Ultra-wideband — old technology discovered again. Vol. 1 — UWB potential

History snapshot

What is UWB?

  • Wireless communication technology that uses a wide bandwidth:
  • -10dB bandwidth greater than 500MHz,
  • -10dB fractional bandwidth greater than 20%.
  • For unlicensed usage, FCC allows the usage of frequencies between 3.1 and 10.6GHz and forces extremely low spectral density comparable to a floor level [Fig2].
  • It uses impulse radio with truly short pulses (less than 2ns).
  • Fast data communication (around 27–31Mbps),
  • Precise two-way ranging and positioning.
  • Base mode — highest data range,
  • Extended mode — balance of the data rate and sensitivity,
  • Long-range mode — best sensitivity, best range.

UWB signal formats

  1. Impulse radio UWB (IR-UWB) — this signal format was used in the previous chapter as the “typical UWB usage” — transmission is based on a short, high frequency and low energy pulses.
  2. Direct sequence (DW-UWB) — Similarly to the IR-UWB, it is a single-band approach that uses a short pulses and time domain signal processing but this time it is also combined with a direct sequence spread spectrum (DSSS) techniques. Signal is coded (multiplied) with the pseudorandom spreading sequence [Fig4]. Due to signal spreading, the output power is extremely low and hard to detect / interfere with / by other systems.
  1. Fig. 4 DSSS technique
  2. Multiband UWB (MB-UWB) — UWB spectrum is divided into multiple frequency sub-bands [Fig5]. This technique allows the usage of frequency (band) hopping. Based on time frequency codes (shared between the transmitter and received), devices are changing the frequency band currently used for the transmission.

UWB signal modulation

  • On-Off Keying (OOK) — pulse is transmitted only when logical ‘1’ is to be sent. Otherwise, no signal is transmitted.
  • Pulse Position Modulation (PPM) — pulse is shifted whenever ‘0’ is to be sent. When ‘1’ is to be sent, no pulse shifting is used.
  • Binary Phase Shit Keying (BPSK) — ‘0’s are phase shifted by 180º in relation to ‘1’.
  • Pulse Amplitude Modulation (PAM) — Information is encoded by the signal amplitude. ‘0’ will have different amplitude than ‘1’.

Advantages of UWB

  • Low power == little interferences — according to the FCC, the max allowed power requirement is 41.3dBm/MHz [Fig7]. This restriction causes the UWB transceiver to be placed below of typical narrowband devices. We can easily use the UWB with additional radio interfaces without almost any interference. This is especially crucial when it comes to a mixed solutions in which UWB is just one of many wireless communication interfaces.
  • Resistance to harsh environment — according to the previous equation, channel capacity is only logarithmically dependent on the signal to noise ratio, thus even though the SNR can be quite low, we can still get a large channel capacity due to the outstanding bandwidth.
  • High data rate — as the bandwidth increases, the maximum data throughput increases as well. We can define a data rate in terms of the channel capacity — so the maximum rate at which data can be transmitted through specific channel. One of the simplest ways to define the channel capacity is to use the Shannon-Hartley theorem defined as follows:
  • Excellent location precision — UWB can measure the proximity / location with a precision of few centimeters. It brings the UWB to the first place regarding the objects positioning.
  • Resistant to multipath phenomenon — multipath problem [Fig8] is related to the possibility to capture a radio pulse reflected from other (than targeted) object which can significantly impact the accuracy of the system. Problem is presented on the picture below.
  • Outstanding obstacles penetration — thanks to the wide range of the frequencies (to be more precise, the low frequencies included in the UWB spectrum) it is possible to penetrate varied materials especially including walls. Which makes the UWB perfect for the penetrating radars applications.
  • High security, low detection — due to the low power of the emitted signal, it is much more problematic to intercept the data. The potential attacked must be very close to the transmitter to be able to detect the transmission. Moreover, UWB uses codes unique for each transmitter / receiver pair.
  • Small antenna — due to high frequencies, it is possible to use smaller antennas that in typical narrowband use-cases.
  • Safety — nowadays there is a lot of discussions related to the safety of the wireless interfaces, especially when 5g is slowly taking over the market. One can argue if these discussions are meaningful or not, still due to the strict regulations, UWB ensures that in comparison to other wireless interfaces it is harmless. The power of UWB pulses is much lower (10 000 times lower or even more) than the power of other radio transmitters which are located in the typical mobile phone.
  • Simpler transceiver — UWB technology requires much less complicated transceivers.

Main applications

  • Precise location
  • Radars,
  • Proximity detection,
  • Device localization with a precision of few centimeters.
  • Data transmission
  • High data rate in a short distance.
  • Secure use-cases
  • Payment solutions, Close proximity, more secure than NFC,
  • It is much more resistant to the interferences, harsh environment use-cases,
  • Access control, Vehicle access — protection from the eavesdropping / relay attacks,
  • Easier access — no need to take out the mobile phone out of the pocket.
  • Healthcare
  • Diagnostic,
  • Health condition detection,
  • WBAN — wireless body area network.
  • Sport
  • Player’s tracking.

What’s next?



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