Sum-rate optimization for movable antenna enabled wireless powered communication network

In this paper, we study two schemes for the fair resource allocation in wireless powered communication networks (WPCNs): a non-orthogonal multiple access (NOMA) scheme, and a proportional fair (PF) scheduling scheme. The considered WPCN consists of a base station (BS) that broadcast radio frequency (RF) energy over the downlink, and N energy harvesting users (EHUs). If NOMA is employed, all EHUs concurrently transmit information over the uplink with successive interference cancellation employed at the BS. If PF scheduling is employed, a single EHU is selected for uplink transmission in each frame. For both schemes, we arrive at optimal allocations for the BS transmit power and the time sharing between uplink and downlink transmissions that maximize the uplink sum-rate, while maintaining high level of system fairness. For the PF scheme, we also derive the optimal scheduling policy. Compared to the state-of-the art schemes based upon time division multiple access (TDMA), both schemes significantly improve the system fairness at the expense of minor (or nonexistent) rate degradation. Key words: energy harvesting; wireless powered communication networks; non-orthogonal multiple access; successive interference cancelation; proportional fair scheduling REFERENCES: [1] P. Grover, A. Sahai: Shannon meets Tesla: wireless information and power transfer, Proc. IEEE ISIT 2010, pp. 2363–2367, Austin, USA, June 2010. [2] D. Gunduz, K. Stamatiou, N. Michelusi, M. Zorzi: Designing intelligent energy harvesting communication systems, IEEE Commun. Magazine, 52, 1, 210–216 (Jan.2014). [3] C. K. Ho, R. Zhang: Optimal energy allocation for wireless communications with energy harvesting constraints, IEEE Trans. Signal Proccessing, 60, 9, 4808–4818 (May 2012). [4] H. Ju, R. Zhang: Throughput maximization in wireless powered communication networks, IEEE Trans. Wireless Commun., 13, 1, 418–428 (Jan. 2014). [5] X. Kang, C. Ho Keong, S. Sun: Optimal time allocation for dynamic-TDMA-based wireless powered communication networks, Proc. IEEE Globecom 2014, Austin, USA, Dec. 2014. [6] H. Ju, R. Zhang: Optimal resource allocation in full-duplex wireless-powered communication network, IEEE Trans. on Commun., 62, 10, 3528–3540 (Oct. 2014). [7] T. Takeda, K. Higuchi: Enhanced user fairness using non-orthogonal access with SIC in cellular uplink, VTC 2011, San Francisco, USA, pp. 1–5, 2011. [8] Z. Ding, Z. Yang, P. Fan, H. V. Poor: On the performance of non-orthogonal multiple access in 5G systems with randomly deployed users, IEEE Signal Process. Lett., 21, 12, 1501–1505 (2014). [9] S. Timotheou, I. Krikidis: Fairness for non-orthogonal multiple access in 5G systems, IEEE Signal Process. Lett., 22, 10, 1462–1465 (2015). [10] H. Chingoska, Z. Hadzi-Velkov, I. Nikoloska, N. Zlatanov: Resource Allocation in Wireless Powered Communication Networks with Non-Orthogonal Multiple Access, IEEE Wireless Communications Letters, 5 (6), 684–687 (2016). [11] P. Viswanath, D. N. Tse, R. Laroia: Opportunistic beamforming using dumb antennas, IEEE Trans. Information Theory, 46, 6, 1277–1294 (June 2002). [12] N. Tekbiyik, T. Girici, E. Uysal-Biyikoglu, K. Leblebicioglu: Proportional fair resource allocation on an energy harvesting downlink, IEEE Trans. Wireless Communications, 12, 4, 1699–1711 (April 2013). [13] H. Chingoska, I. Nikoloska, Z. Hadzi-Velkov, N. Zlatanov: Proportional fair scheduling in wireless powered communication networks, 23rd International Conference on Telecommunications (ICT), May 2013. [14] Z. Hadzi-Velkov, I. Nikoloska, H. Chingoska, N. Zlatanov, Proportional fair scheduling in wireless networks with RF energy harvesting and processing cost, IEEE Comm. Letters, 20, 10, 2107–2110 (2016). [15] T.-D. Nguyen, Y. Han: A Proportional Fairness Algorithm with QoS Provision in Downlink OFDMA Systems, IEEE Comm. Letters, 10, 11 (Nov. 2006). [16] Z. Hadzi-Velkov, I. Nikoloska, G. K. Karagiannidis, T. Q. Duong: Wireless networks with energy harvesting and power transfer: joint power and time allocation, IEEE Signal Process. Letters, 23, 1, 50–54 (Jan. 2016). [17] R. Jain, D. Chiu, W. Hawe: A Quantitative measure of fairness and discrimination for resource allocation in shared computer systems, Tech. Rep. TR-301, DEC, September 1984. [18] W. Yu, R. Lui: Dual methods for nonconvex spectrum optimization of multicarrier systems, IEEE Trans. Commun., 54, 7, 1310–1322 (Jul. 2006). [19] L. Liu, R. Zhang, K.-C. Chua: Wireless information transfer with opportunistic energy harvesting, IEEE Trans. Wireless. Commun., 12, 1, 288–300 (Jan. 2013).

