small cell forum release 5 - · pdf file8/6/2015 · small cells. small cell forum...

www.scf.io/ www.smallcellforum.org

DOCUMENT

Backhaul Issues for Rural and Remote Small CellsJune 2015

155.05.1.02

scf.io/

SMALL CELL FORUM

RELEASE 5.1

VIRTUALIZATION

Supported by the Metro Ethernet Forum (MEF)

If you would like more information about Small Cell Forum or would like to be included on our mailing list, please contact:

Email [email protected]

Post Small Cell Forum, PO Box 23, GL11 5WA UK

Member Services [email protected]

Small Cell Forum works to drive the wide-scale adoption of small cells and accelerate the delivery of integrated HetNets.

We are not a standards organization but partner with organizations that

inform and determine standards development. We are a carrier-led organization. This means our operator members establish requirements that drive the activities and outputs of our technical groups.

Our track record speaks for itself: we have driven the standardization of key elements of small cell technology including Iuh,FAPI/SCAPI, SON, the small cell services API,TR-069 evolution and the enhancement of the X2 interface.

At the time of writing, Small Cell Forum has more than 140 members, including 68 operators representing more than 3 billion mobile subscribers – 46 per cent of the global total – as well as telecoms hardware and software vendors, content providers and innovative start-ups.

This document forms part of Small Cell Forum’s Release 5.1: Virtualization that analyzes the costs and benefi ts of different approaches to small cell virtualization in terms of the point at which base station functionality is split into physical and virtual parts. This is in response to the many operators that have a roadmap to centralizing and virtualizing their macro RAN, and need to understand how small cells will integrate into this new approach to network design.

The Small Cell Forum Release Program has now established business cases and market drivers for all the main use cases, clarifying market needs and addressing barriers to deployment for residential, enterprise and urban small cells.

Small Cell Forum Release website can be found here: www.scf.io

All content in this document including links and references are for informational purposes only and is provided “as is” with no warranties whatsoever including any warranty of merchantability, fi tness for any particular purpose, or any warranty otherwise arising out of any proposal, specifi cation, or sample.

No license, express or implied, to any intellectual property rights is granted or intended hereby.

©2007-2015 All rights reserved in respect of articles, drawings, photographs etc published in hardcopy form or made available in electronic form by Small Cell Forum Ltd anywhere in the world.

Four5.1SMALL CELL FORUM

RELEASE

Report title: Backhaul for Rural and Remote Samll CellsIssue date: June 2015Version: 155.05.2.02

ABOUT THE MEF

The MEF is a global industry alliance comprising more than 220 organizations including telecommunications service providers, cable MSOs, network equipment/software manufacturers, semiconductor vendors and testing organizations. The MEF’s mission is to accelerate the worldwide adoption of carrier-class Ethernet networks and services for business and mobile backhaul applications. The MEF is the defi ning industry body for Carrier Ethernet, developing technical specifi cations and implementation agreements, and educational work to promote interoperability, certifi cation and deployment of Carrier Ethernet worldwide. For more information about the Forum, including a complete listing of all current MEF members, please visit www.MetroEthernetForum.org

THE MEF, CARRIER ETHERNET AND MOBILE BACKHAUL

Ethernet adoption has been accepted by the vast majority. The MEF’s Carrier Ethernet 2.0 for Mobile Backhaul brings answers to the challenges associated with managing rapid backhaul data growth while scaling costs to new revenues. MEF Mobile Backhaul Phase 2 Specifi cation (MEF 22.1 with MEF 22.1.1 amendment) covering use of Carrier Ethernet services, synchronization 4G/LTE Deployment and Small Cell Introduction. The MEF also publishes business, technical and best practices papers and provides presentations on optimizing MBH with multiple classes of service, packet synchronization, resiliency, performance objectives, microwave technologies and converged wireless/wireline backhaul.

Report title: Backhaul for rural and remote small cells Issue date: 09 June 2015 Version: 155.05.1.02

Executive summary

Small cell technologies are coming of age thanks to scaling of deployments in residential, enterprise and now urban markets. These maturing technologies can now be applied to a range of rural and remote use cases that may not otherwise be viable using traditional deployment approaches. Small cells are well suited to deployment in rural villages, remote industrial sites, on transportation, and for temporary networks.

This paper helps operators, backhaul and service providers to understand the particular needs of rural and remote small cells from a backhaul perspective. It summarizes key aspects that must be considered when designing and deploying the transport network, and points to sources of further information.

Key findings are:

• Remote deployments by definition are far from existing network infrastructure and thus are potentially expensive to backhaul with terrestrial links. Satellite becomes cost effective here and has proven suitability for backhaul.

• Rural deployments are not necessarily remote, and may be ‘in the next valley’ from a larger town with connectivity. Shorter range backhaul and copper connectivity can be used here.

• Small cells deployed on ships, planes and trains require backhaul that can connect to a moving cell site. Non LOS and satellite backhaul have been demonstrated for these applications in [i].

• Temporary deployments typically require rapidly deployable backhaul. Low power consumption is desirable to make a wider range of supply technologies viable.

• Backhaul to remote areas is likely to have limited performance:

• As little as 50kbps capacity is sufficient to provide a basic 2G voice and SMS service.

