Massive MIMO testbed: Validation - mammoet- · PDF fileWhy do we need a testbed? 2 ØTheoretical results show that massive MIMO has very promising features for future wireless generation,

Massive MIMO testbed: Validation STEFFEN MALKOWSKY, LUND UNIVERSITY, SWEDEN

Why do we need a testbed?

2

Ø Theoretical results show that massive MIMO has very promising features for future wireless generation, however they cannot answer all questions:

1) How does it perform under real-life conditions? 2) How can we model massive MIMO channels?

3) Implementation challenges/issues? 4) Required reciprocity calibration accuracy?

5) Is pilot contamination a problem?

3

LUMAMI TESTBED

LuMaMi Testbed: Parameters

4

Ø 100 BS antennas Ø Serving up to 12 UEs Ø 50 SDRs + 6 SDRs as UEs

Ø 4 Central Processing units performing MIMO processing

Ø 3.7 GHz carrier frequency

Ø LTE-like parameters Ø Uncoded transmission

LuMaMi Testbed: Processing

5

O FDM TX/RXAntenna Com bi ner/

BW splitter

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

BW Combiner/Antenna Splitter

SubbandChannelEstimate

Subband MIMOPrecoder

WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….



WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….



WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

DetectorNI USRP-2943R SDR

PXIe-8135 Controller

PXIe-7976R FlexRIO


Subband MIMO

Precoder

WMMSE

OFDM TX/RXAntenna Combiner/

BW splitter

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX


Group of 8 USRP RIOs

8x

….

8x

….

BW Combining

(bytes)

Video Display

QAM Demapping

QAM Mapping

BW Splitting (bytes)

Video Streaming

System Configuration

Channel Visualization

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….

8x

….

Up to (4) MIMO Processor FPGAs

Up to (8) Groups of 8 USRP RIOs (16 antennas per group)

8x

….

8x

….

8x

….

8x

….

8x

….

Ø  Per-antenna (OFDM) processing performed on USRP SDR Ø  Data of up to 8 USRPs combined and send to centralized

processing


6


BW splitter

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX




WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….



WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….



WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO



PXIe-7976R FlexRIO


Subband MIMO

Precoder

WMMSE


BW splitter

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX



8x

….

8x

….

BW Combining

(bytes)

Video Display

QAM Demapping

QAM Mapping


Video Streaming



SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….

8x

….



8x

….

8x

….

8x

….

8x

….

8x

….

Ø  Centralized processing distributed over 4 units, each working on ¼ bandwidth

Ø  3 detector types implemented: MRC/MRT, ZF and regularized ZF


7


BW splitter

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX

O FDM TX/RX




WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….



WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….



WMM SE

QAM Demapping

QAM Mapping

SubbandGenerate

MMSE Matrix

SubbandMIMO



PXIe-7976R FlexRIO


Subband MIMO

Precoder

WMMSE


BW splitter

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX

OFDM TX/RX



8x

….

8x

….

BW Combining

(bytes)

Video Display

QAM Demapping

QAM Mapping


Video Streaming



SubbandGenerate

MMSE Matrix

SubbandMIMO

Detector

8x

….

8x

….



8x

….

8x

….

8x

….

8x

….

8x

….

Ø  A standard windows computer hosts the complete system Ø  Configures system Ø  Visualizes parameters, e.g. channel impulse response and

acts as source and sink for video streams

8

FOUR TESTS

Indoor Measurements

Ø Serving 12 users in groups of 4 on UL and DL in a lecture hall

Ø Record BERs while sweeping amplifier gains (0-30 dB)

Ø UL: Sweep the gain of the UEs transmitter Ø DL: Sweep the gain of the BS transmitters

Ø 18 Million bits transmitted per step Ø Compare performance of MRC/MRT vs. ZF

9

Setup

10

Closely spaced UEs

BS Base station placed at the front of the lecture hall

Users are distributed in groups of 4 with close spacing inside each group

Amplifier Gain [dB]0 10 20 30

BER

10-4

10-3

10-2

10-1

100

UE0UE1UE2UE3UE4UE5UE6UE7UE8UE9UE10UE11

T T

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

C

C

C

C

C

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

CT

C

CT

C

CT

C

C

TT

C

C

C

C

C

C

TC

C

C

C

4

5

6

7

8

9

10

11

0

1

2

3BS

Uplink BERs (QPSK)

11

TX saturates

Ø ZF detector Ø Close by users (UE8-11)

show best BERs

Ø Far users (UE0-UE3) show worst performance

Ø UE0/1 interference limited Ø Bad performance at full

power close to saturation

Gain Offset [dB]0 10 20 30

BER

10-4

10-3

10-2

10-1

100


T T

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

C

C

C

C

C

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

CT

C

CT

C

CT

C

C

TT

C

C

C

C

C

C

TC

C

C

C

4

5

6

7

8

9

10

11

0

1

2

3BS

Uplink BERs (16-QAM)

