An Introduction to Ultra Wideband Communication

By Xingpeng Mao

Aug. 2006

Harbin Institute of Technology (Weihai)

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References:

1. J. H. Reed. An Introduction to Ultra Wideband Communication Systems.

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Contents

Chapter 1 Introduction Chapter 2 Channel Measurement and

Simulation Chapter 3 Channel Modeling Chapter 4 Antennas Chapter 5 Transmitter Design

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Contents (continued)

Chapter 6 Receiver Design Principles Chapter 7 The Coexistence of UWB and NB

Systems Chapter 8 Simulation Chapter 9 Networking Chapter 10 Applications

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Chapter 1 Introduction1.1 Fundamentals1.1.1 Overview What is UWB? Ultra wideband (UWB) communication

systems can be broadly classified as any communication system whose instantaneous bandwidth is many times greater than the minimum required to deliver particular information.

Development: The first UWB: Marconi Spark Gap Emitter All the users efficiently share the common spectral

resource carrier-based communication Operate unlicensed UWB systems concurrent with existing

narrowband signals 2002, FCC (Federal Communications Commission)

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Difference between UWB and Narrow Band (NB) systems

1. Large instantaneous bandwidth enable fine time resolution for network time distribution, precision location capability, or use as a radar

2. Short duration pulses are able to provide robust performance in dense multipath environments by exploiting more resolvable paths.

3. Low power spectral density allows coexistence with existing users and has a Low Probability of Intercept (LPI).

4. Data rate may be traded for power spectral density and multipath performance.

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Large Relative (and Absolute) Bandwidth

UWB is a form of extremely wide spread spectrum where RF energy is spread over gigahertz of spectrum Wider than any narrowband system by orders of magnitude Power seen by a narrowband system is a fraction of the total UWB signals can be designed to look like imperceptible random

noise to conventional radios

Narrowband (30kHz)

Wideband CDMA (5 MHz)

UWB (Several GHz)

Frequency

Part 15 Limit

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FCC defines UWB as a signal with either a fractional bandwidth of 20% [2(fH-fL)/(fH+fL)] of the center frequency or 500MHz(when the center frequency is above 6GHz).

Two main problems faced: How does a particular user recover a particular

data stream? How do are the users efficiently share the

common spectral resource? Can a UWB system be built with a sufficient

performance or cost advantage over conventional approaches to justify the effort and investment?

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1.1.2 Brief History The modern era started in the early 1960s (Harmuth); A major breakthrough occurred in 1960s (Tektronix and

Hewlett-Packard, sampling oscilloscope); The first ground-penetrating radar commercialized in

1974 (Morey); Nomenclature UWB is created around 1989 (the

Department of Defense); A multiple access technique for UWB communication

system in 1993(Robert Scholtz, University of Southern California)

First FCC certified commercial system was installed in 2003, and the first FCC-compliant commercial UWB chipset were announced.

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1.1.3 Types of UWB signals Impulse UWB (I-UWB)

No carrier, the transmit signal is a series of base band pulses.

Fig.1.1 Comparison

of the Bandwidth

of NB and UWB

systems

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Multicarrier UWB (MC-UWB) OFDM (Orthogonal Frequency Division Multiplexing)

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survey

Impulse UWB (I-UWB) TH-UWB (Time Hopping) DS-UWB (Direct-Sequence)

Multicarrier UWB (MC-UWB) OFDM (Orthogonal Frequency Division

Multiplexing) PAMPPM

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Relative Merits of Impulse Versus Multicarrier Spread spectrum (SS) can be applied to reduce the

impact of interference on UWB system for both forms of UWB.

MC-UWB is well-suited for avoiding interference to or from NB systems;

MC-UWB provides more flexibility and scalability. Implementing a MC-UWB can be challenging, continuous

variations in power, high-speed FFT processing.

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Relative Merits of Impulse Versus Multicarrier (continued)

I-UWB signals require fast switching times for the transmitter and receiver and highly precise synchronization.

