Post on 30-Dec-2015
description
OFDM and Multicarrier Communications – an overview, issues and knowledge gaps
POZNAN UNIVERSITY OF TECHNOLOGYPOZNAN UNIVERSITY OF TECHNOLOGY
Hanna BoguckaHanna Bogucka
WPR1 Kick-off meeting, Paris,WPR1 Kick-off meeting, Paris, June June 2525, 2004, 2004
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Outline
OFDM and multicarrier modulation concept
Applications
OFDM advantages
OFDM drawbacks
Interesting directions of research
Knowledge gaps
Discussion
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OFDM and multicarrier modulation concept
Orthogonal Frequency Division Multiplexing (OFDM), is a form of multicarrier transmission, in which a high-rate data stream is transmitted in a parallel manner over a number of low-rate orthogonal subcarriers
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OFDM spectrum, cyclic prefix and postfix
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Applications
High-speed digital subscriber lines (HDSL, ADSL, VDSL)
Digital broadcasting systems (DAB, DVB-T)
Wireless LANs (HIPERLAN/2, IEEE 802.11a, IEEE 802.16, MMAC)
Fixed broadband wireless access (IEEE 802.11g)
Considered for wireless ATM network (Magic-WAND),
Considered for future broadband radio area networks and multimedia communications (European and American projects).
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OFDM Advantages Robustness against multipath fading and intersymbol interference
and narrow-band interference (MC-CDMA)
High spectral efficiency, no side bandwidth required for system operation,
Simple frequency domain equalization
Single-frequency network configuration possibility
Inherent flexibility, especially with the application of
– adaptive bit and power loading,
– adaptive modulation and coding,
– adaptive subcarrier allocation,
– space-time processing, MIMO, smart antennas,
– multicarrier CDMA, MC-DS-CDMA, and so on
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OFDM Drawbacks High Peak-to-Average Power Ratio (PAPR) of the transmitted
signal resulting in:
clipping noise (limited quantization levels, rounding and truncation, during IFFT and FFT computation)
nonlinear distortions of power amplifiers
BER performance degradation,
energy spilling into adjacent channels,
intermodulation effects on the subcarriers, warping of the signal constellation in each subchannel.
Sensitivity to frequency offset and phase noise, which are sources of intercarrier interference,
Whitening of impulse noise
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Interesting directions of research
PAPR reduction
Clipping and windowing, recursive clipping
Reference signal subtraction
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PAPR reduction, cont. Coding
Golay complementary codes
generalized Reed-Muller codes
Parallel combinatory OFDM signaling
Multiple signal representation
Pre-distortion
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Interesting directions of research, cont.
Conflating adaptive modulation and coding for OFDM
Adaptive bit and power loading
Adaptive resource management (subcarrier and spreading code allocation)
Throughput-oriented, power-oriented and delay-oriented adaptation strategies
Frequency-domain processing for single-carrier modulation
The use of IOTA (Isotropic Orthogonal Transfer Algorithm) function
Fast OFDM (FOFDM) with intercarrier frequency spacing equal to half of the inverse of the signalling interval
Filtered multitone FDMA
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Impulse noise rejection for OFDM
– Non-linear clipping
– Median filtering and spectrum analysis
– Application of guard frequencies
– Application of pilots and DSP algorithms
– MSE monitoring and R-S coding Adaptation of decision areas for data symbols
Rejection of OFDM block in case of a number of non-reliable blocks exceeding a certain threshold
Rejection of R-S symbols containing bits transmitted on non-reliable subcarriers
Interesting directions of research, cont.
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MC-CDMA and MC-DS-CDMA
Frequency hoping OFDMA
MC-CDMA for the down-link in 4G cellular system
MC-CDMA for the up-link with parallel interference cancellation or joint detection
MC-DS-CDMA for the up-link (power efficiency of a terminal)
Adaptive MC-CDMA with capacity optimization
Impulse noise rejection
OFDM MIMO, space - time diversity, e.g. cyclic delay diversity
Smart algorithms for phase-noise and frequency-offset compensation, channel (turbo) estimation and equalization, pre-equalization, joint detection for multiuser OFDM, and so on.
Interesting directions of research, cont.
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Knowledge gaps PAPR reduction methods without or minimized transmission
overhead For OFDM
For MC-CDMA
Fast link adaptation techniques for mobile users Fast channel prediction
Minimization of feedback information delay
Simple optimisation algorithm
Cross-layer optimization (set up the basis in the physical layer)
Multi-criteria optimization for high capacity energy-aware networks and systems
„Safe” impulse noise rejection
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