y that is, higher reliability lower link distance, i.e., 99.999% (5 nines) downtime 5 min/year 99.99% (4 nines) downtime 53 min/year Most of the available 70/80 GHz systems are designed with "4 nines" link availability since the link distance gets less than a kilometer with 99.999% availability. Figure 7.4 shows that Gigabit radios can cover around 2.5 km in northern Pakistan with 99.99% availability. This scenario was conducted with 60 mm/hr rain rate which only occurs during the monsoon season. These radio links are expected to be designed with 99.99% availability instead of 99.999% in order to cover a reasonable distance. 7.3.2.2 Standardization The propagation models from ITU-R and channel arrangement recommendations from CEPT (European Conference of Postal and Telecommunications Administrations) are the two key sources of standard- ization work on Gigabit radios. In the US, FCC (Federal Communications Commission) and in UK Ofcom (Office of Communications) granted the use E-Band (71-76 GHz, 81-86 GHz, 92-95 GHz) for millimeter wave telecommunication applications in 2003 and 2007 respectively. The radio frequency channel arrangement for fixed point-to-point systems operating in the bands 71 - 76 GHz and 81-86 GHz is stated in ECC Recommendation (05)07 | [3]. There are 19 channels where each channel can occupy a bandwidth of 250 MHz (Figure 7.5). These channel bandwidths can be summed up to form a single 5 GHz channel. Transmission Networks f1 f2 f4 f5 f1'/f2'/f3'/f4'/f5 71 GHz 19x250 MHz channels 19x250 MHz channels Figure 7.5 Single FDD arrangement with duplex separation of 10 GHz. Reproduced from C 2009 ECC CEPT [3] The individual channel has a separation of 250 MHz which can be aggregated up to a single channel covering the width of entire band. The specified channels may be used to form either TDD or FDD systems within the single band or in combination with the two bands. The recommended characteristics and requirements for equipment and antennas are given in ETSI EN 302 217-3 [4]. Currently, the 70/80 GHz