Distance-based code-collision control scheme using erasure decoding in Orthogonal Code Hopping Multiplexing

Orthogonal Code Hopping Multiplexing (OCHM) [1][2] 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 [8] at the receiver. Therefore, the performance of MSs except the nearest MS is not degraded, compared with that of the conventional perforation scheme.