Publications

Wireless communication paradigm has evolved from single-user single-input single-output (SISO) and multiple-input multiple-output (MIMO) systems to multi-user (MU) MIMO counterparts, which are shown greatly improving the rate performance by transmitting to multiple users simultaneously. The sum-capacity and the capacity region of a single-cell MU MIMO downlink system or the so-called MIMO broadcast channel (MIMO-BC) can be attained by the nonlinear “Dirty Paper Coding (DPC)” scheme [1] [2] [3]. However, DPC requires a high implementation complexity due to the non-linear successive encoding/decoding at the transmitter/receiver, and is thus not suitable for real-time applications. Other studies have proposed to use alternative linear precoding schemes for the MIMO-BC, e.g., the block-diagonalization scheme [4], to reduce the complexity. More information on the key developments of single-cell MIMO communication can be found in, for example, [5] [6] [7].

With the aggravation of aging society and the general trend of home-based elderly care, how to combine community forces to provide all-round protection for the elderly has become an urgent problem to be solved. The system focuses on meeting the diverse needs of the elderly. It is divided into three roles: relatives, the elderly and community administrator. It realizes the functions including health monitoring, meal ordering, entertainment and so on. The system is developed by spring, spring MVC and Mybatis website technology to realize the background management function. The Android system mobile phone is used as the mobile terminal, combined with the sensor function of the mobile phone to identify the falls of the elderly, and uses the smart bracelet to detect the heart rate, so as to provide the basic guarantee for the elderly at home and meet the daily needs of the elderly.

In cognitive radio networks based on spectrum sharing, cognitive beamforming (CB) enables the multi-antenna secondary user (SU) transmitter to suppress the interference to the primary user (PU) receiver and yet maximize the SU link throughput. In our prior work, a design framework was proposed for realizing CB based on finite-rate cooperative feedback from the PU receiver to the SU transmitter. The above cooperative feedback design is based on the orthogonal CB (OCB) algorithm. Specifically, the beamformer at the SU transmitter attempts to null the interference to the PU receiver by restricting the beamformer to be orthogonal to the SU-to-PU channel direction fed back by the PU receiver. In this paper, a new CB algorithm, called non-orthogonal CB (NOCB), is proposed by relaxing the orthogonality constraint for OCB. The NOCB algorithm computes the SU beamformer based on the feedback from the PU receiver including the quantized channel direction information (CDI) and interference power control (IPC) signal that is designed to regulate the SU transmission power. Furthermore, feedforward of the secondary-link CDI from the SU transmitter to the PU receiver is proposed, which enables more efficient IPC feedback design for the SU receiver and thereby allows larger SU transmission power. The proposed NOCB algorithms with cooperative PU feedback and SU feedforward are shown to substantially improve the SU link performance over the existing OCB designs.

Topology control algorithms have been recently studied to reduce the energy consumption in heterogeneous multi-hop wireless networks. Instead of transmitting at full power, these algorithms seek to find the minimum power at which all the nodes should be transmitting while preserving the network connectivity. However, most existing topology control problems have been solved as range assignment problems, which neglect the fact that, in heterogeneous networks, devices have different characteristics. In this paper, we propose the residual energy aware dynamic (READ) topology control algorithm for heterogeneous wireless networks, which is solved as a power assignment problem. As such, READ considers the sensitivity of the receivers, the senders' maximal transmission power, and the nodes' residual energy to determine the final topology. The algorithm dynamically recruits the links that optimize the workload between different wireless devices while keeping the network connected. Simulation results demonstrate that READ can efficiently increase the network lifetime and the packet delivery rate when compared with R&M and LMST, two well-known position-based topology control mechanisms

In this letter, we study the wireless point-to-point communication from a transmitter (Tx) to a receiver (Rx), which is jointly aided by an active intelligent reflecting surface (AIRS) and a passive IRS (PIRS). We consider two practical transmission schemes by deploying the two IRSs in different orders, namely, Tx <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow $ </tex-math></inline-formula> PIRS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow $ </tex-math></inline-formula> AIRS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow $ </tex-math></inline-formula> Rx (TPAR) and Tx <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow $ </tex-math></inline-formula> AIRS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow $ </tex-math></inline-formula> PIRS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow $ </tex-math></inline-formula> Rx (TAPR). Assuming line-of-sight channels, we derive the achievable rates for the two schemes by optimizing the placement of the AIRS with the location of the PIRS fixed. Our analysis shows that when the number of PIRS elements and/or the AIRS amplification power is small, the AIRS should be deployed closer to the Rx in both schemes, and TAPR outperforms TPAR with their respective optimized AIRS/PIRS placement. Simulation results validate our analysis and show the considerable performance gain achieved by the jointly optimized AIRS/PIRS deployment over the existing benchmarks under the same power and IRS element budgets.

