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Showing posts with label WiMAX Technical. Show all posts
Showing posts with label WiMAX Technical. Show all posts

Monday, 23 November 2009

WiMAX Femtocell System Architecture


So what does it take to build a WiMAX Femtocell solution?

WiMAX Femtocell can be visualized as a scaled down version of WiMAX macro-cell solution. In addition to the capabilities of a WiMAX macro-cell, other required features of a WiMAX Femtocell are the following:

Spectrum: WFAP operates over licensed spectrum using standard WiMAX wireless air interface and protocol.

Form factor: WFAP can be standalone (similar to WiFi access points) or integrated with DSL or cable modems.

Transport: WFAP uses transport network of subscribers’ DSL, FTTH or cable-based broadband connection.

User Capacity: Since WFAP is deployed inside a building; a WFAP needs to support at least 5-6 subscribers.

Power Output: With a range of roughly 10 meters, power output should be kept very low, no more than a 2.4 GHz WiFi product.

Deployment Support: Operating in a licensed spectrum a WFAP may face interference from neighboring base stations (femto or macro). Therefore, a WFAP should have the capabilities to automatically adjust to minimize the interference.

Local Breakout: A WFAP should optionally support the capability to route incoming or outgoing traffic directly to the destination through the Internet Service Provider (ISP) network. This approach will bypass the WiMAX service provider network, thus offloading WiMAX service provider network and reducing the cost of service to the subscriber.

Performance: A Femtocell solution should fit as per the WiMAX network architecture defined by the WiMAX forum. The deployment should not limit the number of WFAPs that are able to connect with a designated ASN Gateway unless operator specified. A network deployment should allow different ISPs to connect WFAP with ASN Gateway in the core network.

Hand-over: A Femtocell solution should allow handovers between WFAP and WiMAX macro cells or with other adjacent WFAPs.

Security: A Femtocell solution should use a secure channel of communication (for both control plane and data plane) with ASN Gateways in the core network. The core network must authenticate and authorize a WFAP before it starts offering services to MS/SS in its coverage area. A WFAP may authenticate the ASN Gateway with which it gets connected. A WFAP should keep its air interface disabled unless it is authenticated and authorized to start communication with the ASN Gateway in the core network. A Femtocell may support close subscriber group (CSG) database i.e. a list of subscribers allowed to access the WFAP, and its management.

Accounting: For providing different rate plans to subscribers accessing services through WFAP, a WFAP needs to make sure that it is recognized by the core network.

Location Information: A WFAP should support location identification procedures with the core network. Location information can then be used for emergency services or location based services.

Air Interface: A WFAP should provide at least 10 meters of coverage area in a residential set up without any exclusion zone around it.

Network Synchronization: A WFAP should support mechanism to synchronize with external network to provide services that require strict air interface co-ordination. Some of the services are soft-handovers, support for idle mode paging, and multicast-broadcast (MCBCS) services.

Quality of Service: A WFAP should support marking of incoming/outgoing packets with appropriate DSCP code, as configured by a service provider. This would allow support for defined service level agreements (SLAs) when the service is delivered through a WFAP.

Manageability: A WFAP should implement DSL forum’s defined TR069 protocol to allow an operator to remotely manage a WAFP. It must allow an operator to remotely disable/enable the air interface service.


The WiMAX network architecture for femtocell systems is based on the WiMAX basic network reference model that differentiates the functional and business domains of NAPs from those of the network service providers (NSPs). The NAP is a business entity that provides and manages WiMAX radio access infrastructure, while the NSP is the business entity that manages user subscriptions, and provides IP connectivity and WiMAX services to subscribers according to negotiated service level agreements (SLAs) with one or more NAPs. A NAP is deployed as one or more access service networks (ASNs), which are composed of ASN gateways and BSs, while the NSP includes a home agent, authentication, authorization, and accounting (AAA), and other relevant servers and databases.

In a WiMAX network supporting a femtocell, a new business entity called the femto-NSP is introduced, which is responsible for the operation, authentication, and management of WFAPs. The femto-NSP is logically separated from the conventional WiMAX NSPs responsible for MSs’ subscriptions, and it includes femto-AAA and femtocell management/self-organizing network (SON) subsystems.

The femtocell management system is an entity to support operation and maintenance (O&M) features of the WFAP based on TR-069 or DOCSIS standards. Because potentially many femto BSs will be deployed in overlay coverage of macrocell BSs and have to support handover to/from macrocell BSs or neighbor femto BSs, the operating parameters of femto BSs have to be well organized and optimized. Femto BS parameter configuration and network performance, coverage, and capacity optimization can be done in an autonomous fashion by using SON functions. A SON server provides SON functions to measure/analyze performance data, and to fine-tune network attributes in order to achieve optimal performance.

