Wednesday, July 4, 2007

Handset Sound Capabilities

Handsets need audio coders and decoders for a variety of reasons, the most fundamental
being the encoding and decoding of human speech for telephony services.
However, with a typical handset now supporting multimedia functions, the sound
capabilities will support music, the audio that accompanies a video clip, and applications
such as games and ringtones.

Ringtones
Ringtones have become big business as users attempt to differentiate their handset
models from all identical models. The ringtone represents an easy route to phone
personalization. There are numerous formats (Figure 4.28) in which to provide
ringtones, and this represents the dramatic changes in capability from the very
early phones, which could only support monophonic tones, to the devices of today,
which are able to support complex music files coded with the same techniques used
to record CDs.

Some of the ringtone formats that have appeared in the marketplace are proprietary
and are perhaps only supported by a limited range of models from one
supplier or a small number of suppliers.

Ringtone Formats
Many early handsets had very limited capability in terms of ringtone support —
the tone output was monophonic as the sound elements could only play one note at
any moment in time. The manufacturer would maybe supply a handful of built-in
ringtones for the user to choose from, and there was no capability for downloading
new tones. Monophonic tones have a very artificial sound to them.

Increased capability brought polyphonic ringtones to handsets and, combined
with features and services that allowed users to download new tones on their
phones, the market for ringtones was created. There are a number of polyphonic
ringtone formats (see Table 4.2), including the Musical Instrument Digital Interface
(MIDI). MIDI differs from the other tone formats in that the MIDI file does
not actually contain coded music, but rather a set of instructions about the notes
to be played, the voice to be used for each note, and the duration and depth of each
note. The consequence is that MIDI files are very compact and therefore ideally
suited to ringtone downloads.

An improvement on MIDI is Scalable Polyphonic MIDI, which allows the same
content to be played on devices that differ in terms of their polyphonic capability.

A low-end phone might only have four-note polyphony while a high-end phone
might have 32-note polyphony; the same file could play on both handsets through
a process of scaling.

The eXtensible Music Format (XMF) was introduced to overcome the limitations
of the 128 fixed instrument pallet of MIDI. XMF allows downloading of new
sounds to replace the default MIDI sounds.
More recently, ringtones have been provided as MP3 files using the same audio
coding techniques used for music distribution. These files offer much more realistic
sound capabilities, and the availability of chart music as ringtones is evidence of the
popularity of this format.

There are a number of manufacturer-specific ringtone formats in use and also
formats devised by third parties; for example, the polyphonic Synthetic music
Mobile Application Format (SMAF) from Yamaha is supported on a range of
phones from different manufacturers.

Audio Coding
As with ringtones, handsets must be capable of supporting a wide range of audio
formats if an end user wants to decode audio from a variety of sources. There are
two distinct families of audio coder found in handsets. The first family is related
to the need to code the human voice for telephony services, although some of the
coders used are derivatives that support signals with a wider bandwidth than speech
(e.g., music). The second family of coders consists of those that comprise the audio
layer used in video coding techniques.

GSM handsets were originally built around the Full-Rate (FR) codec, which
was later supplemented by the Half-Rate (HR) codec, the Enhanced Full-Rate
(EFR) codec, and the Enhanced Half-Rate (EHR) codec (Figure 4.29). All these
coding mechanisms are built around a model of the human voice and, therefore,
while they offer good quality for speech, they are not optimized for non-speech
signals such as music.

The GSM specifications moved on to an Adaptive Multi-Rate (AMR) codec
that was also adopted as the standard by 3GPP for UMTS networks. This codec
could switch rates according to needs and conditions, but was still speech oriented.
However, recent improvements have been made to the codec, first by improving
quality, and second by extending the audio bandwidth and adding stereo capability.
Thus, the codec has evolved to support not only voice, but also high-quality
audio, including stereo music.

The second family of codecs found in handsets is based on the Advanced Audio
Codec (AAC) taken from the MPEG specifications. As with the AMR codec, the
AAC codec has evolved to improve quality and support stereo signals.

Display Technologies

The displays used in handsets are based on liquid crystal diode (LCD) technology
that has been used in consumer products for some time. Liquid crystal materials
have some special properties that are exploited to create displays; most importantly,
the crystals have a twisted structure and the amount of twist can be altered by
applying a voltage to the crystal material.

