Ultra-wideband (UWB) is a short-range wireless communication technology—like Wi-Fi or Bluetooth— that makes use of a really massive relative and/or absolute frequency band to ship and obtain data. In response to the FCC rules, a UWB device can be operated on an unlicensed basis in the 3.1–10.6 GHz band (PDF).
On this article, we’ll check out a few of the vital traits of UWB expertise.
UWB Shares the Radio Spectrum
Elements of the frequency vary allotted for UWB are already utilized by current communication techniques. For instance, as proven beneath, each 802.11ac—a high-throughput WLAN communication protocol—and UWB are allowed to make use of the frequency band round 5 GHz.
Determine 1. Diagram of the UWB working beneath the “noise flooring.” Picture used courtesy of ITU
UWB makes an attempt to extra effectively make the most of the scarce spectrum assets.
How can the UWB expertise use the identical spectrum as current wi-fi techniques with out inflicting interference? That is achieved by limiting the ability spectral density of the electromagnetic sign emitted by a UWB transmitter.
In response to the FCC (the U.S. frequency regulator), the ability spectral density of an indoor UWB transmitter ought to be beneath -41.3 dBm/MHz between 3.1 and 10.6 GHz. This limits the interference brought on by a UWB gadget.
Determine 2 exhibits the spectral masks mandated by the FCC for an indoor UWB transmitter.
Determine 2. The spectral masks for an indoor UWB transmitter. Picture used courtesy of Ultra-Wideband Wireless Communications and Networks
UWB presents benefits with respect to knowledge switch fee, immunity to the multipath impact, excessive ranging accuracy, low energy consumption, and the simplicity of implementation. Let’s think about a category of UWB techniques referred to as impulse radios to realize a greater perception into the important thing options of this expertise.
Whereas standard narrow-band communication techniques transmit a steady waveform, an impulse radio transmits ultra-short length pulses (lower than 1 ns) to speak data.
After every pulse, the transmitter stays “silent” for a comparatively lengthy time frame. For instance, an impulse radio may transmit solely a single 1-ns pulse throughout each 100-ns time intervals. On this case, we are saying that the obligation cycle is 1% (the heart beat is current only one% of the transmission time).
Determine 3. A typical pulse sequence transmitted by an impulse radio
These pulses will be modulated in several methods to convey data. Determine 4 beneath exhibits how pulse place modulation and bi-phase modulation change an unmodulated sequence.
Determine 4. Pulse place and bi-phase modulations change an unmodulated sequence. Picture used courtesy of Ultra Wideband Signals and Systems in Communication Engineering
Word that a short while length corresponds to a large bandwidth within the frequency area. Subsequently, relying on the sign length, a wideband sign can be emitted by the UWB transmitter antenna.
Determine 5. The alerts transmitted by an impulse radio occupy a big frequency band. Picture used courtesy of the Time Domain Corporation
Each the middle frequency and the bandwidth of the transmitted alerts utterly rely on the width of the heart beat.
Low Energy Consumption
Because the pulses are transmitted solely throughout a small proportion of the transmission time, the typical energy emitted by the transmitter may be very low. Having a transmission energy on the order of microwatts, a UWB gadget can lengthen the battery lifetime.
Excessive Information Fee
Though the emitted energy is restricted, UWB allows unlicensed utilization of a particularly wideband spectrum. This permits us to have excessive knowledge charges (>100Mbit/s). Nonetheless, this excessive knowledge fee will be achieved solely over a comparatively quick transmission distance of 10 m. It is because solely very low energy is emitted for every bit of data.
At decrease knowledge charges (<1 Mbit/s), we will make use of a big spreading issue to help longer distances. The next desk compares the information fee and vary of UWB with different indoor wi-fi communication applied sciences.
Robustness to the Multipath Impact
UWB alerts exhibit extra robustness to the multipath impact than standard wi-fi applied sciences. Assume that along with a direct path for the electromagnetic wave propagation from the transmitter to the receiver, there’s one other path brought on by the reflections from an object.
Determine 6. Depiction of a multipath impact
The time (t) it takes for the transmitted sign to journey the whole distance (d) of a given path will be obtained by the next equation:
d = c x t
the place c denotes the pace of the electromagnetic wave that’s roughly 3✕108 m/s. Therefore, for each pulse that we transmit, two pulses seem on the receiver enter. That is illustrated in Determine 7 wherein the transmitted and the obtained pulses are proven in a single diagram.
Determine 7. For each pulse transmitted, two pulses seem on the receiver enter.
On this determine, the 2 obtained pulses are simply recognizable as a result of they don’t overlap with one another. Nonetheless, this isn’t the case basically. Inspecting the above determine, we will see that the pulses won’t intrude—provided that the delay distinction between the 2 paths (t1-t0) is bigger than the heart beat width (PW).
Since UWB pulses have a really quick length, the pulses coming from the totally different paths usually tend to not intrude with our desired pulse. Therefore, we will simply extract the specified sign from these originating from undesirable reflections. This provides a UWB system extra immunity to the multipath impact. Alternatively, the power will be summed collectively by a rake receiver.
Excessive Ranging Accuracy
As mentioned above, the sharp time decision of UWB alerts permits us to have a system that may resolve multipath parts with out resorting to complicated algorithms. This makes UWB fitted to time-of-arrival (ToA)-based vary estimation functions.
It’s worthwhile to say that though these time-base ranging schemes profit from the excessive time decision of UWB alerts, they’ve their very own limitations. For instance, as a result of the UWB pulses having a really quick length, clock jitter turns into a limiting issue.
As we have seen with impulse radios, UWB generally is a useful short-range communication expertise due to its knowledge switch fee, immunity to the multipath impact, excessive ranging accuracy, low energy consumption, and ease of implementation. For these causes, many commercial developers are turning to UWB as an alternative of near-field communication (NFC) choices to reinforce design implementation and safety.