We introduce an ultra-dense network architecture designed for silicon photonics at the optical network unit (ONU). This network relies on only 3.333 GSa/s and 417 MSa/s converters at the OLT and ONU, respectively, and offers up to 12 Gbit/s of symmetric traffic in a single 12.5-GHz optical channel. Multiple access and lowest processing speeds at the ONU are enabled by choosing 10 DFT-spread OFDM subbands. We demonstrate this FDMA network architecture in a proof-of-principle experiment with up to eight 300-MBd 16QAM subbands offering a bidirectional data rate of 9.6 Gb/s. Real-time signal processing is realized for downstream transmission. Finally, we shortly address future improvements of this network architecture by employing integrated silicon photonics and analog signal processing to enable fine FDM for next-generation access networks.

In this paper we present an FPGA based, ultra-high speed OFDMA system which is intended to be used as a bandwidth efficient, advanced modulation format in optical access networks like fiber-to-the-home. The aggregate bandwidth of the network reaches up to 50 GBit/s while handling hundreds of different subscribers, sharing the same optical bandwidth. Compared to other domains using OFDM like e.g. wireless communication, data rates in the multi GBit/s range require very high performance signal processing components at a central office and at the subscribers. With modern FPGA technologies like the Xilinx Virtex-6 family and massive parallelization of the algorithms the necessary processing power can be provided. Besides the OFDMA processing blocks themselves also their connections to a suitable analog front end as well as to data sources and sinks have to be considered. The presented system uses digital-to-analogue (DAC) and analogue-to-digital (ADC) converters with up to 25 GSa/s at the central office and up to 3.125 GSa/s at the subscribers. The connection to data sources and sinks is realized via 10G Ethernet links. The whole system is therefore transparent for Ethernet packets making its integration into existing infrastructure very easy.

An open converged metro-access network approach allows for sharing optical layer resources like fibers and optical spectrum among different services and operators. We demonstrated experimentally the feasibility of such a concept by the simultaneous operation of multiple services showing different modulation formats and multiplexing techniques. Flexible access nodes are implemented including semiconductor optical amplifiers to create a transparent and reconfigurable optical ring network. The impact of cascaded optical amplifiers on the signal quality is studied along the ring. In addition, the influence of high power rival signals in the same waveband and in the same fiber is analyzed.

We demonstrate, to the best of our knowledge, the first real-time single-carrier frequency division multiple access transmitter designed to be used in photonic communication networks. It is capable of providing 10 Gbit/s net bitrate at 3.125 GHz slot bandwidth, providing data to nine quasi-Nyquist spectral groups. The transmitter is designed with respect to logic efficiency and a fine user grid allowing the operation of narrow bandwidth, low-cost optical network units. Moreover, it offers runtime flexibility, an efficient 96-point discrete Fourier transform and a multiplier-free differential phase encoder. The article concludes with a presentation of the transmitters hardware setup and an evaluation of its performance in the case of direct electrical AWG-ONU Rx interconnection and the optical back-to-back case.

We demonstrate two efficient processing techniques for Nyquist signals, namely computation of signals using dynamic precision as well as arbitrary rational oversampling factors. With these techniques along with massively parallel processing it becomes possible to generate and receive high data rate Nyquist signals with flexible symbol rates and bandwidths, a feature which is highly desirable for novel flexgrid networks. We achieved maximum bit rates of 252 Gbit/s in real-time.

In this paper the authors describe a novel system on chip (SoC) that is especially developed for digital signal processing of high-speed orthogonal frequency division multiplexing (OFDM) signals with data rates up to gigabits per second. Besides offering a new degree of freedom for the tradeoff between flexibility and performance during runtime, the modular concept of the SoC also allows a tradeoff between performance and costs during design time. The flexibility to adapt the OFDM system parameters by software enables even system designers without a good knowledge of hardware design to implement high-speed OFDM systems. An example configuration of the architecture was implemented on a Virtex-6 FPGA in order to set up a software-defined OFDM transmitter, achieving data rates of several gigabits per second. The paper closes with implementation and performance results of experiments using the developed transmitter and an optical transmission of the generated OFDM signals.

A remotely seeded flexible WDM network solution with 31.25 Gbit/s based on Nyquist sinc-pulses is demonstrated. The low-speed, colorless ONUs use remote heterodyne detection with electrical up- and down-conversion and SOAs for potential cost reduction.

