Selective mapping (SLM) and partial transmit sequence (PTS) are attractive schemes for mitigating the high peak power inherent in orthogonal frequency division multiplexing (OFDM) signals. However, ...the high computational complexity and redundant side information (SI) bits have been identified as the main limitations for such techniques. The high computational complexity is mainly due to the need to perform several inverse fast Fourier transforms (IFFTs), and phase optimization process at the transmitter side. Therefore, this paper presents new SLM and PTS designs using a low complexity T-transform rather than IFFT. The use of the T-transform with SLM achieves a considerable computational complexity and peak-to-average power ratio (PAPR) reduction. Furthermore, we apply the T-transform to PTS and derive two different configurations that compromise the SI requirements and PAPR reduction. All the proposed schemes do not affect the original power spectrum of OFDM signals. The complexity analysis show that the proposed schemes have much lower complexity as compared to conventional schemes. Moreover, simulation results demonstrate that the proposed schemes are resilient to dispersion arising from multipath propagation, which is due to the frequency diversity introduced by the T-transform.
In this paper, we consider Power Line Communications (PLC) for Smart Grid (SG) using Multiple-Input Multiple-Output and Orthogonal Frequency Division Multiplexing (MIMO-OFDM). We investigate a ...<inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> MIMO-OFDM system and propose a novel nonzero comb pilot (NZCP) design for channel estimation that can cope with pilot contamination without the need for zero-pilot insertion in adjacent channels. The Bit Error Rate (BER) performance vs. <inline-formula> <tex-math notation="LaTeX">E_{b}/N_{0} </tex-math></inline-formula> is demonstrated using numerical simulations for uncoded and coded systems using Low Parity Density Check (LDPC) error correcting codes. The performance is compared with conventional Zero-comb pilot (ZCP) and the block pilot methods through frequency-selective multipath PLC channels and in the presence of Additive White Gaussian Noise (AWGN) and symmetric <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>-stable (<inline-formula> <tex-math notation="LaTeX">\text{S}\alpha \text{S} </tex-math></inline-formula>) type of impulsive noise. Additionally, a novel averaging method is introduced to reduce the effects of AWGN, <inline-formula> <tex-math notation="LaTeX">\text{S}\alpha \text{S} </tex-math></inline-formula> and Mean Square Error (MSE) metric is used to assess the quality of the channel estimation. The numerical results presented demonstrate that the NZCP approach using averaging outperforms all the methods considered, e.g. for the uncoded system at a BER of <inline-formula> <tex-math notation="LaTeX">10^{-5} </tex-math></inline-formula> an improvement in <inline-formula> <tex-math notation="LaTeX">E_{b}/N_{0} </tex-math></inline-formula> of 3.6 and 4 dB against ZCP and block approaches, respectively. In contrast, in the coded system, the coding gain is of the order of 20 dB compared to the uncoded cases with the NZCP proposed method outperforming all the other considered approaches by at least 0.5 dB. Furthermore, the presented BER results demonstrate that the <inline-formula> <tex-math notation="LaTeX">\text{S}\alpha \text{S} </tex-math></inline-formula> impulsive noise has a greater impact on the performance of the MIMO-PLC system. It is shown that when utilizing a hardlimiter to limit the effects of <inline-formula> <tex-math notation="LaTeX">\text{S}\alpha \text{S} </tex-math></inline-formula>, the BER can reach <inline-formula> <tex-math notation="LaTeX">8\times 10^{-5} </tex-math></inline-formula> at an <inline-formula> <tex-math notation="LaTeX">E_{b}/N_{0} </tex-math></inline-formula> of 45 dB when <inline-formula> <tex-math notation="LaTeX">\alpha =1.5 </tex-math></inline-formula>. In contrast, when <inline-formula> <tex-math notation="LaTeX">\alpha =1 </tex-math></inline-formula>, which represents a more severe case of <inline-formula> <tex-math notation="LaTeX">\text{S}\alpha \text{S} </tex-math></inline-formula>, a BER level of <inline-formula> <tex-math notation="LaTeX">3.5\times 10^{-4} </tex-math></inline-formula> is attained at an <inline-formula> <tex-math notation="LaTeX">E_{b}/N_{0} </tex-math></inline-formula> of 90 dB. However, the proposed averaging-NZCP system can robustly estimate the channel frequency responses (CFR) of the MIMO-PLC channel over <inline-formula> <tex-math notation="LaTeX">\text{S}\alpha \text{S} </tex-math></inline-formula> noise outperforming other commonly used pilot approaches.
