Wireless LANs: physical properties of infra-red systems vs. mmw systems

Abstract

Interest in wireless indoor communications has been spectacular. As we tend to need relatively broad bandwidths for such communication, the choice of carrier frequency would seem to be between the millimeter-wave/upper microwave bands and infra-red. The authors consider those systems which operate with one cell or multiple cells within a room. Such systems in the longer term must offer speeds compatible with fiber distributed data interface (FDDI) or the integrated broadband communications network (IBCN). Keeping this in mind, the authors look at the capability of systems supporting transmission rates of 100 Mb/s, though of course useful networks can be realized with much lower single user data transfer rates. As with mmw, infrared (IR) radiation is essentially restricted to the room in which it is generated; apart from leakage through windows and doors it will not normally be detected outside a room and should not interfere significantly with similar systems in neighboring offices. However, IR is not suitable for operation in very large rooms. In addition it is seen that mmw offers certain advantages in both large and small rooms.