  Since the discovery of turbo codes 20 years ago and the subsequent
re-discovery of low-density parity-check codes a few years later, the field of
channel coding has experienced a number of major advances. Up until that time,
code designers were usually happy with performance that came within a few
decibels of the Shannon Limit, primarily due to implementation complexity
constraints, whereas the new coding techniques now allow performance within a
small fraction of a decibel of capacity with modest encoding and decoding
complexity. Due to these significant improvements, coding standards in
applications as varied as wireless mobile transmission, satellite TV, and deep
space communication are being updated to incorporate the new techniques. In
this paper, we review a particularly exciting new class of low-density
parity-check codes, called spatially-coupled codes, which promise excellent
performance over a broad range of channel conditions and decoded error rate
requirements.