• Data service bandwidth will likely be limited by the willingness to pay for backhaul bandwidth. Compression techniques and avoiding the need for IPsec overheads can bring significant value here.

• Latency of around 300ms one way is tolerable for voice, but can limit TCP connection bandwidth if acceleration technologies are not implemented. Localized call switching and content access avoids backhaul limitations where applicable.

• The Metro Ethernet Forum (MEF) has implementation agreements which are also applicable in Rural areas. Standard SLAs help operators work with a range of different last mile providers, and multi CEN (Carrier Ethernet Networks) provide a framework for defining end-end performance over multiple connections from different providers.

• Networks can be deployed with intermittent or even no backhaul connectivity by localizing core functionality. These isolated networks can still provide local call routing and access to local content, bringing the benefits of COTS telecoms to remote and private networks.

Backhaul solutions are available which meet the challenges of deploying small cells cost effectively in rural and remote use cases. Different solutions are described which address the challenges of rural and remote deployments in order to deliver cellular voice and data to COTS devices in these applications.

Report title: Backhaul for rural and remote small cells Issue date: 09 June 2015 Version: 155.05.1.02

Contents

1. Introduction .....................................................................1 2. Rural and remote applications and their backhaul

challenges ........................................................................2 2.2 Rural ................................................................................. 3 2.3 Remote or ‘isolated’ ............................................................. 3 2.4 Moving ............................................................................... 4 2.5 Temporary .......................................................................... 4 2.6 Dedicated ........................................................................... 5 2.7 Summary ........................................................................... 5 3. Network architectures ......................................................6 4. Carrier Ethernet based mobile backhaul ...........................7 4.1 Rural area backhaul ............................................................. 8 4.2 MEF references ................................................................... 9 5. Backhaul technologies for rural and remote ................... 10 5.1 Satellite ........................................................................... 10 5.2 Non line of sight ................................................................ 13 6. Working with limited backhaul performance .................. 14 6.1 Limited capacity ................................................................ 14 6.2 Higher latency ................................................................... 15 6.3 Working over consumer grade links ..................................... 15 6.4 Synchronization ................................................................ 16 References ................................................................................ 17

Tables Table 2-1 Characteristics of the Use Case ......................................................... 2 Table 5-1 Summary table: Satellite ................................................................ 12 Figures Figure 2-1 Summary of backhaul challenges ...................................................... 5 Figure 3-1 Canonical architecture for multi-cell R-SCN with local-switching ............ 6 Figure 4-1 Carrier Ethernet Mobile Backhaul over Different Access Technologies .... 7 Figure 4-2 MEF mobile backhaul terminology ..................................................... 8 Figure 4-3: Carrier Ethernet mobile backhaul with two providers ........................... 9

Report title: Backhaul for rural and remote small cells Issue date: 09 June 2015 Version: 155.05.1.02 1

1. Introduction

This document details backhaul for small cells deployed in Rural and Remote scenarios:

Small cells can enable operators to provide coverage of voice and data in places that would otherwise not be viable due to cost, time to deploy, power source connectivity or space available. This is made possible by their self-deployable small form factor with plug and play technologies that can work over consumer grade backhaul. Illustrative examples of small cells applications within the scope of this document are:

• Remote: Rural villages and towns, remote industrial sites, oil rigs, mines etc. • Rural: At or just beyond the edge of existing coverage • Moving: Planes, Trains, ships • Temporary: Disaster recovery, humanitarian, first responder, field/military • Standalone: Private networks, dedicated networks for high value/essential

services

[2] details the business drivers for the range of use cases which we group under rural and remote. This document focusses on challenges of delivering backhaul connectivity, and is structured as follows:

We first look at the different rural and remote use cases, analyzing the challenges specific to backhaul, and identifying the potential solutions, in section 2.

Section 3 then summarizes network architectures and provides the context for the backhaul connection.

The MEF’s implementation agreements detailed in our Urban backhaul document [3], contain a multi CEN aspect applicable to rural and remote use cases. Relevant specifications are described in section 5.

Rural and remote small cells are expected to have backhaul limited performance. In section 6 we identify lower performance limits and describe technologies which can optimize backhaul traffic for the performance typically available.


2. Rural and remote applications and their backhaul challenges

This section considers the different rural and remote use cases for small cells and the challenges in supplying backhaul connectivity to them. We outline the types of backhaul solutions which apply in each case, and cover them in more detail in a later section.

Rural and remote use cases: • Rural community: Coverage for underserved community beyond range of

normal service • Remote Industrial: Coverage for community of workers at a site hard to

reach from existing infrastructure • Public safety: Coverage for emergency services & first responders. • Disaster recovery/humanitarian: Rapid reinstatement of coverage after

extensive damage to mobile infrastructure, and support for ongoing humanitarian efforts.

• Special event: Services for temporary planned gathering • Military: Service for military personnel • Transportation: Services for passengers and operational needs on all

classes of shipping, aircraft and trains

The use cases themselves represent just some of the examples of how small cells can be applied to bring mobile connectivity into areas that would otherwise be cost prohibitive. We show in Table 2-1 a set of characteristics which may always or sometimes apply to the example use cases.

