AHMADI LAYOUT 5/15/09 1:10 PM Page 84 WIMAX UPDATE An Overview of Next-Generation Mobile WiMAX Technology Sassan Ahmadi, Intel Corporation ABSTRACT embarked on the development of a new amend- ment of the IEEE 802.16 standard (i.e., IEEE The growing demand for mobile Internet 802.16m) as an advanced air interface to meet and wireless multimedia applications has moti- the requirements of the International Telecom- vated the development of broadband wireless- munication Union — Radiocommunication/ access technologies in recent years. Mobile International Mobile Telecommunications (ITU- WiMAX has enabled convergence of mobile R/IMT)-advanced for fourth-generation (4G) and fixed broadband networks through a com- systems, as well as the next-generation mobile mon wide-area radio-access technology and network operators. flexible network architecture. Since January Depending on the available bandwidth and 2007, the IEEE 802.16 Working Group has multi-antenna mode, the next-generation been developing a new amendment of the IEEE mobile WiMAX will be capable of over-the-air 802.16 standard (i.e., IEEE 802.16m) as an data-transfer rates in excess of 1 Gb/s and sup- advanced air interface to meet the require- port a wide range of high-quality and high- ments of ITU-R/IMT-advanced for 4G systems, capacity IP-based services and applications as well as for the next-generation mobile net- while maintaining full backward compatibility work operators. with the existing mobile WiMAX systems to Depending on the available bandwidth and preserve investments and continuing to support multi-antenna mode, the next-generation mobile first-generation products. There are distinctive WiMAX will be capable of over-the-air data- features and advantages such as flexibility and transfer rates in excess of 1 Gb/s and of support- the extensibility of its physical and medium- ing a wide range of high-quality and access-layer protocols that make mobile high-capacity IP-based services and applications WiMAX and its evolution more attractive and while maintaining full backward compatibility more suitable for the realization of ubiquitous with the existing mobile WiMAX systems to pre- mobile Internet access. serve investments and continuing to support The next-generation mobile WiMAX will first-generation products. This tutorial describes build on the success of the existing WiMAX the prominent technical features of IEEE technology and its time-to-market advantage 802.16m and the potential for successful deploy- over other mobile broadband wireless access ment of the next generation of mobile WiMAX technologies. In fact, all OFDM-based, mobile in 2011+. broadband access technologies that have been developed lately exploit, enhance, and expand INTRODUCTION fundamental concepts that were originally uti- lized in mobile WiMAX. The growing demand for mobile Internet and The IEEE 802.16m will be suitable for both wireless multimedia applications has motivated green-field and mixed deployments with legacy the development of broadband wireless-access mobile stations (MSs) and base stations (BSs). technologies in recent years. Mobile WiMAX The backward compatibility feature will allow was the first mobile broadband wireless-access smooth upgrades and an evolution path for the solution based on the IEEE 802.16e-2005 stan- existing deployments. It will enable roaming dard [1] that enabled convergence of mobile and and seamless connectivity across IMT-advanced fixed broadband networks through a common and IMT-2000 systems through the use of wide-area radio-access technology and flexible appropriate interworking functions. In addi- network architecture. The mobile WiMAX air tion, the IEEE 802.16m system utilizes multi- interface utilizes orthogonal frequency division hop relay architectures for improved coverage multiple access (OFDMA) as the preferred mul- and performance. This article briefly describes tiple-access method in the downlink (DL) and the salient technical features of IEEE 802.16m uplink (UL) for improved multipath perfor- and the potential for successful deployment of mance and bandwidth scalability. Since January the next generation of mobile WiMAX in 2007, the IEEE 802.16 Working Group has 2011+. 