Impact of shadow fading in a mm-wave band wireless network

The interest in using higher frequency bands for high data rate wireless communication is increasing. Large unlicensed bandwidths are available specifically around 60 GHz. At this frequency, the propagation characteristics allow small cells and efficient frequency reuse. However, wireless communication at 60 GHz is mainly limited to Line-of-Sight (LOS), due to the high absorption loss of most materials. For indoor applications, e.g. wireless LANs, the shadowing caused by persons walking across the LOS can therefore severely degrade the link performance. In this paper, we show and quantify how the loss in received power and the stronger multi-path fading due to shadowing objects yield impaired path loss margins and increased bit error rate. We show that shadowing causes at least 6 dB power loss for 10% of the time. Also, link-layer simulations with a 1024-carrier DQPSK/OFDM air-interface show an error floor of 2.10 at shadowing densities that correspond to typically crowded places, such as train stations or shopping malls. The fast-changing shadowing situation will require frequent hand-over between Access Points (APs). Instead, we propose the use of the Virtual Cellular Network (VCN) concept, where signals are simulcast from a number of APs. We show that a VCN has to be well designed in order to mitigate the shadowing effects.