DESIGN FOR TEST
The IEEE 802.16 standard WiMAX is based on the IEEE 802.16 standard and on ETSI HiperMAN. The latest version of IEEE 802.16, 802.16-2004 (previously known as Revision D, or 802.16d), was ratified in July 2004. 802.16-2004 is a wide-ranging standard, that includes previous versions (802.16-2001, 802.16c in 2002, and 802.16a in 2003) and covers both LOS and NLOS applications in the 2-66 GHz frequencies. As is customary with IEEE standards, it specifies only the Physical (PHY) and Media Access Control (MAC) layers. The changes introduced in 802.16-2004 were focused on fixed and nomadic applications in the 2-11 GHz frequencies. Two multi-carrier modulation techniques are supported in 802.16-2004: OFDM with 256 carriers and OFDMA with 2048 carriers. The first WiMAX Forum certification profiles are based on OFDM as defined in this version of the standard. In December 2002, Task Group e was created to improve support for combined fixed and mobile operation in frequencies below 6 GHz. Work on the 802.16e amendment is approaching completion and its ratification is expected by the end of 2005. The new version of the standard introduces support for SOFDMA (a variation on OFDMA) which allows for a variable number of carriers, in addition to the previously-defined OFDM and OFDMA modes. The carrier allocation in OFDMA modes is designed to minimize the effect of the interference on user devices with omnidirectional antennae. Furthermore, IEEE 802.16e offers improved support for Multiple Input Multiple Output (MIMO) and Adaptive Antenna Systems (AAS), as well as hard and soft handoffs. It also has improved power-saving capabilities for mobile devices and more extensive security features. Both OFDM- and OFDMA-based products can take advantage of the newlyadded capabilities. As with 802.16-2004, 802.16e will incorporate previous versions of the standard and add
paper, we refer to 802.16e WiMAX profiles as most likely to adopt SOFDMA, and to 802.16-2004 profiles as using OFDM with 256 carriers. The new version of the 802.16 standard is backwards-compatible, so new specifications of the OFDM mode are compatible with previous versions. However, OFDM and SOFDMA modes are not compatible as they are based on two distinct modulation techniques. As a result, a single-mode OFDM CPE will not work within a SOFDMA network and, conversely, an SOFDMA CPE will not work within an OFDM network. WiMAX Forum Profiles WiMAX is a set of profiles based on IEEE 802.16 developed by the WiMAX Forum and its members. While 802.16 supports a wide range of frequencies (up to 66 GHz), channel sizes (1.25 MHz to 20 MHz) and applications (LOS and NLOS; PTP and PMT), the WiMAX profiles narrow the scope of 802.16 to focus on specific configurations. The selection of a limited number of profiles is essential to ensure interoperability across vendors and to generate the economies of scale that lead to lower prices and a more appealing technology. The choice of profiles is driven by market demand, spectrum availability, regulatory constraints, the services to be offered, and vendor interest. For instance, the availability of spectrum for broadband wireless access services in several countries motivated the creation of initial profiles in the 3.5 GHz band. The availability of license-exempt spectrum and the demand for fixed services determined the creation of a profile in the 5.8 GHz band. Demand for mobile services and spectrum availability make the 2.3 GHz and 2.5 GHz bands likely targets for future 802.16e profiles. WiMAX Forum profiles are defined by the following parameters: • Spectrum band.
•
with unpaired or license-exempt spectrum, and Frequency Division Duplex (FDD).
FDD requires two channels, one for uplink and the other for downlink traffic. In a TDD network traffic occupies a single channel, with uplink and downlink traffic assigned to different time slots.
•
allocated by regulators. Initial profiles are limited to 3.5 MHz and 7 MHz in the
licensed spectrum as these are the prevalent spectrum channels allocated in the 3.5 GHz band. As wider channels are made available to operators, so the WiMAX Forum members will add certification profiles with wider channel bandwidths.
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IEEE standard. 802.16-2004 profiles use OFDM with 256 carriers. 802.16e profiles
are most likely based on SOFDMA. Only the latter support mobility.
