TELECOMMUNICATIONS STANDARDS ADVISORY COMMITTEE WORKING GROUP ON COMMON CONNECTION STANDARDS (CCS)
Development of IMT-Advanced and
the Related Work of the Standards Development Organizations
IMT-Advanced發展和標準開發組織相關工作
Introduction Worldwide deployments of the International Mobile Telecommunications-2000 (IMT-2000) systems, i.e. the third generation (3G) mobile systems, have begun for some years. To meet the ever increasing demand of the users for higher data rates and to allow the operators to provide more attractive mobile communications services, ITU has started work on the development of mobile telecommunications systems beyond IMT-2000, i.e. the IMT-Advanced systems. This paper introduces the work of IMT-Advanced in ITU and the contributions of other Standards Development Organizations (SDOs).
International Telecommunication Union (ITU) 2. Not long after the adoption of the first set of IMT-2000 standards1, ITU published in June 2003 the ITU-R Recommendation M.1645 describing the framework and overall objective of the future development of IMT-2000 and systems beyond IMT-2000. The recommendation addresses that there may be a need for a new wireless access technology to be developed around 2010 and to be deployed in some countries around 2015, capable of supporting high data rates with high mobility. Later in World Radiocommunication Conference-2003 (WRC-2003), the ITU Radiocommunication Sector (ITU-R) was invited to further study the technical and operational issues, including spectrum requirements, related to the future development of IMT-2000 and systems beyond IMT-2000.
Resolutions of Radiocommunication Assembly on IMT 3. In the Radiocommunication Assembly of October 2007 (RA-2007), the RA passed the Resolution ITU-R 56 concerning the naming for International Mobile Telecommunications (IMT), resolving that:
1
ITU adopted the following IMT-2000 standards in the Radiocommunication Assembly of 2000: ● CDMA Direct Spread (UTRA FDD, commonly referred to as W-CDMA) ● CDMA Multi-Carrier (cdma2000)
● CDMA TDD (UTRA TDD, TD-SCDMA)
● TDMA Single-Carrier (GSM/EDGE GPRS and TIA/EIA-136 evolved) ● FDMA/TDMA (DECT)
In late 2007, ITU adopted one additional standard into the IMT-2000 family, i.e. OFDMA TDD WMAN, which is commonly referred to as mobile WiMAX (TDD mode). Mobile WiMAX is a version of IEEE 802.16e developed by the WiMAX Forum.
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(a) the term “IMT-2000” encompasses also its enhancements and future developments; (b) the term “IMT-Advanced” be applied to those systems, system components, and
related aspects that include new radio interface(s) that support the new capabilities of systems beyond IMT-2000; and (c) the term “IMT” be the root name that encompasses both IMT-2000 and
IMT-Advanced collectively. The RA also passed the Resolution ITU-R 57 outlining the essential criteria and principles for the development of recommendations and reports for IMT-Advanced. In addition, ITU-R was instructed to provide the necessary support and to implement suitable procedures for the development of recommendations and reports for IMT-Advanced, including the sending of a circular letter calling for proposals for Radio Interface Technologies (RITs).
Frequency Spectrum for IMT 4. Following RA-2007, in WRC-2007 ITU-R (in response to the invitation in WRC-2003 as mentioned in para. 2 above) reported the results of studies on the spectrum requirements for IMT-2000 and IMT-Advanced (hereafter collectively referred to as IMT). Subsequently, additional globally harmonized spectrum was identified in WRC-2007 for use by IMT. At present, the frequency bands identified by ITU in WARC-19922, WRC-2000 and WRC-2007 for IMT, either globally or regionally, include the following: (a) (b) (c) (d) (e) (f) (g)
450 - 470 MHz (additional band allocated in WRC-2007) 698 - 960 MHz (additional band allocated in WRC-2007) 1710 - 2025 MHz 2110 - 2200 MHz
2300 - 2400 MHz (additional band allocated in WRC-2007) 2500 - 2690 MHz
3400 - 3600 MHz (additional band allocated in WRC-2007)
Invitation for IMT-Advanced Proposals 5. Pursuant to the instruction of RA-2007 (as mentioned in para. 3 above), ITU-R sent a circular letter dated 7 March 2008 to the ITU member states and ITU-R sector members inviting for proposals for the candidate RITs for the terrestrial components of IMT-Advanced. The circular letter also initiates an ongoing process to evaluate the candidate RITs, and invites the formation of independent evaluation groups. Within ITU-R, the work on IMT-Advanced now comes under the responsibility of Working Party 5D (WP5D) of Study Group 5.
