Indoor Wireless

Indoor Wireless Innovation: Preparing and Deploying Advanced Indoor Coverage End-to-End in Japan

By L. Richards, M. Sharrock, J. Sekine, A. Uchida

What if all indoor traffic were backhauled over IP, every home had its own base

station, and your customers business case suggested that a whole new architecture

approach was the best way to support it? Read on.

Nihon ni yokoso/Welcome to Japan.Mobile telephone usage is higher here than anywhere else in the world, and the millions ofsubscribers demand a quality service wherever they go. Unfortunately for the operator, thesesubscribers generally go to the places hardest to cover with a macrocellular wireless network, due to Tokyos unique topology: high-rise office buildings, subway stations, dense urban streets, shoppingand entertainment areas with irregular busy hours, hundreds of railway lines, and small apartments in large apartment buildings.

Add to this the enormous difficulty and expense of obtaining and building new sites in which toplace macro base stations, and the problem amplifies. Therefore, the operators in Japan want to solvethis problem without adding more traffic on the macro layer. This is why more and more picocellular (ultra-small) BTS solutions are being deployed, including the Alcatel-Lucent 3G picocellularsolution for Softbank.

This high-tech city also has some key advantages that help in solving the problem. The telecomsinfrastructure is first class, thus access to bandwidth for data backhaul is readily available. In addition,high-quality IP access is available in businesses, public places and homes. This is why Alcatel-Lucentis deploying for Softbank a pico solution with native IP connectivity at both the radio networkcontroller (RNC) and Node B a first for the industry. This will allow Softbank to take advantage of existing IP infrastructure including Digital Subscriber line (DSL), to backhaul mobile traffic veryefficiently, and offload the macro network layer. And, of course, improve the customer experience.

Now that Alcatel-Lucent and Softbank are deploying IP backhaul solutions for pico Node Bs, andgaining lots of experience along the way, both companies are ready to deploy Alcatel-Lucent femtobase stations in the home. Softbank can now offload the macro network layer when users are athome, give them high bandwidth and QoS, offer cheap flat-rate pricing plans, and provide fullsupport for all existing terminals in the network all backhauled over existing DSL lines. Quality 3G can now be available in every home.

Supporting native IP backhaul is a big step forward, but is the existing legacy mobile infrastructurethe most efficient way of supporting millions of femto base stations? The business case studiesundertaken by Alcatel-Lucent and Softbank in Japan have shown that there is a better way: a new,flat architecture utilizing the concept of the Base Station Router (BSR).

enriching communications > premier issue > 2007 | http://www.alcatel-lucent.com/enrich 1

Native IP backhaul of 1000s of pico Node BsAt Softbank, the increased demand for improved indoor coverage means that lower-power indoorbase stations in much smaller sizes are being deployed. Deploying hundreds or thousands of smallindoor sites with ATM/TDM1-based leased line backhaul is costly, especially in Japan. Dark fiber mayminimize the leasing cost for the expensive lines, but will still incur cost for initial implementationand construction. To overcome this, there is a need to utilize IP over existing infrastructure such asDSL and FTTx.2 For 3G network operators like Softbank, the solution is IP UTRAN,3 with theintroduction of a native IP pico Node B and IP RNC.

An IP pico Node B can be deployed flexibly in a variety of indoor scenarios. Due to its size andweight, these small-sized base stations can be installed in locations that have stringent siteconstraints. Needing no floor space for installation, pico Node B is suitable for shopping malls,subway stations, office buildings and other public indoor locations. The low output power andoptimized channel capacity is well suited to provide enhanced indoor mobile service.


Figure 1: Pico Node deployment

1 Asynchronous Transfer Mode/Time Division Multiplexing

2 Fiber to the X

3 UMTS Terrestrial Radio Access Network

Alcatel-Lucents solution is a pico Node B and RNC with native termination of IP to accommodatea 3GPP 4-compliant Iub5-over-IP interface. The IP pico solution offers major cost benefits in operatorspending, especially with the flexibility to use a public IP network or even a secure private IPnetwork as backhaul. An IP pico solution enables the operators to install the Node B units either in:

Wide Ethernet service with IPSec tunnels carrying traffic between RNC/SGW and pico Node B;

IP-VPN service carrying traffic between RNC/SGW and pico Node B;

Public IP backbone with IPSec tunnels carrying traffic between IP pico Node B and RNC (withfirewalls protecting private networks).

