Dual QoS loading algorithms for multicarrier systems offering different CBR services

We propose a novel loading algorithm for discrete multitone (DMT) modulation or orthogonal frequency division multiplex (OFDM) systems simultaneously providing two constant bit rate (CBR) services. Furthermore, these two services have different quality of services (QoS) characterized respectively by their target bit error rates (BER). We derive the optimal solution and show that it is NP-hard. Thus, we propose a method namely, disjoint bandwidth (DBW) which is O(N log N) that still gives near optimal performance. The reduction in complexity is enabled by the set selection procedure we propose. Simulation results for frequency selective Rayleigh fading channels with additive white Gaussian noise show that the DBW method is within 0.1% of the optimum for a total number of carriers N>12 and that it performs on the average 15% better than any previously reported method in the literature