We propose a method and hardware architecture for error-correction encoding of downstream traffic in a passive optical network. The encoder can handle multiple users using multiple error-correction codes. Our solution further allows transmission of a codeword across multiple timeslots allotted to a user. his ability to spread out the user payload allows decimation of the data processing rate at the user end, leading to lower energy consumption. Hardware emulation based on the developed design shows that our multi-user encoder consumes significantly less power than a system using conventional encoders in parallel.

With the proliferation of advanced and interactive services together with the high demand for premium quality of experience, upstream traffic in passive optical networks is growing fast in recent times. Motivated by this, a new power saving mechanism called the sleep-transmit mode (STM) is proposed, which enables the optical network units (ONUs) at customer premises to transmit upstream data during sleep periods without turning on the receiver, thus conserving energy and improving upstream transmission delay. These advantages are achieved by pre-allocating bandwidth for upstream transmission to ONU before it enters the sleep state. Our analysis results show that using STM (1) the power consumption of an ONU is reduced by up to 29% compared to interrupting the sleep mode, and (2) the average additional upstream packet delay due to sleep mode is reduced by up to 10-fold compared to transmitting the upstream packets only after the sleep duration expires.

Decoders for Low Density Parity Check (LDPC) codes, used commonly in communication networks, possess inherent tolerance to random internal computation errors. Consequently, it is possible to apply voltage over-scaling (VOS) in their implementation to save energy. In this paper, the impact of VOS on timing errors is characterized for a typical min-sum LDPC decoder architecture using circuit simulations. Failure modes are analyzed for arithmetic circuits performing variable and check node computations. It is shown that a rather unconventional register placement in the variable node unit is beneficial for voltage scaling, and that the check node unit may be designed such that only the least significant bits are more likely to experience errors. Insights into timing error characteristics obtained through this analysis can be used to estimate the limits of voltage scaling and associated energy saving in practical LDPC decoder designs.

In order to achieve the maximum power-saving performance in optical access networks, all network elements including the access node or optical line terminal (OLT) and the optical network unit should be considered. In this paper, appropriate power-saving mechanisms are determined for each network element in point-to-point (PtP) and time-division-multiplexed passive optical network (TDM-PON) systems to maximize the achievable power-saving performance while satisfying the quality-of-service requirements for different applications. By applying these power-saving mechanisms in PtP and TDM-PON systems, it is found that 1) the power consumption of OLTs in the central office is reduced by up to 51% and 38%, respectively, and 2) the total power consumption per subscriber is reduced by up to 61.5% and 67%, respectively. Using simulations, the most energy-efficient optical access network technology for different Internet applications is also identified.

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.

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.

A broadcast network in which a sender transmits to several receivers, each receiving different data, is considered. A time division multiplexing scheme based on bit-interleaving, where each receiver is given an allocation of bit positions occurring in periodic intervals within the frame, is assumed. In previous work, bit-interleaving was shown to yield 30× power savings. However, to enable bit-interleaving, a descrambler design capable of operating on the downsampled data corresponding to the receiver's allocation is required. Several efficient methods are presented to accomplish this task both for fixed and variable allocations to the receivers. The proposed methods can be used to implement a power-scalable, low complexity, and low cost descrambler that operates at the receiver's data rate, which is typically far lower than the total transmission rate.

We consider an extension to the disk model in one dimension where communication links established between nodes may fail. With the help of the method of first and second moments, we investigate the zero-one laws for the property that there are no isolated nodes in the underlying random graph. Two specific situations are discussed: For the unit circle we prove a full zero-one law and determine its critical scaling. For the unit interval we derive a zero-law and a one-law which capture deviations from different critical scalings; a completely symmetric zero-one law is established under an additional condition. Analysis and simulations both indicate the possible presence of a gap between the one-law critical scalings for the unit interval and the unit circle. This discrepancy is quite surprising given that the zero-one laws for the absence of isolated nodes are identical in the geometric random graphs on the unit interval and on the unit circle. Connections to recent results by Yi et al. are discussed.

We develop the concept of hierarchical fingerprinting introduced in our recent work (ISIT2009). The object of two-level fingerprinting is content protection against coalitions of t pirates in such a manner that one of the pirates can be identified exactly if t ≤ t2or localized to within a small group if t21, where t1and t2are parameters of the system. In this work, we require the additional property that in the latter case no innocent users are accused of belonging to the pirate coalition. We construct two-level fingerprinting codes with polynomial complexity of identification that satisfy the strong definition of hierarchical fingerprinting described above.

We introduce the notion of two-level fingerprinting and traceability codes. In this setting, the users are organized in a hierarchical manner by classifying them into various groups; for instance, by dividing the distribution area into several geographic regions, and collecting users from the same region into one group. Two-level fingerprinting and traceability codes have the following property: As in traditional (one-level) codes, when given an illegal copy produced by a coalition of users, the decoder identifies one of the guilty users if the coalition size is less than a certain threshold t. Moreover, even when the coalition is of a larger size s (≫ t), the decoder still provides partial information by tracing one of the groups containing a guilty user. We establish sufficient conditions for a code to possess the two-level traceability property. In addition, we also provide constructions for two-level fingerprinting codes and characterize the corresponding set of achievable rates.

We address the maximum attainable rate of fingerprinting codes under the marking assumption, studying lower and upper bounds on the value of the rate for various sizes of the attacker coalition. Lower bounds are obtained by considering typical coalitions, which represents a new idea in the area of fingerprinting and enables us to improve the previously known lower bounds for coalitions of size two and three. For upper bounds, the fingerprinting problem is modeled as a communications problem. It is shown that the maximum code rate is bounded above by the capacity of a certain class of channels, which are similar to the multiple-access channel (MAC). Converse coding theorems proved in the paper provide new upper bounds on fingerprinting capacity.

We study the maximum attainable rate or capacity of fingerprinting codes under the marking assumption. It is proved that capacity for fingerprinting against coalitions of size two and three over the binary alphabet satisfies 0.25 ≤ C2,2≤ 0.322 and 0.083 ≤ C3,2≤ 0.199 respectively. For coalitions of an arbitrary fixed size, we derive a closed-form upper bound on fingerprinting capacity in the binary case. Finally, for general alphabets, we establish upper bounds on the fingerprinting capacity involving only single-letter mutual information quantities.

New lower bounds are established on the rate of fingerprinting codes secure against coalitions of an arbitrary constant size t. In particular, it is proved that there exist sequences of binary fingerprinting codes with vanishing probability of misidentification and rate approximately 1/(t 2t). In the case of t = 3 it is shown that there exist codes of rate 0.064 which is better by an order of magnitude than previously known results.