Table 2-1 Characteristics of the Use Case

The characteristics refer to the needs of the users, rather than the types of solution which apply. We define them as:

• Rural: area outside of towns and cities • Remote Far from existing coverage and mobile infrastructure • Moving On-board coverage moving with users • Temporary Rapidly deployable short term coverage • Dedicated limited to specific service or user group

In general, each use case has a defining characteristic that always applies – Transport is always moving, disaster recovery is always temporary, etc. Other characteristics may only sometimes apply. For example, whilst Rural communities are always outside of towns and cities, they are not necessarily remote from existing mobile infrastructure. As we consider the backhaul for these different use cases, we see that certain characteristics point to particular backhaul challenges: Moving use cases require mobility in the backhaul. Temporary use cases require portable backhaul that


can be rapidly deployed – often at low power. In the following sections we consider the backhaul challenges of each of the use case characteristics, and the types of solution which apply.

2.2 Rural

Here we consider the provision of mobile services to towns, villages and communities which could be in very remote areas, or just beyond the edge of existing coverage. These scenarios are characterised by low population densities and hilly or mountainous terrain – both of which making it difficult to provide cost effective mobile coverage. We see that all of the use cases can potentially fall in rural areas.

Backhaul challenge and solutions: Rural communities are not necessary remote - they may be ‘just over the next hill’ and therefore reachable with using shorter range backhaul technologies.

• xDSL services may already be in place providing consumer broadband suitable for residential, enterprise or community femtocells.

• Wireless spectrum is generally less congested in rural areas, so license exempt bands and TV white space1 are more likely to have sufficient quality of service for backhaul

Where the rural community is remote from existing coverage, the challenges and solutions in the following section apply. Very long range connectivity of order hundreds of kilometres may more cost effectively be supplied using satellite, than terrestrial fixed links.

2.3 Remote or ‘isolated’

We define ‘remote’ as far from existing mobile coverage and infrastructure, such that a significant investment would be needed to provide most forms of connectivity to the site. This is often compounded by a relatively small number of subscribers with which to fund the investment. On the other hand, the perceived value of mobile connectivity may be greater in remote locations such as industrial sites or military bases. ‘Morale networks’ may be great value for industries needing to retain staff at such sites.

One rule of thumb used by the satellite community for a remote location is one that would require three or more hops of terrestrial point to point fixed links. The range of this depends on carrier frequencies and terrain, but could be of order 100miles.

Backhaul challenge and solutions: Cost effective connectivity over a long range, commensurate with a potentially small number of subscribers.

• Satellite backhaul costs are largely independent of the location served, and become the most cost effective in remote areas.

• Terrestrial fixed links using microwave and millimetre wave frequencies from 1-80GHz are widely used today for long range transport. Return on investment may be challenging for small scale deployments to which small cells are best suited.

• At such long range, transport capacity and latency performance are on the low side for backhaul applications, but are still usable, as described later.

1 “Backhauling in TV White Spaces”, Gerami, C. ; WINLAB, Rutgers Univ, IEEE Globecom, Dec 2010, http://goo.gl/Oi35qN

http://goo.gl/Oi35qN


2.4 Moving

Where people spend time on planes, trains and ships, good quality mobile service can be achieved through ‘on board’ small cells which move with their users. This makes most sense where the transport in question passes through remote areas far from other forms of mobile coverage – ships and planes, for example. Trains often pass through urban, rural and remote locations, and may therefore have adequate coverage for at least part of the journey. However, for consistent coverage that even works at high speed an on board system is preferable.

Backhaul challenge and solutions Placing a small cell on the transport may alleviate mobility problems for the access air interface, but they re-appear in the backhaul, which must support mobility at potentially high speeds. Mobility dictates wireless solutions must be used:

• Satellite works well for clear sky scenarios including maritime and aviation. They are able to deal with high speed, and continental sized coverage footprints. With geostationary satellites the coverage remains stationary on the surface of the earth meaning backhaul handover is needed rarely, if ever. Challenges of using satellite backhaul are principally the higher latency and the high cost per bit of capacity. Client side antenna pointing can also be difficult or expensive especially with high latitude deployments using geo-stationary satellites. .

• “NLoS” sub 6 GHz solutions work in much the same way as LTE or WiMAX air interfaces, and can support mobility. [i] includes a case history of the application to Formula 1 racing to carry telemetry data from car to trackside. Backhaul coverage footprints are smaller than satellite and may require multiple hubs with handover in between.

• Cellular as backhaul: e.g. 3G small cell backhauled over 4G. Depending upon the use case, LTE itself may have sufficient performance and features to be suitable for backhaul. It can be used to backhaul a 3G or 2G small cell, or used in an in-band relay configuration to backhaul LTE. Whilst this uses highly valued access spectrum for backhaul, it may not be in short supply in the remote and rural environments considered here.

2.5 Temporary

Small cells are compact and lightweight and lend themselves well to deployments of a temporary nature such as disaster recovery, first responder and special events. Temporary deployments require equipment that is portable and that can be rapidly installed and commissioned to provide or restore essential communications infrastructure in times of great need. Temporary deployments are not constrained by the economics of providing services to a low density of consumers with diminishing ARPU.

Backhaul challenges and solutions: Backhaul equipment must also be portable and rapidly commissionable to be suitable for temporary deployment. In addition to the physical and functional design of the cell site equipment, the ‘other end’ of the link and upstream transport towards the core network must also be in place to ensure rapid end to end backhaul connectivity can be established.