LCD Display Structure
A basic LCD display is a sandwich of layers through which light passes.
One of these layers is the liquid crystal that is situated between two layers of glass
that contain electrical connections. By altering the signal to these connections, the
crystals can be made to alter their twist, which has an effect on the polarization of
the light and can be used to create the dark/light contrast necessary for a display.
The specific LCD technology found in many displays is super twisted nematic
(STN), which relates to the special form of liquid crystal that is used. Displays can
be characterized as being either reflective or transmissive. A reflective display relies
on incident light from the front of the display, passing through all the layers to a final
reflective layer where it is reflected back to the front of the display. It is possible to
provide front-lighting or back-lighting to reflective displays. A transmissive display
uses backlight from within the display. The use of back- or front-lighting will increase
the energy consumption of the display; and when used in handsets, the lighting has
an associated sleep circuit to switch off the light after a few seconds of user inactivity.
There are a number of variants of the twisted nematic (TN) display, although
they all generally employ the same principles of operation.

Color Displays
Adding color to a display is relatively simple. Each pixel in the display
has three separate filters associated with it: one red, one green, and one blue.
Therefore, each pixel is effectively divided into three sub-pixels. The filters can be
activated so that only light of a particular color can pass through for that pixel. The
three sub-pixels can be manipulated to create a range of colors.

Display Types
The way pixels in a display are addressed, so that they can be switched between states,
has led to two main display technologies, the so-called passive and active displays.
In a super-twisted nematic display, a passive display (often called STN,
the individual pixels are addressed by row and by column signals, one
pixel at a time, and thus the display is relatively slow because it takes time to build
up an image pixel by pixel.

On the other hand, active displays add another component in the form of a
transparent transistor at each pixel, hence these displays are referred to as thin film
transistor (TFT). Using the active technology allows a whole row (or column) of
pixels to be addressed at once, which means that creating an image is much more
rapid than in an STN display.

The disadvantages of STN displays are their relatively slow operation, and
there are also issues relating to brightness and angle of view. However, they are
cheap to manufacture and use less energy than a TFT display,
which corrects the major problems of the STN format. In handsets with two
displays, where a simple display is used for phone functions and a higher specification
display is used for viewing videos and playing games, it is common to
find both technologies deployed — STN for the simple display and TFT for the
high-quality display.

Other display technologies are being developed; one in particular, the organic
LED (OLED), is receiving a lot of interest. OLED are emissive devices and thus
do not require a backlight, they can also be created on very thin layers of polymer
(almost like printing), and they consume much less energy than LCD displays,
which makes them ideal for handsets and other power-constrained devices.
OLEDs are being demonstrated in consumer products and much research is
being conducted into these components to overcome some of their limitations, at
which point widespread deployment would become a reality. For example, the lifespan
of blue OLED elements is only a few thousand hours, which means their use
in a TV or phone display is not yet commercially possible.

Types of Mobile Terminal Memory

Mobile handsets have always required elements of memory and storage as somewhere
for the operating system code to reside and execute. In early
phones, the user may have had access to a very limited area of memory to store contacts,
as an alternative to storing these on the subscriber identity module (SIM).

The increase in volume of applications such as messaging and the ability for
modern phones to support multimedia has increased the demands for storage
capacity within the handset. A typical handset contains a range of memory or storage
elements, which typically include the SIM card, hardware memory elements,
removable cards or memory sticks, and, most recently, hard disk drives.
With users now storing pictures, videos, music, and games on their handsets,
the total storage requirement has risen very rapidly; combined with this is the
increased complexity of multimedia signal processing, placing additional demands
on memory requirements.

Handset Hardware Memory
In common with any processing platform, a mobile handset requires a number of
different memory types to support its processing sequences. The two broad categories
of memory are Random Access Memory (RAM), which is as a working area
and as memory for user and application data storage; the other type of memory is
used to store the main program code and other applications. RAM is volatile and
will lose its contents unless power is maintained, whereas the E2PROM or Flash
memory used for the code storage is nonvolatile.

The RAM types found in mobile handsets include Static RAM (SRAM) and
Dynamic RAM (DRAM). SRAM will hold its contents as long as power is maintained
and, unlike DRAM, does not require refreshment on a regular basis. DRAM
memory stores bits of data as a charge on a capacitor; this charge must be regularly
topped up to avoid it leaking away.

Electronically Erasable Programmable Read-Only Memory (EEPROM or
E2PROM) is a nonvolatile memory type that can be programmed and reprogrammed
many times by means of electrical signals. E2PROMs have life cycles of
between 100,000 and 10 million write operations, although they may be read any
number of times. A limitation of E2PROM devices is that only one memory location
can be written to at any one time, this can be overcome by using Flash memory
devices, which can have a number of locations written in one operation.

