Wireless Options | Wide Area Network Technology Options

George Gilder, a well-known champion of "infinite bandwidth," says the [wireless] spectrum is infinite, ubiquitous, instantaneous, and cornucopian. Current industry trends certainly support his hyperbole. Wireless Internet services, low earth orbit satellite services, Bluetooth, fixed wireless, and many other permutations of communications over the air are providing services that were either not available or prohibitively expensive in the past.

Following are some of the technologies and applications that have the potential to streamline operations or to serve as less-expensive, ersatz landlines.

VSAT and Geosynchronous Satellites

In the 1950s and 1960s, many organizations maintained private, point-to-point networks of terrestrial lines, often with multiple "drop-off points" in more remote areas. It was expensive and arduous to maintain this cobbled together network. For a network manager dealing with locations in the hundreds of thousands, it meant maintaining contacts with many small local exchange carriers (e.g., Bob and Pat's Telephone Company) and a relatively high level of downtime (for specific sites).

As commercial satellites began to be deployed in numbers during the 1970s, the use of VSAT (very small aperture terminals) networks increased significantly. Exhibit 1 shows a simplified diagram of a VSAT network.

Exhibit 1: Typical VSAT Configuration

By using a satellite to transmit all traffic within a large geographic region (e.g., Canada, the United States, and Mexico), the need for terrestrial lines is eliminated except for the backhaul (high-capacity terrestrial circuit from the commercial satellite hub to the organization's headquarters location).

Following are advantages and disadvantages of VSAT systems versus traditional terrestrial networks:

  • Advantages:

    • Less expensive for data communications. Satellite systems become less costly per site as the number of sites increases. The cost differential is most significant in rural areas where terrestrial access lines (e.g., for Frame Relay) are costly.

    • Less expensive for video communications. Terrestrial lines with the bandwidth to support video are expensive (typically requiring a minimum of 384 kbps for good quality). VSAT can deliver one-way video for a fraction of the cost of a terrestrial solution (point-to-point solutions or ATM).

    • Known, reliable technology. VSAT technology has been around for decades, with the dishes progressing from type I to the current type III technology. In many areas of the world, including oil rigs in the ocean, VSAT communications is the only practical alternative. Over time, techniques to optimize common protocols such as TCP/IP over higher delay satellite networks have been developed.

    • Much quicker to deploy. In some remote areas, the local telephone company can take months to install a data circuit. In some cases, the LEC may not be willing to incur the up-front cost. VSAT equipment, on the other hand, can be set up relatively quickly — in a week or two. The only requirements are that electrical power be available and that the satellite be within the VSAT dish line-of-sight (proper angle).

    • Available in remote and underdeveloped areas. VSAT technology functions well in northern Alaska, Pitcairn Island, and Tierra del Fuego.

  • Disadvantages:

    • Only moderately high uptime. Satellite communications cannot provide an extremely high uptime, such as 99.999. Providers such as Hughes will typically quote numbers such as 99.5 to 99.8 percent uptime. Unavoidable events such as extremely heavy rain, sunspots, and even solar transit outage cause the signal to degrade and thus interrupt transmission. In some cases, interference from improperly configured ground stations (bad polarity, for example) from other carriers can weaken the signal.

    • Transmission (propagation) delay. Because the signal must go up 22,300 miles from the VSAT and down the same distance to the hub (ground station), there is a noticeable lag time for interactive systems (0.25 second one way, 0.5 second round trip). This reduces the popularity of VSAT for traditional voice communications, although it can work in a "take your turn Roger over" mode.

    • High initial cost. VSAT equipment will cost an initial $6 to $8K per site, plus any monitoring equipment that the organization chooses to use. Also, satellite contrasts are lengthy, generally five years.

    • Limited uplink bandwidth. While large volumes of data can typically be downloaded from the satellite (e.g., for video), uplink from a single VSAT dish is typically less than 128 kbps.

    • Single point of failure. Satellites have a limited life (a 15-year-old satellite is an antique) and are subject to limited fuel to keep them in proper orbit, electrical breakdowns, meteors, being hit by other satellites, and other sources of destruction. For example, PanAmSat lost its Galaxy-IV satellite in 1998, resulting in widespread loss of paging services across the United States for a few days. To mitigate this risk, organizations can obtain rights to use a backup satellite from their provider. If the primary satellite fails, VSAT dishes must be repositioned to point to the backup satellite. Repositioning can take anywhere from a few days (best case) to several weeks for a large number of sites.

An important economic consideration for an organization with a large VSAT network is hub ownership. Firms with a smaller number of sites typically use their provider's hub and receive all communications via a dedicated leased line from the provider to their headquarters site. However, even at a cost of roughly $1 million, at some point hub ownership becomes a viable option. Only organizations committed to VSAT over a relatively long time period should consider this option, because the technical staff and expertise to operate a satellite hub are considerable.

Comparison of terrestrial network costs to comparable satellite numbers depends on a number of factors, such as:

  • Number of sites

  • Uplink and downlink bandwidth

  • Service level agreements and disaster recovery requirements

  • Price of the VSAT equipment

  • Maintenance costs of the equipment (dish, RF equipment)

In one recent study, the cost of supplying comparable bandwidth to 1000 sites was found to be approximately $400 to $450 per site with Frame Relay and $150 per site using VSAT services (Global VSAT Forum, http://www.com-sys.co.uk/vsatind.htm). The authors have seen similar figures for other firms. Including video in the mix would make the cost disparity even greater.

