Non-coherent Ultra-wideband Research Articles

A Low-Power Squaring Circuit with Regulated Output and Improved Settling Time in 180 nm CMOS for 3–5 GHz IR-UWB Applications

Abstract. This paper demonstrates a low-power squaring circuit for 3–5 GHz non-coherent Impulse-Radio Ultra-Wideband (IR-UWB) receivers for Pulse Position Modulation (PPM) in a low-cost 180 nm CMOS technology. The squaring, which is the key element in typical IR-UWB receivers, is performed exploiting the non-linear transfer function of a MOS transistor. For a high gain at low power consumption the transistor is biased in the moderate inversion region, where the second-order derivative of the transconductance gm and, as a result, the quadratic term in the transfer function reaches a maximum. A control loop was implemented to set the dc output voltage to a defined value and thus to allow a comparison of the squarer output signal with a defined threshold voltage, which can easily be set and adjusted (e.g. by a DAC). To speed up the settling time of the output and hence to reach higher data rates, a novel slew-rate booster is implemented at the output. Thereby, the squarer is capable of data rates of up to 15.6 Mbit s−1, which is more than two times higher compared to the circuit without the slew-rate booster, while only consuming 72.4 µW in addition. In the extracted post-layout simulations the whole circuitry consumes 724 µA at a 1.8 V power supply, resulting in a power consumption of 1.3 mW.

Deep Learning Noncoherent UWB Receiver Design

Ultrawideband (UWB) is a promising technology for positioning and wireless communications in Internet-of-things (IoT) applications. However, UWB system's performance is limited by multiple interferences for low complexity noncoherent signal detection methods. Further, deep learning (DL)-based solutions have been envisioned for wireless communications in inaccurate system modeling scenarios. In this letter, we propose a deep learning noncoherent (DLN) UWB receiver to overcome the effect of various interferences such as multiuser interference (MUI), narrowband interference (NBI), and intersymbol-interference (ISI). The DLN is trained offline using the UWB channel statistics, and then, it is used online for data symbol detection. The proposed DLN efficiently learns a nonlinear relationship between input and output in an interference scenario and gives highly accurate data symbol detection, even for training data obtained in a very short period. Numerical results clearly show the proposed DLN UWB receiver's superiority, especially MUI, NBI, and ISI scenarios, over the conventional noncoherent detection method.

Noncoherent IR-UWB Receiver Using Massive Antenna Arrays for Wireless Sensor Networks

Noncoherent impulse radio ultrawideband (UWB) receivers do not require channel state information and are also robust against pulse shape distortions. However, their performance is suboptimal, especially at low signal-to-noise ratios. In this article, we propose simple noncoherent UWB receivers for wireless sensor network applications using massive antenna arrays. Two receivers are proposed: based on instantaneous received UWB signal energy and based on weighted instantaneous received UWB signal energy. The proposed receivers use the law of large numbers resulting from the massive receiver arrays and utilize the large degrees of freedom available in a UWB multipath channel. Furthermore, the proposed receivers do not require training symbols for the estimation of decision threshold. Both these receivers outperform the existing noncoherent receivers as verified using simulation results on the standardized IEEE 802.15.4a UWB multipath channel.

Modeling and Identification of Ultra-Wideband Analog Multipliers

Analog multipliers are employed in many applications. In conventional RF front ends, for example, they are widely used for frequency conversion tasks. In noncoherent energy detectors or autocorrelation receivers, they multiply the (broadband) input signal by itself to achieve a down-conversion. Unfortunately, there exist no ideal hardware realizations of such devices, hence multipliers inevitably create undesired signal content at their output. To be able to deal with these effects or correct for them, we need to be able to model and identify realistic RF multipliers. This paper proposes and validates a multiple-input single-output Wiener–Hammerstein model for ultra-wideband (UWB) analog multipliers. The structure of the proposed model gives insight in the distortions created. It thus provides the possibility to study the realistic behavior of systems involving those multipliers, e.g., the influence of undesired nonlinear signal content onto noncoherent UWB receivers. A comparison of the model performance is shown with respect to measurements and circuit simulations.

