Xiaoyan Bi

Antenna pairing for space-frequency block codes in edge-excited distributed antenna systems

Space-frequency block codes (SFBC) combined with frequency switched transmit diversity (FSTD) is used in the downlink of 3GPP LTE system, where all transmit antennas are collocated at eNodeBs. However, all transmit antennas serving a cell are distributed at the cell edge in edge-excited distributed antenna systems. The performance of SFBC is greatly affected by the different large scale fading from different remote antenna units. In this paper, we investigate the tradeoff between the coding gain and average receive SNR of SFBC in DAS layout and propose to set apart the two antennas of SFBC transmission as far as possible. The optimal antenna pairing schemes in the edge-excited DAS cells compatible with 3GPP LTE system are those with the maximized average distance of SFBC transmission. According to the system level simulations in multicell environment, the 5% outage spectrum efficiency and average throughput per cell of SFBC transmission are improved by as much as 21.8% and 11.6% respectively in DAS3 cells,compared with those in LTE system. The DAS6 cells achieve even high gains in outage spectrum efficiency by 123.6% and average throughput per cell by 22.5%.

Dynamic fractional signature sequence reuse (DFSSR) scheme for CDMA system

Inter-cell interference management is an notorious issue in cellular communication. Traditionally, static techniques were used to manage the interference: frequency reuse for GSM or universal reuse for CDMA. More recently, fractional frequency reuse for LTE has been common. Based on this idea, the next set of ideas consider coordination among base stations to dynamically manage the interference among the cells. Typically this is done in the context of OFDM systems (LTE), and in particular distributed antenna system (DAS) for LTE (coordinated beamforming). In this paper, the implications of this approach in CDMA systems (example: HSPA+) are discussed. The key idea is that it is not just important to reduce total inter-cell interference, but also the dimension (measured in chips over a spreading sequence length - 16 chips in HSPA) over which the interference is caused. This leads to novel interference management techniques that are specific to CDMA technology, which we term dynamic fractional signature sequence reuse (DFSSR).