• Satellite backhaul is available with portable terminals, and the very wide area coverage means that connectivity is potentially available over a wide area. The satellite transport infrastructure is resilient to most terrestrial natural disasters.

http://scf.io/document/151



• Other wired and wireless backhaul solutions may also be available, depending on the local conditions, and extent of any infrastructural damage.

2.6 Dedicated

Dedicated networks are designed to support a specific user group or service, and may not necessarily be required to provide open access for consumer voice and data. Examples of such subscriber group networks might be for public safety or military communications, or for portable point of sale terminals at an event. Some dedicated networks may be private and operate in an off-net standalone manner. [4] describes how virtualised core network functions can be localised down to cell site itself, avoiding the need for backhaul altogether. In other applications, there are no backhaul requirements specific to dedicated networks – although the end application may place more stringent requirements on security and resiliency

Backhaul challenges and solutions: Backhaul may not be needed for isolated networks. Otherwise, no special requirements.

2.7 Summary

Figure 2-1 Summary of backhaul challenges


3. Network architectures

A detailed analysis of the network architectures needed for the different rural and remote use cases can be found in our architectures document [5]. This develops three generic or ‘canonical’ architectures covering single cell, multi-cell and multi-cell with local switching. Figure 3-1 shows the latter of these three, which is the most sophisticated. The other two are effectively simplifications of these. Backhaul connects the small cell core with the (optional) localised elements and small cells themselves.

Figure 3-1 Canonical architecture for multi-cell R-SCN with local-switching

Rural small cell architectures may include Backhaul Adaptor functions, since the backhaul may be a special type, such as long-delay satellite links or unreliable links. The adaptors account for the special anomalies of the backhaul and attempt to provide a stable operation for the remote small cell network. The adaptor acts on the user plane traffic only, and control signalling is not modified. [5] and section 6 of this document describe a number of adaptor functions typically used in satellite links.

For larger scale remote small cell networks, localised functions may be implemented to mitigate low performance backhaul – these include concentrating data for multiple cell and localised handling of handover. These functions are similar to those in enterprise small cell networks described in [6] and [7].




4. Carrier Ethernet based mobile backhaul

The Metro Ethernet Forum (MEF) has developed an Implementation Agreement for Mobile Backhaul that describes the requirements of Carrier Ethernet services for mobile backhaul. Known as MEF 22.1, the mobile backhaul implementation agreement is a “tool box” for mobile backhaul based on MEF service types, i.e., E-Line, E-LAN and E-Tree (MEF 6.2), and the related Ethernet Service Attributes (MEF 10.3) and Circuit Emulation Service (MEF 8). The implementation agreement supports all 3GPP generations from 2G to 4G/LTE over Ethernet backhaul, and includes one amendment (MEF-22.1.1) that describes specific use cases for small cell backhaul.

Ethernet services are becoming increasingly available, even at sites with access to legacy circuits. LTE and LTE Advanced mobile equipment (including small cells) utilize Ethernet interfaces for transport; therefore Ethernet based services are most suitable for backhauling mobile traffic.

Carrier Ethernet services provide the connectivity in the mobile backhaul network, and allow for convergence of services with traditional fixed business and residential services. MEF Carrier Ethernet services can be supported over any transport (referred to as the TRAN layer in MEF 4) as shown in Figure 4-1. These definitions aim to support a wide range of mobile network topologies (including small cell backhaul topologies).

Figure 4-1 Carrier Ethernet Mobile Backhaul over Different Access Technologies

MEF 22.1 defines the role of a mobile operator (the Subscriber or Customer who purchases the Ethernet backhaul service) and Carrier Ethernet Network (CEN) operators (backhaul or service provider). A mobile operator (with a RAN network) purchases a Carrier Ethernet backhaul service from a CEN operator that is demarked


at a UNI, as shown in Figure 4-2. These roles can also be applied to business units within the same operator, for example, where a wireless business unit might obtain

the MEF service from the same operator’s transport business unit.

Figure 4-2 MEF mobile backhaul terminology

The mobile backhaul may consist of more than one segment provided by different CEN operators to achieve connectivity between the base station sites and network controller/serving gateway sites.

The mobile operator is not constrained to using Carrier Ethernet services end to end as they may only require service for a portion of the mobile backhaul if, for instance, they already own some portion of the backhaul.

A mobile operator can also choose to use Carrier Ethernet services from a CEN operator for some network segments of the mobile backhaul and use non MEF services for other portions of the network. An example of this is where an IP VPN service is available and desirable. When combinations of MEF and non-MEF services are used, the mobile operator is responsible for the end-to-end performance across the different segments.

4.1 Rural area backhaul

While Ethernet services are nearly ubiquitous in urban mobile backhaul deployments, legacy circuits are still widespread for rural backhaul. As a result, transitioning those circuits to support Carrier Ethernet, or even deploying a replacement network, is the first challenge in rural deployments.

