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
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