1. Supplementary Channel for Talk-around Direct Communications
Document Number:
IEEE S802.16n-11/0154
Date Submitted:
Source:
Jihoon Choi, Young-Ho Jung
Korea Aerospace University
Sungcheol Chang, Seokki Kim, Eunkyung Kim, Miyoung Yun, Won-Ik Kim,
Sungkyung Kim, Hyun Lee, Chulsik Yoon, Kwangjae Lim
ETRI
Re:
Call for comments on the n AWD
Base Contribution:
IEEE C802.16n-11/0154
Purpose:
To be discussed and adopted by TGn
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2. Introduction
Frame structure for TDC (talk-around direct communication)
Sync-CH (synchronization channel)
Ded-CH (dedicated channel)
Sup-CH (supplementary channel).
Sup-CH
Ranging channel
CQI (channel quality indicator)
Feedback channel

3. Sup-CH Structure Resource elements for Sup-CH
One m-tile (mini-tile) is a (5 OFDM symbols)  (2 sub-carriers) rectangular region.
One Sup-SubCH (supplementary subchannel) is composed of 4 distributed m-tiles (mini-tiles).
Relationship between Ded-CH and Sup-CH
One-to-one mapping between Ded-SubCH (dedicated subchannel) and Sup-SubCH.
Each slot supports up to 9 Sup-SubCHs (also supports up to 9 Ded-SubCHs).
Example
5th Sup-SubCH is composed of m-tiles 5,14,23, and 32.

4. Ranging Channel Structure
Estimation of time offset, frequency offset, SINR (signal to interference plus noise ratio), etc.
Periodically transmitted, where the starting slot number and the period are determined during link initialization.
Sequence allocation for ranging channel
The ranging sequence is defined by a binary code
with length 8, given by
[S0 S1 S2 S3 S4 S5 S6 S7] = [1,-1, -1,1, -1,1, 1,-1]
The same sequence is repeatedly transmitted for 5 OFDM symbols.

5. CQI Channel Structure CQI channel
Used for feedback of measured channel quality such as SINR or MCS level.
One CQI channel payload carries up to 4-bit information.
Mapping of information in the CQI channel
Sequence generation
See the following slide.
BPSK modulation
0 mapped to +1 and 1 mapped to -1
Symbol sequence to subcarrier mapping
See the right figure.

6. CQI Sequence Generation
Sequence mapping table for CQI channel
Sequence permutation
where
Index
Sequence
Usage
level 0 1
level 1 2
level 2 3
level 3 4
level 4 5
level 5 6
level 6 7
level 7 8
Reserved 9 10 11 12 13 14 15

7. CQI Transmission CQI channel CQI payload Property of CQI sequences
Periodically transmitted, where the starting slot number and the period are determined during link initialization.
The ranging channel and the CQI channel should be assigned to separate time slots by adjusting the starting slot number and the transmission period.
CQI payload
The AMS estimates the SINR using the Ded-CH preamble and the pilot symbols included in the Ded-CH.
The CQI index is determined using the estimated SINR.
Property of CQI sequences
Correlation between CQI sequences is minimized for non-coherent detection.
CQI sequences are designed to have small correlation with the ranging sequence.
Using this property, an AMS without knowledge of CQI transmission slots can separate the ranging channel and the CQI channel.

8. Feedback Channel Structure
Uses the same sequences as the CQI channel.
Includes the following control signals.
ACK channel, NAK channels
MCS Change Confirm: a response message to the MCS Change Command
RCHG (resource change) indication: a response message to the RCHG Command
Transmitted using the slots which are not used by the ranging channel and the CQI channel.
Sequence mapping
Index
Sequence
Usage
ACK 1
NAK for frame 0 2
NAK for frame 1 3
NAK for frame 2 4
NAK for frame 3 5
MCS Change Confirm 6
RCHG Indication 7
Reserved 8 9 10 11 12 13 14 15

9. Simulation Results

10. Simulation Environments
Parameters
Estimation and detection
Using the ranging channel, the time and frequency offsets were estimated in the frequency domain.
For the CQI and feedback channels, non-coherent detection was used.
Parameter
Value
Carrier frequency
2.3 GHz
Bandwidth
10 MHz
FFT size
1024
CP size
128
Sampling rate
11.2 MHz
Number of transmit antennas 1
Number of receive antennas
Velocity of transmitter
30 km/h
Velocity of receiver
Moving direction of transmitter
/6
Moving direction of receiver
-/4
Timing offset
16 samples
Normalized frequency offset
0.02
Fading channel
Bad Urban Macro NLOS of 16m EMD
(modified for TDC)

11. Ranging Channel Requirements Performance
MSE (time offset) < 100, MSE (freq offset) < 4.4x10-5
Performance
When SNR = 5 dB, the requirements can be satisfied by accumulating more than 30 ranging channels.

12. Sequences for CQI and Feedback Channels
Sequences for 6-bit, 5-bit, 3-bit payload
Index
Sequence 32 1 33 2 34 3 35 4 36 5 37 6 38 7 39 8 40 9 41 10 42 11 43 12 44 13 45 14 46 15 47 16 48 17 49 18 50 19 51 20 52 21 53 22 54 23 55 24 56 25 57 26 58 27 59 28 60 29 61 30 62 31 63
Index
Sequence 16 1 17 2 18 3 19 4 20 5 21 6 22 7 23 8 24 9 25 10 26 11 27 12 28 13 29 14 30 15 31
Index
Sequence 4 1 5 2 6 3 7

13. Simulation Results – CQI and Feedback
AWGN
Considering the power spectral density, the Sup-CH requires 1.25 dB gain to achieve the same coverage as m PFBCH.
The Sup-CH with 4-bit payload has slightly better coverage than 16m PFBCH.
Fading channel

14. Conclusion Ranging channel CQI and feedback channel Note
Only 8 subcarriers are used for the channel channel in TDC, while 72 subcarriers are used for the ranging channel in m.
The ranging period needs to be shortened.
For example, when the ranging period is 100 ms, the adjustment of time and frequency requires about 3 sec.
CQI and feedback channel
When the 4-bit payload is used, the CQI and feedback channels for TDC perform comparable to m PFBCH.
Note
The performance can be improved by
Using more transmit and receive antennas
Employing more elegant estimation algorithms or detection schemes.