In rural markets, in the US at least, there is a proliferation of small transport operators especially for `first mile` access. This often results in a mobile operator requiring multiple mobile backhaul service providers to provide transport between the

RAN Radio Access Network RAN BS RAN Base Station

RAN NC RAN Network Controller RAN CE RAN Customer Edge –Mobile network node/site

UNI


RAN BS and the RAN NC. This is typically provided by connecting the mobile backhaul operators with an ENNI (External Network-Network Interface, MEF 26.1) as is shown in Figure 4-3. There can be multiple variations of this based on the mobile operator`s SLA arrangement(s) with the service providers, including whether the access provider is aggregating multiple first mile providers.

Figure 4-3: Carrier Ethernet mobile backhaul with two providers

The use of MEF E-Access services (MEF 33) standardizes last mile access. Enhancements such as class of service (CoS) and Service OAM Fault Management (FM) and Performance Monitoring (PM) allow for predictable performance that can be managed within each CEN and end-to-end. In addition, service protection mechanisms can be used end-to-end in the mobile backhaul network. The Access Provider (AP) may also provide MEF Virtual NID (vNID) functionality (MEF 43) with its E-Access service. The vNID allows the Service Provider (SP) to monitor and configure selected objects associated with the remote UNI. The vNID functionality is similar to what would otherwise require the SP to place a Network Interface Device (NID) at the remote customer’s location.

4.2 MEF references [8], [9], [10], [11], [12], [13], [14], [15], [16]


5. Backhaul technologies for rural and remote

A full range of small Cell Backhaul Technologies are detailed in our backhaul solutions paper [17]. Here we focus on those most applicable to Rural and Remote use cases: Satellite and Non LoS

5.1 Satellite Satellites are deployed in one of three orbital locations Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geostationary Earth Orbit (GEO), using any of the following frequencies (C-, Ku- or Ka-band) to provide global coverage with varied capacity and performance levels to meet the challenges of rural and remote networks. Satellite backhaul offers unique characteristics in terms of its nearly universal coverage, availability, and ability to be rapidly deployed. Single Channel Per Carrier (SCPC) or Time Division Multiplexing (TDM)/Time Division Multiple Access (TDMA) are technologies used in satellite communication. SCPC solutions use dedicated frequencies, particularly for the return channel traffic. TDM/TDMA systems employ a statistical multiplexing scheme to share information among multiple remotes on the satellite forward-link within the same spectrum pool, and use a demand-assigned, multi-frequency TDMA approach to enable remotes to transmit information to the core network. TDMA dynamically multiplexes and shares the same frequency across many sites. While TDM/TDMA solutions can serve Small Cells best when sites share the same satellite bandwidth, SCPC is well suited to connect individual sites that require high constant traffic with no sharing of frequency.

A satellite backhaul link for a small cell typically requires the installation of a small parabolic dish or flat panel antenna and a satellite modem. The dish is similar to a TV satellite dish, typically from 69 – 120cm in diameter. The modem is a small outdoor-mounted box (typically 25 x 25 x 8 cm). Such equipment can normally be installed in an hour or so at most locations, directly mounting on a building or on a flat roof using a non-penetrating mount, similar to a tripod. Consequently, a remote small cell can be installed and integrated using a relatively low skill level in half a day. However, in common with most leased line tariffs, satellite service incurs an ongoing operational cost that is related to the bandwidth that needs to be leased on a satellite transponder. The advent of next- generation satellites that use multiple spot beam technology, known as High Throughput Satellites (HTS), versus conventional legacy wide beam satellites, is radically lowering the cost of satellite bandwidth to levels that easily justify the business case for use of satellite for backhaul in almost all remote and rural cases.

Small cell satellite backhaul - use cases • Remote and Rural - Satellite backhaul can be deployed anywhere that has visibility

of a suitable satellite. In practice, this means that practically any location (except the northern side of mountains in the northern hemisphere and the southern side in the southern hemisphere) can be linked, irrespective of distance from other backhaul technologies. Thus, satellite backhaul can be employed at locations where there is no xDSL or fiber, and where establishing microwave links would be too expensive—for example, cases where multiple hops would be needed to serve a single site, as in rural remote or rural areas.

• Mobility - The use of small cells in a variety of mobile situations can be achieved simply by using satellite backhaul. These use cases include the use of small cells on airplanes (business or large-bodied jets), ships (ranging from large yachts to commercial vessels and cruise ships) and land-deployed ‘cells on wheels’ deployed


to provide extra coverage in case of disaster situations or for special events. For ships and airplanes special stabilised antenna systems are used to point at the satellite. The systems also have to be able to switch between different satellites as the ship or airplane moves from one coverage area to another, and also to compensate for Doppler effects. For ‘cells on wheels’ applications, the antenna is only deployed when the vehicle is stationary and can be pointed manually or automatically by an auto-point antenna.

• Rapid deployment - Small cells are compact and lightweight and are well suited to deployments of a temporary nature such as disaster recovery, first responder, and special events. Temporary deployments require equipment that is portable and that can be rapidly installed and commissioned to provide or restore essential communications infrastructure in times of great need—a perfect application for satellite.

Capacity Satellite can provide practically any reasonable capacity from a few kilobit/s—useful for Supervisory Control and Data Acquisition (SCADA)-type applications—to 350 Mbit/s. The only real constraints are that the size of the dish and power amplifier increase with capacity and, more importantly, the operational cost is directly proportional to the capacity required. Typical link capacities provided for small cell sites by satellite would be in the range of 1 Mbit/s satellite forward-link by 512 kbit/s satellite return-link for a rural voice-only site in a developing country to 10 Mbit/s forward-link by 2 Mbit/s return-link for a voice and data service in a developed country. To address the space segment requirement for a backhaul application or general content access needs, the satellite industry answer is HTS. The economics of satellite backhaul are discussed separately in the Rural Small Cell white paper, also available from the SCF.

