Cellular providers with CDMA-based systems often have to disappoint their customers who travel to Europe, Asia, or the Middle East. According to the CDMA Development Group, there were 256 million CDMA subscribers worldwide as of March 2006 compared with approximately two billion GSM subscribers. Western and Eastern Europe are almost exclusively GSM, while GSM subscribers outnumber CDMA subscribers by ten to one in the Middle East and Africa.

Now, however, it’s possible for CDMA-based carriers to offer coverage in parts of the world where the land-based infrastructure is exclusively or predominantly GSM-based. Recently, cruise lines have begun deploying on-board cellular extension systems, and carriers around the world can now offer their customers coverage overseas through roaming agreements with these cruise ships and their data service providers. Within two years, every major cruise line in the world will offer on-board cellular coverage, and most of these vessels will be using dual-mode systems that support both GSM and CDMA calls.

Before 2004, cellular coverage aboard most ships depended on the proximity of the nearest land-based cell tower. For passengers in outdoor areas of a ship, cruises in areas near land-based cellular sites could get signals in some locations, since these signals can travel up to a mile or more over open water. But “sometimes” isn’t good enough for passengers who expect the phone to work at all times. And when the cruise is in the Mediterranean or other GSM-dominated parts of the world, CDMA users have been completely out of luck.

But what began as a way to ensure cellular coverage aboard ships is also helping CDMA-based carriers deliver service in places where they otherwise could not. According to cruise line executives, cellular coverage is becoming a “must-have” amenity for business as well as pleasure travelers, and some bookings depend on whether or not the ship can provide it. Some of those passengers have CDMA phones, and they want coverage, too.

Most of the world’s major cruise lines have begun deploying shipboard cellular systems that support both GSM and CDMA. Already, dozens of ships from major cruise lines like Carnival, Holland America, Norwegian Cruise Lines, and Royal Caribbean offer shipboard cellular coverage. In addition, most European ferry operators have also deployed shipboard systems. The number of installations will nearly double by the end of 2006.

CDMA at Sea

To enable cellular service at sea, the ship company must install a cellular base station (BTS) and a distributed antenna system (DAS). These systems are provided by companies such as Wireless Maritime Services of Orlando, Florida and Maritime Communications Partner of Norway, using equipment provided by vendors such as Alvarion and LGC Wireless. The ship owner pays for the deployment, which runs $100,000-$300,000, depending on the size of the vessel. Deployment typically takes from one to three weeks.

A shipboard cellular system transmits cellular signals via a satellite antenna on the ship’s superstructure. Ships already use this antenna for data traffic, linking to networks operated by service providers such as Maritime Telecommunications Network (MTN) of Miramar, Florida. Once the service operator receives the cellular traffic, it routes each call to the user’s home network through a roaming agreement with that particular carrier. MTN has hundreds of such roaming agreements with carriers around the world.

From the antenna, the signal goes via coaxial cabling to a cellular base station (BTS) located in the ship’s telecommunications room. The cellular base station links the shipboard traffic with the service provider’s network, and is much like the base stations used at each land-based cell tower. From the base station, the signal moves throughout the ship via a distributed antenna system, or DAS.

Cruise lines typically enable coverage in most public areas, meeting rooms, passenger cabins, and sometimes the crew’s quarters. Cruise operators were initially concerned that some passengers wanting a getaway would complain about the noise from other passenger’s cell phones on a ship, but these fears have proven groundless – most people accept cell phones as a fact of life everywhere.

Still, there are financial, technical and logistical problems with bringing reliable and pervasive cellular coverage to cruise ships. A liner’s steel construction attenuates wireless signals quickly, so a shipboard system requires deployment of antennas throughout the vessel. The antennas must put out sufficiently strong signals to overcome any interference from other radio sources. And the system should provide end-to-end management as well, so the ship’s IT staff can learn about problems without waiting for passenger complaints.