A new form of multiuser diversity, named \emph{multiuser interference diversity}, is investigated for opportunistic communications in cognitive radio (CR) networks by exploiting the mutual interference between the CR and the existing primary radio (PR) links. The multiuser diversity gain and ergodic throughput are analyzed for different types of CR networks and compared against those in the conventional networks without the PR link.

In this paper, we investigate the optimal transmission schemes for dying channels, which were introduced in (M. Zeng et al., 2008). The dying channels are resulted in wireless networks subject to random fatal impacts, e.g., sensor networks under sudden physical attacks or cognitive radio networks with unpredictable primary user occupancy. Due to the non-ergodic and delay- limited nature of a dying channel, the outage capacity is adopted as the performance metric. Firstly, we show that the optimal power allocation profile is non-increasing when fading gains are independently and identically distributed (i.i.d.). Secondly, when the fading gains over the blocks are the same, we prove that the optimal number of blocks over which a codeword should be spanned is K = 1. At last, we consider the case where uniform power allocation is utilized and fading gains are i.i.d. In this case, we derive the upper and lower bounds for the outage probability. Moreover, for the high signal-to-noise ratio (SNR) case with Rayleigh fading , we derive analytical results on the optimal number of coding blocks K. For the low SNR case, we show that repetition transmissions are approximately optimal.

The establishment of a comprehensive evaluation model for college students' associations can give a scientific and concrete assessment to the working conditions of each student's associations, and can also play a leading role in the development direction and self-regulation of the students' associations. By using analytic hierarchy process (AHP), the evaluation indexes are determined from three aspects: organization construction, activity development and honor contribution, and a comprehensive evaluation model of college students' associations is set up, which provides ideas for the assessment and development of college associations.

No abstract is provided for this article.

Wireless power transfer (WPT) via dedicated radio frequency (RF) transmission is an appealing technology to provide cost-effective energy supply to low-power devices in the future era of Internet of Things. To achieve efficient power delivery over moderate distance, WPT usually relies on highly directional power transmission from the energy transmitter (ET) to the energy receiver (ER). To this end, the ET needs to be equipped with a large number of antennas and employ adaptive energy beamforming to flexibly control the energy focusing directions to the ER based on the multipath channels between them. However, this renders the conventional fully digital beamforming with one dedicated RF chain for each transmit antenna too costly, in terms of both hardware implementation and energy consumption. To overcome this issue, we study in this paper, a new WPT system based on the hybrid analog or digital beamforming technique, where the number of RF chains is in general significantly less than that of transmit antennas. We first show that for a general point-to-point multiple-input multiple-output WPT system over frequency-selective channels, hybrid beamforming is able to achieve the optimal performance as the fully digital beamforming, as long as the number of RF chains at the ET is no less than twice the number of sub-bands used or twice the number of channel paths. Furthermore, for the special cases of line-of-sight channel or multiple-input single-output WPT, the required number of RF chains can be further reduced to equal the number of channel paths only. Finally, for the scenarios when the given number of RF chains is insufficient to achieve the fully digital beamforming performance, we propose efficient algorithms for the hybrid beamforming design to maximize its efficiency. Numerical results are provided to validate our analytical results and demonstrate the effectiveness of the proposed hybrid beamforming design.

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.

Intelligent reflecting surface (IRS) is a new and promising paradigm to substantially improve the spectral and energy efficiency of wireless networks, by constructing favorable communication channels via tuning massive low-cost passive reflecting elements. Despite recent advances in the link-level performance optimization for various IRS-aided wireless systems, it still remains an open problem whether the large-scale deployment of IRSs in wireless networks can be a cost-effective solution to achieve their sustainable capacity growth in the future. To address this problem, we study in this paper a new hybrid wireless network comprising both active base stations (BSs) and passive IRSs, and characterize its achievable spatial throughput in the downlink as well as other pertinent key performance metrics averaged over both channel fading and random locations of the deployed BSs/IRSs therein based on stochastic geometry. Compared to prior works on characterizing the performance of wireless networks with active BSs only, our analysis needs to derive the power distributions of both the signal and interference reflected by distributed IRSs in the network under spatially correlated channels, which exhibit channel hardening effects when the number of IRS elements becomes large. Extensive numerical results are presented to validate our analysis and demonstrate the effectiveness of deploying distributed IRSs in enhancing the hybrid network throughput against the conventional network without IRS, which significantly boosts the signal power but results in only marginally increased interference in the network. Moreover, it is unveiled that there exists an optimal IRS/BS density ratio that maximizes the hybrid network throughput subject to a total deployment cost given their individual costs, while the conventional network without IRS is generally suboptimal in terms of throughput per unit cost.