P19251: Local Positioning System
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Systems Design

Table of Contents

Team Vision for System-Level Design Phase

In this phase, we brainstormed ideas on how to meet all customer and engineering reqirements. Taking all our ideas into considerations, we narrowed down to two ideas that will accomplish our task. This phase allowed us to start doing research and development on the various technologies needed and understand implementations of each. Although our two selections are very different, they have their weaknesses and strengths that both make them viable candidates. At the end of this phase, we ultimately want to choose one of these selections and proceed into diving down and designing an acutal solution.

Functional Decomposition

Functional Decomposition

Functional Decomposition

Benchmarking

There are several options on the market currently and we chose to compare the two popular ones found. One is Pozyx and the other is a Indoor Navigation Position System by RobotShop. These two system fundamentally work differently. Pozyx works on ultra wide-band (UWB) frequencies and the one from Robotshop uses Ultrasonic. The details of the differences are below.

Benchmarking

Benchmarking

Morphological Chart

Taking the existing systems out there and our engineering reqirements, each system was broken down into mutliple attributes. For each attribute, mutiple solutions were generated. Several of these were taken to narrow down to two concepts.

Morphological Chart

Morphological Chart

Concept Development

Ultrasonic Time-of-Flight Distancing

The Ultrasonic concept works by transmitting ultrasonic waves (air pressure differences) and having a receiver pick them up. Ultrasonic waves travel at the speed of sound (343 m/s) which, being slower than EM waves, allows for greater error detection (time between bounced signals is greater than EM). Ultrasonic waves bounce off of physical objects which allow for complex algorithms to determine the layout of a room, however this also means two nodes separated by a wall will never be able to talk to each other.

EM Time-of-Flight Distancing

The EM concept works by transmitting electro-magnetic waves at a certain frequency and having a receiver pick them up. These waves travel at the speed of light (~3x10^8 m/s) which allows for very high bandwidth signaling. This means that a complete system would be able to refresh much faster as the delay between transmitted signals could be much lower than with Ultrasonic. Unlike Ultrasonic waves, EM waves go through or get absorbed by physical objects. This means that if there is a wall between two nodes, they may be able to communicate with each other ( If the wall is not made out of metal) however the received signal would be picked up at a relatively much later time which would skew distance calculations without an external reference.

Concept Feasibility

Ultrasonic Time-of-Flight Distancing

The Ultrasonic concept is feasible when dealing with low to medium speed/distance applications and where direct line of sight is available (although advanced algorithms can work with bounced signals). Because ultrasonic waves bounce off obstacles, any obstruction between nodes will cause direct signal loss, however this can be used advantageously. While the distance between nodes may not be accessible, the distance from the transmitter to the obstacle can be found which could be useful. In addition, with an advanced enough algorithm, any bounced waves can be picked up by a multitude of receivers and be processed to estimate node distances. Ultimately, Ultrasonic time-of-flight, in our current project scope, is somewhat feasible as the primary objective is node-to-node distancing and not environmental mapping which is mainly what ultrasonic is used for.

EM Time-of-Flight Distancing

The EM concept is feasible for low/long range applications with no large metallic/electric obstructions. Metallic objects absorb EM waves which would either distort or completely get rid of the transmission. EM waves can go through other materials however which is useful when dealing with nodes in multiple obstructed areas. Because these EM waves propagate in a spherical pattern, the orientation of the transmitter is not important. In the current project scope, which is node-to-node distancing, EM time-of-flight, is more feasible than ultrasonic as it can propagate through materials. Even though Metal obstructs the transmission, it is better than Ultrasonic which cannot penetrate any material.

Feasability Tests

Feasability Tests were done to visually see the difference between the two concepts and specifically the driving technology. Understanding the technology will help us ensure our final product will meet all criteria. A pugh chart helped us choose which concept was the better one.

Pugh Chart

A comparison between the two concepts were done showing the Ultrasonic Time-of-Flight and EM Time-of-Flight.

Pugh Chart

Pugh Chart

This shows that the EM option fits our crieteria given by our customer the best.

Hardware Concepts

These two concepts were developed with no restraints. These are only for design and will be taken and improved when further mechanical constraints are set. There are thermal and electrical characteristics that need to be defined. This will only be done after a concept selected as each concept has its own characteristics.
Concept 1

Concept 1

Concept 2

Concept 2

Designs and Flowcharts

The high level systems design shown below describes the two design paths that the team can choose to develop a product solution to the problem statement. The first path involves the use of electromagnetic wave propagation and timing through the modulated signal in order to determine distance between nodes. The second design is a similar peer to peer node architecture, however the mechanism of distance calculation changes to ultrasonic wave propagation.
High Level System Design

High Level System Design

The following hardware flowchart describes the high level flow of how the hardware will behave when probed by the embedded system.
Hardware Flowchart

Hardware Flowchart

Note that once an interrupt to probe the hardware is set, the microcontroller will send the proper communication to the controller of the wave propagation mechanism on the device to initiate wave propagation. The controller is implemented onto the expansion board which contains the electromagnetic wave propagation SoC.
Software Flowchart

Software Flowchart

The software flowchart describes in a high level how the boot sequence for the system will behave. In order to continue a safe, stable network, each set of devices on startup will need to manage who/what is the established network. The flow described will handle this case, and consequently the case where the master or Wifi host node is removed from the network (i.e. network no longer has gateway).
Ultrasonic Data Scheme

Ultrasonic Data Scheme

For the Ultrasonic Concept, we needed to visualize how data communication would happen. This data scheme outlines information traveling over the WiFi aswell as the Ultrasonic Sound frequencies. Because information traveling over the wireless netowrk is instantaneous, we use this to our advantage. Each blue box shows information over the wireless network and it allows for handshakes between all nodes. The orange boxes show information through the Ultrasonic network. By timing exactly when the each node hears the information over the ultrasound network, one can find the distance. This should all be done by the server/orchestrator node.
Network Topology

Network Topology

The network topology will implement a client server architecture. In short, the master node will also be the gateway node, i.e. 10.0.0.1, which will deliver static IP addresses to all other nodes in the network. All nodes under the 10.0.0.x subnet mask will be able to communicate to other nodes through the gateway. More specifically, the client nodes will send information to the master nodes when requested by ICMP messaging system. The master node will send information via the gateway, and deliver distance probing to each node on the network. In the case that the node is blocked by a physical structure, where WiFi would not be capable of being received by the master node, the client node will be able to connect to surrounding nodes on the network via an ad-hoc mode. In terms of communication, the physical structure should have no impact on the WiFi portion of this system. In terms of distancing, however, physical structures would have an impact on determining position of that node.

Next Steps

Anmol

Dean

Mena

Mike

Jai


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