An Oversampled Modulated Filter Bank Based Transmultiplexer With Precoding and Equalisation

This paper addresses an oversampled filter bank transmultiplexer applie d to a power line commmunications scenario. We proposed structure has a low oversampling ratio and therefore introduc es only a small amount of redunancy. Of particular interest are the possibility to iterate the filter bank in order to shorten the overa ll response, which is traded-off against the use of precoding or equalisation in order to target remaining ISI is only a low nu mber of multiplexed bands are used. However, we demonstrate the iteration of the filter banks does not reduce the problme f timing synchronisation. I. I NTRODUCTION TRANSMULTIPLEXING using filter banks is one of the oldest mult ip exing methods in telecommunications [1]. While the design of critically sampled structures, which are free of redundancy, was a break-through in terms of signal processing theory [2], [3], these systems loose thei r orthogonality when communicating over dispersive channe ls. This has been remedied by means of equalisation, which howev er r quires cross-terms between subbands [4] — equivalent to [5] for the dual operation of signal decomposition — in ord er to achieve a meaningful performance. This can be addressed by oversampling [6], [7], leading to si mplified transceiver structures [8]. Under the cost aspect, oversampled modulated filter banks (OSFB) that are derived b y modulation from a prototype lowpass filter have been shown to be most efficient with implementations detailed in e . g. [9], [10]. Oversampling offers additional advantages i n the presence of structured noise and interference [11], [12 and advantages over OFDM systems in terms of redundancy and resilience to synchronisation errors have been demonst rated [8], [13], [14], [15]. The aim of this contribution is firstly to demonstrate the use of an OSFB design in [16] for transmultiplexing with low interference between subbands, often referred to as intercarrier interference. Secondly, to remove ISI within subba nds due to a dispersive channel response, we will be investigate a nu mber of non-linear precoding and equalisation methods [17] , [18] in comparison to equalisation only [4], [21], [22]. Thi rdly, we want to design OSFB and precoding/equalisation suc h that the errors encountered in these two system components a re balanced. II. SYSTEM SETUP A. Transmultiplexer The transmultiplexer system with a synthesis filter bank S as multiplexer, transmission over a dispersive channel wit h impulse responsec[m], and an analysis filter bank A as demultiplexer is depicted in Fig. 1. The input to the multi plexer S is an N -element vectorx[n] containing signalsxi[n], i = 0 · · · (N − 1). The multiplexer outputx[m] runs at a rate K > N higher than the input. The present approach utilises the ana logy between such a transmultiplexer and the subband decomposition of signal intoK subbands decimated by a rate N < K. As an example, Fig. 2 shows the different band allocations ofxi[n], i = 0 . (N − 1) in x[m] for a subband decomposition design [16] with N = 14 andK = 16, clearly showing the narrow guard bands due to oversampling.