Tdma technology

MAY 2006

TDMA Technology
Bringing Increased Capacity and Functionality
to Professional Digital Two-Way Radio

w h i t e pa p e r

contents

3 Executive Summary
4 Advantages of Digital Two-Way Radio
5 Digital Radio Market and Standards
7 Multiple Access and Spectral Efficiency
7 TDMA: How It Works
9 Advantages of Two-Slot TDMA for
Professional Organizations
12 The Right Choice for Professional
Two-Way Digital Radio: TDMA

TDMA Technology

Executive Summary
Licensed, professional two-way radio is on the verge of making the biggest leap forward since the
invention of the transistor — the move from analog to digital. Digital radio offers many advantages
over analog, including improved voice quality at greater range, better privacy, sophisticated call-control
features, the ability to easily integrate with data systems, and more.
We’re now at the beginning of what will quickly become a large-scale migration to digital radio in
professional applications. At the same time, regulatory pressures combined with real-world operating
needs are driving radio manufacturers and users to communicate more information in a given slice of
RF spectrum — in other words, to increase “spectral efficiency.” Channels that historically carried a
single call at a time are now being divided so they can carry two.
Two technologies exist to enable this “splitting” of channels, allowing multiple access on a single
channel. Frequency-Division Multiple Access (FDMA) splits the channel frequency into two smaller
sub-channels that can carry separate calls side-by-side. Time-Division Multiple Access (TDMA)
preserves the full channel width, but divides it into alternating time slots that can each carry an
individual call. Both technologies are already being used in North America to accomplish the FCC-
mandated split of 25 kHz channels into 12.5 kHz channels, and they’re both being used worldwide
to accomplish similar increases in spectral efficiency whether currently mandated or not.
In the coming years, new regulations will almost certainly require improvements in the effective
capacity of 12.5 kHz channels: it is only a matter of time before the ability to carry two voice paths in
a single 12.5 kHz channel — also known as 6.25 kHz equivalent efficiency — becomes a requirement.
But because the technology exists today to accomplish this goal, there’s no need for professional
radio users to wait for the regulations to catch up with benefits that are immediately available. Even
in the absence of a mandate, professional users can double the capacity of their existing licensed
channels by adopting digital technologies that enable 6.25 kHz equivalent efficiency. With potential
benefits including increased capacity, lower equipment costs, data integration, added features, and
more, now is a compelling time for analog radio users to make the switch to digital systems that offer
6.25 kHz equivalency.
This white paper examines the two leading digital modulation technologies that are capable of
achieving this doubling of spectral efficiency: 6.25 kHz FDMA and two-slot 12.5 kHz TDMA.
Businesses looking to migrate to the most efficient professional digital systems to achieve
greater capacity and performance will need to choose one or the other — FDMA and TDMA
are not interoperable.
Two-slot 12.5 kHz TDMA-based systems, providing 6.25 kHz equivalency is the right choice for most
mobile professionals. Professional radio standards based on TDMA technology are already widely
used around the world, and future requirements for even greater spectral efficiency are almost certain
to be based on TDMA as well. Today and tomorrow, TDMA technology provides advantages of
feature flexibility, lower equipment costs, longer battery life, future-readiness, and the proven ability
to increase spectral efficiency without risking increased congestion or radio channel interference.

TDMA Technology

Advantages of Digital Two-Way Radio
Since the first wireless transceiver was installed in a Bayonne, New Jersey police car in
1933, two-way radio has been a mission-critical technology for police, firefighters, search
and rescue workers and others on the front lines of public safety. And increasingly, as new
models have reduced the size and cost of two-way radios, the technology has been adopted
by business professionals as well.

Industries including transportation, education, construction, manufacturing, energy and
utilities, private security, government, hospitality, retail, and many others are finding that two-
way radio can improve efficiency, worker productivity, and responsiveness by allowing mobile
teams to share business and customer information instantly.

Through most of its history, two-way radio has meant analog voice — the representation of
sound waves as either amplitude modulated (AM) or frequency modulated (FM) radio waves.
In fact, this is one of the last areas of professional communications to be touched by digital
technology. But that’s changing, very quickly, for very good reasons.

Modulating the voice into digital signals, rather than analog, provides several advantages.
First and foremost, digital technology provides better noise rejection and preserves voice
quality over a greater range than analog. Especially at the farthest edges of the transmission
range, users can hear what’s being said much more clearly — increasing the effective range
of the radio solution and keeping users responsive to changing situations in the field.

