Two-Way Networks: When Adaptation is Useless

When Power Adaptation is Useless or Harmful

We consider the design of optimal strategies for joint power adaptation, rate adaptation and scheduling in a multi-hop wireless network. Most existing strategies for ad-hoc networks control either power and scheduling, or rates and scheduling, but not the three together as we do. We assume the underlying physical layer allows finegrained rate adaptation (like in 802.11a/g, HDR/CDMA, UWB). Our g...

Power Allocation Strategies in Block-Fading Two-Way Relay Networks

This paper aims at investigating the superiority of power allocation strategies, based on calculus of variations in a point-to-point two-way relay-assisted channel incorporating the amplify and forward strategy. Single and multilayer coding strategies for two cases of having and not having the channel state information (CSI) at the transmitters are studied, respectively. Using the notion of cal...

When ultrasound-guided catheterization is useless: back to landmarks!

A study by Maizel and colleagues [1] in a recent issue of Critical Care shows that a resident skilled at inserting a central venous catheter (CVC) via the ultrasound-guided (UG) technique may face difficulties inserting a CVC via the anatomical landmark (LM) technique. Because several studies have demonstrated significantly increased safety, effectiveness, and efficiency of UG vascular access, ...

Parity is Positively Useless

We give the first examples of non-trivially positively-useless predicates subject only to P 6= NP. In particular, for every constraint function Q : {−1, 1}4 → R, we construct Contraint-SatisfactionProblem (CSP) instances without negations which have value at least 1 − ε when evaluted for the arity-four odd-parity predicate, yet it is NP-hard to find a solution with value significantly better th...

When two-dimensional structure led the way.