TECHNOLOGY: All for One, One for All

Wireless connectivity is quickly becoming a common and pop- ular affair. It
is also becoming much more complex. Today, personal wireless communication is
accomplished mainly through cellular networks. However, that is changing rapidly
with the developments such as deployment of 802.11 networks and the
proliferation of Bluetooth WPAN networks.

All these, coupled with the ongoing evolution of wireless standards and
networks, are clear indicators that the wireless world will be increasingly
heterogeneous. Such heterogeneity would most likely create demand for ubiquitous
access to data via the 'best available network.' To fulfill this demand,
small-form-factor clients such as handsets would have to overcome huge
technology and usability challenges. 

The Handheld Client

Addressing the opportunities and challenges of a heterogeneous network will
require that handheld devices evolve considerably from today's limited and
often fixed-function/fixed-network devices, to flexible devices that can
intelligently interact with multiple, heterogeneous networks and services.

To meet these demands, a higher form of handheld such as a universal
communicator will have to evolve. It will need to be a flexible, personal
communication device that can provide access to any available network, at any
time, including seamless roaming.

Technology Challenges

Enabling such ubiquitously connected devices poses numerous difficult
technology challenges. Let us look at some of the major difficulties in
connecting instant and hassle-free connectivity.

Multiple Radio Integration and Coordination: Building a ubiquitously
connected device begins with the challenge of integrating multiple radios. Such
devices typically have discrete radio solutions residing in close proximity to
each other. However, simultaneous use of all those radios poses significant
design challenges.

For example, direct frequency level interference such as between 802.11b and
Bluetooth radios operating in the 2.4 GHz range is a common problem. Coexistent
radios operating simultaneously at different frequencies can also cause
interference problems for each other.

One solution could be, instead of integrating multiple discreet radios, using
such radios in the device that are flexible, i.e., can to shift between many
protocols-usually called 'agile' or 'software-defined' radios.

Intelligent Networking-Seamless Roaming and Handoff: Today, cellphone users
expect to roam between cellular networks. Tomorrow they will expect to do the
same thing for both cellular and non-cellular networks.

Although Mobile IP technology addresses several of concerns for roaming
between IP-based networks, it has limitations. Providing support for voice
handoff between cellular and non-cellular networks is one such issue. For
example, a user who begins a voice-over-WLAN call within an enterprise network
can want that call to seamlessly continue should the user walk out of the
building. Such a handoff places significant demands on the client. It must be
able to initiate, receive, and mux simultaneous voice streams in order to 'replace'
one call with another during the handoff process.

Power Management: Power management is always an issue when building a
handset. There are two broad approaches to extending battery life. The most
obvious is to reduce the power consumption. The second approach is to utilize
new power sources, such as fuel cells.

Cross-network Identity and Authentication: Providing a trusted, efficient,
and usage-model appropriate means of establishing identity is one of the key
issues in cross-network connectivity. The handheld client must play a key role
here. It must provide a trusted repository of identity, ensure security while
transmitting data over the air, and provide users with a convenient yet trusted
way to identify themselves to the device.

Support For Rich Media Types: With the coming of broadband wireless
connection, such as a WLAN or 3G cellular networks, capability to rich media
will be essential for the handheld devices.

With respect to graphics and rich gaming, devices will need to support the
emerging handheld graphics APIs:

• OpenGL ES, a scaled-down version of OpenGL for handheld devices
• JSR 184, the recently released standard for Java-based 3D handheld
  graphics

Flexible and Powerful Computing Platform: With so many
demands, the heterogeneous, universal communicator-class device must be based on
a flexible, powerful, general-purpose processing platform. The general-purpose
processing platform makes it easier to add wireless applications to the device
so that it can take advantage of the information and services unanticipated by
the original device developer. The processor must also provide the computing
power to run applications while executing the complex tasks required for
navigating heterogeneous networks.

Overall Device Usability: The final challenge inherent in
building a mixed-network device is usability. Attaching a broadband connection
to a small device carries with it higher user expectations regarding what the
device can do. For example, fast access to e-mail or corporate documents will
likely mean that users will want some amount of data entry and manipulation
capability on the device. Access to rich media content will necessitate larger
screens to view that media. Also, access to a large data and media files will
require larger storage capabilities.

Laying the Foundation

Clearly, the device requirements described so far present daunting
challenges to handset designers and manufacturers. The industry leaders have
begun to take important initial steps toward overcoming those hurdles.

The 'universal communicator' concept platform features a
mix of broadband data functionality with both cellular (GSM/GPRS) and Wi-Fi
(802.11b) network connectivity. It allows demonstration of potential usage
models for multi-mode handsets, including the ability to transition voice and
data sessions between networks, simultaneous use of wireless protocols, and
enhanced user experience through high quality multimedia capabilities.

