An Overview on Beamforming and its Issues for 60 GHz Wireless Communications Gouri Nayana N. 1 , Student Member, IEEE, Nishesh Tiwari 2 , Student Member, IEEE, T. Rama Rao 3 , Member, IEEE Department of Telecommunication Engineering, SRM University, Kattankulathur-603203, Tamil Nadu, India 1 gaurie_nanda25@yahoo.com, 2 nitizaz@gmail.com, 3 ramaraotr@gmail.com Abstract— In recent days, the unlicensed millimeter (mm) wave spectrum in the 60 GHz band is becoming a promising technology for multi-gigabit wireless communication. Compared to other lower frequency systems, the spectrum around 60 GHz holds several advantages including huge unlicensed bandwidth (upto 7 GHz), compact size of transceiver due to small wavelength (about 5 mm) and less interference owed by high atmospheric absorption. However, there are several challenges associated with this spectrum, such as reflection and scattering losses, high penetration loss and high path loss, which limits the range of coverage at 60 GHz. The 60 GHz links in indoor environment is also susceptible to line of sight (LOS) blockage due to its lack of ability to diffract around various objects. To overcome all these challenges, directional transmission is very vital. Thus, a technique known as beamforming utilizing multi- element antenna arrays is considered important for 60 GHz wireless communication. This paper focuses on providing a general understanding of beamforming and its techniques at 60 GHz and reviews the various issues associated with it. Keywords— Millimeter wave, 60 GHz, Beamforming, Multi- gigabit wireless communication. I. INTRODUCTION Due to expected congestion at lower radio frequencies, the 60 GHz band in the millimeter wave spectrum is becoming an attractive arena for upcoming multi-gigabit wireless communication systems, meeting requirements of most demanding applications. In addition to high data rates that can be achieved in this 60 GHz spectrum, energy propagation in this band has unique properties that provide many benefits such as high security, frequency re-use and excellent interference immunity. The 60 GHz frequency band is highly exploited mainly for the development of future Wireless Local Area Network (WLAN) and Wireless Personal Area Network (WPAN) systems. 60 GHz communication can be used in multiple deployment scenarios such as static-to-static, static-to- handheld and handheld-to-handheld [1]. The WiGig Alliance envisions that 60 GHz technology will be a platform for the existence of the widest ecosystem of interoperable systems, as it need not be adapted for future applications [2]. According to Friis’ transmission equation, operation at 60 GHz causes an additional propagation loss of around 22 dB when compared with the 5 GHz band upon considering the same gains of antennas, same transmitter (TXr) – receiver (RXr) separation and equal transmit powers [3]. Although the high path loss seems to be a disadvantage of 60 GHz, the effective interference levels for 60 GHz are less severe than those systems located in the congested lower radio frequency bands such as 2-2.5 GHz and 5-5.8 GHz, since it confines the 60 GHz operation to a limited area such as an indoor environment [4]. Due to small wavelength (about 5 mm), 60 GHz also favours the use of antenna arrays with large number of elements thus enabling the integration of multiple antennas into portable devices. The principle of diffraction states that beamwidth is inversely proportional to operating frequency. Thus, at 60 GHz, antennas have narrow pencil type beams. For point to point communication, highly focused antennas are required so that the transmitted energy is just directed to the intended receiver. At 60 GHz, the use of highly focused antennas with narrow beamwidth minimizes the possibility of interference thus maximizing performance [5]. Directional transmission is very vital for any deployment scenario involving 60 GHz radios in order to benefit the high bandwidth potential and to cope with the poor link budget confronted in this band due to high path loss and low output power of power amplifiers. Thus, a technique called beamforming is necessary to mitigate the link budget problem, wherein, the signals on various antennas are smartly combined so that transmit and/or receive beams can be formed in the desired directions. In NLOS scenarios, beamforming can be used to electronically steer the transmit-receive beam-patterns towards the strongest reflection available [6]. Beamforming techniques can be utilized for maximizing the Signal to Interference plus Noise Ratio (SINR) at the output of the antenna system. Beamforming can be considered as a spatial filtering technique where, transmission/reception is made possible in certain directions, meanwhile suppressing the transmission/reception to/from unwanted directions. This leads to interference reduction which is highly desirable at 60 GHz [7]. II. CONCEPTS OF BEAMFORMING In beamforming, each transmitter/receiver signal is multiplied with complex weights that adjust the phase and magnitude of the signal to and from each antenna. This causes the output from the array of antennas to form a transmit/receive beam in the desired direction and minimizes the output in other magnitude of the signal to and from each