Masayuki Miyashita

Field Evaluations on a Prototype System of Cooperative Multi-Cell MIMO Transmission for Asynchronous Inter-Site Base Station Networks

For next generation cellular mobile communication systems, cooperative multi-cell MIMO transmission (cooperative MIMO) technologies, in which multiple base stations (BSs) coordinate their wireless transmission, have recently been receiving considerable attention due to their potential cell-boundary throughput improvement. However, there are few studies that provide field evaluation of cooperative MIMO in real radio-propagation environments. To evaluate cooperative MIMO in a real field, BSs located at different sites should be synchronized to each other with high accuracy in asynchronous inter-site BS networks. We develop a prototype of an experimental system by using a GPS (Global Positioning System)-based inter-BS synchronous controller. We conduct field experiments on two cooperative MIMO transmission schemes: (i) cooperative MIMO-SDM based on space division multiplexing and (ii) Cooperative MIMO-SFBC based on space frequency block coding. We confirm that cooperative MIMO technologies improve the cell-boundary throughput in real radio-propagation environments. This paper describes the developed field experimental system and its field evaluation results. It also shows the effectiveness of cooperative MIMO wireless transmission at the cell-boundary.

A Cell Identification Performance Improvement in Co-Channel Heterogeneous Cellular Networks with Cell Range Expansion

Recently, data traffic has been explosively increasing in cellular mobile communication systems due to the prevalence of smart phones. A co-channel heterogeneous cellular network overlaid with pico-cells (HetNet), in which pico-cell base stations (BSs) with low transmission power are placed at the hot spot area of a macro-cell base station with a high transmission power, has been receiving attention in order to deal with the increasing traffic. In general cellular mobile communication systems, synchronization signal (SS) symbols for the initial serving-cell identification and for the neighboring-cell identification at user equipments (UEs) are periodically transmitted from base stations (BSs). For HetNet, Cell Range Expansion (CRE), in which a bias value is used for the reference signal received power from pico-cell BSs, has been investigated as a promising approach to offload the traffic into the pico-cell from the macro- cell. Unfortunately, there is an issue that the cell identification delay at pico-cell area increases with the CRE bias value, since larger CRE bias value suffers from larger interference from macro-cell base stations (Macro-BSs) at the received SS symbols transmitted from pico-cell base stations (Pico-BSs) in the pico-cell area expanded by CRE. This paper investigates the cell- identification performance improvement possible with transmission power coordination of the SS symbols for HetNet with CRE. Then, it evaluates the cell-identification characteristics of a cell search operation based on the hierarchical SS structure of 3GPP LTE/LTE-Advanced, and also clarifies the effectiveness of the transmission power coordination of the SS symbols in terms of the pico-cell identification for HetNet with CRE.

Investigation on Inter-Cell Interference Cancellation Scheme for Small-Cell User Equipments in Heterogeneous Networks Employing Cell Range Expansion

Recently, data traffic is explosively increasing in cellular mobile communication systems due to the prevalence of smart phones. A heterogeneous cellular network overlaid with small-cells to a macro-cell (HetNet), in which small-cell base stations (BSs) with a low transmission power are placed at the hot spot area of a macro-cell base station with a high transmission power, has been receiving attention in order to deal with the increasing traffic. For HetNet, Cell Range Expansion (CRE), in which a bias value is used for the reference signal received power (RSRP) from small-cell BSs, has been investigated as a promising approach to offload the traffic into the small-cell from the macro-cell. However, User Equipments (UEs), located in the small-cell area expanded by CRE, suffers large inter-cell interference (ICI) from the macro-cell BSs for the case of co- channel HetNet in which the same carrier frequency is used between macro-cells and small-cells. Hence, it is required for co-channel HetNet to mitigate ICI. In order to improve the downlink user throughput characteristics for co-channel HetNet employing large CRE bias value, this report investigates a successive interference cancellation (SIC) technique of codeword level SIC. The codeword level SIC (CWSIC) realizes a large ICI mitigation effect employing the output of the channel decoder for interference signals. Simulation results confirm that CWSIC based on soft replica effectively mitigate the ICI from the macro-cell BSs, compared to CWSIC based on hard replica.

An Inter-Cell Interference Cancellation for Downlink Layer-1/Layer-2 Control Channels in LTE/LTE-Advanced Heterogeneous Networks

Recently, data traffic is explosively growing in cellular mobile communication systems due to the prevalence of smart phones. 3GPP focuses on Pico-cell overlaid HetNet, in which small-cell base stations (pico eNB: pico-cell evolved Node-B) with a low transmit power, are placed at the hot spots within a macro cell in LTE/LTE-Advanced heterogeneous network (HetNet). Cell Range Expansion (CRE) has been proposed as a promising approach to offload the traffic into the pico-cell from the macro-cell. In the CRE scheme, user equipment in pico-cell (pico-cell UE) suffers the strong interference from the macro-cell eNB (macro eNB) to the pico-cell UE, when large CRE offset value is used for received power of reference signal from the pico-cell. In order to mitigate the interference, this paper proposes an inter-cell interference (ICI) canceller on the downlink Layer-1/Layer-2 control channels (L1/L2 Control Channels) for LTE/LTE-Advanced HetNet. This paper evaluates and confirms the effectiveness of the proposed ICI canceller in L1/L2 Control Channels, and associated performance improvements in H-ARQ retransmission in the downlink shared channel (DL-SCH).