Channel Modeling for 60 GHz WLAN Systems

1. Channel Modeling for 60 GHz WLAN Systems Date: 2008-07-14 Authors: Alexander Maltsev, Intel

2. Abstract • This presentation discusses general characteristics of the 60 GHz radio propagation channel, provides an overview of the measurements results and the available channel models, and proposes approaches to the channel modeling for IEEE VHT 60 GHz Alexander Maltsev, Intel

3. Agenda • Characteristics of the 60 GHz propagation channel • IEEE 802.15.3c WPAN channel models review • Possible approaches to IEEE VHT channel modeling • Conclusion Alexander Maltsev, Intel

4. General Characteristics of 60 GHz Propagation Channel • The propagation characteristics at the 60 GHz band are significantly different from that for the current WPAN / WLAN bands of 2 - 5 GHz. • The main difference is that the 60 GHz propagation has a quasi-optical nature. • The 60 GHz propagation loss (under the same TX and RX antenna gains) is 20 to 30 dB higher than for 2 – 5 GHz band. • The diffraction effects (propagation of the EM field behind the obstacle) are significantly smaller in comparison with 2 – 5 GHz band (shadowing zones are very sharp in 60 GHz). • The penetration loss for 60 GHz band is also higher than for2 – 5 GHz band. • The cross polarization level of the received signal for the 60 GHz band is on average significantly below than for 2 – 5 GHz and the impact of the polarization may be more important for 60 GHz than for 2 – 5 GHz. Alexander Maltsev, Intel

5. General Characteristics of 60-GHz Propagation Channel (Cont’d) • The EM field for 2 - 5 GHz signal is composed of multiple waves coming from primary signal source and multiple secondary sources – diffracted and reflected (multiple times) waves. The EM field has a complex structure with no preferable directions of arrival and departure of the communication signals. The multiple antenna algorithms are focused on exploitation of the spatial diversity of the EM field in different points. • Due to specific properties of 60 GHz EM field listed above it has a structure consisting of a few rays coming from the direct path (if available) and from several main reflectors with the directions of arrival and departure very close to that predicted by the ray tracing (geometrical optics) laws. So the antenna processing for 60 GHz should be focused on the spatial filtering of one or few rays to maximize the received signal power. High directional antennas may do that. Alexander Maltsev, Intel

6. Typical EM Field Structure for 2 – 5 GHz [1] • The EM field has complex quasi random structure consisting of multiple running and standing waves overcoming obstacles due to strong diffraction and reflection effects. • The field structure is ideal for statistical description and statistical channel modeling [2] Alexander Maltsev, Intel

7. 60-GHz Propagation Measurement Results (Office) [3] • The 60 GHz received signal is mainly a combination of the direct path and first-order reflected signals, which may be predicted by the image-based ray-tracing procedure Alexander Maltsev, Intel

8. 60-GHz Propagation Measurement Results (Aircraft) [4] • TX antenna – open waveguide (5 dBi), RX antenna – omni-directional in azimuth (2 dBi) • The signal consists of the LOS component and multiple reflected signals bounced from the walls of the aircraft (the estimated reflection coefficient is about -8 … -10 dB) Alexander Maltsev, Intel

9. 60-GHz Propagation Measurement Results (Home and Office) [5] Residential Office • The good matching between measured cluster positions and simulated cluster positions using ray tracing was obtained Measured Simulated Alexander Maltsev, Intel

10. IEEE 802.15.3c Channel Modeling • The channel modeling was done by the IEEE 802.15.3c group in Q1’2006 – Q1’2007. • Different application scenarios for WPAN systems were identified and the goal was set to develop the channel models for all considered scenarios. • The statistical channel models developed by the IEEE 802.15.3c group included the following features: • LOS and NLOS components; • Based on the generalized Saleh-Valenzuela channel model with clustering in both the time and angular domain; • Clusters arrival time and intra-cluster rays arrival time are two Poisson processes; • The distributions of the clusters and intra-cluster rays amplitudes are log-normal; • The distribution of the clusters angle-of-arrival (AoA) is uniform. AoAs of different clusters are independent. The distribution of rays AoA inside the cluster is Gaussian; Alexander Maltsev, Intel

