Tomoya Tandai

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.

20.4 A fully integrated single-chip 60GHz CMOS transceiver with scalable power consumption for proximity wireless communication

A fully-integrated single-chip CMOS transceiver with MAC and PHY for 60GHz proximity wireless communication is presented. A 60GHz wireless communication single-chip transceiver has not yet been reported due to large power consumption issues. However, by limiting the application to high-throughput proximity transmission, thermal issues arising in a single-chip have been overcome. A 2GHz broadband OFDM single-chip transceiver suffers from SNR degradation due to the reference clock (REFCLK) and baseband clock (BBCLK) spurs in RF/analog circuits. Low frequency spurs in the clock generator (CLKPLL) due to the mixing of the ADC/DAC sampling clock (SCLK) and other clocks such as REFCLK and BBCLK have been eliminated by careful frequency planning of those clocks. In addition to that, spur suppression in digital baseband and noise-tolerant RF/analog circuit designs are employed. The spurs have been successfully suppressed to less than -35dBc. The chip achieves a PHY data-rate of 2.35Gb/s and MAC throughput of 2.0Gb/s at a distance of 4cm. Power consumption is scalable to the throughput by the introduction of fast Sleep and Awake modes. The average power consumption at a throughput of 0.2Gb/s is reduced to 36% of that at 2.0Gb/s.

Cross-Layer-Optimized User Grouping Strategy in Downlink Multiuser MIMO Systems

This paper proposes a cross-layer-optimized user selection and packet transmission technique for the downlink multi-user (MU) multiple-input multiple-output (MIMO) system in IEEE 802.11 wireless LAN (WLAN). In IEEE 802.11 WLAN, packet duration is decided by a data size and a selected transmission mode (modulation and coding scheme, MCS), and therefore, in general, the packet duration of each user varies according to the channel conditions and the applications. If multiple users whose packet durations are considerably different are selected as the target of the downlink MU-MIMO transmission, then the efficiency of spatial multiplexing degrades and the network throughput cannot be enhanced. When selecting users as the target of the downlink MU-MIMO transmission, the degree of spatial channel correlation among users (from the viewpoint of the physical layer) and the packet waiting times in a queue (from the viewpoint of the MAC layer) have to be considered. In addition to these criteria, in IEEE 802.11 WLAN, uniformity of the packet durations among users has to be considered as a criterion. In the proposed method, data size is adjusted in order to make the packet durations of the users uniform after selecting the users based on the spatial compatibility and the packet waiting times. This means that the proposed downlink MU- MIMO transmission is optimized in 3 dimensions by the cross- layer approach: the spatial channel correlations, packet waiting times and the uniformity of the packet durations. Computer simulations are performed and the results show the effectiveness of the proposed method.

Compressed Block Ack, an efficient selective repeat mechanism for IEEE802.11n

The standardization of IEEE802.11n which aims to achieve 100 Mbps at MAC-SAP (medium access control - service access point) is under work in IEEE802.11, wireless LAN standardization committee. The frame aggregation scheme in which MAC (medium access control) frames are aggregated into one PHY (physical) frame is proposed for IEEE802.11n, because it decreases MAC overhead. In this paper, we propose the compressed block ack mechanism as a selective repeat mechanism to be adapted to the frame aggregation scheme. We present simulation results to compare performance of the compressed block ack mechanism and the legacy block ack of IEEE802.11e and show that the proposed method improves the total throughput by 10% than the conventional method

A MAC Protocol for Coexistence between 20/40 MHz STAs for High Throughput WLAN

IEEE 802.11 is widely known as a standard of WLAN and has a number of amendments and supplements. The one now attracting a great deal of attention is IEEE 802.11n, which is aimed at achieving high throughput. To achieve high throughput, one of the main discussion points is the channel bundling method which extends the channel bandwidth from 20 MHz to 40 MHz. By doubling the channel bandwidth, the data rate can be increased. But a question how to cope with the legacy 20 MHz stations will arise. For this problem, we are proposing to control the 20 MHz and 40 MHz STAs by setting NAV to them in MAC layer. This paper explains our coexistence proposal for the system where transmission in both 20 MHz and 40 MHz channel bandwidths is enabled, and the performance is examined to confirm the effect of our coexistence proposal

