28-Jan-2014 Fanny Mlinarsky octoScope, Inc. Testing MIMO Radios Day 2: All You Ever Want to Know About Channel Emulation 28-Jan-2014 Fanny Mlinarsky octoScope, Inc.

Wireless Channel Frequency and time variable wireless channel Multipath creates a sum of multiple versions of the TX signal at the RX Mobility of reflectors and wireless devices causes Doppler-based fading MIMO is used to optimize transmission in the presence of multipath and Doppler fading Channel Quality MIMO=multiple input multiple output

Multipath and Flat Fading In a wireless channel the signal propagating from TX to RX experiences Flat fading (e.g. through walls) Multipath/Doppler fading +10 dB 0 dB Multipath fading component Signal impairments in a wireless channels include flat fading (aka attenuation), multipath and Doppler fading. Multipath is caused by multiple versions of the transmitted signal formed by reflections from stationary and mobile objects. When multiple versions of the signal add out of phase, a null is formed. A typical multipath component of a received waveform is shown in the lower right plot and an example of a 15 dB flat fading component is shown below it. Of course, typically receive signal exhibits flat, multipath and doppler fading – all superimposed. When reflectors are mobile the nulls in the multipath components shift around in time and this effect is known as doppler fading. A common way of dealing with the nulls resulting from multipath is by receiving the signal using a variety of multiple antenna techniques. These techniques range from simple antenna diversity to MIMO. More on this later. Flat fading increases as a function of frequency and this relationship is given by the formula on the left. A number of times through this presentation we mentioned that lower frequency spectrum exhibits lower losses and hence provides for higher operating range. So here are some numerical examples showing that a 915 MHz signal exhibits 9 dB less loss than a 2.4 GHz signal and 16 dB less loss than a 5.8 GHz signal. As a rule of thumb, given typical impairments in a wireless channel ~6-9 dB of link budget increase typically doubles the outdoor range ~9-12 dB of link budget increase typically doubles the indoor range (more multipath indoors, eating up the link budget) -15 dB flat fading component Time

Wireless Channel Multipath cluster model Composite angular spread Per path angular spread Composite angular spread Line of sight Multipath and Doppler fading in the channel

Clusters and Power Delay Profile Single cluster of energy bouncing back and forth and dying out vs. time. Cluster 3 Power Delay Profile (PDP) of 802.11n model D 346 feet

SCME Urban Micro Model SCME UMi PDP [12] 990 feet Source of plot: [16] SCME = spatial channel models extended UMi = Urban Micro PDP = power delay profile

SCME Urban Macro Model SCME UMa PDP [12] 0.9 mile Source of plot: [16] SCME = spatial channel models extended UMa = Urban Macro PDP = power delay profile

Fader for Validating Radio DSP A variety of channel conditions and complex MIMO algorithms for adapting to these conditions make a fader necessary for developing and testing radio DSP in the Baseband layer Fader Controlled programmable channel conditions Multipath Doppler Noise DUT1 TX DUT2 RX Fader = Channel Emulator

RF or digital IQ coupling to DUTs Fader Block Diagram Multiple RF modules can connect for scalability Digital IQ (CPRI/OBSAI) RF Front End downconverts and digitizes signal from the DUT antenna ports Traditional faders connect to DUTs conductively – without antennas Antennas and antenna arrays have traditionally been emulated for conductively coupled faders; defined as part of the channel models Channel Emulator DSP RF Front End RF Front End RF or digital IQ coupling to DUTs Fader = Channel Emulator

SISO Fading Channel Logic Tapped Delay Line (TDL) models a fading channel, H h1 Complex time-variable coefficients, h Input TX x h2 Delay 2 Output x + RX Delay 3 … hK Delay K x where K is the number of taps in the TDL

4x4 Uni-directional Fader Block Diagram Digitized Fader logic Quad Quad RF I/O RF I/O IQ Quad Atten IQ 4 RF RF 4 Quad circulator Quad circulator 16 Fading Channels, H Quad Atten 4 RF return path