Depending on the technologies used, digital systems can also be designed to:
• Make more efficient use of available, licensed RF spectrum
• Combine voice and data access in the same device, delivering more information while
empowering field workers with systems that are more portable, flexible, and much easier
to use than two different and incompatible systems
• Enable integration and interoperability with back-end data systems and external systems
• Combine analog and digital voice in the same device, easing the migration to digital while
preserving investments in analog technology
• Provide strong, practical, easy-to-use privacy solutions without the significant loss in voice
quality that analog scrambling can cause
• Enable flexible and reliable call control and signaling capabilities
• Flexibly adapt to changing business needs and new applications through a modular architecture

DIGITAL
Enhanced Digital Excellent

Audio Performance audio quality
Area of Improved
Performance
AUDIO QUALITY

ANALOG

coverage

Minimal Acceptable Audio Quality

Digital voice retains better
quality than analog as signal Poor
strength decreases.
Strong SIGNAL STRENGTH Weak

TDMA Technology

The clear advantages of digital radio — along with increasing regulatory pressures to use RF
spectrum more efficiently — will drive widespread adoption of professional two-way digital
radio solutions in the coming years. If you’re using analog today, you’ll almost certainly be
migrating to digital tomorrow. Now is the time to research the available technologies so
that, when you’re ready to make the move, you’ll choose systems that provide the greatest
benefit over the long term.

Digital Radio Markets and Standards
Although the market landscape for two-way radio varies somewhat throughout the world,
markets can be roughly divided into three broad categories: (1) commercial and light
industrial applications, (2) professional, business-critical applications, and (3) mission-critical
public safety applications. With some overlap, there are relevant digital two-way radio
standards that are generally applicable to each of these categories.

While we won’t get into the specific regulatory requirements governing radio in various
countries and regions, let’s take a closer look at how the most important, internationally
recognized standards map to the needs of users within the general market categories. An
understanding of the entire market landscape will provide context for our discussion of the
needs of users in the professional/business-critical category.

Market Categories Example Vertical Markets Digital Radio Standards
Emergency Services
Public Safety/
ETSI TIA Project 25 Licensed
Mission Critical Public Transport
TETRA Licensed Trunking Conventional Trunking
Airports/Ports Local Government

Transportation Mining

Professional/
Petrochemical Public Utilities ETSI
Business Critical DMR Tier 2: Licensed Conventional
Manufacturing Taxi DMR Tier 3: Licensed Trunking

Construction Rental Agencies

Private Security
Commercial ETSI
Warehousing
Retail DMR Tier 1: Unlicensed On-site Technologies
Worldwide digital two-way Light Industrial
Agriculture dPMR Tier 1: Unlicensed
radio markets can be roughly Hospitality
divided into three categories

Commercial and Light Industrial. Multiple relevant digital technologies exist for
this market, including on-site digital technologies such as Frequency Hopping Spread
Spectrum (FHSS) utilized in unlicensed 900 Mhz and 2.4 GHz bands. The European
Telecommunications Standards Institute, or ETSI, has also defined two Tier-1 protocols for
digital mobile radio (DMR) in the unlicensed PMR446 band; the DMR Tier-1 protocol utilizes
12.5kHz FDMA, while the dPMR protocol utilizes 6.25kHz FDMA. Both protocols provide
for consumer applications and low-power commercial applications, using a maximum of
0.5 watt RF power. With a limited number of channels and no use of repeaters, no use of
telephone interconnects, and fixed/integrated antennas, Tier-1 DMR/dPMR devices are best
suited for personal use, recreation, small retail and other settings that don’t require wide
area coverage and advanced features.

Mission-Critical Public Safety. This market category is defined by mission-critical
communications, security, and interoperability needs. In countries covered by ETSI, a
relevant digital standard is the TErrestrial Trunked RAdio (TETRA) standard, which is used
to support multiple talk groups on multiple frequencies, including one-to-one, one-to-many
and many-to-many calls. TETRA is a digital standard that uses four-slot TDMA in 25 kHz
channels to increase spectral efficiency and allow multiple access.

TDMA Technology

In the U.S., the Telecommunications Industry Association (TIA) has established Project 25
to define similar capabilities for the mission-critical market. Unlike TETRA, Project 25 Phase I
uses 12.5 kHz channels and currently uses FDMA for both trunked and conventional digital
systems. Phase II will add two-slot TDMA capabilities for digital trunked radio. Both TETRA
and Project 25-compliant systems rely on sophisticated infrastructure to achieve the fault-
tolerant reliability and advanced calling functionality required in public-safety and other
mission-critical applications.

