Hybrid Precoding for Millimeter Wave Systems under Phase Noise problem

I. INTRODUCATION

5G is the next generation of wireless networks. It has faster-lower latency and more flexibility, especially, after observing the amount of wireless voice and data communications which increasing at an exponential pace. Lately, mm Wave wireless systems are the best candidate technology for the next generation cellular communication [1]. To meet the volcanic demands of high-data-rate for the streaming media revolution and the capacity, there are many ways such as massive MIMO in the physical layer, network densification by diffusing small cells [2], and device to device -D2D- communication system [3]. Millimeter wave with frequencies between 30 and 300 GHz considered as the major candidate for overcome the imperfection of wireless frequency spectrum needed to cover a growing number of consumer devices. The characteristics of millimeter wave bands contain the availability of unexploited spectrum and control interference advantage as a result of the line-of-sight (LOS) property. Nevertheless, millimeter wave systems need a huge directional gain with respect to traditional systems to resist their huge path loss obstacle and losses due to oxygen and rain attenuation [4]. Large-sized phased-array antennas are introduced by millimeter wave system as a result of small wavelength which able to offer large beamforming gains to avoid path loss problem [3], [5], [6]. Precoding in simple words known as multiple data streams with beamforming, or we can say that precoding is the superposition of multiple beams for spatial multiplexing of several data streams. Beamforming and precoding are carried out digitally at baseband through digital precoders which can modify the phase and magnitude of the signals in traditional multi-antenna systems. Due to the huge price and power exhaustion of RF chains in mmWave systems (the huge price of mixed signal Components), and unluckily, the performance of analog strategies are suboptimal because of the limitations of analog beamforming hardware such as the difficulty of controlling signal amplitude and the potentially low-resolution signal phase control [7]. Wherefore, a structure of hybrid precoding has recently more attractive with a small number of RF chains, thanks to its ability to obtain high data rates with low energy consumption hardware.

RF chain is a cascade of electronic components, which including analog-to-digital converters (ADCs) and frequency mixer. It is nonlinear electrical circuit that designed to sum and difference frequency at a single output port from two signals applied to its input. One of this two input ports is usually the local oscillator (LO) device, it is one of the main components of radio frequency system, which in charge of the (up/down) conversion of a particular channel. In detail, it has the most important role on modulation and demodulation processes [8]. With reference to the mapping from RF chains to antennas, the hybrid precoding transceiver architectures can be categorized into the partially and fully connected structures. Talking about the constraints of transmitted signal, in fact there are many of factors that corrupt this transmitted signal such as phase noise and amplitude noise of the local oscillator, thermal noise, nonlinear behavior of active components and multipath effects.

In this article, we will discuss the effect of phase noise problem on hybrid precoding algorithms based on the principle of alternating minimization (AltMin), which near to the performance of the optimal fully digital precoder. As mentioned in [5], decreasing the Euclidean distance between hybrid precoder and the fully digital precoder can apparently achieve maximum the spectral efficiency of mmWave system, which makes a hybrid precoder design as a problem with respect to unit modulus constraints. However, there are no studies that cover the issue of hybrid precoding in millimeter wave systems under phase noise problem.

The main concern of the paper is to study the effect of phase noise issue on the hybrid design precoder in millimetre wave MIMO systems, which can create performance degradation for the whole system [9]. By adopting alternating minimization and phase extraction alternating minimization algorithms as the main design rule, the precoder design problem is divided into sub-problems by optimizing the analog precoder and the digital precoder with respect to phase noise problem.

The rest of the paper is tidied as followings. In Section II, the system model under phase noise model is introduced. Also, the problem formulation related to phase noise with phase locked loop is provided. In Section III, the precoding techniques for the proposed system with fully-connected structure are explained. The results are clarify at Section IV. Finally, the conclusion is provided in Section V.