Deployment of the system is also a challenge, because most activity is in retrofitting existing ships rather than adding systems to ships under construction. Cruise operators don’t like stranded investments, so the DAS must be installed over a period of several weeks when the ship is carrying passengers. Typically, contractors do the main installation work during overnight hours or when passengers are on shore excursions to minimize disruptions. Once installed, the antennas themselves look like smoke alarms, fire alarm monitors, or other small, ceiling-mounted units, and passengers seldom notice them.

Technology solutions

There are two main types of DAS on the market—passive and active—but the demands of the ship environment make passive systems the chosen solution.

Passive systems use rigid coaxial cable to distribute the wireless signal to the distributed antennas. They are called passive because the DAS itself uses no electronic components (Figure 1).These systems typically use thicker (7/8” to 1” diameter) cabling in risers between a ship’s decks, and then tap into the riser with thinner, 1/2” cable runs to the antennas on each deck. There may also be coaxial couplers or splitters to achieve the proper geographic distribution of antennas. Still, a passive DAS uses no components to boost the signal as it goes along, relying instead on a fat distribution pipe.

The coaxial cable used to distribute radio signals is inherently capable of supporting multiple carrier frequencies. These systems are often touted as “broadband” systems because the DAS itself supports any wireless frequency delivered to the coax system, and it can support Wi-Fi traffic as well as cellular traffic.

For a shipboard installation, however, a passive DAS presents several problems. First, the signal in a passive system degrades with the length of the cable run. Since antennas are located at varying distances from the BTS, each antenna will have unique signal strength and noise characteristics. As a result, the antenna placements must be carefully engineered to account for differences in output and coverage. In addition, the coaxial cable in a passive DAS is relatively large and inflexible, which makes it very difficult to install it in tight shipboard cable raceways. Safety regulations prohibit drilling large holes in steel walls and watertight compartments, so deployment is even tougher than it would be in a building. Finally, passive DAS offer little in the way of monitoring or management because the system is basically a dumb pipe.

In contrast, active DAS uses managed hubs in a system that behaves much like an Ethernet network (Figure 2). To distribute the signal from the base station through the DAS, the managed hubs and Remote Access Units (RAUs) amplify the signal as it goes along. Because of this amplification, the active DAS produces uniform signal and noise figures and offers uniform coverage at every antenna, regardless of its distance from the BTS.

Active DAS deployment is also much easier. In many cases, an active system uses the ship’s existing fiber backbone to link a main hub with expansion hubs located on each deck, and then uses CAT-5 cabling to connect each expansion hub to its remote access units and antennas (a remote unit can support several antennas if needed). The smaller cabling also makes these systems easier to install in tight spaces on ships.

Traditionally, an active system has required a separate set of hubs for each carrier frequency, so a system that supports multiple CDMA and GSM-based services would require two or more sets of electronics. However, newer active systems are now on the market that can distribute multiple carrier frequencies via one set of electronics.

Cruise ship operators typically take their cues from their existing wireless data service provider when it comes to specifying which type of system to deploy, but most service providers and ship operators are choosing active DAS.

Services and revenue

No matter which type of system is deployed, shipboard cellular services are a winning proposition for ship operators, passengers, and wireless service providers alike.

For ship operators, on-board cellular offers passenger convenience and enhanced revenues through revenue-sharing agreements on caller minutes. While ships have offered satellite-based telephone service for years, the cost ($7 per minute or more) has kept most users away.

For passengers, on-board cellular coverage enables them to conduct business or stay in touch with friends and relatives as they travel. For meeting planners who may be thinking of booking cruises for corporate meetings, the availability of cellular coverage makes shipboard meetings much more attractive since the ocean-bound executives don’t have to leave their Blackberry devices at home.

For service providers, the benefits include customer satisfaction, churn reduction, and higher revenues. A CDMA-based carrier such as Verizon or Sprint can use ship-board cellular to enable service and generate significant roaming revenues in locations where it would otherwise be impossible.

As shipboard cellular systems become commonplace, CDMA operators have an opportunity to create islands of coverage in parts of the world where they could never support callers before. Since the number of worldwide GSM subscribers dwarfs CDMA subscribers, moving coverage onto ships is a wise move for CDMA-based carriers.

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