Delay and energy efficient task offloading from device to fog nodes involves decision making challenges wherein an integrated optimal scheme for preserving sustainability of the terminal nodes (TNs) and fog nodes (FNs) is extremely important. In this paper, we propose a novel clustering based delay aware energy efficient task offloading scheme in a Software-Defined Networking (SDN) based fog architecture. A bi-objective problem is formulated for optimum clustering of TNs with respect to FNs, selection of offloading parameters and, joint delay and energy minimization. It is then tranformed to a scalarized single objective problem which has a nested structure with the two problems: 1) optimal clustering and 2) optimal offloading for a given set of clusters. Based on this, Optimal Clustering and Offloading Parameters (OCOP) algorithm is designed which has lesser time complexity than the usual quadratic case. Through extensive simulations, we have shown that the use of explicit clustering in the proposed algorithm improves FN participation and reduces activity time and energy levels thereby increasing sustainability of the FNs and TNs as compared with the random case and a similar task offloading algorithm. Moreover, even cluster size distribution lowers our algorithm’s running time than the quadratic case.

Orthogonal time frequency space (OTFS) modulation establishes reliable communication over highly time-varying wireless channels. This work designs a low-complexity linear minimum mean square error (LMMSE) receiver for practical pulse-shaped multiple-input multiple-output (MIMO)-OTFS systems. The proposed design reduces complexity by exploiting inherent channel sparsity and channel-agnostic structure of matrices involved in the LMMSE receiver. The proposed design, with log-linear complexity order, does not make any approximation, and provides exactly the same solution, and consequently the same bit error rate, as that of the conventional LMMSE receiver, which has a cubic complexity order.

Orthogonal time frequency space modulation (OTFS) scheme establishes reliable communication in a rapidly time-varying wireless channel with a high Doppler spread. We design a low-complexity linear minimum mean squared error (LMMSE) receiver for practical-pulse-shaped multiple-input multiple-output (MIMO)-OTFS systems. The proposed receiver exploits the inherent channel sparsity and the channel-agnostic structure of matrices involved in the LMMSE receiver, and has only a log-linear complexity. It provides exactly the same solution, and hence the same bit error rate (BER), as that of the conventional LMMSE receiver with a cubic order of complexity. We also derive, by using the Taylor series expansion and the results from random matrix theory, a tight closed-form approximation for the post-processing signal-to-noise-plus-interference ratio (SINR) expression of the proposed receiver. This expression is derived by assuming imperfect receive channel state information. We show using extensive numerical investigations that the derived SINR expression, when averaged over multiple channel realizations, accurately characterizes the BER of a MIMO-OTFS system.

This paper proposes a new architecture for the Phase Frequency Detector (PFD) with improved gain and lower Blind Zone (BZ). The new architecture introduces a selective reset technique with trailing edge detection, which is less sensitive to process and voltage variations in achieving minimal BZ. The proposed PFD is designed and fabricated in 180 nm CMOS process. The circuit is tested for large variations in the supply voltage (1.3 V and 1.8 V), achieving the BZ of 17.5 ps, which is around three times less compared to earlier reported works. The effect of improvement in gain and BZ of the proposed PFD on the reduction of settling time of a phase-locked loop with which the proposed PFD has been integrated is shown with the post-layout simulation results.

This paper proposes a gain boosted N-path filter with improved out of band (OOB) rejection. The proposed filter contains two stages. The first stage contains a gain boosted N-path filter where two switches in each path are driven by the same clock phase. The second stage contains a two-port passive N-path filter where two switches in each path are driven by clocks of 180 degrees out of phase. The proposed design removes the limitation on OOB rejection due to switch resistance, which saves dynamic power consumption. A four path differential bandpass filter tunable from 0.2-1.2 GHz with a bandwidth of 16 MHz is implemented in 65nm CMOS technology. It achieves a maximum gain of 19.5 dB with a minimum noise figure of 2.3 dB. The maximum OOB rejection achieved is 65 dB. The minimum in-band IIP3 recorded is -4.5 dBm. The minimum third and fifth order harmonic rejection achieved is 20 dB and 27 dB, respectively. The proposed filter draws a maximum power of 16 mW from 1.2 V supply at 1.2 GHz tuning frequency.

Generalized frequency division multiplexing (GFDM) is one of the new waveforms with several attractive features such as lower out of band radiation, higher spectral efficiency, and better immunity to carrier frequency offset errors as compared with orthogonal frequency division multiplexing. However, it requires receivers with high computational complexity. Among different linear receiver structures, the joint minimum mean square error (joint-MMSE) receiver for GFDM achieves the best bit-error-rate (BER) performance, but it is the most computationally complex linear receiver. In this paper, we present a novel low complexity joint-MMSE receiver. We derive the closed-form expression for the joint-MMSE receiver filter by harnessing circulant properties of the matrices involved in the demodulation process. Amidst different operations involved in the receiver processing, inversion of a positive definite circulant-plus-diagonal matrix is found to be the costliest. Two low-complexity algorithms for the inversion of a positive definite circulant-plus-diagonal matrix are developed to design the low complexity receiver. We also propose a low complexity bias correction to improve BER performance. Our proposed receiver achieves a log-linear order of complexity without any noticeable loss in BER performance.

The expected operating scenarios of fifth‐generation (5G) pose a great challenge to orthogonal frequency division multiplexing which has poor out of band spectral properties, stringent synchronisation requirements and large symbol duration. Generalised frequency division multiplexing (GFDM) which is the focus of this work has been suggested in the literature as one of the possible solutions to meet 5G requirements. In this study, the analytical performance evaluation of minimum mean square error (MMSE) receiver for GFDM is presented. The authors also proposed precoding techniques to enhance the performance of GFDM. A simplified expression of signal‐to‐interference and noise ratio (SINR) for MMSE receiver of GFDM is derived using special properties related to the modulation matrix of GFDM, which are described in this study. This SINR is used to evaluate the bit error rate performance. Precoding schemes are proposed to reduce complexity of GFDM–MMSE receiver without compromising on the performance. Block inverse discrete Fourier transform (BIDFT) and discrete Fourier transform (DFT)‐based precoding schemes are found to outperform GFDM–MMSE receiver due to frequency diversity gain while having complexity similar to zero‐forcing receiver of GFDM. It is shown that both BIDFT‐ and DFT‐based precoding schemes reduce peak‐to‐average power ratio significantly. Computational complexities of different transmitters and receivers of precoded and uncoded GFDM are also presented.