LTE Technical Challenges for In-Building Coverage. Introduction

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1 LTE Technical Challenges for In-Building Coverage Introduction LTE technology promises to bring speeds of over 100Mbps downlink and 50Mbps uplink to mobile users using mobile broadband applications. With 196 operators in 75 countries currently investing in the technology, LTE is now generally acknowledged to represent the future of the industry. In turn, demand for data is running at levels that were unimaginable even a couple of years ago. This is due to the emergence of smartphones and other high end devices running multimedia applications such as streaming video and mobile TV. By 2015, it is predicted that total data rates will exceed 6,300,000 terabytes per month. Given that some 50% of total mobile traffic is said to originate or terminate within buildings, we predict a corresponding massive increase in demand for data from our in-building networks. The purpose of this document is to present the figures relating to this growth in data demand and to assess how we may scale our existing in-building DAS networks to handle this growth. We consider options such as deploying smaller cells to improve capacity in localised areas; utilising MIMO technologies to offer higher data rates; and upgrading, all or part of our existing DAS networks to LTE technology. The document is structured as follows: First we highlight the figures behind the hype surrounding this ever-increasing demand for data. We look at the number of devices such as smartphones and tablet PCs, both now and in the years to come, and multimedia services such as video, VoIP, gaming etc. These figures will help us benchmark the requirements of future in-building network designers. Working with these figures for data demand, we must consider the performance of both existing cellular technologies (HSPA and HSPA+) and emerging technologies (LTE and LTE-Advanced). We need to estimate how these technologies will be able to cope with increasing demand and for how long. One of the key factors in increasing the performance of wireless networks is the introduction MIMO technologies. MIMO will play an important role in our decisions on future network design. A section in this document has been dedicated to explaining multiple antenna technologies. We consider how an in-building DAS may be designed to cope with the volumes of data that will be required in the coming months and years. In the case of 4G networks, the challenge from the outset will be to engineer the networks to deliver capacity, as opposed to coverage, where it is needed. Finally we look at a couple of possible solutions for migrating a DAS to LTE with 2x2 MIMO, with one option simply doubling up on existing infrastructure and a more novel approach using CAT5/6 cabling to carry the DAS signals.

2 This document is designed to highlight the challenges involved in designing a DAS to support the massive data demands generated by the proliferation of smartphones and the like, together with applications such as video streaming and multimedia gaming. It is not the objective to propose any solutions but hopefully to stimulate discussion. Exponential growth in data consumption Over the period of the last three years to 2010, the volume of data being consumed over mobile networks has almost tripled year on year. In 2010, according to Cisco, total global mobile data traffic was in excess of 230 petabytes per month (1 petabyte = 1,000, 000 gigabytes). This is over three times greater than total global internet usage in the whole of the year Whilst this rate of growth is forecast to level out during 2011, Cisco has forecast that by 2015 we will see a 26 fold increase in 2010 rates, with monthly usage of 6.3 exabytes per month (1 exabyte = 1,000 petabytes). Please see figure 1 below. Moreover, Alcatel Lucent has forecast a 16-fold increase in mobile data traffic to 2015 but warned that it could grow as high as 40 times today s levels [2]. Terabytes per Month 92% CAGR ,000,000 6,000, EB 5,000,000 4,000,000 3,000,000 2,000,000 1,000, EB 2.2 EB 1.2 EB 0.24 EB 0.6 EB Source: Cisco VNI Mobile, 2011 Figure 1: Cisco Forecasts 6.3 Exabytes (6,300,000 Terabytes) per Month of Mobile Data Traffic by 2015 This description of the growth in data rate consumption includes some new terminology used to describe the vast quantities of data under discussion. The chart opposite shows the values of these new terms, such as petabytes and exabytes relative to the more recognisable figures such as gigabytes. Exabyte 1,000,000,000,000,000,000 Petabyte 1,000,000,000,000,000 Terabyte 1,000,000,000,000 Gigabyte 1,000,000,000 Megabyte 1,000,000 Kilobyte 1,000 Copyright: Cellular Asset Management Ltd Page 2