4x4 Bi-directional Fader Block Diagram Digitized Fader Logic Quad Quad RF I/O Quad Atten RF I/O IQ IQ 4 RF RF 4 Quad circulator Quad circulator Fader Logic Quad Quad Quad Atten

4x4 (NxM) MIMO Fader Logic H21 H31 H11 H41 + M1 H22 H32 H12 H42 + M2 H23 H33 H13 H43 + M3 N1 H24 H34 H14 H44 N2 + M4 N3 N4

Complex tap coefficients [h1,1 1, h1,1 2, … , h1,1 T] H1,1 [h2,1 1, h2,1 2, … , h2,1 T] + H2,1 M1 [h1,2 1, h1,2 2, … , h1,2 T] H1,2 [h2,2 1, h2,2 2, … , h2,2 T] + M2 H2,2 2x4 Fader Logic [h1,3 1, h1,3 2, … , h1,3 T] H1,3 [h2,3 1, h2,3 2, … , h2,3 T] + M3 H2,3 [h1,4 1, h1,4 2, … , h1,4 T] H1,4 [h2,4 1, h2,4 2, … , h2,4 T] + M4 N1 H2,4 N2

Complex Tap Coefficient Generator Doppler spectrum 1,1k..K Spatial correlation matrix Polarization matrix Tap coefficient factors 1,1 h1,1k..K Doppler spectrum 1,2k..K Tap coefficient factors 1,2 h1,2k..K … … Doppler spectrum n,mk..K Tap coefficient factors n,m hn,mk..K … … Doppler spectrum N,Mk..K Tap coefficient factors N,M hN,Mk..K where k is the tap number, K is the maximum number of taps and h is the time-variable coefficient

Doppler Spectrum Generator Doppler filter AWGN Generator Doppler filter Classical Specified for most 3GPP channel models; Classical = Jakes; Classical 3 dB and 6 dB Bell Specified for 802.11n channel models; variations of this filter include Bell-spike, which is used by 802.11 model F to model a 40 km/hour spike in the spectrum Static Models LOS on first tap; used in custom channel modeling Flat Can also be implemented using RF attenuators via an identity matrix (i.e. connecting inputs to outputs through attenuators) Rounded Variations of this filter include Rounded 12 dB Gaussian Constant phase Butterworth Pure Doppler Rician LOS component only, no Reilly

Notes on Doppler Filter Implementation AWGN sources are connected to Doppler filters. Doppler filters provide the desired spectral shape of the fading. For 802.11n models, the filter is Bell-shaped for models A through F and Bell-Spike for model F. The Bell spectrum models Doppler fading due to walking-speed motion in the environment at an average speed of 1.2 km/hr. The spike in the Bell-Spike spectrum adds the effect of a vehicle moving at an average speed of 40 km/hr. For 3GPP models, the Doppler spectrum is Classical.

Doppler Spectrum – 802.11n Model F Example of Doppler spectrum plots for IEEE 802.11n model F Environment velocity is 1.2 km/hour and is modeled on all taps for all models Tap 3 for model F includes automotive velocity spike at 40 km/hour Source: [24] Simulated Theoretical Frequency, Hz The Doppler spread is 3 Hz at 2.4 and 6 Hz at 5.25 GHz for environment speed of 1.2 km/hour

Doppler Spectrum – 802.11n Model F, Tap 3 length 1024 periodograms with 50% overlap Source: [24] FFT-based power estimation using entire long realization Frequency, Hz speed of light

Tap Coefficient Factors hn,mt x + + x Interpolation to TDL clock rate     Fluorescent light   PDP weighting LOS component NLOS component Tap coefficient factors n,m Source: [24] where t is the tap number, h is the time-variable complex coefficient, K is Rician K-factor

Doppler Spectrum – 802.11n Model E, Tap 3 Source: [24] Fluorescent light effects at 120, 360, and 600 Hz – harmonics of the power line frequency of 60 Hz Frequency, Hz

Cumulative Distribution Function (CDF) Source: [24] Tap 1 with LOS component IEEE 802.11n, Model F, CDF for 18 taps

