  A new ensemble of structured codes is introduced. These codes are called
Quasi Linear Codes (QLC). The QLC's are constructed by taking subsets of linear
codes. They have a looser structure compared to linear codes and are not closed
under addition. We argue that these codes provide gains in terms of achievable
Rate-Distortions (RD) in different multi-terminal source coding problems. We
derive the necessary covering bounds for analyzing the performance of QLC's. We
then consider the Multiple-Descriptions (MD) problem, and prove through an
example that the application of QLC's gives an improved achievable RD region
for this problem. Finally, we derive an inner bound to the achievable RD region
for the general MD problem which strictly contains all of the previous known
achievable regions.
