Extending 3G Coverage to Remote and Rural Areas Solving the Backhaul Conundrum

Transcription

1 Extending 3G Coverage to Remote and Rural Areas Solving the Backhaul Conundrum 1

2 After a decade of domination by GSM standard 2nd generation (2G) mobile phone networks, the world has embraced 3rd generation technology (3G). 2G systems laid a broad foundation for extending voice communication to the vast majority of the world s population. Yet 3G holds even greater promise, enabling mobile operators to deliver both voice and data connectivity to subscribers and greatly expand their revenue potential. Specifically, 3G technology provides a more profitable path to serving rural subscribers in both developing and developed countries. For many of these customers, 3G service represents the most affordable access to high-speed Internet connectivity, sometimes even the only access. According to the International Telecommunication Union (ITU), only 15.8% of the population in developing countries has Internet access and only 22.5% have a computer. In the future, Internet access will primarily be through mobile devices, and this represents a significant opportunity for mobile operators. In fact, a new report by Cisco projects that mobile data traffic will increase 26-fold worldwide by 2015, with the population of mobile-only Internet users surging from 14 million in 2010 to 788 million in What s stopping mobile operators from pursuing these opportunities? One key challenge is backhauling rural network traffic in a way that makes it affordable for mobile operators to extend their services. Fortunately, 3G operators can look to recent progress in the expansion of 2G into rural areas through satellite backhaul as a model for similar growth. This paper will examine how mobile operators can leverage several parallel trends falling infrastructure costs, the transition to IP and advancements in satellite backhaul technology to bring 3G to the rural market. 1

3 How 2G Operators Cracked the Rural Market Through Satellite Backhaul While satellite systems have been used for many years to backhaul 2G Base Transceiver Station (BTS) traffic in extremely remote situations, the market did not open significantly until recent technology innovations. The traditional approach relied on a technology called SCPC (Single Channel Per Carrier). This technology extends an E1 (or T1) fractional link from the Base Station Controller (BSC) site to the BTS using a pair of devices called SCPC modems. It was a simple solution, and good for sites that had a high level of traffic, but was operationally inefficient for many locations. With SCPC, the satellite link was treated as though it was an extremely long microwave hop that happened to pass via a satellite. The inefficiency comes from the fact that the capacity of the satellite link between these two modems has to be configured for peak usage which typically occurs for only a few hours on the busiest day of the year. The rest of the time there is unused capacity that has to be paid for. Since satellite bandwidth is usually the most expensive element in budgeting for a remote base station, wasting capacity is not a good value proposition (see Figure 1). Satellite backhaul over an SCPC network made sense when there was enough network traffic to justify a dedicated link, and several mobile operators did deploy SCPC networks to reach the remote and rural markets. But many of these potential sites had populations that were simply too small and could not generate the traffic to justify the build-out, so they have been left without service. While alternatives to satellite exist, they have distinct economic and technical limitations for connecting remote and rural locations. Fiber: Extending fiber networks into remote and rural areas is not a feasible option as it comes with a very high capital cost and a long lead time. Fiber installation costs and dark fiber rental costs vary enormously, but if a new build of tens of kilometers is needed to hook up a base station to an existing fiber network the delay and capital expense (capex) make it unlikely to be economically feasible. Microwave: Microwave links are similarly problematic for remote sites. Depending on the terrain a relay tower might be needed every kilometers, requiring land acquisition, power supply and equipment. If no population exists near the relay sites then these just add to the capital cost and complexity of the solution. Unlike fiber, which typically requires only the end points to be upgraded, an increase in capacity requirements often necessitates replacing equipment at all intermediate sites; for example, migrating from 3G to 3G+ HSPA. Figure 1: Comparison of per-site bandwidth usage under SCPC and TDMA systems TDMA Mode Dynamic Traffic Bandwith Usage SCPC Mode Dynamic Traffic Bandwith Usage 2