The optimal energy signal design for wireless powered communication networks (WPCNs) enabling energy-sustainable communication for a large number of low-power devices is still an open problem in practical systems. In this work, we study a multi-user WPCN, where a multi-antenna base station (BS) sends an energy signal to multiple single-antenna users, which, in turn, harvest energy from the received signal and utilize it for information transmission in the uplink. In contrast to the existing works on multiple-input single-output (MISO) WPCN design, in this paper, we jointly optimize the energy signal waveform and downlink beamforming at the BS for energy harvesting (EH) devices described by non-linear circuit-based models. To this end, we assume that the BS broadcasts a pulse-modulated signal employing multiple energy signal vectors and we formulate an optimization problem for the joint design of the downlink transmit energy signal vectors, their number, the durations of the transmit pulses, and the time allocation policy for minimization of the average transmit power at the BS. We show that for single-user WPCNs, a single energy signal vector, which is collinear with the maximum ratio transmission (MRT) vector and drives the EH circuit at the user device into saturation, is optimal. Next, for the general multi-user case, we show that the optimal signal design requires a maximum number of energy signal vectors that exceeds the number of users by one and propose an algorithm to obtain the optimal energy signal vectors. Since the complexity of the optimal design is high, we also propose two suboptimal schemes for WPCN design. First, for asymptotic massive WPCNs, where the ratio of the number of users to the number of BS antennas, i.e., the system load, tends to zero, we show that the optimal downlink transmit signal can be obtained in closed-form and comprises a sequence of weighted sums of MRT vectors. Next, based on this result, for general WPCNs with finite system loads, we propose a suboptimal closed-form MRT-based design and a suboptimal semidefinite relaxation (SDR)-based scheme. Our simulation results reveal that the proposed optimal scheme and suboptimal SDR-based design achieve nearly identical performance and outperform two baseline schemes, which are based on linear and sigmoidal EH models. Furthermore, we show that, if the system load of the WPCN is low, the performance gap between the proposed suboptimal solutions is small and becomes negligible as the number of BS antennas tends to infinity.

Wireless powered communication network (WPCN) is a new networking paradigm where the battery of wireless communication devices can be remotely replenished by means of microwave wireless power transfer (WPT) technology. WPCN eliminates the need of frequent manual battery replacement/recharging, and thus significantly improves the performance over conventional battery-powered communication networks in many aspects, such as higher throughput, longer device lifetime, and lower network operating cost. However, the design and future application of WPCN is essentially challenged by the low WPT efficiency over long distance and the complex nature of joint wireless information and power transfer within the same network. In this article, we provide an overview of the key networking structures and performance enhancing techniques to build an efficient WPCN. Besides, we point out new and challenging future research directions for WPCN.

