Indoor Building Distributed Antenna System
Introduction
& Objectives:
Indoor sites are built to cater
capacity and coverage issues in indoor compounds where outdoor macro site can’t
be a good solution.
In dense urban clutter where buildings
structures and indoor environment losses are quite large for macro site which
makes it‘s an inappropriate solution. Generally floors underground (basements
and lower ground) have poor RSSI. Major part of reflections takes place from
ground and because of this portion below ground have poor signal coverage.
On the other hand floors above third
have quality and DCR issues. Due to fewer obstacles in the LOS path, path
losses are less compared to ground floors. So there is a multiservers
environment due to less path losses and cells overshooting which leads to ping
pong handovers and interference issues inside the compound.
In urban areas there are buildings
that generate high traffic loads like commercial buildings, offices; shopping
malls may need indoor systems to take care of the traffic demands. For such
areas indoor is the efficient solution regarding cost, coverage and capacity.
In indoors downlink is
the critical link in the air interface. There is no need to use the uplink diversity in an indoor system or use amplifiers like TMA for improving the uplink signal .Multi-antenna indoor system is providing diversity as uplink signals received by several antennas.
the critical link in the air interface. There is no need to use the uplink diversity in an indoor system or use amplifiers like TMA for improving the uplink signal .Multi-antenna indoor system is providing diversity as uplink signals received by several antennas.
In-building solutions DAS-IBS
technology is one of the fastest changes in mobile network rollouts. It has
been estimated that 70-90% of all mobile calls are made inside the buildings;
therefore to improve the QOS, operators today have started concentrating more
on this aspect of network rollouts.
The most efficient way to achieve
optimal quality, coverage & capacity result inside the building is to use
Microcell with Distributed Antennae System (DAS)
Hayat Telecom LCC has set up support
to Venders in rolling out IBS network & gathered both planning tools and
professionals for attaining quality rollouts with utmost levels of customer
satisfaction.
Indoor Building Systems Solution, Specifically
the Solutions of Radio Network Design is needed to enhance QOS and Capacity of
the network. Most of calls are generated from inside of buildings so it ‘does require
special attention for enhancing the network performance’.
The key essentials for a potential
IBS system for planning are:-
- Identification of potential buildings for IBS.Design Distributed Antenna system using passive & active elements and, Prepare complete Link engineering diagram with each antenna's EIRP proposal report.
- Implementation of IBS solution with best professional way without disturbing aesthetic of building.
- LOS & Link Planning to connect site.
- RF parameter planning, RF walk test and call quality testing.
As
moving ahead details of key part explain in detail.
Types
of indoor cells:
There are mainly three types of
indoor cell.
1-Micro Cells
2-Pico cells
3-Femto Cells
Micro cells constitute most of the
indoors deployed for BTS coverage. They are more costly and also on large scale
with respect to Femto or Pico cells. They consist of indoor micro /metro BTS
and distributed antenna system for signal propagation in indoor environment
.Usually they have passive components but where large distance to be required
amplifiers especially optical amplifiers are deployed called active components.
A Pico cell is wireless
communication system typically covering a small area, such as in-building
(offices, shopping malls, train stations, etc.), or more recently in-aircraft.
A Pico cell is analogous to a WIFI access point. In cellular wireless networks,
such as GSM, the Pico cell base station is typically a low cost, small
(typically the size of a sheet of A4 paper and about 2-3cm thick), reasonably
simple unit that connects to a Base Station Controller (BSC). Multiple Pico cell
'heads' connect to each BSC: the BSC performs radio resource management and
hand-over functions, and aggregates data to be passed to the Mobile Switching
Centre (MSC) and/or the GPRS Support Node (GSN).
In telecommunications, a Femto
cell—originally known as an Access Point Base Station—is a small cellular base
station, typically designed for use in residential or small business
environments. It connects to the service provider’s network via broadband (such
as DSL or cable); current designs typically support 5 to 100 mobile phones in a
residential setting. A Femto cell allows service providers to extend service
coverage indoors, especially where access would otherwise be limited or
unavailable. The Femto cell incorporates the functionality of a typical base
station but extends it to allow a simpler, self contained deployment; an
example is a UMTS Femto cell containing a Node B, RNC and GPRS Support Node
(SGSN) with Ethernet for backhaul. Although much attention is focused on UMTS,
the concept is applicable to all standards, including GSM, CDMA2000, TD-SCDMA
and WiMax solutions.
