Energy efficiency (EE) and spectral efficiency (SE) are among the key performance metrics for any wireless standards. In this work, we study the trade-off between EE-SE for supporting the downlink data rate as well as opportunistically harvesting the ambient radio frequency (RF) energy. The goal is to maximize EE while maintaining the requisite data rate for the downlink. We consider a case of downlink full duplex multi-input single-output (MISO) system where the transmitter having multiple antennas is transmitting to a user equipped with single antenna. At the transmitter, few antennas are reserved for selfenergy recycling (S-ER) while the remaining antennas are utilized for information transmission. S-ER enhances the EE of the system at the expense of SE due to loss in the array gain. In order to improve the SE, we incorporate the adaptive S-ER scheme which utilizes selection of antennas corresponding to higher gains for information transmission. This compensates the loss in the SE along with the increase in EE of the system. Both linear and nonlinear transmitter cases have been considered for analyzing the trade-off and the simulation results are shown by obtaining the outage probability.

In this paper, we evaluate the performance of carrier aggregated dual band (DB) multi- user (MU) multi-input-multi- output (MIMO) orthogonal frequency division multiplexing (OFDM) system in the presence of transmitter nonlinearity and frequency-selective fading channels. As a benchmark, the performance has been compared with a linear DB MU-MIMO-OFDM system which employs a conventional transmit preprocessing technique to mitigate the inter-user interference. A two-dimensional (2D) memory polynomial (MP) is considered to model the transmitter nonlinearity. We show that transmitter nonlinearity leads to nonlinear interference in a DB MU-MIMO- OFDM system which can not be eliminated by the conventional transmit preprocessing techniques. As a consequence, there is an irreducible error floor which degrades the performance of the nonlinear DB MU-MIMO-OFDM systems. We have also shown that the irreducible error floor is the function of number of aggregated bands as well as number of users present in the system. The impact of number of bands and users has been shown by comparing the symbol error rates of a nonlinear single band (SB) MU- MIMO-OFDM system vis-a-vis nonlinear DB MU-MIMO-OFDM system for a multi-path frequency selective Rayleigh fading channel.

Device to Device (D2D) communication is one of the key enhancement of Long-Term Evolution (LTE) Advanced standard which is a precursor to fifth generation (5G) cellular standard. D2D has gained considerable attention due to several drawbacks associated with the existing mobile networks such as multi-hop transmission, higher latency, high power consumption and significant path loss. In an underlay D2D communication, both cellular and D2D users coexist by simultaneously sharing the licensed cellular spectrum. However, the performance of an underlay D2D communication is limited by the amount of interference from the cellular user(CU) to the D2D user and vice versa. In this paper, we design and develop a test-bed to evaluate the real-world performance of the underlay D2D communication framework. We demonstrate the impact of interference caused by CU on D2D receiver's throughput at different cellular angles and position with respect to the base station (BS). The demonstration has been performed on National Instruments Universal Software Radio Peripheral (USRP) RIO platform with LTE application framework module of LabVIEW communication system design suite as a supportive Application programming interface (API).

This paper presents the theoretical characterization of the impact of nonlinear amplification on the spectral content of a carrier aggregated orthogonal frequency division multiplexing (CA-OFDM) system. Specifically, we derive a simplified mathematical expression of power spectral density (PSD) at the output of a nonlinearly amplified dual band CA-OFDM system. We show that nonlinear distortions caused due to nonlinear amplification severely affects the spectral content of dual band CA-OFDM signal, thus considerably increasing the adjacent channel power ratio (ACPR) at the output. Further, through the obtained results, we also demonstrate that the nonlinear amplification has far more adverse impact on a CA-OFDM system vis-a-vis non-aggregated OFDM system. A two-dimensional (2D) enhanced Hammerstein (EH) model is used to model the nonlinear behavior of the transmitter due to high power amplifier (HPA). A good agreement between the theoretical and simulation results demonstrates the accuracy of our analysis.

Recent studies have shown that carrier-aggregated multi-user (MU) multi-input-multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems can deliver unprecedented improvements in network throughput and capacity when compared with existing systems. However, most of these studies fail to take into account the nonlinear constraints that limit the performance of such systems. This paper proposes an analytical framework to evaluate the end-to-end performance of a carrier-aggregated dual-band (DB) MU-MIMO-OFDM system in the presence of transmitter nonlinearity. Specifically, we derive the closed-form expression for signal-to-interference-plus-noise ratio (SINR) and further utilize this expression to evaluate the average capacity and symbol error rate of a nonlinear DB MU-MIMO-OFDM system in a multi-path Rayleigh fading channel. We show that the transmit preprocessing technique conventionally used to mitigate inter-user interference in a linear DB MU-MIMO-OFDM system fails to eliminate inter-user interference in a nonlinear DB MU-MIMO-OFDM system. As a consequence, there is an irreducible error floor which is function of number of aggregated bands as well as number of users present in the system. The irreducible error floor has been shown to considerably deteriorate the performance of nonlinear DB MU-MIMO-OFDM system. Simulation results are also reported to validate the efficacy of the proposed analysis.

This paper analyzes the impact of nonlinear distortion caused by high power amplifier (HPA) on a dual band carrier aggregated multi input multi output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. A two dimensional (2D) general memory polynomial (GMP) has been used to characterize the behavioural model of HPA. The inband and cross modulation distortion, caused by nonlinear HPA on the carrier aggregated MIMO-OFDM system can be modelled in terms of complex phase shift and Gaussian nonlinear noise that distorted the received data symbol. The mathematical expressions for the complex phase shift and variance of Gaussian nonlinear noise have been formulated. Furthermore, this analysis is also augmented to evaluate the overall performance of aggregated MIMO-OFDM system in terms of probability of symbol error for Mary quadrature amplitude modulation (M-QAM) in presence of multi-path Rayleigh fading channel. Simulation results demonstrate the validity of analytically derived expressions.