MB-OFDM Ultra Wideband Research Articles

NEURO FUZZY BASED PERFORMANCE ANALYSIS OF MULTIBAND ULTRA WIDE BAND ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM

This study proposes an efficient channel-estimation scheme for Multiband (MB) Orthogonal Frequency Division Multiplexing (OFDM)-based Ultra Wide Band (UWB) communication systems. One of the challenges in wireless system is the frequency selective fading caused due to multipath channel between the transmitter and receiver. The signal bandwidth in broad band cellular wireless systems typically exceeds the coherence bandwidth of the multipath channel. To overcome such a multipath fading environment with low complexity and to increase the performance, UWB OFDM system is used. To practically realize MB-OFDM UWB, one needs to cope with numerous design challenges, particularly in receiver designs such as symbol timing, Carrier Frequency Offset (CFO) and sampling frequency offset compensation, as well as Channel Frequency Response (CFR) estimation. A channel estimation scheme using a Takagi-Sugeno (T-S) fuzzy based neural network under the time varying velocity of the mobile station in a UWB OFDM system is proposed in this study. In our proposal, by utilizing the learning capability of Adaptive Neuro-Fuzzy Inference System (ANFIS), the ANFIS is trained with correct channel state information then the trained network is used as a channel estimator. To validate the performance of our proposed method, simulation results are given and found that it gives more accurate prediction of channel coefficients as compared with fuzzy channel estimator under various highly noisy multipath channel conditions.

DWT-IDWT-based MB-OFDM UWB with digital down converter and digital up converter for power line communication in the frequency band of 50 to 578 MHz

Over the last few years, power line communication (PLC) has gained importance for high-speed data communication. One of the major concerns in PLC is noise and high data rate, thus, several schemes have been adopted to minimize noise over PLCs and improve data rate. One of the promising approaches is the use of multi band (MB)–orthogonal frequency division multiplexing (OFDM) ultra wideband (UWB) to achieve date rates over 200 Mbps. One of the approaches is to integrate MB-OFDM UWB with digital down converter (DDC) for power line communication. A modified discrete wavelet transform (DWT) architecture with reduced memory, two-stage DDC, and modified DDS blocks are designed to generate MB-OFDM signal for PLC. From the results obtained, it is found that DWT-based MB-OFDM UWB outperformed FFT-based MB-OFDM UWB by approximately 6-dB gain in bit error rate (BER). Haar wavelet showed best performance over Biorthogonal (bior3.3, bior5.5), Daubechies (db2, db4), and reverse Biorthogonal (rbior3.3, rbior5.5) by approximately 2 dB. Though QPSK yielded better BER through observations, it is used for a constant power output transmitter, while QAM works better for a linear transmitter.

Bit and Power Allocation Algorithm for OFDM UWB Systems

Ultra-wide-band (UWB) is a promising short-range indoor wireless communication technology for large communication capacity, high transmission rate, low power consumption, etc. Multi-band orthogonal frequency-division multiplexing ultra-wide-band (MB-OFDM UWB) system can achieve much higher anti-noise capability and flexibility. However, the transmission power of UWB systems is strictly restricted for avoiding the interference with other wireless communication systems existing in the same frequency spectrum range. It is necessary that adequately utilizes channel estimation to allocate bit and power effectively. According to the change of channel gain, UWB systems modify the allocation factor to optimize the performance of systems and reduce power allocation remainder. Simulation shows modified bit-power allocation algorithm can enhance power allocation efficiency. Furthermore, it is found that the power remainder of modified allocation factor algorithm is less influenced by the bit error rate.

Simple 60-GHz MB-OFDM Ultrawideband RoF System Based on Remote Heterodyning

A simple 60-GHz radio-over-fiber system employing a combination of uncorrelated optical heterodyning and envelope detection is proposed and experimentally demonstrated. At the central office, a multiband orthogonal frequency division multiplexing ultrawideband (MB-OFDM UWB) signal is used for the external modulation of a dual-arm Mach-Zehnder Modulator to generate an optical signal-sideband signal, which is then coupled with an unmodulated free-running continuous wave laser. Optical heterodyne mixing at the base station and envelope detection at the customer unit are utilized. The experimental results confirm that photonic millimeter-wave signal generation and detection can be achieved without the need for complex optical phase-locked loops and high-frequency microwave sources. As a proof of concept, successful transmission of a 3.84 Gb/s 16-QAM MB-OFDM UWB signal over 48-km standard single-mode fiber without chromatic dispersion compensation and a further 4-m wireless channel is experimentally demonstrated.

