LMDS: Broadband Out of Thin Air
LMDS may be the key to delivering broadband multimedia applications to millions of customers worldwide over the air.

Thinking of broadband access for the last-mile—now being recognized as the first-mile—everyone talks about optical fibre or ADSLs. However, frustrated by the complexities, cost and time involved in digging and laying optical fibre—or implementing DSL, with only 1.5 Mbps to offer, on incumbent's copper infrastructure—one would certainly like to look for an easy way out. And that is offered by the air. Air space represents higher freedom and the ability to move fast. That has made wireless the fastest transmission medium to deploy, and generally inexpensive too. Microwave technology has truly come to the rescue there.

George Gilder, in his latest book "Telecosm", says, "Above 14 GHz—at wavelengths running from millimeters of microwaves down to the nanometers of visible light—is the new frontier of the millenium, empires of air and fibre that command some fifty thousand times more communications potential than all the lower frequencies we now use put together. A purely human invention, they provide the key arena of economic activity for the new century." Rightly, to be able to exploit the freedom associated with air, one looks to microwave technologies.

The First-Mile: Missing Gigabit Link

Advances in fibre technology have extended the capacity of WANs to terabits per second—i.e. trillions of bits per second. With gigabit computers and gigabit Ethernets, LANs have also evolved to Gbps. However, to connect the two is still the biggest challenge: to help solve the customer's nightmare of crawling at kilobits speed, which a typical Internet user faces, between these gigabit worlds.

The LMDS Way

Local Multipoint Distribution Service (LMDS) is an ideal solution for bringing high-bandwidth services to homes and offices within the last-mile—an area where cable or optical fibre may not be convenient or economical. Having architectural similarities with cellular networks, LMDS is a fixed (non-mobile) point-to-multipoint wireless access technology that typically operates in the 28 GHz band and offers Line-of-Sight (LoS) coverage up to 3-5 km. Depending on the local licensing regulations in a country, such broadband wireless systems may operate anywhere from 2 to 42 GHz.

Though data transfer rates for LMDS can reach 1.5 to 2 Gbps, in reality it is designed to deliver data at speeds between 64 Kbps to 155 Mbps (as against 9.6 Kbps offered by 2G cellular networks like GSM), a more realistic downstream average being around 38 Mbps.

Vendors are taking steps to meet the fast increasing demand for capacity. For instance, Giganet has expanded its 115 Mbps products to handle higher data rates and has introduced upgrades to its FibreAir product to deliver 311 and 622 Mbps data rates using the same amount of spectrum. In the US, operators could offer as much as 622 Mbps using the typical 50 MHz wide channel. Giganet also offers ability to interface with various transport protocols, including IP, ATM and Sonet, the solutions being available in a range of frequencies.

At such speeds, LMDS may be the key to bringing multimedia data—supporting voice connections, the Internet, videoconferencing, interactive gaming, video streaming and other high-speed data applications—to millions of customers worldwide over the air.

As with other wireless networks, LMDS technology offers the advantage that it can be deployed quickly and relatively inexpensively. New market entrants who do not have an existing network—like incumbent's copper wires or fibres—can rapidly build an advanced wireless network and start competing. LMDS is also attractive to incumbent operators who need to complement or expand existing networks. For example, operators who are setting up a service primarily based on DSLs, but who want their service to be universally available, could use it to fill in the gaps in their coverage. And while cable modems are making inroads into the residential (and home-office markets), the business market is the niche for LMDS.

LMDS operates in a large—previously unallocated—expanse of the radio spectrum, thus offering a huge bandwidth opportunity, hitherto unexploited. In the US, the Federal Communications Commission (FCC) auctioned to LMDS operators a total bandwidth of about 1.3 GHz in the 'millimeter' waveband at frequencies of about 28 GHz. Canada has 3 GHz of spectrum set aside for local multipoint communications systems (digital cellular phone systems operate at about 800 or 900 MHz with a typical bandwidth allocation of 30 MHz or less).

