Adriaan J. de Lind van Wijngaarden

Concatenated Coded Modulation for Optical Communications Systems

The use of trellis-coded modulation (TCM) in combination with an outer block code is considered for next-generation 100-Gb/s optical transmission systems. Two block codes are employed as an outer code: a 16 times interleaved byte-oriented (255,239) Reed Solomon (RS) code and a code consisting of two interleaved extended three-error correcting Bose Chaudhuri Hocquenghem (BCH) (1020,988) codes. Simulations show that soft-decision decoding of a selected TCM inner code in combination with hard-decision decoding of the outer RS code achieves a net coding gain (NCG) of 8.42 dB at a bit-error rate of 10-13. When the concatenated code based on the two interleaved BCH codes is used as the outer code, the NCG is 9.7 dB. The impact of quantization on the performance of the concatenated TCM scheme with the two interleaved BCH outer codes is evaluated, and it is shown that 4-bit quantization is sufficient to approach the infinite precision performance to within 0.15 dB.

A low-energy rate-adaptive bit-interleaved passive optical network

Energy consumption of customer premises equipment (CPE) has become a serious issue in the new generations of time-division multiplexing passive optical networks, which operate at 10 Gb/s or higher. It is becoming a major factor in global network energy consumption, and it poses problems during emergencies when CPE is battery-operated. In this paper, a low-energy passive optical network (PON) that uses a novel bit-interleaving downstream protocol is proposed. The details about the network architecture, protocol, and the key enabling implementation aspects, including dynamic traffic interleaving, rate-adaptive descrambling of decimated traffic, and the design and implementation of a downsampling clock and data recovery circuit, are described. The proposed concept is shown to reduce the energy consumption for protocol processing by a factor of 30. A detailed analysis of the energy consumption in the CPE shows that the interleaving protocol reduces the total energy consumption of the CPE significantly in comparison to the standard 10 Gb/s PON CPE. Experimental results obtained from measurements on the implemented CPE prototype confirm that the CPE consumes significantly less energy than the standard 10 Gb/s PON CPE.

XG-FAST: Towards 10 Gb/s copper access

Traditionally, copper network operators complement a Fiber-to-the-Home (FTTH) strategy with a hybrid fiber-copper deployment in which fiber is gradually brought closer to the consumer, and Digital Subscriber Line (DSL) technology is used for the remaining copper network. In this paper, we propose the system concepts of XG-FAST, a technology capable of delivering 10 Gb/s connection speeds over short copper pairs. With a hardware proof-of-concept platform, it is shown that multi-gigabit speeds are achievable over typical drop lengths from front yard to customer premises equipment of up to 70 m. When an additional pair is available, 10 Gb/s service is shown to be possible up to 30 m by exploiting bonding and phantom mode. The XG-FAST technology will make Fiber-to-the-Door deployments feasible, which avoids many of the hurdles accompanying a traditional FTTH roll-out. Single subscriber XG-FAST devices would be an integral component of FTTH deployments, and as such help accelerate a worldwide roll-out of FTTH services. Standardization is required to specify the physical layer and the interface with the fiber network.

Forward error correction in optical core and optical access networks

Forward error correction (FEC) techniques are essential for optical core and optical access networks. In optical core networks, the emphasis is on high coding gains and extremely low output bit error rates, while allowing decoder realizations to operate at a throughput of 100 Gb/s and above. Optical access networks operate at 10 Gb/s or above and require low-complexity FEC codes with low power consumption. Coherent optical transmission with higher order modulation formats will become mandatory to achieve the high spectral efficiencies required in next-generation core networks. In this paper, we provide an overview of these requirements and techniques, and highlight how coding and modulation can be best combined in optical core networks. We also present guidelines for modulation and low-complexity FEC system design for optical access networks.

Pilot-based crosstalk channel estimation for vector-enabled VDSL systems

Recently, the International Telecommunication Union has consented the ITU-T G.993.5 recommendation on vectoring in VDSL2 technology, which specifies the required functionality for interoperability between chipsets of different vendors to achieve vectoring. This paper will briefly review the principles of vectoring and the underlying precoding and channel estimation techniques. This framework is then used to introduce mechanisms for crosstalk channel estimation that exploit channel smoothness with the aid of frequency-dependent pilot sequences, as well as mechanisms that allow fast and simultaneous initialization by targeted assignment of pilot sequences. A pilot-based technique is described that exploits the robustness of the synchronization symbols to estimate crosstalk emanating from “legacy” VDSL2 lines within a vectoring group. This allows cancellation of crosstalk from legacy lines without replacement of the installed VDSL2 customer premises equipment. Some of these techniques are compatible with the current version of ITU-T G.993.5 recommendation, while others require changes that are under consideration for possible inclusion in future amendments.