Adaptive low-rank channel estimation for multi-band OFDM ultra-wideband communications

In this paper, an adaptive channel estimation scheme based on the reduced-rank (RR) Wiener filtering (WF) technique is proposed for multi-band (MB) orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) communication systems in multipath fading channels. This RR-WF-based algorithm employs an adaptive fuzzy-inference-controlled (FIC) filter rank. Additionally, a comparative investigation into various channel estimation schemes is presented as well for MB-OFDM UWB communication systems. As a consequence, the FIC RR-WF channel estimation algorithm is capable of producing the bit-error-rate (BER) performance similar to that of the full-rank WF channel estimator and superior than those of other interpolation-based channel estimation schemes.

A High-Linearity 264-MHz Source-Follower-Based Low-Pass Filter with High-Q Second-Order Cell for MB-OFDM UWB

Source-follower-based (SFB) continuous-time low-pass filters (LPF) have the advantages of low power and high linearity over other filter topologies. The second-order SFB filter cells, which are key building blocks for high-order SFB filters, are often realized by composite source follower with positive feedback. For a single branch 2nd-order SFB cell, the linearity drops severely at high frequencies in the pass band because its slew-rate is restricted by the Q factor and the pole frequency. The folded 2nd-order SFB cell provides higher linearity because it has two DC branches, and hence has another freedom to increase the slew rate. However, because of the positive feedback, the folded and unfolded 2nd-order SFB cells, especially those with high Q factors, tend to be unstable and act as relaxation oscillators under given circuit parameters. In order to obtain higher Q factor, a new topology for the 2nd-order SFB cell without positive feedback is proposed in this paper, which is unconditionally stable and can provide high linearity. Based on the folded 2nd-order SFB cell and the proposed high-Q SFB cell, a 264MHz sixth-order LPF with 3 stages for ultra wideband (UWB) applications is designed in 0.18µm CMOS technology. Simulation results show that the LPF achieves an IIP3 of above 12.5dBm in the whole pass band. The LPF consumes only 4.1mA from a 1.8V power supply, and has a layout area of 200µm × 150µm.

Adaptive data distribution technique for enhancing MB-OFDM UWB link performance in detect and avoid environments

Detect-and-avoid (DAA) mechanisms were developed to minimise potential interference caused by ultra wideband (UWB) systems to in-band active narrowband links. Interference is reduced by minimising emitted power in overlapping bands to create a spectral notch, which provides a certain level of isolation between both systems. Although it has been proved that this procedure deteriorates UWB link performance significantly, no research suggested any scheme to mitigate it. In this paper, we introduce the adaptive data distribution (ADD) technique, which we developed to enhance UWB link performance upon employment of DAA. ADD technique is confined to the physical layer and is fully transparent to the MAC sub-layer. Results have shown a significant reduction in error rates that could provide an SNR gain of at least 4 dB for most covered scenarios. In addition, ADD technique renders performance less sensitive to transmission mode variation and augments its coexistence capability by enabling a UWB device to safely notch 16-55% of its bandwidth.

Some interesting results on compatible BER analysis issues related to multi-band timing and frequency synchronizers applicable for MB-OFDM based UWB communications

A closed form expression of bit-error-rate (BER) has immense importance for insightful understanding on the performance of a communication system. In this paper we provide the BER analysis of a convolution coded MB-OFDM Ultra-Wideband (UWB) system that captures the log-normal fading statistics of UWB channels and also considers the estimation error variances of timing and carrier frequency offset (CFO) estimation by our already published synchronizers ATS (Sen et al., 2008 [1,2]) and MBAFS (Sen et al., 2008 [3,4]) respectively. By invoking the moment generating function (MGF) for log-normal fading statistics and using the Gauss-Hermite quadrature integration the average BER for rate Rc coded QPSK modulation with ATS and MBAFS synchronizers and channel estimation by least square (LS) method is obtained. We compare the analytical result with simulation results in highest delay spread UWB channel model CM4 and validate the consistency of our theoretical analysis.

