Evolution to Fourth-Generation (4G) Mobile Cellular Communications

During the first decade of the twenty-first century, there was a significant increase in the number of mobile subscribers. The milestone of reaching one billion subscribers was achieved in 2002, but the number grew rapidly, surpassing five billion in 2010. This exponential growth was fueled by the surge in the volume of mobile broadband traffic, which exceeded that of cellular voice traffic for the first time. However, it imposed a challenge for cellular networks that were primarily optimized for voice communications and had to operate both a packet-switched network for data delivery and a circuit-switched network for voice calls since the data services were introduced in the 2.5G systems.