Power Delay Profile (PDP) – Model F Source: [24] Tap 18 Tap #, 1-18

Notes on Tap Coefficient Factors  

802.11n/ac Correlation Matrix The spatial correlation matrix is a function of the angular spread of each cluster, angle of arrival (AoA) and angle of departure (AoD). 802.11n models assume that RX and TX antenna systems are uniform linear arrays with equally spaced antenna elements. Spatial correlation is implemented using the Kronecker product of the transmit and receive correlation matrices, Rtx and Rrx, respectively. These matrices are comprised of correlation coefficient terms, ρ, that depend on the PAS, AoA, AoD, tap powers and distance D between antenna elements. Faders can compute the real and imaginary parts, RXX(D) and RXY(D), respectively, for each ρ. This allows spatial correlation based on the complex field (i.e., using ρ =RXX(D)+jRXY(D)) or real power (i.e., using ρ =RXX2(D) +RXY2(D)). AoA = angle of arrival AoD = angle of departure

802.11ac Correlation and Polarization MU-MIMO modeled for AoD and AoA Polarization matrix added since 802.11ac devices are expected to have cross-polarized antennas AoA = angle of arrival AoD = angle of departure MU-MIMO + multi user MIMO

802.11n Channel Models - Summary Distance to 1st wall (avg) # taps Delay spread (rms) Max delay # clusters A* test model   1 0 ns B Residential 5 m 9 15 ns 80 ns 2 C small office 14 30 ns 200 ns D typical office 10 m 18 50 ns 390 ns 3 E large office 20 m 100 ns 730 ns 4 F large space (indoor or outdoor) 30 m 150 ns 1050 ns 6 * Model A is a flat fading model; no delay spread and no multipath The LOS component is not present if the distance between the transmitter and the receiver is greater than the distance to 1st wall.

Channel Sampling Rate Expansion Factor 802.11ac Channel Models 802.11ac channel models are an extension of 802.11n models [2] System Bandwidth W Channel Sampling Rate Expansion Factor Channel Tap Spacing W ≤ 40 MHz 1 10 ns 40 MHz < W ≤ 80 MHz 2 5 ns 80 MHz < W ≤ 160 MHz 4 2.5 ns W > 160 MHz 8 1.25 ns

Fader Requirements Summary 802.11ac LTE (36-521 Annex B) 80 MHz 160 MHz RF bandwidth (no channel aggregation) 40 MHz 20 MHz EVM (avg down-fading is -40 dB) -28 dBm (64QAM) -32 dBm (256QAM) -22 dBm (8% 64QAM) TDL Taps 18 35 69 9 Delay resolution 10 ns 5 ns 2.5 ns TDL = tap delay line EVM = error vector magnitude QAM = quadrature amplitude modulation

3GPP and 802.11 Channel Models Parameter Model Name References and Notes 3GPP Models LTE: EPA 5Hz; EVA 5Hz; EVA 70Hz; ETU 70Hz; ETU 300Hz; High speed train; MBSFN 3GPP TS 36.521-1 V10.0.0 (2011-12) 3GPP TS 36.101 V10.5.0 (2011-12) GSM: RAx; HTx; TUx; EQx; TIx 3GPP TS 45.005 V10.3.0 (2011-11) Annex C 3G: PA3; PB3; VA30; VA120; High speed train; Birth-Death propagation; Moving propagation; MBSFN 3GPP TS 25.101 V11.0.0 (2011-12) 3GPP TS 25.104 V11.0.0 (2011-12) SCME: UMa; UMi 3GPP TR 25.996 IEEE 802.11n/ac Models A, B, C, D, E, F IEEE 802.11-03/940r4 IEEE 11-09-0569

Summary Chanel emulators (aka faders) have been used to test the baseband layer of modern radios SISO channel emulators have only one fading channel, H MIMO channel emulators have N*M fading channels where N is the number of inputs and M is the number of outputs in each direction of the signal path Faders model PDP, Doppler and MIMO antenna arrays Standards based channel models have been developed by 3GPP and IEEE SISO = single input single output MIMO = multiple input multiple output PDP = power delay profile 3GPP = 3rd Generation Partnership Project IEEE = Institute of Electrical and Electronics Engineers

