One aspect of the design of IMT-Advanced systems that has not received sufficient attention so far is the emergence of high data-rate local services. Such local services can provide the high data rates needed to consume rich multimedia services through mobile computers such as tablets, laptops, netbooks and smart phones.
As an example, one may consider the case where a media server is put up at a music concert from which visitors can download promotional material using a Device-to-Device (D2D) connection. Currently, only Wireless Local Area Network (WLAN) or Bluetooth operating on a license-exempt band could be used to setup a direct connection to the media server. On the other hand, only a licensed band can guarantee a controlled interference environment, which increases the reliability of the data transfers. Hence local service providers might prefer to pay a small amount of money to gain access to licensed spectrum when the license-exempt bands become crowded. Cellular operators may offer such cheap access to spectrum with controlled interference enabled by D2D communication as underlay to the cellular network. The licensed spectrum may be used as the only resource for communication or it may be complemented by license-exempt spectrum.
Figure 9.1 illustrates a D2D network underlaying a cellular network. The communication is facilitated by a cellular Base Station (BS), ...