Low-density parity-check codes for noncoherent UWB communication systems

In order to guarantee reliable data transmission, powerful channel coding techniques are usually required in noncoherent ultra- wideband (UWB) communication systems. Accordingly, several forward error correction (FEC) codes, such as Reed-Solomon and convolutional codes have been used in noncoherent UWB systems to improve the bit error rate (BER) performance. In this paper, low-density parity-check (LDPC) codes are further studied as more powerful FEC candidates for noncoherent UWB systems. Two LDPC codes and the corresponding decoding procedures are presented for noncoherent UWB systems. Moreover, performance comparison between the LDPC codes and other FEC codes are provided for three major noncoherent UWB communication systems, namely, noncoherent pulse position modulation (NC-PPM), transmitted reference (TR) and transmitted reference pulse cluster (TRPC). Both theoretical analysis and simulation results show that the two investigated LDPC codes outperform other existing FEC codes with limited penalty in terms of complexity and therefore they are promising FEC candidates for noncoherent UWB systems with low- cost and low-power consumption.

Factor Graph Aided Multiple-Symbol Differential Detection in the Broadcasting Phase of a Network Coding Based UWB Relay System

A factor-graph-aided multiple-symbol differential detection (FG-MSDD) is proposed and its performance is analyzed and evaluated in the broadcasting phase (i.e., the downlink phase) of an ultra-wideband (UWB) two-way relay system (TWRS). In the downlink of the TWRS, the relay is transmitting network-coded information to the sources, and each source node aims to calculate a posteriori probabilities (APPs) of the information symbols from the relay node. A sampling method based on the modified autocorrelation receiver is proposed for FG-MSDD, which has a trellis structure. The trellis can be decomposed into multiple subtrellises depending on the FG factorization. Then, a methodology for APPs is derived when the forward-and-backward message passing is performed on the subtrellises. The main advantage of FG-MSDD is that it exploits soft information accurately with the aid of the bidirectional message passing. In addition, the proposed FG-MSDD, in conjunction with any soft-input soft-output (SISO) decoding scheme, is capable of obtaining an iterative detection algorithm. Various performance evaluation results obtained by means of computer simulations have verified that the proposed algorithm improves detection performance for the noncoherent UWB TWRS.

On dual peak detection UWB receivers in noise and interference dominated environments

We propose the use of a non-coherent dual peak detection architecture for ultra wideband (UWB) receivers. To benchmark our proposed architecture, the performance of non-coherent UWB receivers based on single peak, dual peak, and energy detectors in the presence of noise and interference is analyzed and compared. Theoretical derivations are presented to evaluate the performance in additive white Gaussian noise (AWGN) channels, and simulations are run to verify these results and analyze the detector performance in a multipath fading environments. It is observed that receivers based on peak detection can perform on par or better than receivers based on energy detection in interference dominated environments (such as urban areas) in both AWGN and multi-path fading channels. This allows for the realization of non-coherent UWB receivers with simplified hardware without sacrificing performance. As such, the receiver would operate with increased energy efficiency, making it attractive for low power, low data rate transceivers such as those used in wireless sensor networks.

A Survey on Various Coherent and Non-coherent IR-UWB Receivers

The recent developments in radio technologies, paves its way to impulse radio (IR) ultra-wideband (UWB) communication, which is used for low power, short range and high bandwidth communication, thereby exploiting a large portion of radio spectrum. In this paper, a brief review of the work done by various researchers on coherent and non-coherent IR-UWB receivers has been analysed, based on their bit error rate (BER) performances, as well as pros and cons of using these receivers. An in depth study on the receivers concludes that, non-coherent IR-UWB receiver is preferred over its counterpart coherent IR-UWB receiver even though it comes at the expense of poor BER performance. The simulation results prove that, though the performances are same, the low complexity of energy detector (ED) receivers gives an edge over the autocorrelation receivers. Further, ED receiver suffers from noise, which paves way to using weighted ED (WED) receiver. The superiority of WED receivers over all the other non-coherent UWB receivers is further confirmed by the simulation performed in AWGN and IEEE 802.15.4a UWB channels. It can also be concluded from the review that, some special receivers such as generalized likelihood ratio test, multi-symbol differential detector and decision feedback differential transmitted reference, when clubbed with UWB systems, lead to further improvement in BER performance.

