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Posted: September 1st, 2022
This chapter starts with a brief description of hardware architecture and its implementation in the HILS, there are two technologies: Bluetooth low energy 4.0 module and ultrasonic module. Section 5.1 describes the different component of HILS and there operational mode, section 5.2 describes the algorithm and software component and section 5.3 describes the hardware design and implementation.
The HILS combines two technologies embedded in one system, BLE 4.0 module and ultrasonic module in order to compensate the limitations of each technology. On one hand, The BLE 4.0 provides low power consumption and have a unique ID for the area covered by the radio, but with low localization accuracy because of instability of the RSS measurement as a described previously in the chapter 4, on the other hand, the Ultrasonic technology provides very high accuracy compared to other technologies used in indoor environment but with high power consumption as described in cricket [11].
The combination of two technologies or more could be a good strategy to build an indoor location system and tracking system with increased localization accuracy and availability. The node in the HILS acts as a fixed reference nods in indoor environment, each node attached to the ceiling, and periodically broadcasting a beacon message (RF Bluetooth signal “hi I am here “) containing some unique information.
When a smartphone or smart devices (tablet, smart watch…) is within the transmission range of nodes, it could determine its location using the three access points (nodes) RF signal or more, with a highest RSS measurement by using method propagation model in the specific environment as described previously in chapter 4. When the user cannot make sure of his right location, he should use the button on App to update new location on the smartphone, it will activate only the three close nodes (which have high RSS this method was described in the previous chapter 4) in its range by asking them one by one, by transmitting three request RF signal; by default, only three nodes will respond and each node of them will transmit an ultrasound Beep which the smart device receives using its microphone and then give a feedback by using TDoA technique to calculate distance between nodes and smartphone. Trilateration algorithm helps the smartphone to determine its location in indoor environment.
HILS requires deployment of equidistant nodes consisting of the transmission units on the ceiling, as illustrated in figure 1. Each node provides ranging of about 15 m and is an access point that can communicate with smart devices within its transmission range. During the experiment, a total of 9 nodes were deployed attached on the ceiling with a distance of six meters between each node. Nodes broadcast a beacon RF signal (Bluetooth signal) carrying important information including id, temperature and battery state, in all directions every 400ms and switch to sleep mode. The Nodes can also emit an ultrasonic sound when requested by a smart device.
Figure 2 illustrates the basic use case of HILS one too one. In this figure Smart device (S) could play different roles according to the usage scenario such as scanning node in indoor environment and sort it or receiving acoustic beep signal in HILS node broadcast a RF beacon message (hi I am here) each 400
ms and switch to sleep mode to save energy, While S enters into the RF range coverage of the corresponding emitting node (nodes are referred to as known fixed reference nodes (N, AP)) by clicking on the button in the App, the Smartphone send a three RF signal request to nodes which has highest RSS measurement to send acoustic Beep signal and start a internal timer in the side of S as soon as N receive Smartphone’s RF signal request, the node will generate acoustic beep as soon as Smartphone detects the acoustic beep via its microphone, the internal timer will stop, and then give a feedback by using TDoA technique to calculate the distance between Node and Smartphone.
Figure 3 illustrates the basic use case of HILS one too many. In this illustration, HILS contains many nodes attached to the celling and each one broadcasts a random RF beacon message (hi I am here) each 400
msand switch to sleep mode to save energy, While S enters into the RF range coverage of the corresponding emitting node, when the user notices that the location it is not right or want to update his new location by clicking in button in the Smartphone’s App, the Smartphone broadcasts three RF signal requests to three nodes (with three IDs which has high RSS measurement ) that send an acoustic Beep signal and start a internal timer in the side of S as soon as Nodes receive Smartphone’s RF signal request, the node will generate an acoustic beep, as soon as Smartphone detect the acoustic beep via its microphone the timer will stop, and then gives a feedback by using TDoA technique to calculate the distance between the Node and Smartphone , then we will get three distances between three nodes and a smartphone , it will be easy to define the relative position via the Trilateration algorithm
To realize this system structure, multiple development tools were used such as IAR Embedded for written firmware, debugging and programing communication protocol; Matlab software and smart devices (such as smartphones, tablets and laptops) to analyze the data, The HILS consists of two main hardware components. Node development boards and an Android smartphone. The node supports both the advertising and scanning states of the BLE 4.0 protocol stack and sending beep sound. The minimum required Android version is Android 4.3, which is the earliest release that supports BLE 4.0 . The smartphone needs to support both BLE 4.0 scanning and advertising states in order to be fully functional.
