Facilitating Cooperation for Wireless Systems Cooperative Communications: Hardware, Channel & PHY focuses on issues pertaining to the PHY layer of wireless communication networks, offering a rigorous taxonomy of this dispersed field, along with a range of application scenarios for cooperative and distributed schemes, demonstrating how these techniques can be employed. The authors discuss hardware, complexity and power consumption issues, which are vital for understanding what can be realized at the PHY layer, showing how wireless channel models differ from more traditional models, and highlighting the reliance of PHY algorithm performance on the underlying channel models. Numerous transparent and regenerative relaying protocols are described in detail for a variety of transparent and regenerative cooperative schemes. Key Features: Introduces background, concepts, applications, milestones and thorough taxonomy Identifies the potential in this emerging technology applied to e.g. LTE/WiMAX, WSN Discusses latest wireless channel models for transparent and regenerative protocols Addresses the fundamentals as well as latest emerging PHY protocols Introduces transparent distributed STBC, STTC, multiplexing and beamforming protocols Quantifies regenerative distributed space-time, channel and network coding protocols Explores system optimization, such as distributed power allocation and relay selection Introduces and compares analog and digital hardware architectures Quantifies complexity, memory and power consumption of 3G UMTS & 4G LTE/WiMAX relay Highlights future research challenges within the cooperative communications field This book is an invaluable guide for professionals and researchers in communications fields. It will also be of interest to graduates of communications and electronic engineering courses. It forms part of an entire series dedicated to cooperative wireless systems.

Cooperative Communications: Hardware, Channel and PHY

Coherent optical communication has been well established as the technology of choice for long haul and high bit rate communication systems since a decade ago. Recent technology advances and ongoing price erosion further open the window of opportunity for the application of coherent optical transmission technology in other domains. This paper describes in detail the capabilities, design and implementation of a coherent ultra dense WDM technology for optical metro and access networks. Its capabilities enable a number of attractive options, such as variable downstream bit rates from 150 Mbit/s up to 10 Gbit/s per user, embedded OTDR and the coexistence with legacy systems such as GPON, EPON, XGPON or RF-Video in optical distribution networks. Due to its flexibility and capacity, it is also suitable for deployments in metropolitan networks, as well as for mobile front-haul and back-haul applications.

Coherent Ultra Dense WDM Technology for Next Generation Optical Metro and Access Networks

In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Coherent Access: A Review

Starting from a previously proposed frequency-domain Volterra series nonlinear equalizer (VSNE), whose complexity evolves as O(N3), with N being the frequency-domain block length, we derive a symmetric VSNE filter array formulation for polarization-multiplexed (PM) signals, whose full VSNE equivalent is up to 3 × more computationally efficient, with zero performance penalty. By gradually reconstructing the third-order kernel from its column/diagonal components, the full VSNE can be reduced to a restrict set of Nk frequency-domain filters, leading to O(Nk N2) complexity, associated with negligible performance loss. Finally, a simplified VSNE approach with invariant Kernel coefficients is proposed, delivering O(Nk N) complexity at the expense of controlled performance penalty. The proposed array of symmetric VSNE filters significantly increases the scalability of the previous matrix-based VSNE, providing a more flexible balance between performance and complexity, which can be freely adjusted to match the available computational resources. Performing a direct comparison between the simplified VSNE and the widely used split-step Fourier method in a long-haul 224 Gb/s PM-16QAM transmission system, we demonstrate a reduction of over 60% in terms of computational effort and 90% in terms of equalization latency.

Simplified Volterra Series Nonlinear Equalizer for Polarization-Multiplexed Coherent Optical Systems

We experimentally demonstrate a bi-directional Terabit+ UDWDM coherent PON with Nyquist shaped 16QAM modulation, offering up to 10 Gb/s service capabilities per user/wavelength in a total spectrum of 12.8 nm over 40 km of SSMF.