Joint Power Allocation and Path Selection for Multi-Hop Noncoherent Decode and Forward UWB Communications

With the aim of extending the coverage and improving the performance of impulse radio ultra-wideband (UWB) systems, this paper focuses on developing a novel single differential encoded decode and forward (DF) non-cooperative relaying scheme (NCR). To favor simple receiver structures, differential noncoherent detection is employed which enables effective energy capture without any channel estimation. Putting emphasis on the general case of multi-hop relaying, we illustrate an original algorithm for the joint power allocation and path selection (JPAPS), minimizing an approximate expression of the overall bit error rate (BER). In particular, after deriving a closed-form power allocation strategy, the optimal path selection is reduced to a shortest path problem on a connected graph, which can be solved without any topology information with complexity O(N3), N being the number of available relays of the network. An approximate scheme is also presented, which reduces the complexity to O(N2) while showing a negligible performance loss, and for benchmarking purposes, an exhaustive-search based multi-hop DF cooperative strategy is derived. Simulation results for various network setups corroborate the effectiveness of the proposed low-complexity JPAPS algorithm, which favorably compares to existing AF and DF relaying methods.

BER Analysis of Decision-Feedback Multiple-Symbol Detection in Noncoherent MIMO Ultrawideband Systems

In this paper, we investigate noncoherent multiple-input-multiple-output (MIMO) ultrawideband (UWB) systems where the signal is encoded by differential space-time block code (DSTBC). DSTBC enables noncoherent MIMO UWB systems to achieve diversity gain. However, the traditional noncoherent symbol-by-symbol differential detection (DD) for DSTBC-UWB suffers from performance degradation compared with coherent detection. We introduce a noncoherent multiple-symbol detection (MSD) scheme to enhance the performance of DSTBC-UWB systems. Although the MSD scheme can boost the performance more as the observation window size becomes larger, the complexity of the exhaustive search for MSD also exponentially increases in terms of the window size. To decrease the computational complexity, the concept of decision feedback (DF) is introduced to the MSD for DSTBC-UWB in this paper. The resultant DF-MSD yields reasonable complexity and solid performance improvement. We provide the bit-error-rate analysis for the proposed DF-MSD. Both theoretical analysis and simulation results validate the proposed scheme.

Analysis and Design of Noncoherent Ultra-wideband Transceiver with FEC Coding for u-Home Networks

Analysis and Design of Noncoherent Ultra-wideband Transceiver with FEC Coding for u-Home Networks

Simulated Annealing Mechanic Based Noncoherent Signal Detection for Ultra-wideband Sensor Networks

Ultra-wideband (UWB) sensors have extensive commercial and military applications. Unfortunately, coherent signal detection in the presence of intensive multipath propagations may generally become impractical due to complicated realization algorithms and hardware requirements. In this article, we deal with noncoherent UWB signal detection within a promising biological framework, which can also be generalized to the binary-hypothesis target-detection problem, i.e. identification of the presence or absence of a target. Through the developed characteristic representations, signal detection is firstly formulated as a two-group pattern (or target) classification problem in a 2-D feature plane, in which an optimal decision bound can be numerically derived given the supervised training instances. This optimization problem is addressed by using the nature-inspired simulated annealing algorithm (SA), which essentially emulates the physical annealing process of forming the freeze state with the minimum energy. In sharp contrast to traditional optimization techniques, by probabilistically permitting search movement towards worse solutions, SA algorithm can converge to the global optimal with an asymptotical probability of 1. The numerically derived detection performance demonstrated that our present technique is much superior to the existing noncoherent schemes, which provides the appealing signal/target detection architecture for the emerging UWB sensor networks.

