RAN Sharing NEC s Approach towards Active Radio Access Network Sharing

Transcription

1 White Paper RAN Sharing NEC s Approach towards Active Radio Access Network Sharing NEC Corporation Executive Summary The volume of data carried by wireless networks is expected to increase rapidly in the next few years [1][2]. Meeting this demand for increased capacity will require substantial new investment on the part of mobile network operators (MNOs). However revenues are not keeping pace with the growth in and many MNOs are therefore turning to network sharing as a way to reduce both their capital expenditure (CAPEX) and operational expenditure (OPEX). Network sharing is already used by several 2G and 3G operators, and will become more widespread with the introduction of LTE. NEC recognizes operators need for network sharing and has developed a comprehensive solution to meet this demand. This white paper presents a brief overview of NEC s solution. A key feature of NEC s solution is an innovate Radio Resource Management (RRM) approach based on a Network Virtualization Substrate (NVS) in the enodeb that allows radio resources to be virtualized and shared in an efficient way. On the backhaul, is separated by VLANs with additional mechanisms for shaping. A flexible Operations, Administration and Maintenance (OAM) architecture is also provided to allow customized data collection and control for each operator. enefit Network sharing may be defined as any arrangement by which multiple operators share the capacity of a physical network. This includes the case of two or more MNOs pooling their network infrastructure by leasing capacity to each other, as well as the case in which a network owner leases 1 capacity to one or more mobile virtual network operators (MVNOs). RAN sharing refers specifically to the sharing of radio access network assets, and can be classified as either passive or active. In the case of passive RAN sharing, operators share only cell sites. Active RAN sharing extends this to the sharing of transport infrastructure, radio spectrum and baseband processing resources. In the last five years a significant number of operators have already adopted passive RAN sharing in their 2G and 3G networks. Operators are now deploying LTE to support ever growing volumes of data. Due to the level of investment required, LTE RAN sharing will be essential to the future success of many operators. RAN sharing is particularly advantageous for deploying large networks of small-cell base stations, for which site acquisition and backhaul installation are especially challenging. The following are some of the main benefits of RAN sharing. CAPEX and OPEX savings: The principal benefit of RAN sharing for operators is the cost saving in planning, rolling out, maintaining and upgrading their networks. Network owners can subsidise their costs by leasing capacity to MVNOs, whilst MVNOs benefit from not having to deploy and maintain their own infrastructure. According to a market survey, mobile infrastructure sharing has already been deployed by over 65% of European operators in various ways and this trend is expected to grow in the future [2]. The savings are even greater in the case of active RAN sharing. Furthermore, virtualization of the radio spectrum and enodeb hardware resources also greatly

2 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]. 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 new revenue 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 during periods 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 2 physical Network sharing Gateway Core Network (GWCN) and Multi-Operator Core Network (MOCN), as shown in Figure 1. + S1 MME eutran GW MME eutran GW MME Figure 1: Network Sharing Architectures supported by 3GPP S1 GW 3GPP TSG RAN WG2 and WG3 have developed 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 of common RAN resources (e.g. pooling of unallocated radio resources). A means to flexibly, dynamically and automatically allocate RAN resources ondemand 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.

3 NEC Solution NEC s solution supports both of the 3GPP architectures shown in Figure 1. Figure 2 illustrates the key features of NEC s active RAN sharing architecture for the case of MOCN with two MNOs. MNO B PGW MME SGW SeGW Downlink Traffic Shaping Backhaul MNO A (Network Owner) MME PGW DHCP Server SON/ OAM SeGW SGW S1 Flex Multiple VLANs per operator ` enodeb Uplink Traffic Shaping NVS MAC Scheduler Figure 2: NEC s end-to-end RAN Sharing Solution NEC s 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 shaping is performed in the enodeb (for uplink) and the gateway (for downlink). The OAM server allows each operator s virtual network to be separately configured and managed. These features are described in more detail in the following sections. 1) Radio Resource Management At the RRM level, NEC s 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: Reserved resources are guaranteed to be always available to the operator that owns them. 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). Each operator may select a customized mixture of reserved and shared resources according to their individual requirements. Virtualization of radio resources presents many challenges which can be summarized in the following three key objectives. 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. NEC s 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 for each operator to set different RRM parameters based on individual RRM policies. NEC s 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. Spectral Efficiency: Efficient use of the physical radio resources should be made in order to maximize the overall network capacity. NEC s NVS achieves high spectral efficiency by means of dynamic scheduling, which is described further below. 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. 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 operator s is scheduled only within its dedicated PRBs. An example of this Static Reservation scheme with two operators is shown in 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 3

4 rate available to users of one operator when there is low in the cell from other operators. NEC s 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 Figure 3(b). nearly the same user throughput as with the Full Sharing scheduler when the load of operator B is low. When the load of operator B is high NEC s NVS method provides the same isolation as Static Reservation, avoiding any degradation in operator A s user throughput. (a) Static Reservation (b) NEC NVS Solution Frequency MAC Scheduler MAC Scheduler Time A B Frequency NVS Slice Scheduler MAC Scheduler Time Figure 3: (a) Static Reservation versus (b) NEC NVS solution NEC s NVS scheduler has been thoroughly evaluated 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 load of operator A is assumed to be fixed at 4 Mbps/cell, and the load of operator B is varied from 0 to 10 Mbps/cell. We compare the user throughput of NEC s NVS scheduler with both the Static Reservation case (as shown in Figure 3(a)) and a Full Sharing scheduler which does not distinguish at all between the 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 ). The Static Reservation case provides complete physical isolation between operators so the mean user throughput of operator A s does not change with the load of operator B. However, it also unnecessarily limits the user throughput of operator A when the load of operator B is low. With NEC s NVS method, operator A achieves Figure 4: Simulation Results: Mean User Throughput Figure 5 shows the fraction of cell resources consumed by each operator when the load of operator B is 8 Mbps/cell. Since the 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 the network. Static Reservation allows operator B to use only 50%, but this leaves some resources unused because operator A does not have enough to fill the remaining 50%. NEC s NVS method allows operator B to use the resources that operator A currently does not need, improving the service to operator B s users and maximizing the overall spectrum usage. Resource Usage [%] Full Sharing Unfair Allocation Static Reser vat ion Unused Resour ces NEC NVS 's Shar e 's Shar e Figure 5: Simulation Results: Resource Usage at High Load 4

