Since the US Federal Communications Commission authorized the unlicensed use of ultra-wideband (UWB) radio technology in 2002, most commercial applications using this technology (such as wireless USB) are based on frequency domain modulation techniques for high data rate transmission ( Such as OFDM). UWB's proven technology can also be used for nanosecond ultrashort pulse data transmission. This system, known as pulse radio (IR), can transmit information by modulating pulse parameters such as position or amplitude. At the same time, by measuring the transmission time of the pulse, it is also possible to perform the measurement to the centimeter. This opens up a whole new world for a large number of new location-aware applications in different areas of logistics (package tracking), manufacturing, search and rescue (such as communication and positioning with firefighters) or smart guides. Figure 1: The system consists of a non-customized Xilinx ML506 board connected to a custom UWB daughter board. The second phase of PULSERS in Europe is an industry-led UWB radio technology cooperation project involving 30 major industry and academic organizations, aiming to design and implement a data transmission rate of megabits per second, ranging. IR-UWB communication and ranging system with an accuracy of 4 cm. The system consists of a set of identical autonomous nodes, each of which can communicate with other nodes in the network and determine the distance between them. Each node is connected by a custom UWB daughter board to an off-the-shelf Xilinx ML506 development board (see Figure 1). The superior performance of the Virtex-5 SXT architecture complements the flexibility of the MicroBlaze soft processor, allowing us to deploy the entire baseband signal chain and all advanced system layers in a single FPGA. Figure 2: A periodic beacon frame consisting of three beacon slots is interspersed between time-hopping frames. IR-UWB communication and ranging The system transmits information using simple pulse localization modulation that supports four possible time shifts (4-PPM), where each pulse encodes two data bits. As shown in Figure 2, the pulses are grouped into frames and transmitted in a grid of predefined beacon frames and time-hopping frames. Each beacon frame contains three identical beacon slots that the client can use for ranging or communication. We originally planned to use time-hopping frames for high data rate transmission based on time-hopping coding, but we will use this technology in future products, and now all data transmissions are only done in beacon frames. We now use two-way ranging to measure. Two-way ranging is achieved by measuring the time delay from sending a ranging request to receiving a reply from a remote node (see table below). The ranging request is typically sent in beacon slot 1, and the ranging response is typically returned to beacon slot 3. This gives the remote node a complete beacon slot interval (beacon slot 2, approximately 33 microseconds) to process the received ranging request and schedule the returned ranging response. Table 1: Characteristics of UWB communication and ranging systems. Ultra-wideband daughter boards with pulse transmitters and non-coherent receiver ASICs were designed for this project using IHP's 0.25 micron SiGe:C BiCMOS technology. As shown in Figure 3, the transmitter ASIC used to generate the UWB pulse is capable of modulating the amplitude and position of the generated pulses. It includes a 3.84 GHz counter that accurately schedules the transmission time of the output pulses and measures the arrival time of the received pulses. Figure 3: The UWB pulse consists of a 7.68 GHz carrier and a Gaussian envelope. The receive path is split into two in the receiver ASIC. The first branch with relatively narrow bandwidth (120MHz) is mainly used for communication and less accurate pulse timing, while accurate pulse timing is achieved by using a second branch of full pulse bandwidth (750MHz). The incoming pulse is detected by a high speed comparator on the branch. The output can trigger the readout of a 3.84 GHz counter running inside the transmitter ASIC. Therefore, each received pulse arrival time can be measured at a resolution of 260 picoseconds, i.e., the spatial resolution is approximately 8 cm. The daughter board communicates with the baseband module in the Virtex-5 FPGA over two 120MHz data buses. The communication (COMM) bus is responsible for transmitting the ADC samples, while the arrival time bus is responsible for transmitting the high resolution time stamp associated with the received pulses. Both buses pass the XC95144XV CPLD, which is not a must, but it is still an excellent debugging tool. We can set the CPLD to output a series of pseudo-random numbers on the bus to the FPGA. Then we use the CPLD output to adjust the input timing of the FPGA and verify the integrity of the bus line. It would be very difficult to verify the bus line without knowing the sequence of transmitted data.
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