Throughput Maximizing FIR Filterbank For MIMO LTI Wireline Channels Ahmed F. Shalash Analog Devices New Jersey Design Center Somerset, NJ 08873 Email: ahmed.shalash@analog.com Mohammed Nafie Cairo University Department of Electronics and Communications Geeza, Egypt Email: mnafie@eng.cu.edu.eg Abstract— There is an ever growing need for higher speed communications over existing wireline plant. To achieve even higher throughput, bonding and joint op- timization of multiple-input-multiple-output cable bundles attracted attention recently. In this paper we first explain a technique which allows several users to use the same communication medium while at the same time allowing their transmission to be separated at the receiver. This technique would handle single-channel-multiple-users case. The technique is then extended to handle multiple input multiple output (MIMO) channel by jointly optimizing the transmit filters to maximize the throughput over the MIMO channel. This optimization is suitable for multiple- channels-single-user and multiple-channels-multiple-users cases. A 2-D MIMO channel example is given and sim- ulation results show that the joint optimization achieves higher throughput than independent optimization for each channel. I. I NTRODUCTION With the full deployment of wide band digital commu- nications over wireline channels, many new interesting technical as well as marketing problems arise. The problem of optimizing transmit filters for increasing the throughput of the communication channel has attracted attention lately [1], [2], [3]. The research in that area was primarily concerned with single user transmitting over additive white Gaussian noise channels. However, the need for multi-user or multi-task links can be envisioned for homes or small business users. One of these applica- tions is exhibited by the so-called channelized voice over digital subscriber loops (DSL). For these applications, the users can utilize one of the classical multiple access approaches but none are without drawbacks. A transmit filter optimization technique for the multiple-access environment was shown in [4]. However, with the growth of the DSL, the need for even higher data rates keeps mounting. This, coupled with the fact that the cost of fiber deployment still makes it attractive to utilize the loop plant to achieve maximum possible throughput, led to the emergence of such project as the G.BOND. The G.BOND project, adopted by the International Telecommunication Union (ITU), supports the topology that one user would combine multiple DSL pairs to increase the data rate. This opens the door for jointly optimizing the transmit filters to maximize the overall throughput over multiple links. The work done in the dynamic spectrum management project [5] clearly shows the advantage of jointly optimizing the MIMO channel to achieve better data rates. In this paper, numerical optimization is performed on FIR filter bank to maximize the information rate. In this paper, we introduce an optimization technique that can be utilized to allow either multiple-access over a single wireline channel (single loop) or single/multiple user(s) operating on multiple loops. We model the prob- lem of the multiple loops as a MIMO channel problem. The authors cannot emphasize enough that even though the problem formulation as a filter bank, [6], [7], [8], looks similar to the known multi-dimensional modula- tion used in wireless communications, there are many fundamental differences between wireless and wireline problems. First the wireline channels are linear-time- invariant (LTI). Second, unlike the wireless channels, complete synchronization can be guaranteed for the wireline case. Third, unlike the wireless channel, the wireline channel can be measured and known a priori. Previous work show efficient ways to estimate the chan- nel characteristics [9][10]. The receiver is assumed to be a multi-dimensional DFE [11]. The remainder of the paper is divided as follows. Section II has the problem formulation. Section III has the solution methodology for fractionally-sampled multi- dimensional filter banks over a single channel. Section IEEE Communications Society 0-7803-8533-0/04/$20.00 (c) 2004 IEEE