White Paper
Hughes Radio Access Network Satellite Backhaul Solution
Introduction The uptake of mobile communication devices for voice and data applications has consistently surpassed all forecasts in all regions of the world. With over 70 percent penetration of global wireless communication devices and growing, a significant challenge remains... reaching underserved rural areas. Often these rural markets are located in difficult-toserve areas where terrestrial fiber or microwave services are not readily available to support the backhaul links for these remote base station locations. Cellular operators worldwide are increasingly looking to expand into these rural markets with cost-effective modular, self-sustaining green-powered radio access networks (RAN) and satellite solutions. While meeting various government regulatory and universal service obligation (USO) targets are among the key drivers for connecting rural and hard-to-serve areas, the competitive need for operators to grow their subscriber base has become equally important. Satellite, with its ability to very rapidly deploy broadband infrastructure in hard-to-reach areas, is the obvious choice for interconnecting cellular base stations in rural and hard-to-reach areas. Time Division Multiplexing (TDM)/Time Division Multiple Access (TDMA)-based satellite solutions can be very cost effective in reaching these locations, particularly when traffic is dynamically shared and assigned on an as-needed basis among multiple sites.
Satellite Backhaul Access Techniques There are two main satellite backhaul access techniques—TDM/TDMA and Single Channel Per Carrier (SCPC). QQ TDM/TDMA – Outroutes employ a statistical multiplexing scheme compliant with DVB-S2 for sharing information among multiple remotes on the outroute, while inroutes use a demand-assigned, multi-frequency TDMA approach to allow remotes to transmit to the hub. QQ SCPC – using dedicated frequencies to transmit and receive information to a single user. With TDM/TDMA, remote base station sites share the same satellite capacity for their traffic and the capacity is dynamically assigned as needed to each base station in a GSM system or Node B in the case of a 3G system. In a dispersed multi-site network, busy hour traffic occurs at different times at different site locations. This is very suitable for dynamic sharing of the same satellite capacity, a key attribute of a TDM/TDMA system. Basically, a TDM/TDMA system will switch traffic to different sites and times on as needed basis. This is in contrast to SCPC solutions where the capacity is allocated or variable on a per site basis only. Hughes offers a full range of satellite-based RAN backhaul solutions that have been specifically designed for mobile operators to enable rapid and cost-effective service expansion into rural or hard-to-serve markets. These solutions provide high-quality links while optimizing space segment resource utilization by coupling the appropriate satellite technology with intelligent traffic optimization. In addition, the time to implement a satellite backhaul connection is quite short. Once the satellite station is installed, the service can begin immediately. Also, satellite offers a significantly lower capex versus the cost of establishing (installing) and maintaining a terrestrial backhaul system using fiber or microwave (with multiple hops) to hard-to-reach rural areas. To demonstrate the suitability and efficiency of TDM/TDMA over SCPC, this paper compares the cost of operating a backhaul solution from a space segment standpoint. While some vendors have recently introduced a TDM/SCPC system on the same platform, it should be noted that those systems require reservation of bandwidth resources to be used for switchover to SCPC in the inbound and hence, this approach is not technically efficient and is more expensive to operate.
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The Hughes industry standard satellite-based backhaul solution has been tested successfully with small cells of various sizes (femto, pico, and macrocells) from major RAN manufacturers covering GSM, CDMA, and WiMax standards. Using star and mesh configurations, Hughes has successfully certified and commercially deployed several thousand remote base station sites supporting 2G and 3G voice and data services based on infrastructure from various vendors including Ericsson, Huawei, Nokia Siemens Networks, Alcatel-Lucent, Altobridge etc.
Selecting the Right Backhaul Technology
Backhaul Link Capacity
The HX System, which is based on TDM on the outroute and TDMA on the inroute, is the primary Hughes solution for cellular backhaul. Figure 1 below shows that when multiple RAN sites need to be backhauled with high bandwidth capacity required per site and the distance to the core is less than 40 miles, fiber and microwave, when available, will be preferred from a technical and economic choice. Beyond this distance, when microwave repeaters are required and sometimes impossible to implement and fiber is not economically viable, TDM/TDMA satellite systems become the preferred choice. In addition, TDM/ TDMA systems are the most cost-effective solution for dynamic traffic sharing of space segment among multiple sites. See the example of bandwidth sizing below. When relatively high traffic needs to be shared among multiple sites, the HX System combined with High Throughput Satellites (HTS) becomes the preferred solution. SCPC can be the appropriate solution for few point-to-point links with high and constant traffic requirement per link.
