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Cardiff, Barry
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Cardiff, Barry
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Cardiff, Barry
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Now showing 1 - 10 of 13
- PublicationA Low-Complexity Correlation-Based Time Skew Estimation Technique for Time-Interleaved SAR ADCsThis 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.
440Scopus© Citations 12 - PublicationUser-Antenna Selection for Physical-Layer Network Coding Based on Euclidean DistanceIn this paper, we present the error performance analysis of a multiple-input multiple-output (MIMO) physical-layer network coding (PNC) system with two different user-antenna selection (AS) schemes in asymmetric channel conditions. For the first antenna selection scheme (AS1), where the user antenna is selected in order to maximize the overall channel gain between the user and the relay, we give an explicit analytical proof that for binary modulations, the system achieves full diversity order of min(N A , N B ) × N R in the multiple-access (MA) phase, where N A , N B , and N R denote the number of antennas at user A, user B, and relay R, respectively. We present a detailed investigation of the diversity order for the MIMO-PNC system with AS1 in the MA phase for any modulation order. A tight closed-form upper bound on the average SER is also derived for the special case when N R = 1, which is valid for any modulation order. We show that in this case, the system fails to achieve transmit diversity in the MA phase, as the system diversity order drops to 1 irrespective of the number of transmit antennas at the user nodes. Additionally, we propose a Euclidean distance (ED) based user-antenna selection scheme (AS2) that outperforms the first scheme in terms of error performance. Moreover, by deriving upper and lower bounds on the diversity order for the MIMO-PNC system with AS2, we show that this system enjoys both transmit and receive diversity, achieving full diversity order of min(N A , N B ) × N R in the MA phase for any modulation order. Monte Carlo simulations are provided which confirm the correctness of the derived analytical results.
393Scopus© Citations 7 - 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.
594Scopus© Citations 15 - PublicationPhysical-layer network coding with multiple antennas: An enabling technology for smart citiesEfficient 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.
469Scopus© Citations 5 - PublicationOn Symmetry Properties of Intrinsic Interference in FBMC-OQAM SystemsFilter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is a modulation technique which is widely considered as a strong contender to replace cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM), for the future 5th generation (5G) of mobile wireless communication networks. FBMC-OQAM exhibits good spectral confinement properties, high spectral efficiency and immunity to synchronization errors, mainly due to its prototype filter's localization properties. But these desirable traits come with the loss of orthogonality, rendering it only orthogonal for real symbols with imaginary interference appearing in both the frequency and time domains. In this work, we prove a set of symmetry properties of this interference for a general class of FMBC-OQAM systems, and use these relationships to derive autocorrelation matrices for interference from neighboring symbols and also for noise contributions. These matrices find application in receiver design and also in channel estimation. The derived symmetry properties are also demonstrated through numerical examples for various standard prototype filter designs.
413Scopus© Citations 3 - 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.
503Scopus© Citations 2 - PublicationTransmit Antenna Selection for Physical-Layer Network Coding Based on Euclidean DistancePhysical-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.
340Scopus© Citations 1 - PublicationFundamental Limits of Spectrum Sharing for NOMA-Based Cooperative Relaying under a Peak Interference ConstraintNon-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.
286Scopus© Citations 20 - PublicationA High-Precision Time Skew Estimation and Correction Technique for Time-Interleaved ADCsThis 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.
764Scopus© Citations 41 - PublicationBlind SAR ADC Capacitor Mismatch CalibrationThis paper presents an all-digital background blind calibration technique for the capacitor mismatch problem in SAR ADCs. It utilizes the redundancy offered using a sub-radix-2 DAC architecture to blindly estimate the mismatch and the assigned weight for each comparator decision. The weights are estimated by building partial histogram windows for the comparator decision vectors. To remove the dependency on the input signal's probability density function, the histogram windows are normalized with respect to their peaks. Matlab simulation results show that an ENOB within 0.12bit of the optimal is attained using the proposed algorithm.
446Scopus© Citations 6