Author:

Keywords:

SISTA

Abstract:

The ability to easily exchange and access data has transformed the way we work, study, inform and entertain ourselves. In particular, the Internet has had an effect on people's lives in the past two decades that is profound.Profound as this effect may be, people seem not to grow tired of it. On the contrary: as of today, the Internet revolution is far from over. The thirst for bigger amounts of data at higher speeds and ubiquitous connectivity seem not to abate.This thirst for more, faster and better quality data is both a huge challenge and a huge opportunity for the broadband access industry. The opportunity lies on the fact that, as of the end of 2012, there were 600 million subscribers to broadband services around the world. Plus, even though the market is already enormous, it still has big growth potential. The challenge lies on the connections between the network backbone and the user, the so-called local loop. In the local loop the network thins out and usually consists of lower quality channels in comparison to the network backbone.Of the technologies currently available to bridge this local loop, digital subscriber lines (DSL) is by far the market leader. This technology uses twisted copper pairs, the same used for decades for standard telephony services. If on the plus side the telephone network infrastructure is ubiquitous through the globe, making costs of installation very small, on the minus side DSL operates in a medium not initially designed for broadband communications. One of the consequences of this is severe levels of multi-user interference, commonly known as crosstalk.In this thesis, we develop signal and spectrum coordination techniques that aim at avoiding, minimizing or even profiting from crosstalk. The collection of these techniques is commonly known in the literature as dynamic spectrum management (DSM). DSM has repeatedly been shown to provide formidable gains in the performance of DSL networks. It is an enabler for next generation DSL services and it is the unifying topic of this thesis.In Part I of this thesis, we focus on spectrum coordination. Here we focus on a single input, single output (SISO) interference channel. The goal is to come up with a fair power allocation through frequency so that every user strikes a balance between maximizing its own data rate and minimizing interference to others. We propose two algorithms for the solution of the weighted rate sum maximization problem subject to per-user power constraints. Both approaches start with the re-writing of the problem with different variables. The classical way to represent the design variables of this problem is with cartesian vector coordinates, where each position of the vector denotes the power allocation of one user. We use spherical coordinates, which consists of representing the design variables with a radius and a direction vector with a norm constraint. Spherical coordinates allow us to find a surprising amount of structure in this problem, which can be used to save considerably on computational complexity. Our first proposed algorithm can be up to 100 times faster than the relevant previous proposal. Our second algorithm is 2-15 times faster than the relevant previous proposal.In Part II, we focus on combined signal and spectrum coordination. First, we focus on a scenario that is referred to as the discrete multitone multiple-input, multiple-output interference channel (DMT MIMO IC). This scenario consists of multiple interfering users, each operating a distinct number of transceivers as a MIMO system. Coordination is done both on the signal level (with per-user MIMO techniques) and on the spectrum level (with multi-user power allocation). We propose two algorithms for the DMT MIMO IC weighted rate sum maximization problem. We focus both on per-user and on per-transceiver power constraints. In the first algorithm, we profit from recent work showing the close relation between the weighted rate sum maximization problem and the weighted minimum mean squared error (MMSE) minimization problem. We show that with a simple extension, we can adapt the previous work to the scenario of interest. In the second algorithm, the signal and spectrum coordination parts are solved separately. For the signal coordination part, we obtain multiple independent single tone MIMO IC's, which allows us to leverage on the previous work on the topic. For the spectrum coordination part, one of the interesting results of our analysis is a generalization of the waterfilling power allocation formula for the multiple input, multiple output (MIMO) interference channel. This formula takes into account the matrix structure of the channel and includes a penalty for the user that causes excessive interference. Simulation results demonstrate that both algorithms obtain significant gains when compared to pure spectrum coordination algorithms.Still in Part II, we develop a general system framework that encompasses the whole complexity of DSL networks. Our framework includes every other previously studied situation as a special case, including all other scenarios mentioned in this thesis. We also propose an algorithm that uses this framework and works for all cases, including any number of users, any number of transceivers, any number of tones, any kind of coordination on both the transmitter and on the receiver sides, and synchronous or asynchronous transmission.