Hybrid Beamforming for 5g and Cognitive Radios

Abstract

The pathloss experienced by the proposed mmwave for the 5G spectrum, is much more than the microwave signals currently used in most wireless systems. The decrease in wavelength of the mmWave, makes possible the use of large scale antenna arrays (LSA). The beamforming gain provided by these arrays helps us to overcome pathloss. Beamforming with multiple data streams is known as precoding and increases the spectral efficiency. Beamforming and precoding in 4G are done digitally at baseband for multi-antenna systems. The high cost and power consumption of digital precoding in mmWave LSA systems, however, make analog processing in the analog domain more cost efficient. The RF chain structure provides a hardware limitation to purely digital precoders. The hybrid beamforming architecture provides a solution to utilize the sparse structure of the mmWave channel and to leverage the beamforming potential of the large antenna arrays. The well-known algorithm of Orthogonal Basis Pursuit is used to approximate optimal unconstrained precoders and combiners. Cognitive radios attempt to share spectra by introducing a spectrum sensing function, so that they are able to transmit in unused portions at a given time, place and frequency. In this paper we propose an underlay cognitive transceiver design that enable the mmWave spectrum access while negating the interference of the Primary User. As such the results of applying the Hybrid beamforming architecture is shown comparatively for the presence and absence of the Primary User.