Optimizing next-generation wireless networks.
A marketplace shift is on the horizon in the wireless industry as carriers realize they need to cost-effectively support the evolution of new, enhanced services and the service level required by tomorrow's next-generation wireless networks. And "tomorrow" is quickly becoming "today."
For starters, in addition to voice traffic loading, the types of services supported by wireless networks are expanding. When first launched, most wireless switching systems were designed to carry voice traffic alone. Now, more and more high-speed applications are emerging for next-generation wireless data transmissions--including Internet/intranet access, voice over ATM, ATM over satellite, and fixed wireless.
These new services up the ante in terms of both bandwidth requirements and service quality requirements of the next generation of wireless networks. The reason: the glitches that can be tolerated during voice conversations--such as crosstalk, momentary disconnects, or static, as calls are handed off between switches--are no longer acceptable when it comes to data communications.
Soft hand-off, a technology that is available today, helps solve this problem. And fortunately, ATM, because of its high speed and high reliability, is a formidable and cost-effective platform used to implement soft hand-off.
"Glitches in today's wireless service are caused by hard hand-offs, as callers move across various service areas," explains Paul Prah, data and ATM applications manager, Lucent Technologies. "Soft hand-off, implemented using ATM technology, can help avoid the glitches."
That brings us to another factor impacting the wireless marketplace shift: the evolution of new switching technologies to support a new range of broadband services--assuming the bandwidth is available to carry those services.
ATM switching systems consolidate network traffic, significantly reducing the need for the point-to-point connections between switches as the network grows. Without centralized ATM switches, the lack of cost-effective solutions could affect market acceptance of such advanced services.
With an ATM infrastructure, the need for costly point-to-point links between wireless switches in a given service area can be substantially reduced, even while bandwidth and growth potential are significantly increased.
Rather than running point-to-point OC3 links between all selection distribution units (SDUs) in all metropolitan service centers/base station controllers in a wireless network, the wireless switches are locally linked with short fiber runs to the ATM switches (See Figure 1). The ATM switches are then bunked together, reducing facility requirements. ATM permanent virtual circuits do the rest.
[Figure 1 ILLUSTRATION OMITTED]
"A metropolitan service area with just three new CDMA (code division multiple access) ATM switches, each equipped with three SDUs, can add up to significant facility cost savings in a relatively short period of time," Prah says. "Once you implement ATM, potential cost savings become even more beneficial, because now you have an infrastructure that can support other next-generation voice, fax, and data services."
In addition to the reduced facility costs, further cost savings can accrue with ATM because the bandwidth capacity of this technology will empower wireless carriers to pool fewer voice handlers (vocoders) in their networks.
These devices are required to make digital wireless calls compatible with the public switched telephone networks (PSTN). In the current configuration, each base station can only reach a single SDU; therefore, each SDU pool must be large enough so that a call can reach a vocoder when needed. As customers move from base stations on one SDU to another, they typically change SDUs by performing hard hand-off.
Conversely, with ATM, a call remains connected to its initially assigned SDU, even as the user travels a service area. This technique, known as soft hand-off, allows a call to be "softly" transitioned from base station to base station and wireless switch to wireless switch as the caller moves throughout various service areas.
"ATM provides predictable speed and reliability. With soft hand-off, interswitch transitions of a call occur without interruption," says Prah. "Future transmission applications, whether they're voice, data or fax, also can remain virtually error-free. This is in contrast to, and a tremendous improvement over, services implemented using hard hand-off, where the call is momentarily disrupted."
Soft hand-off can be done because of the CDMA handset's ability to communicate simultaneously to multiple paths over multiple base stations. Soft hand-off also is enabled by the vocoder's ability to seamlessly select the best quality call path out of multiple paths presented to it as the caller moves.
Since the vocoder gets frames of information from the base station, the path between the vocoder and the base station must be fast and reliable. ATM allows information to get from base station to vocoder quickly and reliably over a much broader area (See Figure 2).
[Figure 2 ILLUSTRATION OMITTED]
The ATM backbone easily provides the bandwidth required to support this capability. In fact, ATM is an open, standards-based technology that can enable soft hand-off because of the technology's inherent ability to seamlessly support voice, data, and video.
ROBUST ATM SWITCH
Achieving the benefits of ATM in wireless networks requires a particularly robust and reliable ATM switch equipped with the active and redundant components required to offer full protection switching. In short, to be successful in a wireless environment, the ATM switch must be just as reliable as today's central office voice switch.
In addition to reliability, the capacity of the ATM switch must be considered. Start with something you can ensure will grow to meet future capacity needs--say 20 Gbps. This assures that capacity will be available as service grows.
Then there is the need for "evolvability": "With so many unknowns in terms of future technology developments," says Prah, "it is important to deploy an ATM switch that features a modular and evolutionary architecture, such as one based on a shared memory fabric."
Shared memory fabric is of particular importance for CDMA soft hand-off because of its low latency requirement.
The goal is to invest in a technology platform that can evolve to support much greater bandwidth and application requirements in the future, as well as support future ATM standards--all while protecting the investment wireless service providers make today.
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|Title Annotation:||Technology Information|
|Date:||Oct 1, 1997|
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