IMT-Advanced Key Features 6. In parallel with ITU-R’s circular letter of 7 March 2008, WP5D issued two documents providing information on the background on IMT-Advanced, and describing the submission and evaluation process (including time schedule for the work). The key features of IMT-Advanced as identified in the WP5D document include the following:
(a) high degree of commonality of functionality worldwide, while retaining the flexibility
to support a wide range of services and applications in a cost efficient manner; 2
WARC-1992 is World Administrative Radio Conference-1992. The conference was renamed to World Radiocommunication Conference (WRC) from 1995.
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(b) compatibility of services within IMT and with fixed networks; (c) capability of interworking with other radio access systems; (d) high quality mobile services;
(e) user equipment suitable for worldwide use; (f)
user-friendly applications, services and equipment; (g) worldwide roaming capability; and
(h) enhanced peak data rates to support advanced services and applications (100 Mbit/s
for high and 1 Gbit/s for low mobility were established as targets for research).
IMT-Advanced Time Schedule 7. According to WP5D, the time schedule applicable to the first invitation for the candidate RIT proposals for IMT-Advanced is as follows:
(a) Submission of proposals can begin from the date ITU-R issued the circular letter (i.e.
7 March 2008) until 7 days before the 6th WP5D meeting to be held in October 2009. (b) Evaluation of the candidate RITs by the evaluation groups (may be outside
ITU-R) commenced around March 2009 and will last for about 16 months. The end of this period, which is around June 2010, is the cut-off for the submission of evaluation reports to ITU-R by the evaluation groups. (c) Review and coordination of outside evaluation activities, review to assess
compliance with minimum requirements, and the consensus building process (to harmonize different proposals and to increase the potential for wide industry support) also commenced around March 2009 within ITU-R and will last for about 20 months. At the end of this period, which is around October 2010, WP5D will decide the framework and key characteristics for the IMT-Advanced RITs. (d) Development of IMT-Advanced Recommendations will start around March 2010
and last for about one year. It is scheduled that around February 2011 WP5D will complete the development of the Recommendations. 8. To assist the work on IMT-Advanced, ITU-R has created a web page (http://www.itu.int/ITU-R/go/rsg5-imt-advanced/) which contains information relevant to IMT-Advanced. In addition to the documents mentioned in the paragraphs above, the web page also contains the following new ITU-R Reports:
(a) M.2133 which specifies the requirements, evaluation criteria and proposal submission
templates for IMT-Advanced; (b) M.2134 which specifies the minimum technical requirements on spectral efficiency,
bandwidth, latency, mobility, handover, and VoIP (Voice over IP) capacity for the candidate IMT-Advanced RITs (a summary of these requirements is given in the annex); and (c) M.2135 which provides guidelines for the procedures and criteria to be used in
evaluating the proposed IMT-Advanced RITs. Moreover, the IMT-Advanced RIT submissions and their evaluation reports, when available, will also be posted on the web page.
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Development in Other Standards Development Organizations 9. Like IMT-2000, the candidate RITs for IMT-Advanced will be developed outside ITU. At present, three major SDOs, 3GPP (Third Generation Partnership Project), 3GPP2 (Third Generation Partnership Project 2) and IEEE (Institute of Electrical and Electronics Engineers), are working in this respect. The possible proposals from them for IMT-Advanced are: (a) LTE-Advanced (Long Term Evolution-Advanced) from 3GPP
(b) UMB Enhancement (Ultra Mobile Broadband Enhancement) from 3GPP2 (c) 802.16m from IEEE 802.16 Working Group on Broadband Wireless Access (BWA) The paragraphs below describe the evolutionary approach of these SDOs and, where appropriate, the technical characteristics of their proposed standards.
