A Two-Way Time of Flight Ranging Scheme for Wireless Sensor Networks

Abstract

Abstract.Relative ranging between Wireless Sensor Network (WSN) nodes is considered to be an important requirement for a number of distributed applications. This paper focuses on a two-way, time of flight (ToF) technique which achieves good accuracy in estimating the point-to-point distance between two wireless nodes. The underlying idea is to utilize a two-way time transfer approach in order to avoid the need for clock synchronization between the participating wireless nodes. Moreover, by employing multiple ToF measurements, sub-clock resolution is achieved. A calibration stage is used to estimate the various delays that occur during a message exchange and require subtraction from the initial timed value. The calculation of the range between the nodes takes place on-node making the proposed scheme suitable for distributed systems. Care has been taken to exclude the erroneous readings from the set of measurements that are used in the estimation of the desired range. The two-way ToF technique has been implemented on commercial off-the-self (COTS) devices without the need for additional hardware. The system has been deployed in various experimental locations both indoors and outdoors and the obtained results reveal that accuracy between 1m RMS and 2.5m RMS in line-of-sight conditions over a 42m range can be achieved.

Comparability of RF-based indoor localisation solutions in heterogeneous environments: an experimental study

“…This is the model used by Mazomenos et al (2011). The calibration step consists of estimating the constant offset t off by averaging over various ToF measurements according to equation (2).…”

“…The resolution of a single clock allows for a spatial precision equal to ∆ d = c 2ftimer . For a 12 MHz clock, the resulting spatial resolution is 12.5 m. To achieve higher resolution, one can average over a series of measurements, as proposed by Mazomenos et al (Mazomenos et al, 2011). This way, sub-clock precision can be achieved.…”

Efficient cross-correlation via sparse representation in sensor networks

“…Fig. 1(a) shows a received signal trace recorded for a duration of 0.1 s sampled at 48 kHz, and its cross-correlation with the reference copy (a linear chirp of [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] kHz/0.01 s) is depicted in Fig. 1(b).…”

“…However, the resources required for signal detection are a deciding factor for the cost, size and weight of the sensing platform, and this essentially strikes a trade-off between localization accuracy/coverage range and energy efficiency. Low-cost systems [1][2][3][4] utilize simple detection methods to estimate the arrival time of the pulse, but they tend to be less reliable due to their limited capability to counter environmental noise and multipath reflections [5].…”

Wireless sensor node localization

“…Lanzisera et al [11] have built a sensor node that is even able to achieve reasonable accuracy in such unfavourable RF environments as a coal mine under LOS conditions. Recently, however, Mazomenos et al [12] demonstrated metre-scale accuracy using COTS sensor nodes and actual radio messages. They estimated the extra delay of the measurement by placing the two nodes right next to each other while performing a large number of ranging operations and considering the actual propagation time to be zero.…”