Technical Report 2016-003

A Tradeoff Between Data Rate and Regulation Performance in Networked Data Flow Control

Torbjörn Wigren

January 2016

The report investigates fundamental trade-offs related to the static regulation performance in networked control systems with delay and saturation in the feedback loop. The trade-offs are a consequence of required L2 stability of the networked system, in the limit where the delay tends to infinity. First a relation between the relative static regulation accuracy and the static gain of the part of the plant that affects the disturbance is derived. Based on this, the special case with one directional networked flow of an arbitrary medium is considered, where the saturation is a consequence of assumed one-directional flow. For this case it is shown that the trade-off becomes one between relative static regulation accuracy and flow capacity. In the wireless case this implies that there is a tradeoff between the relative static regulation performance and the achievable end to end Shannon data rate. A numerical study of a wireless transmit queue data flow controller illustrates and validates the discovered fundamental trade-offs and limitations.

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