An Introduction to Ultra Wideband Communication By Xingpeng Mao Aug Harbin Institute of Technology (Weihai)

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

Harbin Institute of Technology (Weihai) 3 Contents  Chapter 1 Introduction  Chapter 2 Channel Measurement and Simulation  Chapter 3 Channel Modeling  Chapter 4 Antennas  Chapter 5 Transmitter Design

Harbin Institute of Technology (Weihai) 4 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

Harbin Institute of Technology (Weihai) 5 Chapter 1 Introduction 1.1 Fundamentals 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)

Harbin Institute of Technology (Weihai) 6  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.

Harbin Institute of Technology (Weihai) 7 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

Harbin Institute of Technology (Weihai) 8  FCC defines UWB as a signal with either a fractional bandwidth of 20% [2(f H -f L )/(f H +f L )] 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?

Harbin Institute of Technology (Weihai) 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.

Harbin Institute of Technology (Weihai) 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

Harbin Institute of Technology (Weihai) 11  Multicarrier UWB (MC-UWB)  OFDM (Orthogonal Frequency Division Multiplexing)

Harbin Institute of Technology (Weihai) 12 survey  Impulse UWB (I-UWB)  TH-UWB (Time Hopping)  DS-UWB (Direct-Sequence)  Multicarrier UWB (MC-UWB)  OFDM (Orthogonal Frequency Division Multiplexing)  PAM  PPM

Harbin Institute of Technology (Weihai) 13  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.

Harbin Institute of Technology (Weihai) 14  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.

Harbin Institute of Technology (Weihai) 15 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 Systems 3. Indoor Systems 4. Outdoor Hand-held Systems  Vehicular Radar Systems 5. collision avoidance, improved airbag activation, suspension systems, etc.

Harbin Institute of Technology (Weihai) 16 Summary of Preliminary R&O Limits ApplicationFrequency Band for Operation at Part 15 Limits User Restrictions Imaging3.1 to 10.6 GHz (GPR <960 MHz) Yes Through-wall and Surveillance 1.99 to 10.6 GHzYes Communications (indoor & outdoor)* 3.1 to 10.6 GHzNo Vehicular24 to 29 GHzNo *Indoor and outdoor communications devices have different out-of-band emission limits

Harbin Institute of Technology (Weihai) 17 UWB Emission Limit for Indoor Systems

Harbin Institute of Technology (Weihai) 18 UWB Emission Limit for Outdoor Hand-held Systems

Harbin Institute of Technology (Weihai) 19 UWB Emission Limits for GPRs, Wall Imaging, & Medical Imaging Systems

Harbin Institute of Technology (Weihai) 20 UWB Emission Limits for Thru-wall Imaging & Surveillance Systems

Harbin Institute of Technology (Weihai) What makes UWB unique?  Time domain design  Frequency dependant pulse distortion imparted by RF components or the wireless channel  Time jitter generated by non-ideal oscillators  Impact of the antenna  Cover multi-octave bandwidths in order to transmit pulses on the order of a nanosecond in duration with minimal distortion

Harbin Institute of Technology (Weihai) What makes UWB unique? (continued)  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.  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

Harbin Institute of Technology (Weihai) What makes UWB unique? (continued)  Difficulties in using DSP technology  Very high data rates and ADC (Analog to Digital Converters) sample rate  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)

Harbin Institute of Technology (Weihai) What makes UWB unique? (continued)  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

Harbin Institute of Technology (Weihai) I-UWB System Model  overview of the I-UWB system An unmodulated I-UWB pulse train:

Harbin Institute of Technology (Weihai) 26  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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Harbin Institute of Technology (Weihai) 28 III.FCC rules make UWB transmission most practical in the GHz band.  Gaussian modulated sinusoidal pulse is more practical.

Harbin Institute of Technology (Weihai) 29  Modulation Schemes I. Pulse Amplitude Modulation (PAM) II. Pulse Position Modulation (PPM) Time-Hopping (TH)

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Harbin Institute of Technology (Weihai) 32  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

Harbin Institute of Technology (Weihai) 33  Multiple Access Schemes  Receiver Decision Statistic In diversity system

Harbin Institute of Technology (Weihai) The MC-UWB System Model  Overview of the MC-UWB System

Harbin Institute of Technology (Weihai) 35  OFDM UWB  Can have gaps between subcarries  A proposed physical layer standard for * a Wireless Personal Area Network (WPAN)