Peak and Power Reduction in Multicarrier Communication Systems

Sammanfattning: Broadband multicarrier communication suffers from a large signal span, causing problems in both wireless and wireline systems. This is commonly referred to as a high peak to average ratio (PAR), and leads to a high power consumption, which is an important limitation in many communication systems. This thesis puts focus on PAR reduction for wireline communication systems, in particular for the multicarrier-based DSL family. Special interest is put on the tone reservation method, where some subcarriers are used to construct a peak-canceling signal in counterphase to the signal peaks. A part of the thesis investigates properties of this method, in particular the proper placement of these subcarriers. Applying PAR reduction in existing DSL systems raises the issue of standard compliance. This puts a number of requirements on the PAR algorithms. The thesis examines what can realistically be achieved in existing systems, with special attention given to the impact of a limited PSD mask. We derive bounds on achievable performance, address the optimization criterion, analyze implementational trade-offs, and describe guidelines for system design. For the system engineer, early indications of realistic performance can then be deduced for different designs, without need for extensive simulations for each parameter choice. Implementation of the reduction algorithms, with the PSD mask taken into account, may efficiently be done with a proposed active-set based algorithm. The complexity is demonstrated to be well below 100 MIPS.