Abstract-A full-duplex (FD) multiple antenna access point (AP) communicating with single antenna half-duplex (HD) spatially random users to support simultaneous uplink (UL)/downlink (DL) transmissions is investigated. Since FD nodes are inherently constrained by the loopback interference (LI), we study precoding schemes for the AP based on maximum ratio combining (MRC)/maximal ratio transmission (MRT), zeroforcing and the optimal scheme for UL and DL sum rate maximization using tools from stochastic geometry. In order to shed insights into the systems performance, simple expressions for single antenna/perfect LI cancellation/negligible internode interference cases are also presented. We show that FD precoding at AP improves the UL/DL sum rate and hence a doubling of the performance of the HD mode is achievable. In particular, our results show that these impressive performance gains remain substantially intact even if the LI cancellation is imperfect. Furthermore, relative performance gap between FD and HD modes increases as the number of transmit/receive antennas becomes large, while with the MRC/MRT scheme, increasing the receive antenna number at FD AP, is more beneficial in terms of sum rate than increasing the transmit antenna number.

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Cognitive underlay amplify-and-forward (AF) two-way relay links require signal-to-interference-and-noise-ratio (SINR) balancing and maximizing strategies. And both secondary-to-primary and primary-to-secondary interference must be taken into consideration. To achieve these goals, we develop several joint distributed beamforming and power allocation algorithms. The development is based on the assumption of the availability of channel state information (CSI) of the relay-transceiver channels and the second-order-statistics (SOS) of all channels. For single-relay and multi-relay systems, a closed-form solution and an exhaustive-search optimal algorithm, respectively, are developed. This optimal algorithm, despite its high computational complexity, serves as a useful benchmark. Moreover, two low-complexity suboptimal algorithms are proposed, both of which compute sub-optimal power allocations and beamformers. A 10-dB SINR improvement by the optimal algorithm and similar gains by both proposed suboptimal algorithms are achievable.Index Terms-Amplify-and-forward relaying, cognitive radio, distributed beamforming, power allocation, second-order statistics of channel gains, SINR balancing, two-way relay, underlay.

We analyse the end-to-end (E2E) outage probabilities (OPs) of zero-forcing beamforming and maximal-ratiotransmission/combining (ZFB-MRT/MRC) for an underlay network, which consists of a single-antenna fixed-gain amplifyand-forward (AF) two-way relay and two multi-antenna terminals. Assuming both path loss effects and small-scale fading and considering both secondary-to-primary (S2P) and primary-tosecondary (P2S) interferences, the exact and asymptotic E2E OPs are derived.Index Terms-Amplify-and-forward relaying, cognitive radio, outage probability, underlay, ZFB-MRT/MRC.

In order to facilitate the advanced measurement system with real-time interaction in smart grid and to satisfy the requirements for power quality management, a wireless ad hoc smart metering system for power quality using Internet of things (IoTs) technology is presented in the paper. By utilizing the energy metering module to collect energy information, the ZigBee ad hoc networks to transmit energy information, and the user monitoring terminal to support power grids management, the proposed system is able to efficiently realize the power quality information collection, transmission, processing and sharing. Experimental results demonstrate that the system performs real-time and precious monitoring of the distributed client power quality information, together with friendly and intelligent interaction capability.