Enhancement of Data Rate and Packet Size in Image Sensor Communications by Employing Constant Power 4-PAM

Image sensor communications (ISC) is a scheme to make the LED lamp replace access points or beacons in indoor environments. Its application has been limited, however, due to its low data rate and small packet size. To resolve these problems, we propose a new ISC scheme using 4-PAM modulation and a parallel packet structure. The constant power 4-PAM signal was designed to have constant optical power in each symbol to eliminate the flickering effect. The experiments show that a data rate more than 2.6 times higher than the existing on-off keying schemes was achieved. In addition, it is demonstrated that the packet length can reach more than several frames while it is limited to less than a frame using the existing schemes. The limiting factors of N-PAM levels and packet size are analyzed in this paper to further improvement. All these results are demonstrated through simulations and experiments.