Selected mapping (SLM) is a technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. SLM requires the transmission of several side ...information bits for each data block, which results in some data rate loss. These bits must generally be channel-encoded because they are particularly critical to the error performance of the system. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of several OFDM systems using either QPSK or 16-QAM modulation, we show that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output provided that the number of subcarriers is large enough.
This paper derives the closed-form bit error probability (BEP) of massive multiple-input, multiple-output (M-MIMO) systems using orthogonal frequency-division multiplexing (OFDM) and zero-forcing ...(ZF) detection. We improve the BEP accuracy by increasing the Neumann series expansion (NSE) to second order for the system that was previously analyzed in 1 employing a derived probability distribution function (PDF) of the effective noise. The proposed PDF is then utilized to evaluate the BEP, the PDF of output signal-to-noise ratio (SNR), and the outage probability as a function of the output SNR of the system. Furthermore, a simplified closed-form expression for the effective noise PDF, in terms of the Gaussian distribution, and the noise variance are firstly derived in this paper for simplifying the performance analysis. Monte-Carlo simulation results confirm that the outcome from the derived equation and the approximation closely matched those obtained by simulation. In addition, we employ the proposed noise variance to estimate the log-likelihood ratio (LLR) instead of the approximate noise variance for the low-complexity soft-output ZF detection. The computational complexity of the proposed detection is thus significantly reduced, whereas its bit error rate (BER) is lower than that of the classical detection. Focusing on a 10 × 200 Coded-OFDM-M-MIMO system, 97.81% of multiplications, required for producing the LLR from the estimated symbol, were minimized by utilizing the proposed detection. Therefore, the derived equations can be efficiently used for analyzing the performance of OFDM-M-MIMO systems, and reducing the computational complexity of the soft-output ZF detection.
In this work, two efficient low complexity Antenna Selection (AS) algorithms are proposed for downlink Multi-User (MU) Massive Multiple-Input Multiple-Output (M-MIMO) systems with Matched Filter (MF) ...precoding. Both algorithms avoid vector multiplications during the iterative selection procedure to reduce complexity. Considering a system with N antennas at the Base Station (BS) serving K single-antenna users in the same time-frequency resources, the first algorithm divides the available antennas into K groups, with the kth group containing the N/K antennas that have the maximum channel norms for the kth user. Therefore, the Signal-to-Interference plus Noise Ratio (SINR) for the kth user can be maximized by selecting a subset of the antennas from only the kth group, thereby resulting in a search space reduction by a factor of K. The second algorithm is a semiblind interference rejection method that relies only on the signs of the interference terms, and at each iteration the antenna that rejects the maximum number of interference terms will be selected. The performance of our proposed methods is evaluated under perfect and imperfect Channel State Information (CSI) and compared with other low complexity AS schemes in terms of the achievable sum rate as well as the energy efficiency. In particular, when the Signal-to-Noise Ratio (SNR) is 10 dB, and for a system with 20 MHz of bandwidth, the proposed methods outperform the case where all the antennas are employed by 108.8 and 49.2 Mbps for the first and second proposed algorithms, respectively, given that the BS has perfect CSI knowledge and is equipped with 256 antennas, out of which 64 are selected to serve 8 single-antenna users.
In this study, non-orthogonal multiple access (NOMA) is considered for multiusers wireless communications over Rayleigh fading channel. The base station (BS) utilises NOMA technique to secure ...connectivity, users fairness and high spectral efficiency for multiusers with different channel conditions. Moreover, a power allocation mechanism is applied at the BS by giving each user its required power allocation factor (PAF) in order to share the available power. Therefore, this technique allows the users of interest to communicate with the BS over the same frequency band simultaneously in the power domain. Moreover, successive interference cancellation is applied for users with the lower PAF to remove the strong signal of the other users. Furthermore, exact expressions are derived for different performance metrics, and the probability density function of the signal-to-interference-plus-noise ratio is derived at each terminal and then exploited to obtain the outage probability and the probability of error. The performance analysis is verified via Monte–Carlo simulations demonstrating closed-match with theoretical analysis.