Third Generation Partnership Project (3GPP)
10. In the 3GPP Release 99 specifications covering the UMTS (Universal Mobile Telecommunications System) which uses the W-CDMA technology, a peak downlink data rates of 2 Mbit/s was specified. HSDPA (High Speed Downlink Packet Access) was introduced in 3GPP Release 5 and Enhanced Uplink (or HSUPA (High Speed Uplink Packet Access)) was introduced in 3GPP Release 6 to the UMTS to increase the peak downlink and uplink data rates to 14.4 Mbit/s and 5.8 Mbit/s respectively. HSDPA and HSUPA are collectively referred to as HSPA (High Speed Packet Access). Enhancements to HSPA (commonly called HSPA Evolution or HSPA+) were specified in 3GPP Releases 7 and 8. With the introduction of advanced antenna techniques like MIMO (Multiple Input Multiple Output) and higher order modulation (e.g. 64QAM) as well as other advanced features, HSPA+ boosts the peak data rates to 42 Mbit/s (downlink) and 12 Mbit/s (uplink). 11. Also covered in 3GPP Release 8 is the evolution of UMTS called Long Term Evolution (LTE). Unlike UMTS which uses CDMA technology, LTE uses a different multiple access technology called OFDMA (Orthogonal Frequency Division Multiple Access). Members may refer to CCS-WG Paper No. 8/2008 for the technical characteristics and the standardization process of LTE. But LTE is still not 3GPP’s answer to ITU’s request for IMT-Advanced RITs because LTE is inadequate to meet the requirements of IMT-Advanced on data rates, bandwidth, spectral efficiency, etc. LTE-Advanced, which will be backward compatible with LTE, is being developed by 3GPP to meet the IMT-Advanced requirements. It is expected that 3GPP will specify further advancements to LTE (i.e. LTE-Advanced) in Release 9, and will specify LTE-Advanced to meet the IMT-Advanced requirements in Release 10. The 3GPP Releases 9 and 10 specifications are expected to be completed in the 2011 and 2012 timeframes respectively.
12. In mid-2008, 3GPP published a technical report TR 36.913 describing the requirements of LTE-Advanced on peak data rate, latency, spectral efficiency, mobility, coverage, and VoIP capacity, specifically addressing the requirements of IMT-Advanced described in the ITU-R Report M.2134. A summary of the requirements of LTE-Advanced as described in TR 36.913 is given in the annex. According to TR 36.913, 3GPP’s work schedule for LTE-Advanced is as follows:
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(a) An “Early Proposal” submission containing a high level description of some main
features of LTE-Advanced has been sent to ITU-R via the 3rd WP5D meeting of October 2008. (b) A “Complete Technology” submission has been sent to ITU-R for onward submission
to the 5th WP5D meeting of June 2009. The submitted document is an initial technology submission of the 3GPP LTE Release 10 and beyond (LTE-Advanced). This submission consists of a FDD component and a TDD component, and is based on the current approved work within 3GPP. A copy of this document is available from the ITU website at http://www.itu.int/md/R07-WP5D-C-0496/en. (c) A “Final” submission incorporating updates, additional specific details or feature
additions, and the required self-evaluation will be sent to ITU-R for submission to the 6th WP5D meeting of October 2009.
Third Generation Partnership Project 2 (3GPP2)
13. cdma2000 EVDO (Evolution-Data Optimized) is part of the cdma2000 family of standards developed by 3GPP2 for High Rate Packet Data (HRPD) transmissions in mobile networks. There are several versions of EVDO, starting with EVDO Release 0 which was developed to meet the IMT-2000 requirement for a peak downlink data rate of 2 Mbit/s. EVDO Revision A is an evolution of Release 0 which increases the peak data rates to 3.1 Mbit/s (downlink) and 1.8 Mbit/s (uplink) in 1.25 MHz bandwidth. EVDO Revision B is a multi-carrier evolution of Rev. A, which aggregates multiple 1.25 MHz channels (not necessarily contiguous) and uses higher order modulation (e.g. 64QAM) to deliver high data rates. EVDO Rev. B supports peak data rates of 4.9 Mbit/s (downlink) and 1.8 Mbit/s (uplink) in a single 1.25 MHz channel. With three 1.25 MHz channels in 5 MHz bandwidth, peak data rates of 14.7 Mbit/s (downlink) and 5.4 Mbit/s (uplink) can be achieved. EVDO Rev. B allows up to 15 channels to be aggregated in 20 MHz bandwidth to deliver peak data rates of 73.5 Mbit/s (downlink) and 27 Mbit/s (uplink).
14. Beyond EVDO Rev. B, 3GPP2 developed the standard for Ultra Mobile Broadband (UMB), a technology designed from the ground up for delivering broadband data and real-time applications such as VoIP, video telephony. Like LTE, UMB is based on OFDMA. Using larger bandwidth (up to 20 MHz) and higher order modulation (e.g. 64QAM), UMB can deliver peak data rates of 288 Mbit/s on the downlink and 75 Mbit/s on the uplink. 3GPP2 published the initial UMB specifications in April 2007, and the technical updates and revisions in September 2007 and August 2008. Some technical characteristics of UMB are given in the annex.
