Abstract
Ultra-wideband (UWB) is an alternative wireless communications technology that offers high bandwidth wireless communications without the constraints of spectrum allocation. Fundamentally different from conventional radio frequency communications, UWB relies on a series of narrow, precisely timed pulses to transmit digital data. Transmitters and receivers that use UWB can be much simpler to build than their conventional counterparts, resulting in lower cost and higher power efficiency. Moreover, the inherent properties of UWB emissions allow them to potentially coexist with conventional wireless systems on a noninterfering basis. In April 2002, the Federal Communications Commission (FCC) released UWB emission masks and introduced the concept of coexistence with traditional and protected radio services in the frequency spectrum, which allows the operation of UWB systems mainly in the 3.1 to 10.6 GHz band, limiting the power level emission to -41dBm/MHz. Within the power limit allowed under the current FCC regulations, Ultra-wideband can not only carry huge amounts of data over a shortto- medium distance at very low power (this range can be extended by using ad-hoc or mesh networks), but it also has the ability to carry signals through doors and other obstacles that tend to reflect signals at more limited bandwidths and a higher power (Reed, 2005). At higher power levels, UWB signals can travel to significantly greater ranges. In March 2005, the FCC granted the waiver request, filed by the multiband Orthogonal Frequency Division Multiplexing (OFDM) alliance (MBOA), in which it approved the change in measurement for the all UWB technologies (neutral approach) (Barret, 2005). The FCC’s waiver grants effectively removes the previous transmit power penalties for both frequency-hopping (OFDM) and gated UWB technologies (TH and DS). Hence, they are allowed to transmit at higher power levels and then become idle for some time, as long as they meet the limits for average power density. This new rules allow those technologies to achieve up to four times better performance and double the range.
TopBackground
Definitions
The concept of Ultra-wideband communication originated in the early days of radio. In the 1900s the Marconi spark gap transmitter (the beginning of radio), communicated by spreading a signal over a very wide bandwidth (Zhi & Giannakis, 2004). The basic concept is to develop, transmit, and receive an extremely short duration burst of radio frequency (RF) energy, typically a few tens of picoseconds (trillionths of a second) to a few nanoseconds (billionths of a second) in duration. These bursts represent from one to only a few cycles of an RF carrier wave. The resultant waveforms are extremely broadband, so much so that it is often difficult to determine an actual RF center frequency, which is known as “carrier-free.” Early methods of signal generation utilized “baseband” (i.e., nonRF) fast rise-time pulse excitation of a wideband microwave antenna to generate and radiate the antenna’s effective “impulse” response. More modern UWB systems no longer utilize direct impulse excitation of an antenna because of the inability of such an approach to adequately control emission bandwidths and apparent center frequencies (Ghavami, Michael, & Kohno, 2004).
Key Terms in this Chapter
Automatic Speech Recognition (ASR): ASR is becoming more commonplace these days, especially for enquiry/help desk/call center applications—in other words, where the working vocabulary is somewhat constrained. This makes the task of phoneme/whole word matching much more feasible. The de facto ASR approach is a stochastic one—Hidden Markov Models—in which the probability (likelihood) of encountering a particular phoneme next in sequence is dependant on the ones that have gone before.
Input/Output Devices: Computer I/O is normally limited to a user’s five senses, with sight, hearing, and touch being dominant.
Graphical User Interfaces (GUI): The (ubiquitous) de facto computer interface in use nowadays. They first originated with Doug Englebart’s work on the Xerox Alto workstation during the 1970s, and are based on the underlying WIMPS (Windows, Icons, Mouse, & Pointer) paradigm as well as the desktop analog (metaphor). GUIs superseded (text-based) command line interfaces during the 1980s.
Multiple User Interface: MUI refers to the interaction styles pertinent to different device paradigms, specifically graphical vs. Web vs. handheld device.
Human-Computer Interaction (HCI): The term has been in common use since the 1980s, replacing the earlier “man-machine interaction.” HCI incorporates not only technical considerations of computer interfacing, but extends into system design, cognitive science, psychology, sociology, ergonomics, and graphic design.
Usability: Is a measure of the effectiveness, efficiency, and satisfaction with which users achieve specific goals in a particular environment with the interface in question.
Multimodal Interface: Implies Input/Output via a combination of several different modes, usually related to the user’s senses—primarily touch, sight, and hearing.
User Interface Evaluation: The main goals of user interface evaluation are assessment of both system functionality and user experience, as well as the identification of specific system problems. Various evaluation approaches are in widespread use, which can be classified along the dimensions of analytical vs. empirical, and/or expert analysis vs. end user participation.