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A Prototype Optical Tracking System Investigation and Development - page 87 / 170

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Chapter 6

Communications

This chapter describes communications between the Black Spot modules and the Soft Hub. This is a key element in the system as it delivers the data that the pose estimation algorithm requires to the Soft Hub. The need for timely delivery of this data places requirements on the communications system and these are described below.

The system comprises two layers and these are a physical layer and a transport layer. The physical layer consists of the physical connections between the camera modules, i.e., the physical bus and the bus transceivers. The physical layer must allow multiple camera modules to be connected concurrently; it must have sufficient bandwidth to allow the nec- essary data to be delivered to the Soft Hub as well as command packets to be delivered to the camera modules from the Soft Hub.

The transport layer comprises a protocol that both the Soft Hub and camera modules use. This is necessary as it defines the order of the interactions between the Soft Hub and camera modules (the protocol logic) and the format of the data (the data format). The protocol is

broken into two parts: the data format and the control logic.

The data format must be compact to allow sufficient messages to be transferred each image frame. The communications link must have low latency and this is determined by the protocol and the bandwidth of the physical layer. Latency is used here to describe the time between data becoming available for transmission and it being available to the receiving party or parties.

The communications system must also be reliable to ensure that data sent by the camera modules arrives at the Soft Hub without errors. This can be achieved by error correcting codes in the protocol or by using a reliable communication medium. In this system the

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