Availability As with most telecoms link technologies the availability of a satellite link is a function of the engineering rules applied to it. If the need is, for example 99.9% link availability, then the equipment and satellite bandwidth will be less expensive than that required to realise a 99.999% link availability, given the same locations, satellite transponder, etc.

TDMA satellite systems incorporate adaptive modulation and coding (AMC) techniques and automatic power control so that the effects of varying atmospheric conditions (or rain fade) can be compensated for. The choice of satellite band and geographic location strongly influence the degree of rain fade that can be expected. Lower frequency bands (C-band: 4 – 6 GHz) are practically unaffected by weather. The most commonly used band (Ku-band: 10 – 12 GHz) is slightly more affected. However, the highest currently used band (Ka-band: 20 – 30 GHz) could expect up to 24 dB of rain fade.

That said, the integration of the satellite system’s QoS (Quality of Service) scheme with automatic power and AMC control means that the bandwidth for a given site can be maintained according to its SLA (Service Level Agreement) throughout fading conditions. The link capacity is first calculated using ‘clear sky’ conditions and then extra capacity is added to allow for the increased capacity requirement of the maximum expected percentage of sites that will be in a deep fade at any time. The allocation of this capacity is automatic and transparent to the end systems.


Jitter and delay A TDMA satellite system uses a shared satellite forward-link carrier and time division access to the satellite return-link carrier(s). Therefore, the jitter characteristics are typically much more challenging than on a terrestrial link. Typical average values to be expected on the satellite forward- link would be 5ms with a maximum of 25ms. Similarly, on the satellite return-link the jitter may average 10ms with a maximum of 50ms.

There are two components that make up delay. One of these is the fixed ‘speed of light’ delay in the signal travelling from the ground to the satellite and back to the ground. Typical values here are 240 – 260ms for Geostationary satellites, depending on the exact geographic locations of remote site, hub site, and satellite. In addition, there are the packetization and processing delays which add 35ms – 50ms, leading to typical one-way trip times of 275 – 310ms.

Note, these latency values can also be experienced by residential small cells (depending on the xDSL service used for backhaul) and hence small cells, that have already been designed to accommodate the severe propagation delays experience in residential opportunities, are well suited to satellite deployments, e.g., compared with legacy 3G NodeBs.

Satellite service provision In most cases, the satellite service (including installation, management, and repair) is provided by a satellite network operator (SNO). There are at least 350 SNOs worldwide [18], ranging from transnational to regional to country operations. Occasionally the mobile network operator will decide to operate the satellite network itself if it is economically advantageous to do so. In some cases, operators rent managed services that include remote terminal equipment and satellite bandwidth. Given the lower cost of ownership and operations of Small Cells, a new trend is emerging—this is where in-country satellite operators use the same common Infrastructure to provide bundled Small Cell and satellite managed services to multiple operators. To empower clients, a customer portal into the network management system provides the real-time and statistical information required by the mobile operator.

Aspect Summary Capacity Up to 350 Mbit/s outbound, 15 Mbit/s forward link, but pay per Mbit/s so

realistic b/w per small cell might typically be: 2 – 10 Mbit/s downlink, 1 -2 Mbit/s uplink

Latency / Jitter 300 ms one-way latency. Jitter 5 – 30 ms. Often requires special parameters/settings

Coverage Almost ubiquitous. Includes mobile cases (such as ships, planes or trains)

Availability / resiliency

Link availability can be engineered as required

QoS support Varies by vendor, but carrier-class solutions with extensive site/application/VLAN QoS are available and required for good voice quality/data throughput

Equipment at small cell site

Small IP67 outdoor unit, 25cm x 25cm x 10 cm plus small dish 69 cm upwards

Installation Satellite installation possible by a TV antenna engineer or similarly skilled technician

Table 5-1 Summary table: Satellite


5.2 Non line of sight

NLOS backhaul technologies can provide a very efficient means of delivering backhaul connectivity to Rural and Remote locations. Point-to-point, point to multi-point and relay topologies can be leveraged to extend the reach of a wired network into under-served remote areas or moving locations such as trains and other transportation. Due to the low density of usage in these scenarios, cost per Mbps becomes a major factor in the choice of backhaul technology, and leveraging sub 6GHz NLOS technology where mass product access technology is re-used can help bring the TCO to sustainable levels. Furthermore, rural and remote areas contain less interference in license-exempt bands (e.g. 5.xGHz), removing the cost of licensed spectrum in the TCO.

NLOS technology does not require a clear path between end points and is resilient to the following:

• Building or vegetation clutter • Moving clutter such as vehicles or people

For moving targets such as transportation, the clutter environment is chaotic and the end point moves through different environments – NLOS technology is resilient to this.

In addition, fast handover and Doppler Correction techniques can be used at sub6GHz frequencies, and mobile backhaul solutions on the market today leverage cellular handover techniques.

