Kiyoshi Toshimitsu

An efficient uplink multiuser MIMO protocol in IEEE 802.11 WLANs

This paper proposes an uplink Multi-User (MU) Multiple-Input Multiple-Output (MIMO) protocol in IEEE 802.11 WLANs. In order to realize the uplink MU-MIMO transmission in 802.11 WLANs, there are several problems to be solved. Synchronized transmission among the stations (STAs) is one of the problems and the spatial compatibility between the transmitting STAs is another problem. Therefore, it is considered that many overheads are needed to realize the uplink MU-MIMO transmission. In the proposed protocol, after an access point (AP) informs the start of the uplink access phase by transmitting the indication frame, the STAs having data to be sent to the AP transmit the uplink access requests in the OFDMA manner. The AP recognizes the uplink access requests by detecting the subcarrier signals and it requests the detected STAs to transmit the pilot signals in the TDMA manner. The AP calculates the channel state information (CSI) between each STA from the received pilot signal and selects the STAs to be permitted to transmit the uplink frames based on the CSIs. The AP notifies the information about the permitted STAs and about the capable transmission rate, and then the permitted STAs simultaneously transmit the frames at the notified transmission rate. In the protocol, an efficient OFDMA-based uplink access request transmission scheme is also proposed. Thus, by adopting the proposed protocol, the overheads can be reduced and the network throughput can be enhanced. Computer simulations are performed and the results show the effectiveness of the proposed method.

Broadband multi-media communication system with asymmetric wireless access link, SDL-Net

SDL-Net (super high speed downlink network) is proposed as a wireless access link to a broadband multi-media network, and its physical-layer and datalink-layer protocols are described. In SDI-Net, the transmission data rate in the downlink is 100 to 1000 times faster than the transmission data rate in the uplink. Since the backward channel is much narrower than the forward channel, a sophisticated ARQ technique is indispensable for errorless data transmission through such an asymmetric air interface. Considering the ARQ scheme and the transmission quality in the downlink, the downlink throughput and the uplink traffic are investigated for large file transfer services such as an electronic publishing. The round trip delay which is one of the important performance measures, is analyzed. The backbone networks for the SDL-Net are also discussed.

Optimum real-time data transmission scheduling for channel searching in IEEE 802.11 wireless LANs

In transmitting real-time data over IEEE 802.11 wireless local area networks (WLANs), interference considerably degrades the quality of service (QoS). To minimize this damage, the radio channel should be switched to an unused new channel as soon as interference is detected on the current channel. For that purpose, the system has to know in advance,which channels are in use and which are not. The paper proposes an efficient method to search in advance for channels that are not in use by downlink real-time data transmission scheduling. The proposed method enables all stations (STAs) belonging to the basic service set (BSS) to perform fair and time-randomized other channel measurement. Therefore, the probability of detecting packets in other channel measurement becomes higher, and the BSS can select a channel that is not in use if interference is detected on the current channel. Adopting the proposed method, the BSS can successfully obtain stable throughput for real-time data transmission. The simulated throughput (video streaming) and packet detection probability in other channel measurements confirms the effectiveness of the proposed method.