This paper considers a single-antenna wireless- powered communication network (WPCN) over a flat- fading channel. We show that, by using our probabilistic harvest-and-transmit (PHAT) strategy, which requires the knowledge of instantaneous full channel state information (CSI) and fading probability distribution, the ergodic throughput of this system may be greatly increased relative to that achieved by the harvest-then- transmit (HTT) protocol. To do so, instead of dividing every frame to the uplink (UL) and downlink (DL), the channel is allocated to the UL wireless information transmission (WIT) and DL wireless power transfer (WPT) based on the estimated channel power gain. In other words, based on the fading probability distribution, we will derive some thresholds that determine the association of a frame to the DL WPT or UL WIT. More specifically, if the channel gain falls below or goes over these thresholds, the channel will be allocated to WPT or WIT. Simulation results verify the performance of our proposed scheme.

Wireless power transfer (WPT) plays a critical role in relaxing concerns related to limited operational lifetime of wireless networks. Different from traditional network devices, which rely on batteries for their energy need, devices in wireless powered communication networks (WPCNs) are able to scavenge energy from radio-frequency (RF) signals. As such, it eliminates the burden of battery recharging and/or replacement and hence provides networks with theoretically perpetual lifespans. However, due to the dramatic growth of wireless data traffic and the rapid movement towards the so-called Internet of Things (IoT), WPCNs are facing security and throughput challenges in which the traditional mechanisms are not sufficient to satisfy the user requirements. Its network performance is therefore compromised. In this chapter, we first provide an overview of the WPCNs by introducing the background of WPT, followed by a summary of the research conducted in the field. We then describe the physical-layer security (PLS) problem in WPCNs, including the causes and the impacts of the problem on the performance of WPCNs. At last, we close this chapter by discussing the applications of WPCNs in the IoT.

This paper focuses on solving a special kind of multimodal multi-objective optimization problems (MMOPs) in which solutions are of variable length. First, problem definition and solution framework is suggested to allow using standard multimodal multi-objective evolutionary algorithms (MMEAs) to solve the considered type of problems. Next, a real-life example of the considered type of problems is suggested concerning optimal antennas’ layout-allocation design for a wireless communication network. Finally, a modification to NSGA-II is suggested and employed to solve such layout problems. When compared with other MMEAs, it is shown that the proposed algorithm provides not only better solution diversity in the decision-space, but also solutions with superior performance vectors. It is suggested here that this is attributed to the type of archive that is used here.

Wireless powered communication network (WPCN) is a novel networking paradigm that uses radio frequency (RF) wireless energy transfer (WET) technology to power the information transmissions of wireless devices (WDs). When energy and information are transferred in the same frequency band, a major design issue is transmission scheduling to avoid interference and achieve high communication performance. Commonly used centralized scheduling methods in WPCN may result in high control signaling overhead and thus are not suitable for wireless networks constituting a large number of WDs with random locations and dynamic operations. To tackle this issue, we propose in this paper a distributed scheduling protocol for energy and information transmissions in WPCN. Specifically, we allow a WD that is about to deplete its battery to broadcast an energy request buzz (ERB), which triggers WET from its associated hybrid access point (HAP) to recharge the battery. If no ERB is sent, the WDs contend to transmit data to the HAP using the conventional $p$-persistent CSMA (carrier sensing multiple access). In particular, we propose an energy queueing model based on an energy decoupling property to derive the throughput performance. Our analysis is verified through simulations under practical network parameters, which demonstrate good throughput performance of the distributed scheduling protocol and reveal some interesting design insights that are different from conventional contention-based communication network assuming the WDs are powered with unlimited energy supplies.

