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simplifies the management of a shared

network by allowing the capacity of the

network to be decoupled from the underlying

physical resources. One study has concluded

that operators worldwide could reduce

combined OPEX and CAPEX costs by up to$60 billion over a five year period through

network sharing, and at least 40% of these cost

savings are expected to come from active

RAN sharing [1].

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New revenue sources: Virtualization of radio

resources allows network owners to package

and lease radio spectrum more flexibly and in

smaller units than has previously been possible.

As a result, network owners can now offer a

much wider range of contracts to MVNOs.

This offers the possibility of creating newrevenue streams from new types of MVNOs

who would not previously have been able to

justify the investment needed to enter the

market, such as start-up companies and

entrepreneurs offering specialized services to

end users.

Service-centric networks: Sharing of network

infrastructure will encourage a shift from

competition on the basis of network coverage

to competition on the basis of features and

services, promoting innovation and growth

which will benefit the whole industry.

Environmental benefits: RAN sharing is a

greener option than traditional single-operator

networks since sharing equipment and sites

means that operators can reduce their energy

consumption and minimize environmental

impact by deploying fewer antenna masts.

Active RAN sharing enables pooling of

baseband processing resources, resulting in

further energy savings particularly duringperiods of low load.

3GPP Standardization Status

From early on, NEC has been actively

contributing to the standardization of RAN sharing

for UMTS and LTE in 3GPP. The key RAN

sharing functions introduced by 3GPP are

summarized below.

3GPP TSG SA WG2 provided a framework in

reference [3]by defining two main architectures for

physical Network sharing Gateway Core Network

(GWCN) and Multi-Operator Core Network

(MOCN), as shown in Figure 1.

eUTRAN

OperatorA+OperatorB

eNB

eNB

eNB

eNB

eUTRAN

OperatorA OperatorB

MME GWMME GWMME GW

S1 S1

Figure 1: Network Sharing Architectures

supported by 3GPP

3GPP TSG RAN WG2 and WG3 havedeveloped protocol specifications allowing for

differentiation of up to six operators via multiple

PLMN identifier support [4][5][6]. There is

provisioning on the S1 interface for the exchange

of supported PLMN identifiers between eNodeB

and MME to enable selection of the correct CN. On

the X2 interface, a similar exchange of supported

PLMN identifiers between eNodeBs allows for

handover target selection. On the Uu interface,

broadcasting of the supported PLMN identifiers

enables UEs to perform network selection.Currently, the 3GPP RAN Sharing

Enhancements Study Item of the TSG SA WG1 is

defining new scenarios in which multiple operators

share network resources [7]. The objective of this

work is to formulate requirements for sharing

common RAN resources, with an aim to provide

the following:

A means to verify that the shared network

elements allocate RAN resources according to

the sharing agreements and sharing policies.

A means to enable efficient sharing ofcommon RAN resources (e.g. pooling of

unallocated radio resources).

A means to flexibly, dynamically and

automatically allocate RAN resources on-

demand at smaller timescales than the ones

currently supported.

NEC is playing a major role in this effort as the

official Study Item rapporteur and is authoring

some of the key contributions.

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Each operator may select a customized mixture

of reserved and shared resources according to their

individual requirements.

NEC Solution

NECs solution supports both of the 3GPP

architectures shown in Figure 1. Figure 2 illustrates

the key features of NECs active RAN sharing

architecture for the case of MOCN with two MNOs.

Virtualization of radio resources presents many

challenges which can be summarized in the

following three key objectives.

eNodeB

NVS MAC

Scheduler

Uplink Traffic

Shaping

Multiple

VLANs per

operator

S1 FlexDownlink

Traffic

Shaping

MNO A (Network Owner)MNO BMME

SGW

PGW DHCP Server SON/OAM

Backhaul

MME

SGW

PGW

SeGWSeGW

`

Isolation: Each operator must always receive

at least the minimum agreed share of the

physical radio resources, and must be

protected from any adverse effects caused by

fluctuations in other operators traffic. NECs

NVS achieves this goal by converting the

physical radio resources into virtual resources

called slices [8]. Each slice is entitled to use a

certain share of the physical resources.

