User's Manual

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3.3. PLANNING THE PRODUCT AND CREATING THE DESIGN
To plan the product and create the design, perform the following steps:
• Develop a usage model
• Develop a message model
• Define a service strategy
• Define remote diagnostic functionality
• Investigate and obtain regulatory approval
3.3.1. Developing a Usage Model
The usage model answers the question, “How will the end product be used - will it be portable or mobile, how many hours a day
will it be used, how many days a week?” and so on.
Perhaps the most important factor for success is a clear understanding and decision regarding how the final product is to be used.
This guides the development process, since all design considerations drive toward meeting the needs of the end user. For example,
design issues related to a mobile device, such as alternator noise and vibration, are completely different from considerations
required for a fixed-point telemetry application powered by a solar panel. Defining what is and is not important to the end user
helps to make the critical engineering trade-off decisions that are inevitable in every product design.
As the integrator, it is your responsibility to develop the usage model. Motorola is available to provide assistance and answer
questions, but is not directly involved in this phase of the project.
3.3.2. Developing a Message Model
The message model defines the number of messages that are sent and received and their frequency. To create the message model,
determine the quantity and frequency of data sent in each of the uplink (terminal to network) and downlink (network to terminal)
directions.
Answer the question, “Is there a requirement for the terminal to be powered on and ready to receive eight hours a day, or does the
user turn the unit on only when making a query to the host system?” The answer has a direct bearing on the battery size and
capacity requirement for powering the device. The amount of data sent and received is relevant in calculating the cost of airtime
and deciding which type of network connection to use. In short, the message model is essential for making many engineering
design decisions, especially in calculating values such as sleep time versus wake time and in determining battery capacity
requirements.
You are responsible for developing the message model. The typical approach to creating the model is to define the peak and average
network throughput requirements based on input from the user. Motorola can provide current consumption figures for each of the
various modes of operation, for example, receive and transmit.
The network throughput of the host device depends on various factors, in addition to the raw throughput of the radio channel. For
example, in addition to the overhead involved in forward error correction and support for packet headers, the number of active
users on the network can directly affect network throughput.