A Technique for Frequency Synchronization in Multi-Band OFDM in Realistic UWB Channel

This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to verify their feasibility of implementation in practical UWB receiver design.     

Frequency Offset Estimation by Multi-Band Averaging Method: A New Approach for MB-OFDM Based Ultra-Wideband Communication System

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).     

An Efficient Packet Detection Method with a Verification Mode in MB-OFDM UWB Systems

In this paper, we propose a novel packet detection method using a cross-correlation scheme with a verification mode in ultra wide-band (UWB) systems adopting multi-band OFDM (MB-OFDM) techniques. In the packet detection process, a cross-correlation scheme has the advantage of performing the acquisition of transmitted time-frequency code (TFC) for frequency hopping as well as packet detection with low hardware costs; however, it suffers from performance degradation caused by an imperfect decision process using a threshold value compared with an auto-correlation method. By using a verification mode, the proposed method improves detection performance of a cross-correlation technique considerably. This is because the verification mode can reduce a false alarm probability on packet detection by reconfirming whether or not the desired signal is received and can effectively reject temporal small correlation peaks due to the noise or sub-path signals having smaller energies. For the verification of proposed algorithm, we employ CM1 and CM4 channel models given in IEEE802.15.3a and compare the detection performance between conventional algorithms as well as the proposed one by using computer simulations. Experimental results show that the proposed scheme can reduce a packet detection error probability (PDER) to about 10⁻³ in CM1 channel and about 10⁻² in CM4 channel at SNR = 9 dB compared with conventional methods having more than 10⁻¹ PDER. From the experimental results, we can find that the proposed algorithm can compensate for performance degradation under high SNR condition caused by using a fixed single threshold value. We also estimate the power consumption of algorithms by utilizing both the total number of multiplications and additions employed in the algorithms and the consuming power of hardware elements under 0.13 um CMOS technology. Next, we discover that the proposed method can reduce computational complexity by a minimum of 24.5% compared with conventional cross-correlation algorithms. From the experimental and power estimation results, we can see that the proposed method is very useful for packet detection in UWB MB-OFDM systems, in which low-power implementation is an important issue.     

On the Performance of a Constellation-rotated Time-spreaded Space-frequency Coding Scheme for 4 × 1 MISO OFDM Transceivers

In this article, we propose a time-spreaded quasi-orthogonal space-frequency coded OFDM system with constellation rotation. A constellation rotated quasi-orthogonal OFDM system could offer full rate and full diversity in a frequency selective fading channel. Time spreading can give additional time diversity gain in a fast fading channel. Assuming that complex channel gains between adjacent subcarriers are approximately equal, we develop a coding scheme for 4 × 1 MISO transceiver and its BER performance is evaluated for different Doppler frequencies in an OFDM system. The simulation results show that 2 dB gain can be achieved at BER of 10⁻³ using the proposed scheme compared to a scheme without time spreading and constellation rotation when 512 subcarriers are used at maximum Doppler frequency of 300 Hz. Also, the proposed system is analyzed for different delay spread of the channel and the results show that if adjacent subcarriers are correlated, it is better in SF-OFDM decoding.     

Peak to Average Power Ratio Reduction in ECMA-368 Ultra wideband Communication Systems Using Active Constellation Extension

Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) is an efficient approach for The ECMA-368 Ultra Wideband (UWB) wireless communication Standard. However, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals, limits the power efficiency of the High Power Amplifier (HPA) due to nonlinear distortion. Hence the need to reduce the PAPR of MB-OFDM UWB signals. In this paper, the efficiency of some recently proposed methods including the Active Constellation Extension Approximate Gradient-Project technique (ACE-AGP) is evaluated in real ECMA-368 communication system, with the use of typical HPA models and the UWB channel models defined in IEEE 802.15.3a standard. The PAPR measure and the bit error rate (BER) are used as performance measures in this evaluation.The results indicate that the ACE-AGP algorithm introduces a significant reduction of PAPR about 6.7 dB and reduces the BER degradation in all UWB channel models with different data rates.     

Max-SINR Based Timing Synchronization Scheme in Hexagonal Multicarrier Transmission

In this paper, the maximizing Signal-to-Interference-plus-Noise Ratio (Max-SINR) criterion is applied in Hexagonal Multicarrier Transmission (HMT) system for timing synchronization. An iterative approach for Max-SINR timing over doubly dispersive (DD) channel with exponential power delay profile and U-shape Doppler spectrum is proposed. Theoretical analysis shows that there is an allowable SINR gap between the mean delay of DD channel and the optimal timing point. Meanwhile, a low complexity suboptimal timing approach based on instantaneous channel frequency response is proposed. Theoretical analysis and simulation results show that Max-SINR timing scheme outperforms traditional timing method about 2–15 dB in SINR and the suboptimal timing algorithm achieves a smaller Mean Square Error than 10^?4 over DD channels. In addition, the Iterative Projection Sequence Detection (IPSD) receiver is proposed and the Match Filter Low Bound (MFLB) in HMT system is given. Simulation results show that the Bit Error Rate (BER) of the proposed IPSD approach based on iterative Max-SINR timing approximates to the MFLB and outperforms traditional timing scheme about 3dB at BER = 10^?3.     

