An Overview of Multigigabit Wireless through Millimeter Wave Technology: Potentials and Technical Challenges

Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2007, Article ID 78907, 10 pages doi:10.1155/2007/78907 Research Article An Overview of Multigigabit Wireless through Millimeter Wave Technology: Potentials and Technical Challenges Su Khiong Yong1 and Chia-Chin Chong2 1 Communication and Wireless Connectivity Labarotory, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, South Korea 2 NTT DoCoMo USA Labs, 3240 Hillview Avenue, Palo Alto, CA 94304, USA Received 14 June 2006; Revised 11 September 2006; Accepted 14 September 2006 Recommended by Peter F. M. Smulders This paper presents an overview of 60 GHz technology and its potentials to provide next generation multigigabit wireless communications systems. We begin by reviewing the state-of-art of the 60 GHz radio. Then, the current status of worldwide regulatory efforts and standardization activities for 60 GHz band is summarized. As a result of the worldwide unlicensed 60 GHz band allocation, a number of key applications can be identified using millimeter-wave technology. Despite of its huge potentials to achieve multigigabit wireless communications, 60 GHz radio presents a series of technical challenges that needs to be resolved before its full deployment. Specifically, we will focus on the link budget analysis from the 60 GHz radio propagation standpoint and highlight the roles of antennas in establishing a reliable 60 GHz radio. Copyright © 2007 S. K. Yong and C.-C. Chong. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. INTRODUCTION Despite millimeter wave (mmWave) technology has been known for many decades, the mmWave systems have mainly been deployed for military applications. With the advances of process technologies and low-cost integration solutions, mmWave technology has started to gain a great deal of momentum from academia, industry, and standardization body. In a very broad term, mmWave can be classified as electromagnetic spectrum that spans between 30 GHz to 300 GHz, which corresponds to wavelengths from 10 mm to 1 mm [1]. In this paper, however, we will focus specifically on 60 GHz radio (unless otherwise specified, the terms 60 GHz and mmWave can be used interchangeably), which has emerged as one of the most promising candidates for multigigabit wireless indoor communication systems [2]. 60 GHz technology offers various advantages over current or existing communications systems [3]. One of the deciding factors that makes 60 GHz technology gaining significant interest recently is due to the huge unlicensed bandwidth (up to 7 GHz) available worldwide. While this is comparable to the unlicensed bandwidth allocated for ultra wideband (UWB) purposes [4], 60 GHz bandwidth is continuous and less restricted in terms of power limits. This is due to the fact that UWB system is an overlay system and thus subject to very strict and different regulations [5]. The large bandwidth at 60 GHz band is one of the largest unlicensed bandwidths being allocated in history. This huge bandwidth represents high potentials in terms of capacity and flexibility that makes 60 GHz technology particularly attractive for gigabit wireless applications. Furthermore, 60 GHz regulation allows much higher transmit power compared to other existing wireless local area networks (WLANs) and wireless personal area networks (WPANs) systems. The higher transmit power is necessary to overcome the higher path loss at 60 GHz. While the high path loss seems to be disadvantage at 60 GHz, it however confines the 60 GHz operation to within a room in an indoor environment. Hence, the effective interference levels for 60 GHz are less severe than those systems located in the congested 2–2.5 GHz and 5–5.8 GHz regions. In addition, higher frequency reuse can also be achieved per indoor environment thus allowing a very high throughput network. The compact size of the 60 GHz radio also permits multiple antennas solutions at the user terminal that are otherwise difficult, if not impossible, at lower frequencies. Comparing to 5 GHz system, the form factor of mmWave systems is approximately 140 times smaller and can be conveniently integrated into consumer electronic products. 2 EURASIP Journal on Wireless Communications and Networking 2.1. 802 4a 15. Home RF 1a 802.1 10 1b 802.1 Disatnce (m) 100 802 .11 n UW Bluetooth 802 .15 .3c B 1 1M 10M 100M 1G 10G Data rate (bps) Figure 1: Data rates and range requirements for WLAN and WPAN standards and applications. Millimeter wave technology, that is, IEEE 802.15.3c is aiming for very high data rates. Despite the various advantages offered, mmWave based communications suffer a number of critical problems that must be resolved. Figure 1 shows the data rates and range requirements for number of WLAN and WPAN systems. Since there is a need to distinguish between different standards for broader market exploitation, the IEEE 802.15.3c is positioned to provide gigabit rates and longer operating range. At these rate and range, it will be a nontrivial task for mmWave systems to provide sufficient power margin to ensure reliable communication link. Furthermore, delay spread of the channel under study is another limiting factor for high speed transmissions. Large delay spread values can easily increase the complexity of the system beyond the practical limit for equalization. The remainder of the paper is organized as follows: Section 2 describes the worldwide regulatory efforts and standardization activities; Section 3 presents a number of application scenarios and highlights the requirements for a specific application namely uncompressed high definition video streaming; Section 4 analyses the achievable data rate in both additive white Gaussian noise (AWGN) and fading channel based on the application requirements described in Section 3 and the roles of antenna in 60 GHz communications are also discussed; Section 5 describes the technical challenges that need to be resolved ahead for the full deployment of 60 GHz radio; finally, in Section 6 appropriate conclusions wrap up this paper. 2. WORLDWIDE REGULATIONS AND STANDARDIZATION In 2001, the United States Federal Communication Commissions (FCC) allocated 7 GHz in the 54–66 GHz band for unlicensed use [6]. In terms of the power limits, FCC rules allow emission with average power density of 9 μW/cm2 at 3 meters and maximum power density of 18 μW/cm2 at 3 meters, from the radiating source. These figures translate to average equivalent isotropic radiated power (EIRP) and maximum EIRP of 40 dBm and 43 dBm, respectively. FCC also specified the total maximum transmit power of 500 mW for an emission bandwidth greater than 100 MHz. The devices must also comply with the radio frequency (RF) radiation exposure requirements specified in [6, (...truncated)