Wooyul Lee

Greener Copper with Dynamic Spectrum Management

Power-saving benefits of Dynamic Spectrum Management (DSM) result from its increased robustness to channel and noise changes, as in this paper. A proposed intermittent noise model enables evaluation of the performance of DSM algorithms. Polite Level-1 DSM algorithm consumes much less power than non-polite DSL management algorithms in the presence of intermittent noise. Secondly, a proposed robust level- 2 DSM algorithm compares favorably with methods that change the PSDMASK only upon modem initialization or retraining. The proposed robust level-2 DSM algorithm significantly reduces power consumption. This DSM reduction of DSL transmit power can be even more significant when considering the additional loss of robustness and stability of non-DSM methods.

SPC09-6: Band-Preference Dynamic Spectrum Management in a DSL Environment

This paper introduces an algorithm for spectrum management for digital subscriber line (DSL) systems based on band preference. The proposed method influences the usage of spectrum through band preference factors that subtly modify the loading algorithm of DSL modems. Ad-hoc algorithms for computing such band preference factors are discussed. Simulation results in a practical ADSL environment show that the performance of the proposed method is better than that of Iterative Water-filling (IWF) [1] and is close to that of Optimal Spectrum Balancing (OSB) [2], even with a small number of control parameters.

Relay with Side Information

This paper establishes necessary and sufficient conditions for reliable transmission of a source over a relay channel when source side information is available non-causally (a) only at the receiver, (b) only at the relay, or (c) at both the relay and the receiver. For the cases of side information only at the receiver and at both the relay and the receiver, we establish tight necessary and sufficient conditions that apply to any relay channel and show that source-channel separation is optimal. When side information is available only at the relay, we establish a necessary condition for reliable transmission and show that it is tight for the class of degraded relay channels and that source-channel separation is optimal in this case.

Optimal Delay Region for Cross-Layer Resource Allocation

This paper characterizes the delay region that is quite useful for multi-user packet scheduling. In a quasi-static channel, the optimal delay region is defined as every set of total delay vectors achieved by some scheduling policies when there are no further packet arrivals. Each users total delay is equivalent to the amount of time until that users queue backlog is cleared. The optimal delay region shows the fundamental limit on each users achievable queueing delay and describes the trade-off among the users in terms of queueing delay when different scheduling policies are applied. In addition, the concept of the delay region is shown to be extendable to each packets average delay as well as total delay.

Randomized Scheduler for Temporally-Correlated Channels

In a slowly time-varying fading broadcast channel, a proposed randomized scheduler achieves multi-user diversity gain while reducing the amount of feedback. The scheduler requests feedback of signal-to-noise ratios (SNR) from a random subset of users in conjunction with the previously scheduled user, and then selects the user with the largest SNR. With temporal correlation, this scheduler achieves near optimal sum-rate even with feedback from a small subset of users, which considerably reduces the amount of feedback.

Greening the copper access network with dynamic spectrum management

This paper investigates the benefits of dynamic spectrum management (DSM) in terms of reducing the power consumption and improving the data rates and robustness in digital subscriber line (DSL) networks. Non-DSM solutions cause strong interference in a shared DSL binder and lead to instability in the network. However, DSM mitigates such interference, stabilises DSL service, and saves power consumed by the DSL networks. This paper compares the savings in power and the improvement in data rates and robustness of the DSL networks when the proposed DSM methods are used instead of other non-DSM techniques. The power savings, data rate increase and quality-of-service improvement by DSM make the operation of DSL networks greener and more efficient, which in turn reduces operational expenditure and brings higher customer satisfaction for DSL service providers.

Energy-Efficient Random-Access Scheduler for Delay-Limited Traffic in Wireless Networks

This paper considers energy minimization for a fast-fading random-access network, where each user sends a single fixed-length packet by selecting a single time-slot within a strict delay-limit. The proposed algorithms assume that each user causally knows its channel state information from electromagnetic reciprocity. With the channel distribution known to all users, the proposed dynamic-programming solution provides an optimal scheduler that minimizes the sum of energy used to transmit a packet and outage cost incurred by a packet drop. Without the knowledge of the channel distribution, a heuristic scheduler is additionally proposed, which learns channel statistics by observing initial time slots.