Business-Critical Professional. In between the commercial/light industrial and mission
critical/public safety market categories lies a huge market for organizations who aren’t
engaged in mission-critical work and don’t have the budget or need for expensive, fault-
tolerant infrastructure—but who can still benefit from increased capacity in licensed channels,
advanced features, wide area coverage and other benefits usually associated with mission-
critical systems. Businesses in this category include transportation, education, construction,
manufacturing, private security, small municipalities, and many other industries.

The ETSI DMR Tier-2 standard is the relevant digital radio standard targeted to these
users, providing spectral efficiency, advanced voice features and integrated IP data
services in licensed bands for high-power communications. ETSI DMR Tier-2 calls for two-
slot TDMA in 12.5 kHz channels. Two-slot TDMA technology is the primary focus of our
discussion in this paper.

Analog radios have been used in business-critical applications for years. However, as
manufacturers introduce high power digital radios to this market, they have a choice: they
can either build their communications system using a proprietary technology such as digital
6.25kHz FDMA, or they can leverage standards-based TDMA. The two are not compatible
or interoperable.

Motorola believes that two-slot TDMA is the best fit for most professional, business-
critical digital two-way radio applications. Moreover, ETSI has selected TDMA as the
standard protocol for Tier-2 professional two-way radio applications, and it satisfies ETSI
channel emissions requirements and goals for spectral efficiency. Although the FCC does
not mandate standard protocols, devices conforming to the ETSI Tier-2, two-slot TDMA
standard will meet existing FCC channel emissions requirements for 12.5 kHz channels
and exceed forward-looking requirements for spectral efficiency in the U.S. With technical
advantages for the professional market, and the backing of the world’s most influential
telecommunications standards bodies, two-slot TDMA is the clear choice for organizations
looking to deploy new digital two-way radio systems, or to upgrade their existing analog
radio to digital.

Let’s take a closer look at two-slot TDMA and why it’s the best multiple-access technology
for the majority of professional applications.

TDMA Technology

Multiple Access and Spectral Efficiency
The primary goal of any multiple-access RF technology is to achieve greater spectral
efficiency, allowing more users to share a given channel in the licensed RF spectrum.
Historically, the licensed airwaves were divided into relatively large 25 kHz channels. There
was plenty of room for the broadcasters using these channels to exist side-by-side, without
significant interference problems. Over the years, however, the airwaves have become
increasingly crowded, creating a need for new standards and technologies that allow more
radio users to share the available spectrum in any given area.

The demand for greater spectral efficiency is being driven, in part, by regulatory agencies.
In the U.S., for example, the FCC is requiring manufacturers to offer only devices that
operate within 12.5 kHz VHF and UHF channels by 2011. By the year 2013, all VHF and
UHF users will be required to operate in 12.5 kHz — making it possible for roughly twice as
many users to share the airwaves as compared with today’s 25 kHz licenses.
The next logical step is to further improve the effective capacity of 12.5 kHz channels. While
there’s no current mandate requiring a move to 6.25 kHz, discussions are continuing at the FCC
and other agencies, and it’s only a matter of time before the ability to carry two voice paths in a
single12.5 kHz channel, also known as 6.25 kHz equivalent efficiency, becomes a requirement in
VHF and UHF bands. In the meantime, two-slot TDMA offers a way to divide a 12.5 kHz channel
into two independent time slots, achieving 6.25 kHz-equivalent efficiency today.

With two-slot TDMA-based devices, there’s no reason to wait for a government mandate
to achieve more capacity on existing licensed channels. Business can take the initiative to achieve
greater spectral efficiency well ahead of the inevitable regulations — and ahead of the competition.
And even without a regulatory mandate, greater spectral efficiency offers many operational
benefits. We’ll discuss those benefits later, but first let’s explore how two-slot TDMA works.

TDMA: How It Works
TDMA stands for “Time-Division Multiple Access.” Like FDMA, or “Frequency-Division Multiple
Access,” TDMA is a technology that allows multiple conversations to share the same radio
channel. Although the goal is the same, the two technologies work very differently.

