OFDM-UWB Signals Research Articles

A software reconfigurable optical multiband UWB system utilizing a bit-loading combined with adaptive LDPC code rate scheme

Abstract In this paper, an effective bit-loading combined with adaptive LDPC code rate algorithm is proposed and investigated in software reconfigurable multiband UWB over fiber system. To compensate the power fading and chromatic dispersion for the high frequency of multiband OFDM UWB signal transmission over standard single mode fiber (SSMF), a Mach-Zehnder modulator (MZM) with negative chirp parameter is utilized. In addition, the negative power penalty of −1 dB for 128 QAM multiband OFDM UWB signal are measured at the hard-decision forward error correction (HD-FEC) limitation of 3.8 × 10 −3 after 50 km SSMF transmission. The experimental results show that, compared to the fixed coding scheme with the code rate of 75%, the signal-to-noise (SNR) is improved by 2.79 dB for 128 QAM multiband OFDM UWB system after 100 km SSMF transmission using ALCR algorithm. Moreover, by employing bit-loading combined with ALCR algorithm, the bit error rate (BER) performance of system can be further promoted effectively. The simulation results present that, at the HD-FEC limitation, the value of Q factor is improved by 3.93 dB at the SNR of 19.5 dB over 100 km SSMF transmission, compared to the fixed modulation with uncoded scheme at the same spectrum efficiency (SE).

Wavelet packet transform‐based time of arrival estimation method for orthogonal frequency division multiplexing ultra‐wideband signal

This study discusses the estimation of time of arrival (TOA) used for ranging and positioning applications in orthogonal frequency division multiplexing ultra-wideband- (OFDM-UWB) based system. The correlation-based method applied for impulse radio-UWB (IR-UWB) is not suitable for OFDM-UWB because OFDM-UWB signal is much longer than IR-UWB in time domain. This study proposes a new method for TOA estimation of OFDM-UWB signal based on wavelet packet transform (WPT). The author's method estimates TOA of OFDM-UWB signal through the time information of the frequency band of UWB, which is one of the branches of WPT decomposition of the oversampled received baseband signal. It does not need the whole OFDM signal to estimate TOA of UWB signal because every segment of OFDM-UWB signal in time domain contains all information of UWB frequency band; therefore the resolution of TOA is improved. Signal-to-noise ratio can also be improved because WPT decomposes the power of additive white Gaussian noise equally in all wavelet packet branches, and false alarm rate can be controlled. The author's method is robust in that it can counter narrow band noise and impulse noise effectively. Numerical results show our method is effective for accurate estimation of TOA for OFDM-UWB signal.

Transmission improvement due to pre-emphasis of multi-band OFDM-UWB signals in LR-PONs using directly modulated lasers

The transmission improvement obtained through the usage of pre-emphasis (PE) of single-band and multi-band orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) signals using directly modulated lasers (DML) along long-reach passive optical networks is experimentally evaluated. Additionally, OFDM-UWB sub-bands with central frequencies above the cut-off frequency of the DML are experimentally considered in order to evaluate extending the transmission capacity through the usage of PE. In case of single-band transmission, PE improves the bit error ratio (BER) of several OFDM-UWB sub-bands by more than two orders of magnitude in back-to-back conditions as well as after transmission along 100 km of standard single-mode fiber transmission (SSMF). Such improvement is limited by the reduced intensity modulation response variation of the DML within the passband of each OFDM-UWB sub-band, as fixed modulation index is considered in all tested cases. Considering multi-band transmission along 100 km of SSMF, PE allows doubling the number of transmitted sub-bands before a BER exceeding is achieved for any of the sub-bands and an optical signal-to-noise ratio of 25 dB0.1 nm. Such improvement is obtained as PE changes the effective modulation depth of each transmitted OFDM-UWB sub-band, so that equalized signal power after detection and almost identical BER in all OFDM-UWB sub-bands occur.

