1 / 13

Beamforming Array Gain to Intended and Unintended Users

Beamforming Array Gain to Intended and Unintended Users. Date: 2013-03-20. Authors:. Introduction. In this presentation we show array gain experienced by intended and unintended users Unintended user typically sees significantly lower array gain than the intended user because:

orenda
Download Presentation

Beamforming Array Gain to Intended and Unintended Users

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Beamforming Array Gain to Intended and Unintended Users Date: 2013-03-20 Authors: Nihar Jindal, Broadcom Corporation

  2. Introduction • In this presentation we show array gain experienced by intended and unintended users • Unintended user typically sees significantly lower array gain than the intended user because: • Beamforming weights are matched to the intended user’s channel • Any difference between intended/unintended users’ channels reduces array gain at unintended user • Unintended and intended user’s channels are different due to different multipath propagation Nihar Jindal, Broadcom Corporation

  3. Array Gain Computation • Draw channel to intended user & form BF vectors based on this channel • Draw channel to unintended user • Unintended user’s channel may have different statistics than intended, e.g., different delay spread or K factor • Array gain = RX power at unintended user with BF on versus with no BF • RX power is averaged over 20 MHz Nihar Jindal, Broadcom Corporation

  4. Channel Models • Channel models from Jagganatham-Erceg paper [1] • Intended user (indoors): exponential PDP with spike with 6.3 dB spike + LoS component on 1st tap • 14 nsec/7.5 dB are median values for delay spread/K factor for 1st tap for LOS co-polar at 3 meters (plotted below) • 13 nsec/11.7 dB are 90% values for delay spread/K factor for 1st tap for LOS co-polar at 3 meters • Because shorter delay spread yields more array gain, 90% value for delay spread is chosen at 10% point of CDF (smaller than median) • Unintended user (outdoors): 100 nsecrms delay spread, 0 dB K factor on 1st tap, no spike [2] Nihar Jindal, Broadcom Corporation

  5. Results for Nt=2/3/4/6/8 • Using median values for delay spread/K factor and 90% point of multipath array gain Nihar Jindal, Broadcom Corporation

  6. Results for Nt=2/3/4/6/8 • Using 90% values for delay spread/K factor and 50% point of multipath array gain Nihar Jindal, Broadcom Corporation

  7. Summary of Results • Considerably smaller array gain with 90 % delay spread/K-factor and 50% point of multipath compared to 50% delay spread/K-factor and 90% point of multipath • With either choice of parameters array gain seen is considerably smaller than maximum value of 10log10(Nt) Median values for delay spread/K factor and 90% point of multipath array gain 90% values for delay spread/K factor and median values for multipath array gain Nihar Jindal, Broadcom Corporation

  8. Conclusion • In this presentation we show that beamforming array gain is reduced to the unintended user because of different propagation channel • For 4 transmit antenna case gain reduction is in the 2-3.4 dB range, depending on the statistical analysis method applied Nihar Jindal, Broadcom Corporation

  9. References • [1] Aditya K. Jagannatham and Vinko Erceg, “MIMO Indoor WLAN Channel Measurements and Parameter Modeling at 5.25 GHz”, IEEE 60th Vehicular Technology Conference, 2004, VTC2004-Fall., Vol. 1, 26-29 Sep'04, Pages:106 - 110, Vol. 1. • [2] Mark E. Beach, Matthew W. Webb, and Carmen Stan, “Virtual MIMO performance in a measured outdoor-to-indoor cellular scenario”, Antennas and Propagation (EUCAP), Proceedings of the 5th European Conference, 11-15 April 201, Pages: 2933 – 2937. Nihar Jindal, Broadcom Corporation

  10. Appendix Nihar Jindal, Broadcom Corporation

  11. Sensitivity to delay spread • Nt = 4, Intended user has 6.3 dB spike + 7.5 dB K factor on 1sttap, and unintended user has 0 dB K factor on 1st tap, no spike • Blue: vary delay spread of intended user while keeping unintended user delay spread equal to 100 nsec • Green: vary delay spread of unintended user while keeping intended user delay spread equal to 14 nsec • Increasing delay spread of intended or unintended user significantly reduces array gain • This illustrates the importance of properly modeling the channel statistics to intended/unintended user, e.g., indoor/outdoor Nihar Jindal, Broadcom Corporation

  12. Sensitivity to K-factor • Nt = 4, Intended user has 14 nsecrms delay spread and 6.3 dB spike on 1sttap, and unintended user has 100 nsecrms delay spread and no spike • Blue: vary K-factor of intended user while keeping unintended user K-factor equal to 0 dB • Green: vary K-factor of unintended user while keeping unintended user K-factor equal to 7.5 dB • Increasing K factor of intended or unintended user increases array gain, although not considerably beyond nominal values of 7.5/0 dB K factor to intended/unintended Nihar Jindal, Broadcom Corporation

  13. Median vs. 90% Values • Blue: Median rms delay spread and K-factor, 90% point for multipath • Green: 90% values for rms delay spread and K-factor, 50% point for multipath • Median K-factor with 90% multipath array gain gives 3.7 dB array gain, whereas 90% K-factor with 50% multipath array gives only 2.6 dB Nihar Jindal, Broadcom Corporation

More Related