6.25 kHz FDMA
In FDMA, a channel frequency is split into smaller subdivisions — for example, splitting
a 25 kHz band into two narrower “sub-channels” that transmit side-by-side to achieve
12.5 kHz equivalent spectral efficiency. The same technique can be used to achieve 6.25
kHz equivalent efficiency in a 12.5 kHz channel — although how well this technique will
perform hasn’t yet been established in real-world implementations on a large scale.

As the subdivisions of a licensed channel become narrower, there’s a growing likelihood
of problems due to congestion and interference in an FDMA-based 6.25 kHz-equivalent
system, as shown in the illustration.

12.5 kHz Channel Regulatory
Emissions Mask

12.5 kHz Signal 6.25 kHz 6.25 kHz
When FDMA technology is used to split Signal Signal
a channel into two sub-channels, the
resulting signals must still fit within the
channel’s required emissions mask 12.5 kHz Channel 12.5 kHz Channel

TDMA Technology

When you try to squeeze two 6.25 kHz signals into one 12.5 kHz channel, you still have
to meet the channel’s regulatory emissions mask. In order to do, the signal deviation
(represented by the height and width of the lobes in the illustration) must necessarily be
smaller than what can be achieved with a single 12.5 kHz signal. This smaller deviation
means reduced sensitivity, which in turn reduces effective signal range in real world
conditions. At the same time, there is very little tolerance for errors introduced by oscillator
aging, and the 6.25 kHz signal contains more energy near the edges of the mask — making
it more prone to adjacent channel interference and near/far interference problems. This
results in reduced quality of service in real world conditions.

Two-Slot TDMA
By comparison, TDMA offers a proven method for achieving 6.25 kHz equivalency in
12.5 kHz repeater channels — a major benefit for users of increasingly crowded licensed
bands. Instead of dividing the channel into two smaller slices, TDMA uses the full channel
width, dividing it into two alternating time slots. As a result, TDMA essentially doubles
repeater capacity while preserving the well-known RF performance characteristics of the
12.5 kHz signal.

Voice Call 1

Time Slot 1 Time Slot 2 Time Slot 1 Time Slot 2

Voice Call 2
or Data Exchange

TDMA divides a 12.5 kHz channel into two alternating time slots to achieve
6.25 kHz equivalent spectral efficiency when used with a repeater.

From the perspective of RF physics — that is, actual transmitted power and radiated
emissions — the 12.5 kHz signal of two-slot TDMA occupies the channel, propagates,
and performs essentially the same as today’s 12.5 kHz analog signals. With the added
advantages of digital technology, TDMA-based radios can work within a single repeater
channel to provide roughly twice the capacity of analog while offering RF performance
equivalent to, or better than, today’s analog radio.

As we will see, the two time slots can potentially be used for a variety of purposes.
Most organizations considering TDMA-based two-way radio will probably be interested in
doubling the voice capacity per licensed repeater channel. By enabling 6.25 kHz equivalency,
TDMA supports two simultaneous, independent half-duplex calls in a single 12.5 kHz
repeater channel.

TDMA Technology

If you’re used to thinking about analog radio, this two-for-one capacity in two different
time slots might seem problematic. Wouldn’t the two calls cut in and out as the time slots
alternate, making both conversations nearly impossible to understand?

But remember, this is the digital world, where voices are encoded in bits. Although analog
signals represent the actual duration of spoken words, digital signals can encode that
duration in a way that allows for significant compression without compromising voice
quality. Each TDMA time slot is quite brief — on the order of 30 milliseconds. The circuitry
that translates voice into bits is actually able to pack 60 milliseconds worth of digitized
speech into each 30 millisecond time slot. The receiver, in turn, unpacks those bits into
speech that has its full 60 millisecond time value.

That’s why, with TDMA, two conversations can happen simultaneously and seamlessly via
a single repeater. The alternation of time slots is something that happens in the technology
only, not in the user’s experience. In fact, digital technology offers better background
noise suppression than analog while preserving the integrity of the signal at the farthest
reaches of the transmitter’s range — so both digital conversations are likely to be much
clearer than a single analog conversation would be over the same channel. And because
both conversations use the channel’s full bandwidth, there’s no degradation in range
performance, and no added risk of interference with adjacent channels.

