GFDM_NI RF Roundtable 2012

Report
Vodafone Chair Mobile Communications Systems, Prof. Dr.-Ing. G. Fettweis
Case Study: Implementation Aspects of a
GFDM-based Prototype for 5G Cellular
Communications
Ivan Simões Gaspar
 With the Vodafone Chair (Prof. Fettweis) since
February 2012
 Studies: Electrical Engineering (M.Sc.) at the
National Institute of Telecommunications in
Brazil – INATEL
 Research area: robust non-orthogonal multicarrier modulation schemes for future cellular
systems
NI RF Roundtable 2012
December 10-11, 2012, Bristol, UK
Motivations for 5G
 M2M dominating subscribers
• diverse requirements (high and
lows) :
 data rate, latency, mobility, quality,
security
 asynchronous and non-orthogonal
modulation
 Opportunistic use of spectrum
• time and frequency agility
• accurate sensing
• no interferer (filtering)
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Challenges
RRM
flexible fine-grained
sharing of fragmented
spectrum
CoMP
High rate, low latency,
interactive video, apps,
increased signaling
f
vast # M2M devices
low rate / complexity
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t
asynchronous access
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Wireless Access:
• flexible
• scalable
• content aware
• robust
• reliable
3
Our approach

Question the strict synchronism, orthogonality and high out
of band radiation of OFDM based systems with the
introduction of new non-orthogonal filtered waveforms that
carry the data on the physical layer.

Deal with crosstalk and interference with a transceiver
structure termed GFDM (Generalized Frequency Division
Multiplexing).

Explore the tradeoff of an increased computational
complexity at the Base Stations with a more flexible
construction of millions of machine type communications
(MTC) devices

Proof of concept prototype with a highly scalable
implementation on NI’s PXI platform
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GFDM Transmitter Model
 generalization of OFDM
• 1 up to M symbols per subcarrier
• Pulse shaping with circular convolution (block structure - burst)
Up sampling
Filtering
Up conversion
Mapping
M = number of symbols per subcarrier
K = number of active subcarriers
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Matrix Model, x=Ad

The A matrix contains all the possible impulse responses of the system
Circular impulse response
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First Demo – ‘Player Approach’
Demo Setup
control
computer
spectrum
analyzer
FlexRIO
Ethernet
RT-OS
FPGA
board
Transmit Signals
Transceiver
board
coax
System Parameters
10
power spectral density in dB
DAC
OFDM
GFDM
parameter
value
Channel bandwidth
20 MHz
Max. number of subcarriers
2048
PRB
30
-30
active subcarriers
360
-40
occupied bandwidth
9.8 MHz
-50
carrier frequency
2,4 GHz
-60
modulation
QPSK
filter, roll-off
RRC, a = 0.5
block size
14
0
-10
-20
-70
-4
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-2
0
2
frequency in MHz
4
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First Demo – ‘Player Approach’
 Few weeks after
receiving the HW we
get a real time signal
coming out of the box
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A Low Complexity Model
Time approach:

up sampling, circular convolution and up conversion
 j 2
n 

N
    d k [ m ] [ n  m N ]  # gg T x [ n ] ·e

m 

k
x[n ] 

k
Frequency approach:

DFT, spectrum repetition, windowing and position shift, IDFT


1
x [ n ]  F   F  d k [ m ] [ n  m N
 m
k

N tim es repetition of F
k
 j 2
n 


N
] ·F  g T x [ n ]  # F  e






d k [m ] [n  m ]

 m

copy from m em ory

low com plex
k 

f 

N 

shift in m em ory
im plem entation!
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A Low Complexity Model
zero stuff
repetition
circ. convolution
windowing
Subcarrier processing
time vs. frequency domain
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Subcarrier superposition
in frequency domain
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Low Complexity Model (Matrix)
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Low Complexity Model
GFDM Matrix Model
GFDM non sparse spectrum
GFDM Low Complex
OFDM reference
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LabView Style TX Model
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Second Demo – Offline TX
LabVIEW interactive transmitter (offline)
 LabView based
implementation
in less than 2
months after
basic training
 Very friendly
graphical
interface
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Out of band Radiation
GFDM (red curve) vs. OFDM (blue curve)
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Third Demo – Online TX
LabVIEW interactive transmitter (online)
 PXI based
implementation
in less than 6
months
 Very friendly RT
and FPGA
enviroments
integration
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Third Demo – Online TX
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Current studies (RX)
Math model
Block Diagram
ICI
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Channel
distortions
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Future directions
UHF white spaces
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Conclusions
 Pulse shaped subcarriers can be achieved in GFDM at
reasonable computational cost
 Out of band radiation in GFDM can outperform OFDM by
several orders of magnitude
 Outlook
• A hardware implementation of the GFDM transceiver and its
multi-user case application
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Vodafone Chair Mobile Communications Systems, Prof. Dr.-Ing. G. Fettweis
Thank you.

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