Aircom Whitepaper Lte Small Cell Selection

LTE Small Cell Selection

considering geo-located traffic, backhaul availability and street furniture

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Executive summary

Planning a small cell network is far from a simple exercise. A robust methodology is required to

cost-effectively address capacity and throughput demands while keeping network interference

and costs in check.

There are many variables to be considered, but two key factors that will determine the best

approach are: site locations - are there pre-defined candidate site locations or is a “greenfield”

approach required? and traffic data: what type of information is available and at what

resolution?

The availability of street furniture databases (lamp posts, traffic lights etc.) is becoming more

popular. These provide fixed site locations, which somewhat limit design flexibility, but

significantly simplify and speed up site acquisition and the site build process.

Geo-located trace data is also becoming increasingly prevalent and is, at present, probably the

most commonly available traffic modelling option which provides sufficient accuracy for small cell

planning.

This paper looks at a small cell planning methodology where a street furniture database and

geo-located traffic data exists, a case which will be applicable to many operators looking to

deploy small cells. It proposes a 5 step process, using the most commonly available tools, for

operators to design the best possible LTE small cell network within budgetary and technical

constraints.

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Introduction

With wireless data predicted to exceed wired data in the next few years and network capacity

demands to increase 10-15 fold over the next 5 years1, mobile operators are under pressure to

dramatically increase their network capacity and maintain data throughput rates, in a cost

effective manner.

To cope with the insatiable demand for data from customers and the difficulty of building

additional macro sites in dense urban environments, mobile network operators will look to small

cells to ensure their LTE networks have sufficient capacity and coverage to meet customer

demand.

This paper looks at a small cell planning methodology where a street furniture database and

geo-located traffic data exists, a case which will be applicable to many operators looking to

deploy small cells. It proposes a 5 step process, using the most commonly available tools, for

operators to design the best possible LTE small cell network within budgetary and technical

constraints.

The process consists of 5 key steps:

1. Traffic forecast

2. Candidate locations

3. Site ranking

4. Automatic site selection

5. Design verification

Traffic forecast

The first step in the design of a small cell network is to determine the capacity required and

more specifically where the traffic hotspots are. Due to the short inter site distance between

small cells it is critical to know the location of your traffic to a high degree of accuracy. Geo-

located traffic data, while not as accurate as desired (50m accuracy at best) is the preferred

option given its relative prevalence and ease of data acquisition. More accurate methods exist

but they are significantly more costly in terms of effort for a relatively small gain in accuracy.

Another challenge to overcome is the current status of the LTE macro network into which the

small cell network needs to be integrated. It is quite possible that the LTE macro network has

not yet launched or is newly launched with a very low penetration of users. In these cases it is

not feasible to use geo-located macrocell LTE traffic as a basis for a small cell network plan.

Our experience has shown that the best compromise is to use geo-located traffic from the

mature UMTS network as a solid starting point. This data then needs to be adapted to the

1 Cisco VNI 2012-2017 link to report

http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11-520862.html

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expected usage profile of an LTE user, while still respecting the traffic hotspot information from

the UMTS network. In 2012 an LTE connection generated 19 times more traffic than a non LTE

one but LTE penetration was less than 1%2 so this number is likely skewed by early adopters

and the heaviest users migrating first. An operator needs to consider all available forecast data

to improve the LTE traffic model to be used for dimensioning.

Depending on the planned usage of the LTE network it may also be necessary to consider voice

traffic (if a VoLTE strategy is planned).

Once the geo-located traffic forecast is obtained it can be used throughout the rest of the

process:

To visualise the traffic distribution in the map view of a radio planning tool.

To load the simulated network into the radio planning tool.

For RSRP & RSRQ array statistic reports in the radio planning tool.

For the weighting of RSRP & RSRQ targets in an ACP tool.

For the calculation of captured traffic in an ACP tool and the corresponding traffic

offloading due to captured traffic limits.

Candidate locations

For many LTE network deployments the first step will be to co-locate an LTE macro site with all

UMTS macro sites for areas where contiguous LTE coverage is required, such as city centres and

business districts. In many cases however, it is unlikely that this strategy will create good indoor

coverage with sufficient capacity, especially if the LTE frequency band is higher than the existing

UMTS one.

