This paper shows that wirelessly powered backscatter communications is subject to a fundamental tradeoff between the harvested energy at the tag and the reliability of the backscatter communication, measured in terms of SNR at the reader. Assuming the RF transmit signal is a multisine waveform adaptive to the channel state information, we derive a systematic approach to optimize the transmit waveform weights (amplitudes and phases) in order to enlarge as much as possible the SNRenergy region. Performance evaluations confirm the significant benefits of using multiple frequency components in the adaptive transmit multisine waveform to exploit the nonlinearity of the rectifier and a frequency diversity gain.

Wireless power transfer and backscatter communications have emerged as promising solutions for energizing and communicating with power limited devices. Despite some progress in wirelessly powered backscatter communications, the focus has been concentrated on backscatter and energy harvester. Recently, significant progress has been made on the design of transmit multisine waveform, adaptive to the Channel State Information at the transmitter (CSIT), in point-to-point backscatter system. In this paper, we leverage the work and study the design of transmit multisine waveform in a multiuser backscatter system, made of one transmitter, one reader and multiple tags active simultaneously. We derive an efficient algorithm to optimize the transmit waveform so as to identify the tradeoff between the amount of energy harvested at the tags and the reliability of the communication, measured in terms of Signal-to-Interference-plus-Noise Ratio (SINR) at the reader. Performance with the optimized waveform based on linear and nonlinear energy harvester (EH) models are studied. Numerical results demonstrate the benefits of accounting for the energy harvester nonlinearity, multiuser diversity, frequency diversity and multisine waveform adaptive to the CSIT to enlarge the SINR-energy region.tags can operate with low power as they do not require RF components to generate carrier signal. Although backscatter communications has originally been limited to simple radio frequency identification (RFID) applications, it has received a renewed interests in recent years with advances in backscatter communication theory, including coding [5], beamforming [4], performance analysis of large networks [6], [7].RF transmitter in backscatter communications typically transmit sinusoidal continuous waveform (CW). Significant progress has recently been made on the waveform design in wireless power transfer (WPT), in order to improve the efficiency and DC output power of the energy harvester. In particular, [8] studies the nonlinear behaviour of RF-to-DC converter and suggests that significant DC power gain can be obtained by using multisine waveform with zero phase between the sinewaves. In [9], a multisine waveform transmission has been introduced to extend the reading signal.[10] presented multisine waveform method to improve power sensitivity of the tags and conduct a survey of reading range improvement for several commercial RFID tags. Motivated by the promising gains, a systematic approach towards waveform design for WPT was proposed in [11]. In [11], optimized multisine waveforms, adaptive to the CSIT, have been shown to provide significant gain by exploiting the rectifier nonlinearity and the frequency selectivity of the channel.Backscatter communication can leverage this recent progress in WPT waveform design and depart from the conventional CW transmission. Recently, [12] studies the tradeoff between harvested energy and backscatter communication in point-to-point deployment. It is noted that waveform design for WPT and backscatter communicati...

In this paper, we study the Simultaneous Wireless Information and Power Transfer (SWIPT) in a Single-Input Single-Output (SISO) two-user Orthogonal Frequency Division Multiplexing (OFDM) Interference Channel (IFC). We assume that the transmitters are non-cooperative and have perfect knowledge of the local Channel State Information (CSI). We show that the necessary condition for the optimal transmission strategy at high SNR is for the energy transmitter to transmit its signal by allocating its transmit power on a single subcarrier. Accordingly, we propose a one-subcarrier selection method for the energy transmitter and identify the achievable rate-energy region. In addition, we further enlarge the achievable rate-energy region by enabling a basic form of transmitter cooperation where messages are exchanged to inform the energy transmitter about the subcarriers unutilized by the information transmitter.

Cache-enabled Fog radio access network (F-RAN) is a promising technology to alleviate the traffic congestion and boost the contents delivery success rate. The efficiency of disseminating the cached contents in F-RAN can be boosted by enabling multicast service at the fog access points (F-APs). This paper proposes a joint random caching and multicasting optimization scheme for wireless backhauled F-RAN. Using tools from stochastic geometry, the expression of the successful transmission probability (STP) is derived by carefully analyzing the different types of serving F-APs and interferers. Then, a closedform expression of the asymptotic STP in the high SNR region is derived to reduce the complexity. The joint caching and multicasting optimization problem is formulated to maximize the STP. The optimization problem is complex and non-convex in general. A novel projected cuckoo search algorithm (PCSA) is proposed to obtain the optimal content placement that maximizes the STP. The numerical simulation results show that PCSA outperforms the original cuckoo search algorithm (CSA) and the proposed asymptotically joint caching and multicasting scheme outperforms the benchmark caching schemes by up to 15% higher STPs.

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