Driven by the exceedingly high data rates achieved in single-user implementations, interest in a multi-user (MU) full-duplex (FDX) transmission for digital subscriber line (DSL) networks is surging. However, near-end crosstalk (NEXT) is no longer avoided in such networks, and hence, appropriate dynamic spectrum management (DSM) techniques are needed. Therefore, this paper proposes three novel DSM algorithms for the MU FDX DSL network. First, an optimal spectrum balancing (OSB) algorithm is derived that calculates the globally optimal resource allocation but does so at an exceedingly high computational cost. The key to this algorithm is a novel multiple access channel broadcast channel (MAC-BC) duality for the specific case of perfect NEXT cancellation at the distribution point unit. The two low-complexity distributed spectrum balancing (DSB) algorithms are then proposed, for which simulations show that their performance is very close to what is achieved by the OSB algorithm. Therefore, these DSB algorithms can be used to estimate the achievable performance of an MU FDX DSL network. Such performance estimations show that the FDX transmission can indeed lead to significant gains in MU DSL networks as well.INDEX TERMS DSL, dynamic spectrum management, G.mgfast, multi-user full-duplex, vectoring.

Fellow, IEEEOFDM and DMT transmission systems add a cyclic prefix (CP) or zero pad (ZP) to the transmitted signal. Interference-free transmission requires this CP/ZP to be similarly long as the channel impulse response (CIR), reducing the achievable data rate in highly dispersive channels. A first strategy for dealing with long CIRs without increasing the CP/ZP overhead consists of applying a channel shortening filter to the received signal. A second strategy consists of spectral resource allocation, i.e. bit and power allocation to reduce interference. As little effort has been made towards joint channel shortening and resource allocation, a new algorithm to simultaneously optimize the channel shortening per-tone equalization (PTEQ) filters and the resource allocation is presented.In addition, transmitter-side channel shortening filters are considered, more specifically so-called per-tone precoding (PTPC) filters which apply the channel shortening filter before the IDFT modulation of the ODFM/DMT transmitter. At first glance, the FIR filter optimization for PTPC seems much more involved than the relatively straightforward FIR filter optimization for PTEQ. However, it will be demonstrated that any OFDM/DMT system with PTPC is -after time-reversing the CIR -equivalent to an OFDM/DMT system employing PTEQ. With this result in hand, systems with PTPC can take full advantage of the straightforward FIR filter optimization in systems with PTEQ, as well as of the aforementioned resource allocation algorithm. Simulation results show that the performance obtained for systems with PTPC is nearly indistinguishable from that obtained for systems with PTEQ, making PTPC an interesting alternative channel shortening strategy.

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