Dual-Mode, Dual-Band Handsets | Voice Communications

Multimode and multiband refers to a type of wireless system that supports more than one technology for its mode of operation and more than one frequency band. An example of a multimode wireless system is one that supports both American Mobile Phone Standard (AMPS) and Code Division Multiple Access (CDMA) systems for analog and digital communication, respectively. An example of a multiband wireless system is one that supports both 800 MHz and 1900 MHz for cellular and Personal Communications Services (PCS), respectively. Of course, wireless telephone systems can be both multimode and multiband, depending on the standards and frequencies supported.

Multimode and multiband wireless systems allow operators to expand their networks to support new services where they are needed most, expanding to full coverage at a pace that makes economic sense. From the subscriber perspective, multimode and multiband wireless systems allow them to take advantage of new digital services that are initially deployed in large cities, while still being able to communicate in areas served by the older analog technologies.

With its multimode capabilities, the wireless system preferentially selects a digital channel wherever digital service is available. If the subscriber roams out of the cell served by digital technology—from one served by CDMA to one served by AMPS, for example—a handoff occurs transparently. As long as subscribers stay within CDMA cells, they will continue to enjoy the advantages the technology provides, such as better voice quality and soft handoff, which virtually eliminates dropped calls. When subscribers reach a cell that supports only AMPS, voice quality diminishes and the chances for dropped calls increases.

The chipsets used in the handsets permit the wireless phones to switch between modes and frequency bands. Handsets using these chipsets have been available since 1995. When sending data, some of the newer chipsets offer even more flexibility, permitting the subscriber to use the Public Switched Telephone Network (PSTN) as well.

Dual-mode AMPS/N-AMPS handsets

N-AMPS, or narrowband AMPS, is a system-overlay technology that allows enhanced digital-like features, such as Digital Messaging Service, to phones operating in a traditional analog-based AMPS network.

Among the vendors offering dual-mode AMPS/N-AMPS handsets is Nokia, the world's second largest manufacturer of cellular phones. The company's 232N is a N-AMPS version of its Nokia 232. The new phone features a large 16-character display with permanent signal and battery strength indicators, four one-touch dialing keys for instant access to emergency services, voice mail, frequently called numbers, and a user-friendly menu interface. In addition, the 232N is data ready via an optional cable which connects the phone to any compatible PCMCIA modem card, allowing the user to send and receive faxes, data, and e-mail via a cellular network.

To support Digital Messaging Service, an optional enhanced service offered by most N-AMPS cellular networks, the 232N is capable of receiving and storing up to 20 short messages in the same manner as a pager. These messages can take the form of short text messages such as CALL HOME or CALL OFFICE, the calling party's phone number, or a notification that voice mail is waiting. The 232N even simplifies the process of responding to messages by enabling the user to call back a number left in a message or to retrieve voice mail messages with a single keystroke.

In its standard configuration with a 550-mAh NiMH battery, the Nokia 232N weighs 7.6 ounces, provides 1 hour 10 minutes of talk time and 15 hours of standby time. Optional NiCd and NiMH slim and ultra extended battery packs are available which provide up to 2.5 hours of talk time and 32 hours of standby time.

Dual-mode AMPS/TDMA handsets

The inherent compatibility between AMPS and TDMA, coupled with the deployment of dual-mode/dual-band handsets, offers full mobility to subscribers, with seamless handoff between PCS and cellular networks. TDMA systems with IS-136, use the Digital Control Channel (DCCH) for support of new applications and teleservices. This enables operators to offer a new generation of advanced wireless capabilities including:

• Revenue-generating features such as Short Message Service (SMS) and Private Networks
• Fraud protection features such as Voice Privacy, Authentication, and Signaling Message Encryption
• Enhanced subscriber features such as Alphanumeric System Identification (SID), Calling Number Identification Presentation (CNIP), Calling Number Identification Restriction (CNIR), and Message Waiting Indicator (MWI)
• Network features such as Enhanced Registration
• Private Networks, which enable service providers to create virtual private networks that charge special billing rates and/or offer group feature set packages
• Over-the-Air Activation, which allows new subscribers to activate cellular or PCS service with just a phone call to the service provider's customer service center

Several manufacturers now offer dual-mode AMPS/TDMA cellular phones, including Nokia, Lucent Technologies, and Nortel.

