Cooperative DF Cognitive Radio Networks with Spatial Modulation with Channel Estimation Errors

Pair-wise error probability (PEP) is analyzed in the presence of channel estimation error (CEE) for orthogonal frequency division multiplexing (OFDM) in a quasi-static Rayleigh fading channel. Subcarriers in OFDM are grouped in an equi-spaced manner with the number of subcarriers in a group equal to the number of channel taps. One group is dedicated for training and the rest are for data transmission. A linear minimum mean square error (LMMSE) based channel estimation for coherent detection is considered in this paper. This enables the signal dependent CEE to be uncorrelated to the data. Since ML decoding employed with perfect CSI becomes suboptimal in the presence of CEE, an optimal ML decoding is derived. It is observed from our training-based PEP expression that the CEE does not reduce the diversity order but contributes to a loss of coding gain. Moreover, a code design criterion is established. To reduce the loss of coding gain, an optimal training scheme is developed, based on the PEP expression. Loss of performance due to an imperfect channel estimate is quantified in terms of bounds on bit error probability (BEP) for high SNR. Our analytical findings are corroborated by simulation examples.

In this paper, we analyze the performance of the differential space-time modulation (DSTM) in Rayleigh fading channels. By using the moment-generating function (MGF)-based approach, we derive a number of closed-form expressions for the pairwise error probability (PEP) of the DSTM in various fading environments. For spatially independent channels, we derive a closed-form expression for the exact PEP of the DSTM for both slow- and fast-fading cases. In the case of fast-fading channels, we show that an irreducible error floor exists in the PEP and in the block error rate of the DSTM, and derive a closed-form expression for the PEP error floor in terms of the fading rate. For spatially correlated channels, we derive a new closed-form expression for the PEP at asymptotically high signal-to-noise ratios and show that an existing asymptotic PEP expression derived by the residue method can also be obtained by using the MGF-based approach. Finally, we use computer simulations to verify the theoretical results.

In this paper, a new multiple-input multiple-output (MIMO) transmission technique, which is called double spatial modulation (DSM), is proposed as a new high-rate generalized spatial modulation (SM) scheme. DSM scheme aims to improve the spectral efficiency of classical SM by increasing the number of active transmit antennas. In the DSM scheme, incoming data bits determine two modulated symbols as well as their corresponding activated transmit antenna indices. One of the modulated symbols is directly transmitted over its corresponding activated transmit antenna, while the other one is transmitted with a rotation angle, which is optimized for M-ary quadrature amplitude modulation (M-QAM) signal constellation, over the second activated transmit antenna. The error performance of the proposed DSM scheme is compared with the recently proposed emerging SM schemes such as quadrature SM (QSM) and enhanced SM (ESM). Our computer simulations show that the DSM scheme provides considerably better error performance than QSM and ESM schemes for different spectral efficiency values. In addition, the pairwise error probability (PEP) of DSM is derived and the average bit error probability (ABEP) over uncorrelated Rayleigh fading channels is obtained for different M-QAM constellations.

This paper presents the performance analysis of decode-and-forward (DF) relaying system in presence of both channel estimation error (CEE) and radio frequency impairments (RFI). First, the end-to-end signal-to-noise-plus-distortion-and-error ratio (SNDER) expression is derived, followed by an exact closed-form outage probability (OP) expression for Nakagami-m fading channel. As a special case, the OP analysis for Rayleigh fading channel is also provided. From the derived expressions, the relation amongst CEE and RFI is analyzed. For a complete study, the high SNR analysis of the derived equations is also carried out. The analytical results have been verified using the Monte Carlo simulations. Finally, intriguing results are presented with the help of plots shown in the numerical analysis.

In this thesis we investigate the effects of the physical constraints such as antenna aperture size, antenna geometry and non-isotropic scattering distribution parameters (angle of arrival/departure and angular spread) on the performance of coherent and non-coherent space-time coded wireless communication systems. First, we derive analytical expressions for the exact pairwise error probability (PEP) and PEP upper-bound of coherent and non-coherent space-time coded systems operating over spatially correlated fading channels using a moment-generating function-based approach. These analytical expressions account for antenna spacing, antenna geometries and scattering distribution models. Using these new PEP expressions, the degree of the effect of antenna spacing, antenna geometry and angular spread is quantified on the diversity advantage (robustness) given by a space-time code. It is shown that the number of antennas that can be employed in a fixed antenna aperture without diminishing the diversity advantage of a space-time code is determined by the size of the antenna aperture, antenna geometry and the richness of the scattering environment. In realistic channel environments the performance of space-time coded multipleinput multiple output (MIMO) systems is significantly reduced due to non-ideal antenna placement and non-isotropic scattering. In this thesis, by exploiting the spatial dimension of a MIMO channel we introduce the novel use of linear spatial precoding (or power-loading) based on fixed and known parameters of MIMO channels to ameliorate the effects of non-ideal antenna placement on the performance of coherent and non-coherent space-time codes. The spatial precoder virtually arranges the antennas into an optimal configuration so that the spatial correlation between all antenna elements is minimum. With this design, the precoder is fixed for fixed antenna placement and the transmitter does not require any feedback of channel state information (partial or full) from the receiver. We also derive precoding schemes to exploit non-isotropic scattering distribution parameters of the scattering channel to improve the performance of space-time codes applied on MIMO systems in non-isotropic scattering environments. However, these schemes

