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This paper studies the performance of wireless power transfer in distributed antenna systems (DAS). In particular, the distributed remote radio heads (RRHs), which are conventionally distributed in the network to enhance the performance, are also used to increase the energy harvesting (EH) at the energy-constrained users. Based on this idea, the network area is divided into two zones, namely: 1) EH zone and 2) interference zone. The users in the EH zones are guaranteed to harvest sufficient energy from the closed RRH, while the users in the interference zones harvest energy from the surrounding RRHs. A harvest-then-transmit protocol is adopted, where in the power transfer phase the multiple antennas RRHs broadcast energy signals to the users. In the information transmission phase, the users utilize the harvested energy to transmit their signals to the RRHs. In addition, zero-forcing is applied at the RRHs receivers, to mitigate the interference. The system spectral efficiency is evaluated in two different scenarios based on the channel state information (CSI) namely: 1) CSI is unknown at the RRHs 2) CSI is perfectly known at the RRHs. In contrast to conventional EH-muliple-input multiple-output (MIMO) systems, performance analysis of EH DAS-MIMO is a challenging problem, because the channels are characterized by non-identical path-loss and EH effects which make the classical analytical methods non-tractable. In light of this, new analytical expressions of the ergodic spectral efficiency are derived and then Monte Carlo simulations are provided to verify the accuracy of our analysis. The effects of main system parameters on the EH-DAS performance are investigated. The results show that there is an optimal value of the EH time for each users locations that maximizes the system performance. In addition, size of the EH-zone area depends on the required harvested power at the users which is dependent essentially on the target spectral efficiency. [ABSTRACT FROM AUTHOR]

Distributed multiple-input multiple-output (D-MIMO) is a promising technique for next-generation wireless networks, which offers a remarkable spectral efficiency gain over the conventional colocated MIMO (C-MIMO). In contrast to C-MIMO, which can be regarded as a special case of D-MIMO, performance analysis of D-MIMO is a challenging problem. This is because radio channels between a user and the distributed radio ports (RPs) are characterized by nonidentical path-loss and shadowing effects that render the classical analytical methods nontractable. In this paper, new accurate expressions for the uplink spectral efficiency of D-MIMO and C-MIMO systems are presented and compared for given large-scale coefficients. We further consider the uplink spectral efficiency for a single-cell distributed large-scale MIMO (D-LMIMO) system with linear zero-forcing (ZF) receivers that account for path loss along with shadow fading and multipath fading effects. Exact expressions for the average spectral efficiency over shadow fading in the asymptotically very large number of RPs antenna regime is explicitly derived, and a tight closed-form lower bound on the asymptotic spectral efficiency is presented. We demonstrate that, the transmit power of each user in D-LMIMO can be scaled down proportionally to the inverse of the number of RP antennas with no performance reduction. Moreover, we study the spectral efficiency of a D-MIMO in a multicell environment taking into account accurate cochannel interference (CCI) models. These expressions provide meaningful insights into the impact of signal-to-noise ratio (SNR), RPs and user positions, number of RPs antennas, shadow fading, and out-of-cell interference on the spectral efficiency of D-MIMO over practical scenarios. Finally, numerical results are validated by simulation to confirm our analysis. [ABSTRACT FROM AUTHOR]

In this paper, we consider a wireless-powered communication network in which a multiple-antenna two-way AF relay transfers power to multi-pair of single antenna users. A harvest-then-transmit protocol is adopted where the relay first broadcasts wireless power to all the users during a power transfer phase. Multiple pairs of users then use the harvested energy to exchange information through the relay over two phases: up-link and down-link. In the up-link phase, all the users transmit their independent signals to the relay, whereas in the down-link phase, the relay amplifies and forwards the received signals to the intended users. In order to mitigate the interference, zero-forcing reception and transmission is applied at the relay. To characterize system performance, we consider ergodic spectral and energy efficiencies in three different cases based on the knowledge of the channel state information (CSI) at the relay in the power transfer phase, namely: 1) unknown CSI; 2) partially known CSI; and 3) perfectly known CSI. In light of this, new analytical expressions for the ergodic spectral and energy efficiencies are derived for the three cases and Monte Carlo simulations are provided throughout to validate our analysis. The impacts of some important system parameters, such as energy harvesting time, energy harvesting efficiency, number of user-pairs, and relay antennas, on the adopted performance metrics are investigated. [ABSTRACT FROM PUBLISHER]

This letter investigates the trade-off between the downlink ergodic spectral efficiency (ESE) and the energy efficiency (EE) of distributed antenna systems (DAS) by using a new mathematical approach. Maximum ratio transmission (MRT) and fractional frequency reuse (FFR) are applied and composite Nakagami- m fading and log-normal shadowing are considered. The performance evaluation of DAS in FFR mode using MRT is greatly simplified using the proposed analytical approach. [ABSTRACT FROM PUBLISHER]

Orthogonal frequency division multiplexing (OFDM) over wireless channels is sensitive to carrier frequency offset (CFO), which destroys orthogonality amongst sub-carriers, giving rise to inter-carrier interference (ICI). Different techniques are available for estimating and compensating for the CFO at the receiver. However, in practice, a residual CFO remains at the receiver after CFO estimation, where the estimation accuracy depends primarily on the fractions of time and power used by the estimator. In this paper, we propose to measure the efficiency of OFDM systems with CFO estimation errors in terms of the spectral efficiency, which accounts for both, the degradation in signal-to-interference plus noise ratio (SINR) due to the residual CFO, and the penalty of the extra power and spectral resources allocated to achieve the desired CFO estimation accuracy. New accurate expressions are derived for the spectral efficiency of wireless OFDM systems in the presence of residual CFO and frequency-selective multipath fading channel. These are used to compare between two common CFO estimation methods in wireless OFDM systems, namely, the cyclic prefix based and the training symbols based CFO estimation techniques for fixed and variable pilot power. These results are further extended to include OFDM systems with transmit diversity techniques. In addition, the impact of imperfect channel estimation on the overall spectral efficiency is also included. Numerical results reveal that the cyclic prefix based CFO technique is more efficient than the training symbols based CFO technique when perfect channel state information (CSI) is known blindly at the receiver. Furthermore, fixed pilot power results in a spectral efficiency ceiling as SNR increases, whereas spectral efficiency increases with SNR without bound in the equal pilot and signal powers case. [ABSTRACT FROM PUBLISHER]

Multiple-access interference (MAI) and intercarrier interference (ICI) due to a carrier frequency offset are two major factors that deteriorate the performance of multicarrier code-division multiple access (MC-CDMA) in wireless communications. This paper presents a new mathematical analysis for the spectral efficiency of asynchronous MC-CDMA communication systems over a frequency-selective Rayleigh fading environment. It employs accurate statistical models for MAI and ICI that account for the correlation between adjacent subcarriers to derive a new simple expression. An approximate expression for the spectral efficiency is also provided, which reduces complexity. [ABSTRACT FROM AUTHOR]