Diverse network paths to avoid rain
Terrestrial wireless networks have been seen as a cost-effective solution for broadband communication and broadcast services. LMDS is a wireless communications tool that is based on two stations, and can transmit large amounts of information between the two locations using radio signals. LMDS can be tailored to the individual customer's needs providing ease, low deployment costs and fast realization of revenue. LMDS cellular networks using 40GHz range offer the possibility of considerable potential bandwidth. However LMDS signals at those frequencies are affected by moisture or rain, resulting in bit errors and signal disruption. Path diversity attempts to counteract heavy fading due to localised rain by providing another Radio Frequency (RF) path to a different base station. The IST project EMBRACE addressed the need for diverse routes across a broadcast radio frequency access network when fade conditions prevent the use of the current base by using MPLS (Multi-Protocol Label Switching) techniques. MPLS is a label-switched system that sends information over a wide area network (WAN) in frames or packets. Each frame/packet is labelled and the network uses the label to decide the destination of the frame. A user station may optionally be connected to two or more base stations. One of the routes is defined as the direct flow whereas the other routes are designated as shadow flow. Shadow flow becomes active when a rain fade is detected on the direct flow. The shadow flow will carry data through a different MPLS labelled path and will recombine with the direct flow on leaving the diversity domain taking good packets from either flow. Shadow flows will be turned off once the rain fade is over. The diversity solution supports the idea for combined business market and mass market since the business market can be offered better service availability and capacity still using a mass-market system. The combination of diversity and nomadic mechanisms using extensions to MPLS would result in a significant change packet routing practices.
