Nikolaos Papandreou

Bit and power allocation in constrained multicarrier systems: the single-user case

Multicarrier modulation is a powerful transmission technique that provides improved performance in various communication fields. A fundamental topic of multicarrier communication systems is the bit and power loading, which is addressed in this article as a constrained multivariable nonlinear optimization problem. In particular, we present the main classes of loading problems, namely, rate maximization and margin maximization, and we discuss their optimal solutions for the single-user case. Initially, the classical water-filling solution subject to a total power constraint is presented using the Lagrange multipliers optimization approach. Next, the peak-power constraint is included and the concept of cup-limited waterfilling is introduced. The loading problem is also addressed subject to the integer-bit restriction and the optimal discrete solution is examined using combinatorial optimization methods. Furthermore, we investigate the duality conditions of the rate maximization and margin maximization problems and we highlight various ideas for low-complexity loading algorithms. This article surveys and reviews existing results on resource allocation in constrained multicarrier systems and presents new trends in this area.

A new computationally efficient discrete bit-loading algorithm for DMT applications

This letter presents a new bit-loading algorithm for discrete multitone systems that converges faster to the same bit allocation as the optimal discrete bit-filling and bit-removal methods. The algorithm exploits the differences between the subchannel gain-to-noise ratios in order to determine an initial bit allocation and then performs a multiple-bits loading procedure for achieving the requested target rate. Numerical results using asymmetric digital subscriber test loops demonstrate the computational efficiency of the proposed algorithm.

Resource Allocation Management for Indoor Power-Line Communications Systems

Power-line communications (PLC) is recognized as an alternative technology for delivering broadband services in home and small-office environments. Multicarrier modulation is one of the most effective solutions for combating the imperfections of the power-line channel. One of the technical challenges in increasing the potentiality of PLC technology is the utilization of the available spectrum when different users compete for the available resources. Due to the frequency and time-varying characteristics of the power-line network, the various users experience different channel conditions, thus the application of efficient resource allocation will increase the overall network performance. This paper addresses the problem of subchannel and power allocation for indoor PLC networks with multiple links employing power spectral density limitations, and presents an efficient multiuser loading algorithm. The proposed solution encounters both uplink and downlink traffic, guarantees a set of minimum data rates to all users, and allocates the available resources with fairness according to the channel quality of each link. We demonstrate the performance of the proposed algorithm using an illustrative example of a typical indoor network and we examine its effectiveness under various channel conditions

Fair Resource Allocation With Improved Diversity Performance for Indoor Power-Line Networks

The problem of fair resource allocation in power-line networks with multiple links is considered. A new bandwidth allocation criterion with improved multiuser diversity characteristics is presented, which provides an increased total data rate compared with other existing solutions. Simulation results demonstrate the effectiveness of the proposed method under different network loading conditions.

Real-time FEXT crosstalk identification in ADSL systems

FEXT crosstalk identification results in improved frequency spectrum utilization in ADSL systems. The accurate determination of the crosstalk transfer function is a demanding task that is affected by various system impairments. We investigate the performance of a real-time method that exploits the exchange of signaling information of a new activated ADSL line in order to determine the crosstalk function between this line and an existing operational line.

Transmission systems prototyping based on Stateflow/Simulink models

In this paper we describe an efficient methodology for rapid prototyping of data transmission systems based on Stateflow/Simulink models using a multi-level system development and testing approach. Transmission systems incorporate multi-domain functions and algorithms, i.e. physical layer circuits and communication protocol controllers. The Stateflow/Simulink environment enables the development of precise simulation models that include signal and protocol processing units. The proposed prototyping methodology is based on the progressive translation of high-level model blocks into hardware/software modules of the prototype architecture using custom and/or automated code generation tools. A custom data exchange and synchronization interface between the Stateflow/Simulink workspace and the circuit modules enables the integration of the simulation model and the prototyping platform into a complete functional system. The application of the proposed methodology in the development of an ADSL modem in a custom prototyping platform is also described.

Far-end crosstalk identification method based on channel training sequences

Far-end crosstalk identification results to improved frequency spectrum utilization in asymmetric digital subscriber line (ADSL) systems. The accurate determination of the crosstalk coupling function is a demanding task that is affected by various system impairments. In this paper, we present a new real-time method that exploits the exchange of signaling information between the modems of a new activated ADSL line in order to determine the crosstalk function between this line and any other active line in the binder. Each remote modem subtracts the decoded data from the received signal, decreases the noise effect of the previously identified crosstalkers, is synchronized to the disturbers timing and then applies a least-squares estimator for identifying the new crosstalk coupling function. The method is used along with a maximum margin bit-loading algorithm in order to provide the best possible estimation results. The estimated crosstalk coupling functions, the transfer function of each line and the noise measurements can be exploited by a centralized bit-loading algorithm for maximizing the total system performance in terms of maximum achievable data rate and/or bit error rate.

Fair Resource Allocation in Multiuser Indoor Power Line Communications

Multicarrier modulation is one of the most promising technologies for achieving high performance communications in the indoor power line network. Due to the fading and time-varying characteristics of the power line channel, the various users experience different channel conditions, thus the application of efficient multiuser transmission schemes will enhance multiuser diversity. This paper addresses the problem of fairness in bandwidth and power allocation for the indoor power line channel with multiple multicarrier links and presents a multiuser discrete loading algorithm that consists of two phases. First, a set of minimum data rates is provided to all users, and then, the available resources are allocated with fairness according to the quality of each link. We examine the proposed algorithm using an illustrative example of an indoor power line network and we demonstrate its performance. Comparative numerical results of various allocation strategies are also presented

Dynamic bit-loading in pDSL communications systems

This paper presents a dynamic discrete bit-loading algorithm for multicarrier pDSL communication links that utilize the indoor power line network. In order to confront the time varying behavior of power line transmission media, the proposed algorithm provides fast adaptive bit and power loading with reduced complexity using channel state information and a subchannel link-allocation profile. Numerical results based on simulated network loading scenarios demonstrate the performance and the complexity of the proposed method.

Subchannels allocation on multiple pDSL lines

The pDSL technology is used for providing multiple, high-speed broadband links over power lines in the indoor environment This work addresses the problem of bandwidth allocation between the various links of a pDSL network and proposes an algorithm for determining the allocation of the various subchannels during network activation and periodically during the normal network operation. The paper also demonstrates the performance of the proposed algorithm using an illustrative example.