Next Session Day 3: MIMO Over the Air (OTA) Test Methods Wednesday, January 29th, 2014 2 pm EST Visit www.octoscope.com for more material and test solution information

References IEEE, 802.11-03/940r4: TGn Channel Models; May 10, 2004 IEEE, 11-09-0569 , “TGac Channel Model Addendum Supporting Material”, May 2009 IEEE, 11-09-0334-08-00ad-channel-models-for-60-ghz-wlan-systems Schumacher et al, "Description of a MATLAB® implementation of the Indoor MIMO WLAN channel model proposed by the IEEE 802.11 TGn Channel Model Special Committee", May 2004 Schumacher et al, "From antenna spacings to theoretical capacities - guidelines for simulating MIMO systems" Schumacher reference software for implementing and verifying 802.11n models - http://www.info.fundp.ac.be/~lsc/Research/IEEE_80211_HTSG_CMSC/distribution_terms.html TS 25.101, Annex B, “User Equipment (UE) radio transmission and reception (FDD)”, file: 25101-b00-AnnexB.doc TS 36.101, Annex B, “Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception”, file: 36101-a50-AnnexB.doc TS 36.521-1, Annex B, “Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) conformance specification Radio transmission and reception Part 1: Conformance Testing”, file: 36521-1-a00_s09-sAnnexB.doc TS 45.005, Annex C, “GSM/EDGE Radio Access Network; Radio transmission and reception”, file: 45005-a30-AnnexC.doc TS 51.010-1, “Mobile Station (MS) conformance specification; Part 1: Conformance specification”, file: 51010-1-980_s00-s11.doc 3GPP TR 25.996, "3rd Generation Partnership Project; technical specification group radio access networks; Spatial channel model for MIMO simulations“ IST-WINNER II Deliverable 1.1.2 v.1.2, “WINNER II Channel Models”, IST-WINNER2, Tech. Rep., 2008 (http://projects.celtic-initiative.org/winner+/deliverables.html) 3GPP TS 34.114: “User Equipment (UE) / Mobile Station (MS) Over The Air (OTA) Antenna Performance Conformance Testing” CTIA, “Test Plan for Mobile Station Over the Air Performance - Method of Measurement for Radiated RF Power and Receiver Performance”, Revision 3.1, January 2011 3GPP TR 37.977 V1.2.0 (2013-11), “Verification of radiated multi-antenna reception performance of User Equipment (UE)”, Release 12, November 2013 “MIMO OTA in a Small Anechoic Chamber”, by Dr. Nicholas Kirsch and Fanny Mlinarsky, NSF EARS event 10/2013, http://www.octoscope.com/English/Resources/Presentations.html CTIA, “DRAFT CTIA Test Plan for 2x2 Downlink MIMO OTA Performance”, Revision 0.1, 3 March, 2013

References (continued) Azimuth ACE, Spirent VR5, Anite Propsim faders are the most popular faders on the market today. octoScope’s multipath emulator, MPE, is a simpler non-programmable fader that comes built into a controlled environment test bed with 2 octoBox anechoic chambers. IEEE P802.11ac/D6.0, “Draft STANDARD for Information Technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications Amendment 4: Enhancements for Very High Throughput for Operation in Bands below 6 GHz”, July 2013 “802.11 Data Rate Computation” spreadsheet, 12/2013, http://www.octoscope.com/cgi-bin/start.cgi/Array_Pages/Entrance_RequestArticles.html?SourceCode=Whitepapers “octoBox Isolation Test Report”, 12/2013, http://www.octoscope.com/English/Collaterals/Documents/octoBox_Isolation_Measurements.pdf IEEE P802.11.2/D1.0, “Draft Recommended Practice for the Evaluation of 802.11 Wireless Performance”, April 2007 “Software Based Channel Emulator”, by Dr. Samuel MacMullan and Fanny Mlinarsky, http://www.octoscope.com/English/Collaterals/Whitepapers/octoScope_WP_MIMOChannelEmulator_20101202.pdf