1. Frame structure supporting multiple CP sizes
Document Number:
IEEE S802.16m-08/436, Frame structure supporting multiple CP sizes
Date Submitted:
Source:
Hongwei YANG, Dong LI, Liyu CAI, Keying WU, Xiaolong ZHU Voice: Ext 7796
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Venue:
IEEE m-08/016r1 Call for Contributions on Project mSystem Description Document (SDD)
Target topic: Comments to IEEE m-08/003r1
Base Contribution:
IEEE C802.16m-08/436r2
Purpose:
For m discussion, adoption into the SDD and eventual adoption for standardization
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2. Introduction
In the latest SDD (IEEE m-08/003r1), two CP sizes are defined 1/8 and 1/16 ratio. But there are some big issues:
Not sufficient for supporting various environments and MBS service.
For 1/16 CP, the number of OFDM symbols (51) within one frame cannot be distributed into 8 subframes evenly, resulting in unfixed subframe duration.
Unfixed subframe duration leads to the fact that the CP size can only change frame by frame, which disables
Co-existence of unicast and MBS service within one carrier
Legacy support with 1/8 CP size
In this contribution, we proposed the frame structure with fixed subframe duration for supporting multiple CP sizes.

3. Proposed frame structure supporting multiple CP sizes
Normal CP: 11.43us, 128 samples
Short CP: 3.21us, 36 samples
Long CP: 18.93us, 212 samples
Half OFDM used for long and short CP to fit the fixed subframe duration

4. Numerology for the proposed frame structure
Nominal Channel Bandwidth (MHz) 5 7
8.75 10 20
Over-sampling Factor
28/25
8/7
Sampling Frequency (MHz)
5.6 8
11.2
22.4
FFT Size
512
1024
2048
Sub-Carrier Spacing(kHz)
10.94
7.81
9.77
Tu ((s)
91.4
128
102.4
Cyclic Prefix (CP)
Number of samples per each OFDM symbol per sub-frame[1]
Idle Time(s) 1 2 3 4 6
Normal CP
128/1024[2]
128/1024
N/A
62.86
Short CP
36/1024
40/512
Long CP
214/1024
212/1024
212/512
Note:
1) These values are for sampling frequency of 10MHz BW and can be extended straightforwardly to BWs of 5MHz and 20MHz.
2) A/B: A denotes the CP length and B denotes the useful OFDM symbol length, both in samples.

5. Summary of the proposed solution
Advantages and notes of the frame structure supporting multiple CP sizes with fixed subframe duration
Advantage: CP size can change subframe by subframe, that is, multiple CP sizes can be flexibly configured within one frame, which enables within one frame
multiple CP sizes adaptation to co-existence of unicast and MBS services and
legacy support with 1/8 CP size
Notes: the utilization of half OFDM symbol doesn’t increase the complexity apparently (in details, only simple half symbol extraction at transmitter and half symbol duplication at the receiver are required).
Suggest to adopt the text proposal in base contributions.