EchoStream systems can integrate a number of end-devices, including smoke alarms, alarm pendants, door and window alarms, glass break alarms, temperature measurement devices, as well as two-way end-devices, and RF modules that can be incorporated into almost any existing product.
The first question that must be answered when designing your EchoStream system is: what types of end-devices are necessary to meet your needs? The answer to this question and to the next, what kind of network communication you will use, will determine the type of RF gateway you require.
The EchoStream Commercial Mesh Network includes two kind of messaging: broadcast messaging and directed messaging.
A network using broadcast messaging is easy to set up. The repeaters are operational out of the box, without configuration. The RF gateway is typically a receive-only device, such as a serial receiver or add-on receiver.
A network using broadcast messaging is adequate for any relatively small network, including a dozen or so repeaters and around one hundred end-devices. Broadcast messaging serves the needs of the vast majority of Inovonics customers perfectly well.
Using broadcast messaging, end-devices broadcast multiple, redundant rounds for each message, which are then echoed by repeaters, extending the range in all directions. No delivery confirmation is received by the end-device or by the repeater. A network that uses broadcast messaging will only include one-way end-devices.
In a broadcast network, every repeater begins transmitting immediately after it receives a message, and transmits multiple rounds of each message. It is this message redundancy that provides the high probability that every message will be received by the serial receiver.
Potentially all repeaters in the network can end up repeating the same message, including repeaters further away from the RF gateway than the end-device, and repeaters on the other side of the RF gateway.
Directed messaging uses a combination of smart routing and message management to reduce RF traffic and allow larger wireless networks. Due to the two-way requirements of directed messaging, a network coordinator must be used as the RF gateway. Directed messaging is more suitable for large systems with lots of end-devices and repeaters. Directed messaging is also a requirement for networks that employ two-way end-devices. Directed messaging is usually not necessary for small, lightly loaded systems containing only a dozen or fewer repeaters and one hundred or fewer one-way end-devices.
In a network using directed messaging, repeaters use a scheme of message management and acknowledgement to provide a highly reliable network with fewer transmissions per message. This address field contains the unique identification number (UID) of the target device. This UID is used to deliver directed messages. When the target device receives a message addressed specifically to it, it returns a short acknowledgement message to the sending device. After receiving the acknowledgement, the sending device returns to normal operation, and the target device becomes responsible for the message. Other two-way devices that are in range of the directed message, but are not the target of the message, may still receive the message, but when the target address is decoded and found to contain an address different from its own, the device returns to normal operation.
A broadcast outbound message is always available for sending messages in a two-way system, whether it is using broadcast or directed messaging.
Broadcast outbound messaging can be useful for sending messages to a mobile two-way end-device, for instance. When a broadcast outbound message is sent, every repeater in the network will retransmit the message.
There are two types of RF gateway: the network coordinator and the serial receiver. The network coordinator is used for a two-way system and directed messaging; the serial receiver is a used for a one-way system and broadcast messaging.
The network coordinator is a two-way RF gateway that coordinates signals between end-devices, high-power repeaters, and your application controller. The network coordinator is necessary to establish a two-way RF system as well as directed messaging. Only one network coordinator can be used at a site.
The serial receiver is a RF gateway that decodes signals from end-devices and high-power repeaters, and outputs the data to your application controller in a common serial data format. The serial receiver is used when the system includes only one-way end-devices and high-power repeaters. The serial receiver does not support two-way end-devices or directed messaging.
The number of end-devices, high-power repeaters and the frequency of data transmission determine the number of RF messages the RF gateway must process. The result is known as system load. Because the interplay of these variables is extremely complex and subject to unique site conditions, it is recommended that system designers contact Inovonics Wireless technical support to determine the maximum number of end-devices possible for your system. Doing this will help to avoid overload, a condition resulting when an RF gateway gets bombarded with more messages than it can reliably process, increasing the possibility of missing critical data or alarm messages.
The EchoStream survey kit is a portable survey system used to determine the optimal location for the RF gateway, high-power repeaters and end-devices. The survey kit contains the equipment needed to measure RF signal strength, signal margin and message type, providing an indication of the propagation of radio signals in your environment. This kit is strongly recommended to assist you in designing configurations of RF gateways, high-power repeaters and end-devices.