XG-fast: the 5th generation broadband

Traditionally, copper network operators complement a fiber-to-the-home (FTTH) strategy with a hybrid fiber-copper deployment in which fiber is gradually brought closer to the consumer, and digital subscriber line (DSL) technology is used for the remaining copper network. In this article we propose the system concepts of XG-FAST, the 5th generation broadband (5GBB) technology capable of delivering a 10 Gb/s data rate over short copper pairs. With a hardware proof-of-concept platform, it is demonstrated that multi-gigabit rates are achievable over typical drop lengths of up to 130 m, with net data rates exceeding 10 Gb/s on the shortest loops. The XG-FAST technology will make fiber-to-the-frontage (FTTF) deployments feasible, which avoids many of the hurdles accompanying a traditional FTTH roll-out. Single subscriber XG-FAST devices would be an integral component of FTTH deployments, and as such help accelerate a worldwide roll-out of FTTH services. Moreover, an FTTF XG-FAST network is able to provide a remotely managed infrastructure and a cost-effective multi-gigabit backhaul for future 5G wireless networks.

Analysis of a probing-based cyclic sleep mechanism for passive optical networks

Recent standardization efforts to reduce power consumption in optical access networks include the use of cyclic sleep modes to more effectively scale energy consumption with activity. This paper analyzes a probing-based cyclic sleep mode mechanism that is applied to the downstream of a passive optical network. The analysis studies the effectiveness of the sleep mode mechanism and provides explicit mathematical expressions for the power consumption and packet response delay in the optical network unit (ONU) at the customer premises, and the amount of buffered traffic per ONU in the optical line terminal at the central office. The analytical results are confirmed and complemented by numerical simulations, and used to provide guidelines for selecting sleep mode configuration parameters.

Smart power management for mobile handsets

Mobile terminals are rapidly evolving from enhanced phones to powerful platforms capable of offering a multitude of services and critical applications. They have a small form factor and are typically equipped with powerful processors, a large display, a high-resolution camera, and specialized sensors. The hardware has to simultaneously support applications that have varying run-times and varying communication and computation requirements. As a consequence, power-intensive applications can easily drain the battery and leave the mobile terminal useless in no time. In this paper, we develop concepts for advanced power-aware task management. A power-aware task monitor in the mobile terminal keeps track of the battery state, the communication channel, and the processor(s). It takes the application profile, channel quality, anticipated duration, and other factors into account to determine the required resources and the impact on the battery life, and it also updates the battery and application profiles. A power-aware task scheduler in the mobile terminal uses information provided by the power-aware task monitor to determine whether or not to execute applications. It can reserve power for critical services such as emergency calls, authentication, and payment and banking applications. Network-based power management and application-based power management can be achieved for mobile terminals when information about the handsets battery power and application profile is communicated to the network. A network-based power manager can help determine when and how to support power-intensive applications, and may provide the handset with location-based coverage information and adjust the communication strategy to reduce the power required for communication and processing in the handset. A power manager in the application server can help to minimize power consumption by adjusting the flow and the contents communicated to the mobile terminal.

Analysis of Inverse Crosstalk Channel Estimation Using SNR Feedback

Digital subscriber line (DSL) data rates for short loops are typically limited by crosstalk between adjacent lines rather than by background noise. Precoding can reduce crosstalk in the downstream from the access node to the customer premises equipment significantly if an accurate estimate of the inverse crosstalk channel is provided. Recently, a backward-compatible method has been proposed for estimating downstream crosstalk channels using standardized signal-to-noise ratio (SNR) reports. This paper develops a probabilistic model of the estimation process and, within this model, provides conditions under which successive updates of the precoder are guaranteed to converge to the ideal inverse precoder. Bounds on estimator variance and convergence times are obtained and optimized with respect to system parameters. The analysis can be applied to the situation in which a new line is being activated and added to a group of precoded lines seamlessly, that is, with controlled impact on the SNR of the active lines. Two phases are proposed to achieve seamless activation; the protection phase is used to let the active lines learn the crosstalk from the activating line and the acquisition phase is used to let the activating line learn the crosstalk from the active lines. Results of the analysis are illustrated by numerical simulations.

Design and Analysis of Synchronizable Error-Resilient Arithmetic Codes

An error-resilient variable-length arithmetic code is presented whose codewords are represented by binary digits. The input sequence is partitioned in subsequences, each of which is individually encoded using an arithmetic coding scheme with an integrated bit-stuffing technique that restricts the number of consecutive ones in the output sequence. An all-ones sequence of fixed length is appended to serve as a sync marker when the codewords are concatenated. The bit-stuffing technique ensures that the sync markers do not occur anywhere except at the boundaries between the codewords. Expressions for the optimal choice of the marker length and the block length are derived. The performance of the proposed code is determined in terms of redundancy and error resilience. An upper bound on the average error rate is derived and its tightness is confirmed with computer simulations. The proposed code shows to significantly suppress the error rate at the expense of a minimum increase in redundancy.