Modified SNR gap approximation for resource allocation in LDPC-coded multicarrier systems

The signal-to-noise ratio (SNR) gap approximation provides a closed-form expression for the SNR required for a coded modulation system to achieve a given target error performance for a given constellation size. This approximation has been widely used for resource allocation in the context of trellis-coded multicarrier systems (e.g., for digital subscriber line communication). In this contribution, we show that the SNR gap approximation does not accurately model the relation between constellation size and required SNR in low-density parity-check (LDPC) coded multicarrier systems. We solve this problem by using a simple modification of the SNR gap approximation instead, which fully retains the analytical convenience of the former approximation. The performance advantage resulting from the proposed modification is illustrated for single-user digital subscriber line transmission

Bit Loading For Precoded Dsl Systems

Crosstalk is one of the main impairments of digital subscriber line (DSL) systems. To combat this impairment, several techniques were proposed in the literature that employ some form of precoding in the downstream. However, most existing bit allocation algorithms are not applicable to precoded DSL system when the power in each transmission line is constrained, In this paper, we propose a bit allocation algorithm for this scenario. The proposed algorithm maximizes the bit rate given the available power. It somewhat extends single-user algorithms in that it sequentially allocates bit to the "best" user and tone. In the proposed algorithm We use a definition of "best" that is suitable for preceded systems. Simulation results show that the proposed algorithm achieves almost the same rates as those of power allocation algorithms, which do not take into account the discrete nature of the transmitted information. © 2007 IEEE.3III353III356Starr, T., Cioffi, J.M., Silverman, P.J., Understanding Digital Subscriber Line Technology (1999) Prentice Hall Communications Engineering and Emerging Technologies Series, , Prentice HallGini's, G., Cioffi, J.M., Vectored transmission for digital subscriber line systems (2002) Journal on Selected Areas in Communications, 20 (5), pp. 1085-1104. , JuneCendrillon, R., (2004) Multi-User Signal and Spectra Coordination for Digital Subscriber Lines, , Ph.D. thesis, Katholieke Universiteit Leuven, Leuven, Belgium, DecemberCampello, J., Practical Bit Loading for DMT (1999) Proc. IEEE International Conference on Communications (ICC'9.9), pp. 801-805. , Vancouver, Canada, JuneLee, J., Sonalkar, R.V., Cioffi, J.M., Multiuser Bit Loading for Multicarrier Systems (2006) IEEE Transactions on Communications, 54 (7), pp. 1170-1174. , JulyForney, G.D., Ungerboeck, G., Modulation and coding for linear Gaussian channels (1998) IEEE Transactions on Information Theory, 44 (6), pp. 2384-2415. , OctoberLee, B., (2004) Binder MIMO Channels, , Ph.D. thesis, Stanford University, Stanford, USA, November(2004) G.993.1 VDSL (Very High Speed Digital Subscriber Line Transceivers), , ITU-T, International Telecommunication Unio

BIT LOADING FOR PRECODED DSL SYSTEMS

Crosstalk is one of the main impairments of digital subscriber line (DSL) systems. To combat this impairment, several techniques were proposed in the literature that employ some form of precoding in the downstream. However, most existing bit allocation algorithms are not applicable to precoded DSL systems when the power in each transmission line is constrained. In this paper, we propose a bit allocation algorithm for this scenario. The proposed algorithm maximizes the bit rate given the available power. It somewhat extends single-user algorithms in that it sequentially allocates bit to the “best ” user and tone. In the proposed algorithm we use a definition of “best ” that is suitable for precoded systems. Simulation results show that the proposed algorithm achieves almost the same rates as those of power allocation algorithms, which do not take into account the discrete nature of the transmitted information. Index Terms — Frequency division multiplexing, Multiaccess communication, Digital subscriber lines, Resource management, Crosstalk