Noise analysis of a wide-band multiuser fieldbus communication scheme with discrete multitone

We analyze the signal-to-noise ratio (SNR) of a multiuser fieldbus communication scheme which applies discrete multitone (DMT) modulation. In particular, we derive very accurate analytical expressions on the SNR in down- and uplink. Thereby each subscriber is modeled by a transmit and receive circuit which comprises major noise sources. It turns out that a strong noise funneling arises in uplink where several subscribers have simultaneously access to the channel. For that reason, we derive two low-complexity optimization strategies where one compensates for the near-far effect and the other optimizes the operating point of the digital-to-analog converter. The presented methods provide fairness between subscribers and a significant gain in uplink SNR, simultaneously. Besides, we analyze exemplary networks and show that simulation results are in excellent agreement with our analytical expressions. Additionally, both illustrate that optimization can yield gains of several dBs in uplink SNR such that the fieldbus communication scheme offers comparable SNR performance in both communication directions.