Cascaded Sites using Shifted Phase Transmission Chapter 10RADWIN 5000 HPMP User Manual Release 3.2.00 10-3Cascaded Sites using Shifted Phase TransmissionThe solution offered here is not a “universal cure”. The following conditions are necessary, butin any specific case may not be sufficient:• The GSU sites (marked 1, and 3 above) are sufficiently far apart as to ensure thatthere is no mutual interference between communicating sites (1-2 and 2-3 above)• There should be no interference between non-communicating sites (1 and 3 above).To see how it works, we use Figure 10-2. The GSU towers are numbered and marked forcascading, 1-2 and 2-3. There shouldnot be a link between 1 and 3.The GSU can synchronize the TDD timing of several sites enabling the cascading of consecu-tive links without mutual interference.To use cascading, the TDD timing of the even-ordered links (GSU 2 above) must be “shifted”(Shifted Phase) and odd-ordered links (GSU 1 and GSU 3 above) must be “unshifted” (NormalPhase). The phase shift is half of the Radio Frame Duration (RFD) from the chosen RFP. Thescheme is shown in Figure 10-3.Since the GSU is always HSS master (HSM), at each GSU location, the GSU can “force” thesynchronization of its collocated radios. By half RFD shifting, alternate collocated sites cantalk to each other.Figure 10-3: Phase shifted transmission - phase shift is 1/2 the RFDChoice of normal or shifted phase is configurable per GSU using the RADWIN Manager.GSU RedundancyThe GSU is designed to support redundancy, improving the robustness of a GSU based topol-ogy.In redundancy mode, two GSUs are installed at the same HSS site. One of them self-config-ures to generate HSS sync signals. We will call it the Primary unit. The other one, the Second-ary unit remains dormant merely polling the first GSU. If the Primary GSU fails, then theSecondary GSU becomes active immediately. If the Primary unit becomes active again, itremains dormant, reversing the original roles. The choice of the Primary GSU is random andof no significance.If the Primary GSU fails, and then the Secondary GSU also fails to receive sync signals fromits GPS, then it moves to self-generation HSM mode like an ordinary HSM ODU until its GPSrecovers.