3 Smartphones, Tablet PCs and Data Hungry Applications The general pattern of accelerating growth in usage of advanced data services is linked to a strong uptake in the usage of smartphones and other high end devices such as Tablet PCs and mobile gaming consoles. Smartphones, running applications such as streaming video and interactive gaming are extremely data hungry. In 2010, the typical smartphone generated 24 times more mobile data traffic than a basic-feature cell phone. Cisco VNI To make matters worse (for the network designer) the iphone and the Android based devices will consume 5 to 10 times as much data as a regular smartphone. Typically a high end smartphone will generate around 79MB per month compared with 3.3MB per month for a basic feature set phone. The table below gives an idea of the levels of traffic generated by different device types. Device type Basic mobile phone Smartphone Handheld gaming console Tablet PC Laptop Traffic Generated cf. Basic Mobile Phone x1 x24 x60 x122 x515 Table 1: Figures Courtesy Cisco VNI 2011 Impact of smartphones from the Mobile Operator s perspective Figures collated and released by the Global Mobile Suppliers Association (GSA) show a substantial growth in revenue throughout 2010 which has been driven by the success of the smartphone throughout Europe, the USA and Asia Pacific. Vodafone UK: 2010 data revenue growth up 30%; driven by smartphone success Vodafone Italy: 2010 data revenue growth up 22% ; smartphone sales 50% of total handset sales AT&T USA: 2010 data revenue growth up 27%; 7.4 million device sales; 4.1 million iphone sales in 2010 PCCW Asia: >80% of new subscribers are smartphone users; 3G data revenue grew by 156% in H Copyright: Cellular Asset Management Ltd Page 3

4 This phenomenal growth in smartphone adoption and the exponential increase in data usage is further borne out by the following figures and predictions: Google state that 300,000 Android phones are activated worldwide daily. The ITU estimates that the global number of smartphones is expected to quadruple from today's (2010) estimate of 200 million handsets to almost 1 billion by Figure 2: Courtesy Global Mobile Suppliers Association According to Informa Telecoms & Media, whilst smartphone penetration currently runs at just 13%, this accounts for 65% of all mobile cellular traffic worldwide. This usage figure is set to increase exponentially over the next five years with the average traffic per smartphone user increasing by 700% by In addition to the success of the smartphone, there are ranges of other, data hungry devices that have recently emerged on the scene and are being adopted by the consumer at a rate: Worldwide sales of media tablets such as the ipad will reach 19.5 million by the end of 2010 and exceed 54 million in Gartner. Shipments of mobile broadband-enabled consumer products, including e-book readers, mobile digital cameras, camcorders, personal media players and mobile gaming devices will increase 55-fold between 2008 and 2014 with total shipments reaching 58 million units per year in ABI Research Given that a tablet PC can generate about five times as much data as a high end smartphone, the potential data usage of a combination of all these devices is beyond any figure that the original mobile networks were designed to handle. Copyright: Cellular Asset Management Ltd Page 4

5 Predictions on Future Demand for Data on In-building Systems Using these figures as a guideline we can model the potential impact on an in-building DAS of the rapidly increasing demand for data due to: The level of penetration (market share) of smartphones increasing from 13% currently to 50% and beyond by 2015 A seven fold increase in traffic per smartphone: Cisco VNI In predicting the demand on an in-building network we make the following assumptions: 1. In an in-building scenario we assume the majority of the traffic will come from mobile phones. We do not include laptops or other devices. (smartphone traffic + basic phone traffic = composite traffic). 2. There will be no significant increase in the number of handsets within a given in-building scenario as we assume the building population will not change significantly over time. 3. Although the DAS for each individual building will experience different traffic changes over time, we can assume a prediction for a generic scenario such as a shopping centre. Tables 2 and 3 show the predicted traffic levels as described above per device: Table 2: Current traffic levels (MB per month) Traffic per Month Penetration % Traffic x Penetration Basic Phone % Smart Phone % Composite Traffic Table 3: Predicted traffic levels in 2015 (MB per month) Traffic per Month Penetration % Traffic x Penetration Basic Phone % 1.65 Smart Phone % Composite Traffic Combining the figures for increase in penetration of smartphones with the seven fold increase in data demand from these devices, we can see from the tables above that in-building traffic per device is predicted to increase from 13.2 to MB per month by 2015, more than a doubling of data year on year. Copyright: Cellular Asset Management Ltd Page 5

