5 research outputs found
A practical system for improved efficiency in frequency division multiplexed wireless networks
Spectral efficiency is a key design issue for all wireless communication systems. Orthogonal frequency division multiplexing (OFDM) is a very well-known technique for efficient data transmission over many carriers overlapped in frequency. Recently, several studies have appeared that describe spectrally efficient variations of multi-carrier systems where the condition of orthogonality is dropped. Proposed techniques suffer from two weaknesses: firstly, the complexity of generating the signal is increased. Secondly, the signal detection is computationally demanding. Known methods suffer either unusably high complexity or high error rates because of the inter-carrier interference. This study addresses both problems by proposing new transmitter and receiver architectures whose design is based on using the simplification that a rational spectrally efficient frequency division multiplexing (SEFDM) system can be treated as a set of overlapped and interleaving OFDM systems. The efficacy of the proposed designs is shown through detailed simulation of systems with different signal types and carrier dimensions. The decoder is heuristic but in practice produces very good results that are close to the theoretical best performance in a variety of settings. The system is able to produce efficiency gains of up to 20% with negligible impact on the required signal-to-noise ratio
Spectrally efficient FDM communication signals and transceivers: design, mathematical modelling and system optimization
This thesis addresses theoretical, mathematical modelling and design issues of Spectrally Efficient
FDM (SEFDM) systems. SEFDM systems propose bandwidth savings when compared to
Orthogonal FDM (OFDM) systems by multiplexing multiple non-orthogonal overlapping carriers.
Nevertheless, the deliberate collapse of orthogonality poses significant challenges on the
SEFDM system in terms of performance and complexity, both issues are addressed in this work.
This thesis first investigates the mathematical properties of the SEFDM system and reveals the
links between the system conditioning and its main parameters through closed form formulas
derived for the Intercarrier Interference (ICI) and the system generating matrices. A rigorous
and efficient mathematical framework, to represent non-orthogonal signals using Inverse Discrete
Fourier Transform (IDFT) blocks, is proposed. This is subsequently used to design simple
SEFDM transmitters and to realize a new Matched Filter (MF) based demodulator using the
Discrete Fourier Transforms (DFT), thereby substantially simplifying the transmitter and demodulator
design and localizing complexity at detection stage with no premium at performance.
Operation is confirmed through the derivation and numerical verification of optimal detectors
in the form of Maximum Likelihood (ML) and Sphere Decoder (SD). Moreover, two new linear
detectors that address the ill conditioning of the system are proposed: the first based on
the Truncated Singular Value Decomposition (TSVD) and the second accounts for selected ICI
terms and termed Selective Equalization (SelE). Numerical investigations show that both detectors
substantially outperform existing linear detection techniques. Furthermore, the use of the
Fixed Complexity Sphere Decoder (FSD) is proposed to further improve performance and avoid
the variable complexity of the SD. Ultimately, a newly designed combined FSD-TSVD detector
is proposed and shown to provide near optimal error performance for bandwidth savings of 20%
with reduced and fixed complexity.
The thesis also addresses some practical considerations of the SEFDM systems. In particular,
mathematical and numerical investigations have shown that the SEFDM signal is prone to high
Peak to Average Power Ratio (PAPR) that can lead to significant performance degradations.
Investigations of PAPR control lead to the proposal of a new technique, termed SLiding Window
(SLW), utilizing the SEFDM signal structure which shows superior efficacy in PAPR control
over conventional techniques with lower complexity. The thesis also addresses the performance
of the SEFDM system in multipath fading channels confirming favourable performance and
practicability of implementation. In particular, a new Partial Channel Estimator (PCE) that
provides better estimation accuracy is proposed. Furthermore, several low complexity linear
and iterative joint channel equalizers and symbol detectors are investigated in fading channels
conditions with the FSD-TSVD joint equalization and detection with PCE obtained channel
estimate facilitating near optimum error performance, close to that of OFDM for bandwidth
savings of 25%. Finally, investigations of the precoding of the SEFDM signal demonstrate a
potential for complexity reduction and performance improvement.
Overall, this thesis provides the theoretical basis from which practical designs are derived to
pave the way to the first practical realization of SEFDM systems
A pragmatic bit and power allocation algorithm for NOFDM signalling
In this paper, a novel pragmatic bit and power allocation algorithm for Non Orthogonal Frequency Division Multiplexing (NOFDM) systems is presented. It is based on the well-known Campello approach and takes into account the lack of orthogonality between adjacent waveforms. Simulation results in a typical NOFDM wireless applicative scenario show the effectiveness of the proposed algorithms. Index Terms- Resource Allocation, Bit and Power Loading, Non-Orthogonal Frequency Division Multiplexing. © 2009 IEEE
A Pragmatic Bit and Power Allocation Algorithm for NOFDM Signalling
In this paper, a novel pragmatic bit and power allocation algorithm for Non Orthogonal Frequency Division Multiplexing (NOFDM) systems is presented. It is based on the well-known Campello approach and takes into account the lack of orthogonality between adjacent waveforms. Simulation results in a typical NOFDM wireless applicative scenario show the effectiveness of the proposed algorithms