In this paper, collision avoidance beamforming(CA-BF) technology is proposed to mitigate inter-cell interference in cooperative wireless communications system with limited feedback. Each acess terminal(AT) selects both the best BF weight vector for a serving base transceiver station(BTS) and the most interfering BF weight vectors of interfering BTSs within a cluster, and sends it back to a cluster scheduler. At the cluster scheduler, a set of transmit BF weights of BTSs and the corresponding scheduled ATs are jointly determined to avoid collision among beams formed by BTSs within a cluster, which enhances system throughput by mitigating inter-cell interference. It is shown that the proposed CA-BF outperforms existing non-coordinated BF schemes in terms of the average system throughput.
In this paper, for a relay-based cellular network, a interference avoidance beamforming technique is proposed to enhance direct link capacity while minimizing loss in the capacity of concurrent relaying link. A direct link is transmitted by beamforming at the transmitter, and the relaying link with the least interference to the direct link is scheduled to transmit data by a collision avoidance scheduling algorithm. Simulation results show that the proposed IA beamforming provides a considerable direct link capacity enhancement while minimizing relaying link capacity loss by effectively mitigating inference between concurrent direct and relaying links only with limited feedback.
3GPP LTE C-V2X(cellular vehicle-to-everything) 모드 4에서 각 차량 단말은 SB-SPS(sensing-based semi-persistent scheduling) MAC(medium access control) 알고리즘에 의해 분산적으로 사용 가능한 무선자원을 선택하고 메시지를 전송한 다. 차량 단말 밀도가 증가할수록 패킷 충돌 발생 확률이 높아지고, 이로 인해 PDR(packet delivery ratio)과 IPG(inter-packet gap) 성능이 열화된다. 따라서 본 논문에서는 LDM(local dynamic map)의 동적 계층에 의해 추정된 차량 단말 혼잡도 정보 를 이용하여, 각 차량 단말들이 해당 혼잡도에 따라 분산적으로 메시지의 전송주기(transmission time interval, TTI)를 조절 하는 분산 혼잡 제어(distributed congestion control, DCC) 기술을 제안한다. MAC 계층 시뮬레이션을 통해 차량 단말 혼잡 도에 따른 제안 기술의 최적 메시지 전송주기(TTI)를 도출하고, 제안 기술이 PDR과 IPG 측면에서 기존 CBR(channel busy ratio) 기반 분산 혼잡 제어(DCC) 기술보다 우수한 성능을 제공함을 분석하였다.
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