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High-Throughput Satellite Gateway Architectures

DEV Systemtechnik and Quintech Electronics Solutions for HTS Gateway Architectures

18th July 2016, Friedberg, Germany

Executive Summary

High-Throughput Satellites (HTS) represent state-of-the art satellite communication systems, which deliver internet access at high data rates for various applications, including mobile and cellular backhaul required for the delivery of broadband services. HTS systems offer higher capacities compared to traditional satellites architectures at reduced cost per bit. As satellite ground segment gateways are responsible for feeding the HTS system with data, efficient gateway architectures are indispensable. Critical requirements for HTS gateway architectures include size, energy consumption and other cost savings, and most importantly reliable operation, including sufficient redundancy schemes, and automated operation enabling virtually unmanned operation.

Introduction

Satellite communications represent a flexible and efficient platform for delivering versatile services including voice, data or video signals. Since satellite communication systems do not rely on existing communication infrastructures, such as electrical or optical cable networks, all regions of the globe can be reached, regardless of their remoteness or specific geographical location. To meet the challenge of rapidly increased demand for higher data transmission rates, HTS satellites are being utilized particularly for data and multimedia platforms and services such as mobile and cellular backhaul applications.

Fig.1: Schematic drawing of an HTS system
Schematic drawing of an HTS system

Figure 1 shows a schematic drawing of a HTS system, consisting of a HTS gateway, the HTS satellite and the corresponding spot beams. One main difference from traditional satellite transmission schemes is the usage of multiple spot beams in HTS systems. This so-called ‘frequency re-use’ operation allows the transmission of different signals at the same frequency and polarization, to several geographic areas i.e. spot beams (s. Fig. 1). With this technology the capacity per utilized frequency band for the overall system is significantly increased.

Typically, HTS satellites are operated in the Ka-Band as the requested bandwidth can only be delivered by these additional frequencies. Furthermore, these higher frequencies allow for highly focused spot beams and smaller antennas leading to economically efficient solutions with very high data rates.

The HTS gateway also referred to as “Hub” or “Ground Station” links the satellite network to the terrestrial telecommunication infrastructure, providing broadband connectivity to the internet, typically via an optical digital network. Figure 1 illustrates a HTS gateway composed of equipment for IP processing and satellite throughput management, modulator and demodulators, RF switching and transmission equipment and corresponding satellite gateway antennas. Gateway antennas provide ‘Out-route Connectivity’ from the Gateway to the User Terminal via a TDM Forward Link and corresponding User Spot Beams and ‘In-route Connectivity’ via a TDMA User Beam Uplink and HTS Return Link. Generally, the HTS gateway is composed of multiple Gateway antennas as well as one Diversity Antenna to secure transmission in case of adverse weather conditions. Typically the HTS satellite is fed from multiple Gateway locations to increase the overall system capacity for a given number of Spot Beams.

Radio Frequency (RF) Equipment is positioned ‘at the heart’ of HTS gateway architecture and plays an integral role providing reliability, redundancy and strength of overall signal quality. The following sections discuss in detail different viable architectures for RF equipment in HTS gateways.

RF Solutions for HTS Gateway Architectures

Different configurations of RF Equipment in HTS Gateway architectures with their specific benefits and drawbacks are outlined below. The representative configurations vary depending on the requirements as determined by the specific properties of the Gateway geographic location, site construction and Quality of Service (QoS) requirements.

Fig.2 Typical RF Equipment Configuration for HTS Gateway Architectures
Typical RF Equipment Configuration for HTS Gateway Architectures

Figure 2 illustrates one typical configuration of RF equipment inside a HTS Gateway. This HTS Gateway consists of several Gateway antennas (in Fig. 2 up to i), which share the satellite transponders in order to optimize the carrier to noise ratio per transmitted Satellite forward link. On the Uplink paths, N Transponder Signals from various Modulators are combined to P L-Band signals by using an NxP L-Band Combining Matrix Switch. Subsequently, these L-Band Signals are amplified and transformed to higher transmission frequencies by a Block Upconverter (BUC) and a high power amplifier (HPA) and are transmitted to the satellite via the Gateway antenna.

On the Downlink satellite return path, signals are received by the Gateway antenna, amplified and transformed via Low Noise Amplifiers and Block Downconverters (BDC) into L-Band Signals. These L-Band Signals are distributed to M Demodulators using a MxP L-Band Distributing Matrix Switch.

Employing L-Band matrix switches for the uplink and downlink path allows for the dynamic routing of signals between different Gateway antennas, and consequently for dynamic allocation of bandwidth to specific spot beams (s. also Fig. 1). However, the pure electrical transmission of L-Band signals to the Gateway antennas does pose some limitations to the achievable signal quality and transmission distance, as electrical transmission losses of L-Band signals can be significant. To prevent this loss and L-Band signal degradation at electrical transmission, optical L-Band transmission schemes can be employed. Typically this so-called RF-over-Fiber technology is considered for transmission distances starting at about 50 meters.