Objective
of IBS design:
The basic aim of indoor building
solution is increasing the quality of indoor signal at different public and
business locations. The Public locations are such as said before Shopping
Malls, Airport terminals, Hospitals, Residential flats and business exhibition centers,
Govt and private offices etc
The fig shown the obligation of IBS
.With BTS site deep indoor signal penetration is not good in dense urban areas
specially in high rise Building Areas.IBS cover this obligation .
IBS Design solution Scenarios:
There
are various solutions that can be implemented for a particular site. For a
design approach, we will select the most cost-effective solution to meet the
performance criteria.
Distributed
antenna network:
The
useful application of antennas in indoor systems is the idea of distributed
antennas. The philosophy behind this approach is to split the transmitted
power among several antenna elements, separated in space so as to provide
coverage over the same area as a single antenna, but with reduced total power
and improved reliability. The smaller coverage footprint of each antenna
element provides for controlled coverage and reduces excessive interference and
spillage effects.
A
distributed antenna system can be implemented in several ways, a number of
which are listed below.
DAS-1-Passive
coaxial network design:
The
network is made up of passive components such as coaxial cable, combiners,
splitters, directional couplers, etc. Antennas that are utilized can be of
wide-bandwidth to support multi-band and/or multi-system requirements. The
advantage of this approach is that the network is simple and requires minimal
maintenance.
DAS
-2-Leaky feeder system:
The
ultimate form of a passive distributed antenna system is a radiating cable
(leaky feeder) that is a special type of coaxial cable where the screen is slotted
to allow radiation along the cable length. With careful design, such cables can
produce virtually uniform coverage. This type of system is best suited for
applications requiring in-tunnel coverage (such as in subways). The radiating
cable in this case is run along the entire length of the tunnel. The cable is
either a radiating coaxial cable or radiating wire.
DAS-3-Fiber
Optic Solution:
In
this method, RF signals are converted to optical signals before being
transmitted to distribution units via optical fibers. Single-mode and
multi-mode fibers can be used but multi-mode fiber requires frequency
conversion before RF- to-optic conversion. The fiber optic solution is ideal
for wide-area deployments such as in buildings with extensive floor areas and
high-rise office buildings. The installation cost can be well contained if the
existing optical fiber infrastructure within a building can be re-used. This
solution is also useful for expanding on an existing distributed antenna system
that is operating on coaxial solutions.
DAS-4-Repeater
Solution:
This
solution is implemented to expand the coverage of an indoor or outdoor cell. If
coverage is to be expanded to an isolated place, a repeater solution can be
used. This input signal to the repeater can be sourced either from an existing
off-the-air RF signal or fiber-fed from a remote location. In large buildings,
where coaxial cable network is required to use, EBTS power will not be enough
to power all the antennas. In this instance, in-line repeaters are used to
boost up RF signal.
DAS-IBS Deployment Design:
Passive IBS
Mostly
passive IBS is deployed as an indoor solution. Passive IBS contains splitters,
couplers, attenuators, combiners, coaxial cable, DAS but there is no active
element involved.
Active IBS
Active
IBS is generally used when the EIRP required is more than the available.
Usually this happen when distance involve are large and antenna elements are
more as well. Active IBS is actually a hybrid IBS as it contains an active
component (repeater) and passive IBS.
DAS-IBS-Design Entities:
Antenna:
Mostly
antennas used in IBS design are Omni directional and flat panel directional
antennas.The selection of antenna types is based on the availability,
feasibility. Retain ability, compatibility and performance with selected
solution .The usage of different type of antennas varies for different physical
atmosphere. The antennas are connected with coax feeders inside the building.
The antenna selection depends upon the general Product Description and
specification shared by venders.