TDM/TDMA (HTS Inclusive) Fiber/Microwave SCPC
Miles
Distance to Core Network
Figure 1: Solutions for RAN Backhaul
HX System for RAN Backhaul The HX System offers operators who want to operate their own VSAT network for RAN backhaul, an effective total cost of ownership and scalable solution. Figure 2 illustrates the star architecture of the Hughes satellite cellular backhaul solution on the HX platform.
RAN Core
Hughes Satellite Router
HX Hub
Remote Site
IP BTS/NodeB/Femtocell
IP Network Cloud
Hughes Satellite Router
TDM TDMA
Remote Site
IP BTS/NodeB/Femtocell
Figure 2: Star Architecture of Hughes Satellite Cellular Backhaul Solution
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The HX System supports high-quality, low latency, and jitter bandwidth in a very cost-effective and scalable configuration. Individual remote terminals can be configured for guaranteed or flexible dynamic inroute bandwidth allocation. The HX System can be operated in star or mesh mode. When operated in star mode, the HX Gateway receives traffic from the Base Station Controller (BSC) and transmits over the TDM outroute to the HX remote terminal serving the designated Base Transceiver Station (BTS). The HX remote terminal forwards the received traffic to its correspondent BTS. The BTS communicates back to the BSC through the HX remote using TDMA channels serviced at the HX Gateway. The HX Gateways are fully redundant and incorporate advanced bandwidth management features. The HX remote terminals are rack mountable and support high-speed inroutes of up to 9.6 Mbps. Additionally, the HX System is capable of supporting mesh connections for traffic that does not need to be routed through a central hub. Many operators support backhaul connections served by multiple and geographically distributed BSC locations. The star configuration is not cost effective in this type of cellular backhaul deployment—either multiple HX star gateways are required to be installed co-located with each BSC site, or terrestrial backhaul connections need to be run between each BSC site and the central HX Gateway location. Mesh connectivity is an ideal solution for this type of backhaul network as the HX System can implement a direct, single-hop connection from the BTS locations into their associated BSC location, as illustrated in Figure 2. Since the HX mesh solution enables single-hop connectivity to multiple BSC locations, the need for terrestrial backhaul connections is eliminated.
RAN Core
HX Hub
IP Network Cloud BTS/Node B
BTS/Node B BSC/RNC
BTS/Node B
BTS/Node B BSC/RNC
Regional PSTN
TDM TDMA
Regional PSTN
Figure 3. Mesh Architecture of Hughes Satellite Cellular Backhaul Solution – Example of Regional PSTN Connectivity
Key Benefits of the HX System Hughes HX solution is highly bandwidth efficient and supports several features specifically suited for backhaul application and they are: Outbound QQ DVB-S2 – the world’s most successful satellite air interface, approved by TIA, ETSI, and ITU. QQ Adaptive Coding and Modulation (ACM) – allows the system to dynamically vary the modulation and coding of the forward channel for each transmission leading to more robust system and 30% bandwidth gain over DVB-S system. QQ Generic Stream Encapsulation (GSE) – Hughes implementation of GSE reduces encapsulation overhead and provides improvement in bandwidth efficiency of ~4 to 14 percent (depending on the distribution of user IP packet sizes). QQ Scheduling Bypass and Real Time Fast Track – together these features reduce the latency and jitter in the outroute by not queuing real-time traffic.
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Inbound QQ Adaptive Coding – similar to ACM on the forward channel, adaptive coding on the return channel enables a remote terminal to dynamically adjust its transmissions to handle fade conditions by selecting the most efficient coding rate that enables the transmission to be received and leads to 20 percent increased throughput as extra rain margin is not configured. QQ Adaptive Low Density Parity Check (LDPC) – using LDPC on the return channels enables Hughes to achieve a 12 percent bandwidth efficiency increase over existing Turbo Coded return channel systems. QQ Just In Time (JIT) TDMA burst forming – ensures that data packets are transmitted at the earliest possible opportunity and thus reduces the Real Time Transport Protocol (RTP) latency in the inroute. QQ Jitter Buffer (JB) – An integrated jitter buffer feature enables an operator to configure the desired jitter performance. While in mesh. JB allows the system to reduce jitter for traffic sent between mesh peers. While in star, JB reduces the packet jitter in the inroute direction. Other benefits QQ Very low Latency RTT ~600ms and Jitter ~20ms one way for efficient delivery of real time sensitive traffic such as voice and video QQ Simple and economical network expansion QQ Add more channels without any remote hardware change QQ Remote equipment competitively priced QQ No upgrade required to the standard HX Gateway QQ Easy integration with other Hughes platforms for service expansion QQ High-speed inroutes up to 9.6 Mbps QQ Strong QoS features enabling easy prioritization and transmission of critical traffic QQ Mesh connectivity with HX Mesh GW stations enabling cost-effective, single-hop connections for BSC to-BTS traffic QQ End-to-end network management and support SNMP for higher network management connectivity. QQ Transparent to cellular traffic—supports GSM (2,3 and 4G/LTE protocols), CDMA and WiMax standards QQ Works with all major cellular equipment vendor BSS QQ Overall lower total cost of ownership
Bandwidth Optimizer Overview For applications such as GSM where the backhaul traffic is not already IP, the Hughes solution for cellular backhaul incorporates an appliance (bandwidth optimizer) that not only converts the traffic to IP for transmission over satellite, but also optimizes both the data and control channels to significantly reduce the traffic sent over the space link. Key functions of the optimizer are: QQ Reducing voice channel bandwidth – Silence/idle frames are suppressed at the source and regenerated at the destination QQ Optimizing A.bis signaling bandwidth – TRX signaling data is extracted out of TRX channels and statistically multiplexed
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The above techniques deliver over 50 percent bandwidth savings over traditional SCPC links, depending on the efficiency achieved by the optimizer manufacturer. Hughes has conducted extensive integration and certification testing with many of the industry-leading IP optimizers. In addition, Hughes has successfully integrated and certified its HX system platform with IP-enabled Packet Abis BTS solutions from all major BSS manufacturers.