4 The time to acquire and build the relay sites may take years and the effort and cost is effectively doubled if route diversity is required to meet link availability targets. Any link requiring more than four intermediate relays is certain to require diversity to meet typical SLAs. Leased lines: In the case of leased lines, essentially the same problems apply as for the first two points except that the PTT will have to undertake the network build instead of the operator. Likely, at least some of the build costs will be charged back to the operator and there will then be an ongoing leased line charge to pay, normally related to distance and speed. The mobile operator can expect a very long delay in the build-out and in this case has the extra disadvantage that the planning and deployment are outside their control. In the long term, the reliability is also outside the mobile operators control and may become an issue. The fundamental shift in the market began when the mobile operators started to deploy IP networks to improve efficiency and management of their voice and data networks. Until the mid-2000s, all 2G mobile networks used Time Division Multiplexed (TDM) links both in their core networks and also for the base station backhaul links. These were ideally suited for microwave and other fixed bandwidth link technologies. Starting around 2005, the amount of data traffic in mobile networks became more important, starting a gradual migration towards the use of IP technology. While TDM is well suited to voice traffic, it is highly inefficient for data traffic, which is almost always highly peaky. This characteristic makes data traffic a much better fit for IP networks where the capacity can be shared between multiple sites rather than having a fixed amount per site, as in a TDM network. The move from TDM to IP was also mirrored in the satellite industry, where new, all IP-based satellite networks impacted the way satellite services were being managed and deployed. These satellite networks use a concept called TDMA (Time Division Multiple Access) to share the bandwidth across many sites allocating bandwidth on demand based on the real-time requirements at each site. This flexibility is exactly what is needed in an IP environment. Bandwidth allocation can literally start and stop with each sentence spoken or block of data sent or received. The trunking gain achieved by this pooling of bandwidth can be dramatic compared to SCPC with up to 80% less capacity required on a per site basis. With the introduction of IP-based TDMA technology, mobile operators found a more economical way to backhaul data using satellite systems. And today, 2G mobile operators have extended their service through satellite backhaul to thousands of remote and rural sites (see Figure 2). Figure 2: With TDMA many remote sites share the same satellite carrier, allocating capacity according to real-time needs PSTN Mobile Switching Center (MSC) Base Station Controller (BSC) idirect Hub Teleport idirect Router Base Transceiver Station (BTS) 3

5 Will satellite backhaul work over 3G? Increasing data usage and technology evolution make the case even stronger With the adoption of 3G networks, the use of mobile data has grown exponentially and overtaken voice as the primary application used on mobile devices. But can the satellite model for 2G backhaul be used for 3G networks? The answer is that satellite backhaul is even more relevant to 3G than 2G because newer satellite systems are designed primarily for IP data traffic. See the appendix for a more detailed analysis of how today s satellite systems are highly compatible with 3G standards. The satellite industry and mobile vendors have both introduced several technical innovations that make backhaul over VSAT a sound choice for handling data and IP traffic on 3G mobile networks. Three specific innovations are making a direct impact on the business case for supporting 3G: DVB-S2/ACM, TDMA and SCPC on a single platform, and femtocells. TDMA networks are dramatically faster and more efficient since the move to the second generation of the Digital Video Broadcasting standard, or DVB-S2. Most satellite hardware vendors continue to deploy DVB-S2 systems using the broadcast profile, which is far from optimal for interactive VSAT Systems encapsulating IP data within MPEG frames. idirect, on the other hand, has tuned every aspect of its DVB-S2 implementation for the efficient delivery of IP traffic across satellite networks, while still remaining 100 percent compliant with the DVB-S2 specification. Along with DVB-S2 came a technology called Adaptive Coding and Modulation (ACM), which addresses the long standing challenge of rain fade. idirect s implementation of ACM enables each remote to operate at its most efficient coding and modulation scheme at any moment, depending on its location within the satellite contour, antenna size and atmospheric conditions. ACM not only optimizes bandwidth efficiency for maximum throughput on a remote-by-remote basis but also ensures uninterrupted service by automatically adjusting signal strength to maintain connectivity, even in regions prone to deep and sudden rain fade. Another recent innovation, introduced by idirect, is the integration of TDMA and SCPC onto a single networking platform (see Figure 3). While we described SCPC earlier as essentially a legacy technology, there are some circumstances in which it plays a role. For the majority of cellular sites, traffic is variable, changing second by second as conversations and data browsing start and stop. For this reason TDMA is clearly a winner because of the statistical multiplexing effect, the same reason that operators choose IP networking as a replacement for TDM multiplexing in their transmission networks. However, some links remain at a fairly constant capacity where they are saturated by design or due to other constraints, such as having no more RF spectrum available for handling calls and no possibility to add further cell sites to increase capacity. Figure 3: Shared TDMA carriers used for variable traffic volumes; SCPC used for steady traffic volumes TDMA Shared Return SCPC Return 3G Core 4

