Dagnachew Birru

IEEE 802.22: the first worldwide wireless standard based on cognitive radios

In November/2004, we witnessed the formation of the first worldwide effort to define a novel wireless air interface standard based on cognitive radios (CRs): the IEEE 802.22 working group (WG). The IEEE 802.22 WG is chartered with the development of a CR-based wireless regional area network (WRAN) physical (PHY) and medium access control (MAC) layers for use by license-exempt devices in the spectrum that is currently allocated to the television (TV) service. Since 802.22 is required to reuse the fallow TV spectrum without causing any harmful interference to incumbents (i.e., the TV receivers), cognitive radio techniques are of primary importance in order to sense and measure the spectrum and detect the presence/absence of incumbent signals. On top of that, other advanced techniques that facilitate coexistence such as dynamic spectrum management and radio environment characterization could be designed. In this paper, we provide a detailed overview of the 802.22 architecture, its requirements, applications, and coexistence considerations that not only form the basis for the definition of this groundbreaking wireless air interface standard, but that will also serve as foundation for future research in the promising area of CRs

IEEE 802.22: An Introduction to the First Wireless Standard based on Cognitive Radios

In November/2004, we witnessed the formation of the first worldwide effort to define a novel wireless air interface (i.e., MAC and PHY) standard based on Cognitive Radios (CRs): the IEEE 802.22 Working Group (WG). The IEEE 802.22 WG is chartered with the development of a CR-based Wireless Regional Area Network (WRAN) Physical (PHY) and Medium Access Control (MAC) layers for use by license-exempt devices in the spectrum that is currently allocated to the Television (TV) service. Since 802.22 is required to reuse the fallow TV spectrum without causing any harmful interference to incumbents (i.e., the TV receivers), cognitive radio techniques are of primary importance in order to sense and measure the spectrum and detect the presence/absence of incumbent signals. On top of that, other advanced techniques that facilitate coexistence such as dynamic spectrum management and radio environment characterization could be designed. In this paper, we provide a detailed overview of the 802.22 draft specification, its architecture, requirements, applications, and coexistence considerations. These not only form the basis for the definition of this groundbreaking wireless air interface standard, but will also serve as foundation for future research in the promising area of CRs.

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.

Using simple light sensors to achieve smart daylight harvesting

Lighting is the largest single energy consumer in commercial buildings. In this paper, we demonstrate how to improve the effectiveness of daylight harvesting with a single light sensor on each window. Our system automatically infers the window orientation and the cloudiness levels of the current sky to predict the incoming daylight and set window transparency accordingly. We evaluate our system with ten weeks of empirical data traces collected from windows around an office building and compare our approach with non-predictive feedback control. Experimental results show that our scheme can infer the orientation of a window to within ±7° of the actual orientation and improve energy savings by 10% over existing approaches without sacrificing user comfort.

Evolution of spectrum-agile cognitive radios: first wireless internet standard and beyond

Spectrum agile radios, also known as cognitive radios, have received much attention from researchers recently. Although the promise of cognitive radios in terms of increased access to spectrum was widely recognized very early, specific applications that utilize cognitive radio techniques have only recently began to develop. In this paper we briefly describe the first wireless Internet standard that is based on Cognitive Radio techniques, namely IEEE 802.22, and discuss its performance with respect to one aspect of cognitive radios, namely operation over multiple frequency channels. Furthermore, we discuss the evolution of cognitive radios beyond IEEE 802.22 by identifying some of the key factors that affect it, which in turn guide our research in cognitive radio PHY and MAC design.

A novel delay-locked loop based CMOS clock multiplier

On-chip clock-rate multiplication is usually achieved using a phase-locked-loop (PLL) circuit. However, integration of such an analog-intensive and noise-sensitive circuit with a digital circuit constitutes a major challenge. As an alternative solution, this paper proposes an attractive fully integratable delay-locked loop (DLL) based clock-rate multiplier by a modest integer factor. The implementation of the total circuit in the standard digital CMOS process is extremely simple and robust. The circuit can be part of a standard digital cell library and can easily be integrated with digital circuits. Simulation and experimental results are provided to evaluate the performance of the proposed circuit.

Design and Performance of Multi-Band OFDM UWB System with Multiple Antennas

In this paper, we design Multi-Band OFDM (MB-OFDM) UWB systems, with two transmit and two receive antennas, with the goal of achieving 1 Gbps data rate. We study the performance of these systems with different modulation schemes. The Packet Error Rate (PERs) and the operating range of these systems are obtained using frequency domain baseband simulations as well as more realistic full-system simulations, and are compared to those of single antenna systems. Simulation results show that the MHVIO MB-OFDM systems provide significant gains for 1 Gbps transmission over single antenna MB- OFDM UWB systems.

Optimized reduced sample rate sigma-delta modulation

An optimized reduced sample rate sigma-delta modulation technique for application in digital to analog conversion is presented. A general framework of a sigma-delta modulating topology where the major arithmetic computation is done at a rate of an integer fraction of the bit-stream rate Is proposed and analyzed. The effectiveness of the technique is illustrated using simulations of second- and third-order sigma-delta modulators. Its impact on modulator complexity, stability, and performance is discussed. Optimization techniques such as quadratic programming are utilized in choosing proper filter coefficients.

Reduced-sample-rate sigma–delta modulation using recursive deconvolution

A reduced-sample-rate sigma–delta modulation method using a recursive deconvolution technique for application in digital-to-analogue conversion is proposed and analysed. The method allows the sigma–delta modulators to operate at a sampling rate which is lower than the output bitstream rate by an integer factor. With the proposed in-loop mapping algorithm to map an m-bit sample to qb-bit samples, the total system inherits the advantages of a multilevel quantization conventional ΣΔ modulator in the digital part with regard to suppression of tones, improved stability and low power, while its output remains single-bit. The effectiveness of the technique is illustrated using simulations for second-and third-order modulators.

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