  We investigate power allocation for the base matrix of a spatially coupled
sparse regression code (SC-SPARC) for reliable communications over an additive
white Gaussian noise channel. A conventional SC-SPARC allocates power uniformly
to the non-zero entries of its base matrix. Yet, to achieve the channel
capacity with uniform power allocation, the coupling width and the coupling
length of the base matrix must satisfy regularity conditions and tend to
infinity as the rate approaches the capacity. For a base matrix with a pair of
finite and arbitrarily chosen coupling width and coupling length, we propose a
novel power allocation policy, termed V-power allocation. V-power allocation
puts more power to the outer columns of the base matrix to jumpstart the
decoding process and less power to the inner columns, resembling the shape of
the letter V. We show that V-power allocation outperforms uniform power
allocation since it ensures successful decoding for a wider range of
signal-to-noise ratios given a code rate in the limit of large blocklength. In
the finite blocklength regime, we show by simulations that power allocations
imitating the shape of the letter V improve the error performance of a
SC-SPARC.
