Any successful new technology can be described as a combination of features that allow the technology to perform a given application better than those technologies that precede it or that enable new applications to be performed. The consumer has the final word in the success of a technology. If the product that manufacturers are trying to sell to the consumer does not convey a strong sense of benefit or sex appeal, the product becomes a wallflower on the back of store shelves.

In this chapter, the discussion will centre on the features of UWB, a comparison of these features with competing technologies and the emerging applications that demand the improved performance that UWB provides. With UWB, the principal features of interest include speed, cost, location resolution and power consumption. Each of these characteristics will be covered separately.

Speed – specifying UWB

The exciting new applications that are emerging now or will emerge over the next few years will demand, more than any other single attribute, extremely fast speed. Speed is required for one of two reasons. Either the application involves a large file transfer, such as the download of a Blueray DVD (50 GB), [1] or high-resolution video streaming (Displayport up to 11 Gbps). [2] In the case of large file transfers, speed translates into consumer wait time.

If you are interested in a deep theoretical treatise on ultra-wideband, there are several excellent texts, which are listed at the end of this chapter, that we recommend [1, 2]. Essentials of UWB will definitely not fill that need. It is far too concise and practical and it fails to take up the requisite three inches of shelf space that are required to fill that niche in the literature.

If you are an engineer, business professional, regulator or marketing person who needs enough technical information to build, sell or regulate products that include a UWB radio, but don't aspire to become a radio frequency (RF) deity in your own right, this is the text that you are looking for. Our objective in writing this book is to provide a dependable overview of the data that you need to know to understand the technology and the industry. This includes technical overviews, industry organization, intellectual property overview, standardization and regulatory discussions. We will also attempt to provide pointers to source documents for deeper investigation for those who are so inclined. We know where the good data are buried because in many cases we had a hand in putting it there. Dr Aiello founded two UWB start-ups, contributed actively to the US regulatory processes, participated in the IEEE standardization wars and performed much of the early development of UWB modulation schemes and radio designs. He has also been a board member in the WiMedia Alliance for a number of years.

As with the PHY in the previous chapter, this discussion of the MAC is intended to be somewhat cursory. The full detail can be found in the ECMA 368 standard.[1] As demonstrated in Figure 4.1, the MAC layer sits immediately above the PHY.

The media access control (MAC) layer of the radio connects to the service access point (SAP) on top of the physical layer. The PHY SAP is nothing more than the logical gateway through which data flow in a specified format from the MAC to the PHY and back again. When data need to be communicated from one device to another, they must begin at the top of one of the protocol stacks shown above (WUSB, Bluetooth, etc.) and flow down through each layer, out over the connecting media (RF or wire) and up through each of the layers of the equivalent stack in the radio to whom the communication is being sent. Each layer of the stack has a specific task to perform in making sure that the data are successfully transferred.

Where the PHY is responsible for going through the physical steps of placing bits onto the air during a transmission effort and taking them off again during a receive operation, the MAC is responsible for the first level of processing that takes place on data coming out of the PHY.

For instance, a radio channel, by its nature, is relatively unreliable.

The information that one finds in the standards and specifications of a technology are frequently only part of the story. While standardization is critical to achieve industry-wide interoperability, it is also very important for individual manufacturers to be able to differentiate their products. For this reason, standardization bodies generally restrict themselves to describing those elements that are absolutely required to establish interoperability or common customer experience and usually remain silent about the rest of a design.

In the case of UWB, there are several points that are not described in the standards, but which one might wish to be aware of. For instance, there are many cases in which it will be necessary to place a UWB radio alongside one or more other radios as part of a general system. Some effort is required to get these devices to co-exist. There are also trade-offs that a designer will need to make on topics such as the level of integration that is desirable, the chip-packaging trade-offs and the antenna-selection options. Each of these issues is discussed in the sections which follow.

Co-location with other radios on the same platform

Because it is a wireless technology, UWB is subject to more scrutiny in terms of interference – including its effects on neighbouring devices as well as their effects on it. This is to reduce negative effects both to other UWB receivers and non-UWB receivers.

Douglas Adams once said, “Anything that was invented before you're born is normal and ordinary and is just part of the way the world works, anything that's invented between when you're 15 and 35 is technology, anything invented after you're 35 is against the natural order of things.”

