Now showing 1 - 10 of 24
  • 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.
      258Scopus© Citations 19
  • 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.
      434Scopus© Citations 5
  • Publication
    A Generic Foreground Calibration Algorithm for ADCs with Nonlinear Impairments
    This 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.
      547Scopus© Citations 12
  • Publication
    A Low-Complexity Correlation-Based Time Skew Estimation Technique for Time-Interleaved SAR ADCs
    This paper presents a technique to estimate the time skew in time-interleaved ADCs. The proposed method estimates all of the time skew parameters jointly based on observations from a bank of correlators. The proposed method works for an arbitrary number of sub-ADCs. For implementation of the correlator bank, we propose the use of Mitchell's logarithmic multiplier and a hardware reuse mechanism, thereby reducing the complexity and power consumption. Also, we explain why blind estimation techniques alone (including the proposed one) are not always sufficient for time skew estimation for certain classes of input signal; for the proposed approach, however, a simple modification to the analogue circuit (suitable for SAR ADCs) is shown to successfully deal with such problems, with only a minor penalty in power and area. The technique is verified by extensive simulations including a spectrally rich input signal in which an MTPR (multi-tone power ratio) improvement from 29dB to 62dB was achieved for a TIADC system having 16 sub-ADCs.
      416Scopus© Citations 12
  • Publication
    On the Performance of Spatial Modulation MIMO for Full-Duplex Relay Networks
    In 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.
      381Scopus© Citations 34
  • 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.
      469Scopus© Citations 2
  • Publication
    Generalized Least Squares Based Channel Estimation for High Data Rate FBMC-OQAM
    This paper addresses the problem of preamble-based Channel Estimation (CE) in filter bank multi-carrier systems with offset quadrature amplitude modulation (FBMC-OQAM), a task that is problematic due to the presence of intrinsic Inter-Carrier Interference (ICI) and Inter-Symbol Interference (lSI). In this work, we present a theoretical analysis of the Mean Squared Error (MSE) of several CE schemes based on the virtual symbol (VS) approach such as the Interference Cancellation Method (ICM) and the Interference Approximation Method (IAM). We also propose and analyze a generalized least squares (GLS) based CE scheme which is capable of achieving improved performance by taking into account the correlation properties of the noise and interference among sub-carriers. Simulation results are presented which verify the accuracy of the theoretical analysis, and also demonstrate that the proposed GLS-based estimation method yields an improvement of almost 3dB in the CE-MSE with respect to the VS-based approach. Finally it is shown that, for higherorder modulation schemes, this CE-MSE reduction translates into significant improvement in the system's overall bit error rate (BER) performance with only minor additional complexity.
      408Scopus© Citations 4
  • 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%.
      1151Scopus© Citations 6
  • Publication
    Optimization of RIS-aided MIMO Systems via the Cutoff Rate
    The main difficulty concerning optimizing the mutual information (MI) in reconfigurable intelligent surface (RIS)-aided communication systems with discrete signaling is the inability to formulate this optimization problem in an analytically tractable manner. Therefore, we propose to use the cutoff rate (CR) as a more tractable metric for optimizing the MI and introduce two optimization methods to maximize the CR. The first method is based on the projected gradient method (PGM), while the second method is derived from the principles of successive convex approximation (SCA). Simulation results show that the proposed optimization methods significantly enhance the CR and the corresponding MI.
      190Scopus© Citations 19
  • Publication
    A Virtual Full Duplex Distributed Spatial Modulation Technique for Relay Networks
    Spatial 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.
      361Scopus© Citations 5