The Age of Channel State Information

This paper studies an "age of information" problem in fully-connected wireless networks with time-varying reciprocal channels and packetized transmissions. Specifically, a scenario where each node in the network wishes to maintain a table of global channel state information (CSI) is considered. Each node updates its global CSI table in two ways: (i) direct channel measurements through standard channel estimation techniques and (ii) indirect observations of channels through CSI dissemination from other nodes in the network. Information aging, i.e., CSI staleness, occurs due to timeslotting and contention for the common channel resources. This paper derives new lower bounds for the maximum and average CSI staleness of any protocol. These bounds generalize previously developed bounds by allowing for any number of CSI estimates to be disseminated in each packet. A simple one-step greedy protocol is also proposed for any network size and any number of CSI estimates disseminated per packet. Numerical results are provided to demonstrate the achieved staleness of the greedy protocol with respect to the bounds and to also quantify CSI staleness in terms of various network parameters.