All the certification profiles based on 802.16-2004 are based on a common system profile. This includes WiMAX specifications that remain the same whatever the frequency, channel size and method of duplexing. A new system profile is currently being developed for 802.16e certification profiles. If there is sufficient interest from the vendor community, a third system profile may be introduced for 802.16-2004 products to support portability and limited mobility. The initial profiles defined by the WiMAX Forum (Table 2) support fixed and nomadic access in the 3.5 GHz and 5.8 GHz bands. The WiMAX Forum has defined certification releases as shown in Figure 1. The timetable for product certification is driven by product availability since three products are needed to test interoperability across vendors. The certification process includes interoperability testing with products from other vendors, and compliance testing for conformance against the WiMAX system profile. The first certification release for 802.16-2004 is currently under way and includes products submitted within the two 3.5 GHz profiles with a channel bandwidth of 3.5 MHz. The scope of the certification and the list of tests will be extended during subsequent releases. The first release will focus on certification of the air protocol. The second release will add functionality needed to support outdoor services (QoS and security, for instance). The third release will include support for indoor user devices
The profiles for 802.16e have not yet been announced, as the 802.16e amendment to the standard has not yet been finalized. The most likely bands for the first mobile profiles are 2.3 GHz and 2.5 GHz. Better indoor coverage and support for mobile or portable devices make bands below 3 GHz the best targets. However, additional profiles in higher frequencies (3.3 GHz, 3.5 GHz or even 5.8 GHz) may be added if there is sufficient demand for 802.16e-based products for fixed or nomadic access. The WiMAX Forum plans to announce new profiles supporting mobility in the coming months and to open certification labs in the third quarter of 2006. The first 802.16e WiMAX Forum CERTIFIED products are expected by the first quarter of 2007. A comparison between 802.16-2004 and 802.16e profiles The two versions of WiMAX reflect the demand for products that are either optimized for fixed or for mobile access. The requirements for the two types of access vary and different solutions are required to meet them. Several optional features that are supported in both 802-16.2004 and 802.16e profiles are more likely to be implemented in 802.16e products simply because mobile services stand to gain more from the added functionality. Among these, improved support for MIMO and AAS will bring a substantial increase in throughput and NLOS capabilities .
The profiles for 802.16e have not yet been announced, as the 802.16e amendment to the standard has not yet been finalized. The most likely bands for the first mobile profiles are 2.3 GHz and 2.5 GHz. Better indoor coverage and support for mobile or portable devices make bands below 3 GHz the best targets. However, additional profiles in higher frequencies (3.3 GHz, 3.5 GHz or even 5.8 GHz) may be added if there is sufficient demand for 802.16e-based products for fixed or nomadic access. The WiMAX Forum plans to announce new profiles supporting mobility in the coming months and to open certification labs in the third quarter of 2006. The first 802.16e WiMAX Forum CERTIFIED products are expected by the first quarter of 2007. A comparison between 802.16-2004 and 802.16e profiles The two versions of WiMAX reflect the demand for products that are either optimized for fixed or for mobile access. The requirements for the two types of access vary and different solutions are required to meet them. Several optional features that are supported in both 802-16.2004 and 802.16e profiles are more likely to be implemented in 802.16e products simply because mobile services stand to gain more from the added functionality. Among these, improved support for MIMO and AAS will bring a substantial increase in throughput and NLOS capabilities
OFDM and SOFDMA A key difference between 802.16-2004 and 802.16e profiles is the multiplexing technique: the first uses OFDM and the second will most likely use OFDMA. WiMAX profiles based on 802.16-2004 are better suited to fixed applications that use directional antennae because OFDM is inherently less complex than SOFDMA. As a result, 802.16-2004 networks may be deployed faster and at a lower cost. In addition, 802.16-2004 WiMAX Forum CERTIFIED products will be available earlier and will be adopted by service providers that plan to deploy a network in the near future. OFDMA gives 802.16e profiles more flexibility when managing different user devices with a variety of antenna types and form factors. It brings a reduction in interference for user devices with omnidirectional antennas and improved NLOS capabilities that are essential when supporting mobile subscribers. Subchannelization defines subchannels that can be allocated to different subscribers depending on the channel conditions and their data requirements (Figure 2). This gives the operator more flexibility in managing the bandwidth and transmit power, and leads to a more efficient use of resources. For instance, within the same time slot more transmit power can be allocated to a user with less favorable channel conditions, while lowering the power for users in better locations. Improved in-building coverage can be achieved by allocating higher power to sub-channels assigned to indoor user devices.
Sub-channelization in the uplink brings additional performance improvement, as transmit power from the user device is severely limited. In OFDM, user devices transmit using the entire carrier space at once (Figure 3). OFDMA supports multiple access, which allows user devices to transmit only through the sub-channel(s) allocated to them. In OFDMA with 2048 carriers and 32 sub-channels, if only one sub-channel is allocated to a device, all the transmit power will be concentrated in 1/32 of the spectrum available and may bring a 15 dB gain over OFDM. Multiple access is particularly advantageous when wide channels are used. SOFDMA brings an additional advantage over OFDMA. It scales the size of the Fast Fourier Transform (FFT) to the channel bandwidth in order to keep the carrier spacing constant across different channel bandwidths. Constant carrier spacing results in a higher spectrum efficiency in wide channels, and a cost reduction in narrow channels. Handoffs and roaming Support for handoffs is another crucial addition in the 802.16e amendment for mobile access. The ability to maintain a connection while moving across cell borders is a prerequisite for mobility and will be included as a requirement in the 802.16e system profile. While the 802.16-2004 standard offers optional handoff capabilities, support for handoffs is not required by the 802.16-2004 system profile. 802.16e WiMAX will support different types of handoff, ranging from hard to soft and it is up to the operator to choose among them. Hard handoffs use a break-before-make approach . the user device is connected to only one base station at any given time . which is less complex than soft-handoffs but has a high latency. Soft handoffs are
comparable to those used in some cellular networks and allow the user device to retain the connection to a base station until it is associated with a new one (make-before-break approach), thus reducing latency. While applications like mobile Voice over Internet Protocol (VoIP) or gaming greatly benefit from low-latency soft handoffs, hard handoffs typically suffice for data services. QoS and Service Level Agreements (SLAs) are maintained during handoffs. Roaming capabilities across service providers can be implemented in both 802.16-2004 and 802.16e WiMAX, but they are especially valuable for portable and mobile access. The WiMAX Forum does not expect to include roaming requirements in the 802.16e system profile, as roaming is a higher level capability that goes beyond the scope of the certification program, which focuses on the PHY and MAC layers. The Service Providers Working Group and the Network Working Group within the WiMAX Forum are working towards identifying the functional requirements for roaming and establishing a roaming platform.
