Indoor positioning and life detection using radio frequency has been widely researched, but to achieve both indoor positioning and life detection has been a very challenging task until now. Simulations and measurement results of both modes show that A-MFSK has the capability of indoor positioning and life detection.
Introduction
Background
Radars are among the best radio frequency/microwave devices for remote sensing and are divided into two groups: long-range radars and short-range radars. Long-range radars are generally intended for national defense or security purposes, and are also used for civilian scenarios such as meteorological/weather measurement tasks and many others.
Summary
Introduction 5 An example of widely used radars is given here, ultra-wideband (UWB) pulsed radio radars are short-pulse variants of traditional pulsed radar systems as shown in Figure 1.4[5]. Then a correlation is performed between the received pulses and the delayed copy of the transmitted pulses. The UWB radar has a very spatial resolution that enables it to detect small movements through the wall[6].
Moreover, the bandwidth of UWB radar spreads over a very large range of spectrum, which makes UWB radars resistant to interference and multipath effect[7]. UWB shows very promising performance in detecting small movements in the human body such as chest wall motion, however, using an ultra-wide bandwidth, it requires high-performance ADCs to handle the signals, thus increasing the cost.
Introduction
Single tone Continuous Waveform Radar
- Detection Theory
- Discussion
From the equation above, fBis is shown in the baseband signal, which is proportional to the radial velocity of the moving target. The variable part of phase is only dependent on the distance to the target R0, the zero observation point occurs with a target distance every λ/4 from the radar. Previous approaches 9 greater than the amplitude of the baseband signal associated with the heartbeat or breathing activities, making it impractical to simply digitize the full signal with reasonable resolution.
The baseband signal can be shown as below, cardiac and respiratory motion are given by x(t) and y(t), . By applying the arctangent operation to the I/Q signals, accurate phase demodulation can always be achieved regardless of the position of the target[16]. For example, phase equalization by range correlation in conventional interferometry radars with a free-running oscillator deteriorates as the range to the target increases, but a front end of an injector-locking radar system can partially solve the problem [17].
However, it is not suitable for a rescue application where a target location is required.
Step frequency Continuous Waveform Radar systemsystem
- Detection theory
- Discussion
After passing through an I/Q mixer, the output can be modeled as the product of the received signal with a copy of the transmitted signal. However, the third term represents the frequency shift due to target motion, the DSP processor will trade the frequency step for the Doppler frequency shift due to the velocity caused by the range. The fourth term in the equation accounts for changes in the frequency of each pulse as the targets move, resulting in post-hold frequency spreading, which results in some negative effects, including loss of range resolution, range accuracy, and signal-to-noise ratio.
Previous Approaches 14 The key to distinguish between normal motion and a fall depends on the different changes in speed. In the event of a fall, the speed increases continuously until a sudden stop, while during a normal walk or movement the Doppler signal experiences a controlled movement. The frequency of the signal is proportional to the speed of the person during the movement.
As it implies as mentioned above, the step frequency is able to locate the multi-targets and by careful design it can detect the fall event, the key is depending on the different changes in a speed experienced during a fall or a normal movement. a fall, the speed will continuously increase until an abrupt stop.
Hybrid FMCW-interferometry
- Detection theory
- Discussion
This important feature is achieved in the radar prototype presented here by sharing clocks at the transmission and acquisition stages. The distance between radar and target is assumed to be Rτ, and it will remain constant during one chirp period since Tf is very short compared to the target moving speed. With beat frequency, the location information can be estimated. However, due to the limited bandwidth, FMCW cannot meet the requirement of vital signs (Breathing and heartbeat) monitoring.
Thus, interferometry radar is combined with FMCW to solve vital signs monitoring. The theory of interferometry radar detection is presented in Section 2.21. A hybrid radar integrating FMCW mode and interferometry mode is introduced, FMCW mode is used to resolve target location, interferometry mode is used to resolve small displacement. Through this design, indoor positioning and lifetime detection is achieved using two types of waveform: FMCW and single-tone CW.