Nokia introduced the industry's first AMPS/TDMA handset in March 1996. The Nokia 2160 supports all of the most advanced IS-136 TDMA digital features that are available through the Digital Control Channel (DCCH), including authentication, call forwarding, calling line identification, call waiting, selective call acceptance, short message service, and voice privacy. In addition, the 2160 is analog data ready via an optional cable that enables the user to connect the phone to a compatible PCMCIA modem card for sending and receiving faxes, data, and e-mail anywhere within a cellular network.

Lucent Technologies also offers TDMA-based dual-band handsets that support both the cellular (800-MHz) and PCS (1900-MHz) bands with roaming and feature transparency. The dual-band/dual-mode capability of terminals allows a user to move between the 800-MHz and 1900-MHz bands without call interruption. This means operators can use either frequency band to expand geographically into new areas, develop new customer segments, upgrade an existing service offering, to boost capacity.

Nortel's Companion Microcellular System provides seamless communication between private company locations using Meridian 1 PBXs and the public cellular network. Standard IS-136 dual-mode AMPS/TDMA handsets are used with the Microcellular system, which has the capacity to support up to 1500 cellular phones within an area of 10 million square feet. Cellular capacity depends on the coverage provided by the local cellular operator. The system is also capable of handling data transfer applications such as fax and e-mail.

The Microcellular system reuses the standard 800-MHz public cellular spectrum to provide wireless communications inside a building. Because the cellular spectrum is licensed to regional cellular operators by the Federal Communications Commission (FCC), the cellular channels used by the Microcellular system must be obtained from these operators.

When integrated with a Meridian 1 network of systems, the Companion Microcellular System provides the added benefit of a Multi-Site Networking option. This means users can make and receive calls at different company locations throughout the country that use the Companion Microcellular System. If operating in a campus-type environment, this option allows users to make and receive calls from different buildings.

The base stations contain the radio transceiver and may be placed at various locations within a building, up to 3000 feet away from the Meridian 1 system. All radio channels may be simulcast onto all antennas within the same partition to cover high-density areas economically.

Dual-mode AMPS/CDMA handsets

QualComm has been offering dual-mode AMPS/CDMA handsets since 1995. Its QCP-800 portable cellular phone operates at 800 MHz. Using CDMA technology, the QCP-800 portable phone offers superior voice quality, coverage, and privacy while transmitting at RF power levels of only 1/25th to 1/100th as much as an analog cellular phone. This lower power consumption, and the use of lithium ion battery, ensures longer talk and standby time. Users no longer have to carry extra batteries, or lose calls because their phones are turned off to save battery life.

In March 1997, QualComm added several CDMA digital handsets to its QCP series of portable phones. Among the new additions include the QCP-2700, the first CDMA 1900-MHz PCS/800-MHz analog dual-band phone and the QCP-820 CDMA 800-MHz digital/analog dual-mode phone.

The QCP-2700 is QualComm's first dual-band, dual-mode phone that offers expanded coverage for today's PCS only subscribers. The new phone provides carriers with an opportunity to capture customers seeking the inherent benefits of CDMA digital PCS performance and the ability to roam outside their PCS coverage areas.

Dual-mode E-AMPS/CDMA handsets

In 1996, the RF Devices Division of ALPS Electric Co., Ltd. introduced the URP Series transceiver unit for E-AMPS/CDMA dual-mode cellular handsets. Designed for both CDMA (digital) and E-AMPS (analog) systems, the URP Series is a dual-mode cellular transceiver unit that conforms to the IS-98 standard recommended by the Telecommunication Industrial Association (TIA) in the United States.

While CDMA systems are already in commercial use in the United States, Korea, Hong Kong, and other countries, CDMA also faces many competitive challenges in these and other countries. Many operators plan to stay with E-AMPS systems even as they introduce CDMA. In such cases, the same cellular phone will need to be compatible with both systems. Depending on local market conditions, this will provide operators with the means to make an economical transition from E-AMPS to CDMA or enable operators to exploit both technologies to enlarge market share.

Dual-band GSM handsets

In April 1997, Motorola introduced its International 8800 Cellular Telephone, the first dual-band phone capable of operating on both GSM 900 and GSM 1800 networks in Europe. The 8800 allows GSM 1800 subscribers to roam on either their home or other GSM networks (where roaming agreements are in place), using a single cellular telephone.

