Distance-Based Code-Collision Control Scheme Using Erasure Decoding in Orthogonal Code Hopping Multiplexing

Orthogonal code hopping multiplexing (OCHM) was developed to accommodate more downlink orthogonal channels than the number of orthogonal codewords through statistical multiplexing. Therefore, code-collisions may occur due to random code hopping patterns. The conventional code-collision control schemes are synergy and perforation. We propose a distance-based code-collision control scheme using erasure decoding in OCHM. The proposed scheme utilizes the conventional synergy scheme when all of the code-colliding symbols are identical. However, a base station (BS) selects a symbol which the nearest mobile station (MS) among code-colliding MSs wants to receive and transmits it with the controlled signal level in downlink when any of the code-colliding symbols is different from others. This scheme yields better performance at the nearest MS from BS among code-colliding MSs. MSs except the nearest MS receive the symbol with much smaller amplitudes due to different path losses. These smaller signal amplitudes are erased by an erasure decoding scheme at the receiver. Therefore, the performance of MSs except the nearest MS is not degraded, compared with that of the conventional perforation scheme.