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
CoMP
High rate, low latency, interactive video, apps, increased signaling
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vast # M2M devices low rate / complexity
RRM flexible fine-grained sharing of fragmented spectrum f t asynchronous access
Wireless Access:
• flexible
• scalable
• content aware
• robust
• reliable
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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
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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
Ethernet
RT-OS
FlexRIO
FPGA board
DAC
Transceiver board coax
Transmit Signals
10
0
-10
-20
-30
-40
-50
-60
-70
-4 -2 0 frequency in MHz
2
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OFDM
GFDM
4
System Parameters parameter
Channel bandwidth
Max. number of subcarriers
PRB active subcarriers occupied bandwidth carrier frequency modulation filter, roll-off block size
RF roundtable 2012 value
20 MHz
2048
30
360
9.8 MHz
2,4 GHz
QPSK
RRC, a = 0.5
14 spectrum analyzer
7

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 x n
  k m


 d k

[ n
 mN ]

# g
Tx n

· e

Frequency approach:
 DFT, spectrum repetition, windowing and position shift, IDFT j 2
 k
N n



F

1



 k
F


 d m k
[ m ]

[ n
 mN ]

· F
 g
Tx
[ n ]

# F

 e
 j 2
 k
N n





N times repetition of F


 m k
 n
 m ]

 copy from memory low complex implementation!


 f
 k
N

 shift in memory
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A Low Complexity Model zero stuff repetition circ. convolution windowing
Subcarrier processing time vs. frequency domain
Subcarrier superposition in frequency domain
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Low Complexity Model (Matrix)
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Low Complexity Model
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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
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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)
ICI
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Math model
Block Diagram
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.