Planar Antenna Array Hybrid Beamforming for SDMA in Millimeter Wave WPAN 65 Planar Antenna Array Hybrid Beamforming for SDMA in Millimeter Wave WPAN

The increasing demands on bandwidth for personal and indoor wireless multimedia applications have driven the research and development for a new generation of broadband wireless personal area network (WPAN) Alliance (n.d.); IEEE 802.11 WLAN Very High Throughput in 60GHz (n.d.); IEEE 802.15 WPAN Millimeter Wave Alternative PHY Task Group (TG3c) (n.d.); WirelessHD (n.d.). This newWPAN is intended to support data rate up to 5Gbps or more and allows for wireless interconnection among devices, such as laptops, camcorders, monitors, DVD players and cable boxes, etc. Moreover, it could also serve as a wireless alternative to the High-Definition Multimedia Interface (HDMI). In addition to its very large bandwidth, the new WPAN also demands for short-range and secure wireless connections. The characteristics of broad unlicensed bandwidth FCC (2004), high penetration loss Smulders (1995; 2002) and significant oxygen absorption Anderson & Rappaport (2004) at 60GHz radio make it an ideal wireless interface for the next generation WPAN. Furthermore, the millimeter wavelength of 60GHz radio also makes it possible to use tens of tiny antennas to steer radio signals with high directivity to the intended receivers. This feature of high-directivity beam pattern not only improves the wireless link quality Balanis & Ioannides (2007) but also increases the spatial reuse factor, allowing for multiple users to gain access to the wireless channel at the same frequency and time. In view of the great potential of 60GHz radio on WPAN and the advantages of beamforming (BF) for millimeter wave (mmWave) applications, we study in this article a simple hybrid beamforming (HBF) technique for spatial division multiple access (SDMA) using planar antenna arrays (PAAs). Digital BF has been used to compensate the rather fixed radiation patterns of switch-beam or beam-selection antennas to create more flexible hybrid beam patterns Celik et al. (2006); Rezk et al. (2005); Zhang et al. (2003). In conjunction with the phase shifters of the element antennas of PAAs, a hybrid type of BF is considered in Smolders & Kant (2000) which exploits the advantage of BF both in the baseband and the radio-frequency (RF) ranges. Motivated by the above results and taking into account the practical limitation and implementation cost of the full digital BF, we study herein a special type of baseband and RF HBF for SDMA that only requires four digital processing paths to support HBF on a 8× 8 PAA illustrated in Fig. 1. The entire PAA of Fig. 1 is partitioned into four blocks of patch antennas. Each block is driven by a digital BF weight, while each element patch antenna in a block is equipped with 4