Customization: It should be made possible foreach operator to set different RRM parameters

based on individual RRM policies. NECs

NVS meets this requirement by allocating one

or more slices to each operator, and enabling

admission control and MAC scheduling to be

managed separately within each slice.

Figure 2: NECs end-to-end RAN Sharing

Solution

NECs eNodeB product line includes a Network

Virtualization Substrate (NVS) feature which

manages sharing of the radio spectrum and eNodeB

processing resources. On the backhaul, multiple

VLANs are operated and traffic shaping is

performed in the eNodeB (for uplink) and the

gateway (for downlink). The OAM server allows

each operators virtual network to be separately

configured and managed.

Spectral Efficiency: Efficient use of the

physical radio resources should be made in

order to maximize the overall network

capacity. NECs NVS achieves high spectral

efficiency by means of dynamic scheduling,

which is described further below.

These features are described in more detail in

the following sections.MAC Scheduler

In LTE, the MAC scheduler is designed to make

efficient use of the available radio spectrum whilst

maintaining a careful balance between fairness and

total system throughput. Virtualization inevitably

places additional constraints on the MAC scheduler

algorithm, and the key challenge for the MAC

scheduler design is therefore to provide effective

resource virtualization without compromising

overall system performance.

1) Radio Resource Management

At the RRM level, NECs solution enables active

RAN sharing by virtualization of the physical radio

resources. NEC recognizes that as active RAN

sharing becomes more widespread, MVNOs will

expect more flexibility in the way that virtual

resources are provided and managed by network

owners. The NEC solution therefore allows the

network owner to offer two types of virtual radio

resources to operators:

For example, a simple way to share radio

resources is to assign each operator a fixed set of

Physical Resource Blocks (PRBs) such that each

operators traffic is scheduled only within its

dedicated PRBs. An example of this Static

Reservation scheme with two operators is shown

in

Reserved resources are guaranteed to be

always available to the operator that owns

them.

Figure 3(a). However, this solution provides

poor overall spectral efficiency because it restricts

the frequency diversity available to the MAC

scheduler, and unnecessarily limits the peak data

Shared resources are not reserved by any

operator but may be allocated to any operator

based on a policy configured by the network

owner (for example first-come first-served).

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rate available to users of one operator when there is

low traffic in the cell from other operators.

NECs NVS avoids these limitations by

employing a slice scheduler which works in

conjunction with the MAC scheduler. The slice

scheduler monitors the amount of resources that the

MAC scheduler assigns to each slice and

dynamically adjusts the bearer priorities in the

MAC scheduler to maintain the required resource

allocation for each operator. In this way, all

operators have access to the whole system

bandwidth. This is illustrated in

4

Figure 3(b).

Operator A

traffic

Operator B

traffic

Frequency

A

Time

(a) Static Reservation (b) NECNVS Solution

NVSSlice Scheduler

MAC Scheduler

Frequency

Time

B

Operator B

MAC

Scheduler

Operator A

traffic

Operator B

traffic

Operator A

MAC

Scheduler

Figure 3: (a) Static Reservation versus (b) NEC

NVS solution

NECs NVS scheduler has been thoroughlyevaluated by field trials and simulations [8][9][10].

Figure 4 shows the result of one simulation

experiment in which operators A and B each own

an equal share of a network of 21 cells with a

system bandwidth of 10MHz. The mean traffic load

of operator A is assumed to be fixed at 4 Mbps/cell,

and the traffic load of operator B is varied from 0

to 10 Mbps/cell. We compare the user throughput

of NECs NVS scheduler with both the Static

Reservation case (as shown in Figure 3(a)) and a

Full Sharing scheduler which does not distinguishat all between the traffic belonging to each operator.

The user throughput is the rate experienced by

users when they are receiving data (which can be

higher than the mean offered traffic).

The Static Reservation case provides complete

physical isolation between operators so the mean

user throughput of operator As traffic does not

change with the traffic load of operator B. However,

it also unnecessarily limits the user throughput of

operator A when the load of operator B is low.

