1. Submission doc.: IEEE 802.11-14/1446r0 November 2014 Leif Wilhelmsson, EricssonSlide 1 Analysis of frequency and power requirements for UL-OFDMA Date: 2014-11-03 Authors:

2. Submission doc.: IEEE 802.11-14/1446r0 Abstract Frequency errors and near-far effects may severely degrade performance for UL-OFDMA We provide some analytical results that can be used to analyze requirements without lengthy simulations in case of UL-OFDMA We also address the issue with varying received powers and present an approach to analyze requirements on power control Slide 2Leif Wilhelmsson, Ericsson November 2014

3. Submission doc.: IEEE 802.11-14/1446r0 Outline Motivation/Related work Recap of single user case SNR loss due to frequency and power miss-alignment for UL-OFDMA Some simulation results and discussion on requirements for frequency and power alignment Conclusions Slide 3Leif Wilhelmsson, Ericsson November 2014

4. Submission doc.: IEEE 802.11-14/1446r0 Motivation/Related work UL-OFDMA sets requirements on frequency synchronization and power alignment for the signals sent by the STAs [3] and [4] discuss frequency synchronization requirements and compare with what is used in LTE [5] proposes an ACK procedure, but do not discuss corresponding requirements for this to be feasible [6] addresses the same problem but for UL MU-MIMO, by using complete link simulations Here we try to assess requirements for UL-OFDMA analytically for increased insight and fast evaluation Slide 4Leif Wilhelmsson, Ericsson November 2014

5. Submission doc.: IEEE 802.11-14/1446r0 ICI in Single-User Case Slide 5Leif Wilhelmsson, Ericsson November 2014 (1)

6. Submission doc.: IEEE 802.11-14/1446r0 ICI in OFDMA UL Slide 6Leif Wilhelmsson, Ericsson November 2014

7. Submission doc.: IEEE 802.11-14/1446r0 ICI in OFDMA UL Slide 7Leif Wilhelmsson, Ericsson November 2014 (2)

8. Submission doc.: IEEE 802.11-14/1446r0 Slide 8Leif Wilhelmsson, Ericsson November 2014 Case: 64-QAM N 1 =N 2 =26 60,000 Monte-Carlo Simulations Comparison: OFDM formula vs. OFDMA

9. Submission doc.: IEEE 802.11-14/1446r0 Ex: Degradation vs. frequency offset at AP Slide 9 November 2014 Illustration of degradation in UL-OFDMA. Desired signal has relative frequency error of minus 2%, aggressor has relative frequency error of 3% relative APs nominal frequency. Self-ICI is dominating for equal power, because significant MUI is mainly between the very closest sub-carriers. However, with largely different power, MUI can easily dominate Leif Wilhelmsson, Ericsson Frequency offset aggressor Frequency offset desired signal

10. Submission doc.: IEEE 802.11-14/1446r0 Joint power and frequency requirements Slide 10 November 2014 Degradation due to MUI as a function of power ratio and frequency error The requirements for MUI seems reasonable, although rough power control or proper scheduling (selection of users with somewhat similar powers) is required, say within 10 dB Leif Wilhelmsson, Ericsson

11. Submission doc.: IEEE 802.11-14/1446r0 What sets the requirements? Slide 11 November 2014 Referring to the figures above, the degradation due to self interference is the same as the degradation due to MUI if the power ratio is about 15 dB If degradation is set to the same value, say 2 dB, self interference sets the limit (e.g. 2%) if power difference is less than 15 dB, otherwise MUI sets the limit Note: This was for 2 “10 MHz” STAs in one 20 MHz channel. Evaluation for more STAs and other sub-channel BWs is straight forward MUI Self interference 16-QAM 2dB degradation 64-QAM 2dB degradation Leif Wilhelmsson, Ericsson

12. Submission doc.: IEEE 802.11-14/1446r0 Conclusions The derivation (1), based on the single-user OFDM case, is not directly applicable for calculating MUI for the OFDMA UL case as it assumes same frequency error for all sub-carriers and equal power Generalization to OFDMA is straight-forward and allows for evaluation of degradation without detailed link level simulations When the two users transmit with equal powers, the SNR degradation due to MUI is significantly less than what is obtained from (1) Comparing degradation due to MUI and self interference is one means to set requirements on power differences, in addition to e.g. dynamic range in the ADC Slide 12Leif Wilhelmsson, Ericsson November 2014

13. Submission doc.: IEEE 802.11-14/1446r0November 2014 Leif Wilhelmsson, EricssonSlide 13 References 1.Pollet, T.; Van Bladel, M.; Moeneclaey, M., "BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise," IEEE Transactions on Commun., vol.43, no.2/3/4, pp.191-193, Feb./March/April 1995. 2.Faulkner, M.; Wilhelmsson, L.R.; Svensson, J., "Low-Complex ICI Cancellation for Improving Doppler Performance in OFDM Systems," IEEE VTC-2006 Fall. pp.1,5, 25-28 Sept. 2006. 3.11-14/0818r0, “Synchronization requirements” 4.11-13/1388r0, “Uplink multi-user transmission” 5.11-14/1211r0, “Ack procedure for OFDMA” 6.11-09-1036-00 “Uplink MU-MIMO Sensitivity to Power Differences and Synchronization Errors”

14. Submission doc.: IEEE 802.11-14/1446r0 ICI in OFDMA UL Slide 14Leif Wilhelmsson, Ericsson November 2014

15. Submission doc.: IEEE 802.11-14/1446r0 ICI in OFDMA UL Slide 15Leif Wilhelmsson, Ericsson November 2014

16. Submission doc.: IEEE 802.11-14/1446r0 ICI in OFDMA UL Slide 16Leif Wilhelmsson, Ericsson November 2014 (3)