Strategic Considerations on Development of WiMAX and Its Relationship with 3G and 4G

1 Characteristics and Basic Market Positioning of WiMAX
WiMAX (World Interoperability Microwave Access) Forum was set up in April 2001. It originally aimed at 802.16 standards and the frequency band of 10-66 GHz. Its original market objective was Broadband Wireless Access (BWA) Metropolitan Access Network (MAN) technologies, so it is also called IEEE Wireless MAN. Its basic goal is to provide a solution for point-to-multipoint broadband wireless access on MAN with suitable interoperability in an environment of multiple vendors, and to create a globally unified standard according to IEEE 802.16x and ETSI HiperMAN standards to support interoperability. With excellent broadband access performance similar to traditional cable access technologies such as xDSL and Cable Modem, WiMAX is expected to be put into production on an appropriate scale, with a low price and extensive application. With the introduction of Orthogonal Frequency Division Multiplex (OFDM) technology, WiMAX can effectively solve the problem of multipath effect occurring in microwave broadband transmission, obtain the Non-Line-of-Sight (N-LoS) transmission capability to some extent, and support easy installation and maintenance. Besides, it is fit for operation in mobility under certain conditions and with certain rates. Meanwhile, with the rapid growth of WLAN hotspots, users often expect to continue to use wireless services out of the hotspots. In order to meet such a demand, the standard 802.16a and 802.16d have been improved to create another new standard 802.16e. With the development of related standards such as 802.16a, 802.11d and 802.16e and driven by some big companies like Intel, WiMAX Forum has quickened its related work and enhanced the promotion of WiMAX after April 2003. At present, the forum has about 120 members including Intel, Alvarion, Airspan, Nokia, WiLAN, Siemens, OFDM Forum, etc.

  From the standardization point of viewpoint, a Multipoint Multichannel Distribution System (MMDS), as a broadband wireless access technology, is already able to support a multi-vendor environment with diversified operation modes. Moreover, its access platform has been improved generation upon generation. MMDS, however, has no advanced, reasonable and extensible standards yet up to now. But now WiMAX that actually aims at WMAN is expected to be a standard, which not only helps implement interoperation of networks and systems in a multi-vendor environment, but also supports scale production, improves cost-performance ratio and allows evolution with forward and backward compatibility to Next Generation Networks (NGN) and Next Generation Broadband Wireless (NGBW) networks, thus creating better market value.

   From the technology evolution viewpoint, MMDS has three generations if early narrowband Time Division Multiplexing (TDM) P-MP equipment without standardized interfaces is not regarded as the first generation (or is regarded as the zero generation, a starting stage). The first generation uses pure TDM or pure IP as the platform, and has limited adaptability to multi-service operation. It has limited performance control capability for self-adaptive systems. The second generation undertook efforts to improve the multi-service handling capability required by the market, and did so even to pure IP and pure TDM platforms. Thus the self-adaptive TDM+IP mix platform and expensive Asynchronous Transfer Mode (ATM) platform with good QoS control were born. As for N-LoS development, the (x) OFDM (y) technology of the second generation began to attract much attention. Meanwhile, both the air interface protocols of the IP platform and self-adaptive QoS were improved to a certain extent. The third generation synchronously makes use of some basic technologies of 3G/3G+/4G, including Multiple-In Multiple-Out/Space-Time Coding (MIMO/STC), overall adaptive parameters control technologies to improve QoS, coverage and frequency utilization capability, the technologies with high-efficiency such as 64 Quadrature Amplitude
Modulation (QAM), (x) OFDM (y) and Turbo code that are generally used for modulating, coding and N-LoS handling. Even the technologies such as MIMO-STC concatenated with (x) OFDM (y) and Turbo coding (TBC/TPC)/LDPC, as well Smart Antenna / Intelligent Distributed Antenna Base-station, Software (defined) Radio and Softswitch, etc. are utilized. The network management techniques at the network element level are also improved to meet demands of different user groups. The standardization of the third generation technology is gradually coordinating and integrating with IEEE 802.16x and 802.xy. The technical integration of intermediate frequencies and Radio Frequencies (RF) provides better system cost-performance ratio.

  As for WiMAX, with the development of 802.16a/d/e and 802.16f/g standards, the multi-carrier at its physical layer adopts 256 points FFT MAN-OFDM and Time Division Multiple Access (TDMA) (Time Division Duplex (TDD)/Frequency Division Duplex (FDD)), or 2048 points (and 1024, 512 and 128 points) FFT Orthogonal Frequency Division Multiple Access (OFDMA) (TDD/FDD), while the single carrier uses multi-state modulation selection (Binary Phase Shift Keying (BPSK)/Quadrature Phase Shift Keying (QPSK)/4-QAM/16-QAM/64-QAM/256-QAM) and frequency domain adaptive equalization to flexibly deploy the channel bandwidth. Its Media Access Control (MAC) layer adopts self Automatic Repeat Request (ARQ), OFDM/OFDMA support, Dynamic Frequency Selection (DFS), Adaptive Antenna System (AAS) support, mesh structure and dynamic bandwidth distribution for QoS improvement. Besides, WiMAX uses the technologies such as (x) OFDM (y), MIMO and resource parameters adaptive handling to improve its Non-LoS capability and mobility. Accordingly, its transmission bit rate is expected to reach 75-100 Mb/s, and the coverage about 50 km for fixed /stationary cases, also with mobility at certain speeds and coverage, which have become the important attributes of WiMAX. All these show that WiMAX is a new generation WMAN-based broadband wireless access standard with good forward extensibility.

