400 research outputs found
Timely Updates over an Erasure Channel
Using an age of information (AoI) metric, we examine the transmission of
coded updates through a binary erasure channel to a monitor/receiver. We start
by deriving the average status update age of an infinite incremental redundancy
(IIR) system in which the transmission of a k-symbol update continuesuntil k
symbols are received. This system is then compared to a fixed redundancy (FR)
system in which each update is transmitted as an n symbol packet and the packet
is successfully received if and only if at least k symbols are received. If
fewer than k symbols are received, the update is discarded. Unlike the IIR
system, the FR system requires no feedback from the receiver. For a single
monitor system, we show that tuning the redundancy to the symbol erasure rate
enables the FR system to perform as well as the IIR system. As the number of
monitors is increased, the FR system outperforms the IIR system that guarantees
delivery of all updates to all monitors
Timely Estimation Using Coded Quantized Samples
The effects of quantization and coding on the estimation quality of a
Gauss-Markov, namely Ornstein-Uhlenbeck, process are considered. Samples are
acquired from the process, quantized, and then encoded for transmission using
either infinite incremental redundancy or fixed redundancy coding schemes. A
fixed processing time is consumed at the receiver for decoding and sending
feedback to the transmitter. Decoded messages are used to construct a minimum
mean square error (MMSE) estimate of the process as a function of time. This is
shown to be an increasing functional of the age-of-information, defined as the
time elapsed since the sampling time pertaining to the latest successfully
decoded message. Such (age-penalty) functional depends on the quantization
bits, codeword lengths and receiver processing time. The goal, for each coding
scheme, is to optimize sampling times such that the long term average MMSE is
minimized. This is then characterized in the setting of general increasing
age-penalty functionals, not necessarily corresponding to MMSE, which may be of
independent interest in other contexts.Comment: To appear in ISIT 202
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