The
Primary Antenna types in IBS design are:
1-Omni directional antenna
2-Directional antenna
3-Leaky cable
1-Omni Directional Antennas
It transmits signal in all direction .it
contain Low gain. Horizontal direction pattern all over the place but vertical
direction concentrated. General specifications of Omni Antenna as below:
Gain 2-3 dbi
Beam
width 360
Polarized
Vertical
VSWR less than 1
2-Directional Antennas:
It
transmits signal in a specified direction. It Contain high gain.
3-Leaky Coaxial Cable:
It
transmits signal along path of the coaxial cable .Contains closely spaced slots
in the outer conductor of the cable to transmit/Receive signals. There atre Two
types of losses in leaky cable.
I-Feeder
loss- cable attenuation loss
II-Coupling
loss-Average signal level difference between the cable and dipole antenna at
distance of 6m approx.
Some
of the general feature reviews of antennas are given below:
Application:
-WiFi System, ISM application
-Indoor/in-building Coverage
-WLAN Communication Application
-CDMA, GSM, DCS, 3G/4GUMTS Application
-Next Gen Mobile-LTE
Features:
-Low return loss
-Wide beanwidth
-Suitable for wall mounting
-Low, aestheticall pleasing profile
Model: XXXXXXXX (Any )
RF Parameters:
-Frequency: In MHz (its selection
depend upon spectrum allocation)
-Polarization: Vertical, Linear
-Horizontal Beam Width: 360 deg
-Vertical Beam Width: 90 deg (698-960MHz band (its selection depend upon
spectrum allocation))
50 deg (1710-2700MHz band (its selection depend upon spectrum allocation))
-Gain: in dBi
-VSWR ≤ 1.5
-F/B >in dB
-Max Power: in “W”
-Impedance: in Ω
Mechanical Specification:
-Radome Material ABS with UV Protection
-Lightning Protection Direct Ground
-Connector N-female
-Weight in kg
-Size in mm
-Operating Temperature Range in degrees
-Storage Temperature in degrees
Different
technologies antennas are available in market. Customer selects it as per need,
services and requirement. i.e dual band antennas supports two band signal, quad
band antennas suppots threes different band signals etc .
In
addition of antennas detail as mentioned above in Passive Coaxial Cable design Distributed
antennas connected with couplers, Power splitters, Jumpers and feeder cable
Link Budget calculations based on how many couplers and Splitters are we used
& Losses of coupler, splitters and feeder cable length in design. In the
marker 20db, 15db, 10db and 6db couplers 2way, 3way and 4 way splitters ½” inch Jumpers, ½”,7/8”,11/4” inch feeders cables are using. Below Figures
indicates how we cater losses of these coupler, splitter and cable.
Power Splitters
Splitters
are used to split antenna feeder network power equally over the output
ports.Two way, three way and four way splitters are generally used.
Splitters Loss:
2-Way
Splitter Loss – around 3 db
3-Way
Splitter Loss- around 5db
4-Way
Splitter Loss- around 6db
Insertion
loss for these splitters is 0 .2db.
Power Couplers:
Couplers
are used to split antenna feeder power unequally among output ports.Couplers
have tap/coupling loss and through loss e.g 10/0.5 coupler means its coupling
loss is 10 while through loss is 5.Couplers generally are available in ratings
of 3, 6, 7, 10, 15 & 20 db.
Attenuators:
Attenuators
are used to reduce EIRP at antennas where less EIRP required but the other antennas required
high EIRP.
Attenuators
are of values 3, 5, 7, 10 etc.
BTS:
The
Base station capacity specification varies in Vander to Vander. The General
specification of base station is same
as off Outdoor Base station or normal Base station.
Building Specifications and Coverage
and Capacity Demands (Expansions): The capacity requirement enhances and fulfilled by adding
extra Transceivers card into the cabinet of IBS_BTS. You can add as many card
as IBS-base station supports.
For
DAS-IBS coverage design regardless any type of DAS accurate building sketch and
dimensions of building are very important .Designer should must required sketch
map of building because defining he marked the route of cable and plan the
coupler and splitter at right place without effecting KPI of deployment and coverage.
For sacking this many tools in the markets are available .Mostly recommended by
Vander.
