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14 Next-Gen Connectivity for Smart Living In the above BPSK example (Figure 1), two consecutive impulse radio (IR) signals represent one symbol. The IR signal can occupy one of the chip-intervals (T c ) within a frame (T f ). A time-hopping (T H ) code is used to determine the accurate position of a signal in a dedicated time frame to decrease the chance of interference between UWB systems. In this example, the T H codes for the symbols are {2, 1}, {2, 3}, and {1, 0}, respectively, so the first and second signals are shifted by two and one chip-intervals and so on. Here, the information corresponds to the polarity of signals, so the IR stream represents the binary data "101." This BPSK approach, combined with ToF information, enables UWB to calculate precise distance estimates even for indoor environments where multipath reflections are widespread. Using timestamped signals, UWB calculates the time it takes for signals to travel between devices, and then multiplies that time by the signal speed (speed of light) to obtain the distance. Figure 2 shows the advantage of using ToF to calculate distance in an indoor environment. In the diagram, a UWB signal transmitted by the cube-shaped device reaches the circular device via several different paths. One path reaches the circular device directly through an intervening wall, while the other paths are longer because they involve reflections. Because the direct path is the shortest, it reaches the circular device first and is used to calculate ToF. The other signals can be ignored. Think of it like a race: many runners arrive at the finish line, but only the first runner wins. This method works regardless of the signal strength, so it doesn't matter if the direct signal has been attenuated by passing through the intervening wall. In contrast, technologies that rely on RSSI can produce misleading distance and location measurements in indoor environments. A weak signal strength may lead the receiver to think the transmitting object is farther away when, in fact, the signal has been offset because it passed through a wall. Also note that UWB requires single measurements to determine your position accurately and reliably, while other RF technologies require multiple samples plus filtering to obtain a location result. UWB Topologies UWB technology can be implemented in different ways to address a wide range of different needs. The principal topologies are: • Two-way ranging (TWR) • Time difference of arrival (TDoA) • Reverse TDoA • Phase difference of arrival (PDoA) Figure 1: UWB transmits information using short sequences of extremely narrow pulses. (Source: Qorvo) Figure 2: UWB is resistant to multipath effects because it uses ToF to calculate distance. (Source: Qorvo)