Over-the-air performance of spectrally-efficient CDMA signature sets

Military communications face increasingly congested environments requiring spectrally efficient approaches capable of contending with many users and interference. We evaluate the over-the-air performance of recently designed minimum total squared correlation (MinTSC) signature sets compared to maximal length pseudorandom binary spreading sequences (m/PN) under a variety of interference conditions. Pre-calculated MinTSC and PN databases feed into a direct sequence Code division multiple access (DS-CDMA) framework capable of emulating a synchronous multi-user scenario. The framework is constructed in GNU radio and implemented on USRP N210 software-defined radios (SDRs). Packet error rate of a data transfer was measured under varying interference conditions. Signature length, interference profile type and interferer power were varied for both MinTSC and PN signature sets. We address transceiver design and implementation challenges including a two-step acquisition and tracking approach to address the difficulties of preamble synchronization. Under single tone (impulse) interference at the center frequency, MinTSC signature sets experience packet errors primarily on the first signature whereas all PN signatures see errors. Under wide-band interference, individual MinTSC signatures perform more uniformly compared to PN. Understanding of this behavior under varying interference provides the warfighter with greater flexibility to adapt to new conditions and can drive assignment of priority data to specific signatures.