Transmission Network Planning and Design

8/4/2019 Transmission Network Planning and Design

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Transmission Network Planning and

Dimensioning


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Challenges while doing planning

Some of the main challenges in the network design are : Proper dimensioning of capacity, no over-dimensioning the capacities for the

initial phase, when coverage is the main goal of the deployment

Network reliability with total control of the quality and availability of links.

Vast-scale rollout with easy re-deployment.

Reduced dependency on third party carrier.

Assuring the infrastructure built today will be able to scale and carry theincreased traffic when capacity becomes the main goal of the deployment.


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Transmission Planning process

Transmission Network dimensioning is carried out as per the process whereyou need certain inputs and assumptions on the basis of which planningoutput is generated. The process document is separately prepared which canbe referred for details like the steps on the process, Inputs phases, Analysisphases, various interfaces involved in different processes etc. This documentgives in detail the actual planning works involved and guidelines thereof invarious processes.


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Transmission Planning process


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Inputs from customer

The Customer Specifications detail many aspects as to how the network orphase of network should look and be rolled out in case of new Greenfieldscenario.

OR the Customer will have done some investigation as to their networkexpansion requirements, this is done from traffic analysis and marketing input.From this they will have a plan, of which areas they need to include additionalcapacity or coverage. This plan once checked against the planning tool wouldgive the optimum co-ordinates for the sites or Search Ring Centers.A SearchRing is an area around the best location co-ordinates (usually no more than1Km in diameter), which is used to task the site acquisition team to locateoptions.

All phases of rollout should be performed according to the Customers request.

So, The list of new towns to be covered from the customer along with the

traffic details.


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Nominals generation by RF planner

Upon reciept of the Customer requirement, the RF Planning team will do someanalysis of the Search Ring specifications. To identify if it is sufficient to meetthe demands of the rollout, and to confirm that the proposed locations areable to meet the coverage requirement, as requested by the customer.

Should the proposed Search Ring not meet the requirements, then the RF

planning team will issue a change request to move the search ring to aposition that does fit the requirements.

The RF planning team will also specify their antenna height requirements fromthis planning and will make an application for Aviation authority clearance inthe area of that site.

So, finally RF engg to arrive at the final list and count of new town sites andsites in the existing towns and the subscribers in each of these.


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Issuing of search rings

Once all the search rings in an area have been identified and agreed uponthey can be released to site Acquisition and the other departments (includingAccess Transport Network Design).

This allows the other departments to start their processes. For Access thismeans that the Search Ring Centers co-ordinates should be input into thedatabases.From the issue of search rings or even nominals, the NominalTransmission plan can be produced.


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Guidelines/ParametersAt this stage some guidelines as to the planning parameters should be decided upon

with customer and entered into the Planning tool - these will generally include.

A ) For existing coverage area expansion :

No. of frequency spots being used / applied for MW emission ?

Latest NW plan showing various configurations of MW hops on-air along withcapacities.

Minimum antenna size recommended for MW ?

Maximum antenna size allowed ? Maximum loading capacity of a MW radio hop allowed in %age ?

Per hop availability of MW hop required ?

Maximum loading of terminating ports of a BSC allowed ?

Existing Lease line details required along with capacities for Abis traffic, if any?

Existing Lease line details required along with capacities for Ater traffic ?

Minimum no. of BTS required in loop configuration ? Maximum no. of BTS allowed in chain configuration ?

Any STM-1 hop to be planned with 2xSTM-1 XPIC configuration.

Inter BSC traffic running on LL / MW ?

Any POI transmission system to be planned ?

Would transmission be planned for both co-located BTSs in different frequency bands ?


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B) For new Greenfield area expansion :

No. of frequency spots to be considered in each band for MW emission radiation ? Minimum antenna size recommended for MW ?

Maximum antenna size allowed ?

Maximum loading of a MW radio hop capacity allowed in %age ?

Per hop availability of MW hop required ?

Per section availability allowed ?

Maximum loading of terminating ports of a BSC allowed ?

Existing Lease line details required along with capacities for Abis traffic, if any? Existing Lease line details required along with capacities for Ater traffic ?

Minimum no. of BTS required in loop configuration ?

Maximum no. of BTS allowed in chain configuration ?

Any STM-1 hop to be planned with 2xSTM-1 XPIC configuration.

Inter BSC traffic to run on LL / MW ?

List of cities where POI transmission is to be planned.

Any MW repeater to be considered ? Any BTS clubbing allowed ?

Can we consider use of ADPCM for POI traffic concentration?

How much spare height of tower to be kept after planning the GSM/MW antenna?

How much clearance in meters to be kept between Fresnel zone and theobstruction?