A femto-NAP implements its infrastructure using one or more femto-ASNs; an ASN is defined as a complete set of network functions needed to provide radio access to a WiMAX femtocell subscriber. The reference model for a the femto-ASN is defined based on some changes to the conventional ASN to address specific needs of WFAPs, which typically reside at customer premises, and are operated and managed remotely by a femtocell operator over third party IP broadband connection. The femto-ASN reference model includes a WFAP connected to a femto-GW serving as the ASN-GW, through a new entity called a security gateway (SeGW). The SeGW provides IP Security (IPsec) tunnels for WFAPs, and is responsible for authentication and authorization of the WFAPs. The WFAP is connected to a femto-ASN gateway (femto-ASN GW) and other functional entities in the network through this IPsec tunnel. The management system is connected to WFAP through Rm for remote configuration, and it will also include the SON server function, to be defined in the next releases of the femto architecture.

The femto-ASN GW is an entity that controls WFAPs, and performs bearer plane routing to the CSN and Internet as well as control plane functions similar to ASN-GW providing the link to the connectivity service network (CSN) and other ASNs with mobility and security support in the control plane and IP forwarding. In addition to common functionalities of the ASN-GW, the femto-ASN GW supports femto-specific functionalities such as closed subscriber group (CSG) subscriber admission control, femtocell handover control, WFAP low-duty mode management, and femtocell interference management.


Thursday, 5 November 2009

WiMAX Network reference model



Continuing from yesterdays post.

The WiMAX network architecture is designed to meet the requirements while maximizing the use of open standards and IETF protocols in a simple all-IP architecture. Among the design requirements are supports for fixed and mobile access deployments as well as unbundling of access, connectivity, and application services to allow access infrastructure sharing and multiple access infrastructure aggregation.

The baseline WiMAX network architecture can be logically represented by a network reference model (NRM), which identifies key functional entities and reference points over which the network interoperability specifications are defined. The WiMAX NRM differentiates between network access providers (NAPs) and network service providers (NSPs). The NAP is a business entity that provides WiMAX radio access infrastructure, while the NSP is the business entity that provides IP connectivity and WiMAX services to WiMAX subscribers according to some negotiated service level agreements (SLAs) with one or more NAPs. The network architecture allows one NSP to have a relationship with multiple NAPs in one or different geographical locations. It also enables NAP sharing by multiple NSPs. In some cases the NSP may be the same business entity as the NAP.

The WiMAX NRM, as illustrated in Fig. 3, consists of several logical network entities: MSs, an access service network (ASN), and a connectivity service network (CSN), and their interactions through reference points R1–R8. Each MS, ASN, and CSN represents a logical grouping of functions as described in the following:

Mobile station (MS): generalized user equipment set providing wireless connectivity between a single or multiple hosts and the WiMAX network. In this context the term MS is used more generically to refer to both mobile and fixed device terminals.

Access service network (ASN): represents a complete set of network functions required to provide radio access to the MS. These functions include layer 2 connectivity with the MS according to IEEE 802.16 standards and WiMAX system profile, transfer of auathentication, authorization, and accounting (AAA) messages to the home NSP (HNSP), preferred NSP discovery and selection, relay functionality for establishing layer 3 (L3) connectivity with MS (i.e., IP address allocation), as well as radio resource management. To enable mobility, the ASN may also support ASN and CSN anchored mobility, paging and location management, and ASN-CSN tunneling.

Connectivity service network (CSN): a set of network functions that provide IP connectivity services to WiMAX subscriber(s). The CSN may further comprises network elements such as routers, AAA proxy/ servers, home agent, and user databases as well as interworking gateways or enhanced broadcast services and location-based services.

A CSN may be deployed as part of a green field WiMAX NSP or part of an incumbent WiMAX NSP. The following are some of the key functions of the CSN:–IP address management–AAA proxy or server–QoS policy and admission control based on user subscription profiles–ASN-CSN tunneling support –Subscriber billing and interoperator settlement–Inter-CSN tunneling for roaming–CSN-anchored inter-ASN mobility–Connectivity to Internet and managed WiMAX services such as IP multimedia services (IMS), location-based services, peer-to-peer services, and broadcast and multicast services –Over-the-air activation and provisioning of WiMAX devices

Base station (BS): a logical network entity that primarily consists of the radio related functions of an ASN interfacing with an MS over-the-air link according to MAC and PHY specifications in IEEE 802.16 specifications subject to applicable interpretations and parameters defined in the WiMAX Forum system profile. In this definition each BS is associated with one sector with one frequency assignment but may incorporate additional implementation-specific functions such as a DL and UL scheduler.

