VHT 60 GHz Channel Model Recommendation

1. VHT 60 GHz Channel Model Recommendation Date: 2008-05-12 Authors: Vinko Erceg, Broadcom

2. Introduction • Signal propagation characteristics are reasonably well characterized in below 6 Ghz frequency bands, for both indoor and outdoor environments. Path loss models and multipath characteristics for both single antenna systems as well as multiple antenna systems are defined. • For 60 GHz frequency bands, there are considerably fewer measurements performed. Line-of-Sight (LOS) conditions are reasonably well characterized, however, there is a gap in NLOS measurements and modeling, unfortunately. • As proposed in VHT 60 GHz PAR, the system would have WLAN characteristics, which means NLOS conditions in many cases. • In this presentation we discuss some of the existing 60 GHz frequency band channel models and propose modifications and additional important features that would have to be added to the modeling approach. Vinko Erceg, Broadcom

3. LOS Path Loss at 60 GHz • LOS path loss modeling in 60 GHz is well covered. In most published results it is reported that the path loss exponent is less then or equal to 2. In some scenarios there is a “tunneling” effect in which case rays add and yield exponent less than 2, for example 1.5. Good examples are hallways and corridors. • To cover most of the cases it seems reasonable to assume a path loss exponent of 2. • Shadow fading standard deviation can be assumed to be about 3 dB. Vinko Erceg, Broadcom

4. NLOS Path Loss at 60 GHz • NLOS path loss modeling in 60 GHz is considerably less covered than LOS. Published results report on the path loss exponents in the range of 3-10. Depends on the construction of the indoor environment (sheetrock, brick, concrete, glass, wood, etc.). • Reasonable path loss exponent for indoor NLOS environments seems to be 3.5 or 4. • Shadow fading standard deviation can be assumed to be in the range of 5-8 dB. Vinko Erceg, Broadcom

5. Existing 60 GHz Models • Reasonable model was presented/adopted in IEEE 802.15.3c group [1]. • Both path loss and multipath (delay profile) models were presented. • Path loss models agree with the previous few slides in this presentation. • Delay profile models are based on Saleh-Valenzuela clustering approach which is widely recognized and accepted. • Similar clustering approach was adopted in 802.11n channel models and extended to MIMO communication scenarios [2]. • It seems reasonable to use IEEE 802.15.3c channel models or similar as a basis for VHT 60 GHz channel model development. Vinko Erceg, Broadcom

6. IEEE 802.15.3c Path Loss Model • Path loss model was derived using directional antenna measurements. • It is tricky to define a path loss model using directional antenna measurements since the model is only valid for those antennas. • Once directional antennas are used, both antenna gain and antenna Gain Reduction Factor (GRF) [3] must be considered. • GRF indicates what portion of rays is not captured by directional antennas when compared to the omnidirectional case. • Omni antenna captures all rays while directional antennas only a portion of rays. • This results in the following: full gain of directional antennas should not be claimed in a highly scattering environment, especially in NLOS conditions. Vinko Erceg, Broadcom

7. 10 dB 20 dB 30 dB Tx Omni Antenna Rx Omni Antenna Tx Omni Antenna Rx 60o Antenna Tx Omni Antenna Rx 10o Antenna GRF With decreasing antenna beamwidth, LOS component is amplified and reflected components are attenuated by the antenna pattern [4], i.e. reflected energy is lost. Vinko Erceg, Broadcom

8. Human Body Blockage Effects (1) • If the LOS component is blocked by a person, it was reported in the literature that up to 20 dB of signal power can be lost [5, 6]. • This effect can be illustrated by removing LOS component from the delay profiles on the previous slide. • The loss is more pronounced for narrow beamwidth antennas, where LOS component is more pronounced. • For the omnidirectional antennas there is some evidence that the loss is considerably smaller, up to 6 dB [7]. This result should be verified by additional measurements (authors to emulate blockage have removed the strongest LOS path from the delay profile measurements). Vinko Erceg, Broadcom

9. Human Body Blockage Effects (2) • To avoid large signal power loss in the case of the direct LOS path blockage, especially in the directional antenna case, adaptive beam antennas may be preferable. • If a high reliability link is to be expected, the blockage scenario has to be carefully considered and included as a part of the channel model. Vinko Erceg, Broadcom

10. IEEE 802.15.3c Delay Profile Model (1) • The IEEE 802.15.3c assumes only Angle-of-Arrival (AoA). • For the VHT 60 GHz systems, directional antennas may be used at both ends of the communication links. • Therefore, both AoA and Angle-of-Departure (AoD) should be characterized. • The above was mentioned in the submission [8] and modifications were proposed. • We believe that this is an important feature of the model. Vinko Erceg, Broadcom

11. IEEE 802.15.3c Delay Profile Model (2) • Parameters for the NLOS delay profile modeling are missing or were derived from the LOS measurement by removing LOS component. • There is not enough known about NLOS 60 GHz channels. • Both measurements and modeling are needed! Vinko Erceg, Broadcom

12. 60 GHz Channel Model: Summary of Recommendations • LOS and NLOS path loss models are reasonably well defined in the literature. • To base LOS delay profile models on IEEE 802.15.3c model or similar (802.11n) seems like a reasonable approach. Needs to be done: • Include both AoA and AoD in the model. • Define delay profile model parameters for the NLOS conditions, measurements are needed. • Define GRF, measurements are needed. • Investigate and include effect of human blockage in the model, measurements are needed. Vinko Erceg, Broadcom

13. References • [1] 15-07-0584-01-003c-tg3c-channel-modeling-sub-committee-final-report • [2] V. Erceg et al “TGn Channel Models,” IEEE 802.11. document 11-03/0940r4. • [3] L.J Greenstein and V. Erceg “Gain reductions due to scatter on wireless paths with directional antennas,” IEEE Communications Letters, Volume 3, Issue 6,  June 1999 Page(s):169 - 171 • [4] Takeshi Manabe, Yuko Miura, and Toshio Iharw “Effects of Antenna Directivity on Indoor Multipath Propagation Characteristics at 60 GHz,” in Proceedings of IEEE PIMRC, Toronto, 1995, pp. 1035-1039. • [5] K. Sato and T. Manabe “Estimation of Propagation-Path Visibility for Indoor Wireless LAN Systems under Shadowing Condition by Human Bodies,” Vehicular Technology Conference, Vol. 3, 18-21 May 1998, pp. 2109 – 2113. • [6] S. Collonge, G. Zaharia, and G. El Zein “Influence of the Human Activity on Wide-Band Characteristics of the 60 GHz Indoor Radio Channel,” IEEE Trans. on Wireless Comm., Vol. 3, No. 6, Nov 2004. • [7] T. Zwick, T. J. Beukema, and H. Nam “Wideband Channel Sounder With Measurements and Model for the 60 GHz Indoor Radio Channel,” IEEE Trans on Veh Technol, Vol. 54, No. 4, July 2005. • [8] 15-07-0774-01-003c-generalization-tg3c-channel-models Additional references: • P. F. M. Smulders and L. MI. Correia “Characterisation of Propagation in 60 GHz Radio Channels,” Electronics and Comm. Eng. Journal, April 1997, pp. 73-80. • H. Yang, P. F.M. Smulders and M. H.A.J. Herben “Indoor Channel Measurements and Analysis in the Frequency Bands 2 GHz and 60 GHz,” 2005 IEEE PIMRC, pp. 579-583. Vinko Erceg, Broadcom