Communications via updates of shared memory (Corresp.)

A model in which a transmitter
T
sends a message to a receiver
R
via shared random-access memory is analyzed. In the model, the random-access memory consists of
L
individually addressable cells, each of which may be set to a value from a finite alphabet. A message
m
is sent by writing values into some of the memory cells so that the memory state is consistent with some codeword for
m
. The model differs from traditional source coding in several respects. The codeword may specify values for a noncontiguous subset of the memory cells and allow the remaining unspecified cells to be filled in by other users as they wish. Also, the transmitter
T
may attempt to avoid writing a full codeword into memory by first reading some cells to determine the initial memory state partially. Thus, the cells accessed for transmission and the cells specified by a codeword may be distinct, unlike traditional noiseless source coding where the symbols sent and symbols received are identical. Here we analyze the operational characteristics of the transmitter
T
. It is shown that the number of accesses by
T
obeys a generalized Kraft inequality. Lower bounds are given for the worst case and average number of accesses.