12

TX saturates


shows best BERs

Ø Far users (UE0-UE3) show worst performance

Ø UE0/1 interference limited Ø Bad performance at full

power close to saturation


BER

10-4

10-3

10-2

10-1

100


T T

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

C

C

C

C

C

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

CT

C

CT

C

CT

C

C

TT

C

C

C

C

C

C

TC

C

C

C

4

5

6

7

8

9

10

11

0

1

2

3BS

Downlink BERs (QPSK)

13

Ø ZF precoder Ø Close by users (UE8-11)

shows best BERs

Ø Other users (UE0-7) show similar performance

Ø High performance difference between UE8-11 and the UE0-7

Gain Offset [dB]0 10 20 30

BER

10-4

10-3

10-2

10-1

100


T T

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

C

C

C

C

C

T

C

C

C

C

C

C

T

C

C

C

C

C

C

C

CT

C

CT

C

CT

C

C

TT

C

C

C

C

C

C

TC

C

C

C

4

5

6

7

8

9

10

11

0

1

2

3BS

Downlink BERs (16-QAM)

14

BERs floor


show best BERs

Ø Almost all users show a significant BER floor

Ø Performance limited by reciprocity calibration accuracy and/or interference

Drop in BER for closest users


BER

10-4

10-3

10-2

10-1

100

MRC QPSKMRC 16-QAMMRC 64-QAMZF QPSKZF 16-QAMZF 64-QAM


BER

10-4

10-3

10-2

10-1

100

MRC QPSKMRC 16-QAMMRC 64-QAMZF QPSKZF 16-QAMZF 64-QAM

ZF vs. MRC/MRT

15

Ø MRC/MRT showing significant error floors Ø Usable in practical systems?

Ø ZF far superior in real-life channels

Uplink Downlink

Floor for ZF with 64-QAM

Collaborative Measurements in Bristol

Ø First joint measurement campaign with Lund University and University of Bristol in May 2016

Ø Based on Bristol MaMi system with 128 antennas

Ø How many users can be served simultaneously? Ø What spectral efficiency can be achieved?

16

Setup

17

Base station Closely spaced users

Overall setup from base station view

Users BS

Results

Ø 22 users served simultaneously using 256-QAM Ø Uncoded transmission Ø Equating a spectral efficiency of 145 b/s/Hz

18

World record spectral efficiency

First Outdoor Trial I

19

Ø First outdoor test to see whether reciprocity calibration and over-the-air synchronization works outdoor

Ø Focus on achieving good UL and DL constellations with up to 8 users and an additional moving user

Base station with 100 antennas at the roof of the department building, with LOS to 8 UEs

UE

UE

UE BS Both out-door to out-

door and out-door to in-door transmission

UE UE

UE

UE

UE

BS

UE

First Outdoor Trial III

20


UE

UE



UE UE

UE

UL constellations on BS ZF MRC

DL constellations with ZF

Close window half

First Outdoor Trial III

21


UE

UE



UE UE

UE

One user in car Front Panel picture

Good looking

constellation

Joint Mobility Trials in Lund

22

Ø Together with a team from University of Bristol we performed the first mobility test using the LuMaMi testbed

Ø Goal was to analyze how well massive MIMO works in dynamic environments

Ø Tests were performed with up to 12 users, some mounted on cars (up to 40 km/h) and some mounted on cycle carts (walking speed)

Ø Uplink channel data, BERs and LabVIEW front panels were recorded

Setup / Equipment

23

Base station deployed on rooftop

Users mounted on cycle cart

Users mounted on cars

Different tested scenarios I

24

CAR

Parking lot

CAR

Cart Cart Cart Cart

Ø Gradually adding users while observing performance

Different tested scenarios II

25

CAR

Parking lot

CAR

Cart Cart Cart

Ø Scenario with 6 users as pedestrians and 4 users on cars

Ø Video including live BERs and constellations

Ø Playback recorded channel data

10 user mobility test video

26

https://www.youtube.com/watch?v=wPPMrr4rHmo

PLEASE CHECK OUT FOLLOWING LINK

Conclusions

27

Ø The LuMaMi testbed is fully functional and working for UL and DL transmission

Ø In a joint campaign Lund University and University of Bristol achieved a new world record for spectral efficiency

Ø Indoor measurements showed that even with 100 antennas at the BS, MRC/MRT show significantly worse performance than ZF

Ø Mobility measurements showed that massive MIMO works for moving users with relatively good BER performance on UL and DL (more analysis to be performed)

Frame Structure

28

ULP

ilot

ULD

ata

ULD

ata

Switc

h G

uard

DLD

ata

DLD

ata

Switc

h G

uard

Subframe#0

Subframe#1

Subframe#2

Subframe#3

Subframe#4

Subframe#9

One radio frame Tf = 10ms

One subframe Tsf = 1ms

One slot Tslot = 0.5ms

Documents

Massive MIMO testbed: Validation - mammoet- · PDF fileWhy do we need a testbed? 2 ØTheoretical results show that massive MIMO has very promising features for future wireless generation,