Low Earth Orbit Satellite

The economics of wireless communications are not always suited to broad generalizations. Each business case must be considered individually. As an example, consider energy firms that use pipelines to transport natural gas across the United States. The pipelines must constantly be monitored for signs of rust to ensure that a gas rupture does not occur. One engineering technique long used by pipeline companies is cathodic protection, in which a metal rod is attached via wires to the pipelines and serves as a "sacrificial anode" to keep a correct electrochemical balance. In effect, the expendable rod rusts instead of the pipeline itself.

Because the metal rod eventually rusts out, inspections and replacements must occur on a regular basis. Trips to the more remote sites may require hours of "windshield time;" that is, a service technician driving a truck a hundred miles to spend a few minutes inspecting and possibly replacing the anode. Attaching an inexpensive transmitter to each site and then sending appropriate telemetry data to low earth orbit satellites can eliminate many of these inspection trips. The satellites, in turn, transmit to an Earth station. From there, the data is sent to a data acquisition center where appropriate maintenance reports are created.

Whether the above scenario makes economic sense depends on a number of factors: people costs, time on the road, unit capital costs (for the remote field transmitter), and system maintenance costs. Low earth orbit, or LEO, satellite transmission is relatively expensive on a per-packet basis. However, if the application requires only a small quantity of data per month (as in the previous example), LEO technology may be a good fit. Exhibit 2, courtesy of Orbcomm and Leocell, illustrates a typical implementation.

Exhibit 2: Low Earth Orbit Transmission Example


For selected environments and applications, a radio-frequency, personal area network may be superior to its wired counterpart. Bluetooth is a popular, open standard for wireless transmission over a relatively short range (10 to 100 meters). It enables functions such as:

  • Wireless LAN access

  • Synchronization of PDAs and laptops

  • Midrange bandwidth for connection to the Internet (up to 720 kBps): any Bluetooth-enabled device, such as a mobile phone, can link to the Internet if within range of a suitable access point

  • Conferencing functionality: documents and business cards can be quickly exchanged among the participants

  • Faxing

  • Facilitation of electronic paper transmission: for example, a sales rep could fill out a form using a Bluetooth-enabled pen that records the motion of the pen on paper and transmits the order to appropriate servers via a nearby access point or receiving PDA

To some extent, Bluetooth competes with the older Wi-Fi wireless LAN specification. However, Wi-Fi is intended as a cable system replacement and has a higher bandwidth than Bluetooth. Wi-Fi does not fill the same market space.

From a cost perspective, implementation of wireless solutions depends on the organization's workforce. Some car rental companies, for example, use CDPD (wireless) to check out returning customers. Hospitals track patient records using secure wireless technologies as well.

Fixed Wireless Broadband

The slow speed of narrowband wireless communications such as cellular voice transmissions, CDPD, infrared, etc., reinforces the general perception that "wireless" denotes slow and error prone. In fact, there is no theoretical reason why fixed wireless systems cannot transmit very large quantities of data with extremely low error rates. For example, one of the networks discussed below, LMDS (local multipoint distribution services), tops out above OC-3 (155 Mbps) and is typically deployed at 45 Mbps downstream and 10 Mbps upstream. These networks use high-frequency radio connections to send and receive voice, data, and video; from the user's perspective, the result is no different than what would be expected from a copper- or fiber-based solution.

Fixed wireless solutions can often be a lower-cost alternative for broadband access, particularly in rural/low-density areas within the United States. Internationally, fixed wireless is increasingly popular due to its quick deployment, avoidance (from the carrier's perspective) of heavy infrastructure development, and, for some very poor nations, the absence of copper wires, which are sometimes stolen.

From an architectural perspective, broadband wire line access methods, such as xDSL and cable modem, compete with fixed wireless solutions. All these solutions are targeted toward solving the "last mile" problem — getting broadband to the customer's premises. When reviewing options, an organization should consider the following issues:

  • Advantages:

    • Fixed wireless can be the lowest-cost alternative.

    • The technology is quick to deploy. In some U.S. rural or international locations, wired broadband access can take several months (T1 drops can take up to nine months in some areas). Fixed wireless antennas and services can sometimes be implemented in weeks.

    • Coverage increases are incremental (just add more receivers/transmitters).

    • Legal/governmental regulations are much easier to address. For example, easements or special licenses are not usually required from the end customer.

    • Under certain circumstances, fixed wireless can deliver more bandwidth than xDSL or cable.

  • Disadvantages/concerns:

    • Some technologies require line-of-sight from transmitter to receiver.

    • Tall buildings, mountains, and heavy rainfall can interfere with signals for some of the networks.

    • Standards for equipment have not yet crystallized, resulting in uncertainty in the marketplace and a smaller number of equipment vendors creating the equipment.

    • Economies of scale are still needed to achieve lowest pricing to the end user.

Listed below are the most common broadband access options using fixed wireless.

LMDS (Local Multipoint Distribution Services)

Operating in the 28-GHz range of the spectrum, LMDS provides transmission rates exceeding OC-3 (155 Mbps). A typical deployment provides 45 Mbps downstream and 10 Mbps upstream. Well suited for urban areas, LMDS can be considered "ersatz fiber" when installed with sufficient cell overlap to reduce the effects of heavy rain. One limitation is that line-of-sight is required and wireless links (transmitter and receiver) must be less than 2.5 miles from each other.

MMDS (Multichannel Multipoint Distribution Services)

Although it has been used for more than 25 years to transmit television signals, MMDS is now finding a new niche in the high-speed Internet access service world. It does not require line-of-sight transmission and can work effectively over 35 miles. At 10 Mbps, downstream speed is considerably less than LMDS but its lower frequency range makes it less susceptible to weather interference.

After gaining an understanding of the technologies available and the financial consequences of options within each technology, the next step is to perform a comprehensive review of the existing network.