Initial RF Survey:
Following
are the things which are taken under consideration during initial RF Survey:
- Site(Indoor Building) coordinates
- Site Rough Layout sketch
- RSSI and C/I of strong servers in different location of
indoor site using TEMS pocket view mode.
- No. of subscribers’ estimation/ floor or as the
building architectural division.
- Marking of the different areas what they are specified
for.
- Snaps of different floors
- Building structure observation.
Initial RF survey report:
After
the survey report is made in which all the above inputs are put.
Indoor Site Evaluation:
After
the survey it is checkout if any modifications (Hard / Soft Changes) can be
done to the existing neighboring site to improve the condition at the affected
area. Otherwise Site is evaluated as to be an indoor Micro or wall mounted
metro according to the location, requirements and conditions.
DAS-IBS Designing Tools:
iBwave
Design radio planning software automates the design in-building wireless
networks for optimal voice coverage and data capacity. It eliminates guesswork,
to bring strong, reliable wireless communications indoors. iBwave Design is an
integrated solution that takes RF designers through network planning, design,
costing, validation, documentation and reporting. iBwave Design makes it easy
for RF engineers to test scenarios for optimizing network coverage for 2G, 3G
and 4G cellular technologies, as well as WiFi, public safety bands and
femtocell.
Networks
Networks
- RF System Design and
Calculations.
- Components Database to manage
DAS equipment
- Display DAS equipment position
on floor plans
- Create professional project
documentation
- Create automated reports on IBS
project performance and cost
- Standardize IBS design format
- Propagation Module- Simulate
indoor and outdoor propagation prediction in your building
- Optimization module -
Extrapolate outdoor wireless signals inside the building to analyze signal
quality and data throughput before design phase
- Collection module- import
survey data and trace routes from collection devices, and overlaying
survey data onto wireless indoor network design.
- RF professionals to manage
complex in-building network projects, generating cost efficiency,
increasing productivity and delivering a larger return on investment.
- Below address may help us to review and finalize designing tools. We can ask the IBS design module quotations to all RF Tools Venders after mailing info@ to all link presents..
Planning Tools for Wide Area
Wireless Systems
|
||
Radio Planning Tools
|
||
RF Survey with floor Plan:
Once
the indoor site is finalized, floor Architectural Plans are requested from
building Authorities.
RF survey with Floor Plans is carried, RSSI is
checked & recorded at each and every part of the indoor environment and C/I
is checked at worst.
Drive
test tool idle mode log files for different floors are made using floor plans
provided.
During
the RF survey Detailed Analysis/Observations of the building/environment is
carried out as well as what is the ceiling thickness, floor heights, thickness
of the walls in between floors, thin walls and their thickness.
Antenna
locations are finalized using traditional Ray tracing techniques(By simply
analyzing how reflections and propagation going to occur)
Marking of Priority Area:
In
indoor areas like offices and meeting rooms etc have usually high priority. On
the other hand areas like mosques, gyms etc have low priorities. Similarly area
in which outdoor macro coverage and quality is satisfactory should not be
included in intended coverage area for indoor site. For high priority area
coverage should be around -75 dbm at each point while for low priority area
levels should be around -85 dbm. These values vary according to KPI’s doc of
the network.
Indoor Antenna Placement:
Antenna
placement is the most crucial step in indoor planning. Following observations
should be considered during antenna
placement:
- Antennas especially Omni-directional antennas should be
placed at centralized locations.
- Panels should be placed in the corners of corridors or
where design demands while keeping in view the spillage of indoor signals.
- Antennas should be placed at high elevations where
people can’t touch them as it will affect the performance.
- Obstacle free path should be provided for antennas
otherwise coverage in indoor will suffer a lot.
- Antennas should be placed away from conductive objects.
- Exposure levels of the indoor RF signals are below RF
safety standard of WHO, IRPA, IEEE and FCC. However discretely placed
antenna will reduce the unnecessary public concerns about RF exposure.
- If the building with low traffic capacity is to be
planned antennas should be placed in zigzag manner such to get an even
distribution of signals as depicted in fig. below
Link Budget:
Link
Budget calculations are used to calculate the output power (db) at each antenna
element. Passive component (coupler, splitter and attenuator losses) and feeder
cable losses are subtracted from BTS output power. Link budget calculations are
made for band to be used for indoor GSM/DCS/UMTS.