In order to address the energy shortage in communication networks, RF signals are exploited for transferring energy to miniature devices, which yields wireless powered communication networks (WPCNs). A full-duplex aided hybrid-base-station (H-BS) is conceived in a WPCN for simultaneously transferring energy during downlink transmissions and receiving data during uplink transmissions. UEs may deplete all the energy received from the H-BS for supporting their own uplink transmissions. In this full-duplex WPCN, A joint time allocation and UE scheduling algorithm is proposed for the sake of maximising the sum-uplink-throughput of multiple UEs by further considering UEs' actual data uploading requirements. The numerical results demonstrate that the suboptimal solution is capable of achieving almost the same performance with its optimal counterparts, while our scheme outperforms other existing peers in terms of the sum-uplink-throughput.

This paper studies cooperation between two users in a wireless powered communication network (WPCN) with a pricing mechanism for energy saving. First, a two-user WPCN of one hybrid access point (H-AP) with a constant power supply is considered, while in the downlink (DL), wireless energy is transmitted to two users and in the uplink (UL) individually harvested energy is used to transmit independent information from users to the H-AP. Based on the “doubly near-far” phenomenon, a WPCN with user cooperation is proposed where the near user (U2) uses harvested extra energy to help the far user (U1) to relay information to the H-AP. Furthermore, a pricing mechanism is proposed to incentivize uplink cooperative communications to achieve energy saving for the far user (U1). In the ideal case with full cooperation, the payment of U2 equals the energy used by U1 to relay information. However, with partial cooperation, U2 expects to receive extra reward. This paper formulates the U1's pricing and relay data in an ideal case and also considers the communication mode selection and cooperation distance constraints. Finally, numerical simulation results show that the proposed cooperative communication of WPCN with pricing can significantly the decrease far user's expected cost and can also increase the reliability of user's communication in WPCN.

The wireless powered communication networks (WPCN) is a new networking paradigm which only considers energy transmission in the downlink, no the need for information transmission. In many applications of WPCN, it is necessary to consider transmit information in the downlink. How to develop a transmission strategy to weigh the fairness and maximization of each user’s uplink throughput is a research hotspot in WPCN. This paper proposed a new design scheme for joint transmission of energy and information in a strongly interfered multi-cell network. It combined simultaneous transmission of downlink wireless information and energy with WPCN to realize downlink energy transmission and two-way information transmission between base station and users. In this scheme, uplink power allocation, downlink time allocation and beamforming were used to maximize the minimum transmission rates of both uplink and downlink, so that made a tradeoff between performance and fairness of uplink and downlink information transmission for each user. Simulation results show that compared with the traditional transmission method, the proposed scheme significantly improves the minimum transmission rate of the users.

Current wireless and cellular networks are destined to undergo a significant change in the transition to the next generation of network technology. The so called wireless powered communication network (WPCN) has been recently emerging as a promising candidate for achieving the target performance of future networks. According to this paradigm, nodes in a WPCN can be equipped with hardware capable of harvesting energy from wireless signals, that is, their battery can be ubiquitously replenished without physical connections. Recent technological advances in the field of wireless power harvesting and transfer are providing strong evidence of the feasibility of this vision, especially for low-power devices. The future deployment of WPCN is more and more concretely foreseen. The aim of this article is therefore to provide a comprehensive review of the basics and backgrounds of WPCN, current major developments, and open research issues. In particular, we first give an overview of WPCN and its structure. We then present three major advanced approaches whose adoption could increase the performance of future WPCN: backscatter communications with energy harvesting; duty-cycle based energy management; and transceiver design for self-sustainable communications. We discuss implementation perspectives and tools for WPCN. Finally, we outline open research problems for WPCN.

