High Throughput Satellite Gateway Feeder Link (Q/V/W bands) Argyrios Kyrgiazos, Barry Evans and Paul Thompson ICS, University of Surrey, Guildford, UK, GU2 7XH {a.kyrgiazos, b.evans, p.thompson@surrey.ac.uk} Abstract This paper studies the use of W band in a future high throughput satellite (HTS) system alongside the Q/V band. First the available spectrum in W band is reviewed along with the propagation effects that contribute to the signal’s degradation. Then a mathematical framework for the assessment of the global feeder link availability is presented and the design challenges of a combined Q/V+W gateway system are analysed. The advantages and disadvantages are highlighted. A preliminary assessment of the feeder link availability of a combined Q/V+W band systems is given. 1. Introduction Recent studies on ultra-high throughput satellite (HTS) systems, such as [1],[2], indicate that the system consists of more than 200 user beams operating at Ka band for economic reasons and more than 20 gateway earth stations at Q/V band are needed to provide the capacity for users. In order to gain access to more spectrum for a future high throughput satellite, migrating to higher bands (Q/V/W) is a necessity. These higher frequency bands are more subject to propagation impairments during the crossing of troposphere (8-15km). The level of impairments at these frequency bands (higher than 40GHz) is sufficiently high to prevent their use for user links because even with applicable fade mitigation techniques such as adaptive coding and modulation (ACM), the availability of the links would be limited [3]. Therefore the use of these frequency bands seems for now to be dedicated to gateway feeder links only, for which spatial diversity techniques can be considered, and constitutes an efficient way to cope with the strong impairments. In this respect smart gateway diversity [4],[5] have been shown to be among the most promising solutions. However, a recent and ongoing study [2] indicates that a very large number of gateways (50) at Q/V band, even using all the bandwidth, is still needed to support the user beams (302 user beams). Considering the complexity and the cost of these gateway earth stations compared with those of a state of the art Ka band, they increase tremendously, and they begin to dominate the cost of the system. Therefore, the number of gateway sites needs to be reduced to achieve a more cost effective system. A perfect candidate to achieve this is to use the available spectrum in W band (70-80 GHz) [9]. The use of this band is attractive to space system as it is a virgin area. For deep space applications, the interest for W band lies in the possible increase of the spacecraft’s antenna gain compared with the bands used currently. For broadband applications, more spectrum is available which gives more options to engineers to design the system. However, the drawback of using these higher bands, Q/V and W bands, is the fact that the signal is susceptible to the impairments caused by the troposphere, resulting in many dBs of attenuation making it more difficult to achieve high availabilities [9][10]. As a result, the design of fade mitigation techniques to counteract the deep fades is more challenging for Smart Gateway diversity [5]. Herein, we focus on a ground network which combines the Q/V and W band. Instead of using only Q/V bands in the feeder link, we consider a combined Q/V and W band ground earth station as in [6] where it was studied for first time. According to [6], it is possible to halve the number of gateway sites combining Q/V gateway stations with W band gateway stations. This contribution reviews the available spectrum in Q/V and W bands and briefly discusses the atmospheric impairments induced to the signal. Then a mathematical framework for the assessment of the feeder link availability for a combined Q/V and W gateway stations is presented. The design challenges of such a ground segment are discussed and analysed, highlighting their advantages and disadvantages. Lastly, an example is considered to illustrate the impact of a combined Q/V + W ground segment in terms of feeder link availability.