Cognitive radio (CR) systems have been proposed for efficient usage of spare spectrum licensed to primary systems. This leads to the issue of providing as much spectrum to CR users as possible while not degrading the quality of service (QoS) of primary users of the spectrum. This paper proposes a novel cooperation scheme between primary and CR users to guarantee QoS of primary users up to the cell edge while making the licensed spectrum available for opportunistic access by the CR users. Thus the proposed method can provide a so called ¿win-win strategy¿ by benefiting both primary and CR users. The proposed scheme solves efficiently the Gaussian multiple access problem for power allocation of primary systems that cooperates with CR systems. We show that the Gaussian multiple access problem can be formulated as a standard semi-definite programming (SDP) problem. Numerical results show that the QoS of primary users at the cell edge is improved by the proposed cooperative access scheme.

Large intelligent surface (LIS) has recently emerged as a potential enabling technology for 6G networks, offering extended coverage and enhanced energy and spectral efficiency. In this work, motivated by its promising potentials, we investigate the error rate performance of LIS-assisted nonorthogonal multiple access (NOMA) networks. Specifically, we consider a downlink NOMA system, in which data transmission between a base station (BS) and L NOMA users is assisted by an LIS comprising M reflective elements (REs). First, we derive the probability density function (PDF) of the end-to-end wireless fading channels between the BS and NOMA users. Then, by leveraging the obtained results, we derive an approximate expression for the pairwise error probability (PEP) of NOMA users under the assumption of imperfect successive interference cancellation. Furthermore, accurate expressions for the PEP for M = 1 and large M values ( M > 10) are presented in closed-form. To gain further insights into the system performance, an asymptotic expression for PEP in high signal-to-noise ratio regime, asymptotic diversity order, and tight union bound on the bit error rate are provided. Finally, numerical and simulation results are presented to validate the derived mathematical results.

In a cognitive radio (CR) system, an achievable throughput of secondary users (SU) primarily depends on the activity level of primary users (PU) in the channels. More the PU are active in the channels, lesser the opportunity of SU transmission. Protecting the PU from a harmful interference introduced by SU is also a challenging task specifically when multiple PU and SU exist in the system. The trade-off between SU sum throughput and PU occupancy level has been thoroughly analysed considering a zero interference tolerance of an interweave CR system. PU activity level in the channel is measured in terms of duty cycle (DC). The interplay between DC of PU and throughput of SU is presented here for Poisson and binomial distribution based SU arrival processes. The results identify the opportunistic channels when SU aims a particular sum throughput and find the optimal numbers of SU in the channels for various DC.

In this paper, PEP (pairwise error probability) is derived for MIMO systems in the presence of channel estimation error, where the channel is estimated using training insertion and linear channel estimation. This training-based PEP expression is utilized to design the training sequence and for optimal power allocation between the training and data symbols. The loss of coding gain due to the training is quantified at high SNR. It is shown that both the proposed PEP-based and the existing capacity-based optimal training approach of B. Hassibi and B. Hochwald (IEEE Trans. Inform. Theory, vol. 49, no. 4, pp. 951-963, 2003) reveal the same power allocation for constant modulus (CM) constellations. The performance of our optimal power allocation scheme falls between the nonoptimized equal power allocation and perfectly known channel cases, and converges to the latter for larger data transmission intervals. Numerical and simulation results are presented to justify the usefulness of our analytical findings.

In the pursuit of ever increasing demand of higher data rates, modern wireless communication systems are resorting to tighter frequency reuse patterns thereby leading to interference-limited systems. Recently proposed interference-aware receiver [1] is a low complexity and efficient receiver design for interference mitigation in cellular systems. However this advanced receiver necessitates the channel knowledge of both the desired and interfering signals which may not be available in a practical system. In this paper, we investigate the performance of interference-aware receiver under imperfect channel state information (CSI). We consider uncorrelated Rayleigh flat fading channels and model the estimation error as independent complex Gaussian random variables. We derive upper bound on the pair wise error probability (PEP) and show that the interference-aware receiver is characterized by full diversity in the presence of channel estimation errors. We compare the performance of interference-aware receiver with that of MMSE receiver and show that the degradation in the performance of MMSE receiver is much more pronounced than that of interference-aware receiver under imperfect CSI.

