Vol. 75, n° 5-6, May-June 2020
Content available on Springerlink

Power allocation and subchannel pairing for BER minimization in MIMO-OFDM AF relay systems

Mohammad Shamsesalehi¹, Yasser Attarizi¹, Roozbeh Rajabi¹
(1) Electrical and Computer Engineering, Qom University of Technology, Qom, Iran

Abstract The present study investigates the problem of bit error rate minimization in multi-input-multi-output orthogonal frequencydivision multiplexing amplify-and-forward relay systems. It is supposed that channels are frequency selective fading and under a total power constraint. In themulti-antenna transmitter, an independent symbol sequence is transmitted from each antenna. Zero forcing beamforming is performed in the reception and transmission of the relay to cancel out the inter-antenna interference. A power allocation and subchannel pairing scheme is considered as the optimization method. The goal of the optimization problem is to achieve the best bit error rate performance by applying a joint power allocation and subchannel pairing approach for all antennas. To deal with subchannel pairing, at first, we formulate it as a linear assignment problem and then Jonker-Volgenant algorithm is used to solve this problem. The joint scheme is compared with separate power allocation and subchannel pairing for each antenna as the main target. It is found that the joint scheme is superior to the separate method. Simulation results show that the proposed inter-antenna power allocation and subchannel pairing scheme can improve bit error rate and mean square error dramatically compared with separate subchannel pairing and power allocation at the cost of a little increase in complexity.

Keywords  MIMO-OFDM . AF relay . Subchannel pairing . Power allocation . Linear assignment problem

Computational complexity reduction of GreenOFDM

Jorge L. Gulfo Monsalve¹, Denis J. G. Mestdagh¹, Jean-Marc Brossier^2,3
(1) Greenwaves-Technologies, 28 Cours Jean Jaurès, Grenoble, France
(2) University Grenoble Alpes, CNRS, Grenoble INP, GIPSA-lab, Grenoble, France
(3) Present address: Institute of Engineering University Grenoble Alpes, Grenoble, France

Abstract The GreenOFDM technique is a new SeLected Mapping Orthogonal Frequency Division Multiplexing (SLM-OFDM) scheme where the same Peak-to-Average Power Ratio (PAPR) reduction is attained at a reduced number of computed IFFTs. Indeed, for the same performance the SLM-OFDM requires computing U IFFTs while the GreenOFDM requires only 2√U. In this paper, a method specific to the GreenOFDM to further reduce its computational complexity is presented. The results are presented through the probabilistic distributions of the number of computed IFFTs and the total number of operations. The methods being probabilistic, a solution to deal with the induced latency is proposed in order to guarantee real-time operation of the transmitter. Finally, the digital power consumption of the proposed method is proven to be negligible as compared with the High Power Amplifier (HPA) power consumption when implemented in a dedicated processor.

Keywords  OFDM · PAPR · SLM · Complexity reduction

Effective capacity and outage analysis using moment-generating function over Nakagami-m and Rayleigh fading channels in cooperative communication system

Abdulhamid Zahedi¹
(1) Department of Electrical Engineering, Kermanshah University of Technology, Kermanshah, Iran

Abstract Cooperative communication using multiple relays improves quality of service (QoS) parameters of a communication system. To verify this improvement, accurate analysis must be done considering the various fading channels and probability density function (PDF) or cumulative distribution function (CDF) of signal-to-noise ratio (SNR) in relays and destination. In this paper, using the moment-generating function (MGF) method and considering Nakagami-m fading channel, the outage probability and effective capacity are analyzed. Obtaining the closed-form expression of outage probability and effective capacity in Nakagami-m fading channel includes complex mathematical calculations; thus, the Rayleigh fading channel is assumed to be a special case of Nakagami-m distribution to achieve simpler mathematical equations. Simulation results verify the mathematical analysis in terms of effective capacity and outage probability.

Keywords  Effective capacity .Outage probability .Moment-generating function . Nakagami-mfading channel . Rayleigh fading channel

Progressive hologramtransmission using a view-dependent scalable compression scheme

Anas El Rhammad^1,3, Patrick Gioia^1,2, Antonin Gilles¹, Marco Cagnazzo^1,3
(1) IRT b–com, Cesson-Sévigné, France
(2) Orange Labs, Cesson-Sévigné, France
(3) LTCI, Télécom Paris, Institut polytechnique de Paris, Cesson-Sévigné, France

Abstract Over the last few years, holography has been emerging as an alternative to stereoscopic imaging since it provides users with the most realistic and comfortable three-dimensional (3D) experience. However, high-quality holograms enabling a free-viewpoint visualization contain tremendous amount of data. Therefore, a user willing to access to a remote hologram repository would face high downloading time, even with high speed networks. To reduce transmission time, a joint viewpoint-quality scalable compression scheme is proposed. At the encoder side, the hologram is first decomposed into a sparse set of diffracted light rays using Matching Pursuit over a Gabor atoms dictionary. Then, the atoms corresponding to a given user’s viewpoint are selected to form a sub-hologram. Finally, the pruned atoms are sorted and encoded according to their importance for the reconstructed view. The proposed approach allows a progressive decoding of the sub-hologram from the first received atom. Streaming simulations for a moving user reveal that our approach outperforms conventional scalable codecs such as scalable H.265 and enables a practical streaming with a better quality of experience.