The screenshots below show the coverage and quality of a typical LTE macro cell layer in central

London. A similar scenario would likely be encountered in most city centres. The many indoor

locations with Reference Signal Received Power (RSRP) less than -110dBm and Reference Signal

Received Quality (RSRQ) less than -14dB highlight that the LTE macro network will not provide

the coverage or quality expected by customers.

2 Cisco VNI 2012-2017 link to report

http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11-520862.html

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Figure 1: LTE macro layer coverage (RSRP)

Figure 2: LTE macro layer quality (RSRQ)

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Figure 3: LTE macro layer simulation reveals a large number of failures due to signal strength

and capacity

To create a network with sufficient coverage, quality and capacity, only a small cell layer will

provide a long term solution to the problem. It is expected that radio technologies like LTE

advanced and Wi-Fi offloading will help, but will not be sufficient and are either not readily

available or present bigger challenges than small cell deployments.

Loading a vector file of all available street furniture (i.e. traffic lights, lamp posts etc.) obtained

from the city planning department or other sources into a planning tool provides a list of

potential locations.

By configuring a site template in the radio planning tool with all the attributes of a typical small

cell, a nominal design can be quickly created. To maximise the candidate locations considered by

the ACP tool, a candidate small cell is placed at every possible street furniture location.

This nominal design is just the first step in the process - a starting point – and does not consider

specific clutter or capacity requirements. These aspects will be addressed in subsequent steps.

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Site ranking

Backhaul is a much more critical consideration for small cell planning than it generally is for

macro cells. The two reasons for this are that backhaul makes up significantly more of the total

site costs in small cells, and with most small cell deployments happening in dense urban

surroundings backhaul planning is much trickier than it is for macro layers.

By performing LOS (Line-of-Sight) analysis between potential transmission hub and small cell

locations as well as small cell to small cell locations in a microwave planning tool, the best

available backhaul transmission option can be determined using a methodology similar to the

below. Backhaul links are selected from this list in descending order of preference:

For connections between to existing macrocell locations where LOS exists, point-to-point

microwave links are used.

If there is LOS to the point-to-multipoint LOS hub then point-to-multipoint LOS links are

preferred.

If there is limited LOS to one of the point-to-multipoint non-LOS hubs then point-to-

multipoint non-LOS links are preferred.

If there is LOS between two small cell locations then point-to-point E-band microwave

links are preferred.

If none of the above options are possible then fibre optic links are required.

To ensure an optimal design from a performance and cost point of view it is important to rank

all potential site locations according to the most cost effective backhaul which is feasible for that

site location. The options for backhaul to be considered in ascending order of total costs (CAPEX

and OPEX) are as follows:

Point-to-point microwave link

Point-to-point E-band microwave link

Point-to-multipoint LOS microwave links

Point-to-multipoint non-LOS microwave link

Fibre optic

Once the most feasible backhaul technology is determined for each site that site can be given a

weighting according to the cost (CAPEX and OPEX) of the transmission. This helps the ACP tool

determine the most optimal site locations by considering not only RF performance, but backhaul

feasibility and cost too.

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Figure 4: Candidate site backhaul requirements

Automatic site selection

By considering the nominal site plan, the backhaul weighting factors, suitably scaled geo-located

traffic data and appropriate optimisation targets the ACP can optimise the design.

To obtain a high performance, yet cost effective design it is important to specify realistic

optimisation targets. Recommended targets should be in the region of -100dBm for RSRP and -

10dB for RSRQ. It is also recommended that the optimisation targets should be met in 95% of

the optimisation area while minimising costs to provide a good performance/cost trade-off.

Figure 5: Candidate site locations

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Figure 6: Optimised network design

Design verification

Once the ACP completes the design optimisation, the final step is to transfer the new site

settings back into the radio and transmission planning tools and do a final design validation. This

could include small changes to fine tune the design which may be obvious to an engineer’s eye

but were not catered for in the targets and constraints when setting up the ACP. For example, if

a link meets the projected traffic growth with only a few per cent headroom it might be more

cost effective in the long run to install a slightly higher capacity link option and save additional

field work costs should actual traffic turn out to be marginally higher than forecast.