6 In designing an in-building network to deliver these volumes of data there are a number of options available to us: Deploying HSPA+ and LTE technology within buildings to provide high throughput, low latency networks. MIMO antenna systems are an integral part of LTE and HSPA+ technologies and may be used to improve performance, by improving the quality of the radio link, and/or increasing data throughput, under given conditions. Small cell architectures can be used to increase the capacity of a network by delivering the data locally to a smaller number of users. These options will be discussed in the following sections. Copyright: Cellular Asset Management Ltd Page 6

7 Comparative Performance of Cellular Technologies: HSPA, HSPA+ and LTE As the demand for data increases we must consider the technologies being used (within the inbuilding system). Although there are more criteria than just data rates to consider when deciding on a cellular technology, it is one of the most important and we therefore present a comparison of HSPA, HSPA+ and LTE data rates. HSPA and HSPA+ are well established technologies, with hundreds of networks deployed globally. LTE rollouts began late 2010 and in-building LTE is still in the early stages. LTE-Advanced is still in development. (Performance figures quoted in this section are, in the large part, peak data rates, from which we can calculate throughput rates from on-site experience. Throughput figures are quoted where available.) HSPA has been launched by over 99% of WCDMA operators globally: 35% of HSPA networks 30% of HSPA networks 8% of HSPA networks support up to 3.6 Mbps peak DL support up to 7.2 Mbps peak DL support up to 14.4 Mbps peak DL HSPA+ has been deployed in stages, as the technology has evolved. The evolution of HSPA+ technologies can be seen from the data below. HSPA+ using 64QAM, HSPA+ using 16QAM with 2x2 MIMO HSPA+ using 64QAM and 2 x 5Mhz carrier HSPA+ using 16QAM HSPA+ using multicarrier on the uplink supports up to 21 Mbps peak DL supports up to 28 Mbps peak DL supports up to 42 Mbps peak DL supports up to 11.5 Mbps peak UL supports up to 23 Mbps peak UL Further development of HSPA technologies within Release 9 and 10 aims at the following downlink rates: Rel 9 HSPA+ combines multicarrier and MIMO in 10 MHz bandwidth for 84 Mbps peak downlink HSPA+ beyond Release 9 should lead to peak downlink data speeds exceeding 100 Mbps Copyright: Cellular Asset Management Ltd Page 7

8 LTE technology was first rolled out in In-building throughput figures are scarce at this time. The number of commercial networks launched to date is still quite low and actual throughput figures are hard to come by. The peak data rates for LTE are as follows: Peak downlink speeds (64QAM) - Peak uplink speeds supports up to 100Mbps (SISO) supports up to 172Mbps (2x2 MIMO) supports up to 326Mbps (4x4 MIMO) supports up to 50Mbps (QPSK) supports up to 57Mbps (16QAM) supports up to 86Mbps (64QAM) HSPA Current Implementation Downlink Uplink Peak Network Speed Peak And/Or Typical User Rate Peak Network Speed 7.2 Mbps 5.76 Mbps Peak And/Or Typical User Rate HSPA 14.4 Mbps 5.76 Mbps HSPA+ (DL 64 QAM, UL 16 QAM) HSPA+ (2X2 MIMO, DL 16 QAM, UL 16 QAM) HSPA+ (2X2 MIMO, DL 16 QAM, UL 16 QAM) 21.6 Mbps 1.5 Mbps to 7 Mbps 13 Mbps peak 11.5 Mbps 1 Mbps to 4 Mbps 28 Mbps 11.5 Mbps > 3 Mbps typical expected 42 Mbps 11.5 Mbps LTE (2X2 MIMO) 173 Mbps 4 Mbps to Mbps Mbps (in 2 x 20 MHz) LTE (2X4 MIMO) 326 Mbps 86 Mbps Table 2: Comparison of Peak Data Rates: Throughput Figures Shown Where Available. Data courtesy HSPA to LTE Advanced Rysavy Research MIMO technology is discussed in detail in the next section. Copyright: Cellular Asset Management Ltd Page 8