EIRP=
Pout BTS + Ga – Lf - Lc- Ls – La
Pout
BTS= BTS output power at antenna connector
Ga=
Antenna gain (db)
Lf=
Feeder loss
Lc=
Coupler loss
Ls=
Splitter loss
La=
Attenuator loss
With
standard parameters we can calculate link budget of the access site shared by
Vander side
RF Indoor Plan:
After
the path loss and link budget calculations RF plan is made floor by floor on
the autocad layout of the building. Care should be taken while adjusting the
AutoCAD scale. Also antenna, cable lengths and passive elements should be drawn
accurately according to the plan.
Antenna tree diagram:
Antenna
tree diagram is made to have a quick overview of the IBS design. Care should be
taken while calculating the lengths.
Indoor Equipment List:
Detailed
and complete BoQ list essential at site.
Indoor Site frequency planning:
Frequency planning is performed manually selecting suitable frequencies by carefully analyzing the neighboring frequencies.Exclude the co-channel and adjacent frequencies which will likely to interfere.From the remaining set choose the frequency that most likely to cause interference. BCCH frequency should be the least disturbed. Hopping on several frequencies will smooth out the interference.
Following
need to be considered if two much clean frequency options exist:
- Increase signal strength of indoor cell.
- Allocate dedicated 3-5 frequencies for indoor cells.
- Redesign the frequency plan.
- (Indoor sites in our network are single cell; single
band sites, so no frequency reuse is done in indoor)
IBS System Deployment
Recommendations:
Traditional
IBS deployment as said before Passive and active DAS –IBS.
Operators deploy solutions as per regulatory requirements (e.g. GSM or UMTS license) Recently operators deployed their own systems, single users DAS in a buildings. This resulted in multiple DAS in the same building, one for each operator (2-4) cause of
Operators deploy solutions as per regulatory requirements (e.g. GSM or UMTS license) Recently operators deployed their own systems, single users DAS in a buildings. This resulted in multiple DAS in the same building, one for each operator (2-4) cause of
•
Multiple cable runs
•
Multiple Antennas
•
Multiple Maintenance organizations
So
now a day’s regulatory authorities, building developers/owners and operators
are
More
operators are in force of sharing the IBS DAS. As illustrated before, all
operators can share one DAS which cause of less cables and antennas and Shared
maintenance efforts which helps controlling apex of IBS-DAS. This equals less
negative impact on the esthetics of the building, less maintenance activities
and lower cost for DAS.
The
Third party installs the DAS most of the times. Generic Multi Operator DAS
implemented by developer/owner in a building. DAS connected with Coaxial
cables with star configuration, Antennas
(location based on generic guidelines, cables routed back to the nearest
technical room e.g. maximum 90 meter cable run.
Wireless Design Simplicity
Goal - Provide a “-75dBm Coverage
Blanket”for meeting coverage ,QOS KPI’s.
The Antenna Location Design Rules:
- Outside antennas within 20ft of
the edge of the building
- Antennas spaced at 100 ft apart
- One antenna per floor within 20
ft of the elevator core
- One back-to-back antenna every
6 floors in the elevator shaft starting on floor 3
- Cable: Star configuration
Following
rules of thumb Maximum flexibility for the future RF planning
- Omni antennas on a basic 100ft
(30m) grid
- Perimeter antennas < 20ft
(6m) from walls
- If on external wall, utilize
directional antenna
- One antenna < 20ft (6m) from
elevator core
Stairwells:
- If open, Omni antenna every 6th floor,
- If closed, Omni antenna every 2nd floor
Installation
& Certification:
- Each cable run directly to TR < 300ft (90m)
- Install connectors on both ends
- Sweep-test for integrity and loss
- Attach antennas & document cable paths
- Extended warranty
Site Acceptance:
Once
the indoor site is implemented site acceptance request is made by vendors/sub
cons. Implementation team will take care of VSWR calculations, antenna
grounding etc. Following is required from RF Team for acceptance of the indoor
site:
- On site Audit
- Walk test
- Spillage check
1-On Site Audit:
On
site verification of the indoor is performed to check the antenna location as
well as the equipment count.