  WiMAX adopts a series of emerging technologies such as dynamic adaptive modulation, flexible system resource parameter adjustment and M-QAM-(x)OFDM(y)multi-carrier modulation. Besides, it has both flexibility and mobility of wireless access technologies and the similar strong rate/bandwidth handling capability (with up to 75-100 Mb/s) and good QoS and security control with traditional cable broadband access technologies such as xDSL and Cable Modem. These are main strengths of WiMAX. Furthermore, OFDM provides WiMAX with the N-LoS capability, channel bandwidth changeability (e.g. the 20 MHz frequency spectrum can be flexibly divided into 2×10 MHz or 4×5 MHz, etc.), changeable Ts and changeable Tg.

  In a word, as a solution to the "last mile" access, WiMAX is a market need oriented WMAN standard and technology. It has practical significance and strategic values, especially today when the world lacks unified broadband wireless access standards. When we consider coverage, environment limitation and historical factors, WiMAX scores much better over xDSL and Cable Modem in suburbs and rural areas. Moreover, as mentioned above, the standard 802.16e based on 802.16a/d can better expand the WLAN access scope. Therefore, WiMAX and Wi-Fi, with complementary advantages, are expected to work together to strongly promote the effective development of WLAN at hotspots and SOHOs and to develop together with their own individual market positioning to build a healthy and reasonable development pattern. Thus WiMAX won’t replace Wi-Fi. It should be emphasized that the basic market positioning of WiMAX aims at nothing but WMAN.

2 Challenges to WiMAX
The main challenge to WiMAX products is its price. According to the data analysis by Yankee Group, the current cost per user for a WiMAX system including WiMAX antenna deployment reaches 3 000 US dollars, which not only makes operators difficult to gain enough investment returns, but also terrifies and prevents users from using services offered. Furthermore, as to the limited frequency band at 3.5 GHz in China, other MMDSs have had good price performance ratios after several upgrade solutions and technical innovation, so WiMAX will face a great challenge if it enters the market competition with the above-mentioned cost.

  Moreover, WiMAX will coexist with Wi-Fi, 3G and 3G+ in a long term, but they will compete with each other in overlapped application fields. So it is also an important task for WiMAX to allow the interoperability with other systems and improve its own competence. For frequency resource utilization, Wi-Fi has been approved to utilize 2.4 GHz and 5.8 GHz ISM bands, and R (W) LAN 5 GHz plus 455 MHz bandwidth defined by WRC-2003, but the frequency resources for WiMAX and Wireless Broadband Mobile Access (WBMA) (also called as Mobile Broadband Wireless Access (MBWA) or Molile-Fi) including 3.5 GHz, 5.8 GHz, 2.5 GHz, 5.4 GHz,
2.3 GHz, 2.4 GHz and the band less than 3 GHz have many conflicts with those used by 3G, 3G+ and Wi-Fi. Therefore, WiMAX faces the big problem of frequency coordination. A wise solution may be complementary market positioning, mutual coordination and support, and system integration and interoperability. IEEE has approved the WiMAX broadband wireless access standard (802.16-2004). Intel also cooperates with Proxim and Alvarion, as well as Clearwire to promote the production and application of WiMAX systems. However, it is generally estimated that large-scale manufacturing and application of WiMAX won’t be undergone until 2006-2008. In addition, as an important role in mobile portable and handset broadband applications of WiMAX, the standard 802.16e hasn’t finished its research and development yet. According to the approval and implementation timetable of WiMAX, its cost-performance attraction in the 3.5 GHz MMDS market in China, and before the application of the MMDS enhanced systems, it still faces severe challenges and needs positive action because other MMDSs in this market have had good cost performance ratio and can be put into operation immediately when necessary, with many upgrade solutions and incorporating technical innovations.