Would customer be able to provide external interference details ?

Would customer be able to provide maps / DTMs for RF/Tx planning


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Nominal Transmission Plan

The Nominal Transmission Plan (NTP) is a very basic overview of the proposedNetwork layout, typically produced using MapInfo or Mapgrid feature of Pathlosstool. The NTP is produced, by taking the Search Ring Centers / P1 options/nominals, and connecting them together using simple topologies.Considerations as above, to be considered while preparing the NTP.Once the NTP has been verified in the Planning tool, it should be stored as a layerfor presentation to the customer.

From the above data, the number of BSCs required is to be calculated and this isgiven by the RF engg.If number of BSCs are not enough from transmission point of view, planner canjustify and ask additional requirement. Further the projected capacity of A-ter foreach BSC is to be calculated.Also the number of MSCs required is given by the core planner. The number ofinter-MSC E1s, number of ports for each of the POIs is also given by the coreplanner.

Based on the above inputs, the planner should prepare the nominal connectivityplan. This can be done by plotting all the new sites on the tool. Based on theexisting and new BTS distribution, the location of the BSCs can be fixed from thetransmission perspective. The BSCs can then be validated along with the RF engg.The connectivity can be done based on the terrain data in the tool or theknowledge of local area or through the use of GIS systems available. It is veryimportant here for Tx planner to get his plan / bsc boundaries approved from RFengineer.


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BoQ Preparation

Once the nominal connectivity plan is prepared, it can broadlybe known as to how many 7GHz/15GHz/18GHz/23GHz linksare required based on the spectrum availability for a circle.

Further the capacities of each of the link i.e.4E1/8E1/16E1/STM-1 and MUXs can be finalized based on the

above covered inputs on capacity projections. It should benoted that at any point of time the utilization of the MW linkshould be maintained at less than 80% or whatsoever given bycustomer.


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Line of Sight (LOS)

Line of Sight is defined as the visible path between two sitelocations. For Microwave connection this path should beunobstructed to at 100% of first Fresnel zone, and have as anaverage a minimum clearance of 5.0 m over obstructions.

Should it not be possible to obtain LoS confirmation at the sitequalification, then a full survey will have to be completed.


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GENERAL TRANSMISSION NETWORKDESIGN


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Network Architecture

Transmission is of major importantelement in any mobile network,affecting both the service quality aswell as the cost of the mobileoperator. Careful transmissiondimensioning and planning from the

initial state is thus certainlyworthwhile from the business point ofview. Figure illustrates the logicalconnection in GSM network.

TCSM

BSC BSC

TCSM

MSCMGWMSS

BSCBSC BSCBSC

BTSBTSBTS BTSBTSBTSBTSBTSBTSBTSBTSBTS BTSBTSBTSBTSBTS


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The transmission core network is planned for imbibing the capacityrequirements for a 2.5G rollout in the following phases of the rollout.

A three-tier topology is planned for the metro as well as stateNetwork. The multi tier approach will help in the aggregation andmaintenance of the nodes more efficiently.

Tier 1 -The fiber Bb for every circle is planned to carry MGW-MSC servertraffic, Inter MGW traffic and Ater traffic in case of metro circles while in caseof state circle it may carry all MGW-MSC server traffic, Inter MGW traffic andpartial Ater traffic, as in case of state circles MW BB may also carry some Ater

traffic. Tier 2 The MW rings of STM and high capacity PDH radios are formed

starting from the TRS nodes and PoPs. These rings will encapsulate themaximum access capacities and backhauls on to the nearest transmissionnodes. The transmission planned on microwave links offers the fastest meansfor network rollout and capacity expansion in the access. Furthermore,operational expense is considered less expensive than laying own cable or

leasing connection. Tier 3 The PDH 16 E1 radios are deployed on the MW STM rings. These

hops will rope in all the existing traffic on to the nodes. These hops aredowngradable to lower capacity radios by which efficient usage of BW can bedone and hence freq spots can be better managed.

Apart from above three tiers , transmission planner is also committed toprovide POI connectivities which includes connectivity of L1 and L2 exchanges.


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Key Dimensioning Aspects of a NWarchitecture

Reliable and highly available strong STM 1 backbone which can covermaximum possible key locations and highways is recommended.

This will ensure reliable connectivity to cover maximum network elements andreduce dependence on third party carrier networks.

Software capacity upgrade: Pay as You Grow, zero reaction time to trafficpattern changes.

In cases where direct MW hops from a backbone site are not possible, MWrepeaters have been considered.

Most of these repeaters are chosen in such a way that they can be convertedto potential BTS sites in subsequent phases.