Simulation of a non-coherent UWB transceiver design - noise and impairment analysis

The performance of an ultra wideband (UWB) system operating in the 3.1 GHz–10.6 GHz band is investigated in the presence of different system impairments. The UWB system uses a transmitted-reference technique with pulse position modulation for transmission and a receiver with non-coherent detection. The performance of the system is simulated under different channel model conditions including additive white Gaussian noise and multipath fading for a transceiver with imperfect clock timing (jitter). The bit error rate of the overall system is characterised for different combinations of channel and clock impairments. A practical application of the system is analysed for a wireless video link between a laptop and external high definition television. The receiver system noise temperature together with the channel and clock impairments are evaluated, and a novel relationship is developed to calculate the link budget for the required transmission power to achieve a desired signal to noise ratio at the demodulator input.

Compact low-power CMOS squarer for high-speed noncoherent UWB receiver

A compact low-power CMOS squarer with a lowpass filter (LPF) for a high-speed noncoherent ultra-wideband (UWB) receiver is proposed. The proposed squarer; used to generate two differential square outputs, is based on stacked NMOS and PMOS transistor pairs to reuse the static current, and thus save half the DC power. The proposed squarer with the LPF is designed in a 180 nm 1.5 V CMOS process. The simulated results show that the designed circuit consumes only 1.1 mA (0.56 mA for the squarer and 0.54 mA for the LPF) current and provides sufficient voltage gain in the noncoherent receiver for processing a 3–5 GHz on-off keying UWB RF signal at a baseband data rate of 250 Mbit/s.

A novel Parzen probabilistic neural network based noncoherent detection algorithm for distributed ultra-wideband sensors

Ultra-wideband (UWB) has been widely recommended for significant commercial and military applications. However, the well-derived coherent structures for UWB signal detection are either computationally complex or hardware impractical in the presence of the intensive multipath propagations. In this article, based on the nonparametric Parzen window estimator and the probabilistic neural networks, we suggest a low-complexity and noncoherent UWB detector in the context of distributed wireless sensor networks (WSNs). A novel characteristic spectrum is firstly developed through a sequence of blind signal transforms. Then, from a pattern recognition perspective, four features are extracted from it to fully exploit the inherent property of UWB multipath signals. The established feature space is further mapped into a two-dimensional plane by feature combination in order to simplify algorithm complexity. Consequently, UWB signal detection is formulated to recognize the received patterns in this formed 2-D feature plane. With the excellent capability of fast convergence and parallel implementation, the Parzen Probabilistic Neural Network (PPNN) is introduced to estimate a posteriori probability of the developed patterns. Based on the underlying Bayesian rule of PPNN, the asymptotical optimal decision bound is finally determined in the feature plane. Numerical simulations also validate the advantages of our proposed algorithm.

Noncoherent ultra-wideband systems

The need for low-complexity devices with low-power consumption motivates the application of suboptimal noncoherent ultra-wideband (UWB) receivers. This article provides an overview of the state of the art of recent research activities in this field. It introduces energy detection and autocorrelation receiver front ends with a focus on architectures that perform the initial signal processing tasks in the analog domain, such that the receiver does not need to sample the UWB received signals at Nyquist rate. Common signaling and multiple access schemes are reviewed for both front ends. An elaborate section illustrates various performance tradeoffs to highlight preferred system choices. Practical issues are discussed, including, for low-data-rate schemes, the allowed power allocation per pulse according to the regulator's ruling and the estimated power consumption of a receiver chip. A large part is devoted to signal processing steps needed in a digital receiver. It starts with synchronization and time-of-arrival estimation schemes, introduces studies about the narrowband interference problem, and describes solutions for high-data-rate and multiple access communications. Drastic advantages concerning complexity and robustness justify the application of noncoherent UWB systems, particularly for low-data-rate systems.

