Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this ...Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this paper, we apply orthogonal transmit diversity technique to multicarrier CDMA systems. Andlysis and simulation results show that performance benefits can be achieved compared with conventioal MC-CDMA systems in multipath fading channels.展开更多
Distributed transmit beamforming(DTB) is very efficient for extending the communication distance between a swarm of UAVs and the base,particularly when considering the constraints in weight and battery life for payloa...Distributed transmit beamforming(DTB) is very efficient for extending the communication distance between a swarm of UAVs and the base,particularly when considering the constraints in weight and battery life for payloads on UAVs.In this paper,we review major function modules and potential solutions in realizing DTB in UAV systems,such as timing and carrier synchronization,phase drift tracking and compensation,and beamforming vector generation and updating.We then focus on beamforming vector generation and updating,and introduce a concatenated training scheme,together with a recursive channel estimation and updating algorithm.We also propose three approaches for tracking the variation of channels and updating the vectors.The effectiveness of these approaches is validated by simulation results.展开更多
Demand assignment MAC protocols have been used widely in wireless networks. It can effectively utilize wireless bandwidth. Some strategies can he used by demand assignment MAC protocols to further improve their effici...Demand assignment MAC protocols have been used widely in wireless networks. It can effectively utilize wireless bandwidth. Some strategies can he used by demand assignment MAC protocols to further improve their efficiency. The concept of transmit probability is introduced. This concept allows a request slot to be assigned to many different traffic classes at the same time. Based on it, the dynamic random channel reservation （DRCR） protocol is proposed. The DRCR protocol operates dynamically by observing the traffic conditions. It uses information about the recent traffic conditions to assign transmit probability with which an mobile station can select request slots with lower traffic. The performance of DRCR is evaluated and compared with RSCA. The results show that DRCR is more stable than RSCA, it offers shorter delays of requests than RSCA and can relieve heavily stressed traffic classes faster than RSCA.展开更多
In this paper, a time-switched space-time （TSST） coded orthogonal frequency division nmltiplexing （OFDM） scheme against the time-varying channels is proposed. In the TSST-OFDM scheme, it is equipped with four tran...In this paper, a time-switched space-time （TSST） coded orthogonal frequency division nmltiplexing （OFDM） scheme against the time-varying channels is proposed. In the TSST-OFDM scheme, it is equipped with four transmit antennas, but only double of them are used for coding in every time slot. It is shown that the signal to inter-antenna interference ratio is a function of Doppler frequency in time-varying channels for a given space-time code. The analyses and simulations results validate that the proposed scheme not only gets time- switched diversity and lower decoding complexity, but also suffers less time-varying impairments. Hence, it ex- hibits better performance than quasi-orthogonal space-time coded scheme.展开更多
文摘Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this paper, we apply orthogonal transmit diversity technique to multicarrier CDMA systems. Andlysis and simulation results show that performance benefits can be achieved compared with conventioal MC-CDMA systems in multipath fading channels.
基金supported by National Natural Science Foundation of China(No.61271236)Major Projects of Natural Science Research of Jiangsu Provincial Universities(No.17KJA510004)Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX17_0763)
文摘Distributed transmit beamforming(DTB) is very efficient for extending the communication distance between a swarm of UAVs and the base,particularly when considering the constraints in weight and battery life for payloads on UAVs.In this paper,we review major function modules and potential solutions in realizing DTB in UAV systems,such as timing and carrier synchronization,phase drift tracking and compensation,and beamforming vector generation and updating.We then focus on beamforming vector generation and updating,and introduce a concatenated training scheme,together with a recursive channel estimation and updating algorithm.We also propose three approaches for tracking the variation of channels and updating the vectors.The effectiveness of these approaches is validated by simulation results.
文摘Demand assignment MAC protocols have been used widely in wireless networks. It can effectively utilize wireless bandwidth. Some strategies can he used by demand assignment MAC protocols to further improve their efficiency. The concept of transmit probability is introduced. This concept allows a request slot to be assigned to many different traffic classes at the same time. Based on it, the dynamic random channel reservation （DRCR） protocol is proposed. The DRCR protocol operates dynamically by observing the traffic conditions. It uses information about the recent traffic conditions to assign transmit probability with which an mobile station can select request slots with lower traffic. The performance of DRCR is evaluated and compared with RSCA. The results show that DRCR is more stable than RSCA, it offers shorter delays of requests than RSCA and can relieve heavily stressed traffic classes faster than RSCA.
基金Sponsored by the Science and Technology Project of Dalian,China (Grant No. 2011J21DW009)
文摘In this paper, a time-switched space-time （TSST） coded orthogonal frequency division nmltiplexing （OFDM） scheme against the time-varying channels is proposed. In the TSST-OFDM scheme, it is equipped with four transmit antennas, but only double of them are used for coding in every time slot. It is shown that the signal to inter-antenna interference ratio is a function of Doppler frequency in time-varying channels for a given space-time code. The analyses and simulations results validate that the proposed scheme not only gets time- switched diversity and lower decoding complexity, but also suffers less time-varying impairments. Hence, it ex- hibits better performance than quasi-orthogonal space-time coded scheme.