Contact Inovonics technical services for information on how to survey sites using the Inovonics site survey kit.
Results from the site survey may indicate you need to install high-power repeaters to ensure delivery of all messages between end-devices and the RF gateway. The Inovonics survey kit will provide information to assist you in the placement of high-power repeaters. The network of high-power repeaters that relay and rebroadcast messages is called the high-power repeater backbone. The backbone permits systems to cover large areas and circumvent obstacles. A well-designed backbone provides multiple independent transmission paths between all end-devices and the RF gateway.
Because of the nature of RF transmissions, redundancy should be built into the system design to avoid bottle necking. Bottle necking occurs in large high-power repeater backbones when the RF gateway is placed at a distance from the last high-power repeater in the backbone, meaning all signals must pass through a single high-power repeater to reach the RF gateway. Failure of the bottleneck high-power repeater defeats all other system redundancies, and breaks the backbone linkage to the RF gateway. This condition is resolved by adding high-power repeaters to guarantee multiple transmission paths for every signal.
The primary function of a RF gateway is to listen to RF signals and to decode messages from Inovonics end-devices. Then, once the message is successfully decoded, the RF gateway sends the message to your application controller, through the serial port.
Messages can be output from the RF gateway’s serial port at a rate of about 1 millisecond per byte (9600 baud). RF gateways do not buffer messages. Your application controller must be capable of receiving and buffering a virtually continuous stream of message from the RF gateway.
In a two-way system, the RF gateway is also responsible for packaging messages from your application controller and transmitting them via RF to end-devices.
Application Controller Primary Functions
In addition to receiving and buffering messages, your application controller is responsible for processing incoming end-device messages, and registering end-devices and high-power repeaters. Message processing includes handling redundant messages, monitoring end-device and high-power repeater status, calculating data and interfacing with the RF gateway.
In two-way systems, your application controller is also responsible for sending messages to end-devices and high-power repeaters.
When designing your application controller for your EchoStream system you want to consider the following factors to ensure your design is robust, always able to accept and buffer messages, and can perform the processing necessary to support your application effectively.
Each Inovonics end-device and high-power repeater is assigned a unique ID in the factory. This unique ID is included in each message originating from the device. Most applications include a method of associating each device’s unique ID with a description, such as the device’s location, or the type of device it is. The process of registering end-devices and high-power repeaters is the responsibility of your application controller.
End-Device, High-Power Repeater, and RF Gateway Status Monitoring
Most end-device, high-power repeater, and RF gateway messages include two bytes containing information about the status of the device. For example, when the end-device battery capacity drops to a prescribed threshold, the end-device sets a low battery flag in the status byte, sending a low battery warning. Your application controller then needs to notify the user of the device ID and low battery status so that appropriate action can be taken. Your application controller is responsible for decoding device status bytes, and acting on pertinent information.
End devices and repeaters send supervision messages at specified intervals to the RF gateway, and your application controller should notify the user to check on any device which doesn’t report in a timely manner.
In a one-way system, your application controller should also monitor the serial receiver’s messages. In a two-way system, your application controller and network coordinator should monitor each other. If the network coordinator fails to hear from your application controller within the defined window, a message can be sent to all two-way end-devices.
Redundant Message Handling
When most end-devices send data the message is transmitted multiple times on different frequencies to increase the probability the RF gateway hears the message. This transmission technique is a critical factor in the reliability and integrity of EchoStream systems. However, it also creates redundant messages at the RF gateway end of the system.
The RF gateway eliminates most of the redundant messages by comparing the current message to the last message. In busy systems your application controller may still receive redundant messages due to the sequence in which the RF gateway processes the messages; for example, if a redundant message from one end-device is interleaved with other messages. For this reason, your application controller must be able to handle redundant messages. A simplified means of handling them can be implemented by having the software compare each incoming message with a list of recently received messages. The list need only store enough messages to catch interleaved redundancies.
Monitoring Repeaters Not In Your Network
When using directed network messaging, it is a good idea to have your application controller log any messages that might be received from repeaters that are not in your system. That way, competing networks can be detected, and any resulting RF load can be determined.
After receiving and decoding messages from the end-device, your application controller is responsible for processing the data. Some processing options include presenting the information on the screen to the user, storing the data in a database, etc. The requirements of your unique application will determine the exact processing required by your application controller.