6 In these circumstances, and also in the case of raw data throughput simply exceeding the capacity of the TDMA remotes to carry the traffic, the idirect system can switch a standard Evolution series remote to become an SCPC Return terminal. This is done with a few clicks of a mouse in the Network Management System. This flexibility allows operators to change remotes between SCPC and TDMA as often as they like, such as day and night, or during the tourist season for a site at a resort. This also provides an operator the ability to start with a very small variable throughput at a remote site and then switch to a dedicated connection when a site grows and has the business justification for needing SCPC. Rather than having to send a team to physically swap a remote modem, this can be done centrally with the same hardware still in the field. This means a single satellite network can deliver both types of connectivity and adapt as mobile operators add subscribers and resulting traffic to their networks. Clearly, having a single network technology that can deliver both types of service leads to many types of savings such as having a single NMS staff, having only one set of spares and having a platform to train employees. The third key development that is impacting the deployment of 3G networks is the introduction into the mobile market of new products derived from femtocell technology. While femtocells originally gained exposure to mobile operators as a way of offloading data from the wireless network to the terrestrial network, they also have the ability to cost effectively expand the service area for an operator. Firms such as Public Wireless have built vendor agnostic outdoor platforms capable of integrating several femtocell platforms, combined with power amplifiers, power supplies and outdoor enclosures to produce packages that can support voice calls plus HSPA data traffic and backhaul that traffic using any available IP connectivity cable modems, ADSL or satellite. The prices of these packages can be much lower than those from traditional macro-cell vendors and combined with a satellite remote router can deliver a rapid and economic build-out of 3G coverage in rural areas. The same vendors are challenging the traditional mobile vendors with new systems that incorporate the entire 3G core network on the same server platform that hosts the femtocells. The effect of this is to release mobile operators from the need to operate large and extremely expensive proprietary 3G core networks and replace them with much lower cost soft-switches. These devices allow scaling to much smaller networks even to allow entirely separate networks to be operated in a building, ship or aircraft. The introduction of femtocell technology is a game changer specifically in developed nations. It clears a path for mobile operators to extend data service to rural markets, where accessing the Internet over a mobile device can be significantly cheaper and more convenient than computerbased Internet access. Not surprisingly, mobile operators that have already invested in Femto-gateways to link home and office-based femtocells to their core networks are extremely interested in leveraging this same investment for rural coverage. Making the 3G Business Case for Satellite Backhaul With 2G success as a model, how can 3G operators make the business case for expanding into remote and rural markets through satellite backhaul? There are a number of business factors that need to be considered. How do you plan to expand your customer base? Is coverage area inhibiting your current growth? Can you be first to market in new regions? Will expanded coverage lower customer churn? Will my other technology options allow me to expand my coverage quickly and cost effectively? These are all important factors that drive operators to choose to deploy satellite in their cellular networks. Let s examine the typical capital and operating costs associated with satellite backhaul and the typical ROI a mobile operator can expect. Hardware costs When it comes to the cost of a satellite network there are two main variables that are crucial: the cost of the equipment and the satellite bandwidth required to support the service. In a TDMA network, the satellite equipment costs comprise the hub system located typically at or close to a mobile switching center and the remote routers that are located at the base station (Node B in 3G terms) sites. There are, of course, many variables whether the system will be shared with other services, the size of the hub and remote antennas (which in turn depends on the satellite chosen and the bandwidth required), etc. However for a network of a few hundred sites we could estimate the total cost for both hub and remote equipment at $3,000 - $6,000 per site, typically less than the cost of most microwave links. 5

