells and try connect a cell of them. This action may need network operator consent.

! BA list: Broadcast control channel Allocation list. This list is provided by operator. Handset will only find alternative cells in the BA list.

Presentation Structure !  Introduction of CDR ! Mobile network brief ! Access service area ! Data interpretation ! Experiments and results

3. Assess Service Area ! To know the area over which a particular

cell could be expected to provide service. ! Need to consider a lot of factors ! Theoretic modeling and calculation not

sufficient ! Need precise measurement

Method 1:BSPs ! BSP: Best Server Prediction Plots ! Network Operator calculates which cell

has higher signal strength ! May underestimate the power of other

cells ! Result may be inexact ! Hard to track change with time

Method 2: RF mesurements(Survey)

!  Spot sample: single/a few measurement(s) specific point, specific time

! Location sample: some measurements, specific point, period of time

! Area survey: large number of measurements, area, time:N/A, may with GPS

! Cell survey: very large number of measurements, large area, with GPS

Other RF surveys ! Drive survey: may need specific designed

route. ! Walk survey: similar to drive survey, but at

vehicle inaccessible area

4 Interpreting data ! A lot of factors to consider ! Neighbor cells may serve in the non-

dorminant area of another cell site ! Neighbor data must be considered, but

not as primary data. ! Last cell ID may indicate larger service

area due to different cell selection scheme during dedicative mode.

Ex of Derived service area

! Red: this cell serves these area ! Yellow: this cell considered as handover

candidate

Interpreting data !  For drive survey, the derived service area

can be determined by the observations indicating cell service.

! Determination based on subjective judgment, opinion based.

!  ‘derived service area’ is not rigorous judgment.

Presentation Structure !  Introduction of CDR ! Mobile network brief ! Access service area ! Data interpretation ! Experiments and results

5. Experiments and results ! 2 positions 5m apart in a car park, testing

UK 2G network. ! Using: Crownhill Netmonitor System,

TEMS survey equipment, Engineering handset

Experiments ! Ex1: 5 minute data from Position1 then 2 ! Ex2: location sample from 1 and 2 for 1h

respectively ! Ex3: Spot and Location Samples on 1&2

for 1h, and an area survey of 300 meters from the car park.

! Observe whether cell IDs are providing service, as handover candidate, or not included.

Experiment Summery Ex1 ! Cell IDs monitored by a STATIC sampling

device change over time, as well as between similar devices.

! No single individual device detect all ‘legitimate’ cell IDs either as serving or neighbor.

Experiment Summery Ex2 ! Lengthening a static sample period to 1h

does NOT necessarily generate more consistent or accurate data.

Experiment Summery Ex3 ! Area survey produces most consistent

data ! Most cell ID detected, but still most

consistent

Survey methods pros and cons Survey method Pros Cons Spot sample speed Great variety, false

exclusives Location 5m speed, consider

time period Great variety

Location 1h Speed, consider time period

Slightly less variety than above

Area Minimize non-dominant area inconsistency, clear indication

Complicated massive date generated

Cell Demonstrating the cell service area

Not mentioned in the paper

Questions and doubts ! This paper never mentioned how TEMS

and Engineering handsets are used. ! This paper has confusion expression of

data in Ex1. ! This paper does not quantize the data

before making the solution. They should weight the data and process them by some math to make it.

Question time~