3 Relationship Between and Among Wi-Fi, WiMAX, WBMA, 3G, 3G Evolution and 4G
Although the operation rate of WiMAX systems can be 30 times, even higher than original 3G and, with low-state modulation, with its coverage range larger than that of 3G systems, it won’t become a terminator for 3G at all. This is because there is great difference between their market sizes. 3G systems are WWAN with voice and multimedia services and global/regional/nationwide roaming personal handsets, while WiMAX is essentially an important support of 3G and 3G+ on WMAN and multi-point BTS interconnection and back-haul. WBMA or Mobile-Fi related to IEEE802.20x/22x standards after 802.16x standards has more similarities with 3G. Its basic technologies are also similar with those used for 3G+/4G. Its rate can reach 16 Mb/s or more. Besides, it has high-speed mobility and good coverage. However, although WBMA and 3G+/4G are all developing towards new IP or all-IP systems and services, the new technologies related to the latter like HSDPA/HSUPA with phases 2 and 3, have richer connotations. The transmission rate (or bandwidth) goal of 3G+/4G is 20 Mb/s and even up to
100 Mb/s in mobility with a rate of 250 km/h, and 1000 Mb/s for fixed /stationary or indoors.

  As for the relationship between 3G and 4G, the evolution from 3G to 4G will certainly follow the NGN definition and requirements, with forward/backward compatibility and seamless evolution. As a new generation technology for global mobile communication, 4G, just like 3G, should first define its frequency resources, which will be settled at least in 2007-2008. Therefore, the opinion that 4G will replace 3G soon is possibly just sounding sensational, without any scientific basis. In fact, 3G+/4G to be derived from 3G will not emerge in a day. It is a reasonable estimation that 4G will be put into commercial use in about 2010 with service overlap with 3G and 3G+, and that we will go into the 4G age step by step. Accordingly, in parallel promotion of 3G and 3G+ services, emphasis on proprietary innovation and active research into 4G standards, frequency resource planning, related new network and terminal technologies, applications and market segmentation, and differentiated business models with 3G/3.5G are all important strategies. Moreover, from the technology perspective, being a basis for seamless evolution to 4G, it is necessary to use basic 4G or 4G-type technologies into 3.5G and 3G+ systems and get feedback. Furthermore, the network evolution won’t stop, and like the evolution route of 2.5G/3G/3.5G/4G, the future evolution will be 3.5G/4G/4.5G/5G.

  In fact, for transmission rates and basic transmission technologies, both 3G/3G+ technologies developed by
ITU/3GPP/3GPP2 and technologies related to IEEE 802.11a/g/n, 802.15x, Ultra Wide Band (UWB) and 802.20x/22x are integrating during their development. For example, they all use Adaptive Modulation and Coding (AMC), high-state modulations (such as M-(O) QAM, M=16, 32, 64, 128, 256 and more), H.264/AVC coding, (Turbo and) Low Density Parity Check (LDPC) channel coding, MIMO-STC and Smart Antenna, Software (Defined) Radio, OFDM and multi-band OFDM, IP-QoS and security on the NGN layer, and technologies for development and large-scale production of application chips of systems, networks and terminals. Even for evolution solutions of 3G based on WWAN and with the peak rate of only 2 Mb/s, taking High Speed Downlink Packet Access (HSDPA) of 3GPP as an example, its proposed three-stage downlink peak rates can be beyond
10.8 Mb/s, 30 Mb/s and 50 Mb/s (up to 100 Mb/s) respectively. With a long-term consideration, 3GPP plans to change the current unit bandwidth of 5 MHz into 1.25-20 MHz for more flexible networking, and in order to decrease the cost per bit. It also plans to improve the rate capability to 2-4 times of the second-stage rate of HSDPA, with a peak uplink rate of about 50 Mb/s or more. In addition, in the enhanced version A of CDMA2000 1X EV-DO, 3GPP2 improves the downlink and uplink rate from current 2.4 Mb/s and 153 kb/s to 3.1 Mb/s and 1.8 Mb/s respectively. It also directly introduces VoIP into voice services with CDMA2000 1X quality, and further plans to improve user-end access rate to 44 Mb/s by bounding multi-carriers. It is obvious that such enhanced rates can catch up with the rates that Wi-Fi, WiMAX and Mobile-Fi support. Moreover, on one hand, the backward seamless compatibility of next generation mobile networks has great influence on system developments; On the other hand, terminal, application and service-orientation will become the driving force behind the market development and profit source of the next generation mobile networks. So any overlapping standards developed by different standardization organizations with no values will definitely be washed out by market selection.

  Therefore, the only solution for different standardization organizations is to integrate their basic thinking on NGN and 3G evolution and make useful achievements. Fortunately, these organizations have begun to cooperate more on unifying NGN concepts and integrating standards. In fact, as an important support to ITU, ETSI and other organizations have begun to perform research on WBMA definition, Wireless Personal Access Network (WPAN), WLAN, WMAN and WWAN, including the ACTS and IST research plan, NASA and ESA space-involved research plan and development. This has effectively built up a practical basis for future network evolution, convergence and merging. Thus, for organizations such as ITU, ETSI, IEEE and IETF, their work on standardization aims not at replacing and terminating other organizations, but at working creatively while cooperating and integrating with each other to help the big goal of Global Information Infrastructure (GII) and NGN come true in future.

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Manuscript received: 2004-12-28