9 MIMO Technologies This paper is addresses the challenges of rolling out in-building LTE networks. MIMO technology is a fundamental part of LTE, impacting the amount of work and the costs involved in a rollout more than any other single item. We have therefore provided a description of MIMO concepts, terminology and modes of operation as they relate to LTE. MIMO is considered essential for LTE, to maximize system capacity and provide high data rates. Both 2x2 and 4x4 designs are being considered although only 2x2 configurations are being deployed at this time. [5] LTE systems specify three types of antenna techniques; Diversity, Beamforming and MIMO Fig 3: Typical Configurations for Multiple Antenna Systems Antenna diversity can include transmit diversity or Multiple-In-Single-Out (MISO) and receive diversity or Single-In-Multiple-Out (SIMO) configurations: MISO (transmit diversity), uses two or more transmit antennas and a single receive antenna. The same data is sent from both transmitting antennas simultaneously, but coded in such a way that the receiver can identify the data from each transmitting antenna. This technique can make the signal more resistant to fading and is used to improve performance in poor coverage areas. Copyright: Cellular Asset Management Ltd Page 9

10 SIMO (receive diversity) uses one transmit antenna and two or more receive antennas. Only one data stream is transmitted across the path and spatial diversity at the receive end can be used to improve SNR under poor channel conditions. Transmit Beamforming is a technique whereby multiple data streams are transmitted over multiple transmit antennas, and with the help of feedback from the receiver (Channel Quality Information CQI), the relative phase of the transmitted signals can be adjusted such that they will combine constructively at the receiver to focus the RF beam on that device. Transmit Beamforming can be used to improve signal reception and increase the range to a particular receiving device. MIMO (Multiple-In-Multiple-Out) makes use of two or more transmit antennas and two or more receive antennas. Depending on the way MIMO is implemented, multiple antenna configurations can be used to generate higher throughput (spatial multiplexing) or to provide a more reliable link (diversity techniques). Spatial multiplexing is used to increase link capacity. The information to be transmitted is divided into independent data streams and each stream is sent simultaneously from a separate antenna (multiple spatial streams). If we have N transmit antennas then we must also have N receive antennas. If the resultant data streams are sufficiently uncorrelated to be distinguishable from one another, then the total throughput of the link will be N times the single data stream. Spatial diversity can be used to increase the range and/or reliability of a link. The same data is transmitted simultaneously over multiple independent fading signal paths and by making use of the low probability of these signal paths experiencing deep fades at the same time, the incoming signals can be combined to increase SNR, hence improving link reliability and range. For effective diversity, the antennas at the both the transmitter and the receiver must be placed ½ wavelength apart. Single User MIMO (SU-MIMO) is commonly used in LTE systems to increase the data rate to one user in good radio conditions. The most common downlink configuration for LTE is 2x2 SU-MIMO using spatial multiplexing. (see Fig 4). Multi User MIMO (MU-MIMO). Consider two data streams, each stream originating from a different user device (see Fig 4). MU-MIMO relies on the fact that the spatial separation between the user devices is sufficient that the information arriving at the receive antennas will have uncorrelated paths. This maximises the potential capacity gain at the receiver (the enode via DAS antenna). One of the design motivations of the LTE standard is to keep the terminal or mobile device cost low. Therefore in order to minimise actual transmit antennas on the mobile device, multiple user MIMO (MU-MIMO) is being considered as an attractive option. Copyright: Cellular Asset Management Ltd Page 10

11 Fig 4: SU-MIMO and MU-MIMO configuration To summarise the above, MIMO is a method of using more than one antenna at the transmitter and receiver to improve communications performance. MIMO has the potential either to increase the capacity of networks or to enlarge the area of a given cell without the need for additional spectrum. Copyright: Cellular Asset Management Ltd Page 11