A low-spurious fast-hopping MB-OFDM UWB synthesizer

A frequency synthesizer for the ultra-wide band (UWB) group #1 is proposed. The synthesizer uses a phase-locked loop (PLL) and single-sideband (SSB) mixers to generate the three center frequencies of the first band group by mixing 4224 MHz with ±264 MHz and 792 MHz, respectively. A novel multi-QSSB mixer is designed to combine the function of frequency selection and frequency conversion for low power and high linearity. The synthesizer is fabricated in Jazz 0.18-μm RF CMOS technology. The measured reference spur is as low as −69 dBc and the maximum spur is the LO leakage of −32 dBc. A low phase noise of −110 dBc/Hz @ 1 MHz offset and an integrated phase noise of 1.86° are achieved. The hopping time between different bands is less than 1.8 ns. The synthesizer consumes 30 mA from a 1.8 V supply.

Efficacy of Multiband OFDM Approach in High Data Rate Ultra WideBand WPAN Physical Layer Standard using Realistic Channel Models

Multiband Orthogonal Frequency Division Multiplexing (MBOFDM) approach using UWB signals with short duration of pulses provide unique advantages in short-range high data rate wireless applications which include easy penetration through obstacles, high precision ranging and low processing power. In this paper a performance study on MB-OFDM is attempted for high data rate ultra wideband (UWB) WPAN physical layer standard according to modulation techniques such as QPSK, 16-QAM, 64-QAM etc. Different multipath components in the UWB channels are characterized by different delays and attenuation. The channel models chosen in simulation of MB-OFDM UWB communication system are different from standard UWB channels considering realistic multipath resolution and operating frequencies. In this research different amplitude fading statistics for UWB channel (IEEE 802.15.3a) are analysed. The BER performance of MB-OFDM UWB on modified UWB channel models are investigated through simulation study. It is observed that QPSK modulation for the MB-OFDM UWB system performs better than 16-QAM and 64-QAM in the CM3 (NLOS) and CM4 (NLOS) channel environment. We show that, at low data rate (55 Mbps) the MB-OFDM system performs better in the CM4 channel environment than in the CM3, CM2 and CM1 channel model due to its inherent frequency diversity. In high data rate (480 Mbps), the BER performance in CM1 channel model is found to be better than in CM2, CM3, CM4 channel model.

Impact of Optical Transmission on Multiband OFDM Ultra-Wideband Wireless System With Fiber Distribution

Multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) wireless, which provides high data rate access, is required to be distributed by using optical fiber. The performance of MB-OFDM UWB over fiber transmission system is investigated considering optical modulation and demodulation impact. Theoretical analysis of the effect of fiber dispersion, optical transmitter, and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted and verified by our theoretical analysis and good agreement is obtained. It is found that RF modulation index of ~4% is optimum for optical transmitter with Mach-Zehnder modulator, and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. Compared to back-to-back UWB over fiber, optical transmission is mainly limited by laser phase noise converted relative intensity noise and phase distortion induced by fiber dispersion when optimum modulation index is used. Higher modulation index is limited by amplitude and phase distortion to OFDM signal induced by optical transmitter and receiver response nonlinearities and fiber dispersion and the spectral mask. It is also found that highly received optical power is required for transmission of MB-OFDM UWB signal over fiber.

Investigation of the Performance of Multiband Orthogonal Frequency Division Multiplexing Ultrawideband Over Fiber Transmission Under the Presence of In-Band Interferers

Multiband (MB) orthogonal frequency division multiplexing (OFDM) ultrawideband (UWB) wireless, which provides high-data-rate access, must be distributed by use of optical fiber. UWB receivers are anticipated to operate under hostile interference environments. So the study of the coexistence of various communication standards with MB-OFDM UWB over fiber is an important issue. The performance of MB-OFDM UWB over fiber transmission system is investigated, considering the effect of in-band narrowband jammers such as WiMAX, MIMO WLAN, WLAN, and marine radar. Experiments were performed to show the effect of fiber transmission under various interferer power levels. It is found that in-band interferers can cause severe degradation in system performance if any interferer to the UWB peak power ratio is not held below a certain level. The results also show that MB-OFDM UWB over fiber transmission is more vulnerable to certain interferers such as WiMAX and radar signals than to the other in-band jammers.