Transmission of OFDM-UWB Radio Signals in IM–DD Optical Fiber Communication Systems Employing Optimized Dual Parallel Mach–Zehnder Modulators

A dual parallel Mach–Zehnder modulator (DPMZM) used for electro-optic conversion of multi-band orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) radio signals in intensity modulated direct detection optical communication systems is optimized theoretically and through numerical simulation. The optimum DPMZM parameters that allow simultaneous mitigation of the second and third order distortion components created by the joint electro-optic converter and photodiode nonlinearities are identified. The corresponding minimum optical signal-to-noise ratio (OSNR) required to achieve a bit error ratio of 10−9 is also evaluated. An analytical expression showing the relation between the optimum DPMZM parameters under extended voltage levels of the OFDM-UWB signals applied to the DPMZM is proposed and validated. It is shown that the DPMZM performance presents high robustness to deviations from the optimum DPMZM parameters identified. Additionally, it is shown that similar minimum required OSNR levels are obtained with the optimized DPMZM and when the electro-optic conversion is realized by a single MZM.

Performance comparison of power fading mitigation techniques in multiband OFDM-UWB signals transmission along LR-PONs

The single sideband (SSB) modulation is assessed as a means to mitigate the dispersion-induced power fading on the distribution of ortogonal frequency division multiplexing (OFDM) ultra wideband (UWB) radio signals along long-reach passive optical networks (LR-PONs). Particularly, two different SSB architectures, namely, Sieben's architecture and four phase modulator (FPM) architecture are optimized to provide maximum sideband suppression. The minimum optical signal-to-noise ratio (OSNR) required to simultaneously distribute all the 14 OFDM-UWB sub-bands along the LR-PON distances ranging between 80 and 100 km is also evaluated through numerical simulation. FPM architecture is preferable over Sieben's architecture because the latter SSB architecture generates carriers-carriers beat term at the photodetector output with high power, thereby causing significant degradation in the OFDM-UWB sub-bands with lower central frequencies. The simultaneous distribution of the 14 SSB OFDM-UWB sub-bands in the LR-PON using the FPM architecture shows a minimum OSNR penalty of 3 dB compared with the centralized dispersion compensation technique.

Transmission of Multiband OFDM-UWB Signals Along LR-PONs Employing a Mach–Zehnder Modulator Biased at the Quasi-Minimum Power Transmission Point

The influence of the Mach-Zehnder modulator (MZM) bias and driving voltages on the transmission performance of multiband orthogonal frequency division multiplexing ultrawideband radio signals is analyzed theoretically and experimentally. Particularly, the optical signal-to-noise ratio (OSNR) required to achieve a given bit error probability is evaluated for a bias voltage close to the minimum power transmission of the MZM characteristic. In addition, the required OSNR obtained for that bias voltage is compared with the OSNR required when the MZM is biased at the quadrature point. The analysis is performed for different fiber lengths indicated for long-reach passive optical networks (LR-PONs). It is shown that lower OSNR is required when the modulator is biased at the quasi-minimum point than when it is biased at the quadrature point, for all the fiber reaches analyzed. This is due to the compromise between additional distortion induced by the modulator and lower carrier-to-signal-power ratio when the quasi-minimum bias point is employed. In addition, it is also shown that, as for the quadrature bias point, similar optimum driving voltages are obtained for the different LR-PONs reaches analyzed, when the quasi-minimum bias point is employed.

A 1.2 V, 130 nm CMOS parallel continuous-time [formula omitted] ADC for OFDM UWB receivers

The design and implementation in a 1.2V, 130nm CMOS technology of a parallel continuous-time ΣΔ modulator for OFDM UWB signals is described. Once the parallel architecture and the metrics used are presented, the NTF is optimized and implemented using a third order lowpass and a fourth order bandpass modulator. Both are CRFB structures which use active-RC integrators. Then, the circuital blocks are discussed and some comments about the test set-up are given. Experimental results show good agreement with both system-level and layout-level simulations, with up to 15dB DR for QPSK modulation over a signal bandwidth of 528MHz, with a 62.3mW power consumption.