5 2) Backhaul NEC s backhaul solution for RAN sharing provides support for both wired and wireless all-ip backhaul architecture for up to six network operators. The core transport features include: Traffic shaping: The rate of uplink being sent from an enodeb and downlink being sent from a gateway can be limited for each operator or for each forwarding class in each operator to provide guaranteed performance per operator. S1 Flex: The enodeb can be connected to multiple MMEs or SGWs. This flexibility allows MMEs and SGWs to be owned by separate individual operators to enable network sharing, or owned by a single operator for connection redundancy and load balancing purposes. Traffic Isolation: The transport network can be partitioned into multiple virtual domains for separating while efficiently sharing the mobile backhaul bandwidth. Multiple IP addresses are assigned per enodeb to identify and manage each operator s in the backhaul network. QoS control can be enabled per VLAN [11]. An operator s can be mapped to one or multiple VLANs. IPsec: If the enodeb is connected to the CN via untrusted IP backhaul, IPsec can be used to provide end-to-end security for operators. The enodeb can establish multiple IPsec tunnels for each operator, and the SeGW may be shared between operators. 3) OAM NEC s solution supports Configuration Management, Performance Management and Fault Management on a centralized basis. The network owner sets selected parameters, collects performance data, sets alarm trigger conditions and handles alarms related to the enodeb. The network owner also manages the resource assignment for each MVNO according to the contracts with the MVNOs. Performance data is managed on a peroperator basis for up to six operators. Future Enhancements In addition to maintaining a commitment to further standardization of network sharing features, NEC is investigating ways to provide enhanced RAN sharing functionality in future products. NetShare: Future centralized RAN architectures will allow enodeb processing resources to be pooled across multiple cells. This suggests the possibility of enforcing each operator s share of the radio resources on aggregate over a group of cells, rather than in each cell independently. This would allow the sharing mechanism to distribute each operator s share between cells according to the operator s load in each cell. NEC has developed a framework called NetShare for performing this function. Multi-Operator Load Balancing: Another technique which is related to the above is multi-operator load balancing. This involves redistributing between cells on a per operator basis in order to minimize the blocking probability experienced by each operator. NEC is conducting research in this area and is evaluating its potential for increasing system capacity. Conclusion Network sharing offers compelling cost benefits to network operators and is therefore expected to become one of the major features of future LTE deployments. The virtualization of radio spectrum and enodeb resources required for active RAN sharing also makes possible the easy creation and management of virtual networks, opening up a range of new business models through which network owners can increase the revenue from their networks. NEC s enodeb product line allows operators to fully exploit the benefits of network sharing by providing an innovative RRM solution for sharing radio resources, efficient and flexible backhaul sharing, and an OAM architecture that allows network management and monitoring on a peroperator basis. 5

6 References [1] Active RAN Sharing Could Save $60 Billion for Operators, [2] Mobile Network Sharing Report , Development, Analysis & Forecasts, Market Study, Visiongain, 2010 [3] 3GPP TS , Network Sharing; Architecture and functional description [4] 3GPP TS , S1 Application Protocol (S1AP) [5] 3GPP TS , X2 Application Protocol (X2AP) [6] 3GPP TS , Radio Resource Control (RRC) [7] 3GPP TR , Study on RAN Sharing Enhancements, Release 12 [8] R. Kokku, R. Mahindra, H. Zhang, and S. Rangarajan (NEC Laboratories America), NVS: A virtualization substrate for WiMAX networks, ACM Mobicom, 2010 [9] R. Kokku, R. Mahindra, H. Zhang, S. Rangarajan (NEC Laboratories America), "CellSlice: Cellular Wireless Resource Slicing for Active RAN Sharing", 5th International Conference on Communication Systems and Networks (COMSNETS), January 2013 [10] Tao Guo, Rob Arnott (NEC Telecom Modus Ltd.), Active LTE RAN Sharing with Partial Resource Reservation, submitted to IEEE Vehicular Technology Conference, September 2013 [11] IEEE 802.1Q Virtual LANs Abbreviations 3GPP 3 rd Generation Partnership Project CAPEX Capital Expenditure CN Core Network DHCP Dynamic Host Configuration Protocol eutran Evolved UMTS Terrestrial Radio Access Network GW Gateway GWCN Gateway Core Network LTE Long Term Evolution MAC Medium Access Control MME Mobility Management Entity MNO Mobile Network Operator MOCN Multi-operator Core Network MVNO Mobile Virtual Network Operator NVS Network Virtualization Substrate OAM Operations, Administration and Maintenance OPEX Operational Expenditure PGW Packet Data Network Gateway PLMN Public Land Mobile Network PRB Physical Resource Block QoS Quality of Service RAN Radio Access Network RRM Radio Resource Management SA System Aspects SeGW Security Gateway SGW Serving Gateway SON Self-Organizing Network TR Technical Report TS Technical Specification TSG Technical Specification Group UE User Equipment UMTS Universal Mobile Telecommunications System VLAN Virtual Local Area Network WG Working Group NEC Corporation 7-1, Shiba 5-chome, Minato-ku, Tokyo , Japan tel: +81-(0) 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. 6