  This letter proposes a novel method for accelerating iterative detection for
spatially coupled (SC) systems. An SC system is constructed by one-dimensional
coupling of many subsystems, which are classified into training and propagation
parts. An irregular structure is introduced into the subsystems in the training
part so that information in that part can be detected successfully. The
obtained reliable information may spread over the whole system via the
subsystems in the propagation part. In order to allow the subsystems in the
training part to collaborate, shortcuts between them are created to accelerate
iterative detection for that part. As an example of SC systems, SC
code-division multiple-access (CDMA) systems are considered. Density Evolution
for the SC CDMA systems shows that the proposed method can provide a
significant reduction in the number of iterations for highly loaded systems.