In this paper, the performance of a dual-hop multiuser underlay cognitive network is thoroughly investigated by using a decode-and-forward (DF) protocol at the relay node and employing opportunistic ...scheduling at the destination users. A practical scenario where cochannel interference signals are present in the system is considered for the investigation. Considering that transmissions are performed over nonidentical Rayleigh fading channels, first, the exact signal-to-interference-plus-noise ratio (SINR) of the network is formulated. Then, the exact equivalent cumulative distribution function (cdf) and the outage probability of the system SINR are derived. An efficient tight approximation is proposed for the per-hop cdfs, and based on this, the closed-form expressions for the error probability and the ergodic capacity are derived. Furthermore, an asymptotic expression for the cdf of the instantaneous SINR is derived, and a simple and general asymptotic expression for the error probability is presented and discussed. Moreover, adaptive power allocation under the total-transmit-power constraint is studied to minimize the asymptotic average error probability. As expected, the results show that optimum power allocation improves the system performance compared with uniform power allocation. Finally, the theoretical analysis is validated by presenting various numerical results and Monte Carlo simulations.
In this paper, the performance analysis of a full-duplex maximum ratio combining multiple-input multiple-output (FD-MRC-MIMO) system based on equalize-and-forward (EF) relaying with ...self-interference-cancellation (SIC) is derived under imperfect channels state information (CSI). The performance of the system is investigated in the presence of additive white Gaussian noise (AWGN) over Rayleigh fading channels. Self-interference cancellation is performed by applying null-space-projection (NSP) via singular-value-decomposition (SVD). Furthermore, exact, closed-form solutions for the signal-to-interference-plus-noise ratio (SINR) distribution and outage probability are mathematically formulated and evaluated along with the average symbol-error-rate (ASER) for M-ary phase-shift keying (M-PSK) modulation. The coefficients of the EF-relay are obtained to attain the minimum mean square error (MMSE) between the transmission symbols. Comparison of the obtained results with relevant state-of-the-art techniques suggests significant improvements in the SINR figures and system capacity.
In medical applications, implant devices are used to measure and remotely transmit the human biological signals to off-body devices. To date, providing the implantable medical devices (IMDs) with a ...constant and perpetual energy source remains an ongoing challenge. Accordingly, a far-field radio-frequency powering, represented by an access point (AP), in conjunction with energy-harvesting capability is deployed in this paper for continuous powering of the IMDs. In this respect, theoretical analysis is used to establish safe powering conditions in order to comply with the safety limits established by the Federal Communications Commission. The feasibility of the wireless power transfer to the IMDs is investigated by deriving the analytical closed-form expressions for outage probability and average harvested energy, both of which are validated with Monte Carlo simulations. The findings of this paper suggest not to exceed a distance of 0.5 m between the AP and the body surface, as the system performance has experienced high outage probability beyond this value, while the minimum allowable distance is 17 cm at a powering frequency of 403 MHz. It is also presented that the AP should be equipped with a minimum transmit power of 0.4 W in order to maintain an outage probability for the energy harvesting to be less than 10 −1 .
In this paper, we derive the bit error rate and pairwise error probability (PEP) for massive multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems for ...different M-ary modulations based upon the approximate noise distribution after channel equalization. The PEP is used to obtain the upper-bounds for convolutionally coded and turbo coded massive MIMO-OFDM systems for different code generators and receive antennas. In addition, complexity analysis of the log-likelihood ratio (LLR) values is performed using the approximate noise probability density function. The derived LLR computations can be time-consuming when the number of receive antennas is very large in massive MIMO-OFDM systems. Thus, a reduced complexity approximation is introduced using Newton's interpolation with different polynomial orders and the results are compared with the exact simulations. The Neumann large matrix approximation is used to design the receiver for a zero-forcing equalizer by reducing the number of operations required in calculating the channel matrix inverse. Simulations are used to demonstrate that the results obtained using the derived equations match closely the Monte Carlo simulations.
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