84 0163-6804/09/$25.00 © 2009 IEEE IEEE Communications Magazine • June 2009 AHMADI LAYOUT 5/15/09 1:10 PM Page 85 The evaluation R2 (logical interface) scenarios and associ- Core network ated parameters Visited network Home network specified in IEEE service provider service provider R6 802.16m evaluation network gateway 802.16e R1 BS Access service methodology MS R3 Connectivity R5 Connectivity document are based R8 service service network network mainly on those that 802.16m R1 were used for the MS BS R6 evaluation of the ref- Access service erence system to network benchmark the rela- R4 Access Access tive improvements. Layer 1 and layer 2 to service service be specified by IEEE provider provider 802.16m Other access service network network networks (Internet) (Internet) Figure 1. Mobile WiMAX network reference model [9]. IEEE 802.16M SYSTEM The IEEE 802.16m systems are expected to meet all service requirements for IMT-advanced REQUIREMENTS AND systems as specified by Report ITU-R M.1822 EVALUATION METHODOLOGY [7], where compliance is verified through inspec- tion [4]. Full backward compatibility and interoperability The IEEE 802.16m evaluation methodology with the reference system is required for IEEE document [5] provides simulation parameters 802.16m systems, although the network operator and guidelines for evaluation of the candidate can disable legacy support in green-field deploy- proposals against the IEEE 802.16m system ments. The reference system is defined as a sys- requirements [6]. The evaluation scenarios and tem that is compliant with a subset of the IEEE associated parameters specified in IEEE 802.16e-2005 [1] features as specified by the 802.16m evaluation methodology document are WiMAX Forum mobile system profile, Release based mainly on those that were used for the 1.0 [2]. The backward compatibility feature evaluation of the reference system [8] to bench- ensures a smooth migration from legacy to new mark the relative improvements. There are simi- systems without any significant impact on the larities and differences between the evaluation performance of the legacy systems, as long as guidelines, test scenarios, and configuration they exist. Furthermore, the requirements for parameters specified by Report ITU-R M.2135 IEEE 802.16m were selected to ensure competi- [4] and the IEEE 802.16m evaluation methodol- tiveness with the emerging 4G radio-access tech- ogy document [5]. Compliance with Report ITU- nologies while improving and extending existing R M.2134 requirements in at least three test functionalities of the reference system. environments is required. The IMT-advanced requirements defined and approved by ITU-R/Working Party 5D and pub- lished as Report ITU-R M.2134 [3] are referred NETWORK REFERENCE MODEL AND to as target requirements in the IEEE 802.16m M ROTOCOL system requirement document and will be evalu- IEEE 802.16 P ated based on the methodology and guidelines STRUCTURE specified by Report ITU-R M.2135 [4]. The baseline performance requirements will be eval- The WiMAX Network Architecture Release 1.0 uated according to the IEEE 802.16m evaluation [9] specifies a non-hierarchical, end-to-end net- methodology document [5]. A careful examina- work reference model (Fig. 1) for mobile tion of the IMT-advanced requirements reveals WiMAX that can be expanded to further include that they are a subset of, and less stringent than, optional relay entities for coverage and perfor- the IEEE 802.16m system requirements; there- mance enhancement in future releases. fore, the IEEE 802.16m standard can qualify as The IEEE 802.16 standard [1] describes an IMT-advanced technology. Table 1 summa- medium-access-control (MAC) and physical- rizes the IEEE 802.16m baseline system require- layer (PHY) protocols for fixed and mobile ments and the corresponding requirements broadband wireless-access systems. The MAC specified by Report ITU-R M.2134 [3]. In the and PHY functions can be classified into three next sections, we briefly discuss how these categories, namely, data plane, control plane, requirements can be met or exceeded through and management plane. The data plane com- the extension and enhancements of the legacy- prises functions in the data processing path system functional features. such as header compression, as well as MAC IEEE Communications Magazine • June 2009 85 AHMADI LAYOUT 5/15/09 1:10 PM Page 86 Requirements IMT-Advanced [3] IEEE 802.16m [6] DL: 15 (4 × 4) DL: 8.0/15.0 (2 × 2/4 × 4) Peak data rate (b/s/Hz) UL: 6.75 (2 × 4) UL: 2.8/6.75 (1 × 2/2 × 4) DL (4 × 2) = 2.2 DL (2 × 2) = 2.6 Cell spectral efficiency (b/s/Hz/sector) UL (2 × 4) = 1.4 UL (1 × 2) = 1.3 (base coverage urban) (mixed mobility) DL (4 × 2) = 0.06 DL (2 × 2) = 0.09 Cell-edge user spectral efficiency UL (2 × 4) = 0.03 UL (1 × 2) = 0.05 (b/s/Hz) (base coverage urban) (mixed mobility) C-plane: 100 ms (idle to active) C-plane: 100 ms (idle to active) Latency U-plane: 10 ms U-plane: 10 ms Optimal performance up to 10 km/h 0.55 at 120 km/h Graceful degradation up to 120 km/h Mobility (b/s/Hz at km/h) 0.25 at 350 km/h Connectivity up to 350 km/h (link-level) Up to 500 km/h depending on operating frequency Intrafrequency: 27.5 Intrafrequency: 27.5 Interfrequency: 40 (in a frequen- Handover interruption time (ms) Interfrequency: 40 (in a frequency band) cy band) 60 (between