Efficient and Robust Signal Detection Algorithms for the Communication Applications

Signal detection and estimation has been prevalent in signal processing and communications for many years. The relevant studies deal with the processing of information-bearing signals for the purpose of information extraction. Nevertheless, new robust and efficient signal detection and estimation techniques are still in demand since there emerge more and more practical applications which rely on them. In this dissertation work, we proposed several novel signal detection schemes for wireless communications applications, such as source localization algorithm, spectrum sensing method, and normality test. The associated theories and practice in robustness, computational complexity, and overall system performance evaluation are also provided

Adaptive Bit Allocation With Reduced Feedback for Wireless Multicarrier Transceivers

With the increasing demand in the wireless mobile applications came a growing need to transmit information quickly and accurately, while consuming more and more bandwidth. To address this need, communication engineers started employing multicarrier modulation in their designs, which is suitable for high data rate transmission. Multicarrier modulation reduces the system's susceptibility to the frequency-selective fading channel, by transforming it into a collection of approximately flat subchannels. As a result, this makes it easier to compensate for the distortion introduced by the channel. This thesis concentrates on techniques for saving bandwidth usage when employing adaptive multicarrier modulation, where subcarrier parameters (bit and energy allocations) are modulated based on the channel state information feedback obtained from previous burst. Although bit and energy allocations can substantially increase error robustness and throughput of the system, the feedback information required at both ends of the transceiver can be large. The objective of this work is to compare different feedback compression techniques that could reduce the amount of feedback information required to perform adaptive bit and energy allocation in multicarrier transceivers. This thesis employs an approach for reducing the number of feedback transmissions by exploiting the time-correlation properties of a wireless channel and placing a threshold check on bit error rate (BER) values. Using quantization and source coding techniques, such as Huffman coding, Run length encoding and LZWalgorithms, the amount of feedback information has been compressed. These calculations have been done for different quantization levels to understand the relationship between quantization levels and system performance. These techniques have been applied to both OFDM and MIMO-OFDM systems

Time-frequency warped waveforms for well-contained massive machine type communications

This paper proposes a novel time-frequency warped waveform for short symbols, massive machine-type communication (mMTC), and internet of things (IoT) applications. The waveform is composed of asymmetric raised cosine (RC) pulses to increase the signal containment in time and frequency domains. The waveform has low power tails in the time domain, hence better performance in the presence of delay spread and time offsets. The time-axis warping unitary transform is applied to control the waveform occupancy in time-frequency space and to compensate for the usage of high roll-off factor pulses at the symbol edges. The paper explains a step-by-step analysis for determining the roll-off factors profile and the warping functions. Gains are presented over the conventional Zero-tail Discrete Fourier Transform-spread-Orthogonal Frequency Division Multiplexing (ZT-DFT-s-OFDM), and Cyclic prefix (CP) DFT-s-OFDM schemes in the simulations section.United States Department of Energy (DOE) ; Office of Advanced Scientific Computing Research ; National Science Foundation (NSF

Towards low-cost gigabit wireless systems at 60 GHz

The world-wide availability of the huge amount of license-free spectral space in the 60 GHz band provides wide room for gigabit-per-second (Gb/s) wireless applications. A commercial (read: low-cost) 60-GHz transceiver will, however, provide limited system performance due to the stringent link budget and the substantial RF imperfections. The work presented in this thesis is intended to support the design of low-cost 60-GHz transceivers for Gb/s transmission over short distances (a few meters). Typical applications are the transfer of high-definition streaming video and high-speed download. The presented work comprises research into the characteristics of typical 60-GHz channels, the evaluation of the transmission quality as well as the development of suitable baseband algorithms. This can be summarized as follows. In the first part, the characteristics of the wave propagation at 60 GHz are charted out by means of channel measurements and ray-tracing simulations for both narrow-beam and omni-directional configurations. Both line-of-sight (LOS) and non-line-of-sight (NLOS) are considered. This study reveals that antennas that produce a narrow beam can be used to boost the received power by tens of dBs when compared with omnidirectional configurations. Meanwhile, the time-domain dispersion of the channel is reduced to the order of nanoseconds, which facilitates Gb/s data transmission over 60-GHz channels considerably. Besides the execution of measurements and simulations, the influence of antenna radiation patterns is analyzed theoretically. It is indicated to what extent the signal-to-noise ratio, Rician-K factor and channel dispersion are improved by application of narrow-beam antennas and to what extent these parameters will be influenced by beam pointing errors. From both experimental and analytical work it can be concluded that the problem of the stringent link-budget can be solved effectively by application of beam-steering techniques. The second part treats wideband transmission methods and relevant baseband algorithms. The considered schemes include orthogonal frequency division multiplexing (OFDM), multi-carrier code division multiple access (MC-CDMA) and single carrier with frequency-domain equalization (SC-FDE), which are promising candidates for Gb/s wireless transmission. In particular, the optimal linear equalization in the frei quency domain and associated implementation issues such as synchronization and channel estimation are examined. Bit error rate (BER) expressions are derived to evaluate the transmission performance. Besides the linear equalization techniques, a low-complexity inter-symbol interference cancellation technique is proposed to achieve much better performance of code-spreading systems such as MC-CDMA and SC-FDE. Both theoretical analysis and simulations demonstrate that the proposed scheme offers great advantages as regards both complexity and performance. This makes it particularly suitable for 60-GHz applications in multipath environments. The third part treats the influence of quantization and RF imperfections on the considered transmission methods in the context of 60-GHz radios. First, expressions for the BER are derived and the influence of nonlinear distortions caused by the digital-to-analog converters, analog-to-digital converters and power amplifiers on the BER performance is examined. Next, the BER performance under the influence of phase noise and IQ imbalance is evaluated for the case that digital compensation techniques are applied in the receiver as well as for the case that such techniques are not applied. Finally, a baseline design of a low-cost Gb/s 60-GHz transceiver is presented. It is shown that, by application of beam-steering in combination with SC-FDE without advanced channel coding, a data rate in the order of 2 Gb/s can be achieved over a distance of 10 meters in a typical NLOS indoor scenario