Leased line has been considered for faster roll out in phase1 and to reduce theload on MW backbone in specific cases. Also where MW repeater sitesrequirement goes beyond two.

All BSC-Media Gateway connectivity and Media Gateway to MSC server to bewith system redundancy. SNCP protection has been proposed on LL.

BSCs and highway towns are to be connected on the backbone.


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Tier 2 & 3 Network

Figure below illustrates the access portion of a possible network. In thisspecific case, the links carry the same traffic capacity. The access network isfound in the two lowest levels of the network (PDH 34 Mbit/s and STM1). Thebackbone network is found in the highest level (STM1/4).

RNC/MSC

RNC/MSC

RNC/MSC

RNC/MSCSTM1/4

Node/Hub Node/Hub

Node/Hub

STM1

PDH (34 Mbit/s) Node/Hub

Node/Hub

Node/Hub


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Network Topologies


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Ring Topology

In fig BTS-sites are connected as a ring (loop). The capacity requirement isthe total sum of the individual capacity requirements.

BSC/METROHUB

LOCATION

BTS 1

BTS 2

BTS 3

BTS 4

BTS 5

BTS 6

BTS 7

BTS 8


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Pros and Cons of Ring Topology

Improvement of the availability of network, that is, in the event of a failure inone link, the traffic can be re-directed toward the other direction of the ring. Ifthe ring has sufficient capacity to carry all the traffic from every site in bothdirections, then complete redundancy has been achieved.

Unavailable time caused by hardware failure is reduced without the necessityof doubling the radio equipment.

Planned rings may never become rings because conditions and requirementsmay be changed during the network expansion.

If network capacity is not increased, the ability to handle traffic decreases.

Every site must be connected to two sites and line-of-sight might be difficult toaccomplish.

Cross-connectors are required.

Equipment cost might be higher than other solutions. All links must be able to handle full capacity.


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Star Topology

Each BTS is connected to theBSC/Hub Site independent of therest of the traffic. This causes highconcentration of hops at Hub siteresulting in frequency interferenceand threshold degradation. Thistopology is mostly used in areaswith LOS limitations or it applies toan area where we can afford to

loose redundancy of BTSs ascompared to the cost of carryingbackhaul traffic. This is not suitedto city network. The BTS will nothave redundant path and onlyoption is to have equipmentredundancy. The hops used in thistopology can be 1+0 or 1+1

depending on whether there arefurther sites connected in chain toany arm of the star or as percustomer inputs.

BTS 1

BTS 1

BTS 1

BTS 1

BTS 1

BSC / HUB LOCATION


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Pros and Cons of Star Topology

The BTS-sites may be established to expand capacity requirements in aparticular area separately from capacity requirements in other parts of thenetwork.

Each path is traffic-independent so the effect of hardware failure is limited.

Limited number of paths in a chain makes the quality and availabilityobjectives easier to accomplish.

The network may be gradually taken into service in accordance with theestablishment of new sites.

It involves a large number of incoming RNC/MSC routes and theircorresponding antennas. This may cause space and strength problems forantenna support structures. Robust structures are generally more expensive.

The high number of incoming routes may lead to problems in finding sufficientnumber of available channels and then contributing to interferenceenvironment.

Some BTS-sites may be situated too far from the RNC, thus increasing fadingprobabilities.

It might be difficult to find line-of-sight toward each direction.


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Chain Topology

A number of sites connected in sequence, where every intermediate site isconnected to only two sites in the chain. In case there are more than 3 sites ina chain , then the links will be planned as 1+1. In case it is not possible toclose any other route and in case a BSC happens to fall in a chain, redundancyfor the BSC should be planned on alternate media or leased lines.

This type of configuration consists of linking RBS-sites in a chain such that theprevious RBS sites in the chain act as active repeaters for the last one; see the

fig illustrates two chains converging to a common RNC/MSC. In this particularcase, the configuration can also be extended to a tree configuration byadding more RBS-sites to each existing RBS-site, but without closing the treefoliage to become a ring. Parts of a chain can also be used in mixedtopologies.

BSC

BTS 6

BTS 5BTS 4

BTS 3

BTS 2

BTS 1


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Pros and Cons of Chain Topology

Provides often a minimum length per link and is therefore normally a cost-effective solution.

Low concentration of equipment at nodal points.

Utilization of transmission resources in the case of a tree configuration.

Since the links are connected in sequence, it is expected poorer hardwareavailability caused by hardware faults.

Capacity requirement increases along the chain toward the RNC/MSC High capacity links are required near nodal point.

