Robert J. Stacey

A Directional CSMA/CA Protocol for mmWave Wireless PANs

In this paper, we investigate the problem of medium access control in mmWave wireless personal area networks (WPAN), within which directional antennas are used to combat the high path loss incurred in the 60GHz frequency band. The conventional CSMA/CA protocol does not work well with directional antennas due to impaired carrier sensing at the transmitters. We explain why existing directional MAC protocols do not work well at 60GHz and propose a novel directional CSMA/CA protocol designed specifically for 60GHz WPANs. Instead of relying on physical carrier sensing, the proposed protocol adopts virtual carrier sensing and relies on a central coordinator to distribute network allocation vector (NAV) information. Both performance analysis and simulation study show that the proposed mechanism incurs low overhead and has robust performance even when the network is heavily congested.

A CSMA/CA MAC Protocol for Multi-User MIMO Wireless LANs

Multiple-input multiple-output (MIMO) is one form of the smart antenna technology that uses multiple antennas at both the transmitter and receiver to improve communication performance. In this paper, we investigate the problem of medium access control in wireless local area networks (WLANs) with downlink multi-user MIMO (DL MU MIMO) capability. We propose a CSMA/CA MAC protocol with three response mechanisms for DL MU MIMO and compare the performance of DL MU MIMO with the beam-forming (BF) based approach. A novel per-station weighted queuing mechanism is proposed to mitigate the hidden node problem in the network. Performance analysis and simulation study both show that the proposed DL MU MIMO mechanism incurs low overhead and provides significant throughput performance gain over BF based approach in high SNR scenarios.

Investigation into the Doppler Component of the IEEE 802.11n Channel Model

Simulations show that the Doppler component of the IEEE 802.11n channel model results in a dramatic decrease in transmit beamforming gain within only 20 ms delay, even though the model is intended for indoor WLAN environment with stationary devices. However, new measurements collected in an office environment show that degradation to transmit beamforming gain is much less sensitive to delay. With normal environmental conditions in the office environment, it was found that on average there was only a 22% decrease in transmit beamforming gain after 200 ms delay. Even with highly exaggerated motion, reasonable gain is maintained with over 100 ms of delay. Measurements with a moving device were also conducted with resulting sensitivity to delay similar to the 802.11n model. The measurements indicate that the Doppler component of the 802.11n channel model is more comparable to a moving device rather than a stationary device. The use of transmit beamforming in an indoor WLAN environment is more practical than simulations based on the IEEE 802.11n channel models would imply.

Multi-band, multi-radio wireless LANs and PANs

Two trends are reshaping wireless personal area networks (WPANs) and wireless local area networks (WLANs). The first is the convergence of WPAN and WLAN functionality in mobile platforms; a single 802.11 radio will increasingly be used for both functions. The second is the availability of new unlicensed spectrum in the 60 GHz band and 600 MHz TV Whitespace band as well as new technology enhancing use of 5 GHz band. Radios that take advantage of this new spectrum and improved use of existing spectrum are being added to mobile platforms. This paper discusses these trends and looks at network and system architectures that take advantage of multi-band radios to provide increased connectivity and performance.

Performance considerations for efficient multimedia streaming in wireless local area networks

This paper investigates multimedia streaming over wireless local area networks. Physical layer sigmoid analytical models are presented for 802.11a/g and for 2x3 MIMO 802.11n MIMO-based systems are presented. Performance results in a wireless LAN environment are presented for traffic using UDP and TCP transport mechanisms. Packet losses are observed in WLAN environments which affects the overall throughput available. Possibilities for performance improvements with the use of 802.11e and MIMO technologies are discussed. System platform architecture performance issues for wireless video conferencing between Intel PXA27x processor-based handheld platforms are presented and results with retry-limit adaptation are also presented.