In this paper, we apply the notion of opportunistic scheduling in wireless-powered communication networks (WPCNs). The considered WPCN model consists of a base station (BS) and multiple energy harvesting users (EHUs), where the BS broadcasts radio frequency energy to the EHUs over the downlink and receives information from the EHUs over the uplink. We differentiate the WPCNs based upon the battery management policy at the EHUs, i.e., whether an EHU spends the total amount of energy harvested in its battery for each IT (WPCN type 1), or spends only a part of it for the current IT and saves the other part for future ITs (WPCN type 2). We propose two opportunistic scheduling policies, referred to as the harvest-then-select and harvest-or-select protocols, employed at the WPCN type 1 and WPCN type 2, respectively. These protocols have significant practical advantages over the state-of-the-art schemes proposed for maximizing the WPCN sum-rate, because they introduce fairness in the resource utilization by the EHUs, and require much lower amount of channel state information. Both protocols achieve these benefits at the expense of a minor rate degradation relative to the rates achieved by their counterpart protocols employing multiple access, denoted as the harvest-then-transmit and harvest-or-concurrently-transmit protocols.

This paper considers user cooperation and a pricing mechanism in a wireless-powered communication network (WPCN) in which two users harvest energy from a dedicated hybrid access point (H-AP), which has a constant power supply and acts as a power station during a downlink (DL). They also independently transmit their information to the H-AP [which acts as an information receiving station during an uplink (UL)] using the individually harvested energy. Based on the “doubly near-far” problem, this paper proposes a cooperative scheme among users in the WPCN. Compared with the source user (SU), the channel conditions for a helping user (HU), which is closer to the H-AP, is usually better for DL energy harvesting and for transmitting UL information. Thus, the HU can use its harvested energy to forward the SU’s information to the H-AP. Furthermore, energy is usually scarce for each user in a WPCN; therefore, the HU is under no obligation to accept the SU’s cooperative request and can choose to act selfishly to conserve resources. This paper presents a new pricing strategy to motivate the HU to sell its excess energy to help an SU complete a UL information transfer. Two transmission protocols are investigated: in the ideal case, the energy expenditure of the SU equals the energy used by the HU to relay information; in the normal case, the HU seeks additional profit. This paper formulates the SU’s expenditures and relay data in the ideal case as an optimization problem. An investigation of relay placement and the SU communication mode selection problem are also discussed. The numerical results show that the proposed pricing strategy can significantly reduce the expected costs to the SU and improve the reliability of user UL communications in a WPCN.

Far-field wireless energy transmission and energy harvesting have emerged out recently as a potential alternative source to power the next generation communication networks. The capability to provide stability, controllable and on-demand power source in the low power communication devices which present at a distance is realized through the integration of an RF energy harvesting circuit integrated into the device or information receiving unit. This research work is based on a comprehensive survey on the progress of wireless powered communication networks (WPCN) over the past few years. It firstly discusses an overview of the RF energy harvesting communication networks with system architecture, power management techniques used at the receiver and existing techniques available in the literature for the enhancement of WPCN. Energy beamforming in both microwave and mmWave based WPCN are surveyed with specific insights on the evolving of efficient beamforming algorithms for enhancing system performance. Some important technical challenges and research directions are also derived with a purpose to give researchers useful insights in this emerging area of research having a huge scope of improvements in the near future of green communication technology.

We study data fusion schemes for early detection of anomalies in an interconnected power grid and communication network, where power nodes rely on the real-time control via communication nodes, which in turn, depend on the former for power supply. Based on a key observation that failures are spatially correlated and propagate through neighboring nodes, we propose a data fusion scheme, which scans an anomalous cluster, i.e., a connected component of nodes, in each individual network. We show that the proposed scheme can detect weaker signals of anomalies, compared to baseline approaches, and further its detection capability increases with the size of the anomalous cluster. This finding leads us to further exploit the interdependent structure of failures across two networks and design a more powerful data fusion scheme, which jointly detects an anomalous cluster over the two interconnected networks. To analyze the detection gain of the joint data fusion scheme, we first characterize how quickly the anomalous behavior propagates, in both the power grid and the power- communication network, based on random graph and epidemic models. We then present numerical results to quantify the detection gain of the joint data fusion scheme.