Enhancement of orthogonal code/resource hopping multiplexing using smart antenna systems

Abstract

Our previously proposed orthogonal code/resource hopping multiplexing(OCHM/ORHM) schemes were designed to accommodate a large number of bursty downlink users. Symbol-by-symbol random code and resource hopping of the OCHM/ORHM schemes cause symbol code-/resource-collisions. Symbol perforations occurring when all code-/resource-collision symbol values are not identical degrade channel decoding performance, which may undergo link quality degradation (an increase in the required $E_b/I_o$ for a given frame error rate (FER) condition). Transmission signal beamforming is expected to significantly reduce the symbol perforation probability because of its spatial filtering capability. The typical smart antenna systems for transmission signal beamforming are switched-beam array antennas (SBAAs) providing geographical fixed beams and adaptive array antennas (AAAs) providing dynamic per-user beam. The introduction of SBAAs to downlink OCHM leads to the reduction of the user symbol perforation probability due to the spatial codeword reusability obtained from multiple narrow beams. In order to remove user symbol perforations for low number of user channels, the random group-wise hopping pattern allocation (RGHPA) scheme is proposed. Users in a beam obtain their own hopping patterns from one or more collision-free group (CFG) in which a user hopping pattern is orthogonal for other hopping patterns within the same group and is random for hopping patterns in different group(s). The number of CFGs within a beam varies according to the number of required downlink user channels in a beam. Therefore, symbol collisions and its symbol perforations almost don’t occur when the number of required user channels is lower than the number of available orthogonal codewords. Since SBAAs intentionally overlap the neighboring beams, a beam is subdivided into two overlapping beam areas (OBAs) and a non-overlapping area (NOBA). A user in an OBA receives the signals from two ...