7 In a typical SCPC network, each remote operates individually without a centralized hub. From a capex perspective, this makes each remote site more expensive, but you eliminate the cost of the central hub. However the cost of SCPC modems are typically around two or three times that of TDMA systems; hence, once the cost of a TDMA hub has been amortized across perhaps as few as twenty sites, the capital cost for TDMA is lower. As mentioned above, the use of femtocells is really opening up a new opportunity for mobile operators to support customers in remote and rural areas. The capex required for installing a femtocell that will cover a small town or village is much less than needed for a typical macro cell. For a femtocell deployment you need three main things: a site, power and backhaul. Femtocells typically require much less electricity and can be easily attached to an existing structure without the need for a tower to be built. Combine that with a cost effective satellite solution that can scale to hundreds or thousands of sites and the opportunity for covering remote areas cost effectively has greatly increased. Operating costs The largest operating expense (opex) of any satellite network is the monthly bandwidth cost to support the service. For this reason the development of new technologies that maximize the efficiency of bandwidth has been crucial to help mobile operators justify their investments. As mentioned earlier, an SCPC satellite link between two modems has to be configured for peak usage, which usually only occurs for a few hours of each day. This means that an operator will need to allocate a fixed amount of bandwidth per site based on the most pessimistic case. Outside of peak usage there is unused capacity that is sitting idle. This wasted bandwidth is not being re-used, and is an expense to the operator that is not being recouped. When using a TDMA satellite system, such as the idirect Evolution system, the bandwidth cost is directly related to the peak requirement for IP bandwidth across the whole network. This can be derived from the individual 3G remote base station (Node B) busy hour traffic figures, but isn t as simple as just adding them all up, as the busy hours usually occur at different times for different sites, due to local factors and random statistical behavior. We generally find that this decorrelation of busy hours means that the peak bandwidth required is 10% - 15% less than the simple sum of all the bandwidths, which is what you would see in an SCPC satellite solution. This is over and above the typical 50% trunking gain derived from pooling all bandwidth into one dynamically allocated resource pool. idirect has tools designed to help operators make these calculations to determine the impact on their network. After calculating the peak bandwidth (in Mbit/s), and the amount of satellite bandwidth (in MHz), operators can determine the amount of traffic that can be supported on the network. Moving forward, idirect can now support TDMA and SCPC traffic on the same network. This means that an operator can deploy a satellite solution at a remote site and only allocate a very small amount of bandwidth as necessary to enable connectivity at that location. As traffic increases or subscriber numbers in that area grow and the throughput on that particular Node B requires it, you can change the remote satellite router from operating in TDMA mode to a dedicated SCPC link. For operators this means that they can save on bandwidth expenses to launch the service with TDMA, and can move to SCPC at locations where a high level of traffic requires a dedicated link. Operators can also save on equipment because no physical swap of hardware is required at the remote site. The transition from TDMA to SCPC is centrally managed and can be done without any support in the field. Further, a mobile operator will not need two separate networks as many use today for both shared TDMA traffic and dedicated SCPC traffic. This will also provide opex savings, as an operator s personnel will only need to manage and maintain a single network. The Business Case for Deploying 3G Networks Over VSAT On the following page, there are two sample business cases that depict typical costs for extending cellular service to remote and rural areas using satellite backhaul, as well as expected revenue gains. These business cases are based on current pricing and extensive research on deployed networks. 6