Within the last years a discrepancy between the spectrum licenses and the actual usage of spectrum has been observed. While the vast majority of frequency bands attractive for wireless communication are licensed, measurement campaigns have shown that large portions of the spectrum are temporarily unused in many locations. Sensing-based opportunistic spectrum re-usage has been identified as an attractive approach to overcome this discrepancy. In this approach Cognitive Radio (CR) based Secondary Users (SUs) sense the licensed frequency bands owned by Primary Users (PUs) for available spectrum and use the temporarily available spectrum on an opportunistic basis with the constraint to vacate the spectrum as soon as the license holder returns. An apparent challenge for such secondary spectrum usage is the reliable detection of the PU communication. The SUs have to ensure that the licensed spectrum is always vacated in a timely manner and that no harmful interference is created to the PUs. However, not only the protection of the PU communication is a challenging task for such CR networks but also the maintenance of a proper Quality of Service (QoS) for the secondary communication. Due to the strict access priority of the PUs, the secondary communication potentially has to be often relocated to new, temporarily available frequency bands. In this thesis we present and evaluate a CR system design, which is able to cope with these two challenges. We show that the proposed system design can achieve both reliable PU protection and secondary QoS support even for small secondary networks consisting of simple, low complexity CRs using energy detection-based spectrum sensing for the PU protection. Using a proper amount of spectral overhead for spectrum sensing and for secondary QoS support, reliable PU protection and secondary QoS support can also be maintained in environments with very high variability of temporarily available spectrum. We evaluate the tradeoff between both overheads and show that there exists an optimal joint spectral overhead which maximizes the spectral efficiency. We further show that, while the spectral efficiency of initially small network deployments based on the proposed system design might be low, it is still significantly greater than zero. Furthermore, the spectral efficiency is improved, as the network size increases. This makes the proposed CR design an ideal approach for initial deployments of very small and cheap CR networks, which are perfectly scalable: with an increase of network size (which usually goes hand in hand with an increase in spectrum demand), also the spectral efficiency is increased.

In this paper, we analysis wideband spectrum sensing with distance based weight combining for Cognitive Radio (CR) systems. CR systems is implemented the spectrum of the Primary User(PU) by using a energy detection method. Threshold is determined in accordance with the constant false alarm rate (CFAR) algorithm for energy detection. The signal of PU is BPSK signal and the wireless channel between a PU and CR systems is modeled as Gaussian channel. From the simulation results, the wideband sensing with distance based and Distance based weight Combing (DWC) methods shows higher spectrum sensing performance than single CR user spectrum sensing.

In this paper, a new multiple‐input multiple‐output transmission technique calledquadrature spatial modulation (QSM)is proposed and analyzed in the presence of imperfect channel estimation at the receiver. In QSM, conventional spatial constellation diagram of spatial modulation (SM) system is expanded to include both in‐phase and quadrature components. As such, significant enhancement in the overall spectral efficiency is achieved while retaining all inherent advantages of SM technique, such as inter‐channel interference avoidance, single radio frequency chain transmitter and low receiver complexity. It is shown that significant performance enhancements can be achieved as compared with SM, Alamouti, and spatial multiplexing systems. Besides, the impact of Gaussian imperfect channel estimation on the performance of QSM system is studied. A closed‐form expression for the pairwise error probability of generic QSM system is derived and used to calculate a tight upper bound of the average bit error probability over Rayleigh fading channels with perfect and imperfect channel knowledge. Also, simple asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results highlight the accuracy of the conducted analysis. Copyright © 2014 John Wiley & Sons, Ltd.

In this paper, the average bit error rate performance of quadrature spatial modulation (QSM) transmission technique over double complex Nakagami-m fading channels is investigated. In the proposed scheme, in which all terminals are in motion as mobiles or vehicles. The average bit error rate is derived by using pairwise error probability and upper bound union expressions, which are defined for the QSM transmission technique. In this context, the mean vector and variance matrix of double complex Nakagami-m fading channels has been presented using of properties of its statistics. Furthermore, at the receiver side, the impact of Gaussian imperfect channel state information on the performance is considered, and analytical expression is presented. Finally, it has been demonstrated that Monte Carlo simulation results prove the exactness of analytical results under different system settings and the severity of fading parameters.

We evaluate the performance improvement in orthogonal frequency-division multiplex access (OFDMA) achievable with cooperative relaying in the presence of frequency offsets. The relays can operate in either the amplify-and-forward (AF) or decode-and-forward (DF) mode. In each transmission, node S has M relays when transmitting its own signal, and it also helps the other M relays transmit their signals. The total power used to transmit each symbol, including the power consumed in S and the relays, is kept constant. The outage information rates of the proposed cooperative transmission scheme are first derived. The performance improvement in the frequency offset estimation by using cooperative relay is then analyzed. Channel estimation in a cooperative OFDMA network in the presence of frequency offsets is also evaluated, and the pairwise error probability (PEP) of orthogonal space-time coding in cooperative OFDMA due to both the frequency offset and channel estimation errors is derived. Numerical results illustrate the superior performance of the proposed scheme over the conventional transmission with regard to outage information rate, frequency offset estimation error and the PEP.