Multiband Orthogonal Frequency Division Multiplexing Ultra Wideband Research Articles

A CMOS 90 nm 55 mW 3.4-to-9.2 GHz 12 Band Frequency Synthesizer for MB-OFDM UWB

A frequency synthesizer for ultra-wideband (UWB) multiband orthogonal frequency division multiplexing (MB-OFDM) applications is designed in TSMC 90 nm CMOS technology. It is based on two wideband PLLs (8 MHz open loop unit gain frequency) capable of settling in less than 300 ns with a 66 MHz external reference. The PLL tuning range (6.6-9.2 GHz) is extended down to 3.4 GHz by a dedicated circuit able to divide the output frequency by 1, 1.5 and 2 with a power consumption of less than 3 mW. Measured data fit the UWB MB-OFDM specifications with an integrated phase noise of 2.8RMS o at maximum output frequency and an aggregate spurious tone power of less than -27 dBc. The joint power consumption is 55 mW and the synthesizer core area occupies less than 0.5 mm2 .

Frequency Quadrupler for Millimeter-Wave Multiband OFDM Ultrawideband Wireless Signals and Distribution Over Fiber Systems

Performance of millimeter-wave (mm-wave) multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) signal generation using a frequency-quadrupling technique and transmission over fiber is investigated by simulation and experiment, and the error vector magnitude (EVM) is used to evaluate the transmission quality. Frequency hopping within the first three bands of IEEE 802.15.3a has been used in experiments to obtain an MB-OFDM UWB signal. The frequency quadrupling can be achieved by using only one Mach–Zehnder modulator (MZM) and two cascaded MZMs. It is found that using one MZM is better than using two cascaded MZMs in the performance of mm-wave generation. For using one MZM, it is found that transmission through 20 km of fiber degrades the EVM by less than 0.5 dB compared with back-to-back. Also, the EVM is degraded by less than 1 and 0.25 dB for a bias drift of less than 20% and an extinction ratio of more than 10 dB, respectively. Moreover, the EVM of the system using one MZM is improved by more than 2.5 dB compared with the two cascaded MZMs. In addition, it is found that the minimum EVM required of −17 dB can be achieved by using a local oscillator modulation index of ∼63% and 70% at least for using the one MZM and two cascaded MZMs, respectively.

Impact of WiMAX interference on MB-OFDM UWB systems: analysis and mitigation

This paper presents an analysis of the performance of the multiband orthogonal frequency division multiplexing (MB-OFDM) system for ultra wideband (UWB) communication in the presence of interference from IEEE 802.16 WiMAX systems operating in the 3.5 GHz band. We present an exact analysis of the uncoded bit error rate (BER) of the MB-OFDM system, based on Laplace transform techniques. We also present a simple Gaussian approximation for the WiMAX interference, and establish its relative accuracy and usefulness by means of comparison with the exact analysis and simulations. Such a Gaussian approximation is especially useful for simplified performance analysis, as well as for the design of interference mitigation techniques. Motivated by the Gaussian approximation, we propose a simple two-stage interference mitigation technique for coded MB-OFDM transmissions, consisting of interference spectrum estimation during silent periods followed by appropriate bit metric weighting during Viterbi decoding. We compare parametric and non-parametric spectrum estimation techniques for various scenarios of interest. In the presence of WiMAX interference, the two-stage interference mitigation provides substantial gains in performance in return for modest increases in complexity and without requiring any modifications to the MB-OFDM transmitter or signal structure.

