Evolution towards mobile broadband communications
Explosive growth of wireless communications services and products in the past three decades or so has fundamentally changed the way by which the majority of the world's population exchange, distribute and access information. As a strong driver of the growth, cellular telephony has so far been the most successful application of wireless communications. All forms of wireless communications utilize the radio spectrum, a scarce natural resource. Spectrum access is a general term of the technologies by which users utilize the radio spectrum. Cellular telephony uses a cellular concept, which provides an effective spectrum access solution to improve the efficiency of radio spectrum utilization.
In a cellular system, many base stations are deployed to cover a large service area. The service area is divided into a number of cells, each served by a base station, as shown in Figure 1.1. When a user makes a call, it is connected to the base station with the best RF propagation. The base stations are connected to the operator's core networks via backhaul connections such as T1 or fiber optics. Spectrum is reused among the cells. This is possible because a signal decays fast as it travels through the wireless channel. If a signal utilizing some spectrum in a cell is sufficiently attenuated in another cell, then the same spectrum can be reused.