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3GPP Network Sharing Enhancements for LTE

Photograph of Alastair BrydonLast week I was interviewed for a forthcoming report on mobile network sharing and it prompted me to catch up on the latest 3GPP developments in this area. As network sharing becomes widespread in the mobile industry, a range of new capabilities are under development in 3GPP. These will provide network operators with much greater flexibility and control of shared networks, to enable more sophisticated technical and commercial arrangements.

Over the last ten years, network sharing has evolved from a mildly interesting concept to a mission critical requirement for the mobile industry. Mobile network operators face the challenge of rolling out nationwide LTE networks, using a new technology and new network architecture, to deliver substantial uplifts in capacity and throughput while meeting high expectations for coverage and quality. In the meantime their revenues remain stubbornly flat. For many network operators the only realistic way ahead is to make substantial savings in capital and operational costs through network sharing.

We have already seen a string of network sharing arrangements among existing network operators, such as Telefónica O2 and Vodafone in the UK. New network operating models have also emerged, including wholesale network providers such as LightSquared in the USA and Yota in Russia. This is just the start and there is little doubt that network sharing will be fundamental to the mobile industry in the years ahead.

Most of the early network sharing agreements involve “passive” sharing, in which network operators achieve savings by sharing basic resources such as sites, masts, accommodation, power and air conditioning. Until recently there were few examples of “active” sharing, in which operators share network equipment and potentially radio resources, because of the technical, commercial and regulatory complexities involved. However, deeper sharing of this sort brings additional benefits and the need to maximise savings is creating the pressure needed to overcome these barriers.

GSM and early UMTS standards lacked significant support for network sharing. GSM was designed on the basis of one network, one operator. Release 99 opened up the possibility of UMTS network operators sharing a common radio network, if they also shared certain parts of the core network. However, the arrangement was somewhat restrictive and there was little interest in the early 2000s. As the pressure mounted for more substantial solutions for network sharing, 3GPP Release 6 set out a number of fundamental requirements, which were satisfied by new features in Release 6 for UMTS, Release 8 for LTE and Release 10 for GSM/EDGE.

As of Release 11, the 3GPP specifications include two documents dedicated to network sharing matters, along with a variety of supporting features in other specifications:

  • TR 22.951 “Service aspects and requirements for network sharing” gathers together deployment scenarios, network operator and user requirements, and other considerations for network sharing solutions. The document lays down fundamental principles, such as avoiding the need for proprietary mobile terminals to benefit from network sharing, the requirement to support legacy mobile terminals, the need to allow service differentiation between shared network operators, and avoiding compromises to the services offered in shared networks.
  • TS 23.251 defines the architecture and functions needed to allow several core network operators to share a single radio access, in such a way as to meet the requirements of TR 22.951.

TS 23.251 sets out two approaches to sharing an LTE radio access network (eUTRAN), which are illustrated below. The differences are in the core network aspects:

  • With the Multi-Operator Core Network (MOCN) approach, each network operator has its own core network, the Enhanced Packet Core (EPC). Maintaining a strict separation between the core network and the radio network has a number of benefits related to service differentiation, interworking with legacy networks, fall back to circuit switched voice services and the support of roaming.
  • In the Gateway Core Network (GWCN) approach, the network operators also share the Mobility Management Entity (MME) element of the core network, which is responsible for bearer management and connection management between the mobile terminal and the network. The GWCN approach enables additional cost savings compared with MOCN, but it is a little less flexible, and regulators may be concerned that it reduces the level of differentiation that is possible between operators.

Diagram illustrating Multi-Operator Core Network (MOCN) and Gateway Core Network (GCN) approaches to LTE eUTRAN sharing

In each case the network broadcasts system information and supports signalling exchanges that allow the mobile terminal to distinguish between up to six different sharing network operators, to obtain service or undertake handover, without any concern for the underlying network sharing arrangement.

As network sharing becomes a central feature of mobile network operation, there is a need to address a wide variety of technical, commercial and regulatory requirements. Among other things, there is interest in pooling spectrum, sharing resources asymmetrically and dynamically based on financial considerations and load, and the ability for sharing operators to manage and control the use of resources independently. In order to address these and other demands, 3GPP is undertaking further work to capture requirements and deliver solutions. Solutions will start to become available in Release 13, which is likely to come to fruition in 2015.

3GPP TR 22.852 extends the set of network sharing scenarios defined in Release 6 to cover more complex scenarios for co-operation among operators. From these it derives the requirements for further developments to complement the existing system capabilities for sharing 3GPP radio networks. Some of the new aspects addressed by TR 22.852 include:

Resource sharing

  • Asymmetrical sharing of RAN resources, for example in proportion with the financial interests of the sharing parties.
  • Dynamically modifying the allocation of resources as a network approaches capacity, for example taking account of the financial interests of the sharing parties.
  • Load balancing between cells according to the financial interests of the sharing network operators.
  • Variable sharing of network capacity at different times of day.
  • On-demand capacity brokering, for example to support peaks in demand or to utilise excess capacity for background machine-to-machine (M2M) transactions.
  • Fine control of shared sectors, for example providing sharing on some sectors of a base station, but not others, near a national border.

Operations and Maintenance

  • The controlled availability operations and maintenance information for sharing operators.
  • Controlled access to the management of resources by sharing operators.
  • The controlled availability of drive test data to a network operator from mobile terminals that do not necessarily belong to its own customers.

Charging and Billing

  • The application of different network sharing charge levels according to resource usage, to allow for sophisticated management of resources and revenues.
  • Triggering charging events when a mobile terminal moves between a non-shared area and a shared area.
  • Availability of detailed wholesale charging event records for individual network operators sharing network resources.

There is little doubt that mobile network sharing is here to stay and developments of this sort, coupled with innovative solutions from equipment vendors, will spawn a wide variety of new business opportunities for existing network operators and new players in the mobile industry.

Dr Alastair Brydon has worked in digital radio communications for over 25 years. He provides expert advice on 2G, 3G and 4G mobile systems and standards including GSM, UMTS and LTE. He has written over 40 reports on the development of wireless technologies and services and has acted as an expert witness in major patent disputes.

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