With NECs NVS method, operator A achieves

nearly the same user throughput as with the Full

Sharing scheduler when the traffic load of operator

B is low. When the traffic load of operator B is

high NECs NVS method provides the same

isolation as Static Reservation, avoiding any

degradation in operator As user throughput.

Figure 4: Simulation Results: Operator A Mean

User Throughput

Figure 5 shows the fraction of cell resources

consumed by each operator when the traffic load of

operator B is 8 Mbps/cell. Since the traffic load of

operator B is twice as high as that of operator A,

the Full Sharing scheduler allocates two thirds of

the resources to operator B. However this is unfair

on operator A, who owns a half-share of thenetwork. Static Reservation allows operator B to

use only 50%, but this leaves some resources

unused because operator A does not have enough

traffic to fill the remaining 50%. NECs NVS

method allows operator B to use the resources that

operator A currently does not need, improving the

service to operator Bs users and maximizing the

overall spectrum usage.

33.544.5 45.4

66.4 50.054.6

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Full Shar ing Stat ic

Reservation

NECNVS

ResourceUsage[%]

Operator A Operator B

OperatorB's

Share

Unused

Resources

Unfair

Allocation

OperatorA's

Share

Figure 5: Simulation Results: Resource Usage at

High Load



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References

[1]Active RAN Sharing Could Save $60 Billion forOperators,http://www.cellular-news.com/story/36831.php

[2]Mobile Network Sharing Report 2010-2015,

Development, Analysis & Forecasts, Market Study,Visiongain, 2010

[3]3GPP TS23.251, Network Sharing; Architecture andfunctional description

[4]3GPP TS 36.413, S1 Application Protocol (S1AP)[5]3GPP TS 36.423, X2 Application Protocol (X2AP)[6]3GPP TS 36.331, Radio Resource Control (RRC)[7]3GPP TR 22.852, Study on RAN Sharing

Enhancements, Release 12[8]R. Kokku, R. Mahindra, H. Zhang, and S. Rangarajan

(NEC Laboratories America), NVS: A virtualizationsubstrate for WiMAX networks, ACM Mobicom,2010

[9]R. Kokku, R. Mahindra, H. Zhang, S. Rangarajan

(NEC Laboratories America), "CellSlice: CellularWireless Resource Slicing for Active RAN Sharing",5th International Conference on CommunicationSystems and Networks (COMSNETS), January 2013

[10] Tao Guo, Rob Arnott (NEC Telecom Modus Ltd.),Active LTE RAN Sharing with Partial ResourceReservation, submitted to IEEE VehicularTechnology Conference, September 2013

[11] IEEE 802.1Q Virtual LANs

Abbreviations

3GPP 3rdGeneration Partnership ProjectCAPEX Capital ExpenditureCN Core NetworkDHCP Dynamic Host Configuration Protocol

eUTRAN Evolved UMTS Terrestrial RadioAccess Network

GW GatewayGWCN Gateway Core NetworkLTE Long Term EvolutionMAC Medium Access ControlMME Mobility Management EntityMNO Mobile Network OperatorMOCN Multi-operator Core NetworkMVNO Mobile Virtual Network Operator

NVS Network Virtualization SubstrateOAM Operations, Administration and

Maintenance

OPEX Operational ExpenditurePGW Packet Data Network GatewayPLMN Public Land Mobile NetworkPRB Physical Resource BlockQoS Quality of ServiceRAN Radio Access NetworkRRM Radio Resource ManagementSA System AspectsSeGW Security GatewaySGW Serving GatewaySON Self-Organizing NetworkTR Technical ReportTS Technical Specification

TSG Technical Specification GroupUE User EquipmentUMTS Universal Mobile

Telecommunications SystemVLAN Virtual Local Area NetworkWG Working Group

NEC Corporation7-1, Shiba 5-chome, Minato-ku, Tokyo 108-8001, Japantel: +81-(0)3- 3454-1111www.nec.com/lte

Copyright 2013 NEC Corporation. All rights reserved. All

trademarks are the property of respective companies.

Information in this document is subject to change without notice.

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