RF impairments

Direct-conversion architectures suffer from the mismatch between the In-phase (I) and the Quadrature-phase (Q) branches, commonly called I/Q imbalance. Even low I/Q imbalances imply poor performance of Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, we propose a new algorithm that uses both training and data symbols in a decision-directed fashion to jointly estimate the channel and compensate for high receiver I/Q imbalance. Simulation results show that our method can compensate for high I/Q imbalance values and also estimate a frequency selective channel.

Cognitive radio (CR) technology has the potential to detect and share the unutilized spectrum by enabling dynamic spectrum access. To detect the primary users' (PUs) activity, energy detection (ED) is widely exploited due to its applicability when it comes to sensing a large range of PU signals, low computation complexity, and implementation costs. As orthogonal frequency-division multiplexing (OFDM) transmission has been proven to have a high resistance to interference, the ED of OFDM signals has become an important local spectrum-sensing (SS) concept in cognitive radio networks (CRNs). In combination with multiple-input multiple-output (MIMO) transmissions, MIMO-OFDM-based transmissions have started to become a widely accepted air interface, which ensures a significant improvement in spectral efficiency. Taking into account the future massive implementation of MIMO-OFDM systems in the fifth and sixth generation of mobile networks, this work introduces a mathematical formulation of expressions that enable the analysis of ED performance based on the square-law combining (SLC) method in MIMO-OFDM systems. The analysis of the ED performance was done through simulations performed using the developed algorithms that enable the performance analysis of the ED process based on the SLC in the MIMO-OFDM systems having a different number of transmit (Tx) and receive (Rx) communication branches. The impact of the distinct factors including the PU Tx power, the false alarm probability, the number of Tx and Rx MIMO branches, the number of samples in the ED process, and the different modulation techniques on the ED performance in environments with different levels of signal-to-noise ratios are presented. A comprehensive analysis of the obtained results indicated how the appropriate selection of the analyzed factors can be used to enhance the ED performance of MIMO-OFDM-based CRNs.

In this thesis, performance of cooperative relaying with multi-antenna system in Rayleigh/Nakagami-m fading channels has been investigated. The relay is assumed to operate in adaptive decode and forward mode and perform threshold based decoding. Installation of multiple receiving antennas on infrastructure based fixed relay is feasible thereby increasing the probability of relay participation and hence diversity order may be increased for systems which contain such relays. Such systems in different configurations have been analyzed in various path-loss conditions, severity of fading, relay placement at different locations and antennas installed on it. It has been found that for some locations of relay placement, performance of system depends only marginally on the number of antennas installed on relay and combining schemes at relay and destination. System performance can be improved significantly by appropriately positioning the relay. For such positioning, system performance depend...

The present paper analyzes the outage probability of full-duplex (FD) regenerative relay systems over multipath fading channels. Unlike the majority of investigations that assume basic symmetric fading conditions, this analysis considers asymmetric generalized fading conditions, which are more realistic as they are encountered more often in practical wireless transmissions. To this end, it is assumed that the source-relay and sourcedestination links are subject to κ−µ multipath fading conditions, which can represent generalized line-of-sight communication scenarios; on the contrary, the relay-to-destination link is subject to η−µ fading conditions that typically represent generalized nonline-of-sight communication scenarios. Novel analytic expressions are derived for the outage probability (OP) of the considered FD relaying system. These expressions are given in closed-form and have a relatively tractable algebraic form which renders them convenient to handle both analytically and numerically. To this effect, they are subsequently employed in analyzing the corresponding performance for various communication scenarios. It is shown that the OP of the FD relay system is, as expected, highly dependent upon the severity of fading, the relay self-interference and the interference from the direct link. Furthermore, it is shown that at relatively high average signal-tonoise ratio values, the outage probability at low fading severity and at high relay self interference outperforms the respective performance for the case of high fading severity, but with low relay self-interference. Based on this, the offered results can be useful in the design and deployment of future full-duplex based cooperative communication systems.

