Design of Sounding Channel Structure IEEE Presentation Submission Template (Rev. 9) Document Number: IEEE C802.16m-09/904 Date Submitted: Source: Tsung-Yu Tsai, Jiun-Je Jian, Kanchei(Ken) Loa, Yi-Ting Lin, Youn-Tai Lee, Chun-Yen Hsu, Chiu-Wen Chen Institute for Information Industry(III) Yih G. Jan Tamkang University Venue: IEEE Session #61, Cairo Base Contribution: N/A Re: IEEE802.16m-09/0020. “Call for Contributions on Project m Amendnent Working Document (AWD) Content” AWD-Commnets/Area: Chapter (UL-CTRL) Purpose: To be discussed and approval by IEEE m TG 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. ://standards.ieee.org/board/pat

Introduction In this contribution, we propose a sounding channel structure consisting of an antipodal sounding sequence and an orthogonal sounding sequence. We also provide simulation results to prove their effectiveness. The main advantages of the proposed sounding channel structure –Eliminate the inter-carrier-interference due to oscillator mismatch and Doppler shift with low complexity demodulation algorithm More than 1 dB gain in moderate to high SNR (> 5 dB) and achieve smaller error floor (0.2% carrier frequency offset and 30 km/h speed) –For the same transmitted power in an OFDM symbol, the inter-cell- interference can be decreased approximately by 3dB –For the same interference level, the combination gain can bring close 3dB gain for channel estimation in a given tone (Utilize the high correlation between the channel responses of adjacent subcarriers) –The pilot density per user is double

Introduction The features of the proposed sounding channel structure –Work with any sounding channel pattern Such as sounding channel allocation, narrow/wide band sounding –Low demodulation complexity Eliminate most ICI and significantly reduce the estimation error with simple operations (low cost) –Flexible configuration

Antipodal Sounding Sequence Basic Mode Two adjacent subcarriers are allocated to one MS (or antenna) Antipodal signals are transmitted in the set of adjacent subcarriers A x denotes the reference signal transmitted(e.g. Golay sequence)

Antipodal Sounding Sequence Basic Mode In the receiver side (i.e. ABS), the ICI can be self-canceled by simply performing differential demodulation on two adjacent subcarriers which is allocated to the same AMS (or antenna) –That is, obtaining R k -R k+1, where R x denotes the received frequency domain signal from subcarrier x

Simulation NFFT: 1024 Carrier frequency: 2.5 GHz BW: 10 MHz Oversampling factor: 28/25 Carrier frequency offset: -0.2% ~ 0.2% of the subcarrier spacing Channel model : Vehicular A Estimator: MMSE

No. of antenna: 6 Period of sounding channel: 12 Boost: All users boost 2 dB Speed: 30 km/h Proposed sounding channel Decimal mode sounding channel

In low SNR (<5dB), the gain is slightly more than 3 dB When SNR is low, the effect of noise is more significant than that of ICI In moderate to high SNR (> 5dB), the dB gain is provided When SNR increased, the effect of ICI becomes more and more significant

Orthogonal Sounding Sequence Multiplexing Mode Two adjacent subcarriers allocated to two AMS(or antennas) One AMS(antenna) transmits antipodal signals, and the other transmits identical signals

Orthogonal Sounding Sequence Multiplexing Mode In this design, the sequences of the AMS(or antennas) allocated to the same set of adjacent subcarriers are essentially orthogonal. Thus, we can obtain:

The capacity of sounding channel is increased significantly (up to double) by using CDM –The max. capacity is the same as that of decimation mode –The gain of ICI self-cancellation could still be preserved (antipodal users) –The combining gain can bring additional benefits to combat AWGN with no additional spectrum overhead –The pilot density is double per user The implementation (use) of multiplexing such as the number of sounding AMS used in an OFDM symbol can be configured flexibly according to requirements Orthogonal Sounding Sequence Multiplexing Mode

Simulation No. of antenna: 12 Period of sounding channel: 12 Boost: All users boost 2 dB Speed: 30 km/h Proposed sounding channel Decimal mode sounding channel

For users using antipodal sounding sequence, 3-4 dB gain is obtained For users using identical sounding sequence, approximately 3 dB gain is obtained in moderate and low SNR (<5dB) The effect of ICI becomes more significant when the distance between two allocated subcarrier is decreased The error floor of decimal mode in 12 users scenario is higher (0.07) and achieved faster( 8 dB) compared to that of 6 users scenario (0.018, 12 dB)

PAPR If Golay sequence is used for antipodal sounding sequence and identical orthogonal sounding sequence, the PAPR will be less than or equal to 4 (see Appendix)

Proposed text Sounding Sequence [insert the following text] Sounding sequence is transmitted by multiple AMS or multiple antennas per AMS in uplink sounding channel for ABS to determine the corresponding channel responses. For the purpose to improve the accuracy of channel estimation, antipodal sounding sequences could be allocated in adjacent subcarriers to an AMS or an antenna for facilitating the accurate estimation in the corresponding subcarriers. In addition, the AMS or antennas that adopts the antipodal sounding sequences could be multiplexed with other AMS or antennas on the same subcarriers by using orthogonal sounding sequence, where the set of basis spanning the orthogonal sounding sequence is orthogonal to the set of basis spanning the antipodal sounding sequence.

Appendix 1: Derivation of ICI due to Carrier Frequency Offset

Practically, the orthogonality of subcarriers could be corrupted due to various impairments in wireless channels –For example, oscillator mismatch, Doppler effect,etc –The loss of subcarrier orthogonality introduces non-negligible ICI among subcarriers In UL channel, the ICI problem is even worse, since multiple transmitters make the time and frequency synchronization more difficult –ICI decreases the effective SINR and is difficult to be compensated by boosting or interference mitigation Limit the performance of channel estimation even in high SNR situation

Antipodal Sounding Sequence

Appendix 2: Derivation of PAPR

PAPR