Experimental study of coexistence of multi-band OFDM-UWB and OFDM-baseband signals in long-reach PONs using directly modulated lasers

Transmission of coexisting Orthogonal Frequency Division Multiplexing (OFDM)-baseband (BB) and multi-band OFDM-ultra-wideband (UWB) signals along long-reach passive optical networks using directly modulated lasers (DML) is experimentally demonstrated.When optimized modulation indexes are used, bit error ratios not exceeding 5 × 10⁻⁴ can be achieved by all (OFDM-BB and three OFDM-UWB sub-bands) signals for a reach of 100 km of standard single-mode fiber (SSMF) and optical signal-to-noise ratios not lower than 25dB@0.1 nm. It is experimentally shown that, for the SSMF reach of 100km, the optimized performance of coexisting OFDM-BB and OFDM-UWB signals is mainly imposed by the combination of two effects: the SSMF dispersion-induced nonlinear distortion of the OFDM-UWB signals caused by the OFDM-BB and OFDM-UWB signals, and the further degradation of the OFDM-UWB signals with higher frequency, due to the reduced DML bandwidth.

Optical Generation and Distribution of OFDM Ultrawideband Signals Over Fiber

In this paper is presented an architecture aiming the distribution of orthogonal frequency division multiplexing (OFDM) signals, compatible with ultra-wide band (UWB) standards, in wavelength division multiplexing (WDM) radio-over-fiber (RoF) scenario. The suggested WDM architecture allows unicast and multicast transmission of OFDM signals within the standard millimeter-wave (mm-wave) UWB bands, from 3.1 to 10.6 GHz and from 57 to 64 GHz, respectively 8 GHz and 60 GHz. The generation of the OFDM-UWB signals with the desired mm-wave carriers' frequencies is made using an optical frequency-quadrupling technique, thus with lower bandwidth requirements for the optical modulator, and allowing the use of a lower frequency electrical drive signal. The OFDM-UWB signals distribution is fully passive, recurring to a cyclic AWG (Arrayed Waveguide Grating). Two types of modulation are used, double side band (DSB) for up-/down-link unicast transmission and DSB with carrier suppression for down-link multicast. In this later case, we avoid the need for high precision filtering, to remove the optical carrier at the receiver, providing a system with greater tolerance to frequency variations. The system's performance is evaluated for different bit rates, input powers and transmission distances, allowing transmission up to 12 km over single mode fiber (SMF), with a maximum EVM below the maximum permissible relative constellation error which is set to a root mean square (RMS) EVM of 14.13% ECMA-368 International Standard: High rate ultra wide-band PHY and MAC Standard, 2007.

Combined Analysis of OFDM-UWB Transmission in Hybrid Wireless-Optical Access Networks

The hybrid wireless-optical transmission of ultra-wideband signals employing orthogonal frequency-division multiplexing modulation (OFDM) ultra-wideband (UWB) as defined in the ECMA-368 standard is experimentally analyzed in this letter. The OFDM-UWB signals provide 400 Mb/s per user at optical distances from 5 to 50 km on standard single-mode fiber (SSMF). The analysis includes the wireless radiation from 0 to 3 m after optical transmission. The results indicate a maximum error-vector-magnitude degradation of 2.5 dB measured at 1.5-m radio after 50-km SSMF optical transmission for the first two UWB channels. This degradation translates to 1-m maximum wireless-reach penalty.

Up-Conversion of Triple-Band OFDM UWB Signals by a Multimode VCSEL

We present novel experimental results for the all-optical up-conversion of the triple-band orthogonal frequency-division-multiplexing ultra-wideband radio signals from lower frequency band group 1 up to higher frequency band groups 2 or 3 based on the vertical-cavity surface-emitting laser optical second- and third-order nonlinearities. Low conversion losses and error vector magnitude values, respectively, for low bias currents have been demonstrated.

Performance Degradation Due to OFDM-UWB Radio Signal Transmission Along Dispersive Single-Mode Fiber

The performance degradation of orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) radio signals caused by transmission along dispersive single-mode fiber is assessed theoretically and by numerical simulation. It is shown that the performance degradation of OFDM-UWB signals caused by fiber dispersion is due to the power fading induced on the subcarrier showing stronger fading. Results show that the power fading description based on a small signal analysis provides good estimates of the optical signal-to-noise ratio degradation for OFDM-UWB signals with modulation index (defined as the ratio between the root-mean-square voltage of the OFDM-UWB signal and the bias voltage of the Mach-Zehnder modulator) values up to 18%. This is a pessimistic value for some OFDM-UWB carrier frequencies.