Terabit+ (192 × 10 Gb/s) Nyquist shaped UDWDM coherent PON with upstream and downstream over a 12.8 nm band

In this paper, we numerically and experimentally demonstrate a bidirectional Terabit+ ultradense wavelength-division multiplexing (UDWDM) coherent passive optical network with Nyquist shaped 16-ary quadrature amplitude modulation, offering up to 10 Gb/s service capabilities per user/wavelength in a total spectrum of 12.8 nm over 40 km of standard single-mode fiber. This paper first demonstrates the capability of Nyquist pulse shaping to mitigate crosstalk arising from back-reflections and nonlinear effects in UDWDM networks with coherent transceivers. The latter part of the paper experimentally investigates the bidirectional transmission in terms of receiver sensitivity and nonlinear tolerance under different network transmission capacity conditions, e.g., number of users and bit rate per users.

Terabit+ (192 × 10 Gb/s) Nyquist Shaped UDWDM Coherent PON With Upstream and Downstream Over a 12.8 nm Band

This paper addresses transmission aspects on very high aggregate wavelength-division multiplexing based passive optical networks (WDM-PON). The ultradense WDM-PON system evaluated in this paper transports high-order modulation formats such as M-ary phase-shift keying (PSK) and M-ary quadrature amplitude modulation (QAM) in which coherent detection is performed at the optical network unit (ONU), after transmission over 25 km, 60 km, and 100 km of standard single-mode fiber (SSMF). The first part of this work covers the impact on the system's performance of the most relevant fiber nonlinearities such as self-phase modulation (SPM), cross-phase modulation (XPM) and four-wave mixing (FWM), and their interplay between transmission distance and modulation format. Using a Volterra series method allows estimating the error vector magnitude (EVM) of the received constellation related to different fiber nonlinearities. In a 32 × 625 Mbaud system spaced by 3 GHz (0.025 nm), the FWM to XPM ratio (F/X) varied from 25 up to 30 dB for phase-modulated signals (1.25 Gb/s-QPSK and 1.875 Gb/s-8PSK). On the other hand, this ratio ranged from 2.6 to 7.4 dB for amplitude-modulated signals (2.5 Gb/s-16QAM, 3.75 Gb/s-64QAM and 5 Gb/s-256QAM). After applying a frequency-allocation scheme at both transmitter and local oscillator lasers, some of the FWM crosstalk is mitigated by 2.4 to 3.5 dB. This EVM reduction confirms that increasing the transmission distance and the order of the constellation, the system's performance becomes limited by both interchannel FWM and XPM.

Analysis of Nonlinearities on Coherent Ultradense WDM-PONs Using Volterra Series

In this work, Nyquist pulse-shaping technology is exploited for future implementations of optical access networks. The paper first presents technical issues regarding digital implementation of Nyquist spectral shaping for low-symbol-rate systems. Second, the potential benefits regarding mitigation of cross talk (linear and nonlinear) of Nyquist pulse shaping in symmetric and bidirectional wavelength-division multiplexing passive optical networks (WDM-PONs) are presented. Lastly, the paper proposes a WDM-PON solution employing self-coherent detection at the optical network unit and heterodyne coherent detection at the optical line terminal. In this proposed architecture, a multi-objective optimization strategy is developed to enhance the transmission performance of the Nyquist-shaped bands in full-duplex mode.

Performance optimization of nyquist signaling for spectrally efficient optical access networks [Invited]

The aim of this paper is to adapt and evaluate the performance of two classical pilot-aided channel estimation schemes designed for OFDM systems: least square and minimum mean square error, in a relay-assisted scenario. We consider the Amplify-and- Forward, which is the simplest relay protocol for cooperative systems. Also, we consider the use of a single antenna at all the terminals: base station, user terminal and relay node. In our scenario, it is assumed that some of the user terminals deployed in a certain area could act as relaying-able terminals for the communications of other users. In this communication we show that the classical channel estimation techniques designed for conventional wireless communications can be extended for relay-assisted based systems under some modifications.

Darlene M. Neves

Papers

Terabit+ (192 × 10 Gb/s) Nyquist shaped UDWDM coherent PON with upstream and downstream over a 12.8 nm band

Terabit+ (192 × 10 Gb/s) Nyquist Shaped UDWDM Coherent PON With Upstream and Downstream Over a 12.8 nm Band

Analysis of Nonlinearities on Coherent Ultradense WDM-PONs Using Volterra Series

Performance optimization of nyquist signaling for spectrally efficient optical access networks [Invited]

Channel Estimation Schemes for OFDM Relay-Assisted Systems