System and Circuit Design for an MB-OFDM UWB Frequency Synthesizer

This paper presents a complete top-down design and experimental results for a fast-hopping 11-band 3-10-GHz frequency synthesizer. The system requirements for a synthesizer in an ultrawideband (UWB) radio are discussed. The synthesizer specifications for 480-Mb/s- and 1-Gb/s-data-rate multiband orthogonal-frequency-division-multiplexing UWB radios using quadrature phase shift keying and 16-quadrature amplitude modulation, respectively, are provided. The circuit-level implementation of this microwave system is described in detail including layout considerations. Fabricated in a 0.25-mum SiGe BiCMOS process and integrated in a receiver, the synthesizer was characterized in a quad-flat-no-leads package while being mounted on an FR-4 substrate. Measurement results and a model-hardware correlation analysis are presented.

480-Mbps, Bi-Directional, Ultra-Wideband Radio-Over-Fiber Transmission Using a 1308/1564-nm Reflective Electro-Absorption Transducer and Commercially Available VCSELs

We describe 480 Mbps, bi-directional ultra-wideband (UWB) radio signal transmission over 1 km of single-mode optical fiber. Key components are a highly linear, reflective electro absorption transducer (EAT) and commercially available 1308-nm and 1564-nm VCSELs with 4.8-GHz bandwidth. Detailed EAT and 1308-nm VCSEL distortion analyses and measurements are presented highlighting the low intermodulation and harmonic distortion necessary for typical -18-dB wireless channel error vector magnitudes (EVMs). Direct VCSEL modulation with Wimedia supported band group 1 (3.1-4.8 GHz) MB-OFDM UWB signals was modelled with VPItransmissionMaker, suggesting a minimum EVM of -18.733 dB at 0.4502 OMI. This was confirmed by 480 Mbps upstream and downstream EVM measurements over fiber of -21.4 dB or better. Fully functional, half-duplex, bi-directional data transfer was achieved with interlocked RF switches.

Mitigation of UWB Signals Spectral Leakage to the GPS L1 Band via Filtering After Clipping in the UWB Transmitter

Ultra-wideband (UWB) has recently attracted much attention as an indoor short-range high-speed wireless communication. However, the high peak-to-average power ratio (PAPR) limits its capacity due to distortion caused by nonlinear components such as high-power amplifiers. Hence it is necessary to reduce the PAPR of UWB signals. Deliberate clipping is a simple technique for PAPR reduction. But PAPR reduction of UWB signals by clipping may cause spectral leakage. The spectral power leakage to outside frequency bands causes interference with the other systems operating in the vicinity of UWB. Global Positioning System (GPS) has a pivotal role in so many critical systems upon which the public depends for its safety and well-being, and thus it is necessary to assess the interference to the GPS band due to UWB signals spectral leakage. Therefore, in this paper, the interference to the GPS caused by spectral leakage of clipped direct-sequence UWB (DS-UWB) signals and multiband orthogonal frequency division multiplexing UWB (MB-OFDM UWB) signals is assessed, and the effect of filtering after clipping on the spectral leakage is evaluated using power spectral density (PSD) and bit-error rate (BER) as performance measures.