15. Yet, like LTE, UMB still cannot meet the IMT-Advanced requirements. To address and work on IMT-Advanced, 3GPP2 created the Next-generation Technology Ad-Hoc (NTAH) group in July 2007. The NTAH group will discuss and evaluate technology proposals submitted by 3GPP2 members, and contribute to ITU on the IMT-Advanced requirements and evaluation methodology. 3GPP2 has not yet decided on the path to IMT-Advanced, but will discuss the following options: (a) (b) (c) (d)
cdma2000 enhancement EVDO enhancement UMB enhancement
other or new technology framework
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16. While cdma2000 and EVDO are earlier technologies than UMB, and the development efforts for a new technology framework may be substantial, 3GPP2 may work on UMB enhancement in response to ITU’s request for IMT-Advanced RITs. At present, there is not much information about the technical characteristics of UMB enhancement, but technology proposals like advanced MIMO, dynamic interference management, higher order modulation, pre-coded OFDM, collision avoidance beamforming, etc. are being considered by the NTAH group. In February 2009, 3GPP2 published the System Requirements Document S.R0134-0 on the evolution of UMB. The document stipulates the goals for UMB evolution, including several improvements like higher data rates, improved spectral efficiency, new deployment model, new radio link topologies, and utility enhancements (e.g. position location, broadcast/multicast services), but no technical details are given. A copy of it can be downloaded from the 3GPP2 website at http://www.3gpp2.org/Public_html/specs/tsgs.cfm.
IEEE 802.16 Working Group on Broadband Wireless Access (BWA)
17. The first IEEE 802.16 specification was completed in 2001 and intended primarily for telecommunications backhaul applications in point-to-point, line-of-sight configuration. The 802.16-2004 standard released in 2004 added some new features, including OFDMA radio interface, point-to-multipoint and non-line-of-sight applications. In 2005, IEEE completed the mobile BWA standard 802.16e-2005 which adds mobility capabilities. The 802.16 standards consist of many technical options. The WiMAX Forum adopted subsets of these options in the so-called WiMAX profiles, which were commonly known as fixed WiMAX (based on 802.16-2004) and mobile WiMAX (based on 802.16e-2005). With mobility support, mobile WiMAX could be an alternative to the cellular technologies. In fact, in late 2007 mobile WiMAX was adopted by ITU into the IMT-2000 family. Some technical characteristics of mobile WiMAX are given in the annex.
18. There are no existing 802.16 standards which meet ITU’s IMT-Advanced requirements. As such, in December 2006 IEEE set up the 802.16 Task Group m (TGm) to develop an amendment to the 802.16 standard. This amendment, referred to as 802.16m amendment, is a standard which amends the existing 802.16 WirelessMAN-OFDMA3 specification with a view to meeting the IMT-Advanced requirements. The 802.16m systems will be backward compatible with legacy WirelessMAN-OFDMA equipment, and for operation in licensed bands below 6 GHz with scalable bandwidth from 5 to 40 MHz (larger bandwidths may also be used). TGm has published the 802.16m System Requirements Document (SRD) which specifically addresses the IMT-Advanced requirements as specified in the ITU-R Report M.2134. A summary of the technical characteristics of 802.16m amendment as described in the SRD is given in the annex. The 802.16m SRD, work plan and other documents are available for download from the TGm website at http://wirelessman.org/tgm/.
19. In the 4th ITU-R WP5D meeting of February 2009, IEEE made a contribution informing WP 5D its intention to submit an IMT-Advanced RIT proposal based on 802.16m, and reporting the progress of the standardization work. In the 5th WP 5D meeting of June 2009, IEEE made another contribution informing WP 5D the components to be included its 3
WirelessMAN-OFDMA is one of the air interfaces specified in the IEEE 802.16 specifications. It uses the OFDMA multiple access scheme.
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submission package and that the proposal would be submitted to WP 5D by its 6th meeting of October 2009. Copies of these contributions are available from the ITU website at http://www.itu.int/md/R07-WP5D-C-0356/en and http://www.itu.int/md/R07-WP5D-C-0443/en.
