Design, experiment and error analysis of impulse radio-ultra wide band indoor positioning system used in agricultural warehousing

Abstract: For the problem of low positioning accuracy about agricultural goods and AGV (automated guided vehicle) in the warehousing environment, a system model applicable to agricultural warehouse is developed, which uses IR-UWB (impulse radio - ultra wide band) technology. This system adopts SDS-TWR (symmetric double sided - two-way ranging) scheme to set up positioning system model, and uses TOA (time of arrival) location algorithm to locate the mobile station. First of all, this system measures the distance between base station and mobile station, and then gets the optimal solution of error function using nonlinear least squares method. The optimal solution is the coordinate of the mobile station. This system also takes into account the factors of carrier frequency deviation, researches the source of error and tries to find out the method to reduce it. The analysis shows the main source of positioning error in 2 aspects, namely the method of distance measurement, and the method of calculating the position of the target nodes by the distance value. And we put forward the corresponding countermeasures for these 2 aspects, such as the selection of ranging algorithm, and the arrangement of the base stations. IR-UWB has many advantages such as strong anti-interference ability, high range accuracy, low power consumption, fast transmission speed and good security. Because of the convenience to layout network nodes and no strict requirements in the field environment, it is suitable for the field of agricultural warehousing. Finally, we design the positioning system of mobile and base station nodes based on DW1000 RF (radio frequency) chip, and respectively carry out static ranging experiments, static positioning experiments and dynamic positioning experiments. To increase contrast, this article also adds comparative trial, which uses TWR ranging algorithm. The static ranging experiments of this system adopt 6 distances of 10, 15, 20, 30, 40 and 50 m, and collects around 3 000 sets of data respectively. The experiments show that the error of the mean value between the actual distance and the ranging distance is less than 50 mm, and the root mean-square error is less than 41 mm using SDS-TWR ranging algorithm. However, the former is more than 110 mm and the latter is more than 60 mm using TWR ranging algorithm in the same experiment condition. In the static positioning experiments we conduct some experiments to measure coordinates of some spots under the fixed coordinate system. The result shows the positioning error is less than 50 mm and the root mean-square error is less than 69 mm with SDS-TWR ranging algorithm. And the positioning error is more than 90 mm and the root mean-square error is more than 115 mm with TWR ranging algorithm in the same experiment condition. In the dynamic positioning experiments, according to the actual situation of agricultural material warehouse, we move the mobile station along 5 produce aisles and 9 routes, and obtain the distance between the gathered data and the actual path. The experiments show that the positioning accuracy is 85 mm, which can meet requirement of 150 mm positioning accuracy. Comprehensive experiments show the system set up by this paper can satisfy the requirements of practical application in indoor agricultural material storage.