Keywords  Digital holography · Diffraction · Compression · Gabor wavelets · Matching pursuit · Streaming · Scalability

VLSI implementation of an area and energy efficient FFT/IFFT core for MIMO-OFDM applications

Konguvel Elango¹, Kannan Muniandi¹
(1) Department of Electronics Engineering, Madras Institute of Technology Campus, Anna University, Chennai 600004, India

Abstract This research article presents an implementation of high-performance Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) core for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM)-based applications. The radix-2 butterflies are implemented using arithmetic optimization technique which reduces the number of complex multipliers involved. High-performance approximate multipliers with negligible error rate are used to eliminate the
power-consuming complex multipliers in the radix-2 butterflies. The FFT/IFFT prototype using the proposed high-performance butterflies are implemented using Altera Quartus EP2C35F672C6 Field Programmable Gate Array (FPGA) which yields 40% of improved logic utilization, 33% of improved timing parameters, and 14% of improved throughput rate. The proposed optimized radix-2-based FFT/IFFTcorewas also implemented in 45-nmCMOS technology library, using Cadence tools, which occupies an area of 143.135 mm2 and consumes a power of 9.10 mW with a maximum throughput of 48.44 Gbps. Similarly, the highperformance approximate complex multiplier-based optimized FFT/IFFT core occupies an area of 64.811 mm2 and consumes a power of 6.18 mW with a maximum throughput of 76.44 Gbps.

Keywords  FFT . IFFT . Decimation In Time (DIT) . Approximatemultipliers . MIMO-OFDM

Empirical validation and performance of duty cycle–based DTMC model in channel estimation

Dipen Bepari¹, Santasri Koley², Debjani Mitra³
(1) Department of Electronics and Communication Engineering,Vaagdevi College of Engineering, Warangal, Telangana, 506005, India
(2) Department of Electronics and Communication Engineering, DIT University, Dehradun, Uttarakhand, 248009, India
(3) Department of Electronics Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, 826004, India

Abstract This paper explores the learning capability of hidden Markov model (HMM) in capturing the temporal correlation and predicting primary user (PU) activity pattern of real spectrum data of GSM-900 band through an USRP-LabVIEW platform for cognitive radio (CR) systems. The inability of the widely used stationary Markov model in estimating the occupancy pattern of primary channels for a long duration of time has been verified.We proposed an alternative duty cycle (DC)–based two-state discrete-time Markov chain (DTMC-DC) model. Analysis of empirical data indicates that DC required for a nonstationary DTMC-DC model can be well approximated by a trapezoidal shape and the PU spectrum usage pattern estimated using DTMC-DC is capable of learning the statistical behavior (length of idle and busy interval periods) of a real channel accurately with a reduced complexity.

Keywords  Cognitive radio · Spectrum measurement · Duty cycle · Hidden Markov model

Cyclic interleaving scheme for an IFDMA system

J. Arun Kumar¹,  S. Lenty Stuwart¹
(1) Department of Electronics and Communication Engineering, University College of Engineering, Nagercoil, Anna University, Nagercoil, 629004, India

Abstract In this paper, a new interleaving scheme for an interleaved frequency division multiple access (IFDMA) system is proposed. The proposed scheme combines the advantages of code division multiple access (CDMA) with maximal length sequence (m-sequence) and orthogonal frequency division multiple access (OFDMA). Multiaccess interference (MAI) among users is eliminated by employing orthogonal carriers, and the intersymbol interference (ISI) due to multipath channels is minimized by using cyclic interleaving. Diversity gain is achieved in the proposed method with maximal ratio combining (MRC) in
the case of a Rayleigh environment. Compared to complex multiuser (MU) detection, the detection process in the proposed method is relatively simple. Multipath orthogonality is achieved in the proposed method, avoiding the need for channel equalization. The proposed method is compared with the conventional interleaving employing well-known minimum mean square error frequency domain equalization (MMSE-FDE). The Monte Carlo simulation results prove the superiority of the proposed interleaving over conventional interleaving with MMSE-FDE, showing that the present scheme is suitable for both uplink and downlink mobile radio transmissions.

Keywords  Interleaved frequency division multiple access (IFDMA) ·
Minimum mean square error frequency domain equalization (MMSE-FDE) ·
Intersymbol interference (ISI) · Interleaving · Multipath fading

Physical layer security in shotgun cellular systems over
correlated/independent shadow fading channels

Ali Mohammad Khodadoust¹, Ghosheh Abed Hodtani²
(1) Department of Electrical Engineering, Sadjad University of Technology, Mashhad, Iran
(2) Department of Electrical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract The shotgun cellular systems (SCSs) (modeling, generally, a dense cellular or wireless data network deployment and nonideal regular hexagonal grid with site-acquisition difficulties, variable traffic load) are wireless communication systems with randomly placed base stations (BSs) over the entire plane according to a stochastic (e.g., Poisson) point process in n dimensions (n = 1, 2, and 3). Due to the good performance and the importance of the SCSs in today’s communications, the physical layer security of these systems is practically of importance, specifically, in more realistic channel propagation models. In this paper, by assuming that the channel coefficients are known at the receiver, we analyze the performance of the physical layer security for the classic Wyner’s three-node model in the SCSs over correlated/independent log-normal shadow fading channels. For this purpose, first, we calculate the signal-to-interference-plus-noise ratio (SINR) performance at a mobile station (MS) in an SCS. Then, the average secrecy capacity (ASC), the probability of non-zero secrecy capacity (PNSC), the secure outage probability (SOP), and the lower bound of SOP (LSOP) are obtained, and also, their approximated closed-form expressions are derived. Finally, analytical results are validated numerically.

Keywords  Shotgun cellular system · Physical layer security · Signal-to-interference-plus-noise ratio · Secrecy capacity · Secrecy outage · Correlated shadow fading channels