Vasanth Gaddam

The MBOA-WiMedia specification for ultra wideband distributed networks

The WiMedia Alliance is undertaking the development of an UWB-based system specification with participation from more than 170 companies. UWB technology will provide data rates up to 480 Mb/s within a range of up to 10 m. High-rate UWB will enable fast download of content from one consumer electronic (CE) device to the next in seconds instead of minutes or longer. In addition, the low-power characteristic of UWB will make possible the ubiquitous use of this technology in portable and mobile CE devices, such as cameras, MP3 players, and CD players. The WiMedia Alliance is specifying the physical layer, the MAC sublayer, and convergence layers. The WiMedia PHY layer is based on multiband orthogonal frequency-division multiplexing. The WiMedia MAC is completely distributed, making it an excellent candidate not only for the aforementioned UWB applications, but also for the next-generation MAC protocols in the domain of cognitive radios as well as in cooperative communications

First Cognitive Radio Networking Standard for Personal/Portable Devices in TV White Spaces

Recent FCC rules allowing unlicensed use on a secondary basis of the Television White Spaces (TVWS) promise a whole new set of possible applications. The first step towards realizing these applications is the creation and adoption of industry standards. In this paper we present the first such standard for personal/portable devices in the TVWS that complies fully with the existing FCC rules while retaining flexibility for use with other regulatory domains. We describe the physical (PHY) and medium access control (MAC) layers specified in the standard and present performance results to demonstrate the robustness and spectral efficiency of the proposed protocols.

Spectrum Sensing Prototype for Sensing ATSC and Wireless Microphone Signals

Spectrum sensing is the key enabler for dynamic spectrum access in the television (TV) bands as it can allow secondary networks to reuse spectrum without causing harmful interference to primary users. In this paper we describe a sensing prototype that has been developed to demonstrate robust sensing of TV signals as well as wireless microphone signals in the laboratory and field. We will present the algorithms as well as simulation, lab and field test results that validate the prototypes capability to identify these signals down to a level of -116 dBm.

A newly proposed ATSC DTV system for transmitting a robust bit-stream along with the standard bit-stream

This paper describes the proposed improvements to the ATSC DTV standard. The proposed system provides a mechanism for embedding a new robust bit-stream in the standard bit-stream in a backward compatible manner. The robust stream has a higher threshold of visibility (TOV) compared to the standard stream and can be transmitted either in the pseudo 2-VSB mode or in the enhanced-coded 8-VSB (E-VSB) mode. A prototype transceiver system, based on the proposed system, has been developed and was tested in the lab and in the field. The results of these tests will be briefly reviewed in this paper.

Robust Sensing of DVB-T Signals

Following the recent Federal Communications Commissions (FCC) decision to allow unlicensed use of the television white spaces (TVWS) in the US on a secondary basis, other regulatory agencies such as Office of communications (Ofcom) will follow suit as well. Since the incumbent television signals in UK, Europe and many other countries follow the DVB-T standard, there is a need for sensing algorithms that are capable of detecting these signals at very low levels (-114 dBm). In this paper we describe sensing algorithms for extremely robust sensing of DVB-T signals. We present simulation results as well as results from the lab and field tests using real over-the-air signals to verify the algorithms.

Feasibility study of sensing TV whitespace with local quiet zone

Unused TV spectrum, namely TV whitespace, is nearly ready for utilization by unlicensed TV band device (TVBD) given they provide sufficient protection to licensed TV devices, also called incumbents. A combination of a geo-location database and sensing is required to determine channel availability information. Sensing only device is also potentially allowed. From sensing perspective, TVBD should be able to detect incumbent signal as low as −114 dBm. To detect such low level incumbent signal, it is expected that a TVBD will quiet neighboring TVBDs during incumbent detection. Several mechanisms have been discussed in the literature to coordinate sensing. Among others, message based common inband wireless signaling, called quiet signaling, has been proposed to establish local Quiet Zone within which every TVBD suspends transmission to enable incumbent detection. However, there is little study on sensing performance in the presence of interference and the minimum size of local quiet zone required for detecting the weakest incumbent signals. Moreover, the sensing performance in a heterogeneous environment is not clear. In this paper, we intend to answer these questions. We analyze the impact of the incumbent signal strength, the interference power level, the transmission power of quiet signaling, and the minimum SIR tolerable to detect incumbent. We present discussion of homogeneous networks as well as heterogeneous networks where low power personal/portable TVBDs and high power fixed TVBDs may coexist. Although we focus on the detection of ATSC signal only in this paper, the methodology developed in this paper could be also applied to the detection of other primary signals.

Performance of multi-band OFDM UWB system with multiple receive antennas

Performance of a multi-band OFDM UWB system employing two receive antennas is studied. Different antenna selection and combining methods, such as simple antenna selection, antenna selection per sub-carrier, equal gain combining and maximal ratio combining are considered. The packet error rate (PER) and the operating range of such systems is obtained using detailed realistic full-system Monte Carlo simulations, and are compared to those of a single antenna system. Simulation results show that the dual receive antenna systems provide significant gains for the higher data rate modes and moderate gains for the lower data rate modes of the multi-band OFDM UWB system