A High-Performance Doubly-Balanced Mixer in 0.35-μm CMOS for Mode-1 MB-OFDM UWB Receivers

A new design of CMOS doubly-balanced down-conversion mixer intended for Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) receiver of UWB group#1 bands and optimized for 0.35-μm technology is presented. The proposed mixer uses the current-bleeding technique in both the driver and switching stages with wideband impedance matching, consisting of a bandpass filter embedding the RF stage. The mixer performances are optimized for the AMS 0.35 μm CMOS process parameters. Over 3.1–4.8 GHz, the circuit drawing 6 mA from 3-V supply, shows a conversion gain of 14.0±1.0 dB, IIP3 of 0±2 dBm, doubly-sideband noise figure of 4.5–4.8 dB, and port-to-port isolation above 61.0 dB.

超宽带系统在窄带干扰条件下的性能研究

超宽带（Ultra Wide-Band，UWB）系统发射信号的带宽在一个非常大的频段范围内，易与已存在的窄带无线通信系统的带宽形成重叠。因此，有必要研究UWB系统在频段重合范围内的抗干扰能力。文中首先分析了直接扩频超宽带系统在最小均方误差准则检测方式下，RAKE接收机的比特误码率（Bit Error Rate，BERl，然后研究了普通窄带系统的功率谱密度，最后做出了仿真分析。结果表明，在CM1信道传播下，窄带干扰对UWB系统不会造成很大影响，而在CM2信道传播下会照成一定影响，必须通过其他通信手段如信道编码来降低BER，实现通信的可靠性。     

基于最大自相关及最小能量比的MB-OFDM-UWB系统定时算法

该文针对IEEE 802.15.3a提案及ECMA-368标准采用的多频带OFDM超宽带系统,通过算法改进和仿真给出了适用于该系统的定时同步的完整方案。用基于前导序列第1频带信息的最大自相关法进行帧检测及粗定时,用基于全部3个频带信息的最小能量比值法进行细定时。对定时位置两次进行修正,保证了算法的性能。仿真表明该定时同步方案可以把残余定时偏差控制在较小的范围内,从而可以被频域信道估计及均衡吸收,同时该方案具有较低的复杂度。     

A CMOS imaging diversity receiver for gigabit free-space optical MIMO

A 7-channel imaging diversity receiver based on current-summing is implemented in a 180 nm CMOS technology for broadband free-space optical (FSO) multi-input/multi-output (MIMO) communication. Each channel employs a low input-impedance current mirror (CM) as the input stage, which allows the implementation of direct current-summing for equal-gain combining (EGC). The summed current signal drives a second stage transimpedance amplifier (TIA) to generate the output voltage. Electrical characterization was performed using a photodiode emulation circuit and chip-on-board FR-4 assembly, demonstrating a total transimpedance gain of 62 dBΩ, −3 dB bandwidth of 1.2 GHz, and eye diagrams up to 2 Gb/s for 0.25 pF photodiode capacitance. The theoretical sensitivity of the imaging receiver is −16.8 dBm for a bit error rate (BER) of 10⁻⁹ at a photodetector responsivity of 0.4 A/W. The simulated power consumption for a single front-end amplifier circuit is 4.2 mW, and for the second stage TIA is 10.3 mW from a single 1.8 V supply. The diversity receiver is flip-chip compatible to enable hybrid integration to a custom InGaAs photodetector array.     

On the PAR reduction of MB-OFDM ultra-wideband signals

The Peak to Average power Ratio （PAR） of a Multi-Band Orthogonal Frequency-Division Multiplexing （MB-OFDM） Ultra-Wide Band （UWB） signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate （BER） performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.     