A 12-mW 264-MHz high linearity sharp roll-off CMOS opamp-RC low-pass filter for MB-OFDM UWB systems

This paper presents a high linearity wideband sharp roll-off Opamp-RC low-pass filter (LPF) for Ultra wideband (UWB) applications. The proposed LPF is composed of three biquads’ transfer functions with different Q-factors in series. Sharp roll-off is attributed to the steep slope of the peaking of a biquad transfer function with a high Q-factor. The superposition of these biquads also helps extend the bandwidth of the overall LPF transfer function without the cost of extra power dissipation. The effects of biquad arrangements on noise and linearity performances are investigated. A simple operational amplifier (op-amp) is adopted to ensure high frequency characteristics and high linearity performance for the designed filter. The LPF is implemented in 0.13-μm IBM CMOS process from 1.5 V supply. The measured cutoff frequency is 264 MHz with the pass-band ripple of less than 1 dB. Digital frequency tuning is implemented with 40% of tuning range around the cutoff frequency. The amount of out-of-band rejection at 290 MHz and at twice cutoff frequency is 12 dB and about 50 dB, respectively. Good linearity with IIP3 of 23 dBm is obtained. The 6th-order LPF dissipates only 12 mW with the active chip size of 400 × 640 μm2.

A Fully Differential Band-Selective Low-Noise Amplifier for MB-OFDM UWB Receivers

A band-selective low-noise amplifier (BS-LNA) for multiband orthogonal frequency-division multiplexing ultra-wide-band (UWB) receivers is presented. A switched capacitive network that controls the resonant frequency of the LC load for the band selection is used. It greatly enhances the gain and noise performance of the LNA in each frequency band without increasing power consumption. Moreover, a fully differential configuration is employed to suppress the common-mode switching noise that is generated during the band transition interval. Fabricated in a 0.18-mum CMOS process, the BS-LNA achieves a peak power gain of 16 dB, a minimum noise figure of 2.74 dB, and an third-order input intercept point of -8.8 dBm at a current consumption of 7.95 mA from a 1.5-V supply. Little performance degradation is observed when the current consumption is reduced by half. The experimental results also show a worst-case band-switching time of less than 3.4 ns, with a peak switching noise voltage of less than 70 muV at the output.

A Reconfigurable Narrow-Band MB-OFDM UWB Receiver Architecture

This paper presents an analysis on the receiver front-end architectures for multiband orthogonal frequency-division multiplexing ultra-wide-band (UWB) terminals. An interference analysis is carried out in order to derive the main linearity specifications of the receiver front-end. A reconfigurable narrow-band architecture is introduced that can best cope with the main challenges of the UWB receivers: broadband impedance matching and high out-of-band linearity. Simulation results show that linearity requirements can be achieved with sizeable margin.

A High-Speed Two-Parallel Radix-24 FFT/IFFT Processor for MB-OFDM UWB Systems

This paper presents a novel high-speed, low-complexity two-parallel 128-point radix-24 FFT/IFFT processor for MB-OFDM ultrawideband (UWB) systems. The proposed high-speed, low-complexity FFT architecture can provide a higher throughput rate and low hardware complexity by using a two-parallel data-path scheme and a single-path delay-feedback (SDF) structure. The radix-24 FFT algorithm is also realized in our processor to reduce the number of complex multiplications. The proposed FFT/IFFT processor has been designed and implemented with 0.18-μm CMOS technology in a supply voltage of 1.8 V. The proposed two-parallel FFT/IFFT processor has a throughput rate of up to 900 Msample/s at 450 MHz while requiring much smaller hardware complexity and low power consumption.

Performance Analysis of Multiband OFDM UWB Systems With Imperfect Synchronization and Intersymbol Interference

This paper provides performance analysis of MB-OFDM UWB systems that not only captures the characteristics of realistic ultra-wideband (UWB) channels, but also takes into consideration of the imperfection of the frequency and timing synchronizations and the effect of intersymbol interference. The systems are considered in multipath fading channels, the IEEE 802.15.3a channel standard, with four channel models: CM1, CM2, CM3, and CM4. These channel models are characterized by cluster arrival rate, ray arrival rate within clusters, and cluster and ray decay factors. First, an average signal-to-noise ratio with imperfect synchronizations and intersymbol interference is derived. Then a closed-form bit error rate performance formulation that provides insightful understanding of the system performance in various synchronization conditions is obtained under Rayleigh fading assumption. This analytical performance formulation serves as an upper bound on the bit error rate performance of UWB systems. Finally, simulation results under various channel and synchronization conditions are provided to validate the theoretical analysis.