Performance of BICM-OFDM systems in UWB interference

In this paper, we develop an analytical framework for performance analysis of generic bit-interleaved coded modulation orthogonal frequency-division multiplexing (BICMOFDM) systems impaired by ultra-wideband (UWB) interference. For practical relevance we consider multi-band OFDM (MB-OFDM), direct-sequence UWB (DS-UWB), and impulseradio UWB (IR-UWB) interference formats following recent IEEE/ECMA standards or standard proposals. Besides the exact analysis we calculate the bit error rate (BER) for the case when the UWB interference is modeled as additional Gaussian noise. Our results show that in general the BER of the BICM-OFDM system strongly depends on the UWB format and the OFDM sub-carrier spacing. While the Gaussian approximation is very accurate for DS-UWB, it may severely overor underestimate the true BER for MB-OFDM and IR-UWB interference. Our analysis is applicable to e.g. IEEE 802.11 wireless local area networks (WLANs), IEEE 802.16 wireless access systems (WiMAX), and 4th generation mobile communication systems. Furthermore, since the ECMA MB-OFDM standard is also based on the BICM-OFDM concept, our analysis can also be used to evaluate the impact of other UWB signals on ECMA MB-OFDM UWB systems.

Review of Glass and Polymer Multimode Fibers Used in a Wimedia Ultrawideband MB-OFDM Radio Over Fiber System

In this paper, we have exhibited the potential of the glass- and polymer-based multimode fibers to be used in a radio over fiber (ROF) system in order to extend the indoor coverage of the Wimedia multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) standard. After the design of a test setup operating at 850 nm, we have performed the physical characterization of the ROF system especially the mask test compliance, the error vector magnitude (EVM), or the relative constellation error (RCE) variation as a function of the system parameters [radio frequency (RF) power, optical attenuation, fiber length, laser bias current]. The transmission performance of both 200 and 480 Mb/s Wimedia signals is demonstrated through a 100 m link length of glass- and polymer-based multimode fibers: transmission penalties are quantified by RCE with values under the standard requirements. Two different behaviors depending on the core material of the fiber have been identified in this study.

Hardware Implementation of a Genetic Algorithm Based Canonical Singed Digit Multiplierless Fast Fourier Transform Processor for Multiband Orthogonal Frequency Division Multiplexing Ultra Wideband Applications

Problem statement: Ultra Wide Band (UWB) technology has attracted many researchers' attention due to its advantages and its great potential for future applications. The physical layer standard of Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) UWB system is defined by ECMA International. In this standard, the data sampling rate from the analog-to-digital converter to the physical layer is up to 528 M sample sec-1. Therefore, it is a challenge to realize the physical layer especially the components with high computational complexity in Very Large Scale Integration (VLSI) implementation. Fast Fourier Transform (FFT) block which plays an important role in MB-OFDM system is one of these components. Furthermore, the execution time of this module is only 312.5 ns. Therefore, if employing the traditional approach, high power consumption and hardware cost of the processor will be needed to meet the strict specifications of the UWB system. The objective of this study was to design an Application Specific Integrated Circuit (ASIC) FFT processor for this system. The specification was defined from the system analysis and literature research. Approach: Based on the algorithm and architecture analysis, a novel Genetic Algorithm (GA) based Canonical Signed Digit (CSD) Multiplier less 128-point FFT processor and its inverse (IFFT) for MB-OFDM UWB systems had been proposed. The proposed pipelined architecture was based on the modified Radix-22 algorithm that had same number of multipliers as that of the conventional Radix-22. However, the multiplication complexity and the ROM memory needed for storing twiddle factors coefficients could be eliminated by replacing the conventional complex multipliers with a newly proposed GA optimized CSD constant multipliers. The design had been coded in Verilog HDL and targeted Xilinx Virtex-II FPGA series. It was fully implemented and tested on real hardware using Virtex-II FG456 prototype board and logic analyzer. Results: From the synthesis reports, the proposed GA optimized CSD constant complex multiplier achieved 79 and 50% equivalent gates and latency efficiency when compared to the conventional complex multiplier. Conclusion: As a conclusion, we successfully implemented 128-points FFT/IFFT processor with the proposed architecture that can meet the requirement of MB-OFDM UWB system with higher throughput and less area compared to conventional architecture.

