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Flanagan, Mark F.
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Flanagan, Mark F.
Official Name
Flanagan, Mark F.
Research Output
Now showing 1 - 10 of 24
- PublicationSatisfaction Based Channel Allocation Scheme for Self-Organization in Heterogeneous Networks(IEEE, 2018-12-13)
; ; ; The next-generation wireless networks are expected to become denser and more heterogeneous in order to boost the network capacity. However, densely deployed base stations (BSs) in heterogeneous networks (HetNets) can give rise to interference. On the other hand, a limited number of channels is allocated within the HetNets. Therefore, the efficient assignment of channels among BSs is considered to be an important issue. Furthermore, the density and heterogeneity of the networks motivate self-organizing resource management techniques. In this paper, we address the problem of channel allocation in HetNets, and propose a satisfaction based channel allocation algorithm. The problem is modeled as a game in satisfaction form, in which BSs act as the players with the constraint given by the loads at the BSs. The objective is to meet the data rate requirements of user equipments. In this regard, the BSs aim at seeking a satisfaction solution rather than the optimal one. In order to learn the satisfaction equilibrium, a fully distributed algorithm based on the individual utility is applied. Simulation results show that the proposed approach can increase the average BS's throughput compared to the benchmark algorithms.276 - PublicationA Generic Foreground Calibration Algorithm for ADCs with Nonlinear ImpairmentsThis paper presents a generic foreground calibration algorithm that estimates and corrects memoryless nonlinear impairments in both single channel and time-interleaved analog-to-digital converters (TIADCs), and which is capable of correcting for amplifier nonlinearity, comparator offsets, and capacitance mismatch for each channel. It operates by generating, and then using, a look-up table which maps raw ADC output decision vectors to linearized output. For TIADCs, the algorithm also uses information gained during the calibration phase to estimate timing and gain mismatches among the sub-ADCs. The problem of selecting an appropriate timing reference so as to relax the requirements on the time-skew correction circuitry is statistically analyzed, as is the corresponding impact on manufacturing yield. Accordingly, a new method is proposed having superior performance; for example, in the case of an eight sub-ADC TIADC system, the proposed scheme reduces the time skew correction requirement by 44% compared with conventional methods. The architecture is instrumented with some additional circuitry to facilitate built-in self-test, allowing manufacturing test time and cost reductions. Implementation aspects are discussed, and several complexity reduction techniques are presented along with synthesis results from a Verilog implementation of the calibration engine.
341Scopus© Citations 11 - PublicationGibbs Sampling Aided Throughput Improvement for Next-Generation Wi-Fi(IEEE, 2019-12-13)
; ; ; ; Wireless communications, and in particular wireless local area network (WLAN) technology, has undergone a tremendous evolution in the past decades. After the release of the WLAN standard IEEE 802.11a/b in 1999, Wi-Fi technology soon became pervasive, thanks mainly to its deployment on the unlicensed ISM band. However, high traffic, especially in hotspots and areas with dense deployment of Wi-Fi access points (APs) (e.g., stations, airports, etc.) has caused major issues and a severe degradation of communications quality. The latest WLAN standards (e.g., 802.11ac, 802.11ax) have largely succeeded in improving the link quality and data rate by adopting state-of-the-art PHY layer technologies, e.g., OFDMA, MU-MIMO. However, improvement of the MAC layer in these standards is not noticeable due to restrictions such as hardware limitation and backward compatibility issues for legacy APs. As an effort to improve the MAC layer for the next-generation WLAN standard, in this paper we propose a simple algorithm with low computational complexity for channel selection in Wi-Fi networks. The main idea is to take advantage of the potential of the IEEE 802.11ax MAC to avoid major standard modifications. For this purpose, we employ the channel utilization ratio (CUR), which is measured periodically by each AP based on its channel sensing. Time-averaged CUR values are weighted based on a Gibbs sampling approach and a probability associated to each channel is updated. Finally, a channel is selected based on the aforementioned probabilities in predefined time slots. Simulation results show that the proposed approach can improve the system throughput by up to 5% and transmission delay by up to 20%.978Scopus© Citations 4 - PublicationSimultaneous Uplink/Downlink Transmission Using Full-Duplex Single-RF MIMOIn this letter, we introduce a full-duplex protocol for simultaneous transmission between the uplink and the downlink of cellular networks. The protocol takes advantage of the inactive antenna(s) in multiple-input-multiple-output (MIMO) systems with a single active radio frequency (RF) front-end. More precisely, for the downlink transmissions, we make use of spatial modulation (SM), and for the uplink, we make use of the coordinate-interleaved orthogonal design (CIOD)-based space-time block code (STBC). We provide accurate mathematical expressions for evaluating the error-performances and the achievable diversity order at the base station (BS) and at the mobile terminal (MT) in the presence of self-interference. Our results demonstrate clearly the potential of SM and CIOD for full-duplex operation.
