Dynamic Spectrum Access Techniques: TPC-resilient Initial Access in Open Spectrum Bands

Fast frequency channel saturation is one of big challenges in open spectrum bands. System designers may easily come up with TPC (transmission power control) applied to the down-streams of a network, to increase the cell reuse factor, but this scheme alone is likely to encounter initial access issues where beacons are not either receivable or decodable inside the network´s maximum transmission range. Such problems can be handled in two major approaches: first, relaying beacons in a distributed manner to statistically sweep out hidden areas; and second, explicit demand of beacons from a connecting device. The latter is called active scan (or sending probes) and can guarantee successful connections to the network if, and only if, appropriate mechanisms are provided to avoid interference to neighboring networks. In that context, we will explore a wide span of DSA (dynamic spectrum access) techniques and introduce a system, called DPA (discrete probe access)-OFDMA, where probe frames are transmitted with orthogonality maintained in the power and code domain. A group of cognitive techniques to boost the efficiency of active scans will be presented too.