12.5 High Speed Rail Solutions
Outdoor Digital Distributed Antenna Systems (ODDAS) are also a strong tool for deployment along a rail track. The big advantage is the long reach of the optical fiber, and thanks to the digital nature of traffic on the optical fiber ODDAS would have greater resistance to dust and bad connectivity on the optical interface. Unlike traditional ODAS – based on analogue transport, ODDAS can handle an optical link budget in excess of 25 dB without any degradation of RF performance, whereas ODAS struggles after a loss of 4–5 dB (degrading the RF link budget by 8–10 dB); for more detail see Section 12.4. This is a practical, yet important parameter to consider when implementing DAS in the harsh rail environment.
Let us take a closer look on some of the unique challenges related to high speed rail, on top of the general aspects of rail tunnels discussed in Chapter 11, and outdoor DAS in this chapter.
12.5.1 Calculating the Required Handover Zone Size for High Speed Rail
As was discussed in Section 11.2.3 one needs to pay a great deal of attention to the HO zone, how we configure the antennas of the DAS in order to ensure that we have a usable and successful HO zone.
Refer to Section 11.2.3 for all of the detail, but one thing one needs to realize is the sheer size of the HO zone required for high speed rail.
Calculating the Handover Zone Size Required for High Speed Rail
One can easily calculate the required HO zone overlap if one knows the speed of the vehicle ...