Stephen Wang

Energy-Efficient Spectrum Sensing and Access for Cognitive Radio Networks

We consider a cognitive radio system with one secondary user (SU) accessing multiple channels via periodic sensing and spectrum handoff. We propose an optimal spectrum sensing and access mechanism such that the average energy cost of the SU, which includes the energy consumed by spectrum sensing, channel switching, and data transmission, is minimized, whereas multiple constraints on the reliability of sensing, the throughput, and the delay of the secondary transmission are satisfied. Optimality is achieved by jointly considering two fundamental tradeoffs involved in energy minimization, i.e., the sensing/transmission tradeoff and the wait/switch tradeoff. An efficient convex optimization procedure is developed to solve for the optimal values of the sensing slot duration and the channel switching probability. The advantages of the proposed spectrum sensing and access mechanism are shown through simulations.

Antenna selection based spectrum sensing for cognitive radio networks

In a cognitive radio system, the accuracy of spectrum sensing is critical for both primary and secondary systems. Both cooperative sensing and single-user multiple-antenna techniques have been proposed in the literature to enhance the accuracy of spectrum sensing. However, these techniques may require additional signaling and hardware costs, and can lead to user reliability problems or energy consumption issues. To avoid these problems, we propose a scheme that requires no extra signaling and low hardware costs, while still offering substantial diversity gains for enhancing the sensing performance. This is achieved by combining antenna selection with the spectrum sensing mechanism. We analyze the diversity order of the proposed scheme and show that no loss occurs relative to the case of single-user multiple-antenna sensing. This benefit is achieved while keeping a low implementation complexity as only a subset of RF chains are used in a given time period. Simulations show that a substantial sensing gain can be obtained compared to using other traditional multiple-antenna techniques in some practical cases.

Reliable energy-efficient spectrum management and optimization in cognitive radio networks: how often should we switch?

Spectrum handoff is a promising spectrum management approach that enables the secondary user to continue its transmission by switching to a sensed-as-idle channel when the current channel is re-occupied by the primary user. Periodic sensing is commonly employed to facilitate spectrum handoff by improving sensing accuracy so that the secondary user has a better opportunity to avoid transmission collision via switching to a truly idle channel. However, byproducts of spectrum handoff, such as extra energy cost on channel switch, switch delay, and collisions due to excessive switch, have been largely underestimated. These by-products which have significant impacts on the overall performance lead to the questions: Should we switch the channel? How often should we switch? In this article we first review several different periodic sensing and handoff mechanisms. Then we identify the trade-off between the secondary users energy efficiency and transmission reliability. The proposed switch-stay model is elaborated and studied to balance the aforementioned trade-off in light of sensing accuracy, the probability of collision, throughput and delay constraints. Upper and lower bounds of the stay probability on the current channel are illustrated from these constraints. In addition, we discuss the implementation of an antenna-selection sensing mechanism in order to relax these bounds for a better energy-efficient spectrum management solution. Performance evaluation and some open issues are also discussed in this article.

Cognitive antenna selection relay for green heterogeneous healthcare networks

This article presents the latest progress on green healthcare research in heterogeneous networks (HetNet), where devices are capable of switching between multiple radio access technologies (RAT) and each RAT operates on a different frequency channel. After outlining the design features and challenges of a medical service paradigm for green cognitive medical body area networks (MBAN), measurements are made to investigate the turn-on characteristics of a power amplifier (PA) in terms of excess energy consumption and turn-on delay. We then present a multi-mode PA architecture for an MBAN relay system. An energy-efficient PA switch/stay mechanism is also presented. This allows the proposed PA architecture to operate given a transmission outage probability and transmission delay constraint. Antenna selection between two heterogeneous RATs is exploited to improve the transmission reliability. Both measurement and numerical results are provided to corroborate the performance of the proposed architecture and its switch/stay mechanism.