Time reversal-based indoor positioning system (TRIPS) is a promising technology for the centimeteraccuracy indoor positioning, since it exploits the rich multipath propagation in indoor environments as a specific signature for each location. In TRIPS, a database is first constructed via channel probing. Well-calibrated devices are usually assumed in this process, i.e., no hardware impairments. However, a low cost terminal to be located, whose typical impairment is the I/Q imbalance (IQI) at the front-end transmitter, can significantly influence the TRIPS performance. More specifically, IQI creates an interference image of the signal that reduces the metric value used in TRIPS and hence decreases the localization accuracy. In this paper, we analytically investigate the impact of the IQI on the metric of TRIPS. A closed-form approximation of the localization metric inherent to the IQI is derived. In order to improve the TRIPS performance, an effective IQI mitigation method is proposed. Numerical simulations are carried out to validate the derived analytical expression under the IQI impact and the proposed compensation method. Index terms-Indoor positioning system, time reversal, I/Q imbalance, OFDM.

In deterministic networks where relay nodes are stationary, combined relay selection is an efficient relay selection scheme, which is capable of achieving the near-optimal outage performance with much lower system complexity. However, the efficiency of combined relay selection is only validated upon fixed topological settings. To investigate the performance of combined relay selection in spatially random networks (SRNs), we employ the Poisson point process to model the dynamical nature of cooperative networks and study the outage performance of the proposed system. It is surprising that the equivalence principle of combined relay selection appearing in deterministic networks does not hold in SRNs.

A salient feature of millimeter-wave (mmW) wireless systems is their large bandwidths. A direct consequence is that radio frequency (RF) non-idealities, such as phase noise, I-Q imbalance, and non-ideal frequency response of bandpass filters, become more pronounced compared to existing systems operating below 6 GHz. However, investigations of the impact of such nonidealities and techniques for their compensation are limited. In this paper, the problem of I-Q mismatch is investigated, motivated by the authors' recent work on mmW prototype design and development. First, a model for the non-ideal system is developed by modeling the in-phase (I) and quadrature (Q) passband channels separately, rather than the common complex baseband representation. The resulting channel matrix reveals the structure of interference introduced across I-Q channels and frequencies. Second, a new approach is developed for estimating the non-ideal channel using the new model. Third, a linear receiver architecture is developed to compensate for the interference caused by the I-Q mismatch. Finally, the performance of the new proposed system is compared to a baseline conventional system which ignores I-Q mismatch. The results indicate significant loss in performance even for modest values of I-Q mismatch parameters. In particular, the baseline system exhibits a saturation of output signal-to-interference-and-noise ratio (SINR) regardless of the input SNR. The new proposed system does not suffer from such saturation and its SINR can be increased indefinitely by increasing the input SNR. The analytical results are validated with experimental evaluation on a 28 GHz mmW wireless testbed.

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In this paper, an incremental selective decode-andforward (ISDF) relay strategy is proposed for power line communication (PLC) systems to improve the spectral efficiency. Traditional decode-and-forward (DF) relaying employs two time slots by using half-duplex relays which significantly reduces the spectral efficiency. The ISDF strategy utilizes the relay only if the direct link quality fails to attain a certain information rate, thereby improving the spectral efficiency. The path gain is assumed to be log-normally distributed with very high distance dependent signal attenuation. Furthermore, the additive noise is modeled as a Bernoulli-Gaussian process to incorporate the effects of impulsive noise contents. Closed-form expressions for the outage probability and the fraction of times the relay is in use, and an approximate closed-form expression for the average bit error rate (BER) are derived for the binary phase-shift keying signaling scheme. We observe that the fraction of times the relay is in use can be significantly reduced compared to the traditional DF strategy. It is also observed that at high transmit power, the spectral efficiency increases while the average BER decreases with increase in the required rate.

This paper derives an optimum relay position of amplify-and-forward (AF) cooperative communications with the differential transmission. As a performance benchmark, we utilize the probability of outage, which is defined as a probability that the instantaneous signal-tonoise power ratio (SNR) becomes lower than a certain threshold. The optimum relay position is found based on the theoretical expression of the outage probability, Computer simulations are also conducted to verify the validity of the theoretical analysis.

