Random Access in Fast Fading Channels: Signature Code Design and Active User Identification

In this letter, we study the signature code design and active user identification for the random access in fast fading channels. First, we propose a constant-weight signature code construction by utilizing the on-off pattern of the binary subspace chirps. The constructed code has low fading coherence and large size, and thus guarantees good performance with large number of access users. Second, a practical activity detection based on the generalized approximate message passing is proposed. Finally, the performance of the proposed signature code and activity detection is demonstrated by computer simulations.