11. IEEE 802.15.3c Library Channel Model • The Intel team was working in the IEEE 802.15.3c group on the development of the library channel model [6 – 12] • The library channel model was developed based on the high quality experimental data obtained by the German company IMST. • The measurements were performed in the library room with tables, chairs and metal bookshelves with books • 3 types of RX antennas (horn, wideband dipole array antenna, biconical) • Fixed TX lens antenna position at the suspended ceiling, RX measurements range ~2-5m • Time resolution is 1/960MHz ≈ 1ns • Two types of virtual uniform antenna arrays for direction of arrival analysis • 501x1 uniform linear array with 1mm antenna spacing (LOS scenarios) • 301x51 uniform planar antenna array with 1mm antenna spacing (edge scenario) Alexander Maltsev, Intel

12. LOS NLOS Edge Transmitting antenna Receiving antennas Library Channel Model – Measurements Scenarios Plan Alexander Maltsev, Intel

13. Example of 60 GHz Channel for Library Measurements(Time-Angular Energy Distribution Function) • The channel has a “specular” structure with direct ray and several strongly localized reflected rays (clusters) in time/angular dimensions for delays < 50 ns and angles < 700 Alexander Maltsev, Intel

14. 40 35 30 KLOS 25 Relative Power, [dB] 20 KMP 15 10 5 0 0 10 20 30 40 50 60 70 80 Delay, [ns] Generalized Saleh-Valenzuela Channel Model • L – Number of clusters • Kl – Number of MPC in the lthcluster • KLOS – LOS K factor • KMP – Cluster K factor • αk,l – MPC complex amplitude • Tl – Time of arrival of lthcluster • τk,l – Relative time of arrival for kth MPC within lthcluster • θk,l – Relative direction of arrival for kth MPC within lthcluster • Θl – Direction of arrival of lthcluster • δ(·) – Delta function Alexander Maltsev, Intel

15. Extracted Channel Model Parameters • Inter-cluster Power Delay Profile parameters • Exponential PDP:K factor KLOS= 8 [dB], cluster decay Γ = 12 [ns] • Flat-Exponential PDP: K factor KLOS= 8 [dB], cluster decay Γ = 12 [ns], Δ = 11 [dB], τ = 30 [ns] • Inter-cluster DoA – Uniform distribution • Intra-cluster DoA – Gaussian (Angles Spread (AS) σAS = 10 [0]) • Inter-cluster ToA / Intra-cluster ToA – Poisson (Λ = 0.25 [ns-1] / λ = 4 [ns-1]) • Cluster / Ray amplitude – Log-normal (σ1 = 5 [dB] / σ2 = 6 [dB]) • Intra-cluster K factor KMP= -13 [dB] • Intra-cluster ray decay γ = 7 [ns] Note: Two approximations of cluster PDP are proposed: Exponential PDP - for TX omni-directional antenna mounted at the suspended ceiling. Flat-exponential PDP - for TX beam-shaped antenna mounted at the suspended ceiling. Alexander Maltsev, Intel

16. IEEE 802.15.3c Channel Models Summary • Some work done in the IEEE 802.15.3c channel modeling may be reused for IEEE VHT WLAN channel models. • The reuse is complicated by the fact that no raw channel measurement results (except for the IMST data used in the library model) are available now. • The mandatory extensions of the IEEE 802.15.3c channel models should be the support of the both the TX and RX steerable directional antennas and polarization characteristics [12]. • The library channel model is the most suitable and complete (from IEEE 802.15.3c channel models) for the WLAN environment – the measurements are done in a large room with access point sitting near the ceiling and transmitting in quasi-omni mode and the receiver using “virtual” antenna array. The model and the measurements data may be reused for the IEEE VHT channel modeling. Alexander Maltsev, Intel

