## 3 Experimental Results
### Data Transmission Performance  
In our demonstration, the LED display is controlled to display the pattern of the parking sign and broadcast the packets. One packet consists of an 8-bit start frame delimiter (SFD) and a character string \"FULL PARKING\" as the content of the hidden data, as shown in Figure 5. After ASCII encoding, the total length of the data frame is 104 bits. Then, the original information bit is repeatedly encoded by alternate bit-flipping five times according to the ABRC coding scheme, and thus, the final length of the encoded data frame is 520 symbols. The encoded data frame was repeatedly sent 100 times and compared with the received data of the smartphone's APP to measure the BER of the transmission. The BER was used to evaluate the channel capacity, and therefore, we did not utilize any error correction coding in the data transmission experiments. As shown in Figure 6, the BER performance and the data transmission rate with the data transmission distance are evaluated. The black dashed line shows the 7% FEC limit which corresponds to a BER of \(3.8\times 10^{-3}\). When the data transmission distance between the LED display and the smartphone's CMOS camera is increased from 10 cm to 700 cm, the measured BER reaches 0.5, which means that the channel capacity reaches 0. As a result, the experimental proposed LED-DCC system can reach a maximum transmission distance of 700 cm, at which the usable capacity is close to 0, demonstrating the superiority of the proposed long-distance LED-DCC system over the existing LED-DCC systems in terms of data transmission distance. Furthermore, when the data transmission distance is within 175 cm, the proposed system can still achieve successful data transmission under a BER of less than \(3.8\times 10^{-3}\) and a data transmission rate of up to 30 bps, meaning that the proposed system is robust within 175 cm. Note that in this experiment, a clustered \(2\times 2\) LED-DCC point is used as a data transmission channel. An LED display can be viewed as a multi-parallel array of emitters with a high pixel count; thus, it is possible to achieve high data rates of several Mbit/s, despite being limited by the low capture frame rate of CMOS cameras. To verify the effect of the proposed LED-DCC point clustering scheme and the lightweight, back-forth, fast image processing algorithm, the data transmission distance of  
Figure 5: The structure of the packet. Figure 6: The data transmission performance of the proposed LED-DCC system. the proposed system is compared with that of the previous LED-DCC system [14] and a 2 \(\times\) 2 point clustered LED-DCC system, i.e., the previous LED-DCC system using 2 \(\times\) 2 clustered LED-DCC points. The experimental results are shown in Figure 7.  
As shown in Figure 7, the BER increases dramatically with the increment of the data transmission distance. When the BER of the LED-DCC system is higher than 3.8 \(\times\) 10\({}^{-3}\), it may not ensure successful data transmission. The previous LED-DCC system can achieve a maximum transmission distance of 15 cm, whereas that of the 2 \(\times\) 2 point clustered LED-DCC system is 40 cm, which is about 3 times that of the previous LED-DCC system under the BER less than 3.8 \(\times\) 10\({}^{-3}\). This is attributed to the LED-DCC point clustering scheme since it improves the power of transmitted VLC signals by enlarging the light-emitting area in the LED-DCC system. Furthermore, due to the proposed lightweight, back-forth, fast image processing algorithm, which enables high-precision LED light-emitting area detection and, therefore, increases the signal detection on the receiver's side, the proposed LED-DCC system can achieve a maximum distance of 175 cm under the 7% FEC limit, which is about 4 times that of the 2 \(\times\) 2 point clustered LED-DCC system. Therefore, the proposed LED-DCC system has a longer data transmission distance and higher data transmission rate.