On the performance of coherent and noncoherent UWB detection systems using a relay with multiple antennas

In this paper, we present detect-and-forward relaying approaches for a coherent ultra-wideband (UWB) detection (specifically selective-Rake reception) system and for a noncoherent UWB detection (specifically differential transmittedreference, DTR) system in order to achieve greater coverage in multipath fading channels. Multiple-antenna relay system are also proposed to further enhance the overall system performance. The corresponding bit error rate (BER) performance is evaluated theoretically and via simulations. The effect of some design factors on this performance is investigated. Analytical and simulation results verify the performance improvement of the proposed relay systems over the direct transmission systems.

Orthogonal bi-pulse UWB: Timing and (de)modulation

In this paper, we propose a novel orthogonal bi-pulse ultra-wideband (UWB) system, which uses an even pulse and an odd pulse to convey information symbols in an alternating manner. Due to the orthogonality of these pulses, their corresponding received waveforms remain orthogonal after propagating through multipath channels. Then we consider two major challenges in the realization of our proposed UWB system: timing synchronization and symbol demodulation. In particular, the idea of timing with dirty template (TDT) in [L. Yang, G.B. Giannakis, Timing Ultra-Wideband signals with dirty templates, IEEE Trans. on Commun. 53 (11) (2005) 1952–1963] is employed for timing synchronization and the noncoherent scheme in [L. Yang, G.B. Giannakis, A. Swami, Noncoherent Ultra-Wideband (de)modulation, IEEE Trans. Commun. 55 (4) (2007) 810–819] is used to bypass channel estimation. Both of these techniques are characterized by correlating adjacent waveform segments. In the implementation of these techniques, we will gradually reveal the advantages of our proposed system. The correlation of adjacent waveform segments only contains the information of a single symbol. This enables a significant enhancement of the synchronization speed of TDT when no training sequence is transmitted. For the same reason, our demodulation approach completely mitigates the inter-symbol interference (ISI) in the second paper referred to, above, and entails a simple demodulator even in the presence of unknown timing errors. Simulations are also carried out to corroborate our analysis.

An Effective Selective Detection Scheme Based on Pulse Repetition for Noncoherent UWB Systems

We propose a selective detection scheme based on pulse repetition considering the bit-error rate (BER) performance and complexity of noncoherent ultra-wide-band (UWB) systems. To take system complexity into account, the proposed scheme transmits the UWB signals by simple pulse repetition at the transmitter, like conventional pulse repetition coding (PRC). However, to effectively improve the BER performance, the proposed scheme performs selective detection by estimating the signal-to-noise ratio of the received pulse-repeated signals at the UWB receiver. Hence, the proposed scheme effectively improves the BER performance of the noncoherent UWB systems without much increasing system complexity, as compared to the conventional PRC.

Searchback Algorithms for TOA Estimation in Non-coherent Low-rate IR-UWB Systems

Non-coherent ultra-wideband (UWB) receivers offer an attractive low-complexity solution to ranging with UWB radios. They use a simple receiver architecture that can operate at very low sampling rates compared to the Nyquist rate. In this paper, time-of-arrival (TOA) estimation performances of two different searchback algorithms for non-coherent impulse radio UWB systems are analyzed: jump back and search forward (JBSF) and serial backward search (SBS). Average ranging errors for both algorithms are formulated using noise-based ranging thresholds and at sub-Nyquist sampling rates. For JBSF, a lower bound on the average ranging error is obtained using an error-minimizing threshold. Also, a semi-analytic technique for the selection of the searchback window length is presented. For SBS, noise-based threshold selection for both single-cluster and multi-cluster channels are introduced. Computer simulations in IEEE 802.15.4a channels provide insights on the selection of some of the critical parameters for accurate ranging. The simulation results show that JBSF typically performs better than SBS if the inter-cluster delay parameter (K) is not selected appropriately for SBS. In both cases, it is shown that even at sampling rates much smaller than the Nyquist rate, ranging accuracies on the order of 33 cm can be obtained using a non-coherent UWB receiver.