Other Development Efforts
20. In addition to 3GPP, 3GPP2, and IEEE 802.16 Working Group, there are other national and international research and development efforts devoted to the beyond 3G (B3G) mobile communications technologies. They are briefly described below.
Wireless World Research Forum (WWRF)
21. The Wireless World Research Forum (WWRF) was launched in August 2001 as a global and open initiative of manufacturers, network operators, research and development bodies, and academic institutions. The objective of WWRF is to formulate visions on the future research direction in the wireless field, and to identify and promote research areas and technical trends for mobile system technologies, including the B3G systems. WWRF consists of eight working groups, responsible for areas of research like human perspective and future service concepts, service architecture, new air interfaces, smart antenna, spectrum issues, etc. WWRF itself is not a standardization body, but it contributes to SDOs like 3GPP, 3GPP2, ETSI, ITU on the commercial and standardization issues. It also helps simplify the future standardization process by harmonization and dissemination of views of the forum members. Further information can be found from http://www.wireless-world-research.org/.
Wireless World Initiative (WWI)
22. Wireless World Initiative (WWI) is an Europe-based joint effort from the industry, academia and governments launched in January 2004 to carry out researches to lay foundations for the long-term future of global wireless communications. WWI contains a series of projects funded by the European Union (EU). One of them is WINNER (Wireless World Initiative New Radio) which aims to develop a single ubiquitous radio access system adaptable to a wide range of mobile communications scenarios. The WINNER project consists of two phases. Phase I, completed in end 2005, focused on technology assessment and system concept design. Phase II, completed in end 2007, worked on detailed definition and optimization of the system. In April 2008, the WINNER+ project was launched as a continuation of WINNER, and is scheduled to be completed in 2010. WINNER+ will develop, optimize and evaluate IMT-Advanced compliant technologies through collaborative efforts of the European manufacturers and operators, and the research community. WINNER and WINNER+ also contribute to the European Conference of Postal and Telecommunications Administrations (CEPT) on spectrum issues, and to ITU, 3GPP and the WiMAX Forum on the IMT standardization work Further information can be found from http://www.ist-winner.org and http://projects.celtic-initiative.org/winner+/.
Next Generation Mobile Networks (NGMN) Alliance
23. The Next Generation Mobile Networks (NGMN) Alliance was formed in 2006 by a global group of leading mobile operators to provide coherent vision for the B3G technologies. The Alliance has five working groups responsible for issues on spectrum, technology, trials, intellectual property right (IPR) and ecosystem. It specifies spectrum and technical requirements for the NGMN, e.g. peak downlink data rate over 100 Mbit/s, end-to-end
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latency less than 30 ms, spectral efficiency 3-5 times that of HSPA and EVDO, etc. To support the work of the SDOs, the Alliance identifies and evaluates (through trials) candidate standards to ensure that these standards meet the NGMN requirements. Currently, the 3GPP LTE, 3GPP2 UMB and IEEE 802.16m standards are being evaluated by the NGMN Alliance on their suitability for NGMN. More information can be found from http://www.ngmn.org/.
China
24. In 2001, the Ministry of Science and Technology (MOST) launched the national B3G research programme - the FuTURE (Future Technologies for Universal Radio Environment) project. The purpose of the project is to establish a radio experimental environment that can meet the future demand of applications, and to develop key technologies for the period from 2005 to 2010. FuTURE trials have been conducted to verify B3G technologies like MIMO, OFDM, GMC (General Multi-Carrier). Transmission of multimedia streams at 100 Mbit/s data rate under high mobility environment, and inter-sector handover have been successfully demonstrated in the 3.5 GHz band. Under the auspices of the Chinese government, the FuTURE Forum (http://www.future-forum.org/) was created in 2005 to promote the exchange of information and to strengthen international technical cooperation in B3G development.
25. In addition, the IMT-Advanced Working Group established under the Ministry of Industry and Information Technology (MIIT)4 has been working on the coordination of the national development efforts, and participating in ITU’s work on IMT-Advanced. The China Communications Standards Association (CCSA) also participates in the work of the CJK B3G Standards Collaboration, a collaboration between the standards bodies of China, Japan and Korea. Some Chinese companies and organizations also join in the WWRF activities, and contribute to the WINNER projects. As an evolution of TD-SCDMA, China Mobile (中國移動) and Datang Mobile (大唐移動) have been developing the TD-LTE (Time Division-Long Term Evolution) standard. In a TD-LTE demonstration in October 2008, data rates of 100 Mbit/s (downlink) and 50 Mbit/s (uplink) were achieved. China Mobile plans to build a TD-LTE trial network in 2010, and Datang Mobile expects that TD-LTE can be put into commercial use around 2012.