The amount of hardware memory in handsets has increased considerably in
recent years as phones have included evermore complex operating systems and
applications, and also as users have required more memory for storing personal
data and multimedia files.

At the low end, the amount of E2PROM or Flash memory required might be
16 MB with an additional 8 MB of SRAM or DRAM. In addition, even low-end
phones might offer users memory of between 5 and 20 MB.
The manufacturing requirement to get more and more memory in a handset,
while at the same time decreasing the size of the device, has led to new techniques
such as multi-chip packaging (MCP) where one physical chip package houses both
SRAM and Flash.

Memory Growth
Driven by multimedia applications, the amount of hardware memory in handsets
has increased dramatically from the relatively small amount in voice-centric handsets
to a total of between 500 MB and 1 GB in 3G devices. The memory is typically
a mixture of RAM and Flash.

Until recently there were two main types of Flash memory in production, and
both of these are encountered in handsets; they differ in regard to the type of logic gate
deployed in the memory matrix — either NOR or NAND. However, hybrid Flash
memory devices are now appearing in the marketplace that combine the best features
of the two memory types, and these may soon find their way into mobile products.
NOR Flash was developed first; and while it is a true random access memory
(any location can be addressed when necessary), it suffers from relatively slow write
and erase times and a more limited lifespan than NAND Flash, which is both faster
and cheaper.

Memory Cards
Driven by appliances such as digital cameras, a number of removable data storage
formats have been invented, some of which are also deployed in mobile phones.
These memory cards or sticks can be used to store music, pictures, videos, and
games, which might have been downloaded or, in the case of pictures and videos,
captured by the user with the handset camera.

These memory devices are intentionally small, often a few tens of millimeters
square, and weigh only a few grams. Their storage capability however might be up
to several gigabytes. Typically, these devices are based on Flash technology and are
housed within the handset in a manner similar to the SIM.

Handset Processing, Processor Architectures, Coprocessors

As handsets have evolved from simple voice-only analog phones through to complex
3G multimedia platforms, an increasing processing load has been assumed of
the devices. Processing loads and capabilities can be compared using the measurement
of “millions of instructions per second” (MIPS), and device manufacturers
will usually quote the MIPS value for processor chips.

The processing requirement for a 2G GSM phone is in the order of 10 MIPS,
with much of this processing requirement resulting from the voice coding function
(Figure 4.16). The addition of a 2.5G technology such as GPRS raises this figure
to somewhere on the order of 12 MIPS, although the processing complexity of a
2.5G phone will differ significantly across the range of device types encountered,
and may be as high as 40 MIPS.

A UMTS (W-CDMA) handset operating in a 3G network requires a total
processing capability in the region of 500 MIPS, with 40 percent of this requirement
resulting from the relative complexity of the air interface. Adding features,
particularly video processing, will increase the MIPS requirement and there is
already discussion of phones with 1000 MIPS (1 GigaMIP) requirements.
An issue for handset manufacturers and chip designers has always been the
processing limits of DSP chips, which is why handsets typically consist of multiple
processors and hardware accelerators (which remove some of the repetitive tasks
from the DSP and implement these in hardware).


Processor Architectures

The division of tasks between multiple processors within a handset is very common,
and a typical architecture would include a microprocessor (or microcontroller), a
DSP, and hardware accelerators. The role of the hardware accelerator is to remove
from the DSP the more routine repetitive tasks, such as radio channel processing,
leaving the DSP free to focus on other layer 1 tasks and vocoding (implementing a
compression algorithm particular to voice).

In this architecture, the hardware accelerator can be labeled as a coprocessor,
although this is a generic term that may have other meanings in the context of
handsets. Silicon manufacturers have in some cases produced single-chip solutions
that contain the three processing elements; this is an attempt to reduce the area,
volume, and cost of these vital handset components.

The typical task distribution in today’s handsets places the emphasis on the
accelerators rather than the DSP. However, as DSP technology improves, more and
more of the total processing load could be assumed by the DSP, although of course
by that time the evolution of services may be placing even more demands on the
handset processors.

