LOW-COST PER TONE EQUALIZER DESIGN FOR DMT-BASED COMMUNICATION SYSTEMS

The twisted-pair copper access network has existed for more than a century and has well served the needs of voice telephony. Over the latter half of that century, the network has also evolved to support data communications, driving the development of Digital Subscriber Line (DSL) technology to carry high-speed data over the twisted pairs.
Discrete Multitone (DMT) modulation has been adopted by the DSL technologies. In the DMT systems, Time-Domain Equalizer (TEQ) and Frequency-Domain Equalizer (FEQ) are utilized to solve the Inter-Symbol Interference (ISI). To improve the system performance, the technique of Per Tone EQualization (PTEQ) provides an alternative structure of the TEQ design [5]. It transforms the TEQ to the frequency domain and combines the TEQ with the FEQ. This equalization scheme achieves better performance than the TEQ designs [2-4][12-15]. However, the PTEQ suffers from two drawbacks: slow convergence and large storage requirement.
In this thesis, we aim to reduce the cost of the PTEQ design. Firstly, to solve the problem of slow convergence, we propose a novel LMS-then-RLS initialization for the PTEQ. We exploit the special structure of the inputs of the PTEQ. By considering this input structure, we will show that the LMS-then-RLS initialization achieve the convergence speed of RLS with a little overhead of NLMS. Secondly, to solve the problem of the large storage requirement, we propose a Reduced-Complexity PTEQ (RC-PTEQ). The consideration of the received signal in frequency domain is the reason for the good performance of the PTEQ. Therefore, we analyze the signal components in frequency domain and use this signal components analysis to derive a simpler structure to design the PTEQ. We will show that the multiplication complexity and storage is saved about 45% and 96%, respectively, with a little performance degradation.