Handover Control Method for Multiple Base Stations in Millimeter-Wave V2X Communication

In millimeter-wave (mmWave) Vehicle-to-Everything (V2X) communications, dynamic mobility often leads to severe degradation in communication quality due to transitions between line-of-sight (LoS) and non-line-of-sight (NLoS) conditions or interference from surrounding vehicles. To address this challenge, we propose a handover (HO) control scheme across multiple base stations (BSs), and evaluate two distinct approaches: cooperative transmission and null-space expansion. In the cooperative transmission scheme, multiple BSs synchronously transmit identical data, transforming interference into a desired signal to enhance reception during HO. In contrast, null-space expansion suppresses interference by steering nulls toward undesired directions, which is particularly effective during vehicle approach. Through simulations with three BSs, two vehicles, and two blocking vehicles under three scenarios (interference only, blockage only, and combined), we show that cooperative transmission consistently achieves the highest SINR across cell boundaries and during blockage events, whereas null-space expansion provides partial gains under specific conditions. These results highlight the complementary strengths of both approaches and provide practical insights into the design of robust mmWave V2X HO.