Improving Placement Delivery Array Coded Caching Schemes With Coded Placement

Coded caching schemes with low subpacketization and small transmission rate are desirable in practice due to the requirement of low implementation complexity and efficiency of transmission. Placement delivery arrays (PDA in short) can be used to generate coded caching schemes. However, many known coded caching schemes, which have low subpacketizations, realized by PDAs do not fully use the users’ caching content to create multicasting opportunities. So we propose a method to overcome this drawback. As an application, we obtain a new scheme, which has significantly advantages on the tradeoff between memory ratio and transmission rate.