Multitenant units (MTUs) or (MDUs for multi-tenant units) offer a high concentration of potential broadband-access customers whether they are residential or commercial, so carriers are increasingly looking at how to better address telecommunications services within the multitenant building.

In the context of WiMAX networks promised to be built in regions with high density populations like China where potential users are located in huge multi dwelling units, the business case for WiMAX looks promising as long as there is an economical way to distribute the signal among end users in the building to avoid multiple CPE equipment and installation costs.

Cable addresses the residential market and SOHO applications well and will be a competitor in the MDU market. However, unless you are a cable operator, cable is not a technology that can be used successfully for in-building broadband service distribution.

Typically, a carrier would address the larger end of the SME spectrum and power users with fractional, single or bundled E1/T1s, though the majority of the SME market will likely need or have a connection smaller than an E1/T1 today

Once at the building via the broadband wireless link such as WiMAX, the carrier has three ways of addressing the customers in that building:

• The provider could place a fixed-wireless, network-termination (NT) device in one or more of the tenant suites and connect all of the NTs to a single radio-termination (RT) device on the roof of the building. It has the flexibility to use NTs with subscriber ports that fit the customer’s specific needs. For example, a customer might want a single leased line or a combination of leased line and Ethernet service. The carrier also can offer frame relay or ATM services all over the radio link simply by choosing an appropriate network termination.

• The carrier has the flexibility to collocate a 2 or layer 3 switch with the fixed-wireless network termination and distribute services using IP. This option enables the carrier to use a cable from the switch to the customer and simply provide an Ethernet port which can be used for Internet access, e-mail and VPN services.

The wiring is done using Category 5 or 6 copper twisted-pair cable, which in itself, is not expensive. If the carrier is faced with a building with limited or no space left in the cable riser, it will have to pull cable from the switch to the customer and may be required to X-ray, core concrete and install a fire-stop at each floor penetration. This work also may require a permit and inspection, which can delay service delivery. In this case, the wiring installation cost may warrant consideration of a service distribution that makes use of existing in-building wiring instead.

• The carrier can also co-locate a DSL access concentrator (DSLAM) in the building. DSL technology is capable of riding on existing copper twisted pairs, installed for telephony services when the building was built. Some DSL access technologies can make use of in-service copper loops by running the DSL at a frequency band which is not a disturber to plain old telephone service (POTS).

In cases other than large multi-dwelling residential buildings, a DSLAM that was designed for deployment in the neighborhood central office (CO) is not appropriate since it was designed to service hundreds of customers.

The large CO DSLAMs that aggregate bandwidth capabilities may, indeed, be substantially more than the wireless link. However, there are smaller multitenant DSLAMs available, which can support as few as eight customers, scaling up to a mid-size DSLAM with 100 or more subscriber ports.

An in-building distribution network can connect through a router to a service provider via some high-speed network. Such buildings may be apartments (multi-dwelling units or MDUs), office buildings (multi-tenant units or MTUs), hotels, and so on. Collectively, network designers refer to these buildings as MXUs. The first mile contains a mix of media: twisted-pair copper wire, fiber optics, coaxial cable, and (of course) air.

BROADBAND OVER POWER LINES

This technology enables the delivery of a suite of Internet Protocol (IP) based services using their existing power distribution infrastructure.  It enables any power line landlord to use their existing medium and low voltage power lines as high speed data pipelines. The Ambient equipment is easily and safely installed on live lines by standard utility crews or electricians (for Access or In-building use, respectively)

Powerline Communications (PLC) LANs Powerline communications (PLC) uses electrical wiring within a building to distribute data and voice services. Each A/C
outlet becomes a LAN drop, enabling Ethernet-enabled devices, such as PCs, VoIP phones, and servers, to connect to the network.

Most PLC LANs are based on the HomePlug 1.0 standard, which uses orthogonal frequency division multiplexing (OFDM) as the basic data transmission technique. OFDM manages and mitigates the amount of disturbance present at any given time in the powerlines, which is critical to ensuring the integrity of the data transmission. Like WLAN, PLC uses
OFDM to counter sources of interference, such as fluorescent and halogen lamps, switching power supplies, dimmer switches, and amateur band radio transmitters, which can cause significant bit errors in data transmissions.

Since PLC uses a facility’s existing electrical wiring as the data transmission medium, the upfront capital expenditures associated with installing copper or fiber is not a consideration. Most installations are completed in a few hours to a few days, and the size and amount of equipment required for installation is minimal. Further, since no new wiring is needed, the disruption to day-to-day operations often impacting wired installations will largely be avoided with
a PLC deployment.

The advantage of this technology is its low cost. Any power line landlord can use their existing power lines as high speed data pipelines to deliver broadband for high speed data, Voice over Internet Protocol (VoIP) and landlord specific applications.

In-Building coverage of Wireless Networks

Nearly three-fourth of the calls originating indoors is initiated on the mobile phone and a majority of the calls initiated on the mobile phone are from indoors. Steel, concrete and other materials used in building installations block and bounce RF signals, leading to inconsistent signal reception.