Direct-conversion radio transceivers can offer reprogrammable and low-cost hardware solutions for full-duplex (FD) cognitive radio (CR) devices. However, they are susceptible to radio frequency (RF) impairments, such as in-phase (I) and quadrature (Q) imbalance (IQI), which can significantly constrain the spectrum sensing capabilities. This paper is devoted to quantify and evaluate the effects of IQI in the context of spectrum sensing in FD CR systems, in which self-interference suppression (SIS) techniques are employed. Specifically, closed form expressions are derived for the false alarm and detection probabilities, under three different scenarios: imperfect SIS with joint transmitter (TX) and receiver (RX) IQI, imperfect SIS and ideal TX/RX RF front-end, and perfect SIS and ideal TX/RX RF front-end. The derived analytical results are validated through extensive simulations, which reveal that IQI has a detrimental impact on the spectrum sensing performance of the FD CR transceiver, which brings significant losses in the spectrum utilization.

A salient feature of millimeter-wave (mmW) wireless systems is their large bandwidths. A direct consequence is that radio frequency (RF) non-idealities, such as phase noise, I-Q imbalance, and non-ideal frequency response of bandpass filters, become more pronounced compared to existing systems operating below 6 GHz. However, investigations of the impact of such nonidealities and techniques for their compensation are limited. In this paper, the problem of I-Q mismatch is investigated, motivated by the authors' recent work on mmW prototype design and development. First, a model for the non-ideal system is developed by modeling the in-phase (I) and quadrature (Q) passband channels separately, rather than the common complex baseband representation. The resulting channel matrix reveals the structure of interference introduced across I-Q channels and frequencies. Second, a new approach is developed for estimating the non-ideal channel using the new model. Third, a linear receiver architecture is developed to compensate for the interference caused by the I-Q mismatch. Finally, the performance of the new proposed system is compared to a baseline conventional system which ignores I-Q mismatch. The results indicate significant loss in performance even for modest values of I-Q mismatch parameters. In particular, the baseline system exhibits a saturation of output signal-to-interference-and-noise ratio (SINR) regardless of the input SNR. The new proposed system does not suffer from such saturation and its SINR can be increased indefinitely by increasing the input SNR. The analytical results are validated with experimental evaluation on a 28 GHz mmW wireless testbed.

In this paper, an incremental selective decode-andforward (ISDF) relay strategy is proposed for power line communication (PLC) systems to improve the spectral efficiency. Traditional decode-and-forward (DF) relaying employs two time slots by using half-duplex relays which significantly reduces the spectral efficiency. The ISDF strategy utilizes the relay only if the direct link quality fails to attain a certain information rate, thereby improving the spectral efficiency. The path gain is assumed to be log-normally distributed with very high distance dependent signal attenuation. Furthermore, the additive noise is modeled as a Bernoulli-Gaussian process to incorporate the effects of impulsive noise contents. Closed-form expressions for the outage probability and the fraction of times the relay is in use, and an approximate closed-form expression for the average bit error rate (BER) are derived for the binary phase-shift keying signaling scheme. We observe that the fraction of times the relay is in use can be significantly reduced compared to the traditional DF strategy. It is also observed that at high transmit power, the spectral efficiency increases while the average BER decreases with increase in the required rate.

Satellite communication becomes a complacent subject for undergraduate students as not many high end equipment or accurate, clear and well interpreted simulated results are available. Given this limitation in the availability of resources, conducting a laboratory becomes a challenging task. Hence, this paper has been carried out as an extension of Radiofrequency satellite Link on Matlab r2016b. The electromagnetic signal carrying information is inflicted upon a lot of impairments such as Free Space Path Loss, Memoryless Nonlinearity, etc. In the current Simulink radio frequency (RF) satellite Link model, these impairments are modeled in the form of respective blocks with the provision of various mask parameters in each of them which allows us to vary those parameters to see the corresponding changes in the nature of the signal. The primary objective of this paper is to carry out experiments on the similar lines as aforementioned dealing with all impairments and corresponding results...

This work presents the effects of radio-frequency Local Oscillator non-idealities on OFDM inter-carrier interference. The synthesizer has the main role on modulation and demodulation process of base band IQ signals to radio frequency channels which need to fulfill several requirements imposed by standards specifications. Phase and frequency stability are crucial, since the synchronization of the entire system depends on the accuracy of this circuit. The discussed OFDM system is based on a simulation scenario including radio-frequency channel conversion considering Local Oscillator with configurable phase noise power and bandwidth. This feature allows the study of global system based on Local Oscillator output spectrum. Sub-channel spacing, cyclic redundancy and pulse shaping are configurable. The obtained results indicate that free run oscillator phase noise characterization is not appropriate when the Local Oscillator in the radio-frequency front end is based on synthesizer architecture. System evaluation is based on error vector magnitude. The relation of this metric with the Local Oscillator phase noise allows the performance estimation of the global system.