220Scopus© Citations 11 - PublicationA Virtual Full Duplex Distributed Spatial Modulation Technique for Relay NetworksSpatial modulation, a multiple-input multiple-output (MIMO) technology which uses the antenna index to transmit part of the incoming data, is an attractive way to reduce the energy cost and transceiver complexity in future wireless networks. In particular, the recently proposed technique of distributed spatial modulation (DSM) for relay networks can lead to better spectral efficiency, as it allows the relays to transmit their own data while simultaneously relaying the data of the source. A new distributed spatial modulation protocol is introduced in this paper which achieves virtual full duplex (VFD) communication. In this protocol, the source and relays transmit their own data in every time slot; thus, the spectral efficiency is significantly improved compared to conventional DSM. Simulation results indicate that at high signal-to-noise ratio (SNR), the proposed protocol has similar bit error rate (BER) performance versus SNR-per-bit compared to the standard full duplex relaying protocol of successive relaying; however, in contrast to successive relaying, the relays are simultaneously transmitting their own data, which is received at the destination with an error rate similar to that of the source's data.
220Scopus© Citations 5 - PublicationFundamental Limits of Spectrum Sharing for NOMA-Based Cooperative RelayingNon-orthogonal multiple access (NOMA) and spectrum sharing (SS) are two emerging multiple access technologies for efficient spectrum utilization in the fifth-generation (5G) wireless communications standard. In this paper, we present a closed-form analysis of the average achievable sum-rate and outage probability for a NOMA-based cooperative relaying system (CRS) in an underlay spectrum sharing scenario. We consider a peak interference constraint, where the interference inflicted by the secondary (unlicensed) network on the primary-user (licensed) receiver (PU-Rx) should be less than a predetermined threshold. We show that the CRS-NOMA outperforms the CRS with conventional orthogonal multiple access (OMA) for large values of peak interference power at the PU-Rx.
328Scopus© Citations 2 - PublicationA Generic Foreground Calibration Algorithm for ADCs with Nonlinear ImpairmentsThis paper presents a generic foreground calibration algorithm which compensates for memoryless nonlinear impairments in pipeline, SAR or hybrid ADC architectures. Amplifier nonlinearity, comparator offsets, capacitance mismatch and settling time errors are considered. During the calibration process, each element of a look up table is computed by mapping each raw ADC output value to an estimate of the corresponding input, and the most likely input corresponding to each raw ADC output is computed and stored in the table; this table is then used during normal operation to map the raw values to the calibrated ADC outputs. Complexity reduction techniques are presented to facilitate an in-circuit hardware implementation in order to reduce foreground calibration time. The algorithm's performance is evaluated using a SAR ADC model suffering from various nonlinear impairments. Results are presented for settling time errors, capacitor mismatch scenarios, and a wide range of nonlinear amplifier parameters, demonstrating a significant performance improvement in all cases.
286Scopus© Citations 4 - PublicationOn the Performance of Spatial Modulation MIMO for Full-Duplex Relay NetworksIn this paper, we investigate, for the first time, the performance of a full-duplex (FD) relaying protocol, where a single-RF spatial modulation (SM) multiple-input multiple-output (MIMO) system is employed at the relay node. We refer to this protocol as SM-aided FD relaying (SM-FDR). At the destination, a demodulator that takes advantage of the direct connectivity between the source and destination is developed in order to maximize its performance. Based on this demodulator, we introduce a mathematical framework for computing the average error-probability of SM-FDR in the presence of residual self-interference (SI). Furthermore, we derive mathematical expressions for computing the achievable rate of SM-FDR. With the aid of these achievable rate expressions, we provide an estimate on the quality of SI cancellation required for the suitability of FD transmission. In addition, we develop and evaluate three relay selection policies specifically designed for the SM-FDR protocol. The mathematical analysis is substantiated with the aid of extensive Monte Carlo simulations. Finally, we also assess the performance of SM-FDR against traditional FD relaying protocols.
257Scopus© Citations 31 - PublicationPhysical-layer network coded QAM with trellis shaping for the two-way relay channelPhysical-layer network coding (PNC) allows to improve the throughput on the two-way relay channel (TWRC). PNC systems using higher-order modulation present some challenges regarding how to design the PNC mapping at the relay. With higher-order modulation it is also desirable to use constellation shaping which allows to minimize the average transmitted energy. In this paper, we show how low-complexity trellis shaping can be used to provide constellation shaping both at the user nodes and at the relay node. The proposed technique works specifically for sign bit shaping and M-ary quadrature amplitude modulation (QAM). Simulation results show that the proposed scheme provides a significantly increased performance in terms of the achievable BER, with 5.3dB shaping gain available at a BER of 10-3 in the case of 256-QAM signaling.
208 - PublicationNetwork Coded Distributed Spatial Modulation for Relay NetworksDistributed spatial modulation (DSM) is a cooperative diversity protocol for a wireless network, whereby communication from a source to a destination is aided by multiple intermediate relays. The main advantage of the DSM protocol is that it provides distributed diversity to the source's transmission, while simultaneously allowing the relays to efficiently transmit their own data to the destination. In this paper, network coding is combined with DSM in order to increase the data rate of the source-to-destination link while maintaining the same diversity order of 2 for this data. Two methods of detection are proposed for implementation at the destination node: an error-aware maximum likelihood (ML) demodulator which is robust to demodulation errors at the relays, and a low-complexity suboptimal demodulator which assumes correct demodulation at the relays. The system bit error rate (BER) performance is measured under two different relay geometries. Simulation results show that for the same overall system throughput, the proposed network coded DSM protocol can increase the source-to-destination data rate by approximately 33.3% compared to the conventional DSM system, while still guaranteeing a similar BER as for DSM for both of the considered channel geometries.
265Scopus© Citations 2