ASN gateway (ASN-GW): a logical entity that represents an aggregation of centralized functions related to QoS, security, and mobility management for all the data connections served by its association with BSs through R6t. The ASN-GW also hosts functions related to IP layer interactions with the CSN through R3 as well as interactions with other ASNs through R4 in support of mobility.

Typically multiple BSs may be logically associated with an ASN. Also, a BS may be logically connected to more than one ASN-GW to allow load balancing and redundancy options. The WiMAX network specification defines a single decomposed ASN profile (ASN C) with an open R6 interface as well as an alternative ASN profile B that may be implemented as an integrated or a decomposed ASN in which R6 is proprietary or not exposed. The normative definitions of intra-ASN reference points (R6 and R8) are only applicable to profile C. Note that in release 1.5 profile A has been removed to reduce the number of implementation options and create a better framework for network interoperability.

Wednesday, 4 November 2009

Mobile WiMAX technology and network evolution roadmap.


The Mobile WiMAX Release 1.0 System Profile, based on 802.16e or 802.16-2005, was completed in late 2006, and the radio-level certification of products began in 2007. The certification follows a phased approach to address deployment priorities and vendor readiness. System Profile Release 1.0 includes all 802.16-2005 mandatory features, and also requires some of the optional features needed for enhanced mobility and QoS support. This system profile is based on OFDMA, and enables downlink and uplink multiple-input multipleoutput (MIMO) as well as beamforming (BF) features. The release 1.0 system profile is defined only for the TDD mode of operation, with more focus on 5 and 10 MHz bandwidths in several band classes in 2.3 GHz, 2.5 GHz ,and 3.5 GHz bands, but it also includes 8.75 MHz specifically for Korea.

The WiMAX certification for the release 1.0 profile started with a Wave 1 subset, excluding MIMO and a few optimization features, to enable early market deployments. This was followed by Wave 2, which progressively adds more and more feature tests over time based on vendors and testing tool availability. The early phases of certification were also limited to MAC and PHY layer conformance and interoperability testing, which will be expanded to add networklevel testing.

Meanwhile, the development of WiMAX Forum Network Release 1.0 was completed in 2007, based on which the specific network-level device conformance testing as well as infrastructure interoperability testing projects were initiated. The goal was to ensure e2e interoperability of WiMAX devices with networks and also ensure multivendor plug and play network infrastructure deployments. Release 1.0 defines the basic architecture for IP-based connectivity and services while supporting all levels of mobility. Based on operators’ requirements for advanced services and new market opportunities to be more competitive with evolved 3G systems, the WiMAX Forum initiated interim releases for both the system profile and network without major modifications to the IEE 802.16 standard. The work on network release 1.5 network specifications was started in parallel, aimed primarily at enabling dynamic QoS and provisioning of open retail device and support for advanced network services as well as commercial grade VoIP.

The release 1.5 system profile work item was initiated to enable mobile WiMAX in new spectrum including frequency-division duplex (FDD) bands, address a few MAC efficiency improvements needed for technology competitiveness, and align the system profile with advanced network services supported by network release 1.5. All required fixes and minor enhancements needed to support release 1.5 are incorporated in IEEE 802.16 REV2, which combines the IEEE 802.16-2004 base standard plus IEEE 802.16e/f/g amendments and related corrigenda into one specification document.

Following Release 1.5, the next major release mobile WiMAX, Release 2.0, will be based on the next generation of IEEE 802.16, which is being developed in the 16m technical group (TGm) of 802.16. WiMAX Release 2 targets major enhancements in spectrum efficiency, latency, and scalability of the access technology to wider bandwidths in challenging spectrum environments. Currently the expected timeline for the formal completion of 802.16m and WiMAX Certification of Release 2 products are early 2010 and early 2011, respectively.

In parallel with developments in IEEE on the stage 2 system-level description of 802.16m, the requirements for network release 2.0 are being discussed in the WiMAX Forum, where stage 2/3 specifications are expected to be completed by 2010.

Reference: Overview of Mobile WiMAX Technology and Evolution - Kamran Etemad, Intel Corporation