Addressing Noise and Interference Issues

Central to the development of such devices are the issues of noise and
interference-related to co-location of multiple RF circuits. Interference
problems could be reduced by designing the handset so that the radios operate
serially-using only one network at a time, but that would undermine much of
the value in having access to multiple networks. Instead, the device must be
designed in a way that allows simultaneous radio usage while keeping
interference between the radios, antennae, and digital circuits to a minimum.
Such a handset must have a multi-function CPU capable of delivering high quality
user interfaces for audio and video. And it must accomplish this in the small
form-factor structure containing a complex mix of digital, analog, and RF
circuits.

Each circuit must be tuned for optimal individual
performance, but isolated in such a manner as to provide immunity to adjacent
circuit noise during periods of simultaneous use. Methods for high-density
integration such as advanced PCB architectures, techniques for circuit/noise
isolation and shielding, optimizing performance of individual RF circuits, power
management, and overall mechanical structure must all be addressed to achieve
successful coexistence.

The universal communicator prototype provides an example of
how radio isolation and co-existence issues might be addressed. Within the
handset, the GSM/GPRS antenna is located at the top and to the side of the PCB.
Antenna stem to board contact is made via a small jack/receptacle mounted on the
PCB side opposite from the WLAN antenna, with a short 50 Ohm trace connecting
the jack to the radio front end circuitry. The radio/phone subsystem is on the
back upper portion of the PCB.

A modified wave guide/shield is incorporated into the antenna
interface with liberal via stitching to internal ground planes. All layers are
voided in the area directly beneath the antenna interface to help reduce RF
radiation into internal planes. Route obstructs were used on every PCB layer in
the area of the antenna to reduce the opportunity for cross coupling of RF and
digital signals.

The prototype also includes a chip antenna for the internal
802.11b subsystem and utilizes similar implementation techniques as those used
for the GSM antenna interface: plane voids, CPW, routing obstructs on all trace
layers, and so on. This antenna is located on the opposite corner and opposite
side of the PCB as far from the GSM antenna as possible. This optimizes the
natural shielding effect of the internal plane layers. The antenna was located
at the top of the device to reduce the chance for user hand blockage of RF
signals.

As a result of these techniques, the prototype provides
simultaneous network access without significantly sacrificing performance on
either WLAN or WWAN networks.

Addressing Mobility Management Requirements

Mobility management is the ability of a client device to discover the
in-proximity wireless network environment and then interact with the networks in
a way that appears seamless to the user.

It encompasses three categories of functionality:

• Heterogeneous wireless network detection

• QoS characterization

• Support for seamless hand-offs between networks

By taking a cross-network perspective of these problems, the
suggested approach is different, albeit complementary, to single-protocol
approaches such as Mobile IP. So long as significant non-IP wireless protocols
continue to be popular (e.g., GSM), a comprehensive mobility management stack
should support them. Mobile IP is therefore an integral part of, but not a
substitute for, a comprehensive mobility management solution.

Heterogeneous wireless network detection makes applications and
the operating system aware of the holistic RF environment surrounding an enabled
device. Knowing which wireless networks are present at any given time enables
the device to take advantage of the network with capabilities and costs
appropriate for a specific operation.

Dynamic QoS takes the discovery capability a step further by
adding support for ongoing assessments of available wireless networks to
ascertain their performance characteristics. Armed with dynamic QoS information,
applications can take note of occurrences such as signal strength degradation
and act accordingly prior to actually losing connectivity.

Industry leaders are now taking steps to address seamless roaming

Hand-off support complements other mobility management
capabilities by providing the device with hooks to effect connection transitions
while moving between one wireless network and another. Given the right level of
support, applications can use the hand-off features of the MMDS to allow tasks
to span multiple networks with minimal disruption to the end user experience.

The universal communicator prototype implements these
approaches in prototype form.

Seamless Voice Roaming

The prototype demonstrates the ability to seamlessly transition a voice call
between a circuit-switched cellular network and an 802.11b IP network.

The user context for seamless voice roaming is the call
application, but from a platform perspective the underlying enabler is the
mobility management stack. The mobility management stack in the universal
communicator prototype provides the application with information regarding the
heterogeneous wireless network environment such as a dynamic change in GSM and
802.11b coverage areas.

Dynamic QoS in the mobility management stack enables the
voice application to reconfigure as needed — for example, by switching from a
VoCoder over GSM to a wideband audio codec over 802.11b. The mobility management
stack also facilitates the hand-off between networks, thereby enabling the voice
application to give the user a seamless experience.

The Future

As networks proliferate, users will increasingly be able to access the
information and services they need, when and where they need them. The challenge
will be to evolve handheld devices quickly so that they can navigate
heterogeneous networks and deliver on the opportunity presented by ubiquitous
wireless networks. This wil see the emergence of a new class of devices that can
utilize multiple networks to transparently connect users with information and
services.

Roger Hurwitz
and Bryan Peebler, communication technology lab, Intel Corporation