Communication Subsystems for Emerging Wireless Technologies

The paper describes a multi-disciplinary design of modern communication systems. The design starts with the analysis of a system in order to define requirements on its individual components. The design exploits proper models of communication channels to adapt the systems to expected transmission conditions. Input filtering of signals both in the frequency domain and in the spatial domain is ensured by a properly designed antenna. Further signal processing (amplification and further filtering) is done by electronics circuits. Finally, signal processing techniques are applied to yield information about current properties of frequency spectrum and to distribute the transmission over free subcarrier channels

A novel unipolar transmission scheme for visible light communication

This paper proposes a novel unipolar transceiver for visible light communication (VLC) by using orthogonal waveforms. The main advantage of our proposed scheme over most of the existing unipolar schemes in the literature is that the polarity of the real-valued orthogonal frequency division multiplexing (OFDM) sample determines the pulse shape of the continuous-time signal and thus, the unipolar conversion is performed directly in the analog instead of the digital domain. Therefore, our proposed scheme does not require any direct current (DC) biasing or clipping as it is the case with existing schemes in the literature. The bit error rate (BER) performance of our proposed scheme is analytically derived and its accuracy is verified by using Matlab simulations. Simulation results also substantiate the potential performance gains of our proposed scheme against the state-of-the-art OFDM-based systems in VLC; it indicates that the absence of DC shift and clipping in our scheme supports more reliable communication and outperforms the asymmetrically clipped optical-OFDM (ACO-OFDM), DC optical-OFDM (DCO-OFDM) and unipolar-OFDM (U-OFDM) schemes. For instance, our scheme outperforms ACO-OFDM by at least 3 dB (in terms of signal to noise ratio) at a target BER of 10 −4 , when considering the same spectral efficiency for both schemes

Physical Layer Techniques for OFDM-Based Cognitive Radios

Cognitive radio has recently been proposed as a promising approach for efficient utilization of radio spectrum. However, there are several challenges to be addressed across all layers of a cognitive radio system design, from application to hardware implementation. From the physical layer point-of-view, two key challenges are spectrum sensing and an appropriate signaling scheme for data transmission. The modulation techniques used in cognitive radio not only should be efficient and flexible but also must not cause (harmful) interference to the primary (licensed) users. Among all the proposed signaling schemes for cognitive radio, orthogonal frequency division multiplexing (OFDM) has emerged as a promising one due to its robustness against multipath fading, high spectral efficiency, and capacity for dynamic spectrum use. However, OFDM suffers from high out-of-band radiation which is due to high sidelobes of subcarriers. In this thesis, we consider spectral shaping in OFDM-based cognitive radio systems with focus on reducing interference to primary users created by by out-of-band radiation of secondary users' OFDM signal. In the first part of this research, we first study the trade-o between time-based and frequency-based methods proposed for sidelobe suppression in OFDM. To this end, two recently proposed techniques, active interference cancellation (AIC) and adaptive symbol transition (AST), are considered and a new joint time-frequency scheme is developed for both single-antenna and multi-antenna systems. Furthermore, knowledge of wireless channel is used in the setting of the proposed joint scheme to better minimize interference to the primary user. This scheme enables us to evaluate the trade-o between the degrees of freedom provided by each of the two aforementioned methods. In the second part of this research, a novel low-complexity technique for reducing out-of-band radiation power of OFDM subcarriers for both single-antenna and multi-antenna systems is proposed. In the new technique, referred to as a phase adjustment technique, each OFDM symbol is rotated in the complex plane by an optimal phase such that the interference to primary users is minimized. It is shown that the phase adjustment technique neither reduces the system throughput, nor does increase the bit-error-rate of the system. Moreover, the performance of the technique in interference reduction is evaluated analytically in some special cases and is verified using numerical simulations. Due to high sensitivity of OFDM systems to time and frequency synchronization errors, performance of spectral shaping techniques in OFDM is significantly affected by timing jitter in practical systems. In the last part of this research, we investigate the impact of timing jitter on sidelobe suppression techniques. Considering AIC as the base method of sidelobe suppression, we first propose a mathematical model for OFDM spectrum in presence of timing jitter and evaluate the performance degradation to AIC due to timing jitter. Then, a precautionary scheme based on a minimax approach is proposed to make the technique robust against random timing jitter.4 month

AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing

The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spectrum reuse through the deployment of more access points per square mile has the potential to successfully meet the increasing demand for more bandwidth. In theory, the best approach to density increase is via distributed multiuser MIMO, where several access points are connected to a central server and operate as a large distributed multi-antenna access point, ensuring that all transmitted signal power serves the purpose of data transmission, rather than creating "interference." In practice, while enterprise networks offer a natural setup in which distributed MIMO might be possible, there are serious implementation difficulties, the primary one being the need to eliminate phase and timing offsets between the jointly coordinated access points. In this paper we propose AirSync, a novel scheme which provides not only time but also phase synchronization, thus enabling distributed MIMO with full spatial multiplexing gains. AirSync locks the phase of all access points using a common reference broadcasted over the air in conjunction with a Kalman filter which closely tracks the phase drift. We have implemented AirSync as a digital circuit in the FPGA of the WARP radio platform. Our experimental testbed, comprised of two access points and two clients, shows that AirSync is able to achieve phase synchronization within a few degrees, and allows the system to nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC and higher layer aspects of a practical deployment. To the best of our knowledge, AirSync offers the first ever realization of the full multiuser MIMO gain, namely the ability to increase the number of wireless clients linearly with the number of jointly coordinated access points, without reducing the per client rate.Comment: Submitted to Transactions on Networkin

Permutation Coding with Injections for Modified PAM System

Arriving at a good combination of coding andmodulation schemes that can achieve good error correctionconstitutes a challenge in digital communication systems. In thiswork, we explore the combination of permutation coding (PC)and pulse amplitude modulation (PAM) for mitigating channelerrors in the presence of background noise and jitter. Since PAMis characterised with bi-polar constellations, Euclidean distance isa good choice for predicting the performance of such coded modulationsetup. In order to address certain challenges facing PCs,we therefore introduce injections in the coding system, togetherwith a modified form of PAM system. This modification entailsconstraining the PAM constellations to the size of the codeword’ssymbol. The results obtained demonstrate the strength of themodified coded PAM system over the conventional PC codedPAM system

Permutation Coding with Injections for Modified PAM System

Arriving at a good combination of coding andmodulation schemes that can achieve good error correctionconstitutes a challenge in digital communication systems. In thiswork, we explore the combination of permutation coding (PC)and pulse amplitude modulation (PAM) for mitigating channelerrors in the presence of background noise and jitter. Since PAMis characterised with bi-polar constellations, Euclidean distance isa good choice for predicting the performance of such coded modulationsetup. In order to address certain challenges facing PCs,we therefore introduce injections in the coding system, togetherwith a modified form of PAM system. This modification entailsconstraining the PAM constellations to the size of the codeword’ssymbol. The results obtained demonstrate the strength of themodified coded PAM system over the conventional PC codedPAM system

PAPR and BER Analysis in FBMC/OQAM System with Pulse Shaping Filters and Various PAPR Minimization Methods

Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation(FBMC/OQAM) system design based on frequency sampling prototype filter takes into account the low frequency utilization of Orthogonal Frequency Division Multiplexing(OFDM)  caused by adding Cyclic Prefix(CP). The CP decreases spectral efficiency and increases Peak to Average Power Ratio(PAPR). FBMC is an OFDM enhancement. In this paper to reduce the PAPR, we explained companding methods. We have proposed an FBMC that makes use of prototype pulse shaping filters which can be adjusted to meet system requirements in order to defeat these limitations. Due to its significant effect on the performance of FBMC-OQAM, choosing the right filter is crucial. Different prototype filters are used to investigate the performance of the FBMC-OQAM in this paper. Using the validated system, it was found that frequency utilization is more and good out-band suppression as well as an excellent application value in 5G technology. By using ?-law companding method, FBMC/OQAM provides better performance. It produces low PAPR, low out of band(OoB), high BER performance, less computational complexity and high spectral efficiency as compared to other methods