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Huawei Technologies Duesseldorf GmbH
Enhancing
the degrees of freedom
in the waveform design for 5G
Malte Schellmann, Zhao Zhao, Xitao Gong,
Martin Schubert, Egon Schulz
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Outline
Pulse shaping in OFDM –
A new degree of freedom in OFDM waveform design
Design of pulse shaped OFDM (P-OFDM) systems
Selected 5G use cases with benefits from pulse shaping
MIMO applications
Conclusions
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Multi-carrier waveform design
General description of multi-carrier systems :
System design parameters = degrees of freedom
- symbol period, - subcarrier spacing, - transmit pulse shape
CP-OFDM is special case of pulse shaped multi-carrier, defining
transmit pulse shape g and receive pulse shape g as:
Page 3
RX window: “Remove CP”
TX window: “Add CP”
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Pulse shaped OFDM (P-OFDM)
Orthogonal multi-carrier system (OFDM) with pulse shaping as additional degree of freedom
P-OFDM covers CP-OFDM, ZP-OFDM and W-OFDM as special cases
Page 4
FEC
encoder Interleaver QAM
mapping
RE/layer
mapping
OFDM
modulator
IDFT
M
…
P/S
Add CP, windowing, sum and overlap … Subband-wise filtering
Pulse
Shaping
One example of pulse shaping:
windowing operation
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Pulse shape design parameter
Pulse shape
length
Pulse shapes Localization Waveform Additional low
pass filter
K=1 Rect. Time CP-OFDM F- OFDM
K=1 Rect. Time ZP-OFDM UF-OFDM
1< K <1.5 various Time + Frequency W-OFDM
Arbitrary K various flexible General P-OFDM
Length of pulse shape K ≥ 1 (rational)
Yields overlapping symbols
Orthogonal design ensures interference-free
reconstruction time
Page 5
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Pulse shape design criteria
Time frequency localization (TFL)
(Bi)-orthogonality
Length of pulse shapes – the design parameter
For FDD and some cases, the pulse shape length may be long
For TDD, short pulse shapes is favored
Optimization range
Low to mid SNR matched filter design for maximizing SNR (orthogonal)
High SNR pulse shape design for minimizing interference (bi-orthogonal)
yielding high robustness against
distortions in the operational T-F range
Page 6
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Asynchronous access enabled by P-OFDM
P-OFDM signal expands over K symbol intervals of length T
Symbol length in OFDM spans size of one FFT window + CP overhead
FFT window
Symbol duration 4T
CP
OFDM P-OFDM K =4
P-OFDM with properly designed pulse shape is much more robust to timing offsets
With P-OFDM, only symbol-level sync. necessary no timing advance (TA) required
interference vs. timing offset
Δt offset
Page 7
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
MMC uplink without TA
3-5 dB link performance gain vs. LTE-OFDM
LTE- OFDM has high synchronization requirement in UL
P-OFDM can enable TA-free access, facilitating
• massive machine with non-orthogonal access
• short access time and reduced signaling overhead
*
* due to propagation delay in macro-cell with 1.7 km radius
Page 8
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
MMC uplink without TA
Link Spectral Efficiency P-OFDM vs. OFDM w. extended CP
channel delay spread ~4.7μs
Unknown timing offset [0 ~ 13μs]
CP length > max timing offset + max delay spread
Optional: CP- OFDM can extend CP length for
covering timing sync. errors
Extended CP length to cover
max. timing offset + channel delay spread
1) spectral efficiency loss
2) transmit power loss (mismatching)
~150% gain vs. LTE-OFDM (normal CP)
~40% gain vs. LTE-OFDM (extended CP)
Operational range
of 16QAM
P-OFDM
LTE-OFDM (extended CP)
LTE-OFDM (normal CP)
Page 9
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
High Velocity scenarios
Higher robustness against Doppler yields better channel estimation & link performance
Overall 1-3 dB link performance gain
LTE-OFDM is vulnerable for high mobility scenarios
Pulse shaping can balance power localization in T-F
Page 10
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
MIMO performance
Simulation setup: synchronous transmission, no CFO, static conditions, ETU channel, LTE setting.
4x4 MIMO – MLD Alamouti 2x1
MIMO is a natural extension for P-OFDM design, thanks to its full OFDM compatibility:
All algorithms developed for OFDM can be reused requiring the same complexity.
Link efficiency results confirm identical performance for MIMO based on OFDM and P-OFDM
Page 11
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Spectrum shaping and subband partitioning
P-OFDM exhibits low out-of-band leakage
P-OFDM enables in-band coexistence of different numerologies
CP-OFDM Pulse shaped K=1.05
Waveform Guard-carrier
overhead
CP-OFDM ~10%
Pulse shaped
OFDM
~2%
Overhead for 50 dBc OOB protection
Page 12
Huawei Technologies Duesseldorf GmbH
35pt
32pt
) :18pt
Conclusions
Pulse shaping constitutes a new degree of freedom for the waveform design
General multi-carrier framework introduced as pulse shaped OFDM (P-OFDM)
Fully compatible with OFDM, enabling the reuse of all algorithms developed for LTE
In several key scenarios for 5G, P-OFDM can provide clear performance gains
In-band coexistence of different numerologies
MMC massive access
V2V/ V2X
Zero pad
Pulse
Shaping
IDFT
M
…
…
P/S …
DFT N
…
Pulse shaping can be applied also
to single carrier modulation
Page 13
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