Transmit beamforming with receive combining is a simple approach to exploiting the significant di... more Transmit beamforming with receive combining is a simple approach to exploiting the significant diversity provided by multiple-input multiple-output (MIMO) systems, and this technique can be easily extended to frequency selective MIMO channels by employing orthogonal frequency division multiplexing (OFDM). Optimal beamforming requires channel state information in the form of the beamforming vectors corresponding to all the OFDM subcarriers. When the uplink and downlink channels are not reciprocal, this information must be conveyed back to the transmitter. To reduce the amount of feedback information, a new approach to transmit beamforming is proposed that combines limited feedback and beamformer interpolation. Because the length of the OFDM cyclic prefix is designed to be much less than the number of subcarriers to increase spectral efficiency, the neighboring subchannels of a MIMO-OFDM system are substantially correlated. Thus, the beamforming vectors determined by the subchannels a...
In this paper, we propose a new indoor location estimation method which combines the fingerprint ... more In this paper, we propose a new indoor location estimation method which combines the fingerprint technique with the propagation prediction model. The wireless LAN (WLAN) access points (APs) deployed indoors are divided into public APs and private APs. While the fingerprint method can be easily used to public APs usually installed in fixed location, it is difficult to apply the fingerprint scheme to private APs whose location can be freely changed. In the proposed approach, the accuracy of user location estimation is improved by simultaneously utilizing public and private APs. Specifically, the fingerprint method is used to the received signals from public APs and the propagation prediction model is employed to the signals from private APs. The performance of the proposed method is compared with that of conventional indoor location estimation schemes through measurements and numerical simulations in WLAN environments.
ABSTRACT An efficient direct feedback method from coordinated base stations (BSs) to a mobile sta... more ABSTRACT An efficient direct feedback method from coordinated base stations (BSs) to a mobile station (MS) for an uplink (UL) coordinated multipoint (CoMP) reception with supporting hybrid automatic-repeat-request (H-ARQ) transmission is proposed. Acknowledgement (ACK)/negative acknowledgement (NACK) feedback based on local detection at each BS in the CoMP set is directly transmitted from the BSs using shared-feedback resources. Therefore, an MS can obtain global ACK/NACK information without experiencing extra backhaul delay with a small feedback overhead, and we can reduce the H-ARQ retransmission latency for the inter-cell UL-CoMP operation. To minimize the ACK/NACK detection error at the MS, we investigate the optimized design methods for shared-feedback resources. We derived the analytical detection error probability of the proposed feedback method and the optimum sub-block size to minimize misdetection probability for a fixed overhead and false alarm rate. Based on the analytical and computer simulation results, we have verified that the proposed feedback method can provide a reliable detection performance with a small feedback overhead. In addition, system level simulation results show the proposed fast feedback based inter-cell UL-CoMP system increases the system throughput compared to the conventional intra-cell UL-CoMP without increasing the feedback latency.
Transmit beamforming with receive combining is a simple approach to exploiting the significant di... more Transmit beamforming with receive combining is a simple approach to exploiting the significant diversity provided by multiple-input multiple-output (MIMO) systems, and this technique can be easily extended to frequency selective MIMO channels by employing orthogonal frequency division multiplexing (OFDM). Optimal beamforming requires channel state information in the form of the beamforming vectors corresponding to all the OFDM subcarriers. When the uplink and downlink channels are not reciprocal, this information must be conveyed back to the transmitter. To reduce the amount of feedback information, a new approach to transmit beamforming is proposed that combines limited feedback and beamformer interpolation. Because the length of the OFDM cyclic prefix is designed to be much less than the number of subcarriers to increase spectral efficiency, the neighboring subchannels of a MIMO-OFDM system are substantially correlated. Thus, the beamforming vectors determined by the subchannels a...
In this paper, we propose a new indoor location estimation method which combines the fingerprint ... more In this paper, we propose a new indoor location estimation method which combines the fingerprint technique with the propagation prediction model. The wireless LAN (WLAN) access points (APs) deployed indoors are divided into public APs and private APs. While the fingerprint method can be easily used to public APs usually installed in fixed location, it is difficult to apply the fingerprint scheme to private APs whose location can be freely changed. In the proposed approach, the accuracy of user location estimation is improved by simultaneously utilizing public and private APs. Specifically, the fingerprint method is used to the received signals from public APs and the propagation prediction model is employed to the signals from private APs. The performance of the proposed method is compared with that of conventional indoor location estimation schemes through measurements and numerical simulations in WLAN environments.
ABSTRACT An efficient direct feedback method from coordinated base stations (BSs) to a mobile sta... more ABSTRACT An efficient direct feedback method from coordinated base stations (BSs) to a mobile station (MS) for an uplink (UL) coordinated multipoint (CoMP) reception with supporting hybrid automatic-repeat-request (H-ARQ) transmission is proposed. Acknowledgement (ACK)/negative acknowledgement (NACK) feedback based on local detection at each BS in the CoMP set is directly transmitted from the BSs using shared-feedback resources. Therefore, an MS can obtain global ACK/NACK information without experiencing extra backhaul delay with a small feedback overhead, and we can reduce the H-ARQ retransmission latency for the inter-cell UL-CoMP operation. To minimize the ACK/NACK detection error at the MS, we investigate the optimized design methods for shared-feedback resources. We derived the analytical detection error probability of the proposed feedback method and the optimum sub-block size to minimize misdetection probability for a fixed overhead and false alarm rate. Based on the analytical and computer simulation results, we have verified that the proposed feedback method can provide a reliable detection performance with a small feedback overhead. In addition, system level simulation results show the proposed fast feedback based inter-cell UL-CoMP system increases the system throughput compared to the conventional intra-cell UL-CoMP without increasing the feedback latency.
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