12 Correlation in MIMO Channels For MIMO to be effective in achieving its objectives of increased range and capacity, the environment in which it is deployed must provide sufficient multi-path (reflected waves). This is referred to as non-line-of-sight (NLOS) transmission which typically occurs in an indoor environment. In this so called rich scattering environment, the transmitted signals bounce off objects such as walls, such that they are received with distinctly different profiles at the receive antennas; i.e. the signals are easily distinguishable from one another. In mathematical terms, the signals are decorrelated at the receiver. Conversely, in an environment with purely line-of-sight LOS characteristics. there is one predominant signal arriving at the receiver. The advantages of MIMO cannot be as easily realised as the signals are no longer de-correlated. Further description is beyond the scope of this document; however more detail is available on request from CAM. MIMO is a crucial technology for improving in-building cellular coverage. In a rich scattering environment with a high signal to noise ratio, a MIMO system can deliver between 70% to 100% throughput and capacity gains over a single input-single output (SISO) deployment. The rich scattering environment describes most in-building environments and in-building distributed antenna systems (DASs) can provide high signal quality. (ADC June 2010) A challenge for radio planners is leveraging the maximum performance from MIMO systems, this will require in-building systems designed to provide a sufficiently multi-path rich environment while still achieving a high signal to noise ratio. Copyright: Cellular Asset Management Ltd Page 12

13 Challenges for In-building Solutions Thus far in this document we have highlighted the soaring increases in data consumption mainly due to smartphones using data hungry multimedia applications. Predictions for data consumption going forward show more than a doubling of traffic year-on-year from 2011 to This raises the question: how long can the existing 2G/3G in-building DASs cope with the data demands upon them and what would be an appropriate upgrade path to the next generation of networks? How long can an existing DAS support the increasing traffic? In order to estimate how long an existing DAS can support the increasing traffic levels we must make a couple of assumptions: For sites that can split into smaller cells the capacity of the site may be doubled for a doubling of cells. Network support for higher HSPA+ without MIMO will also lift capacity by a factor of two As each of these changes doubles capacity of the site we can see that the existing DAS will be able to support traffic growth for another couple of years within any particular building before MIMO becomes necessary. Added to this is the fact that neither MIMO nor Small Cell topologies will be added as a network wide upgrade, but will be deployed in localised areas only. The network upgrades can be performed gradually over time, spreading both the costs and the risks as we learn from each stage of an upgrade. What Options are Available for Upgrading an Existing In-building DAS? Reducing cell size by sectorisation or using small cells. Large buildings can be divided into smaller cells (or sectors), reducing the number of users per cell (or sector), thereby increasing capacity. The disadvantages are that there are physical limitations to how small cells can be made; smaller cells may mean more cells which in turn require more Node-Bs, which require more space and more power. Re-cabling of the system each time a small cell is added can be expensive. Increasing data rates with MIMO. This has the advantage that capacity can be increased without using more spectrum. This option could prove expensive if cabling had to be doubled up; however, there are options available for running multiple antennas over one cable, or over an Ethernet link. Deploying LTE to specific areas within the building. This is undoubtedly the way LTE will be deployed for the reasons given earlier i.e. capacity is only delivered where it is needed. Any upgrade to LTE technology will follow this upgrade path for reasons of cost and efficiency. The advantages of MIMO are that capacity can be increased without using additional spectrum. The main disadvantage as mentioned above is doubling up on cabling to the multiple antennas. Copyright: Cellular Asset Management Ltd Page 13

14 What Options are Available for Deploying a New In-building DAS? It is a fact that GSM/UMTS will comprise the overwhelming majority of subscribers over the next five to ten years, even as new wireless technologies are adopted. Therefore, even in the light of large increases in data demand, a new DAS deployment would most likely still be based on a building-wide 2G/3G network with smaller areas of high capacity LTE networks, only where the data demand is required. The LTE sections of the network would be similar to the upgrade options given in the previous section. Estimated costs from CAM, for a new DAS installation comprising materials described below, are as follows: 20 antennas 700m co-axial cable 10 splitters 10 couplers Costs: 1. 2G / 3G / 4G SISO System: 22,000 to design and install 2. 2G / 3G / 4G 2 x 2 MIMO System: 32,000 to design and install 3. 2G / 3G / 4G 4 x 4 MIMO System: 46,000 to design and install Figures are based on the fact that the materials are doubled in each case but the labour required for each installation does not double. As a percentage, a 2 x 2 system would be 45% more expensive to install and a 4 x 4 system 109% more expensive. These costs however would only be applicable if we were to deploy MIMO over an equivalent area to the SISO installation. As we have seen in this document, this rollout scenario may not be the most suitable, or the most cost effective. To deliver pools of high capacity, using MIMO, only where it is needed would probably cost more from the point of view of planning and site surveys but will ultimately be cheaper than deploying MIMO throughout the building. This issue is open to discussion. Copyright: Cellular Asset Management Ltd Page 14