Coprocessors

The spread of processing load has led to a number of different strategies for the
use of coprocessors (Figure 4.18). For example, in a dual-mode 2G/3G phone, a
chip manufacturer might offer a main processor that is responsible for the 2G and
2.5G baseband functions and a companion chip that adds 3G baseband functions.
These two processors can then be coupled to their corresponding radio modules.
This solution is perhaps suited to a manufacturer that is looking to evolve a range
of 2G/2.5G to support 3G capability. The basic core design of the handset can be
reused and the 3G functions are added in parallel. Another possible solution is to
use one processor for all the digital baseband processing and to use a separate coprocessor
to handle specific tasks such as multimedia services.

Types of Handset and the Market

Handset Segmentation
Segmentation of mobile handsets is usually based on technology, with a correlation
between technology and price; that is, the more complex or feature-rich the device,
the more expensive it tends to be. However, more recently, and for the foreseeable
future, alternative segmentation strategies have become increasingly important for
both vendors and operators. They both seek to segment handsets and their markets
in a variety of ways to cope with market trends and aid in the differentiation of
their products to attract and retain subscribers:

Technology.

Technology is the traditional handset segment. Handsets are
divided on a technical basis, with a direct correlation to pricing so that a
handset incorporating less of the latest technology is invariably cheaper in
the marketplace than one with greater technical prowess. This can now also
be applied to features on the phone, such as the number of megapixels on a
camera or the amount of storage capacity.


Lifestyle.

This is an increasingly ubiquitous segmentation strategy, reflecting
the growing importance of the end user in the value web. This involves
matching the functionality of a handset with the specific needs of the end–
user (e.g., youth or style).


Price.

This strategy is beginning to be used more, owing to the move into
developing markets where customer income is low. It is primarily based on
the cost to manufacture the handset and the customer market segment at
which it is aimed. It also includes customer purchase profiling.
Application specific. This segments the market by optimizing components of the
handset to focus on a specific application, such as games or music. It is not a
technology-hungry mode, as the handset design is quite flexible and is a comparatively
cheaper process because it eliminates many nonessential components.


Low-end phones.

The term “low-end handset” is used normally to describe those
mobile phones that support only basic voice and data services and perhaps do
not support many features such as color displays or cameras. These phones
are usually targeted at the new user and prepaid user markets. While these
phones are normally at the cheaper end of the market and have traditionally
not supported much in the way of advanced features, the effect of technology
trickle-down is beginning to be felt even in this market sector.

It is not unusual to find color screens, cameras, and even WAP-based Internet
access available on some handsets. Polyphonic ringtones are very popular across all
market sectors and a good revenue generator for the network operators; therefore, it
is in the interest of the operator to enable the downloading and playing of various
types of ringtones, even in the so-called low-end device market.

Also in this segment is the low-cost handset or ultra-low-cost handset. The
GSMA is encouraging handset vendors to address the developing market by producing
handsets at a very low price point, U.S.$40 to U.S.$50, for example. These
devices have very few features in an effort to keep manufacturing costs to the bare
minimum. Often, these devices will support only voice and text messaging and
perhaps a limited selection of preprogrammed, non-changeable ringtones. While
these handsets are designed to address the developing market to make mobile communication
more affordable to those people that have little disposable income, they
may also find a place in the senior (or “gray”) market.

Low-Feature Phones

Low-feature handsets are generally geared toward more mature users and the
replacement market. The main attraction of the mid-range handset is the more
advanced feature set, in comparison to a low-end phone. Designs are more ergonomic,
with shapes and keypads that are easy to hold and handle. Displays are generally bigger than those on low-end phones and are more likely to be color. The
graphics quality and user interface are also expected to be superior, and this segment
is most likely to see the first significant showing of tri-band handsets.


Music and Entertainment

Music entertainment handsets are generally equipped with a mobile music player
for MP3 and AAC files, stereo FM radio, digital recorder, and Flash memory. This
is an extremely popular market segment, largely due to the popularity of standalone
music players such as the Apple iPod. Several handset vendors have launched
mobile phones that address the music market directly. These players are often
shipped to the subscriber with some form of access to a music downloading site,
(e.g., iTunes). One challenge that faces the industry in this market sector is the issue
of copyright and digital rights management (DRM). For the service to be popular,
musical content must be easy to distribute and exchange between authorized music
sites and vendors, as well as between the consumers of the music. This, however,
is at odds with the management of the copyright holder’s rights to the content.
Industry bodies such as the Open Mobile Alliance (OMA) are working on methods
to resolve these issues.


Feature Phones

This segment encompasses devices with high-technology capabilities and a variety of
features but without harboring an advanced OS, which would put them into the smart
phone device category. This segment has many of the attributes assigned to lesser segments
and also incorporates advanced features such as video capture and playback,
music, expandable memory slot, high-resolution screen, and megapixel camera.


