Adaptive MIMO semi-soft handover scheme based on channel variation

Abstract

Recently, the demand for data traffic has been increasing with the advent of the smartphone. To meet the mobil user’s increased demand, the network operators have been concentrating on improving the capacity of the network. The small cell is a possible solution for obtaining the higher capacity. Reducing the coverage can be helpful to deploy a large number of BSs in the same area. However, the small cell has an inevitable drawback that the handover rate increases by its inherent characteristic. Handover causes the degradation of Quality of Service (QoS) originating from the poor signal quality particularly in the cell edge and the handover process delay. This degradation can effectively be canceled by improving the data rate. To overcome the side effects of handover, the researches making the handover seamless in a mobile user’s side have been a hot issue. In this paper, we propose the novel handover scheme using the semisoft handover with new adaptive MIMO mode switching. Considering that the conventional 3GPP LTE-A employs the hard handover, the only one radio link is used in the cell edge region, causing the inferior reliability. Moreover, due to the poor signal quality in the handover region, the 3GPP LTE-A system recommends the adaptive MIMO mode switching between the transmit diversity and Closed(CL) Rank=1 with precoding which is associated with beamforming technology. Contrary to the conventional system, the proposed handover scheme exploits the instants when the SINR becomes high enough to take advantage of spatial multiplexing gain. However this moment usually has a short duration, the open-loop spatial multiplexing, open-loop spatial multiplexing does not require the channel state information feedback from receiver, making the transmission process simple and fast. Since the proposed handover scheme uses fast adaptive MIMO mode switching between the open-loop spatial multiplexing and transmit diversity, the computational complexity is so low that th...