15 A Novel Approach to Deploying In-building LTE Coverage: (Cellular-over-LAN) In previous sections we have discussed the advantages and disadvantages of deploying MIMO technologies for in-building networks. One of the main disadvantages is the cost of running multiple cables to the multiple antennas in a MIMO system. There are a few options whereby multiple antennas can be fed from a single feeder. One option involves feeding the antennas via the existing CAT5/6 cabling within the building. This solution, called Mobile Access VE is designed to deliver in-building LTE cellular services over an existing CAT 5/6 LAN infrastructure, while maintaining full Ethernet and wireless LAN capabilities. The vendor claims the following performance figures and facilities: Extends carrier-grade, 5-bar coverage for 2G, 3G, 4G services with MIMO Reduces installation time by half, as compared with conventional solutions transparently coexists alongside the LAN without impacting LAN performance Supports connectivity to any type of operator RF capacity source Offers proactive end-to-end network monitoring Plug-and-play design scales cost-effectively, allowing customers to choose where new services are activated Results from an actual Mobile Access VE installation give throughput figures for an indoor LTE deployment: -70dBm coverage was tested in 90% of the building, following MobileAccessVE deployment Each VE Pod covered 10,000 square feet. Spatial multiplexed 2x2 MIMO and 64QAM was verified using the LTE LG USB dongle The measured data throughput at MIMO configuration was: 15 Mbps for UL (uplink) data speed 40 Mbps for DL (downlink) data speed SISO performance equivalents offer less than 35% of MIMO throughput (15Mbps UL, 25Mbps DL) ( ) This solution provides an advantage in its quick and easy installation times and MIMO support at 4G, without impacting on the existing LAN performance. MobileAccess VE is also the first cellular solution validated with the Cisco Unified Wireless Network. More detail is available on request from CAM. Copyright: Cellular Asset Management Ltd Page 15

16 LTE Femtocells A Femtocell is a small base station, designed to be deployed within home or small business premises to provide enhanced coverage. The coverage and capacity made available by using the small cell approach within buildings is well suited to LTE deployment. LTE Femtocells are supported within 3GPP as early as Release 8 (2008) and are identified as Home enode-bs (HeNB). However, unlike the 3G Femtocell, there is currently no defined architectural standard in place. The level of interest from operators is driving the Femtocell ecosystem forward at a pace. Enterprise Femtocells that could provide coverage in large buildings are now in the pipeline, supporting femto-femto handovers. Cellular Asset Management will be happy to discuss the potential of Femtocells upon request. Conclusions The purpose of this document has been to promote discussion on the best way to serve the soaring levels of data demand expected over the next few years, using an in-building DAS system and new technologies such as LTE. The main points are: Smartphone devices are expected to more than double the traffic demanded of in-building systems year on year from 2010 to To upgrade an existing in-building DAS for the increase in data there are two main options: reduce the size of each cell and increase the data rates supported by the DAS. To support the data rates of HSPA+ and LTE the in-building systems will need to be upgraded for MIMO antenna technology. Femtocell technology for LTE could provide small cell capacity solutions, although it is still in development. Alternative distribution systems such as MobileAccess VE could provide a quick and simpler upgrade path with extra capacity being added to areas as the traffic increases. Do we upgrade now? In the next two years? More likely we will see networks upgrade gradually, providing extra capacity only in localised areas where it is required and leaving the 2G/3G DAS installations to handle the wider area coverage. Copyright: Cellular Asset Management Ltd Page 16

17 References 1. Cisco Visual Networking Index: Global Mobile Data: Traffic Forecast Update, Mobile Broadband Growth Report: Published by the Global mobile Suppliers Association (GSA) Feb The IET - Engineering and Technology Magazine: Article: Will mobile networks be ready for the 4G data deluge? 4. Ofcom -The Communications Market 2010 (August) 5. Agilent Technologies &lc=eng&cc=GB LTE implementation of MIMO 6. HSPA to LTE Advanced, Rysavy Research Sept NEC Shows How Small Cell LTE Deployment is Smarter Way to Sustainable Future: Mobile Broadband Mobile World Congress Feb Copyright: Cellular Asset Management Ltd Page 17