17. Requirements for VHT Channel Model • The following basic requirements are proposed for IEEE VHT channel model development: • Provide accurate space-time characteristics of the 60 GHz propagation channel for main usage models. • Support the beamforming with the steerable directional antennas at both TX and RX sides. • No limitation on the antenna type (i.e. antenna arrays, sector-switching antennas, non-steerable antennas) and antenna parameters. • Include the polarization characteristics of the antennas and signals. (Additional experimental investigations should be done). Alexander Maltsev, Intel

18. Channel Modeling Approaches for IEEE VHT • The following approaches may be considered for IEEE channel modeling: • Statistical channel model – randomly generation of the channel realizations with the required statistical characteristics based on several input parameters (examples – IEEE 802.11n channel model [2], IEEE 802.15.3c library channel model [10]). • Use of experimental golden sets – to collect a number of experimental golden sets for the typical scenarios and use them for system simulation and performance evaluation. • Combination of ray-tracing and statistical channel model– use the ray-tracing for the cluster parameters identification and generate intra-cluster rays distribution statistically. • More than one approach may be used by the VHT group Alexander Maltsev, Intel

19. Conclusions • The propagation characteristics of signals for 60 GHz frequency band are different from the 2 – 5 GHz band. The mmWave signal propagation has a quasi-optical nature. The main propagation mechanisms for 60 GHz are direct path (LOS) and reflections (NLOS). • The IEEE 802.15.3c group has developed the channel models for 60 GHz WPAN scenarios. Some of those models may be reused for the VHT with an appropriate modification. • The additional measurement campaigns have to be carried out for the WLAN scenarios to obtain the required statistical parameters of the 60 GHz channels. Alexander Maltsev, Intel

20. References • IEEE Standard 802.11a • V. Erceg et al. “TGn Channel Models”, IEEE 802.11 document 11-03/0940r4. • H. Xu, V. Kukshya, and T. S. Rappaport, “Spatial and Temporal Characteristics of 60 GHz Indoor Channels,” IEEE J. Sel. Areas Commun., vol. 20, no. 3, pp. 620–630, Apr. 2002. • M. Peter, W. Keusgen, A. Kortke, M. Schirrmacher, “Measurement and Analysis of the 60 GHz In-Vehicular Broadband Radio Channel”, Proc. of IEEE Vehicular Technology Conference, 2007 (VTC-2007), pp. 834 - 838 • B. Neekzad, K. Sayrafian-Pour, J. Perez, J. S. Baras, “Comparison of Ray Tracing Simulations and Millimeter Wave Channel Sounding Measurements”, Proc. of the 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'07) • IEEE 802.15-06-0022-01-003c, A. Sadri, A. Maltsev, A. Davydov “IMST data analysis ,Preliminary results”, January 2006. • IEEE 802. 15-06-0141-01-003c, A. Sadri, A. Maltsev, A. Davydov “IMST time-angular characteristics analysis”, March 2006. • IEEE P802.15-06-0201-00-003c, A. Davydov, A. Maltsev, A. Sadri “IMST Data Processing Methodology”, April 5, 2006. • IEEE 802.15-06-0230-00-003c, A. Davydov, A. Maltsev, A. Sadri “Resolving the Ambiguity in IMST Measurements”, May 2006. • IEEE 802.15-06-0302-02-003c, A. Davydov, A. Maltsev, A. Sadri “Saleh-Valenzuela Channel Model Parameters for Library Environment”, July 2006. • IEEE 15-07-0715-00-003c, A. Maltsev, R. Maslennikov, A. Khoryaev “Comments on CM3.1 golden set”, May 2007. • IEEE 15-07-0774-00-003c , A. Maltsev, A. Davydov “Generalization of TG3c channel models”, June 14, 2007. Alexander Maltsev, Intel