For temporary installations such as special events, the clutter environment is likely to change as the venue is built, and as users enter and leave the environment – again, NLOS technology is resilient to this.


6. Working with limited backhaul performance

The challenging conditions of rural and remote use cases means that it may not be cost effective or even possible to have the same high backhaul performance as in an urban deployment. In this section we consider how small cells can be made to work over lower performance backhaul, and the implications on services and capacity.

6.1 Limited capacity

Residential femtocells were originally designed to operate over end-customers home internet links, typically provided by xDSL or cable TV technology and delivering data rates from 2 – 100 Mbit/s downstream and 0.5 – 10 Mbit/s upstream. Deployments of urban small cells in metro areas have typically been by either fiber or microwave links with speeds up to several Gigabit/s. By contrast rural deployments are typically deployed in areas where high speed broadband access is limited. The distances from the switching center to a rural community may be too long for economic installation of fiber, too remote for high speed xDSL and the terrain too complex for microwave links. For these types of sites we often have to deploy unconventional backhaul technology, for example Very Small Aperture Terminal (VSAT) satellite links or daisy chained Wi-Fi or other multi-hop contended radio links.

For moving installations, a cabled link may not be possible – on trains, planes, ships and cells on wheels installations in which case the only choice is satellite or some other form of long-haul radio link.

The capacity of satellite backhaul links is mainly constrained by the price of satellite bandwidth. Increased efficiency terms of bit/s/Hz of satellite capacity can be achieved by using larger dishes (but they are less aesthetic) or larger power amplifiers (which consume much more power – also often a constraint in rural locations). Thus the main tool to increase capacity on satellite links (or other similarly constrained long haul radio links) is to increase the bandwidth used. In the case of satellite, the spectrum used for a link is directly paid for in terms of renting transponder capacity at a typical cost (in 2014) of $1000 - $3000 / MHz / Month. The IP capacity of a Megahertz of satellite capacity depends on many variables but is typically between 1 – 3 Mbit/s per MHz.

Given this economic constraint the importance of efficiency becomes of over-riding importance. Selecting the most efficient satellite technology helps, but the transport protocols used for the backhaul of small cells themselves needs to be considered as well – i.e. Abis for GSM, Iuh for 3G and S1 for LTE. With all of these protocols, plus the IPSec encryption that is typically added for security – it is easy to see that they were not optimized for bandwidth utilization. For example – a specially optimized 2G or 3G base station can carry a voice call in around 5 kbit/s whereas a typical GSM base station will take 12 – 20 kbit/s and a 3G small cell 40 – 50 kbit/s. An GSM BTS supporting 8 simultaneous calls can operate on as little as 50kbp/s backhaul bandwidth.

Data can be equally extravagant in terms of bandwidth usage compared to useful data actually carried. Techniques including backhaul compression adaptation (both lossy and lossless), see [4], and caching, see [19], can be used to improve data efficiency for compressible data (such as text, web sites, images) and non-compressible such as streaming music or video.

In the extreme case of intermittent or no backhaul connectivity, core network functionality can be localized to the remote location, and local call switching and data




transfer continue as normal. 3GPP define these in TR22.3462 as isolated networks which include service to Nomadic eNodeBs. Our document on core network virtualization [4] describes how this is applied in small cell networks.

6.2 Higher latency A characteristic of satellite and other long haul radio links, such as multi-hop Wi-Fi is that the latency is much longer than on traditional backhaul links. Using xDSL it is typical to be able to ‘ping’ a server local to the serving DSLAM / B-RAS in 10 – 30ms (or sometimes less) whereas over satellite links the delay will typically be 600 – 1000ms round trip delay depending on the technology used. The effect on voice calls is tolerable provided the delay is at the lower end of this range and provided the call is subject to only one call leg being over satellite or long haul radio. Where calls are local to a single site (village, mining community, cruise ship) this will necessitate two hops through the long latency link. One possible amelioration is to provide local switching as described above at remote sites or clusters of sites to eliminate the double hop. [4] describes such architectures which leverage local gateways and/or local core networking functionality.

For data, the extra latency has a specific impact on TCP/IP connections. This is the well-known throughput constraint due to the TCP slow-start congestion control strategy. In the absence of timely acknowledgements of TCP data packets the TCP protocol assumes that the network is suffering from congestion and slows down the transmission rate. With a high latency link the effect is to limit the throughput to ~ 1Mbit/s per TCP session irrespective of the link capacity available. While this has not been a particular issue for 3G networks where the use of HSPA limits the capacity to typically 16 / 5 Mbit/s (downlink and uplink) and thus a few smartphone users can saturate the capacity - for LTE networks offering 100 Mbit/s+ the provision of high capacity links becomes pointless unless this limitation can be overcome. Fortunately there are well known techniques for spoofing the acknowledgements locally to overcome these limits – but not all backhaul equipment has this feature available.

6.3 Working over consumer grade links

While residential femtocells are deployed over customer-provided consumer-grade xDSL links, most small-cell public access systems have been deployed using backhaul that is part of the mobile operator’s own infrastructure – using fiber or microwave for metro-cells for example. Because these cells are usually public access ‘open’ cells they form part of the mobile operators own network and users will judge the performance accordingly. This contrasts with residential femtocells which are often closed – operating on a white-list and only allowing emergency access to non-white-listed users. As such they are identified as being part of the consumers own home network.