8 Business Case 1 Business Case 2 Inputs Inputs Voice only ARPU Voice + data ARPU Proportion voice only subs $10 $20 50% Voice only ARPU Voice + data ARPU Proportion voice only subs $50 $100 30% # Subs/site 1000 # Subs/site 300 Site capex Amortization months $15, Site capex Amortization months $6, Satellite BW cost (per MHz/month) $3,000 Satellite BW cost (per MHz/month) $3,000 Cost per Site Cost per Site Total cost for BW (per site/month) $8,255 Total cost for BW (per site/month) $10,962 Other sites costs/month $169 Other sites costs/month $219 Amortized capex/month $250 Amortized capex/month $100 Total site cost/month $8,675 Total site cost/month $11,281 Revenues per Site Revenues per Site Total revenue (per site/month) $15,000 Total revenue (per site/month) $25,000 Gross margin (per site/month) $6,325 Gross margin (per site/month) $14,219 Annual Revenue $75,904 Annual Revenue $170,624 Business Case 1: Extending cellular coverage to the MEA market using Ku-band satellite backhaul and macro-cell infrastructure As you can see from the chart above, a 3G mobile operator can expect to net more than $75,000 in annual revenue by serving an individual site with a population of 1,000 subscribers. It s likely that an operator in the MEA region may be able to serve 5,000 such sites within a mid-sized country (Kenya for example). This would total more than $3.75 million in annual revenue. Current research on 2G deployments confirms these projections. Business Case 2: Extending cellular coverage to the European market using Ku-band satellite backhaul and femtocell infrastructure An emerging application for satellite backhaul is extending the reach of 3G+ networks to the small towns that are still not connected with 3G, terrestrial ADSL or cable technology. The sample business case above shows that mobile operators may be able to gain more than $170,000 in annual revenue by serving a 300-subscriber site with femto fill-in. In a country like the U.K., an operator might have 1,000 sites in a network, which could lead to $170 million in revenue. In a larger country like the U.S., an operator may be able to serve 10,000 sites, with nearly $2 billion in potential revenue at play. 7

9 Conclusion There is a market for 3G connectivity using satellite in fact, satellite is the ideal medium to reach the remote and rural sites that are the key areas lacking 3G coverage. The population in these areas will use 3G as their primary means of accessing the Internet and gaining the economic and social benefits that go with this access. The evolution of 3G standards from the initial R99 to the latest R8 technology can all be supported over satellite (see appendix), the latter offering clear advantages in the flexibility of routing traffic according to type. While early satellite used for 2G networks used inefficient SCPC technologies, new developments in IP-based satellite systems mean that they can economically provide efficient 3G backhaul today. The flexibility of the idirect 5IF hub system allows an operator to use different satellites or even multiple bands to reach different types of remote base stations as new systems evolve. This flexibility extends to allow an operator to switch the access method from TDMA to SCPC or vice versa as traffic patterns change over time, ensuring they can always use the best available technology rather than be constrained by legacy equipment. The combination of lower cost and highly efficient satellite backhaul with the new generation of highly economic 3G base stations makes the business case for rolling out 3G to remote and rural areas a clear winner. Want to know more? Send an to mobile@idirect.net The Appendix begins on the following page 8

10 Appendix Does Satellite Work for All 3G Releases? In principle, 3G traffic should be as simple to backhaul using satellite links as 2G. But as with 2G, not all satellite systems are the same when it comes to performance. There are several different generations of 3G standards that need to be evaluated, but these can be segmented into three main categories: Release 99, Release 5, and Release 8, corresponding to an evolution in the requirements to support higher data speeds. Release 99 The original 3G / UMTS systems that were deployed from around the year 2000 until quite recently used a version of the 3G standards called 3GPP R99 or Release 99. In this version of the UMTS hierarchy, the links between the remote base station (called a Node B in UMTS terms) and the Radio Network Controller (RNC) used Asynchronous Transfer Mode (ATM). The use of ATM dates back to the 1990s as a technology enabling carriers to multiplex different kinds of high-speed traffic using hardware / firmware based cell switches. These were used to provide the kind of throughputs that can now be routinely achieved using carrier-grade IP Routers. To carry the Node B-to-RNC traffic typically one or two E1 links would be used per link, using inverse multiplexing if necessary to carry multi-mbit/s traffic over individual 2 Mbit/s E1 links. In order to provide the very high switching rates that were needed to transport multi-mbit/s traffic before high-speed IP routers were available (or affordable), ATM made the task simpler (and thus faster and cheaper) by dividing the traffic carried into fixed-length cells. These cells use 5 byte headers for the source and destination addresses and carried 48 bytes of payload. Since the header has a simple and fixed format and the payload is a fixed length, the hardware required to make routing decisions is simplified and could be implemented on ASICs. The problem now arises of how to carry these legacy ATM links over IP router networks, including satellite-provided IP links. As for legacy GSM base stations using E1 TDM links, there are a variety of mediation device solutions that can encapsulate the ATM cells into IP packets, compress the headers and traffic if possible, and then transmit them over an IP network. Clearly these devices have to be used in pairs, one at each end of a link, in order to convert back to ATM at the far end. In practice the devices come in small and larger packaged versions, providing typically 1 4 E1 ports on the version for the remote Node B site and supporting multiples of 8 ports on plug-in cards at the version for the RNC end of the link, where many remote sites can be expected to connect to one RNC. We have tested with these devices and found them to be reasonably successful, supporting 1 2 Megabit/s throughput. The disadvantage with this approach is the same as in 2G networks: there is no communications between the mediation device and the Node B or RNC, nor is it architecturally possible. The mediation devices exist as an invisible black box, transporting ATM transparently from end to end. This means that no information on network congestion or impairment can be given to the mobile network which can sometimes lead to network instability. In addition, the devices add cost and represent an extra potential point of failure, although they are typically engineered to carrier standards. 3GPP Release 99 traffic wrapped in GTP and then encapsulated in ATM cells HTML HTTP HTML TCP/IP PAY LOAD NODE B R99 3G GTP PAY LOAD ATM CELLS 9