The HILS software architecture consists of two parts each one can play one of the following roles: the firmware running on the Node, and another App, which runs in the smartphone.
In this role, the node transmits periodically the RF beacon and the Beep signal whenever has been requested from the user. The fixed reference node is used as the point of reference in measuring the relative distance.
Each node is a small hardware platform contains two modules developed under microcontroller CC2540, Both the BLE 4.0 and the ultrasonic technology runs in cheap CC2540 (Bluetooth technology 4.0). The cc2540 has also an internal temperature sensor, which can be used to measure ambient temperature at the node. As illustrated in block diagram figure 4 and 5, the essential component in block diagram CC2540, 20 kHz ultrasonic transduces and power supply. The Node consists of 6 parts:
The nodes for indoor localization application are implemented on the TI CC2540 and CC2541 platforms. The CC2540 and CC2541 combine an excellent RF transceiver with an industry-standard enhanced 8051 MCU. The system is highly suited for ultra-low power energy consumption. The TI CC2540 and CC2541 is a true System On Chip (SOC) for Bluetooth low energy solutions.
Power supply: Each node is powered by batteries with a 5v and a typical capacity of 2000mAh, so that the battery life would be approximately 160 days. Since beacons periodically transmit location information, they need a power source that can last for a sufficiently long time. In real life scenario the life will depend on the application implemented by the system.
LED (indicator): led indicate the stat commination of the nodes.
Ultrasonic transmitter: The ultrasonic transmitter we have been using to generate beeps in our research called piezo sound or piezo transducer, which is similar to speakers that applied voltages drive the piezo crystal to move and make a sound. This sub module generates ultrasonic pulses of duration 0.5 µs. In order to get ultrasonic beeps, we need to generate tones with a square wave from the pin of cc2540 microcontroller. The use of the Pulse Width Modulation (PWM) functionality of the pin of cc2540 allows the piezo transducer to generate ultrasonic beeps. To create a piezo transducer to generate 20 kHz, the PWM runs at 5
μs, so it will produce ultrasonic beeps. We use the Piezo Transducer Type W-06A, the table shows its features.
W-06A Features:
| PARAMETER | SPECIFICATION |
| Min. Sound Pressure Level (dB) | 90/22±1KHz/2.83VRMS Sinewave/50cm |
| Power supply | 3.3 to 5 V |
| Maximum measured error | Less than ±1.5 in |
| Resonant Frequency Range (kHz) | 22±1.0 |
| Frequency Range (kHz) | 4 ~ 50 |
| Operating Temperature ºC | -20 ~ +70 |
| Weight (g) | 6.5 |
| Case Material/Color | Fire-resistance ABS/Black |
| Max. Consumption (mA) | Less than 1.8 mA at 5 V |
Temperature sensor.By enabling the internal temperature sensor of cc2540 the node can measure the ambient temperature and send it to smart phone to compensate variations in the speed of sound with temperature.
Power Amplifier: used to amplify the signal before being sent to the piezo transducer in order to increase the signal power and improve the range of the system
Microcontroller: Uses a CC2540 microcontroller operating at 32 Mhz.
Each node periodically broadcasting a beacon protocol RF message which contains an iBeacon prefix, UUID identifier, Major, Minor, Measured Power, temperature, and battery sate. Fig 1 shows the beacon packet structure as shown in example of frame figure 8, the total amount of data is 30 bytes, which fits very well the 31 bytes’ limit that means the consumption of the power is low,
| iBeacon prefix(9 bytes) | UUID |
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