Recognizing LMDS as a means of beaming data and voice over short distances to a switching office, McCaw's Nextlink, in mid-1999, paid nearly $700 million to purchase LMDS licences and the spectrum with aim to provide fixed wireless coverage for 95 percent of the US population.

How LMDS Works

Sending digital signals of the required complexity at 28 GHz is made possible by recent advances in technologies such as Digital Signal Processors (DSPs), advanced modulation systems and Gallium Arsenide (GaAs) integrated circuits, which are cheaper and function much better than silicon ones at these high frequencies.

Unlike a cellular mobile phone network, in which a user can move one cell to another, the transceiver of an LMDS customer has a fixed location and remains within the same cell. Normally the customers' antennas are located on rooftops, to get a good LoS to the hub transceiver.

It Has Limitations Too

Like in other microwave applications, LMDS cell size too is limited by "rain fade", i.e. distortions of the signal caused by raindrops scattering and absorption of the waves. Also, walls, hills and even leafy trees block, reflect and distort the signal, creating significant shadow areas for a single transmitter. Some operators may serve a cell with several transmitters to increase coverage; most prefer one transmitter per cell, sited to target as many users as possible.

Positioning: The Marketing Advantage

The fast deployment helps to capture a customer fast. However, another advantage—faced with a high churn of customers—of the technology is the ability to move around the hub equipment to different customer locations. It is a distinct advantage against the networks of wires, cables, and fibres. Also, LMDS systems send data using asynchronous transfer mode, which allows a mixture of data types to be interleaved. Thus, a high-quality voice service can run concurrently over the same data stream as Internet, data and video applications. LMDS can be positioned as a versatile, cost-effective option for both providers and users of broadband services, using the rapid and inexpensive deployment.

Initially, LMDS operators target SMEs in densely populated, urban areas because of the technological requirement of LoS between the hub base station and the buildings served and the signal propagation range of one to three kilometers.

There are 11 significant LMDS operators in US—the biggest ones being Advanced Radio Telecom (ART), NextLink Communications, Teligent, and Winstar. NextLink, founded by Craig McCaw in 1994, holds the largest number of 28 GHz LMDS licences there. The company has launched commercial services in five of its markets and expects to be operational in 25 markets by the end of this year. Earlier this year, NextLink also bought national ISP Concentric Networks, which enables NextLink to expand its DSL, virtual private network and Web-hosting services.

According to the Strategis Group, by year 2003 LMDS network coverage will be close to 20 percent of businesses as against 5 percent presently. According to IGI Consulting, at the end of 2000 there will be 26,000 LMDS business users, growing to 5,10,000 by 2003.

Action in Asia Pacific

Hong Kong was one of the firsts to issue LMDS licences. The Infocomm Development Authority (IDA) of Singapore approved three organizations to conduct LMDS trials in early 2000. For example, one of them, Pacific Internet's trial will include Broadband Internet (i.e. over 2 Mbps), Video-on-Demand, Voice-over-IP, high-speed digital data transmission, as well as conventional voice calls. It will thus explore opportunities in providing broadband data access to selected corporate and residential customers. It will use ultra high frequency microwave in the 25-31 GHz frequency range to send and receive two-way broadband signals through the base station installations atop buildings. Pacific Internet considers the advantages of LMDS as greater bandwidth than radio, TV and cellular combined, and a low start-up cost relative to costs incurred in installing broadband wireline networks. In Singapore, the heavy rain interference with signals may limit the distance between cells to 1.5 km.

Now in India

In India too, operators like Gateway Systems are offering LMDS solution. Initial focus is on business customers mainly in large cities like Mumbai, Pune, Delhi, Bangalore, etc., which have concentration of offices or apartments located in high-rise buildings.

The day is not far when the thin air will help deliver to us the broadband applications running all the way on the fat fibre-optic pipes, putting George Gilder's empires of air and fibre at mankind's service.

Niraj K Gupta, from my cell, Voice & Data, December 2000.