Smart Phones

The smart phone is generally defined as a converged device whose primary function
is that of a phone with added advanced computing capabilities or PDA functionality
with an advanced operating system (OS). The category was born out of the
amalgamation of mobile phones that offer PDA functionality with an advanced OS
and a PDA with a WWAN connection. Smart phone devices invariably have a large
color display, are inclined to have a larger form factor, and are feature-packed.
There are two primary types of smart phone. There are those that are mainly
rich media devices with advanced OS and computing functionality that are basically
mobile phones embedding a number of additional features outside the usual
ones found on PDAs, such as MP3, camera, MMS, games, Java, or e-mail. These
devices might be used in the business and corporate markets. At the higher end
of the smart phone market, the devices tend to be PDA computers with phone capabilities,
typically manufactured by handheld device vendors such as HP, PalmOne,
and Toshiba; these devices are aimed at the business professional.

Open Service Access

The specification, design, and implementation of services in a telecommunications
network were at one time limited to a very small pool of programmers, as services
were normally written as additional software for network elements (e.g., switches).
Even the advent of Intelligent Networks (IN) did little to improve this situation,
as a service designer still needed an intimate knowledge of telecommunications
networks and protocols.

Open service access (OSA) is an attempt to provide a much more open, yet
secure, environment for service development by abstracting the network functions
into a high-level view and providing access to these functions by means of standard,
well-defined application programming interfaces (APIs) (Figure 4.12). The work
on what is now known by some as OSA was started by the Parlay Group, which
focused on the U.K. network of British Telecom (BT), which the regulator wanted
to open up to third-party service providers. The Parlay Group works on the APIs
and the model for service providers to access the network functions.
The OSA project of the 3GPP is now aligned with Parlay, and the names are
now interchangeable. The OSA consists of an API that exposes, in an abstract manner,
the service capabilities of the network. A service designer can manipulate these
service capabilities to build innovative services (e.g., a service based on the location
of a mobile device).

A major concern for network operators is security and the security of information;
therefore, the OSA gateway that supports service providers also includes
a framework element that is responsible for authenticating service providers and
authorizing what functions (and information) that provider is able to see. Using
standard network signaling protocols such as SS7-based protocols, the OSA gateway
is able to manipulate the network elements to achieve the functions of a particular
service, although the service designer is isolated from the detail of these
protocols. The service provider in an OSA environment could be either within the
network (i.e., the network operators themselves) or a trusted third party.
Live OSA-based mobile services are available in some networks, although the
end user will not be aware that this is how the service is provided. These services
include prepay, location services, virtual private networks (VPNs), and unified
messaging (UM).

Handset and Standards Bodies

The large number of technologies incorporated in a handset is reflected in the fact
that the standards on which this technology is based emanate from a diverse range
of standards organizations and industry forums. From the perspective
of the core cellular functionality, the most significant standards bodies are the two
3G bodies, the Third Generation Partnership Project (3GPP) and the Third Generation
Partnership Project 2 (3GPP2).

3GPP is responsible for the UMTS standard and also assumes responsibility from
ETSI for the GSM standard on which UMTS is based. 3GPP2 is responsible for the
cdma2000 family of technologies, which includes the Evolution systems, 1xEV-DO
(1x Evolution Data Optimized) and 1 x EV-DV (1x Evolution Data and Voice).

Both 3GPP and 3GPP2 have very similar structures, and indeed members.
The two organizations are composed of organizational partners (OPs), which are
national or regional standards organizations such as ETSI or the Telecommunications
Industry Association (TIA). It is important to note that there are cooperative
links between the two bodies as there is a lot of crossover technology that does not
rely on the underlying network standards and can therefore be transferred.
In addition to the OPs, both the 3GPP and 3GPP2 have market representation
partners (MRPs) and observers who contribute to the standards processes.
The technologies covered by the two 3G bodies represent approximately 98 percent
of the global users of mobile or cellular networks. In addition to the 3GPP and
3GPP2 standards, many other organizations have a bearing on handset design and
functionality; these include:

The Internet Engineering Task Force (IETF)
The World Wide Web Consortium (W3C)
The Open Mobile Alliance (OMA)
The International Standards Organization (ISO)
The range of applicable standards in a handset is indicative of the convergence
between telecommunications, Internet technology, and broadcasting and
entertainment.