An Evolved Frame Structure and the use of fractional OFDMA symbols

IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number:

IEEE S802.16m-08_095r2Date Submitted:

2008-01-23Source:

Kiran Thakare, Per Ernström, S. Shawn Tsai Voice: +46 8 58532591Ericsson AB E-mail: per.ernstrom@ericsson.com SE-164 80 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.

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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 seenby legacy MS

Frame as seenby new MS

Backwards compatibility

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

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

time

frequency

T0

1/T=fbase

2·fbase

3·fbase

4·fbase

5·fbase

6·fbase

T/2T/3

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-deploymentInterlaced blanked out legacy frames

Co-existence and co-deploymentInterlaced 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

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.