Measurement-based massive MIMO channel modeling in 13–17 GHz for indoor hall scenarios

In this contribution, a recently conducted measurement campaign is introduced for investigating the characteristics of propagation channels for massive multiple-input multiple-output (MIMO) scenarios in a lecture hall environment. The channel responses for waves of higher frequency band ranging from 13 GHz to 17 GHz was measured with a vertically standing virtual two-dimensional (2-D) 20 × 20 = 400-element planar antenna array at the receiver (Rx) side, and an omni-directional antenna at the transmitter (Tx) side. Measurements were performed for four different locations of the Tx antenna in line-of-sight (LoS) scenarios. The variation of channel characteristics such as the narrowband channel gain, the K-factor and the composite delay spread, across the 2-D array aperture is investigated. The results are important for generating realistic channel realizations for the designing and performance evaluation of the algorithms for massive MIMO communication in the context of the fifth generation (5G) wireless networks.

A Spherical-Wavefront-Based Scatterer Localization Algorithm Using Large-Scale Antenna Arrays

In this letter, a spherical-wavefront-based parametric signal model is proposed by considering the architecture using a large-scale antenna array. A space-alternating generalized expectation-maximization (SAGE)-based localization algorithm is derived and adopted to localize the first-and last-hop scatterers along the propagation paths between the transmitter and the receiver. Simulations are conducted to evaluate the performance of the localization algorithm. An outdoor measurement campaign with a 1600-element virtual planar array is carried out to verify the localization performance in reality. Those results show the advantages of using a spherical-wavefront-based signal model and the SAGE-based algorithm in the scatterer localization.

Energy-efficient heterogeneous antenna selection relaying in wireless body area networks

We present a multi-mode power amplifier (PA) set with an antenna selection mechanism in a body area relaying network for healthcare applications. The PA set of the relay node is designed to work in two modes where the RF switch utilized for antenna selection is located between the highly efficient narrowband PAs and a low-efficiency wideband PA supporting two heterogeneous networks. Our study shows that, unlike in the wideband PA mode, where antenna selection is always desirable for transmission reliability, antenna selection is not always preferred in the narrowband PA mode since in this mode, the PA needs to turn on and off constantly. Consequently, extra switch delay and energy consumption occur. To balance the tradeoff between the relay nodes energy efficiency and transmission reliability, both the switching probability between two modes and bounds on the probability of staying on the current antenna are analyzed. Numerical results are provided to corroborate the improved performance of the proposed architecture and the switch/stay mechanism.

A fair and energy-efficient spectrum management mechanism for cognitive radio networks

This paper considers the spectrum management problem in a secondary cognitive radio network where secondary nodes in the network operate on a single channel. There is a leader node which is responsible for tasks such as primary detection, node coordination and channel scanning. Channels are sensed in the order of their detection probabilities. The leader node changes on each scan depending on the credit history generated using a fair credit based mechanism. It has been shown that the proposed scheme can achieve better energy efficiency in terms of overall low battery consumption, better fairness, and seamless switch over when migrating to another channel.

Convex hull based node selection NLoS mitigation for indoor localization

Using Time of Arrival (TOA) on ultra-wideband (UWB) signal is well known as a promising indoor localization technique. However, Non Line-of-Sight (NLoS) issue resulting from complicated scenarios is considered as a key challenge to transfer this technology into mature products. In this paper, a convex hull based node selection method is proposed to improve the accuracy of NLoS identification and mitigation. In particular, two reference nodes are selected adaptively from four nodes to carry out a 2-dimension (2D) indoor localization in a convex hull based effective localization area (ELA). Performance is evaluated using measurement data collected from a Medav UWB SIMO channel sounder, benchmarked to the parametric identification method and the first peak detection method.

Advances in device-to-device communications and networks

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Advances in Device-to-Device Communications and Networks Lingyang Song, Mérouane Debbah, Rong Yu, Frank Yong Li, Jianzhong Charlie Zhang