ofdm and multicarrier communications – an overview, issues and knowledge gaps
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OFDM and Multicarrier Communications – an overview, issues and knowledge gaps. POZNAN UNIVERSITY OF TECHNOLOGY Hanna Bogucka WPR1 Kick-off meeting, Paris, June 25 , 2004. Outline. OFDM and multicarrier modulation concept Applications OFDM advantages OFDM drawbacks - PowerPoint PPT PresentationTRANSCRIPT
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 Transceiver
Encoder Interleaver QAM mapper
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Decoder De-interleaver
QAM demapper Equalizer S/P CP
removal
A/DRF RXTiming and frequency
synchronization
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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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PAPR reduction - Multiple signal representation
Selected Mapping
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Partial Transmit Sequences
PAPR reduction - Multiple signal representation, cont.
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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 ?