Multiband Orthogonal Frequency Division Multiplexing Signal Research Articles

100-Gb/s DD-MB-OFDM Metro Network With 11-Gb/s Granularity and 2.85-GHz Receiver

An ultra-dense 100-Gb/s multi-band orthogonal frequency division multiplexing (MB-OFDM) system employing virtual-carrier-assisted direct-detection and a 2.85-GHz receiver bandwidth is demonstrated experimentally. Nine OFDM bands with a band spacing of 6 GHz and a band capacity of 11 Gb/s are employed. The proposed system enables single-band extraction with low-complexity, provides high granularity, flexibility, and scalability, and is proposed for metropolitan (metro) networks. The experiments show that the transmission of the 100-Gb/s MB-OFDM signal comprising the nine-bands along metro networks reaching 150 km is successfully accomplished with bit error ratio levels below the forward error correction threshold. Reduced penalty relative to back-to-back operation is observed for optical power levels launched into each fiber span in the range between 0 and 4 dBm.

Ultra-selective flexible add and drop multiplexer using rectangular optical filters based on stimulated Brillouin scattering.

We demonstrate an ultra-selective flexible reconfigurable add and drop multiplexer (ROADM) structure enablingseparation and aggregation operations for multi-band orthogonal frequency division multiplexing(MB-OFDM) signal with ~2-GHz spectral granularity and 300-MHz guard band. The ROADM employs rectangular optical filters based on stimulated Brillouin effect (SBS) in fiber, which have steepedges, ~1-dB passband ripple and tunable bandwidth from 100 MHz to 3 GHz realized by two different kinds of electrical feedback pump control approaches. The ROADM performance is measured with MB-OFDM signals inquadrature-phase-shift-keying (QPSK) and 16-quadrature-amplitude-modulation (16-QAM) formats. For QPSK format signal, the SBS-ROADM induced penalty is ~0.7 dB while the performance for 16-QAM format is also acceptable.

High Granularity Multiband OFDM Virtual Carrier-Assisted Direct-Detection Metro Networks

A direct-detection metropolitan (metro) network employing multiband orthogonal frequency division multiplexing (MB-OFDM) signals (MORFEUS network) is proposed. The MORFEUS network employs virtual carriers to assist the detection of each OFDM band. It represents a cost-effective network enabling high granularity and flexibility, while requiring a reduced receiver bandwidth. The MB-OFDM signal structure and their main constraints are presented. Each MB-OFDM metro node is described and discussed, with particular attention dedicated to the blocks required to insert and extract a given OFDM band of the MB-OFDM signal. Conceptual solutions for the MORFEUS insertion and extraction blocks are also proposed and discussed. The performance of a 42.8-Gb/s MORFEUS network is evaluated through numerical simulation, and the network operation design is optimized. The impact of the optical filtering effect due to band add/drop operations is assessed as well. These studies are accomplished for systems employing band selectors (BS) with different selectivity to assess the performance tolerance to interband crosstalk and in-band amplitude distortion. The studies are performed for three MORFEUS networks, with granularity of 2-, 3-, and 4-bands. A required optical signal-to-noise ratio (OSNR) of 24 dB is demonstrated in a 240-km-long MORFEUS network without optical filtering cascade effect for a bit error ratio of $10^{-3}$. This required OSNR level is achieved for the three networks with different granularity and for the two BS analyzed after suitable optimization of the MB-OFDM system parameters. Compared with an ideal MORFEUS network employing ideal rectangular BS, the analyzed networks present an OSNR penalty not exceeding 2.5 dB. A required OSNR penalty of 1 dB due to optical filtering cascade is obtained after six nodes with band filtering, for BS with a second order super-Gaussian shape.

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.

Mistiming performance analysis of the energy detection based toa estimator for MB-OFDM

In this letter, we apply energy detection based time- of-arrival (ToA) estimation to multi-band orthogonal frequency-division multiplexing signals. We analyze the mistiming performance of the ToA estimator in the Nakagami-m channel. Analysis shows that the slope of the probability of mistiming curve increases with the number of subbands and the Nakagami-m parameter. This is known in communications as diversity. Simulations are carried out in various channels to corroborate our theoretical analysis.

Optical Distribution and Upconversion of MB-OFDM in Ultrawide-Band-Over-Fiber Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Broadband radio-over-fiber networks are raising great interest for intrabuilding distribution and signal processing of ultrawide-band (UWB) signals. In this paper, a unique optical system based on an external modulator biased either in linear or nonlinear regime has been used to realize both distribution of multiband orthogonal frequency-division multiplexing (MB-OFDM) UWB signal and all-optical frequency upconversion of UWB-OFDM subband. The impact of the nonlinearity of the optical link on the MB-OFDM signal is investigated through a simulation model of the complete UWB-over-fiber system. Results have shown enhanced performance of upconverted MB-OFDM subband compared to direct transmission due to optical noise reduction. First experimental results have confirmed simulation results. </para>

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.

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.

PAPR analysis for multi-band OFDM signals

The peak-to-average power ratio (PAPR) statistics in a multi-band orthogonal frequency division multiplexing (MB-OFDM) system, which is being considered as a possible candidate for the IEEE 802.15 high rate alternative PHY, is analysed. In the MB-OFDM system, high PAPR is introduced by a conjugate symmetric input to inverse fast Fourier transform. To alleviate this problem, the selective mapping and partial transmit sequence are introduced for the MB-OFDM signals and the performance comparisons between two methods are discussed.