Ultra-Wideband Part II David Yee

Overview a.k.a. impulse radio because it sends pulses of tens of picoseconds( ) to nanoseconds (10 -9 ) Duty cycle of only a fraction of a percent Uses a lot of bandwidth (GHz) Fourier time scaling property Capacity increases linearly with bandwidth but logarithmically with power Shannon

Overview aka impulse radio because it sends pulses of tens of picoseconds( ) to nanoseconds (10 -9 ) Duty cycle of only a fraction of a precent Uses a lot of bandwidth (GHz) Fourier time scaling property Low probability of detection because it looks like noise to an unintended listener

Overview (con’t) Low Probability of Detection because it looks like noise to an unintended listener Multipath cancellation is not a problem because the direct path gets processed before the multipath signals arrive. (so no need for a rake receiver, though some source suggest it) There is no need for a carrier frequency, but there can be one, most likely to get out of range of GPS (1.6GHz) which is sensitive to noise

Types of Pulses Gaussian pulse Gaussian monocycle (first derivative) Gaussian doublet (second derivative)

Pulse Modulations Pulse Amplitude Modulation (PAM) On-Off Keying (OOK) Bi-Phase Modulation (BPSK)

Pulse Modulations (con’t) Pulse Position Modulation (PPM)

Time Hopping Problem possibility of severe collisions with multiple users Solution add pseudorandom time shifts to the pulse train This will also adds a layer of security, since the receiver must know the shift schedule

PPM with Time Hopping w(t) – system’s waveform (monocycle) T f – pulse repetition time or frame time c f – time hopping sequence T c – delay of the hopping code  – delay of bit 1 from bit 0 d – data symbol N s – number of monocycles per symbol

Comparison: Example Bluetooth Radio Uses FSK Needs VCO and PLL Modulation for carrier Demodulation can possibly be several steps (super- heterodyne) Filter to get rid of images

Comparison: Example UWB Radio Low system complexity Can apply pulse directly to antenna After received signal is amplified, it’s DSP (match filter/correlator then decision)

Receiver Model

Receiver Model (con’t) Received signal A k s (k) – attenuated signal from user k n(t) – white Gaussian noise  – time asynchronism between receiver and transmitter Correlation template v(t) is the difference between two pulses shifted by  One of the pulses is for the transmitted bit 0 and the other for bit 1

Decision Rule Output: If result was negative, 1 was transmitted If result was positive, 0 was transmitted

Performance Energy per bit to noise ratio Bit Error Rate also dependent on peak power

Performance (con’t) Has great throughput over short distances Range is also effected by output power, which the FCC is limiting 1 kilometer with high gain antenna meters normally