Ravishankar H. Mahadevappa

Detect and avoid: an ultra-wideband/WiMAX coexistence mechanism [Topics in Radio Communications]

Cognitive radios have been advanced as a technology for the opportunistic use of underutilized spectrum wherein secondary devices sense the presence of the primary user and use the spectrum only if it is deemed empty. Spectral cognition of this form can also be used by regulators to facilitate the dynamic coexistence of different service types. An example of this is the operation of ultra-wideband devices in WiMAX bands: UWB devices must detect and avoid WiMAX devices in certain regulatory domains. In this article we start by discussing various options for detection and avoidance. We then describe the obstacles faced in achieving robust detection and avoidance with an on-chip implementation of basic DAA functionality. Finally, we present measurement results for operation of a single UWB device with a WiMAX system. This interaction also highlights the problem of dealing with listen before speak primaries where secondary transmission could interfere by blocking the primarys access to the medium.

Implementation aspects of high-speed wireless LAN systems

Wireless local area networks (WLANs) have significantly grown in popularity over the past few years. Future systems based on multicarrier modulation (OFDM) like 802.11n will be operating at bit rates well above 100 Mbps. This paper considers some baseband implementation aspects that enable such high speeds, illustrating the benefits of higher-order modulation, space-time coding and spatial multiplexing.

Rate-feedback schemes for MIMO-OFDM wireless LANs

Through the widespread use of laptop computers and other mobile equipment, wireless LANs have significantly grown in popularity over the past few years. To meet the increasing data rate requirements of future wireless LANs, different physical layer improvements are currently being discussed within the IEEE 802.11n standardization group. This paper considers feedback schemes to increase the data rate and range of a multiple antenna (MIMO) OFDM WLAN system. As is shown, a simple feedback scheme based on switching on/off subcarriers/subchannels can achieve gains up to 3 dB while requiring minimal overhead for feeding back information to the transmitter.

A Fully Integrated UWB PHY in 0.13/spl mu/m CMOS

A direct-conversion RF transceiver and digital PHY are integrated in a single 0.13mum digital CMOS chip. Designed for UWB OFDM operation as proposed by the WiMedia Alliance, the device supports both fixed and frequency-hopped modes in the band of 3.1 to 4.8GHz. The RF transceiver draws 100mA in receive mode and 70mA in transmit mode, and the complete chip occupies 17mm2

Integrated Multiple Antenna Ultra-Wideband Transceiver

Ultra-wideband (UWB) communication systems make efficient use of frequency spectrum from 3.1 to 10.6GHz by transmitting at low output power, distributed over a large bandwidth. Communication systems operating in the same frequency band experience the presence of a UWB system merely as a small increase of the noise floor, resulting in hardly any link degradation. % Two main system designs emerged from the standardization efforts over the past few years. In Impulse Radio (e.g., TAYLOR_UWB95), the narrowband information is spread over a bandwidth much greater than 500MHz by means of a high-rate chipping sequence — a method familiar from CDMA cellular radio technology. In Multiband OFDM (MB-OFDM) wimediaphy