To achieve higher data rates, migration to higher RF bands will likely occur. This increases path and circuit loss dramatically. Thus smart, adaptive arrays will be necessary. In addition there may also be wireless and optical fiber entrance links from the micro or picocells to the base station. Considerable emphasis is being given to adaptive arrays to provide high gain to cut down the path loss, reduce interference, and minimize multipath.
Research requires better tracking algorithms, compact designs, and lower cost.
One approach being studied to reduce size and costs of microcells is to use optical RF signals so that all the complex tasks are taken back to the main base station. A principal additional attraction of that method is air-interface independence since the active RF signal is passed to the main base station without digital processing. The same principle may be applied using a millimeter wave wireless access link for quick, inexpensive deployment. Finally, software radios would allow greater flexibility, but research is needed on high speed, low power DSPs and tunable, inexpensive RF circuits. A second demonstration showed a two-way mobile video system with 2 Mbps forward video and 384 kbps reverse link.