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IEEE C802.16m-08/1151




Project

IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>

Title

MCS Adaptation and Feedback Mechanism in 802.16m MBS

Date Submitted

2008-09-13

Source(s)

Hung-Yu Wei,

Ching-Chun Chou,

National Taiwan University


Voice:

E-mail: hywei@cc.ee.ntu.edu.tw

f95921098@ntu.edu.tw


Re:

MAC aspect of enhanced MBS; in response to the TGm Call for Contributions and Comments 802.16m-08/033 for Session 57

Abstract

This contribution focuses on the MCS adaptation for MBS in IEEE 802.16m. With the feedback mechanisms, different directions of MCS adaptation could be decided by the HARQ report of the MBS and improves the performance of MBS.

Purpose

To be discussed and adopted by TGm for use in the IEEE 802.16m

Notice

This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein.

Release

The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16.

Patent Policy

The contributor is familiar with the IEEE-SA Patent Policy and Procedures:

and .

Further information is located at and .



MCS Adaptation and Feedback Mechanism in 802.16m MBS

Hung-Yu Wei, Ching-Chun Chou

Department of Electrical Engineering, National Taiwan University
  1. Introduction


This contribution describes contents about the necessary features of the Modulation and Coding Scheme (MCS) adaptation for the Multicast/Broadcast Services (MBS) in the IEEE 802.16m system. As MBS is usually used for transmission of real-time traffic, MCS adaptation is necessary to achieve high throughput and better spectral efficiency. While HARQ reports loss or unsuccessful transmission of data blocks, it is natural to combine the HARQ ACK/NACK signaling with MCS adaptation for MBS.
  1. MCS Adaptation and Feedback


MCS feedback is critical for applying adaptive modulation and coding to MBS. As the wireless channels are varying all the times, the adjustment of the MCS is crucial for MBS. As the MBS serves a wide variety of the traffic flows, the MCS adaptation would be indispensable under certain conditions.
The MCS could be set once before the initialization of the MBS, or each time before each data block transmission. Whether we use static or dynamic MCS, the configuration or the adjustment of the MCS requires signaling between the MS and the BS. Since the direction of adaptation requires CSI or PSNR report of CSI from the MS, the feedback to the BS is essential. The feedback for the MCS adjustment could be done through the polling between the BS and the MS. As the MBS group polling would contain the CSI, PSNR, or other reception states information of the subordinate MSs within the group. BS could use polling to initiate the MCS feedback. On the other hand, BS might establish periodic MCS reporting with all MSs in the MBS group. Besides, the signaling could be integrated with the original MBS signaling, and this scheme is given in Section 5. The adjustment of the MCS could be conducted with two methods: positive or negative reporting. One is negative reporting, which means for using more robust or slower rate MCS for the transmission. The other is positive reporting, which collects MCS information to adjust to the accurate MCS level..
  1. Fast Feedback with Negative Reporting


As wireless channel condition might vary significantly, fast feedback for MCS adjustment is needed. When an MS find the current wireless channel condition is unable to support current MCS, the MS will use fast feedback to report this condition. Upon receiving a negative reporting, the BS could apply a more robust MCS for this MBS transmission. Applying MCS with lower rate or more robust transmission should be applied to the system when 1 or more MS sends negative reporting for MCS.This is similar to the NACK feedback issue for reliable MBS described C80216-08_XXX_MBS.doc. Similarly, we could apply Busy Tone Negative Reporting, which is an analogy to the Busy Tone NACK, or Negative-preamble Reporting, which is an analogy to NACK-preamble, for this MCS fast feedback.
  1. Full Probing with Positive Reporting


The MCS fast feedback negative reporting can be used for adaptation to a more robust MCS. However, we will need a feedback mechanism to adjust to a high-rate MCS. The MCS fast feedback negative reporting only provides differentiated information. The full probing mechanism is able to collect complete information. The MCS full probing with positive reporting is an analogy to the cumulative ACK in reliable MBS design in described C80216-08_XXX_MBS.doc.
An MS measures the downlink CSI, determines the appropriate MCS, and reports to the BS. The full probing for MCS is conducted during the initialization phase of an MBS service. The BS could also configure the MBS group so that all MS could send positive reporting periodically. On the other hand, on-demand polling for MCS full probing might also be used.
From the cumulative information of the positive reporting, we could know things such as which MS is in better channel conditions, which is more close to the BS, which has more power, which should be served with higher priority, etc. These are positive reports and should trigger positive MCS adaptation for the specific MSs. Positive adaptation could increase the throughput of the system and spares radio resources for MSs which is in bad channel states.
  1. Joint Signaling for MBS and MCS adaptation


From C80216-08_XXX_MBS.doc and section 3&4, different direction of the MCS adaptation are described separately. However, for the adjustment of the MCS, the signaling between the BS and MSs is necessary. Although it is natural to use the MBS polling scheme for MCS adaptation, this still results in additional signaling overhead. It is possible to signal the ACK scheme in MBS and MCS adaptation simultaneously, utilizing the feedback from the MS back to the BS. We call this joint signaling of reliable MBS and MCS adaptation.

For example, we could use 2 CDMA codes for each MBS group. Code (I) indicates NACK but no changes to MCS is needed. Code (II) for NACK and modification to the MCS is needed. If there is necessity for data retransmission but none for rate adjustment, code (I) is used in this case. If data block is not received and at the same time the channel state is poor, code (II) is applied, which is Negative MCS adaptation. This could combine the signaling of both reliable MBS and MCS adaptation. Beyond this design, we could still use more codes or additional signaling IE to provide more feedback information.



  1. Proposed Text for SDD


----------------------------------------------------Start of the Proposed Text--------------------------------------------------

11.9.1.6.1 E-MBS feedback for MCS selection

MCS feedback mechanism is needed for MCS adaptation in E-MBS. Fast feedback mechanism could be used for quick adjustment of MCS. Full probing mechanism could be used for initialization and accurate MCS selection. MCS adaptation and reliability feedback could be jointly applied for efficient feedback signaling.

11.9.1.6.1.1 Fast Feedback for MCS adaptation in E-MBS

Fast feedback for MCS adaptation could be used for timely adjustment to a more robust MCS transmission in E-MBS. When an MS's CSI cannot support current MCS, the fast feedback trigger the downgrading of MCS to a more robust MCS.

11.9.1.6.1.2 Full Probing for MCS selection in E-MBS

Full probing is needed for selecting the appropriate MCS for robust transmission in E-MBS. MS measures the downlink CSI, determines the appropriate MCS, and reports to the BS. The full probing for MCS is conducted during the initialization phase of an E-MBS service. The full probing could be conducted periodically in time-varying wireless environment.

11.9.1.6.1.3 Joint Feedback for MCS adaptation and Acknowledgement in E-MBS

Joint feedback for MCS adaptation and Acknowledgement is design to provide efficient signaling mechanism for reliable transmission and robust MCS selection in Joint Feedback for MCS adaptation and Acknowledgement in E-MBS. CDMA codes could be used for joint feedback for MCS adaptation and packet reception condition. Joint signaling feedback could be used to indicate Acknowledgement (ACK) or Negative Acknowledgement (NACK) along with MCS adjustment request.

----------------------------------------------------End of the Proposed Text---------------------------------------------------






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