Achieving and maintaining Quality of Service over IP is one of the greatest concerns in using IP. IPDifferentiated Services code points (DSCP) are used to provide appropriate per-hop QoS handling of IP packets. At Radio Link Setup/Radio Link Reconfiguration, both RNC and Node B select theDSCP based on the requested QoS.

When connected to a public IP network, an IP pico Node B and the centralized functions aresusceptible to attacks, spoofing, data interception and modification. It is critical that these nodes areprotected against any malicious attacks, therefore IPSec tunnels are used for OA&M6 and controlplane signaling to and from the IP pico Node B.

Flexible yet cost-effective configuration and deployment methods are required for operators tomanage such a high volume of units scattered in the network. The greater the number of units, themore configuration work is required by the operator to bring them into service. The IP pico solutionsupports a Plug & Play function. For deployment of IP pico Node B units, an off-line configurationtool is used to enable operators to prepare configuration data for introducing the new Node B intothe network, including securing the connection over the IP backbone. During installation, IP picoNode B units will not themselves require manual configuration on site. Instead, once a unit hasestablished connection to the IP backbone, it autonomously obtains the necessary configuration data from a configuration server.

A base station in the homeAs Japan is the worlds second-largest fixed broadband market, with over 25 million subscribers, it isin a unique position to utilize broadband access at home. Existing fixed/mobile convergence services(e.g. Bluetooth/WiFi) limit the use of existing terminals. Femto base stations have recently received a lot of attention from mobile operators, because they offload the macro network but still use theconventional mobile air interface (GSM, W-CDMA7, CDMA). Therefore, the end user can still useexisting handsets and enjoy maximum 3G throughput by utilizing HSPA8 at the highest bandwidth.


4 3GPP Standards body for GSM and UMTS

5 Interface connecting the RNC with the Node B

6 Operation, Administration and Maintenance

7 Wideband-Code Division Multiple Access

8 High Speed Packet Access

Keeping indoor users off the macro network is a key concern for operators, and a key differentiatorfor femto. Because indoor users are often behind walls with high attenuation (typically 10-20dB),they consume more power from the terminal and the base station, and use up scarce macro base stationradio resources. This leaves less to serve outdoor users, and reduces the overall macrocell capacity and coverage. Covering indoor users with indoor femto base stations is two solutions in one; not onlydoes it provide better coverage and user experience for the indoor user, but it frees up macrocellresources to better serve the outdoor users. It is this double benefit that supports the femto solution.

As licensed frequency spectrum is used in the home, there is a regulatory issue. Under the currenttelecoms law in Japan every BTS, including femto, has to be licensed for installation or removal and critically such installation work has to be carried out by a certified radio engineer. It is mootedthat the regulator in Japan will soon change the law to accommodate self-installed femto basestations. This scenario is being repeated around the world as the social, technological and economicalbenefits of the femto BTS convince national regulators that a change is required. A key reason is thedesire to expand 3G coverage into rural areas that would not otherwise be covered by the operator,which is a major concern for regulators.

Since femto is targeted at the mass market, it has to be installed by an end user, and thus must auto-configure for easy installation at home. However, since it is still a BTS utilizing a licensed frequency,it has to support security, emergency calling, and easy operation and management. For example, theIP backhaul signaling and voice traffic is encrypted in an IPSec tunnel, and a firewall is provided to protect against malicious attacks from within the network. Interference with the macro network is another technical issue to be considered, but the femto is able to monitor the surrounding networkand to select its Primary Scrambling Code and adjust transmit power to avoid interference. Inaddition, power levels are periodically monitored and optimized for maximum coverage and capacity,without interfering with the surrounding network.


Figure 2: The femto concept

Base Station RouterAs so far discussed, it is apparentthat an IP-based access network is the way forward for wirelessnetworks, especially when looking to support millions of femto cells.The question which now needs to be asked is whether the legacy2G/3G infrastructure is the best wayto support this evolution to supportsuch a high number of base stations.

It is important to examine theimplications of the femtocell fornetwork infrastructure, introducesome of the technical challenges,and understand how and why theycould be best met by a Base StationRouter (BSR) solution.