Summary
Introduction
Proposed Waveform and Detection theory
- Proposed Approach
- Operation Algorithms
chest wall caused by breathing and heart rate, which can be accurately detected by the CW radar system. RangeR can be written asR0+V ·(n−1)·(TA+TB) in moving target situations, R0 indicates the initial range. If only step A is processed by the processor, A-MFSK within TA can be modeled as a single tone CW with a period of TA and the operating frequency.
As the operating frequency increases from stage to stage, this will only result in greater phase detection sensitivity, meaning that a small shift can cause a significant phase change that can be easily measured. To achieve a relatively longer time to monitor vital signs, the TA is set to 2 ms, so vital signs can be checked every 2 ms. By setting different time periods of step A and step B, MFSK and CW characteristics can be obtained.
CW mode is designed to operate relatively longer compared to MFSK mode to accurately monitor vital signs, and operates 16 times at an interval TB, per TCP I, while MFSK mode operates only once per TCP I for location information. Since TB is too short to have an effect on vital sign monitoring, CW mode can be considered reliable.
Summary and Discussion
On the other hand, when the extracted time reaches TCP I, the MFSK mode is activated, after which both steps A and B are processed to obtain the beat frequency and phase difference. Then (3.3) and (3.4) are used to solve for the range and phase difference. speed information and the range information is ready for the CW mode of the next TCP I.
AMFSK signal generator design
In this design, the ratio constant is set according to the length ratio between stages A and B. First, the clock signal goes into a counter to get the number of pulses, then the pulse count is compared with the ratio constant calculation. The ratio constant is set to limit the output of the clock signal, once the pulse number is above the limit, the output of the comparator will be as a control signal.
Meanwhile, the output will provide feedback via a constant multiple ratio of integers to continuously monitor and compare with the counter's accumulation. Since the 'ctrl' signal keeps two pulses constant at 0 levels, this sign can be used to achieve a. Since the output of two comparators is obtained based on the signal "ctrl", a time delay is required to synchronize the "clk1".
The whole process is repeated until the maximum number "BW" is reached, then the reset circuit will generate a signal to clear the contents of the accumulator and set the output back to the min value.
Simulation Results
The harmonic order is set as 3 because harmonics caused by demodulation method and respiratory motion itself must be taken into account.
Overall System Design
Measurement Results
The time domain I/Q signal shows a different pattern depending on the presence of small displacements. And the frequency spectrum shows different signal strength and breathing frequency, a case of deep breathing produces a higher power on the frequency domain compared to normal breathing. The last graph shows the unwrapped phase caused by displacement, as it turns out that a small displacement causes a large phase difference.
Thus, human breathing can be detected by detecting a small offset, because the human breathing pattern is intermittent, the sudden movement caused by wind or natural force can be ignored. System design and experimental results 34 the possibility of detecting vital signs when a surviving victim needs to be rescued in a fire disaster.
Summary
Although AMFSK's feasibility of indoor positioning and life detection has been proven so far, both respiration and heartbeat are detectable in simulation, but due to complex environment only respiration is practically detectable now, further improved hardware and algorithms need to be developed based on the existing one . The aim of this study is to provide an alternative and better approach for indoor positioning and life tracking, especially such as saving survivors in a fire disaster. With a series of emerging application scenarios, radar technique can serve people through wider aspects, indoor positioning and life tracking are recently widely researched and studied, as it can provide a location of the human in a hidden situation, which is useful for rescue in a emergency situation such as earthquake and fire disaster.
Initially people used ultra wide band radar, because target range detection is not new to radar capability, life detection is crucial in this application. Stepped frequency continuous waveform is proposed for this application, drop event detection is studied with the capability of indoor positioning. With all these merits, MFSK is brought into this study to solve indoor positioning and life tracking problems, with specially designed waveform: asynchronous MFSK and a new tracking algorithm.
This work provides a new and better approach for the challenging task of achieving indoor positioning and life detection, as mentioned in the future works section, more application scenarios can be developed and AMFSK has proven to be a promising technique with an adaptively redesigned signal generator, it can fulfill different monitoring and detection requirements.