Bandwidth Sizing Example For packet Abis traffic over satellite, as illustrated in Figure 4, the Hughes TDM/TDMA solution shows a dramatic bandwidth efficiency over a clear channel implementation using SCPC technology. Consider the following example:
RAN Core
Hughes Satellite Router
HX Hub
IP GSM BTS
Remote Site 1 IP Network Cloud
Hughes Satellite Router IP
TDM TDMA
Remote Site 30
GSM BTW
Figure 4. Hughes Satellite Cellular Backhaul Solution – All IP traffic General requirements: Number of BTS: 30 Erlangs per BTS: 5 Blocking Rate: 1% If the network is supported using SCPC technology, operator will have to provision: 30 SCPC links; each link will need to support 11 voice traffic channels Total voice traffic channels in network = 30 x 11 = 330 Bandwidth per voice traffic channel = 10 kbps Total full duplex bandwidth = 330 x 10 = 3.3 Mbps If the network is supported using TDM/TDMA technology, operator will have to provision: One TDM outbound carrier, one TDMA inbound carrier To support aggregate network traffic 30 x 5 = 150 Erlangs on a single carrier in each direction Total voice traffic channels required = 170 (benefit of a single carrier) Bandwidth per voice traffic channel = 10 kbps Total full duplex bandwidth required = 1.7 Mbps
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Benefits of the Hughes TDMA Solution The Hughes solution results in a significant space segment savings over the SCPC solution. Savings calculated above excludes potential savings due to busy hour differences across BTS. A Hughes solution also provides central management, resulting in additional operational cost savings. Mobile operators should note that while SCPC vendors may claim their solutions offer higher order modulation than TDM/ TDMA solutions, the Erlang calculations are still done on an individual link level in an SCPC architecture. This means that the modulation efficiency is offset by the higher number of traffic channels required to support the same amount of traffic in an SCPC network. As the above calculation shows, a TDM/TDMA solution is more efficient due to its ability to statistically multiplex the cellular traffic across the entire network instead of over a specific point-to-point link. However, mobile operators must ensure that the chosen TDM/TDMA solution has the ability to provide high-quality, low latency and jitter bandwidth to support their cellular traffic. The Hughes HX Systems support guaranteed high-quality, low latency and jitter bandwidth that is proven and well suited for cellular backhaul.
Conclusion The Hughes HX System provides many benefits for RAN backhaul applications. With efficient TDM/TDMA channels and a highly scalable architecture, the HX System provides a lower overall total cost of ownership. The HX System, which is based on DVB-S2 on the outroute and TDMA on the inroute, when combined with High Throughput Satellites, meets most RAN backhaul requirements including very high capacity links, while SCPC solutions work well for single sites with point-to-point applications. Additionally, the HX System has been successfully certified with all major RAN equipment manufacturers, ensuring operators of a time saving successful backhaul implementation using the HX System.
Proprietary Statement All rights reserved. This publication and its contents are proprietary to Hughes Network Systems, LLC. No part of this publication may be reproduced in any form or by any means without the written permission of Hughes Network Systems, LLC, 11717 Exploration Lane, Germantown, Maryland 20876.
©2013 Hughes Network Systems, LLC, an EchoStar company. HUGHES is a trademark of Hughes Network Systems, LLC. All information is subject to change. All rights reserved. HUGHES RADIO ACCESS NETWORK SATELLITE BACKHAUL SOLUTION HUGHES PROPRIETARY H49628 FEB 2013
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