This chapter aims to explain the ‘natural order’ of some of the protocols that enable wireless connections. Consumers rarely see the technology or read the specification for a wireless protocol. Instead, they are in contact with the application layer that determines the normal and ordinary behaviour of the product and its high-level features. If you imagine a layered radio product, the top layer is the application layer. Underneath that, a standardized protocol determines how the radio interacts with the rest of the network. Examples of protocols include CW USB (or wireless USB), WiMedia Layer2 Protocol (WLP), Bluetooth, Wireless 1394 and ZigBee. Below the protocol is a common radio platform, which, depending on its capabilities, could simultaneously support multiple protocols. A diagram of this structure is included in Figure 3.1.

To help explain the various available protocols, consider a common application – sharing photographs. In this sample application, a consumer uses a camera phone to take pictures, and then wants to print the pictures on a local printer and send them to a website. The initial step is to establish a wireless connection between the camera and the printer.

To start this discussion on standards, one should understand that UWB standards and specifications will not be generated by a single standards organization. There are a number of organizations involved in the effort and each of these is engaged for a specific purpose. The following overview gives a flavour of how the division of labour is structured between Ecma International (Ecma), the International Standards Organization (ISO) and the European Standards and Technical Institute (ETSI) in the development of UWB.

Ecma International

The standards organization leading the effort in the development of the UWB physical layer (PHY) and the media access control layer (MAC) is Ecma International. Ecma was initially focused on developing standards for the European computer markets when it was created in 1961, [1] but has since expanded its charter to cover standards in software, consumer electronics and communications on an international scale. Ecma is responsible for developing such well known standards as the DVD (digital video disc) and emerging standards such as near-field communications (NFC), which uses inductive coupling to establish a link between smart cards (credit cards) and their readers. As a side note, the NFC techniques are likely to emerge as a means of association in next-generation wireless LAN and PAN devices.

In UWB, the two principal standards that Ecma is developing are ECMA 368 [2] and ECMA 369.

After more than 80 years of using a regulatory environment that is characterized principally by frequency and, to a lesser extent, spatial division to avoid interference, UWB introduces the significantly different concepts of spectrum underlay and ‘detect and avoid’ (DAA). Both of these concepts are somewhat experimental and clearly evolving over time. It is reasonable to expect that regulations governing UWB around the world may change somewhat over the next few years as we learn more about what does and does not work well in the UWB experiment.

Additionally, regulators are looking to see which applications the industry will choose to deploy UWB for. Some applications are potentially problematic from an interference perspective and others are relatively inert. The choices that UWB manufacturers and implementers make about applications will have an effect on the regulatory environment. If the industry elects to deploy a greater number of problematic applications than was estimated during the regulatory hearings, this will be of material interest to regulators and may cause them to introduce regulatory limits to discourage that deployment. The conscientiousness that the UWB industry shows in its efforts to avoid interference to incumbents will also influence how generous regulators are toward UWB interests in later rounds. As an example, if the UWB industry pushes uncoded and minimally coded video heavily in the crowded lower frequencies, it may be necessary for the regulators to issue more stringent rules to protect the incumbent services.

When a new technology is established as a standard, it gains a degree of validation. Standardization is a statement that the industry has largely consolidated its opinion around an approach for a new technology. This is important from a market-development perspective because it sets the technology onto a path of broad recognition and acceptance. Many people believe that when the standard is completed, the work of coordination in the market is done and the market will develop on its own from there.

The development of the standard is usually the first and most public of a series of activities designed to coordinate the market evolution. The work in the standards body is only meaningful when it is properly coupled with work done in special-interest groups (SIGs). These organizations insure interoperability, establish terms for access to intellectual property, manage brands, speak on behalf of the industry and generally take responsibility for the ongoing management of the market. It is not uncommon for special-interest groups to take an existing standard that has multiple modes or options, which may have been included to obtain political support for the standard, and whittle those down to the essentials. While participation in the standardization process is undoubtedly important to a company developing UWB products, participation in the SIG is at least equally so.

There is no set process through which the industry decides to structure a SIG. As a rule of thumb, a SIG is created when the industry perceives the need to coordinate the activities of manufacturers.

When a property is owned by a single person or entity, it is the responsibility of that person to maintain the property in good condition. If he or she fails to do so, it is entirely to his or her own disadvantage. The value of the property will decline. Likewise, any profit that may be derived is solely to the benefit of the property owner. The owner is therefore motivated to manage the property in a manner that optimizes its profitability.

