Interference free multiuser modulation for mmWave radio links.

Radiocommunications in the mmWave band present strong free-space attenuation, which requires power maximization at the receiver. A code division multiple access (CDMA) modulation system increases the receiver's ability to detect the transmitted signal by means of spectrum spreading. The main benefit of direct sequence spread spectrum for mmWaves is the increase in coverage due to the process gain. The main drawback of its use in high-speed communications is bandwidth reduction. Fortunately, this can be compensated for by the huge bandwidth available at mmWave frequencies. However, most of the codes available for CDMA have mutual interference. The zero correlation zone (ZCZ) codes are orthogonal to each other, but only under the condition that no multipath far echoes are received. This condition is fulfilled in mmWave radio communications, owing to strong propagation attenuation and also because of the beamforming that radio links usually do at this frequency. In this study, a field experiment is carried out consisting of data reception at 28 GHz from many different users who are simultaneously transmitting using CDMA on BPSK modulation and then comparing the performance of conventional maximal pseudorandom (PR) codes versus ZCZ codes. It is verified that the latter are received with the same process gain but no mutual interference, approximately resulting in a 12 dB improvement on the modulation error ratio (MER). [ABSTRACT FROM AUTHOR]