Until recently, few people wouldhave envisioned millions of tiny basestations, each capable of generating

peak traffic bursts of 14 Mbit/s, all connected to a cellular operators network. But this is preciselywhat a femtocell deployment means. And without special counter-measures, an ordinary UMTSnetwork would not be able to cope with such a scenario.

So why not put all the hierarchical complexity in the femto unit itself? For historical reasons, cellularradio access networks are hierarchical in terms of both network topology and protocol architecture.In contrast, the BSR takes a flat approach, collapsing all the hierarchal functions of a radio networkinto a single box (in this case the femto unit in the home). Collapsing the various protocol stacksinto a single node improves round trip delay. Furthermore, connecting directly to the IP network without a hierarchy of intermediate network elements reduces overall network cost and complexity,and eliminates the congestion points found in legacy hierarchical networks.

As a concrete example of this benefit, consider the RNC. An RNC by definition needs to divide its limited processing resources among many base stations. Typically, this means that a single RNCcan only support a few hundred base stations. As a result, without a complex re-design, a massivefemtocell deployment would require thousands of RNCs, making it economically unfeasible. Incontrast, the BSR gets rid of the middleman by implementing its own internal RNC functionality. Inthis way, the BSRs flat IP architecture is precisely what is required to achieve the degree of scalabilityrequired by a massive femtocell deployment.

The more traffic carried through the BSR, the fewer traditional hierarchical 3GPP network elements(RAN9 and Core) will need to be purchased in the future, thus avoiding the cost of wasting thatinvestment when evolving to LTE10/SAE11.


Figure 3: The Base Station Router

9 Radio Access Network

10 Long term evolution

11 System Architecture Evolution

In order to assure seamless interoperability, Alcatel-Lucent has worked closely with operators toensure full support for legacy services, including continuity of service while moving between thefemtocell and macro networks. This combination of forward and backward compatibility means thereis no longer any need for the big bang type of investment required during the transition from 2G to 3G. This means that operators can boldly introduce market offers early that competitors havedifficulty matching in terms of end-user experience, as well as price at the same time as they arelaying the IP Transformation foundation for a long-term, sustainable competitive advantage.

ConclusionOperators need to change in order to take advantage of new technology and, most importantly, to stay ahead of the competition. The time to change to IP-based wireless solutions is now.

The proliferation of IP at the edge of the network with voice-level QoS, in addition to theavailability of native-IP-enabled RNC and Node B infrastructure, mean that IP backhaul is the futureof all macro, pico and even femto base station solutions.

Customers expect to have good quality coverage in the home. If they do, they will use operatorservices more, especially if preferential tariffs can be applied. The femtocell will allow the bestpossible availability of HSPA data bandwidth for the user, and will offload the congested macro layerfor the operator. A win-win solution is just around the corner.

So can the legacy wireless network really support millions of femto connections in its current form? If the answer is yes, it will cost a lot of money and the investment will be for now, not for the future.The business case and the technical study for Base Station Router technology and architecturesupport a new direction, especially when a network needs to support millions of IP-based femtocells.

The only remaining issue for the operator is finding a vendor with the knowledge and experience in more than just wireless solutions. These solutions are no longer just wireless, they are end-to-endsolutions which require key experience in IP, optics, access solutions including xDSL and FTTx, fixed and mobile convergence, and of course radio access.k

Larry Richards is part of the Wireless Solutions team within Customer Solutions for Alcatel-Lucent, based in Tokyo, Japan. Email: [email protected]

Junji Sekine manages the End-to-End Solutions team within Customer Solutions for Alcatel-Lucent, based in Tokyo, Japan. Email: [email protected]

Martin Sharrock is VP of Customer Solutions for Alcatel-Lucent, based in Tokyo, Japan. Email: [email protected]

Atsushi Uchida is part of the End-to-End Solutions team within Customer Solutions for Alcatel-Lucent, based in Tokyo, Japan. Email: [email protected]


Alcatel, Lucent, Alcatel-Lucent and the Alcatel-Lucent logo are trademarks of Alcatel-Lucent. All other trademarks are the property of their respective owners. The information presented is subject to change without notice. Alcatel-Lucent assumes no responsibility for inaccuracies contained herein. 2007 Alcatel-Lucent. All rights reserved.

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