11 Appendix Release 5 Following the early implementations of 3G using ATM, the next important major release - 3GPP R5 - used IP as the transport protocol. This made it possible to connect such base stations directly to an IP-based satellite system such as idirect. However, the protocols used to carry the voice and data are still essentially closed the 3G data is now encapsulated inside IP packets, but the data itself remains wrapped inside the 3G protocol layers. So what impact does this have on cellular networks? This means that routers or other components in the data path cannot easily be aware of the type of traffic they are passing. At the IP level, all the traffic is wrapped up in 3G protocols whether it is voice, data or video. For example, the traffic from a user browsing a Web site will contain standard HTTP(S) protocol at its core, but the routers will not be aware of this they just see a sequence of packets containing 3G traffic that contains something. Thus the routers cannot optimize the transport of HTTP or any other common internet protocols being carried since it is embedded in another complex layer. The effect of this is that the overall connection speed over IP satellite is still dependent on the efficiency of the 3G protocols in operating over a high-latency IP link and with higher levels of jitter than are normally found on terrestrial networks. idirect has worked with specific marketleading vendors to help them understand the impact of satellite transport on their 3G products so they could tune or modify their protocols to work effectively with the characteristics of satellite circuits. We are able to report successful trials showing multi-megabit throughput with directly connected 3G R5 Node Bs connected to their RNCs via idirect networks. 3GPP Release 5 carrying traffic in TCP/IP but still wrapped in GTP HTML HTTP HTML TCP/IP PAY LOAD NODE B R4/5 3G GTP PAY LOAD IP/UDP PAY LOAD 10

12 Appendix Release 8 The latest generation of 3G base stations supports 3GPP Release 8 of the UMTS standards. This has the ability to integrate the RNC functionality into the Node B. The important effect of this is that now data traffic can enter and leave the Node B in its native form. For example, if a user connects their handset to a Web page using HTTP over TCP/IP, that traffic now leaves the base station as a TCP/IP session carrying HTTP. This has all sorts of benefits for mobile network operators. Operators can now choose to treat different types of data in different ways: compressing certain Web pages using Web optimizers, or routing certain traffic via a terrestrial link even an ADSL link while keeping other traffic on their own network. In terms of satellite backhaul, the importance is that the native traffic can be routed efficiently over a satellite router that incorporates TCP/IP spoofing and use other techniques that avoid the slow-start effect of operating TCP/IP over a higher-latency satellite link. Throughputs of tens of megabit/s become possible and the user experience over satellite is not substantially different from using a terrestrially connected base station. 3GPP release 8 onwards - traffic egress as native TCP/IP HTML TCP/IP HTTP PAY LOAD HTML NODE B R8+ Release 8 onwards allows the full benefits of TCP spoofing, acceleration, local switching and multicast content distribution NODE B R8+ TDMA/SCPC idirect Router SOFT SWITCH MULTICAST MUSIC/IPTV 3G CORE NETWORK GQOS PRIORITIZE RTTM ACCELER. SPOOFING VOIP/SIP MUSIC/ IPTV DATA/WEB 11

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