Space-Time-Frequency Code implementation in MB-OFDM UWB communications: Design criteria and performance

This paper proposes a general framework of space-time-frequency codes (STFCs) for multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wide band (UWB) communications systems. A great similarity between the STFC MB-OFDM UWB systems and conventional wireless complex orthogonal space-time block code (CO STBC) multiple-input multiple-output (MIMO) systems is discovered. This allows us to quantify the pairwise error probability (PEP) of the proposed system and derive the general decoding method for the implemented STFCs. Based on the theoretical analysis results of PEP, we can further quantify the diversity order and coding gain of MB-OFDM UWB systems, and derive the design criteria for STFCs, namely diversity gain criterion and coding gain criterion. The maximum achievable diversity order is found to be the product of the number of transmit antennas, the number of receive antennas, and the FFT size. We also show that all STFCs constructed based on the conventional CO STBCs can satisfy the diversity gain criterion. Various baseband simulation results are shown for the Alamouti code and a code of order 8. Simulation results indicate the significant improvement achieved in the proposed STFC MB-OFDM UWB systems, compared to the conventional MB-OFDM UWB ones.

PILOT AND DATA SYMBOL-AIDED FREQUENCY ESTIMATION FOR UWB-OFDM

In this paper, an improved residual carrier frequency ofiset estimation scheme is proposed for ultra-wideband multiband orthogonal frequency division multiplexing (UWB-OFDM) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols convey identical information in an UWB-OFDM system. The mean square error of the synchronization scheme is derived, and its simple expression is also calculated. Finally, simulation results are demonstrated to verify the theoretical analysis in this paper.

A Study on Performance Enhancement of Packet Detection in MB-OFDM UWB Systems

This paper presents a high performance and hardware efficient packet detection structure, which employs a cross correlator for the M-sample time delayed correlation operation and a signal power calculator using the received input samples less than or equal to a zero-padded suffix of length M. We investigate the detailed characteristics of the proposed packet detector. In this paper, the performance of a class of packet detection algorithms in the ultra-wideband (UWB) channel environments is also studied. The best packet detection algorithm for the multi-band orthogonal frequency division multiplexing (MB-OFDM) UWB transmission is determined through analysis and extensive simulations. The results of analysis show that the proposed packet detection structure has advantages in the hardware complexity as well as performance when compared with the existing packet detection structures. In order to effectively conduct the packet detection before the automatic gain control (AGC) mode, we investigate the effects of both a frequency offset and the initial gain level of a variable gain amplifier (VGA) on the performance of the packet detection. We also suggest a VGA gain control technique to enhance the performance of packet detection.

Ultra wideband technologies coexistence in Nakagami-m fading channels

The wide spectrum of ultra wideband (UWB) communications makes it inevitable to consider strategies for avoiding and mitigating interference from narrowband wireless systems such as GPS, UMTS, and WLAN, or other UWB wireless technologies. In this paper, we provide a performance analysis of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB in the presence of binary phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions under Nakagami-m fading. In the bit-error rate (BER) analysis, several UWB interferers are considered to affect the MB-OFDM signal. A Gaussian approximation is considered for the UWB interferers and used in the analysis of the BER performance of the MB-OFDM UWB system. The Nakagami-m distribution is applied to characterise the amplitude of the fading channels for both the reference signal and the interference signals. Furthermore, a waveforming technique is considered for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.

Quasi-orthogonal space-time-frequency codes in MB-OFDM UWB

Quasi-orthogonal space-time-frequency codes (QOSTFCs) will be examined in this paper to advance either data rate or error performance in recently proposed space-time-frequency coded multiband OFDM Ultra-wideband (STFC MB-OFDM UWB) communication systems. It is shown that QOSTFCs can provide significantly better error performance, compared to the conventional MB-OFDM UWB (without STFCs) and to the orthogonal STFCs (OSTFCs) of the same order, at the same data rate, without increasing the total transmission power. Another form of the enhancement would be that QOSTFCs can provide higher data rates with the same error performance, compared to OSTFCs.

Bit Error Performance of STBC MB-OFDM UWB

Bit error performance is investigated in this letter for orthogonal space-time block coded (STBC) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems. As the channel model considers the log-normal fading, the resultant signal to noise ratio (SNR) follows a chi-squared log-normal distribution. Based on this, the bit error probability is derived. Furthermore, simulation verifies this theoretical result.

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.