Spectrum scarcity is a critical problem that may reduce the effectiveness of wireless technologies and services. To address this problem, different spectrum management techniques have been proposed in the literature such as overlay cognitive radio (CR) where the unlicensed users can share the same spectrum with the licensed users. The main challenges in overlay CR networks are the identification and detection of the Primary User (PU) signals in a multi-source narrow-band interference (NBI) scenario. Therefore, in this paper, we investigate the performance of an orthogonal frequency division multiplexing (OFDM) overlay CR network with Secondary Users (SUs) and subcarriers selection schemes. Three approaches for SUs and subcarriers Selection named Direct, Distributed and Incremental selection techniques are proposed in this paper to increase the expected signal to interference and noise ratio based on full or partial knowledge of the channel state information (CSI). We also show that Distributed selection techniques provide all the SUs equal chances to be selected without affecting the selection diversity gain. General as well as simplified outage probability expressions are derived and extensive simulations are conducted to evaluate the performance of the proposed techniques and support the theoretical derivations. To accommodate more SUs, a new approach for asynchronous NBI estimation and mitigation in CR networks is investigated. Without any prior knowledge of the NBI characteristics and based on sparse signal recovery theory, the proposed approach allows the PU to exploit the sparsity of the SUs interference to recover it and approach the interference-free limit over practical ranges of NBI power levels.

To date the majority of research in the area of cooperative communications focuses on maximizing throughput and reliability while assuming perfect channel state information (CSI) and synchronization. This thesis, seeks to address performance enhancement and system parameter estimation in cooperative networks while relaxing these idealized assumptions. In Chapter 3 the thesis mainly focuses on training-based channel estimation in multi-relay cooperative networks. Channel estimators that are capable of determining the overall channel gains from source to destination antennas are derived. Next, a new low feedback and low complexity scheme is proposed that allows for the coherent combining of signals from multiple relays. Numerical and simulation results show that the combination of the proposed channel estimators and optimization algorithm result in significant performance gains. As communication systems are greatly affected by synchronization parameters, in Chapter 4 the thesis quantitatively analyzes the effects of timing and frequency offset on the performance of communications systems. The modified Cramer-Rao lower bound (MCRLB) undergoing functional transformation, is derived and applied to determine lower bounds on the estimation of signal pulse amplitude and signal-to-noise ratio (SNR) due to timing offset and frequency offset, respectively. i I have had the honor and pleasure of working with Dr. Steven D. Blostein throughout my Masters and Ph.D. years at Queen's University. Through Dr. Blostein's help and guidance, we have been able to address many challenging topics in the area of wireless communications and advance the research in this discipline. I would like to thank Dr. Blostein for not just being a supervisor but also for being a great mentor and friend through the ups and downs of this challenging but rewarding program. I look forward to continuing my collaboration with him after the completion of my Ph.D. degree. I would also like thank my beloved fiance, Sonia Perizzolo for being by my side throughout the years. My parents, Fatemeh and GolAli for supportingly me unequivocally. Without their help and support I would have never made it this far. My Sister, Hoda for always cheering me up with her beautiful smile from a very young age. I want to thank you all from the bottom of my heart. To all my friends here in Kingston and British Colombia (BC), who have made the past five years a blast. I would like to specially thank Chris Mitchell, and my

Cognitive radio (CR) technology has the potential to detect and share the unutilized spectrum by enabling dynamic spectrum access. To detect the primary users’ (PUs) activity, energy detection (ED) is widely exploited due to its applicability when it comes to sensing a large range of PU signals, low computation complexity, and implementation costs. As orthogonal frequency-division multiplexing (OFDM) transmission has been proven to have a high resistance to interference, the ED of OFDM signals has become an important local spectrum-sensing (SS) concept in cognitive radio networks (CRNs). In combination with multiple-input multiple-output (MIMO) transmissions, MIMO-OFDM-based transmissions have started to become a widely accepted air interface, which ensures a significant improvement in spectral efficiency. Taking into account the future massive implementation of MIMO-OFDM systems in the fifth and sixth generation of mobile networks, this work introduces a mathematical formulation of...