If a property is communally owned and the individuals are not closely associated with one another, the incentives change. The individuals involved will each attempt to maximize their own personal profit from the property while attempting to minimize their contribution to the upkeep and maintenance. The property becomes overused, while at the same time maintenance is neglected. The value of the property goes into a downward spiral. This behaviour is known in regulatory circles as ‘the tragedy of the commons’ and is frequently used to describe potential risks of unlicensed spectrum. More specifically, this describes spectrum wherein anybody is able to build devices which operate without the enforcement mechanisms that manage use.

Ultra-wideband spectrum saturation

Ultra-wideband is an unlicensed spectrum of this type. Ultra-wideband is somewhat different in considering spectrum saturation than longer-range technologies. The fact that its power is so strictly limited reduces the number of devices that might cause interference to UWB as well as the number of devices that it might interfere.

System identification, as a particular process of statistical inference, exploits two types of information. The first is experiment; the other, called a priori, is known before making any measurements. In a wide sense, the a priori information concerns the system itself and signals entering the system. Elements of the information are, for example:

• the nature of the signals, which may be random or nonrandom, white or correlated, stationary or not, their distributions can be known in full or partially (up to some parameters) or completely unknown,

• general information about the system, which can be, for example, continuous or discrete in the time domain, stationary or not,

• the structure of the system, which can be of the Hammerstein or Wiener type, or other,

• the knowledge about subsystems, that is, about nonlinear characteristics and linear dynamics.

In other words, the a priori information is related to the theory of the phenomena taking place in the system (a real physical process) or can be interpreted as a hypothesis (if so, results of the identification should be necessarily validated) or can be abstract in nature.

This book deals with systems consisting of nonlinear memoryless and linear dynamic subsystems, for example, Hammerstein and Wiener systems and other related structures.

In this chapter, we discuss the problem of identification of a class of semiparametric block-oriented systems. This class of block-oriented systems can be restricted to a parameterization that includes a finite-dimensional parameter and nonlinear characteristics that run through a nonparametric class of mostly univariate functions. The parametric part of a semiparametric model defines characteristics of linear dynamical subsystems and low-dimensional projections of multivariate nonlinearities. The nonparametric part of the model comprises all static nonlinearities defined by functions of a single variable. A general methodology for identifying semiparametric block-oriented systems is developed. This includes a semiparametric version of least squares and a direct method using the concept of the average derivative of a regression function. These general approaches are applied in cases of semiparametric versions of Wiener, Hammerstein, and parallel systems. Section 14.2 gives examples of semiparametric block-oriented systems. This includes the multivariate version of Hammerstein and Wiener systems. In Section 14.3, we give a general approach to semiparametric inference. Section 14.4 is devoted to an important case study concerning the semiparametric Wiener system. Sections 14.5 and 14.6 provide similar considerations for semiparametric Hammerstein and parallel systems. In Section 14.7, we derive direct estimation methods for semiparametric nonlinear systems.

Introduction

In all of the preceding chapters, we have examined various fully nonparametric block-oriented systems.

Thus far we have examined block-oriented systems of the cascade form, namely the Hammerstein and Wiener systems. The main tool that was used to recover the characteristics of the systems was based on the theory of nonparametric regression and correlation analysis. In this chapter, we show that this approach can be successfully extended to a class of block-oriented systems of the series-parallel form as well as systems with nonlinear dynamics. The latter case includes generalized Hammerstein and Wiener models as well as the sandwich system. We highlight some of these systems and present identification algorithms that can use various nonparametric regression estimates. In particular, Section 12.1 develops nonparametric algorithms for parallel, series-parallel, and generalized nonlinear block-oriented systems. Section 12.2 is devoted to a new class of nonlinear systems with nonlinear dynamics. This includes the important sandwich system as a special case.

Series-parallel, block-oriented systems

The cascade nonlinear systems presented in the previous chapters define the fundamental building blocks for defining general models of series-parallel forms. Together, all of these models may create a useful class of structures for modeling various physical processes. The choice of a particular model depends crucially on physical constraints and needs.

In this section, we present a number of nonlinear models of series-parallel forms for which we can relatively easily develop identification algorithms based on the regression approach used throughout the book.