1. 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.

2. 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

3. 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

4. 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

5. 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 n model D
346 feet

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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 n channel models; variations of this filter include Bell-spike, which is used by 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

17. Notes on Doppler Filter Implementation
AWGN sources are connected to Doppler filters.
Doppler filters provide the desired spectral shape of the fading.
For n 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.

18. Doppler Spectrum – 802.11n Model F
Example of Doppler spectrum plots for IEEE n 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

19. 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

20. 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

21. 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

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

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

24. Notes on Tap Coefficient Factors

25. 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) n 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

26. 802.11ac Correlation and Polarization
MU-MIMO modeled for AoD and AoA
Polarization matrix added since ac devices are expected to have cross-polarized antennas
AoA = angle of arrival
AoD = angle of departure
MU-MIMO + multi user MIMO

27. 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.

28. Channel Sampling Rate Expansion Factor
802.11ac Channel Models
802.11ac channel models are an extension of n 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

29. Fader Requirements Summary
802.11ac
LTE
( 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

30. 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 V ( )
3GPP TS V ( )
GSM: RAx; HTx; TUx; EQx; TIx
3GPP TS V ( ) Annex C
3G: PA3; PB3; VA30; VA120; High speed train; Birth-Death propagation; Moving propagation; MBSFN
3GPP TS V ( )
3GPP TS V ( )
SCME: UMa; UMi
3GPP TR
IEEE n/ac Models
A, B, C, D, E, F
IEEE /940r4
IEEE

31. 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

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

33. References IEEE, 802.11-03/940r4: TGn Channel Models; May 10, 2004
IEEE, , “TGac Channel Model Addendum Supporting Material”, May 2009
IEEE, ad-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 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 n models -
TS , Annex B, “User Equipment (UE) radio transmission and reception (FDD)”, file: b00-AnnexB.doc
TS , Annex B, “Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception”, file: a50-AnnexB.doc
TS , Annex B, “Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) conformance specification Radio transmission and reception Part 1: Conformance Testing”, file: a00_s09-sAnnexB.doc
TS , Annex C, “GSM/EDGE Radio Access Network; Radio transmission and reception”, file: a30-AnnexC.doc
TS , “Mobile Station (MS) conformance specification; Part 1: Conformance specification”, file: _s00-s11.doc
3GPP TR , "3rd Generation Partnership Project; technical specification group radio access networks; Spatial channel model for MIMO simulations“
IST-WINNER II Deliverable v.1.2, “WINNER II Channel Models”, IST-WINNER2, Tech. Rep., 2008 (
3GPP TS : “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 V1.2.0 ( ), “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,
CTIA, “DRAFT CTIA Test Plan for 2x2 Downlink MIMO OTA Performance”, Revision 0.1, 3 March, 2013

34. 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
“ Data Rate Computation” spreadsheet, 12/2013,
“octoBox Isolation Test Report”, 12/2013,
IEEE P /D1.0, “Draft Recommended Practice for the Evaluation of Wireless Performance”, April 2007
“Software Based Channel Emulator”, by Dr. Samuel MacMullan and Fanny Mlinarsky,