Cell Edge Throughput Improvement by Base Station Cooperative Transmission Control with Reference Signal Interference Canceller in LTE System

Abstract

Inter-cell interference coordination (ICIC) is attracting attention recently. This is a technique mainly improving cell-edge throughput by coordinating scheduling and signal transmission of multiple BSs. Different from joint transmission (JT), in which the desired signals for a user equipment (UE) are simultaneously transmitted from multiple BSs, the burdens of information exchange among BSs and its attendant signal processing are mitigated in ICIC because it requires only the exchange of scheduling and control information. In ICIC, the cell-edge throughput is improved by adaptively preventing BSs from transmitting signals (in other words, muting BSs) that would otherwise impose strong interference on the cell- edge UEs in the neighbor cells. Although this improves cell-edge throughput, it may degrade cell overall performance because no radio resource is assigned to UEs belonging to the muted BS. To resolve this issue, we first propose a scheduling method, which enables muting only when the throughput improvement (cell-edge UE) obtained by muting is superior to the total throughput possible without muting. Also, when considering applying this ICIC technique to current commercial systems such as LTE, it should be noted that reference signal, also known as pilot signal, is always transmitted regardless of muting because reference signal is a common signal used for channel estimation. To solve this issue, we also propose a reference signal interference canceller, in which the UE cancels the reference signal being transmitted from the neighbor BS. We evaluate the performance improvement by computer simulations and confirm that cell-edge throughput is dramatically improved by introducing the proposed canceller. We also propose a control algorithm that activates the canceller only when throughput improvement is possible. A basic lab experiment was also conducted to confirm the effect of the proposed interference canceller with 3GPP Rel-8 LTE-compliant equipment.