We demonstrate a remotely seeded flexible passive optical network (PON) with multiple low-speed subscribers but only a single optical line terminal transceiver operating at a data rate of 31.25 Gbits/s. The scheme is based on a colorless frequency division multiplexing (FDM)-PON with centralized wavelength control. Multiplexing and demultiplexing in the optical network unit (ONU) is performed in the electronic domain and relies either on FDM with Nyquist sinc-pulse shaping or on orthogonal frequency division multiplexing (OFDM). This way the ONU can perform processing at low speed in the baseband. Further, the ONU is colorless by means of a remote seed for upstream transmission and a remote local oscillator for heterodyne reception, all of which helps in keeping maintenance and costs for an ONU potentially low and will simplify wavelength allocation in a future software defined network architecture. To extend the reach, semiconductor optical amplifiers are used for optical amplification in the downstream and upstream.

The quality of optical signals is a very important parameter in optical communications. Several metrics are in common use, like optical signal-to-noise power ratio (OSNR), Q-factor, error vector magnitude (EVM) and bit error ratio (BER). A measured raw BER is not necessarily useful to predict the final BER after soft-decision forward error correction (FEC), if the statistics of the noise leading to errors is unknown. In this respect the EVM is superior, as it allows an estimation of the error statistics. We compare various metrics analytically, by simulation, and through experiments. We employ six quadrature amplitude modulation (QAM) formats at symbol rates of 20 GBd and 25 GBd. The signals were generated by a software-defined transmitter. We conclude that for optical channels with additive Gaussian noise the EVM metric is a reliable quality measure. For nondata-aided QAM reception, BER in the range 10-6-10-2 can be reliably estimated from measured EVM.

Recent advances in electronic data processing allow constructing reconfigurable optical transmitters and receivers, where modulation formats and symbol rates are set by software-controlled field programmable gate arrays (FPGA). We report on such a real-time optical transmitter for 8 modulation formats, which can be swapped in 5 ns without data loss. With single-polarization 64QAM symbols generated at 28 GBd, we transmit data at 168 Gbit/s in real time. A similar arrangement defines a single-polarization orthogonal frequency division multiplexing (OFDM) transmitter for a data rate of 101.5 Gbit/s, where 58 subcarriers are encoded with 16QAM data. With a different software setup, the FPGA realizes an optical 56 Gbit/s transmitter for sinc-shaped so-called Nyquist pulses, the spectrum of which is rectangular having the minimum theoretically achievable bandwidth (suitable for Nyquist wavelength division multiplexing, N-WDM). For terabit OFDM reception, optical pre-processing is required to demultiplex high-bitrate signals down to lower-bitrate tributaries, which then can be processed electronically. We discuss a 10.8 Tbit/s (26 Tbit/s) receiver employing an all-optical fast Fourier transform to demultiplex 75 (325) optical subcarriers modulated with 16QAM-formated symbols at a rate of 18 GBd (10 GBd). Groups with any number of subcarriers can be selected with a simple hardware reconfiguration step.

In this paper we present a novel approach for time and frequency synchronization of ultra-high speed OFDM systems processing over 78 million symbols per second. A possible application domain of such OFDM systems is located in optical access networks like fibre to the home which are expected to become widely used in several years. The communication channel characteristics of a glass fibre posses lower demands to the synchronization algorithms compared to a wireless communication channel because carrier frequencies and phases at the receiver change slower and there are nearly no signal reflections. In order to achieve very high data rates of up to 50 GBit/s the concept introduced in this paper exploits the special channel characteristics of a glass fibre in order to reduce the required processing power. A realisation of this concept was implemented for Xilinx Virtex-6 FPGAs to prove its feasibility with technology available today.

The quality of optical signals is a very important parameter in optical communications. Several metrics are in common use, like optical signal-to-noise power ratio (OSNR), Q-factor, error vector magnitude (EVM) and bit error ratio (BER). A measured raw BER is not necessarily useful to predict the final BER after soft-decision forward error correction (FEC), if the statistics of the noise leading to errors is unknown. In this respect the EVM is superior, as it allows an estimation of the error statistics. We compare various metrics analytically, by simulation, and through experiments. We employ six quadrature amplitude modulation (QAM) formats at symbol rates of 20 GBd and 25 GBd. The signals were generated by a software-defined transmitter. We conclude that for optical channels with additive Gaussian noise the EVM metric is a reliable quality measure. For nondataaided QAM reception, BER in the range 10(-6) ... 10(-2) can be reliably estimated from measured EVM.