Japan and Korea
26. In Japan, an industry forum, the mobile IT Forum (mITF) (http://www.mitf.org/), has been created to carry out research and development on the B3G mobile communications systems and services. Among the forum’s activities are studies on standardization, coordination with other related bodies, information collection to contribute to the efficient utilization of the radio spectrum. In Korea, the Next Generation Mobile Communications (NGMC) Forum (http://www.ngmcforum.org/), also an industry forum, has been created to realize the B3G mobile systems and services. Activities of the forum include analysis of technical trends, establishment of B3G vision, study on spectrum use, and international cooperation. mITF and NGMC Forum also work in collaboration with China’s FuTURE Forum. In addition, the standards bodies of China, Japan and Korea have established working relationship also. The Telecommunications Technology Association (TTA) of Korea, and the Association of Radio Industries and Businesses (ARIB) and 4
The Ministry of Industry and Information Technology (MIIT) is a newly-enlarged government division formed in mid-2008 from the Ministry of Information Industry (MII) and some other government bodies including the Commission of Science, Technology and Industry for National Defence, and the State Council Informatization Office.
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Telecommunication Technology Committee (TTC) of Japan work closely with China’s CCSA in the CJK B3G Standards Collaboration.
Considerations
Evolution of technologies
27. The 2G mobile communications systems use various multiple access technologies, e.g. GSM systems use TDMA (Time Division Multiple Access) whereas the IS-95 CDMA systems use CDMA. In the 3G era, all three major IMT-2000 standards (W-CDMA, cdma2000 and TD-SCDMA) are based on CDMA. In the evolution to beyond 3G, the emerging technologies (e.g. LTE, LTE-Advanced, mobile WiMAX, 802.16m, UMB) are all OFDMA-based. According to some researches, OFDMA may not have any inherent advantage over TDMA or CDMA for systems using 10 MHz or less bandwidths. With bandwidths larger than 10 MHz and in combination with advanced antenna techniques, OFDMA can achieve higher spectral efficiency and allow less complex implementations than TDMA and CDMA. The multi-carrier nature and small bandwidth per sub-carrier of OFDMA greatly eases multipath mitigation and simplifies channel equalization. Another advantage of OFDMA is that it can easily scale to different amount of available bandwidths which are not necessarily contiguous. This allows OFDMA to be progressively deployed in available bandwidths by using different number of sub-carriers. To support the high data rates as required by IMT-Advanced, systems like LTE-Advanced and 802.16m may use bandwidths of 40 MHz or above (e.g. by aggregating two or more component carriers, each with bandwidth up to 20 MHz).
Multimedia Broadcast Multicast Service (MBMS)
28. Mobile broadcasting/multicasting is a service anticipated to have growing importance. The support of MBMS (Multimedia Broadcast Multicast Service) would be an essential requirement for the 3G and B3G systems. OFDMA is inherently well-suited for MBMS where multiple cells can broadcast or multicast the content at the same frequency for reception by the user terminals, thus creating a so-called Single Frequency Network (SFN). Despite of multipath propagation (transmissions from multiple cells and signal reflections from obstacles), with OFDMA the received signal copies can be soft-combined at the user terminal. MBMS will be further enhanced in the IMT-Advanced candidate systems to provide improved quality and services.
Advanced Antenna Techniques
29. Other techniques to increase the data rates or system capacity include the use of higher order modulation and advanced antenna techniques. The use of high order modulation is limited by channel quality. 64QAM has been used in HSPA+, EVDO Rev. B and mobile WiMAX. The feasibility of using even higher order modulation in LTE, UMB, 802.16m, or their evolutions remains to be observed. Commonly used advanced antenna techniques include MIMO, beamforming and SDMA (Space Division Multiple Access): (a) MIMO : There are two types of MIMO - spatial diversity and spatial multiplexing.