Figure 3 shows another typical configuration of RF equipment inside a HTS gateway. This configuration illustrates a Diversity Gateway Antenna in which the L-Band signals can be redirected in the case of adverse weather conditions in order to maintain the required level and quality of service. In contrast to the previous configurations L-Band signals are transmitted via optical fibers to/from the Gateway antennas. In particular a bi-directional DWDM RF-over-Fiber optical link is used to transfer signals between the Matrices and the Gateway Antennas. DWDM RF-over-Fiber systems enable the low loss transmission of multiple RF signals over one optical fiber with transmission distances up to 100km. As HTS transmission systems are mainly operated with Time Division Multiplexed (TDM) signals (s. also Fig. 1), the time delay between Main and Diversity sites is equalized by an optical delay line in the optical link to the main antenna site.

When compared to the previously discussed configuration, only two Gateway Antennas are employed. To reduce equipment complexity, and consequently CAPEX spending, the distributing RF Matrix Switch can be replaced by RF Distribution Amplifiers, which provide a fixed distribution of L-Band signals to the Demodulators. A similar approach can be employed for the uplink path, where a fixed combining configuration could also be deployed. As weather conditions and importance of transponder signals change frequently, ordinarily a Combining Matrix Switch is employed for the Uplink (s. Fig. 3).

Fig.3 RF Equipment for HTS Gateway Architectures Including DWDM RF-over-Fiber Transmission and Ka-Band Site Diversity Configuration
RF Equipment for HTS Gateway Architectures Including DWDM RF-over-Fiber Transmission and Ka-Band Site Diversity Configuration

Figure 4 represents the most sophisticated configuration for the use of RF equipment for HTS Gateway architecture. It combines the benefits of DWDM RF-over-Fiber transmission with the full RF Matrix routing flexibility for the uplink and downlink path and employs multiple Main Gateway Antennas together with a Diversity Gateway Antenna.

Fig.4 RF Equipment for HTS Gateway Architectures
RF Equipment for HTS Gateway Architectures

RF Equipment for HTS Gateway Architectures

Quintech Electronics and DEV Systemtechnik are leading manufacturers of RF signal management equipment, including RF matrix switches and RF-over-Fiber equipment and solutions. The following are of our products for specific use in HTS Gateway architectures.

Figure 5 shows a front view of DEV’s L-Band Distributing Matrix Switch 8to4ty, which can host an 8x40 switching configuration in a 2 RU chassis. Among other features the 8to4ty Matrix Switch offers optical inputs and unique redundancy configurations.

Fig.5 DEV L-Band Distributing Matrix Switch 8to4ty (DEV1984)
DEV L-Band Distributing Matrix Switch 8to4ty (DEV1984)

Figure 6 shows a front view of DEV’s RF-over-Fiber transmission chassis (left) and corresponding optical DWDM transmitter module (right). The optical chassis provides 20 slots for various optical modules including CWDM, DWDM, EDFA, and other optical modules in 3 RU.

Fig.6 DEV RF-over-Fiber Chassis (DEV7113) and corresponding optical DWDM transmit module (DEV7251)
DEV RF-over-Fiber Chassis (DEV7113) and corresponding optical DWDM transmit module (DEV7251)

Figure 7 shows a front view of Quintech’s L-Band Combining Matrix Switch, the QFM, which hosts a 16x16 switching configuration in a 1 RU chassis. Among other features the QFM Matrix Switch offers Signal Path redundancy configurations by automatically rerouting any failed signal path.

Fig.7 Quintech L-Band Combining Matrix Switch (QFM)
Quintech L-Band Combining Matrix Switch (QFM)

Quintech and DEV’s products are designed for maximum reliability and are based on multiple redundancy design schemes such as power supply redundancy, CPU redundancy, link redundancy or equipment redundancy schemes.

All products are easily managed and controlled via SNMP, Local Control or Graphical User Interface (GUI). The GUI allows for intuitive and full operation, and the complete SNMP-MIB facilitates seamless integration into all common M&C Systems. These differentiating features make Quintech and DEV’s equipment and solutions ideally suited for operation in HTS Gateway architectures.

Further information and technical specifications for RF-over-Fiber and RF Matrix Switches can be found at:

http://www.dev-systemtechnik.com/de/products/rf-over-fiber/

http://www.dev-systemtechnik.com/de/products/matrix-switches/

http://www.quintechelectronics.com/website/HTML/Quintech_L-Band_Matrix_Switches.html

About Quintech Electronics and DEV Systemtechnik:

Quintech Electronics and DEV Systemtechnik are leading manufacturers of RF signal management equipment. They are one company producing RF matrix switches, RF-over-Fiber equipment, routers, test automation and control software, redundancy switches, relay switches, splitters, combiners, amplifiers, and RF accessories such as powering products available in various frequencies. Our products are used in Satellite, Broadcast, Government/Military and Wireless Markets and meet the highest standards of system availability, reliability and controllability.

 The white paper as download click here.