A 4 mW 3–5 GHz current reuse g<Subscript>m</Subscript>-boosted short channel common-gate CMOS UWB LNA

A novel architecture is presented to optimize the noise performance and the power consumption of the transconductance ‘g_m’ boosted common-gate (CG) ultrawideband (UWB) low-noise amplifier (LNA), operating in the 3–5 GHz range, by employing current reuse technique. This proposed CG LNA utilizes a common source (CS) amplifier as the g_m-boosting stage and the bias current is shared between the g_m-boosting stage and the CG amplifying stage. The LNA circuit also utilizes the short channel conductance g_ds in conjunction with an LC T-network to further reduce the noise figure (NF). The proposed LNA architecture has been fabricated using the 130 nm IBM CMOS process. The LNA achieved input return loss (S₁₁) of −8 to −10 dB, and, output return loss (S₂₂) of −12 to −14 dB, respectively. The LNA exhibits almost flat forward voltage gain (S₂₁) of 13 dB, and reverse isolation (S₁₂) of −62 to −49 dB, with a NF ranging between 3.8 and 4.6 dB. The measurements indicate an input-referred third order intercept point (IIP3) of −6.1 dBm and an input-referred 1-dB compression point (ICP_1dB) of −15.4 dBm. The complete chip draws 4 mW of DC power from a 1.2 V supply.     

Compact Efficient Feed-Horn at 30–38 GHz for a Multi-beam Radio Telescope

The requirements for a feed suitable for a radio telescope multi-beam focal plane array are considered. A smooth-walled spline-profile horn covering the 30–38 GHz frequency band to be used in a multi-beam receiving array of a radio telescope has been optimized, manufactured and tested. The achieved cross-section aperture size of the horn allows us to provide a neighboring beam spacing equal or less than 2HPBW for the RATAN-600 radio telescope. The measured sidelobe levels of the radiation pattern is less than −30dB/−24dB/−26dB in H/E/45⁰-planes, cross-polarization levels better than −20 dB, an input return loss better than −18 dB and the −3dB/−10dB-beamwidths are of the order of 40o/ 80o over the frequency band. Mutual-coupling of adjacent horns is less than −38 dB.     

Adaptive Narrowband Interference Suppression in Multiband OFDM Receivers

The analysis and optimization of a notch filter to combat in-band narrowband interference (NBI) for multiband orthogonal frequency division multiplexing (MB-OFDM)-based ultra-wideband (UWB) systems is presented. Unintentional radiation of electronic devices can reside in the UWB band and jam the communication. Erasing the interference with a programmable analog notch filter reduces the requirement for the analog-to-digital converter resolution in the presence of NBI. The order and approximation of the notch filter are determined, and the filter’s bandwidth is optimized to minimize the packet error rate. Simulation results indicate that the UWB system with suppression scheme can handle up to 14 dB more in-band interference power.     

多径瑞利衰落信道条件下射频干扰抵消误差对CCFD系统中OFDM性能的影响

针对同时同频全双工无线通信系统,考虑远端到近端的无线信道为多径瑞利衰落信道,近端发射天线到接收天线的自干扰信道为加性白高斯噪声信道,分析了同时同频全双工传输场景中,自干扰射频抵消幅度及载波相位误差对OFDM误码率的影响。结果表明,在相同信干比和信噪比条件下,幅度和载波相位估计误差的绝对值越小,误码率越低;针对载波频率2.3 GHz, OFDM子载波个数4096,子载波间隔15 kHz的同时同频全双工传输方式,在信干比为-70 dB,误码率为10-2时,若期望信噪比损失小于0.8 dB,则需要射频干扰抵消的载波相位估计误差的绝对值小于610-6,幅度估计相对误差的绝对值小于310-5;若期望获得40 dB的射频自干扰抑制效果,则射频干扰抵消的载波相位估计误差的绝对值小于0.5,幅度估计相对误差绝对值小于1%。     

Compact body-worn MIMO antenna with high port isolation for UWB applications

This article investigates the mutual coupling reduction of a compact two elements wearable ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna. The ground plane of the proposed wearable MIMO antenna structure consists of three connected square ring-shaped stubs and two rectangular slots of narrow height. These ground stubs and slots minimize the mutual coupling effect between antennas and provide high isolation. The suggested MIMO antenna functions from the 1.87 to 13.82 GHz frequency spectrum covering WLAN (2.4–2.484 GHz), UWB (3.1–10.6 GHz), and X band (8–12 GHz) with 152.32% fractional bandwidth. It sustains port isolation above 27 dB throughout the 2 to 13.82 GHz frequency band. Inside the whole working frequency band, the suggested antenna offers a tiny envelope correlation coefficient (ECC < 0.098), greater diversity gain (DG > 9.93 dB), minimum channel capacity loss (CCL < 0.32 bits/s/Hz), and slight magnitude variation in mean effective gain of antenna ports (< 0.1 dB). The recommended antenna yields a SAR level below the designated threshold (<1.6 W/kg), affirming its suitability for body-worn applications. The designed MIMO antenna structure has an overall volume of 32 × 48 × 1.5 mm³.     