The challenge of providing an uninterrupted extension of public wireless network indoors is driving operators, network planners and real-estate stakeholders towards systematic design and implementation of in-building signal distribution technologies. This article discusses the following signal distribution technologies:

• Distributed Antenna System
• Femtocell
• Picocell
• Wi-Fi

Distributed Antenna System (DAS)
DAS distributes the transmitted power along a network of low-power antenna elements. DAS avoids wastage of power in overcoming penetration and shadowing losses and minimizes fading losses by providing better line of sight coverage. DAS has been successfully employed to serve diverse networks such as Cellular, PCS and Public Safety Wireless.
The DAS can be active or passive, depending on the elements used.

Passive DAS
Passive DAS utilizes splitters and feeders. Passive DAS can also be implemented by deploying leaky feeder, a special type of coaxial cable where the screen is slotted to allow radiation along the cable length. Most commonly deployed in sub-ways, leaky feeder can provide uninterrupted coverage if implemented correctly. Passive DAS is gradually making way for active DAS, as passive devices cannot offer the flexibility required to provide an assured quality of service in complex installations and lack support for the numerous burgeoning public wireless network access protocols.

Active DAS
Active DAS utilizes repeater amplifiers. Active DAS takes its input in the form of RF signal from source such as a BTS. Active DAS supports Ethernet-LAN class cabling, thereby simplifying installation. It is scalable, ranging from single frequency/operator installations to multi-frequency/operator installations and can be arranged in single or multiple star topologies. A typical active DAS set-up includes the following components:

• Main Hub: Main Hub is directly connected to the RF source (BTS/Repeater) through a CAT5/6 cable. The main Hub acts as the master distributor for the active DAS setup. After converting the incoming RF signal to optical signal, the Main Hub sends it to the Expansion Hubs via fiber optic cable.
• Expansion Hubs: Single or multiple Expansion Hubs are connected to the Main Hub through single or multi-mode fiber. Multi-mode fiber requires frequency conversion before RF- to-optic conversion. The Expansion Hub converts the incoming optical signal to an electrical signal and distributes it to all associated Remote Access Units (RAU) via twisted-pair cabling connection.
• RAU/Antennas: RAU/Antennas are present on the edge of the active DAS. They re-convert the incoming electrical signal to RF.

Maximum distances supported by the physical media are six kilometers for single-mode fiber, 1.5 kilometers for multi-mode fiber and 170 meters for CAT5/6 cable. Sophisticated DAS can be managed locally or remotely using SNMP traps.

Cost
The minimum cost of Active DAS ranges from USD $20,000 to $40,000.

Availability
Vendors such as LGC, Andrew, Microlab and others have elaborate active DAS products in place.

Femtocell
Femtocell, also known as home BTS or access point/base station, is ideal for single-family home or multi-dwelling units consisting of up to eight users. Femtocells have the potential to emerge as strong competitors to UMA/SIP based FMC installations. However, Femtocells operate in the same frequencies as the macro BTS cells, thereby posing a formidable challenge for frequency allocation. Femtocell vendors are addressing this issue and some of them have claimed successful results in controlled test environment. Femtocell deployment also requires adjustment at the BSC/RNC levels, as the current generation of BSC/RNCs is not equipped to handle network elements in such high quantities. Other challenges include re-alignment in existing carrier security, network operations and air-interface frameworks. A hybrid approach of accommodating Femtocells in the current licenses/unlicensed landscape involves rolling out UMA compatible Femtocells that can be deployed seamlessly in the existing FMC installations. In this approach, the UMA client functions reside in the Femtocell. The UMA Femtocell manages network authentication, IPSec tunneling, UMA Network Controller discovery and seamless handover between access points.

Cost
It is believed that the optimal cost of a Femtocell should be around USD $250 to make it attractive to the end-buyer.

Availability
Companies such Texas Instruments, picoChip and others have developed chipsets for Femtocells. Kineto Wireless has a roadmap for UMA based Femtocells in place.

Picocell
Picocells provide’s localized coverage for installations with high user density with areas ranging from 2500 to 10000 square feet. Typical installation sites include lecture halls, stadiums and similar locations. Picocells are simple to install and utilize the existing IP infrastructure for backhaul. According to Nortel Networks, its 17-kg Univity eCell picocell can be installed by low-skilled staff in 15 minutes. Picocells are compatible with existing GSM handsets. They provide high data throughput for dense wireless terminals by minimizing the bandwidth shared among wireless users. Important Picocell design consideration issues include number and availability of frequency channels, RF scattering, antenna gain, redundancy and RF link symmetry. The size of the Picocell is governed by maximum transmit power, receiver sensitivity and antenna gain of the Access Point and end user client.

Cost
It is estimated that a Picocell installation catering to around 10 users would need to generate USD 1.5/user/business day to be profitable.

Availability
Significant vendors include AirWalk Communications, Contela, Ericsson, InterWave Communications, ip.access, Nokia, RadioFrame, Siemens and Telos.

Adlane Fellah, MBA, is CEO and founder of Maravedis, a world-leader in market research and analysis, specializing in WiMAX and broadband wireless markets. He is leading industry analyst who authored various landmark reports on WiMAX, broadband wireless and Voice over IP. He is a frequent speaker at leading wireless events and a contributor to various prestigious portals and magazines covering the broadband wireless industry including: Telephony Magazine, WiMAX Trends, WiMAX.com, etc...

He is member of the Program Advisory Board for the World WiMAX conference since 2004 and a member of the Word Communications Association International, and Broadband Wireless Association. Prior to founding Maravedis, he held various positions at Harris Corporation in charge of market intelligence and business development for several product lines.