Spatial diversity involves the transmission of signals from multiple antennas or reception of signals at more than one antenna. Together with appropriate space-time coding, spatial diversity allows a higher signal-to-noise ratio to be obtained at the
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receiver side, but it does not increase the data throughout. Spatial multiplexing is the transmission of multiple data streams from multiple antennas over one single frequency. It increases system capacity but does not provide better signal quality. Up to 4×4 MIMO has been specified for the LTE, UMB and 802.16m systems. (b) Beamforming : It is the creation of the desired radiation pattern for antenna arrays
through signal processing so as to focus the transmit power in the direction of the user, thus increasing the received signal strength at the user equipment. With beamforming, the data rates at the cell edges can be kept reasonably high, ensuring that broadband services can be accessed at cell edges without serious degradation. (c) SDMA (Space Division Multiple Access) : Together with beamforming, SDMA
allows multiple users with sufficient physical separations to send and receive different data streams intended for them using the same time-frequency OFDMA resource, thus increasing the system capacity.
With advance in digital signal processing techniques, these antenna technologies may be further enhanced to better fulfil the IMT-Advanced requirements. Such enhancements may include simultaneous MIMO and SDMA operation, higher order MIMO, e.g. 8×8 MIMO as mentioned in the 3GPP Technical Report TR 36.913 for LTE-Advanced.
Femtocell
30. The feasibility of implementing femtocell base stations in B3G systems such as LTE, LTE-Advanced and 802.16m has received extensive attention from the industry and the standardization bodies. Femtocell base stations are low power base stations typically installed in home or Small Office Home Office (SOHO) environments to provide access to closed or open groups of users. Via the femtocell base station, an IP-enabled user equipment can have direct access to other IP capable devices connected to a home network. A femtocell can be linked to the operator’s network via broadband IP connections such as digital subscriber line (DSL). There are considerations that B3G technologies will initially be deployed to provide data services.
31. With the femtocells, the operators can off-load much of the heavy data traffic away from their networks. Study on the technical requirements like access to femtocell, and the associated security and mobility issues has been underway in standardization bodies including 3GPP and IEEE 802.16 TGm. In April 2009, 3GPP published a set of femtocell standard which forms part of 3GPP’s Release 8 specifications. The standard would facilitate production of femtocell equipment in large volume and ensure interoperability between equipment from different vendors.
Timing for launch
32. It is generally expected that initial deployments of LTE will begin in the 2010 timeframe. Many operators have expressed interest in LTE and announced plans for implementation, including some cdma2000 operators such as Verizon Wireless (US) and KDDI (Japan). As for UMB, it was initially targeted to be commercially available in the first half of 2009. However, to date UMB does not appear to have a very good market outlook. No operator has yet announced plans for trial or deployment of UMB. For mobile WiMAX, it has been accepted by ITU as an IMT-2000 standard (under the name OFDMA TDD WMAN), and has emerged as a potential alternative to the cellular technology.
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There are observations that existing mobile operators are taking an observing attitude towards mobile WiMAX while the fixed operators and the new market players have shown more interest. In 2008, operators have begun limited mobile WiMAX network deployments. More information about the current status of WiMAX deployments (both fixed and mobile WiMAX) can be found from the WiMAX Forum website at http://www.wimaxmaps.org/.
33. As for the potential IMT-Advanced standards, LTE-Advanced, 802.16m, and maybe UMB enhancement, are still at the development stage. There is no concrete timetable for their implementation. More information about the targeted implementation date of the candidate IMT-Advanced RITs may be available at a later time. The possible launch date of IMT-Advanced may also depend on the user demand for mobile broadband services, and the evolution of existing technologies like GSM/GPRS (General Purpose Packet Radio)/EDGE (Enhanced Data rates for GSM Evolution), W-CDMA/HSPA/HSPA+, cdma2000/EVDO. In the ITU-R Report M.2072 “World mobile telecommunication market forecast”, ITU forecasts a steady increase in the mobile communications traffic (including voice and multimedia data) from 2010 to 2020. Existing mobile technologies are under continual evolution to provide enhanced capabilities, and they may impact the launch of IMT-Advanced technologies or pre-IMT-Advanced technologies like LTE. There are reports that GSM, initially deployed in 1991, has its subscriber base still growing in 2008, and the deployment and adoption of W-CDMA/HSPA+ started to increase only around mid-2008. It is possible that W-CDMA/HSPA+ and cdma2000/EVDO systems will continue to evolve and co-exist with and complement systems like LTE, mobile WiMAX, and the future IMT-Advanced systems for some time.
Advice Sought
34. Members are invited to note the content of this paper and provide any additional information on the development of IMT-Advanced.
Office of the Telecommunications Authority August 2009
CCS-WG Paper No. 2/2009 August 2009
Page 11
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