Figure 7: Coverage without (left) and with (right) the small cell network

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Figure 8: Call failures without (left) and with (right) the small cell network

With the design verification, the final step in the process, complete an optimised small cell

network design now exists. The site acquisition team can now secure the confirmed locations

and the rest of the network build process can take place.

Conclusion

This document has outlined AIRCOM’s proposed 5 step process for designing the best possible

LTE small cell network, where a street furniture database and geo-located traffic data exist:

1. Traffic forecast – gather geo-located traffic data to understand with a high degree of

accuracy where the traffic is.

2. Candidate locations – determine candidate locations based on the availability of street

furniture for antenna mounting.

3. Site ranking – weight potential site locations based on the availability and cost of

backhaul to the location.

4. Automatic site selection – using an ACP tool optimise the small cell design to

performance and cost targets.

5. Design verification – validate and fine-tune the ACP generated plan.

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Products used

Successful planning of small cell networks requires a number of tools which work seamlessly

together. The following AIRCOM products play an integral role in the small cell planning

methodology proposed in this paper:

ASSET

ASSET is a multi-technology radio network design tool aimed at providing mobile network

planners with comprehensive and powerful capability in planning all the key mobile radio

networks. This includes the main radio design functions such as propagation modelling,

measurement data analysis, coverage analysis, traffic planning and static simulation as well as

more advanced processes including frequency planning and neighbour planning.

MYRIAD

Myriad is a universal propagation model. Following several years of research into propagation,

modelling, optimisation and algorithms, the MYRIAD propagation model is able to automatically

adapt itself to all cell types (micro, mini, small, and macro cells), environments (dense urban,

urban, suburban, mountainous, maritime, and open), and technologies (GSM, UMTS, LTE etc.) in

a frequency range from 200MHz to 5GHz.

For small cell planning the MYRIAD model is configured to utilise building vector data to provide

more realistic pathloss calculations in dense urban environments.

CONNECT

CONNECT is a microwave and backhaul transmission planning tool. It provides a complete

backhaul network planning solution covering microwave, optical, satellite and copper

technologies. It enables you to design and evaluate microwave networks across a variety of

architectures such as branch connections, multiple hops, loops or point to multi-point. It merges

powerful link engineering capabilities with a graphical map view to fulfil all microwave

transmission planning requirements.

Capesso™

Capesso is the market leading automatic cell planning tool. It combines data about the radio

network with planning objectives like coverage, capacity, quality and cost to automatically find

the best network design based on that information. Capesso is complementary to existing

planning and propagation software. It builds on investment in that software by automating the

multiple network processes for a faster more optimised design. Capesso is tightly integrated

with ASSET and delivers great value across the full spectrum of mobile radio standards and their

high performance extensions including GSM, UMTS and LTE.

About AIRCOM International

AIRCOM is an independent provider of network planning, optimisation and management

software and consultancy for mobile networks. Our products, all of which are now LTE capable,

enable operators to regain visibility and control of their network, which in turn drives efficiency

and profitability.

The market leader in the provision and deployment of network engineering tools, AIRCOM

products are in use across 155+ countries by over half the world’s mobile operators. Every day,

the 20 top global operators depend on AIRCOM’s tools and consultants to improve network

coverage and quality for more than 2 billion subscribers worldwide. Established in 1995, we

have built our reputation on creating and releasing additional value from within mobile networks.

As a provider of independent, multi-vendor, multi-technology consulting services, with over four

million hours working on 3G networks alone, our expertise translates into direct and measurable

cost savings for mobile operators. From initial advisory, through planning, optimisation and

operation, we are dedicated to maximising the performance of your network, and therefore your

business.

With offices in 14 countries, we provide regional viewpoints and resource, as well as ensuring

that our operator customers benefit from our global knowledge and expertise. By looking ahead

of the market, we develop the skills and tools, such as our small cell and SON offerings, that

network operators need to remain competitive.

WORLDWIDE HEADQUARTERS

AIRCOM International Ltd

TEL: +44 (0) 1932 442 000

EMAIL: [email protected]

AUSTRIA

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Aircom Whitepaper Lte Small Cell Selection

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