Indoor Building Distributed Antenna System (DAS)

1 Aug

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.

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

  • 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
Mentum Planet ™
Mentum CellPlanner ™
Forsk Atoll
ASSET
Broadband Planner
CelPlan 
WinProp
V-Soft Probe
EDXWireless
x-Wizard

Overture

iBwave

CRC-COVLAB

FUN

Hi-Res

MbP

RedPredict

TAP

RFCAD

Astrix

ComSite

 

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)

Fig  RSSI of different servers with floor plans

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.

Fig : Priority area marking for an indoor site location

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

Fig :  Improvement in indoor coverage

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.

Fig : RF indoor Plan for a floor

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.

 

Fig 5.18: Antenna Tree diagram

Fig : Measurements for Cable lengths

Indoor Equipment List:

Detailed and complete BoQ list essential at site.

Fig: Indoor Equipment List

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

  • 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:

  1. On site Audit
  2. Walk test
  3. 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).

Fig : Rx-Level Idle mode

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.

Fig : Rx-Qual Dedicated mode

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.

Fig Spillage

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.

Source: http://telecom-knowledge.blogspot.nl/2014/09/indoor-building-distributed-antenna.html

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