Time-Frequency Warped Waveforms for Well-Contained Massive Machine Type Communications

This paper proposes a novel time-frequency warped waveform for short symbols, massive machine-type communication (mMTC), and internet of things (IoT) applications. The waveform is composed of asymmetric raised cosine (RC) pulses to increase the signal containment in time and frequency domains. The waveform has low power tails in the time domain, hence better performance in the presence of delay spread and time offsets. The time-axis warping unitary transform is applied to control the waveform occupancy in time-frequency space and to compensate for the usage of high roll-off factor pulses at the symbol edges. The paper explains a step-by-step analysis for determining the roll-off factors profile and the warping functions. Gains are presented over the conventional Zero-tail Discrete Fourier Transform-spread-Orthogonal Frequency Division Multiplexing (ZT-DFT-s-OFDM), and Cyclic prefix (CP) DFT-s-OFDM schemes in the simulations section.Comment: This paper has been accepted by IEEE JSAC special issue on 3GPP Technologies: 5G-Advanced and Beyond. Copyright may be transferred without notice, after which this version may no longer be accessibl

Advanced optical fibre communication via nonlinear Fourier transform

Optical fibre communication using the Nonlinear Fourier transform (NFT) is one of the potential solutions to tackle the so-called capacity crunch problem in long-haul optical fibre networks. The NFT transforms the nonlinear propagation of temporal signal, governed by the nonlinear Schr¨odinger equation (NLSE), into simple linear evolutions of continuous and discrete spectra in the so-called nonlinear spectral domain. These spectra and the corresponding nonlinear spectral domain, defined by the NFT, are the generalized counterparts of the linear spectrum and frequency domain defined by the ordinary Fourier transform. Using the NFT, the optical fibre channel is effectively linearised, and the basic idea is to utilize degrees of freedom in the nonlinear spectral domain for data transmission. However, many aspects of this concept require rigorous investigation due to complexity and infancy of the approach. In this thesis, the aim is to provide a comprehensive investigation of data transmission over mainly the continues spectrum (CS) and partly over of the discrete spectrum (DS) of nonlinear optical fibres. First, an optical fibre communication system is defined, in which solely the CS carries the information. A noise model in the nonlinear spectral domain is derived for such a system by asymptotic analysis as well as extensive simulations for different scenarios of practical interest. It is demonstrated that the noise added to the signal in CS is severely signal-dependent such that the effective signalling space is limited. The variance normalizing transform (VNT) is used to mathematically verify the limits of signalling spaces and also estimate the channel capacity. The numerical results predict a remarkable capacity for signalling only on the CS (e.g., 6 bits/symbol for a 2000-km link), yet it is demonstrated that the capacity saturates at high power. Next, the broadening effect of chromatic dispersion is analysed, and it is confirmed that some system parameters, such as symbol rate in the nonlinear spectral domain, can be optimized so that the required temporal guard interval between the subsequently transmitted data packets is minimized, and thus the effective data rate is significantly enhanced. Furthermore, three modified signalling techniques are proposed and analysed based on the particular statistics of the noise added to the CS. All proposed methods display improved performance in terms of error rate and reach distance. For instance, using one of the proposed techniques and optimized parameters, a 7100-km distance can be reached by signalling on the CS at a rate of 9.6 Gbps. Furthermore, the impact of polarization mode dispersion (PMD) is examined for the first time, as an inevitable impairment in long-haul optical fibre links. By semi-analytical and numerical investigation, it is demonstrated that the PMD affects the CS by causing signal-dependent phase shift and noise-like errors. It is also verified that the noise is still the dominant cause of performance degradation, yet the effect of PMD should not be neglected in the analysis of NFT-based systems. Finally, the capacity of soliton communication with amplitude modulation (part of the degrees of freedom of DS) is also estimated using VNT. For the first time, the practical constraints, such as the restricted signalling space due to limited bandwidth, are included in this capacity analysis. Furthermore, the achievable data rates are estimated by considering an appropriately defined guard time between soliton pulses. Moreover, the possibility of transmitting data on DS accompanied by an independent CS signalling is also validated, which confirms the potentials of the NFT approach for combating the capacity crunch