A High Efficient Code for Visible Light Positioning System Based on Image Sensor

A light-emitting diode (LED) can be modulated in visible light positioning systems so that it acts as a transmitter with a unique ID. However, we must be able to support unique IDs for many different LEDs, and LEDs sometimes also need to transmit other information. Therefore, it is necessary to increase the length of an LED ID. However, long codes are prone to contain excessive continuous strings of 0s or 1s, which is not conductive to correct ID identification. The Manchester code is usually used to eliminate this phenomenon, but its encoding efficiency is low. Furthermore, the Manchester code has no error-correction function. In this paper, we present a new method for encoding a long LED ID. We apply an exclusive OR (XOR) operation to the code using an appropriate mask so that no long continuous strings of 0s or 1s appear in the XOR result. Then the LED transmits the XOR result and the mask serial number. The ID of the LED is obtained by decoding. Compared with the Manchester code, the mask XOR code approach is more efficient. When a 34-bit ID is divided into two blocks, the encoding efficiency of the mask XOR code is 33% higher than that of the Manchester code. Compared with the Manchester code, when the information transmitted by an LED is encoded with the same ID length, the mask XOR code can additionally incorporate an error correction function to reduce the bit error rate. Adding an artificial baffle to the above methods results in a 5% error rate in the Manchester code, but the mask XOR code has no code errors.