Performance comparison of MRC and EGC on a MC-CDMA system with synchronization errors over fading channels

This work derives the average bit error rate (BER) of the uplink and downlink multicarrier code division multiple access (MC-CDMA) systems using maximum ratio combining (MRC) and equal gain combining (EGC) with synchronization errors over fading channels. The derived equation can simultaneously incorporate the parameters of the fading channel and all of the synchronization errors, including frequency offset, carrier phase jitter, and timing jitter. Numerical results indicate that those two combining schemes on the uplink and downlink MC-CDMA systems are degraded by all of the normalized synchronization errors over 10⁻². The comparison outcomes between MRC and EGC reveal that the MRC generally outperforms EGC in the uplink MC-CDMA system. However, EGC achieves better performance when the number of users is small, the normalized synchronization errors are low and the signal to noise ratio (SNR) is high. In the downlink system, EGC mainly outperforms MRC when the SNR and the number of users are gradually increased and the normalized synchronization errors are low. Therefore, the selection of MRC or EGC depends on the SNR, the synchronization errors and the number of users in uplink and downlink MC-CDMA systems.     

Adaptive predistortion of COFDM signals for a mobile satellite channel

In this paper, we consider the optimization of the performance of QPSK and 16‐QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non‐linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non‐linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non‐linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10^?3 when compared to QPSK COFDM without the predistortion scheme and 16‐QAM COFDM provides a gain of 0.5 dB output back‐off and 1.2 dB signal to noise ratio at a BER of 3×10^?5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10^?4 for QPSK and 16‐QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Inverter-based 1 V analog front-end amplifiers in 90 nm CMOS for medical ultrasound imaging

In this paper, we present the design and experimental evaluation of 1 V analog front-end amplifiers designed in 90 nm CMOS technology for capacitive micro-machined ultrasound transducers (CMUTs) for medical ultrasound imaging systems. We propose two front-end amplifier topologies based on an inverter-based cascode amplifier; the first is a continuous time amplifier and the second is a charge sampling amplifier (CSA). The proposed front-end amplifiers are designed to amplify the signals from CMUTs in the frequency bandwidth from 15 to 45 MHz with a centre frequency of 30 MHz. From the measurements, the continuous time single-ended transimpedance amplifier achieves a voltage gain of 19 dB, an output noise power spectral density of 0.042 (μV)/SQRT(Hz) at a centre-frequency of 30 MHz, and a total harmonic distortion of −23 dB at 450 mV p–p output voltage at 30 MHz input signal frequency. It draws only 598 μA per amplifier from a 1 V power supply. Its area measured only about 32 μm × 32 μm per amplifier. On the other hand, a sampling based front-end amplifier [CSA] achieves a transfer gain of 17.4 dB at an input signal frequency of 30 MHz and an upper 3 dB cut-off frequency of 46 MHz at a sampling clock frequency of 100 MHz. It consumes 586 μA per amplifier from a 1 V power supply and achieves a signal-to-noise (SNR) ratio of 45.7 dB with a peak-to-peak output signal amplitude of 500 mV at a sampling frequency of 100 MHz. It occupies an area of 1470.2 μm² (which is equivalent to 38 μm × 38 μm), which also includes the area of the switches for the CSA that will be used for the single CMUT element.     

Improvement of the Performance Characteristic of UWB Antenna Using a Novel Double-Layer FSSs Operating at the Ku-Band

This paper proposed a novel compact design of UWB antenna. Our design used an uni-planar EBG double-layer of FSSs to enhance performance characteristics of UWB antenna in operation frequency of 14 GHz/Ku Band. This UWB antenna occupies a compact size of 40.36?×?29.36 mm² with space/gap between the radiator patch and double-layer of FSSs is 10 mm. We used a simple rectangular truncated-corner as a radiating patch. Double-layer of FSSs consist of a lower layer of FSS that used a unit cell of rectangular loop and an upper layer of FSS applied a wire grid. Optimized size of the truncated-corner is 2?×?0.5 mm², optimal space/gap between radiator patch and double-layer of FSSs is 10 mm, and the width of a rectangular loop in the lower layer of FSS is 1.742 mm. Our proposed uni-planar EBG double-layer of FSSs based UWB antenna reaches S11 parameter of ?42.381, a ?10 dB impedance bandwidth of 1.941 GHz (12.964–14.905 GHz), and a VSWR of 1.0154 in operation frequency 14 GHz. In addition, our UWB antenna design has a high gain about 6.1 dB. Applying of uni-planar EBG double-layer of FSSs improve significantly the performance characteristic of UWB antenna.