The 8800 features fax and data support at up to 9.6 Kbps using one of Motorola's CELLect data cards (available separately). Digital Data Fast (DDF) data compression technology offers even faster communication, with effective data throughput speeds of up to 56 Kbps with the CELLect card.

The Motorola phone includes the Personality interface with user configurable Quick Access, which allows users to access preferred functions with as few as two keystrokes. The large graphics display shows four lines of text and graphic icons.

Dual-band/dual-mode handsets

Ericsson's dual-band/dual-mode systems support communication over both 800-MHz AMPS/D-AMPS and 1900-MHz D-AMPS networks. As such, they offer the following competitive advantages to carriers:

• Identical PCS applications and services are provided to subscribers operating in both bands.
• PCS operators can use the same switch for 800-MHz and 1900-MHz services.
• Seamless interworking between 800-MHz and 1900-MHz networks through dual-band/dual-mode mobile stations.
• Using dual-mode/dual-band phones, subscribers on a D-AMPS 1900 channel can handoff both to/from a D-AMPS channel on 800 MHz as well as to/from an analog AMPS channel.

For PCS operators, dual-band/dual-mode service offers several immediate advantages. Existing 800-MHz infrastructure can be used for 1900-MHz services, providing rapid and cost-effective service availability. Existing radio base and switching infrastructure, as well as trunk networks for 800-MHz cellular networks, can also be used for the 1900-MHz traffic.

Roaming and hand-off between 800-MHz D-AMPS, 800-MHz AMPS, and 1900-MHz D-AMPS networks are supported. This provides numerous advantages to PCS operators at 1900 MHz:

• Full coverage can be offered from day one through cooperation with 800-MHz operators in the same geographical area.
• Extended coverage is available through cooperation with 800-MHz operators, or other 1900-MHz operators, in different geographical areas.
• Existing 800-MHz D-AMPS operators can use the 1900-MHz spectrum to increase capacity and develop new user segments in their 800-MHz networks.

  For example, 800-MHz cells can cater for wide-area coverage and act as umbrellas for 1900-MHz micro- and picocells. The small cells can cover the indoor office environment, shopping malls, airports, and difficult spot coverage. The umbrella cells would cater to the fast-moving users and also users moving between two isolated microcells.

Ericsson's D-AMPS 800/1900 dual-band/dual-mode system architecture consists of four major parts:

• The Switching System controls call processing and subscriber-related functions.
• The Base Station performs radio-related functions.
• The Operation and Support System supports the operation and maintenance activities required in the network.
• The Mobile Station is the end-user device which supports the use of voice and data communications as well as short message services.

Ericsson's intelligent roaming capability automatically chooses the best system for the subscriber to use. The company offers dual-band/dual-mode phones that are offered exclusively by Southwestern Bell and AT&T Wireless Services.

As competing technologies for wireless networks emerged in the early 1990s, it became apparent that subscribers would have to make a choice: the newer digital technologies offered more advanced features, but coverage would be spotty for some years to come; the older analog technologies offered wide coverage, but did not support the advanced features. A compromise was offered in the form of wireless multimode/multiband systems that let subscribers have the best of both worlds.

At the same time, wireless multimode/multiband systems allowed operators to economically grow their networks to support new services where the demand is highest. With multimode/multiband handsets, subscribers can access new digital services as they become available, while retaining the capability to communicate over existing analog networks. The wireless system gives users access to digital channels wherever digital service is available, while providing a transparent handoff when users roam between cells alternately served by various digital and analog technologies. As long as subscribers stay within cells served by advanced digital technologies, they will continue to enjoy the advantages provided by these technologies. When they reach a cell that is supported by analog technology, they will have access only to the features supported by that technology. The intelligent roaming capability of multimode/multiband systems automatically chooses the best system for the subscriber to use at any given time.

There is talk in the industry of developing an integrated phone that can work over all major types of wireless networks. Such a "world phone" would be a frequency agile device that accommodates both GSM in standard frequency bands (900 MHz and 1800 MHz) as well as PCS-1900 in North America, among others. The device could serve more than 25 million GSM subscribers worldwide—a number that may grow as high as 100 million by the year 2000.

Although it is unlikely that there will be only one technical standard in the future, today's dual-mode phones are viewed as the first step in the trend toward increasing integration. Dual-mode wireless may quickly advance to triple mode and more. With rapid advancements in chip technology, multimode phones and multifrequency phones offer the same design costs as today's mainstream wireless phones for the consumer market.