High instantaneous power during the brief interval of the pulse helps to overcome interference but increases the possibility of interference from UWB to NB systems.

RF front-end may resemble a digital circuit, problems associated with mixed-signal integrated circuits.

Simple I-UWB systems can be very inexpensive to construct.

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FCC UWB Device Classifications

5 classes of devices – Different limits for each: Imaging Systems

1. Ground penetrating radars(GPR), wall imaging, medical imaging

2. Thru-wall Imaging & Surveillance Systems

Communication and Measurement Systems3. Indoor Systems

4. Outdoor Hand-held Systems

Vehicular Radar Systems5. collision avoidance, improved airbag activation, suspension

systems, etc.

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Summary of Preliminary R&O Limits

Application Frequency Band for Operation at Part 15 Limits

User Restrictions

Imaging 3.1 to 10.6 GHz

(GPR <960 MHz)

Yes

Through-wall and Surveillance

1.99 to 10.6 GHz Yes

Communications (indoor & outdoor)*

3.1 to 10.6 GHz No

Vehicular 24 to 29 GHz No

*Indoor and outdoor communications devices have different out-of-band emission limits

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UWB Emission Limit for Indoor Systems

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UWB Emission Limit for Outdoor Hand-held Systems

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UWB Emission Limits for GPRs, Wall Imaging, & Medical Imaging Systems

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UWB Emission Limits for Thru-wall Imaging & Surveillance Systems

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1.2 What makes UWB unique?

1.2.1 Time domain design Frequency dependant pulse distortion imparted

by RF components or the wireless channel Time jitter generated by non-ideal oscillators

1.2.2 Impact of the antenna Cover multi-octave bandwidths in order to

transmit pulses on the order of a nanosecond in duration with minimal distortion

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1.2 What makes UWB unique? (continued)

1.2.3 Propagation and channel models The signal may be overlaid on top of

interference (and SIR<0) The introduction of large numbers of multipath

signals that were not resolvable in NB system. 1.2.4 Transmitter and receiver design

The extremely wide bandwidth (BW) Very high peak-to –average power ratio Coexistence of UWB and existing NB systems Most receiver techniques require highly

accurate synchronization with the transmitter

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1.2 What makes UWB unique? (continued)

1.2.5 Difficulties in using DSP technology Very high data rates and ADC (Analog to Digital

Converters) sample rate

1.2.6 Networking issues Wireless Personal Area Network (WPAN) (<10m

radius): self-organized, dynamic, ad hoc network Network security (low probability of intercept) Variable modes of operation (long-range, low data rate

or short-range ,high speed connection) Unique challenges for Medium Access Control (MAC)

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1.2 What makes UWB unique? (continued)

1.2.7 Future Directions Potential interference of UWB emissions to GPS

and air traffic control signals. Help to conserve valuable battery life in sensor

network ensure a secure network Application in the field of medicine

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1.3 I-UWB System Model

1.3.1 overview of the I-UWB system

An unmodulated I-UWB pulse train:

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1.3.2 Pulse Shapes

(Gaussian pulse and its derivatives)

I. Gaussian pulse

II. A UWB antenna may differentiate the generated pulse (assumed to be Gaussian) with respect to time.

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III.FCC rules make UWB transmission most practical in the 3.1-10.6GHz band.

Gaussian modulated sinusoidal pulse is more practical.

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1.3.3 Modulation Schemes

I. Pulse Amplitude Modulation (PAM)

II. Pulse Position Modulation (PPM)

Time-Hopping (TH)

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Due to the low power spectral density (PSD), multiple pulses will be associated with a single symbol. i.e., the pulse rate is often higher than the data rate.

The received signal is modeled as

The channel is modeled as

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1.3.4 Multiple Access Schemes

1.3.5 Receiver Decision Statistic

In diversity system

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1.4 The MC-UWB System Model

1.4.1 Overview of the MC-UWB System

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1.4.2 OFDM UWB Can have gaps between subcarries A proposed physical layer standard for *02.15.3a Wireless Personal

Area Network (WPAN)