Now showing 1 - 10 of 24
  • Publication
    Simultaneous Uplink/Downlink Transmission Using Full-Duplex Single-RF MIMO
    In 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.
    Scopus© Citations 11  294
  • Publication
    Virtual Full-Duplex Distributed Spatial Modulation with SER-Optimal and Suboptimal Detection
    (IEEE, 2018-04-18) ;
    Spatial modulation, a multiple-input multipleoutput (MIMO) technology which uses the antenna index as an additional means of conveying information, is an emerging technology for modern wireless communications. In this paper, a new distributed version of spatial modulation is proposed which achieves virtual full-duplex communication (VFD-DSM), allowing the source to transmit new data while the relay set forwards the source's data in every time slot. Two maximum a posteriori (MAP) detection methods at the destination are proposed for this VFD-DSM protocol: one, called local MAP, is based on processing the signals received over each pair of consecutive time slots, while the other, called global MAP, is based on symbol-error-rate optimal detection over an entire frame of data. Simulation results for the proposed VFD-DSM protocol indicate that for source data detection at high signal-to-noise ratio (SNR), VFD-DSM with local MAP detection can provide a similar error rate performance to that of successive relaying, while providing a significant throughput advantage since the relays can forward the source transmissions while also transmitting their own data. Furthermore, the use of global MAP detection is shown to yield a further 1.8 dB improvement in source data error rate while still maintaining this throughput advantage.
    Scopus© Citations 3  396
  • Publication
    Gibbs Sampling Aided Throughput Improvement for Next-Generation Wi-Fi
    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%.
      1122Scopus© Citations 6
  • Publication
    Physical-layer network coding with multiple antennas: An enabling technology for smart cities
    Efficient heterogeneous communication technologies are critical components to provide flawless connectivity in smart cities. The proliferation of wireless technologies, services and communication devices has created the need for green and spectrally efficient communication technologies. Physical-layer network coding (PNC) is now well-known as a potential candidate for delay-sensitive and spectrally efficient communication applications, especially in bidirectional relaying, and is therefore well-suited for smart city applications. In this paper, we provide a brief introduction to PNC and the associated distance shortening phenomenon which occurs at the relay. We discuss the issues with existing schemes that mitigate the deleterious effect of distance shortening, and we propose simple and effective solutions based on the use of multiple antenna systems. Simulation results confirm that full diversity order can be achieved in a PNC system by using antenna selection schemes based on the Euclidean distance metric.
    Scopus© Citations 5  418
  • Publication
    Network Coded Distributed Spatial Modulation for Relay Networks
    (IEEE, 2018-06-28) ;
    Distributed 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.
    Scopus© Citations 2  382
  • Publication
    Transmit Antenna Selection for Physical-Layer Network Coding Based on Euclidean Distance
    Physical-layer network coding (PNC) is now well- known as a potential candidate for delay-sensitive and spectrally efficient communication applications, especially in two-way relay channels (TWRCs). In this paper, we present the error performance analysis of a multiple-input single- output (MISO) fixed network coding (FNC) system with two different transmit antenna selection (TAS) schemes. For the first scheme, where the antenna selection is performed based on the strongest channel, we derive a tight closed-form upper bound on the average symbol error rate (SER) with M-ary modulation and show that the system achieves a diversity order of 1 for M > 2. Next, we propose a Euclidean distance (ED) based antenna selection scheme which outperforms the first scheme in terms of error performance and is shown to achieve a diversity order lower bounded by the minimum of the number of antennas at the two users.
    Scopus© Citations 1  301
  • Publication
    A High-Precision Time Skew Estimation and Correction Technique for Time-Interleaved ADCs
    This paper presents an all-digital background calibration technique for the time skew mismatch in time-interleaved ADCs (TIADCs). The technique jointly estimates all of the time skew values by processing the outputs of a bank of correlators. A low-complexity sampling sequence intervention technique, suitable for successive approximation register (SAR) ADC architectures, is proposed to overcome the limitations associated with blind estimation. A two-stage digital correction mechanism based on the Taylor series is proposed to satisfy the target high-precision correction. A quantitative study is performed regarding the requirements imposed on the digital correction circuit in order to satisfy the target performance and yield, and a corresponding filter design method is proposed, which is tailored to meet these requirements. Mitchell's logarithmic multiplier is adopted for the implementation of the principal multipliers in both the estimation and correction mechanisms, leading to a 25% area and power reduction in the estimation circuit. The proposed calibration is synthesized using a TSMC 28-nm HPL process targeting a 2.4-GHz sampling frequency for an eight-sub-ADC system. The calibration block occupies 0.03 mm² and consumes 11 mW. The algorithm maintains the SNDR above 65 dB for a sinusoidal input within the target bandwidth.
    Scopus© Citations 38  674
  • Publication
    Physical-layer network coded QAM with trellis shaping for the two-way relay channel
    Physical-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.
      268
  • Publication
    Fundamental Limits of Spectrum Sharing for NOMA-Based Cooperative Relaying under a Peak Interference Constraint
    Non-orthogonal multiple access (NOMA) and spectrum sharing (SS) are two emerging multiple access technologies for efficient spectrum utilization in future wireless communications standards. In this paper, we present the performance analysis of a NOMA-based cooperative relaying system (CRS) in an underlay spectrum sharing scenario, considering a peak interference constraint (PIC), where the peak interference inflicted by the secondary (unlicensed) network on the primary-user (licensed) receiver (PU-Rx) should be less than a predetermined threshold. In the proposed system the relay and the secondary-user receiver (SU-Rx) are equipped with multiple receive antennas and apply selection combining (SC), where the antenna with highest instantaneous signal-to-noise ratio (SNR) is selected, and maximal-ratio combining (MRC), for signal reception. Closed-form expressions are derived for the average achievable rate and outage probabilities for SS-based CRS-NOMA. These results show that for large values of peak interference power, the SS-based CRS-NOMA outperforms the CRS with conventional orthogonal multiple access (OMA) in terms of spectral efficiency. The effect of the interference channel on the system performance is also discussed, and in particular, it is shown that the interference channel between the secondary-user transmitter (SU-Tx) and the PU-Rx has a more severe effect on the average achievable rate as compared to that between the relay and the PU-Rx. A close agreement between the analytical and numerical results confirm the correctness of our rate and outage analysis.
    Scopus© Citations 18  242
  • Publication
    Fundamental Limits of Spectrum Sharing for NOMA-Based Cooperative Relaying
    Non-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.
      454Scopus© Citations 2