An Evolved Frame Structure and the use of fractional OFDMA symbols IEEE Presentation Submission Template (Rev. 9) Document Number: IEEE S802.16m-08_095r2 Date Submitted: Source: Kiran Thakare, Per Ernström, S. Shawn TsaiVoice: Ericsson SE Stockholm, Sweden Venue: Levi, Finland Base Contribution: IEEE C802.16m-08_095 Purpose: To create a Physical Layer Chapter with a Frame Structure section in the System Description Document (SDD). To include the proposed evolved frame structure in frame structure section of the physical layer chapter of SDD. Notice: This document does not represent the agreed views of the IEEE 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 Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and. Further information is located at and.

Introduction We describe an evolved frame structure which is backwards compatible Reduces round trip latency Reduces CQI latency Removes the limitation that the frame length minus the sum of TTG and RTG gaps must equal an integer number of OFDMA symbol times We also describe a method to handle co-existence and co- deployment problems We propose to –Add a section on the frame structure in the SDD –Include the text from IEEE C802.16m-08_095, describing the evolved frame structure, in the frame structure section in the SDD –In clude the text from IEEE C802.16m-08_095, describing the method to handle co-existence and co-deployment problems, in the section on co-existence and co-deployment in the SDD

Proposed evolved frame structure Legacy frame structure Proposed evolved frame structure Proposed evolved frame structure with preamble also in DL burst 2

Frame as seen by legacy MS Frame as seen by new MS Backwards compatibility

Re-use legacy UL/DL MAP and DCD/UCD signalling to make the evolved frame structure transparent to legacy terminals Use existing IE ”Allocation Start Time” in the UL MAP, to signal start of UL Burst 2 Use existing TTG and RTG in DCD to signal the TTG2 and RTG2 values Thus a legacy terminal will treat UL Burst2 as the whole UL part of the 5ms legacy frame Schedule DL resources in DL Burst1 only, to legacy terminals

Backwards compatibility with preamble also in DL burst 2

Legacy control structure also in DL burst 2 –Preamble with different signature from the preamble in DL burst 1 –DL/UL map –DCD/UCD,... Half of the legacy terminals utilise DL burst 1 and UL burst 2 Half of the legacy terminals utilise DL burst 2 and UL burst 1 Handover procedure used for load balancing No waste of resources even when legacy terminals dominate the terminal fleet

Fractional OFDM symbols Every N’th OFDM subcarrier is periodic over a timeperiod of T/N where T is the OFDM symbol time (without CP) Thus these subcarriers are mutually orthogonal over the time period T/N Thus it is possible to shorten the OFDM symbol to T/N (+CP) if only every N’th OFDM subcarrier is used Amount of data carried by fractional OFDM symbol goes down in proportion to the symbol length Energy per bit is maintained since the power per tone can be increased with a factor N, for a given total TX-power Normal FFT module can be reused for modulation/demodulation of fractional OFDMA symbols

Use of fractional OFDMA symbols Removes the limitation that the frame length minus the sum of TTG and RTG gaps must equal an integer number of OFDMA symbol times Can be used to utilise part of legacy TTG and RTG gaps for 16m terminals (valid also in the case when no new switching points are introduced) Can be used to give more flexibility when introducing new switching points and corresponding new TTGs and RTGs Saves resources in the time domain

Co-existence and co-deployment Interlaced blanked out legacy frames

Let legacy BS transmit two interlaced blanked out legacy frames –gives same uplink downlink pattern as the 16m evolved framestructure, and thus eliminates interference problem Half of the legacy terminals utilize interlaced frame 1 Half of the legacy terminals utilize interlaced frame 2 Handover procedure used for load balancing No waste of resources in legacy network to handle 16m co- existence

CQI Latency CQI latency scales with the frame length With the evolved frame structure the framelength is reduced from 5ms to 2.5ms. This will improve performance substantially for mobile terminals. Allowing for a ”graceful degradation of performance as a function of vehicular speed” as required by the System Requirements document

Latency for Legacy Frame Structure In the IEEE WirelessMAN reference system, taking MS and BS processing delays into account, data can be retransmitted three frames after the initial transmission. To reach the required latency of 10ms without modifying the frame structure, data must be retransmitted in the very next frame introducing significant processing burden on MS and BS. Frame 1Frame 2Frame 3Frame 4 DATANACK DATA RE-TX DATANACK DATA RE-TX 20ms

Latency for evolved frame structure With the evolved framestructure the MS can –Receive data in DL Burst 1 –Transmit a NACK in UL Burst2 in the same frame –Receive retransmitted data in DL Burst2 in the next frame Reaching the required latency of 10ms without introducing excessant processing burden on MS and BS. Frame 1Frame 2 DATANACK DATA RE-TX 20ms DL Burst1 Frame 1 UL Burst2 Frame 1 DL Burst2 Frame 2

Proposal Create a section on frame structur section in physical layer chapter in the SDD Include the text in chapter 3, 3.1, 3.2, and 3.3 of IEEE C802.16m-08_095, describing the evolved frame structure, in the frame structure section in the SDD. Include the text in chapter 3.4 of IEEE C802.16m- 08_095, describing the evolved frame structure, in the section on co-existence and co-deployment in the SDD.