2-WALK TEST:
Walk
test summarizing the coverage actual manners. It will be tested at two types of
drive test mode
I-Idle
Mode:
Walk
test in idle mode for the indoor site is performed to check the RSSI and C/I of
indoor site. Logfiles are made on the floor plans provided. (In case of vendor planning
walk test report is to be provided by
them).
II-Dedicated mode:
Dedicated
mode walk test is performed to check the quality and RSSI of indoor after call
setup. Qualities of different TRX are also checked at RF end by locking the
call on different TRX’s. Also handovers with other neighboring sites is tested.
III-Spillage Check:
Spillage
is spill of indoor signal outside the indoor location. Spillage is generally
checked 20m away from the periphery of indoor compound. Generally -85dbm is set
as a threshold and levels below it are problematic as they will cause unnecessary handovers on
the indoor site. However using Cell Reselection Offset parameters and handover
control parameters, the unnecessary reselections and handovers can be avoided.
4-Coverage Acceptance:
Coverage
is checked at each part of the indoor compound and should be within the range.
5-VSWR:
To
be checked by implementation.
6-Parameters fine tuning:
Before
site is accepted by the planning team Fine tuning of parameters is performed to
achieve the below mentioned KPI’s. After achieving the KPI targets planning
will accept this and handed over to optimization team for further fine tuning
KPIs
|
|
1
|
RX Level for 2G for 95% of the Covered Area=-75dBm
|
2
|
RSCP for 95% of the Covered Area=-80dBm
|
3
|
DL Rx Quality for 2G for 95% area of the covered Area less than 2
|
Pilot power of 3G common area less than -75 dBm
Pilot Ec/Io of common area less than -7 dBm
Spillage Test (On
the surrounding main street nearby the building)
1
Signal from indoor system not higher than -95dBm
Frequency Planning for Indoor
Systems Conclusion:
For
improve coverage and Capacity inside building using IBS solution and it shows
an increase of the cellular traffic with up to 70% for larger buildings. For
good coverage we have to assign frequencies manually by excluding the
frequencies of the Surrounding cells and the adjacent frequencies. For avoiding
interference it is good to apply Frequency Hooping to smooth out the
interference. It is good for coverage if we are increasing the BTS power if the
available frequencies are few in numbers.
h
IBS Planning & Implementation:
To
starting planning process of IBS DAS Statically review of the network is very
important and essential .The identification of the right area or building for
IBS DAS design very critical .Once the Area identified with help of stats of
the network, field visits and complains.
Once
location identified standardized planning ladder followed till all entity of
DAS IBS design practical implemented.
Conclusion:
In-building
Solutions as defined in this document is a way to enable efficient usage of
wireless mobile applications inside different kinds of buildings. This requires
that sufficient coverage and capacity with good radio quality is available
inside the buildings. Although the mobile operators will cover most buildings
from outdoor sites in their macro network, there is a need to provide many
buildings with extended radio coverage and capacity. In-building solutions are
well-proven methods for an operator to capture new traffic and new revenue
streams.
One can provide enhanced in-building solutions
to off-load the macro network, thus increasing mobile traffic, and attract
additional subscribers due to the enhanced mobile network quality and
accessibility to mobile Internet applications and other services that require
high data-rates and capacity. There are several different ways to implement
in-building solutions. Dedicated Radio Base Stations, RBSs, that are connected
to Distributed Antenna Systems, DASs, are commonly implemented solutions. These
solutions provide additional capacity as well as covers “black holes” inside
different kinds of buildings. A number of different types of both RBSs and DASs
are available and the solutions can be customized for different buildings and
needs. Repeaters are often used for buildings with a limited need for capacity,
but where additional coverage is needed, like road tunnels and smaller
buildings or parts of buildings.
Indoor
systems can be solution if the coverage is weak from outdoor cells or causing
to bad quality To build indoor systems into the buildings, which are generating
high traffic, can reduce the network load by handling that traffic In developed
business centers, indoor system can replace the fixed network.
Indoor systems
are sometimes the complements that can provide a
good
image.