The exact closed-form expression for the outage probability (OP) of cognitive radio dual-hop amplify-and-forward (AF) relay networks is derived. The tractable expression of the OP, given in the form of elementary functions, readily enables evaluating the effect of primary users on the secondary system performance. It has been shown that the use of AF relaying significantly improves the performance of cognitive radio networks compared to its direct transmission counterpart.

In low-intermediate-frequency (low-IF) receivers, I/Q imbalance (IQI) causes interference on the desired signal from the blocker signal transmitted over the image frequencies. Conventional approaches for data-aided IQI estimation in zero-IF receivers are not applicable to low-IF receivers. In zero-IF receivers, IQI induces self-interference where the pilots of the image interference are completely identified. However, in low IF receivers, the image interference originates from a foreign signal whose training sequence timing and structure are neither known nor synchronized with the desired signal. We develop a dataaided subspace method for the estimation of IQI parameters in low-IF receivers in the presence of unknown fading channel. Our approach does not require the knowledge of the interference statistics, channel model nor noise statistics. Simulation results demonstrate the superiority of our approach over other blind IQI compensation approaches.

This paper considers a dual-hop vehicle-to-vehicle (V2V) communication system equipped with full-duplex relays (FDRs) in the millimeter-wave networks. The performance of this network is studied in a dense multi-lane highway considering cooperative best vehicular relay selection strategy. In fact, two different FDR schemes are analyzed for the given network. In the first scheme that is called self-interference (SI) vehicle relaying selection, the FDR models the source-relay and the relay-relay links by one channel state information (CSI) coefficient (i.e., a single channel estimation of the two links), while in the second scheme that is called individual SI vehicle relaying selection, the CSI of the source-relay and the relayrelay links are estimated separately. Moreover, relay-destination link is modeled by one CSI coefficient in both aforementioned schemes. Dissimilar to traditional V2V schemes where either line-of-sight (LOS) or non-line-of-sight (NLOS) propagation is considered, and the effect of the blockage on V2V communications is not taken into account when analyzing the performance, in this paper, we propose a probabilistic model capturing the occurrences of LOS and NLOS propagations, which depend on the movement of the vehicles between the central and adjacent lanes. Thus, the movement of the vehicles between any two adjacent lanes is assumed to take place independently and is deemed to be according to the Poisson distribution. This vehicle movement model considers the blockage between the source and destination links. In this vein, a LOS link is considered available when the center lane is clear of vehicles between the source and destination nodes, and an NLOS link is assumed otherwise. Furthermore, a Nakagami-m fading channel model is considered due to its excellent representation of the V2V communication environment. The LOS/NLOS probabilities combined together with the probability of blockage are used to analyze the system performance. The cumulative density function expression of the signal-to-interference-plus-noise ratio at the relay is derived for both relaying schemes. Moreover, the lower bound expressions of the end-to-end outage probabilities are developed and used to express throughput. Finally, the theoretical results postulated and presented here are verified by the numerical simulation for a variety of parameters. INDEX TERMS Full duplex relaying, V2V communications, relay selection, Nakagami−m fading channel, outage probability, throughput, blockage probability.

Recent studies investigate single-antenna radio frequency (RF) systems mixed with terahertz (THz) wireless communications. This paper considers a two-tier system of THz for backhaul and multiple-antenna assisted RF for the access network. We analyze the system performance by employing both selection combining (SC) and maximal ratio combining (MRC) receivers for the RF link integrated with the THz using the fixed-gain amplify and forward (AF) protocol. We develop the probability density function (PDF) and cumulative distribution function (CDF) of the end-to-end signal-to-noise (SNR) of the dual-hop system over independent and non-identically distributed (i.ni.d.) α-μ fading channels with a statistical model for misalignment errors in the THz wireless link. We use the derived statistical results to develop analytical expressions of the outage probability, average bit error rate (BER), and ergodic capacity for the performance assessment of the considered system. We develop diversity or...