The quality of optical signals is a very important parameter in optical communications. Several metrics are in common use, like optical signal-to-noise power ratio (OSNR), Qfactor, error vector magnitude (EVM) and bit error ratio (BER). While the BER is the final determinant for a system, a measured raw BER is not necessarily useful to predict the final BER after soft-decision forward error correction (FEC), if the statistics of the noise leading to errors remains unknown. In this respect the EVM is superior, as it allows an estimation of the error statistics. The accuracy of the BER estimate from a measured Q-factor is impaired by the basic requirement that the relevant noise must be Gaussian. Already for plain on-off keying (OOK) signals this assumption is violated if an optical pre-amplifier is employed, and the estimated BER becomes even worse if phase modulation formats are involved. We compare various metrics analytically, by simulation, and through experiments. We employ six quadrature amplitude modulation (QAM) formats at symbol rates of 20 GBd and 25 GBd. The signals were generated by a software-defined transmitter. We conclude that for optical channels with additive Gaussian noise the EVM metric is a reliable quality measure. For nondata-aided QAM reception, BER in the range 10-6...10-2 can be reliably estimated from measured EVM.

Single-laser 32.5 Tbit/s 16QAM Nyquist-WDM transmission with 325 carriers over 227 km at a net spectral efficiency of 6.4 bit/s/Hz is reported.

This paper describes the design and optimization of an ultra- high speed Digital Down Converter (DDC) for a realization by FPGAs. After explaining the general structure of the Digital Down converter we describe in detail how to implement such a design in order to process a digital, massively parallelized signal. The necessary optimizations to achieve an efficient implementation in state of the art FPGAs are explained and a case study for an FPGA optimized Digital Down Converter design suitable for OFDMA systems is presented. The key components of this DDC are highly parallelized half-band filters which are optimized for Virtex- 6 FPGAs and enable the design to decimate a 6 bit wide input signal with a sample rate of 25 GS/s into a 16 bit 1.5625 GS/s signal while achieving an attenuation of around 35 dB. The results include the resource consumption of the DDC for a Virtex-6 XC6VHX380T FPGA as well as the filter response to a chirp test signal. Index Terms ?? FPGA; DDC; OFDMA; FIR; Decimator.

In this paper we introduce the concept for an embedded performance monitor of PCI Express links. This PCI Express Performance Monitor (PPM) enables the analysis of several properties (e.g. amount of available credits), without affecting the performance of the monitored link. By including a PPM in an embedded system it is possible to avoid the need for high cost PCI Express measurement and analyzing equipment. The concept was implemented on a rapid prototyping system to monitor several PCI Express links that connect an Intel Atom processor with an Altera Field Programmable Gate Array (FPGA). In addition we present a framework of functions, which makes it easy to use the utilization of a monitored PCI Express link as trigger condition for self adaptive systems.

We examine the relation between optical signal-to-noise ratio (OSNR), error vector magnitude (EVM), and bit-error ratio (BER). Theoretical results and numerical simulations are compared to measured values of OSNR, EVM, and BER. We conclude that the EVM is an appropriate metric for optical channels limited by additive white Gaussian noise. Results are supported by experiments with six modulation formats at symbol rates of 20 and 25 GBd generated by a software-defined transmitter.

Novel embedded applications are characterized by increasing requirements on processing performance as well as the demand for communication between several or many devices. Networked Multiprocessor System-on-Chips (MPSoCs) are a possible solution to cope with this increasing complexity. Such systems require a detailed exploration on both architectures and system design. An approach that allows investigating interdependencies between system and network domain is the cooperative execution of system design tools with a network simulator. Within previous work, synchronization mechanisms have been developed for parallel system simulation and system/network co-simulation using the high level architecture (HLA). Within this contribution, a methodology is presented that extends previous work with further building blocks towards a construction kit for system/network co-simulation. The methodology facilitates flexible assembly of components and adaptation to the specific needs of use cases in terms of performance and accuracy. Underlying concepts and made extensions are discussed in detail. Benefits are substantiated by means of various benchmarks.

We demonstrate single-laser 32.5 Tbit/s 16QAM Nyquist wavelength division multiplexing transmission over a total length of 227 km of SMF-28 without optical dispersion compensation. A number of 325 optical carriers is derived from a single laser and encoded with dual-polarization 16QAM data using sinc-shaped Nyquist pulses. As we use no guard bands, the carriers have a spacing of 12.5 GHz equal to the symbol rate or Nyquist bandwidth of the data. We achieve a net spectral efficiency of 6.4 bit/s/Hz using a software-defined transmitter, which generates the electric drive signals for the electro-optic modulator in real time.

Nyquist sinc-pulse shaping provides spectral efficiencies close to the theoretical limit. In this paper we discuss the analogy to optical orthogonal frequency division multiplexing and compare both techniques with respect to spectral efficiency and peak to average power ratio. We then show that using appropriate algorithms, Nyquist pulse shaped modulation formats can be encoded on a single wavelength at speeds beyond 100 Gbit/s in real-time. Finally we discuss the proper reception of Nyquist pulses.