MAC Efficiency Enhancement with Prioritized Access Opportunity Exchange Protocol for 60 GHz Short-Range One-to-One Communications

This paper proposes a prioritized access opportunity exchange protocol for enhancing medium access control (MAC) efficiency in short-range one-to-one wireless communications on 60 GHz millimeter wave. A random back-off access protocol is widely spread for distributed wireless networks and is adopted in IEEE 802.11 WLAN standard. When many terminals try to access a wireless medium, the protocol works effectively in terms of fairness and throughput. However, when only two terminals try to access the wireless medium, its overhead becomes large and the MAC efficiency is degraded. In this paper, an access protocol that minimizes the access overhead is proposed for one-to-one communications. In the proposed protocol, a prioritized access opportunity (PAOP) is exchanged between two terminals. A terminal having the PAOP (primary terminal; PT) can access the medium with the minimum period whereas a terminal not having the PAOP (secondary terminal; ST) has to wait the transmission by the PT. If the PT has no data but the ST has data to be transmitted, the PT gives the PAOP to the ST. Then the ST becomes the new PT that accesses the medium with the minimum period. Total throughput and transmission delay performance by the back-off access protocol and by the proposed protocol is evaluated by the computer simulations and the results show the effectiveness of the proposed method.

MAC Efficiency Enhancement with ACK/NACK and AGC Pilot Signal Adaptation Mechanism in Millimeter-Wave Communication Systems

Millimeter-wave (mmWave) wireless systems are a focus of great interest for very high data transmission rate in a short range. Considering short-range communication with a range of the order of several tens of centimeters, only terminals present in this communication range will be influenced. In one-to-one communication, a simpler and more efficient access mechanism is required. Current CSMA/CA based MAC has limits to achieve a high data transmission by reasons of the low MAC efficiency, which is caused by a high overhead of signal exchanges, like interframe space (IFS) and acknowledgement. This paper proposes two methods that enhance the MAC efficiency in shortrange one-to-one communication. The ACK/NACK mechanism uses Negative ACK (NACK) as the acknowledgement policy and solves a problem arising from NACK. The automatic gain control (AGC) pilot signal adaptation mechanism adapts the length of the pilot signals for AGC.

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.

Energy-efficient standby mode algorithm in short-range one-to-one millimeter wave communications

This paper proposes two energy-efficient standby mode algorithms in short-range one-to-one 60 GHz millimeter wave (mmWave) communications. Among the many usage scenarios for mmWave radio, file downloading from kiosk terminals or peer-to-peer sync service with portable terminals are of great interest. For these portable terminals, the power consumption of standby mode as well as connection setup time is important. Comparing the power consumption for a frame transmission with that for a frame reception in short-range one-to-one 60 GHz mmWave, the power consumption for a frame reception may become larger than that for a frame transmission. In this paper, two energy-efficient standby mode algorithms are proposed for one-to-one communications. In the proposed algorithms, each terminal operates based on Interval consisting of several Sub-intervals. One proposed algorithm (Prop1) is that a terminal transmits a connection request frame (CREQ) once at every Sub-interval and the other terminal waits for the CREQ during one Sub-interval per each Interval. Thus, Prop1 saves the power consumption for a CREQ transmission. The other proposed algorithm (Prop2) is that a terminal selects one Sub-interval randomly for each Interval and transmits CREQs repeatedly during that Sub-interval. The other terminal waits for a CREQ during this CREQ transmission period at every Sub-interval. Prop2 saves the power consumption for a CREQ reception. We evaluate the power consumption of standby mode and connection setup time for Prop1 and Prop2 by both numerical analysis and computer simulations. We compare these proposed algorithms under several ratio of the power consumption for transmission and reception.

A software oriented modem architecture for 3G terminal

In this paper we discuss a software oriented modem LSI. At first, the target system is focused on 3GPP DS-FDD mode and signal processing complexity of the developed software simulator is measured. According to the signal processing requirement, modem functions are partitioned into hardware and software. At the same time, a layered modem architecture which is a kind of multiprocessor architecture is proposed. This architecture can perform parallel processing by plural CPU cores, and therefore, it can lower the CPU clock and make software simple. We consider the support service switching possibility for further discussion. Moreover we have developed an evaluation board system. Referring to the implementation results, we discuss hardware complexity and the amount of memory from the viewpoint of LSI development.