At the very bottom of the network hierarchy (farthest from the RNC/MSC), wherecapacity is relatively low (2 Mbit/s), the paths are normally unprotected. Closer to

the RNC/MSC where the capacity is accumulated, it is strongly recommended toimplement some degree of protection. A Cascaded configuration is similar to thechain/tandem configuration described in this section, but the traffic may beconcentrated at some BTS-sites in the chain (hubs). Protection is stronglyrecommended in the feeder link.


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Spur Topology

A spur is a single link connected to a hub site or a chain site. Spurs shall beplanned as 1+0 only unless there is a special requirement to have a 1+1 link

BTS 1

HUB

SITE


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Actual scenarios of tier3 network

In actual, while planning a city access NW on MW, we come across following

limitations :

Non existence of LOS between BTSs..

Limitations of tower heights owing to civil and municipality issues.

As a result of which, we are not able to bring all the sites in loop configuration.

So, it should be tried to keep at least 80 % of sites in protection and rest canbe taken in spur.


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Metro city NW

For e.g. A big city having high penetration of BTSs would like as follows ,where sites are fashioned in star or loop fashion across SDH ring.


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Medium city NW

Sometimes we come across the situation that there are not enough BTSs in acity but a BSC is located in a city so as to cater Abis traffic to remote cities onLease lines . The MW of this city having BSC may look like as follows :


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Small City Network

While a city having LL can be made work in spur or loop protection dependingupon the LL availability and its cost. The MW network of a city litting up on LLmay look like as follow:


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Clusters of Microwave

The network is divided into sub-networks (clusters) having BTS-sitesdistributed around a common centre. All clusters are then connected to acommon centre site.

Clusters present many advantages:

The overall availability is increased if the cluster connections to the centre areprotected.

Shorter paths from all sites to the centre site.More flexible rollout.

Distributed transmission capacity.

This kind of NW is constructed in a city where lot of Fibre points are availableand LL is available from these nodes till BSC in SNCP protection. These smallclusters are also called as islands.

RNC/MSC


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Summary

Chain/tandem configurations are suitable when providing radiocoverage along roads or rivers. In this case the radio basestation is often of omni-directional type.

Tree configurations are suitable in smaller or medium sizednetworks.

Star configurations are suitable for small networks. Ring configurations are suitable when high availability is

required.


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Capacity Planning


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Planning Capacity Requirements

The total capacity requirements of any link are to be arrived at after taking allthe following mentioned needs into consideration. Ensure that the Microwavelink is designed to maintain a capacity utilization of 50-70%. Theaugmentations or upgrades should be carried out in time so that the linkcapacity is not utilized above 70% at any given time.


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Capacity planning per BTS in Rural Each Ultra BTS in the rural scenario should be allocated a

dedicated E1 for a maximum TRX configuration of 4/4/4. Incasethe TRX configuration is designed beyond 4/4/4; allocate asecond E1 for such BTS.

In case of Metro BTS with TRX design of 2/2/2, the E1 can be

shared with another Metro of similar configuration till the totalTRX count remains within 12TRX.


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Capacity planning per BTS in City/Town In case of Metros, allocate 2E1 per BTS. This would cater for TRX

configurations beyond 4/4/4 as the Metro have the required GSMspectrum to go beyond 4/4/4. Also the requirements on EDAP areabout 6 TS and hence 2E1s per BTS.

In case of showcase towns in the circles, allocate 1.5E1 per BTS

to cater for the EDAP pool of 3TS and any configuration beyond4/4/4 wherever feasible.


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Capacity planning for A-ter The A-ter capacity is to be maintained at 70% utilization (on the

main media or route). As soon as the capacity utilization crosses70% take steps to augment the capacity. This will ensure thatduring the interim period the utilization would not cross beyond90%.

Each BSC should have a redundant path for A-ter. This could beMicrowave, BTSOL OFC or any other leased media. At all timesensure that at least 50% of the E1s in the main path are on theredundant media or ring.

For example, at 70% utilization if any BSC requires 20E1s for A-

ter, then on the main Microwave/BTSOL path, the number of E1sshould be 20E1s and on the redundant media like Microwavealternate path/BTSOL/RAILTEL etc the number of E1s should be10E1s. This will ensure that even when the main route goesdown, the redundant route will ensure functioning of BSC thoughwith a limited congestion.


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Capacity planning for POI BSNL Poise to be planned on OFC preferably considering the

future requirements. Wherever the future requirement is notexpected to go beyond 16E1s, MW can be planned.

The POI should be planned for 70% utilization.

Capacity planning for other services

Gb links

MCA and other VAS E1s

OSS connectivity DCN connectivity

IN connectivity

HLR signalling

Documents

Transmission Network Planning and Design