Recent Progress of WiMAX Standards

Nowadays, there are two WiMAX-related standardization organizations: IEEE 802.16 Working Group and WiMAX Forum. The IEEE802.16 Working Group aims to create standards for broadband wireless access, while the WiMAX Forum is an industry-led non-profitable organization committed to promoting and certifying interoperable WiMAX products.
As the first company to put forward the concept of carrier-grade WiMAX network, ZTE has always been devoting itself to the development of WiMAX standards. The company has already submitted more than 400 proposals to the IEEE 802.16 Working Group covering control channel, frame structure, multi-hop relay, Femto Base Station (BS), mobility management, etc. Additionally, as one of 15 board members of the WiMAX Forum, ZTE has submitted over 200 proposals to the forum involving hot topics such as MultiCast BroadCast Service (MCBCS), Emergency Service (ES), IP Multi-media Subsystem (IMS), Policy and Charge Control (PCC), and Simple IP.
Due to their outstanding contribution to the setting of WiMAX standards, many experts from ZTE are honored to lead the standardization process. Among them, Tricci So is elected as Chairman of the MCBCS Working Group in the WiMAX Forum; Jerry Chow is invited to be Chairman of the IEEE 802.16m E-MBS Rapporteur Group; Mary Chion is appointed as Chairman of the IEEE 802.16m Handoff E-MBS Rapporteur Group.

MCBCS
The unicast network offers personalized contents to end users on a one-to-one basis, with each user occupying independent spectrum and network resource. However, this resource could be shared by all users when the same content is delivered. MCBCS can effectively utilize the limited resources to broadcast the same content to multiple users. Mobile TV is a typical application of MCBCS. As the spectrum resource is limited, and most of the users' requirements can be classified, MCBCS is receiving increasing attention in the industry.
At present, a MCBCS subgroup has been established in the Network Working Group (NGW) Release 1.5 of the WiMAX Forum and it plans to finish the related standardization work in two phases. Broadcast and static multicast service will be provided in the first phase and dynamic multicast service will be supported in the second phase. The basic technical documents of the first phase have been finished, which specifies the MCBCS network architecture, service initiation, service setup/release procedures, mobility management, power saving support, data transmission, and data synchronization. They are in the Verification and Validation (V&V) comments resolution process and will be released in the Q1 of 2009.
Being the leader of the MCBCS subgroup, ZTE has been undertaking great responsibilities and has submitted proposals covering almost all key technical points. Despite of the fierce arguments and a wide divergence of views from different operators and equipment vendors, ZTE managed to bring different opinions into agreement and keep the standardization work on schedule.

Multi-Hop Relay
All BSs of current wireless communications system need the support of fixed lines, and their coverage is relatively fixed. Because of the barriers on the transmission routes or long distance transmission, blind areas or edge areas with serious signal attenuation are formed. To expand the coverage and improve the service quality for the edge users, the IEEE 802.16 Working Group proposes the multi-hop relay technology, in which one or more wireless Relay Stations (RSs) are added into the system to decode or demodulate the received signals into source signals for storage and processing. After being coded and modulated, the source signals are sent to the receiver. 
The IEEE 802.16 Working Group has two subgroups related to multi-hop relay: Relay Task Group (RTG) and IEEE 802.16m Task Group (TGm). RTG aims to develop IEEE 802.16j standards, hoping to introduce the multi-hop relay technology based on IEEE 802.16e standards. The IEEE 802.16j D8 is currently under sponsor ballot and the IEEE 802.16j D9, which will be finished in February 2009, will integrate the IEEE 802.16e to form a complete IEEE 802.16 Rev2 standard. The objective of TGm is to provide higher mobility and transmission rate to fulfill the IMT-Advanced requirements. A Relay Rapporteur Group is established in TGm to draft system description related to the IEEE 802.16m multi-hop relay.
The system topology will be changed due to the adding of wireless RSs. Therefore, it is necessary to intelligently adjust the topological relation and configuration between the RSs and BSs. Specifically, the impact on the system from connection, release and handoff of the RSs should be taken into consideration, and full use of the RSs should be made to improve data transmission efficiency. For example, when a RS performs handoff from the serving BS to a target BS, it must allow its connected RSs or mobile terminals to be handoffed first to the target BS. Another case is that the BS must inform the RS to transmit the corresponding data delay so that it can transmit MCBCS data synchronously with the BS. One more example is that the RS can directly forward data for transmission between its connected two mobile terminals without transmitting them to the BS, which improves data transmission efficiency.
ZTE has submitted more than 20 relay-related proposals to RTG and TGm, with content covering data transmission methods, MCBCS, relay data format, as well as connection, release and handoff of the RSs.

Femto BS
Beside the above-mentioned wireless RSs, Femto BS with a coverage radius of tens of meters can be installed indoors to enjoy high speed access and seamless coverage. The introduction of Femto improves system capacity based on the existing spectrum resource.
The IEEE 802.16m Task Group has also set up a Femto BS Rapporteur Group to specify the related system description including definition, handoff, paging, power saving and Ad hoc of the Femto BS.
Because there is a large number of Femto BSs used, it is unnecessary or impossible for users to access each Femto BS. Therefore, the Femo BSs must be quickly identified by users for accessibility. The Task Group agrees that the Femto BSs could be categorized into two different types. One type is accessible only to authorized users and the other type is accessible to all users. 
Accordingly, technologies related to the BSs should be changed based on the Femto BS features. For example, when a user performs handoff from an ordinary Macro BS to a Femto BS, it is necessary to adopt a customized neighbor BS list including accessible BSs for scanning. In the IEEE802.16e standards, if an idle user needs to be awakened, it is necessary to send paging commands to all Macro BSs related to the user; however, if the idle user is in the Femto BS, the paging commands can be sent inside the Femto BS to save the overhead by using the feature of slow speed of user movement. Moreover, as there are few Femto BS users, Femto BS may work in a power saving status when no user is accessed or activated, which reduces the transmission power and hence reduces system interference.　
ZTE has submitted more than 10 proposals to the Femto BS Rapporteur Group, covering definition, handoff, paging, and power saving of Femto BS.

Frame Structure
The format for a resource allocation unit is defined by frame structure, which is one of the most basic technical features in telecommunications system. In specifying the frame structure, the IEEE 802.16m Task Group should take into consideration the backward compatibility of 16m and 16e, the decrease of signaling overhead and transmission delay, and the coexistence with other TDD systems. Three things have been preliminarily determined: the TDD mode is adopted for backward compatibility of 16m and 16e; the concept of Superframe or Miniframe combined with new control channel and synchronous sequence is adopted to reduce signaling overhead; and the rapid feedback and the additional uplink/downlink switch points are adopted to reduce transmission delay.
For the issues concerning low spectrum efficiency in the present 16e system and poor compatibility and scalability between different bandwidths, ZTE put forward its innovative design of frame structure that allows backward compatibility with existing systems while improving spectrum efficiency and ensuring system scalability. Moreover, the frame structure can maximally reduce interference when coexisting with other TDD systems.

Conclusion
Technical standards are of great importance for product commercialization. Higher speed and mobility are the development trends of WiMAX standards. ZTE has always been committed to promoting WiMAX standardization work from the perspective of industry chain, and will certainly make greater contribution to the progress of WiMAX products and standards.