The specific difference between these home networks and the mobile operators own infrastructure is the availability of specific Quality of Service parameters and guaranteed Service Level Agreements (SLAs). The QoS issue is a technical one – a small cell may have several streams of traffic associated with it for voice, data, synchronization, O&M etc. and these may require different prioritization and handling in the backhaul network. The SLA is an operational and technical issue. The mobile operator needs to have guarantees of performance that will satisfy the customers, regulators and business objectives. At a technical level they will require systems that provide consistent performance irrespective of other users of the network, weather 2 “Isolated Evolved Universal Terrestrial Radio Access Network (E-UTRAN) operation for public safety; Stage 1, (Release 13)”, 3GPP TR22.346.






conditions etc. and this is what really divides the consumer from professional grade systems.

6.4 Synchronization

Most 3G small cell technologies are able to derive their frequency synchronization needs over the backhaul link using NTP (or proprietary modifications of NTP) entirely in-band (i.e. with no need for timing-specific support at any intermediate node). While this consumes some bandwidth and can be slow to initialize over a higher jitter link this is generally satisfactory and universally available. LTE-A and TDD deployments generally require phase synchronization demanding the higher level of timing performance available from IEEE 1588v2 (aka PTP) equipment and low latency networks [20]. IEEE 1588 also operates in-band but makes provision for timing regeneration at intermediate nodes in the backhaul network (Boundary Clock) and accounting for delay or jitter through timing-aware links (Transparent Clock).

The performance of all back-haul based technologies is ultimately limited by accumulated uncertainty in delay (including delay changes from re-routing events) and by jitter in the back-haul although jitter can be mitigated by an accurate local frequency reference provided by higher performance oscillator or Synchronous Ethernet. Synchronous Ethernet uses the physical layer of the back-haul technology to transport accurate frequency to the edge of the network. This allows IEEE 1588 to deliver a very significant improvement in phase stability but requires explicit Synchronous Ethernet support in every element of the backhaul network.

In-band technologies benefit from guaranteed availability (as good as the back-haul, at least) and resilience to interference or attack that cannot be offered by radio-based technologies such as GNSS. However, where in-band technologies cannot deliver latency or jitter performance consistent with the synchronization need, the operator may have to deploy GNSS timing receivers (GPS, GLONASS, BeiDou, Galileo, etc.) at each site. The sky visibility needed for such systems is unlikely to challenge where the backhaul itself uses satellite.

Partial Timing Support (G.8271.2) enables the combination of an accurate but potentially intermittent source (such as GNSS) with a continuously available back-haul source to ‘hold-over’ synchronization established by the accurate source for extended durations. For example, phase derived at the sub-microsecond level from GNSS can be maintained by accurate frequency alone derived from Synchronous Ethernet or IEEE 1588 over a high-latency connection.

In many applications the back-haul technology maintains an awareness of at least some aspects of synchronization for its own purposes (for example modem frequency control or TDM marshalling). In practice this information is not yet accessible in a unified way between every different type and brand of equipment.

A detailed description of synchronization requirements and solutions for small cells can be found in our LTE Synchronization document [20].




References

i [SCF151] ‘Rural and remote small cell case studies’, http://scf.io/documents/151 2 [SCF150] ‘Business drivers for connecting the unconnected via small cells’,

http://scf.io/documents/150 3 [SCF095] ‘Backhaul for urban small cells: a topic brief’,

http://scf.io/documents/095 4 [SCF154] ‘Virtualization in small cell networks’, http://scf.io/documents/154 5 [SCF153] ‘Rural and remote small cell network architectures’,

http://scf.io/documents/153 6 [SCF102] ‘Release Two - Enterprise: Overview’, http://scf.io/documents/102 7 [SCF067] ‘Enterprise small cell network architectures’,

http://scf.io/documents/067 8 ‘Mobile Backhaul Implementation Agreement Phase 2’, MEF 22.1 9 ‘Mobile Backhaul Phase 2, Amendment 1 – Small Cells’, MEF 22.1.1 10 ‘Metro Ethernet Services Definitions Phase 3’, MEF 6.2 11 ‘Ethernet Services Attributes Phase 3’, MEF 10.3 12 ‘Implementation Agreement for the Emulation of PDH Circuits over Metro Ethernet

Networks’, MEF8 13 ‘Metro Ethernet Network Architecture Framework Part 1: Generic Framework’,

MEF 4 14 ‘External Network Network Interface (ENNI) – Phase 2’, MEF 26.1 15 ‘Ethernet Access Services Definition’, MEF 33 16 ‘Virtual NID (vNID) Functionality for E-Access Services’, MEF 43 17 [SCF049] ‘Backhaul technologies for small cells’, http://scf.io/documents/049 18 “iDirect Sets New Record In Customer Satisfaction According To Latest Global

Survey”, Sep 2013, http://goo.gl/I9fGdV 19 [SCF088] ‘Urban small cell network architectures’, http://scf.io/documents/088 20 [SCF075] ‘Synchronisation for LTE small cells’, http://scf.io/documents/075

http://scf.io/documents/151








http://goo.gl/I9fGdV



small cell forum release 5 - · pdf file8/6/2015 · small cells. small cell forum...

Documents