Analysis of Narrowband Communication Systems Impaired by MB-OFDM UWB Interference

In this paper, we investigate the effect of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) interference on narrowband (NB) receivers. For this purpose, we first derive the exact moment generating function of MB-OFDM UWB interference. Based on this result, we develop analytical expressions for the amplitude probability distribution (APD) and the bit error rate (BER) of a binary phase-shift keying NB receiver. These expressions can be efficiently numerically evaluated and the presented analysis is general enough to encompass non-fading and various fading NB channels. We show that for NB signals with, respectively, much smaller and much larger bandwidths than the MB-OFDM sub-carrier spacing a Gaussian approximation (GA) and an impulsive GA (IGA) of the MB-OFDM UWB interference lead to accurate performance predictions. However, for most NB channel models and signal bandwidths the exact BER analysis has to be used to obtain meaningful results. An exception is the Rayleigh fading NB channel where both GA and IGA yield tight approximations of the exact BER regardless of the NB signal bandwidth.

Performance Analysis of Multiband OFDM UWB Communications With Application to Range Improvement

Ultrawideband (UWB) radio is a promising solution for high-rate wireless communications over short ranges. In this paper, the performance of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB systems is analyzed using the Saleh-Valenzuela channel model in terms of the packet error rate and the transmission range for indoor environments. The performance improvements resulting from the use of linear precoding and multiple antenna techniques are also analyzed and compared. It is shown both by theory and computer simulations that the two methods can effectively enlarge the transmission range of UWB devices.

Low-Power Limited-Search Parallel State Viterbi Decoder Implementation Based on Scarce State Transition

In this paper, a low-power Viterbi decoder design based on scarce state transition (SST) is presented. A low complexity algorithm based on a limited search algorithm, which reduces the average number of the add-compare-select computation of the Viterbi algorithm, is proposed and seamlessly integrated with the SST-based decoder. The new decoding scheme has low overhead and facilitates low-power implementation for high throughput applications. We also propose an uneven-partitioned memory architecture for the trace-back survivor memory unit to reduce the overall memory access power. The new Viterbi decoder is designed and implemented in TSMC 0.18-mum CMOS process. Simulation results show that power consumption is reduced by up to 80% for high throughput wireless systems such as Multiband-OFDM Ultra-wideband applications.

Frequency Dependence of Fading Statistics for Ultrawideband Systems

The variation of channel fading and dispersion statistics between the ultrawideband (UWB) channel subbands is characterized experimentally. Within the FCC-allocated UWB frequency range (3.1-10.6 GHz), the multipath characteristics in various subbands are found to be highly dissimilar. It is demonstrated that the higher subbands suffer greater attenuation, and the rms delay spread varies significantly with the center frequency. The impact of this variation on multiband-OFDM UWB system performance is evaluated, and a large performance variation across the band is reported

Transceiver Design for Multiband OFDM UWB

Ultra-wideband (UWB) is an emerging broadband wireless technology enabling data rates up to Mbps. This paper provides an overview of recent design approaches for several circuit functions that are required for the implementation of multiband OFDM UWB transceivers. A number of transceiver and synthesizer architectures that have been proposed in literature will be reviewed. Although the technology focus will be on CMOS, also some design techniques implemented in BiCMOS technologies will be presented.

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.

Transmit diversity for multiband OFDM UWB systems

Multiband orthogonal frequency division multiplexing (MB-OFDM) has been proposed as an effective solution for providing high speed data transmission over the ultra-wideband spectrum in short range wireless links. The employment of transmit diversity techniques based on block codes can achieve enhancement in such a wireless system's performance since it greatly reduces the detrimental effects of multipath fading. In a MB-OFDM UWB system the space coded symbols can be distributed as space-time block codes over successive OFDM symbols or as space-frequency block codes over neighbouring subcarriers. The authors investigate the performance of a MB-OFDM UWB system when it operates in conjunction with transmit diversity. More specifically, they analyse the suitability and performance of both space-time and space-frequency block coded MB-OFDM UWB system under various UWB channel models. The study shows that for the channel models considered, space-time block coding provides the best performance.