Acronyms 3GPP 3G Partnership Project 3GPP2 3G Partnership Project 2 AAS Adaptive Antenna System also Advanced Antenna System ACK Acknowledge AES Advanced Encryption Standard AG Absolute Grant AMC Adaptive Modulation and Coding A-MIMO Adaptive Multiple Input Multiple Output (Antenna) AMS Adaptive MIMO Switching ARQ Automatic Repeat reQuest ASN Access Service Network ASP Application Service Provider BE Best Effort BRAN Broadband Radio Access Network CC Chase Combining (also Convolutional Code) CCI Co-Channel Interference CCM Counter with Cipher-block chaining Message authentication code CDF Cumulative Distribution Function CDMA Code Division Multiple Access CINR Carrier to Interference + Noise Ratio CMAC block Cipher-based Message Authentication Code CP Cyclic Prefix CQI Channel Quality Indicator CSN Connectivity Service Network CSTD Cyclic Shift Transmit Diversity CTC Convolutional Turbo Code DL Downlink DOCSIS Data Over Cable Service Interface Specification DSL Digital Subscriber Line DVB Digital Video Broadcast EAP Extensible Authentication Protocol EESM Exponential Effective SIR Mapping EIRP Effective Isotropic Radiated Power ErtPS Extended Real-Time Polling Service ETSI European Telecommunications Standards Institute FBSS Fast Base Station Switching FCH Frame Control Header FDD Frequency Division Duplex FFT Fast Fourier Transform
FUSC Fully Used Sub-Carrier HARQ Hybrid Automatic Repeat reQuest HHO Hard Hand-Off HiperMAN High Performance Metropolitan Area Network HMAC keyed Hash Message Authentication Code HO Hand-Off or Hand Over HTTP Hyper Text Transfer Protocol IE Information Element IETF Internet Engineering Task Force IFFT Inverse Fast Fourier Transform IR Incremental Redundancy ISI Inter-Symbol Interference LDPC Low-Density-Parity-Check LOS Line of Sight MAC Media Access Control MAI Multiple Access Interference MAN Metropolitan Area Network MAP Media Access Protocol MBS Multicast and Broadcast Service MDHO Macro Diversity Hand Over MIMO Multiple Input Multiple Output MMS Multimedia Message Service MPLS Multi-Protocol Label Switching MS Mobile Station MSO Multi-Services Operator NACK Not Acknowledge NAP Network Access Provider NLOS Non Line-of-Sight NRM Network Reference Model nrtPS Non-Real-Time Polling Service NSP Network Service Provider OFDM Orthogonal Frequency Division Multiplex OFDMA Orthogonal Frequency Division Multiple Access PER Packet Error Rate PF Proportional Fair (Scheduler) PKM Public Key Management PUSC Partially Used Sub-Carrier QAM Quadrature Amplitude Modulation QoS Quality of Service QPSK Quadrature Phase Shift Keying
RR Round Robin (Scheduler) RRI Reverse Rate Indicator RTG Receive/transmit Transition Gap rtPS Real-Time Polling Service RUIM Removable User Identity Module SDMA Space (or Spatial) Division (or Diversity) Multiple Access SF Spreading Factor SFN Single Frequency Network SGSN Serving GPRS Support Node SHO Soft Hand-Off SIM Subscriber Identify Module SIMO Single Input Multiple Output SINR Signal to Interference + Noise Ratio SLA Service Level Agreement SM Spatial Multiplexing SMS Short Message Service SNIR Signal to Noise + Interference Ratio SNR Signal to Noise Ratio S-OFDMA Scalable Orthogonal Frequency Division Multiple Access UL Uplink UMTS Universal Mobile Telephone System USIM Universal Subscriber Identify Module VoIP Voice over Internet Protocol VPN Virtual Private Network VSF Variable Spreading Factor VSM Vertical Spatial Multiplexing WiFi Wireless Fidelity WAP Wireless Application Protocol WiBro Wireless Broadband (Service) WiMAX Worldwide Interoperability for Microwave Access
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