Advantages of Two-Slot TDMA for Professional Organizations
If you’re in the professional two-way radio category, and you’re looking for increased system
capacity in 12.5 kHz channels along with higher performance and advanced features enabled
by digital radio solutions, you need to decide which technology to choose: 6.25 kHz FDMA or
12.5 kHz two-slot TDMA. 12.5 kHz FDMA remains an important technology in analog radio
systems, and is currently the standard for mission-critical digital radio under Project 25, Phase I.
However, 6.25 kHz FDMA is not well-proven and does not fit cleanly into today’s 12.5 kHz
channel structure. Professionals looking for a digital solution should strongly consider two-slot
TDMA for the many advantages it provides.

Increased Spectral Efficiency
As we have discussed, two-slot TDMA offers a proven way to enable 6.25 kHz
equivalent efficiency in licensed 12.5 kHz repeater channels. This doubles per-channel
communications capacity, while satisfying future regulatory requirements for 6.25
kHz equivalent efficiency. And unlike 6.25 kHz transmission methods build on FDMA
technology, TDMA fits seamlessly into existing licensed channel structures in UHF and VHF
— known performance, no need for rebanding or relicensing, and no risk of new forms of
radio channel interference. The choice of TDMA digital technology makes it quick and easy
to gain spectrum efficiency and improve your two-way radio communications.

Lower Equipment Costs
Compared to 6.25 kHz FDMA, two-slot TDMA allows you to achieve 6.25 kHz equivalent
efficiency while minimizing investments in repeaters and combining equipment. This is one
reason why TDMA is so well suited to professional applications, where the budget for two-
way digital radio may be limited compared to the mission-critical tier.

FDMA requires a dedicated repeater for each channel, plus expensive combining
equipment to enable multiple frequencies to share a single base-station antenna. It can
be particularly expensive to make combining equipment work with 6.25 kHz signals, and
there’s typically a loss in signal quality and range when it’s used this way.

In contrast, two-slot TDMA achieves two-channel equivalency using single-channel
equipment. No extra repeaters or combining equipment is required.

TDMA Technology

Advanced Features and Flexibility
In a traditional FDMA two-way radio implementation, each transmission occupies a full
12.5 kHz channel. A single channel can accommodate a single, half-duplex call. Proprietary
implementations that use FDMA to achieve two 6.25 kHz equivalent channels enable two
conversations to take place within a 12.5 kHz channel — but again, both of these conversations
are half-duplex, and there’s no flexibility to put the extra capacity to any other use.

TDMA-based digital systems with two time slots aren’t bound by these technical
restrictions. The two time slots can be used to carry two half-duplex conversations —
as with the two sub-channels in an FDMA-based system — but with no need for extra
equipment and no danger of reduced performance. Unlike FDMA, however, it’s also
possible to use the second TDMA time slot for other purposes.

For example, device designs for the first-generation of TDMA-based two-way radio
include the ability to use the second time slot for reverse-channel signaling. This capability
can be used for priority call control, remote-control of the transmitting radio, emergency
call pre-emption, and more. The second time-slot could also be used for transmitting
application data such as text messaging or location data in parallel with call activity —
a useful capability, for example, in dispatch systems that provide both verbal and visual
dispatch instructions.

TDMA-based systems also offer the flexibility to adapt as new applications emerge to
make additional use of the two time slots — preserving initial investments while providing
an open path to future usage models for digital two-way radio. For example, the future
roadmap for two-slot TDMA applications includes the ability to temporarily combine slots
for increased data rates, or to use both slots together to enable full-duplex private calls.

Additional capabilities will also emerge, as driven by the real-world needs of two-way radio
users in the professional marketplace. By choosing TDMA, professionals can immediately
gain benefits such as 2:1 voice capacity and reverse-channel signaling within a single
channel, with the option to add other capabilities as they become available. FDMA, in
contrast, is optimized for a single purpose — half-duplex calling.

One call per
repeater and channel
Two-channel Analog or Digital FDMA System

Repeater 1
Frequency 1
Combining
Equipment
Repeater 2
Frequency 2
Radio Groups

Two calls per
repeater and channel
Two-channel Digital TDMA System

TDMA saves licensing and equipment
costs by enabling the equivalent of
two 6.25 kHz channels within a single Repeater
licensed 12.5 kHz channel Frequency 1

Radio Groups

10 TDMA Technology

Longer Battery Life
One of the biggest challenges with mobile devices has always been battery life. In the
past, there have only been a couple of options for increasing the talk time on a single
battery charge. One way is to increase battery capacity. Battery manufacturers have
already done a remarkable job of maximizing capacity, but further gains are only possible by
increasing the size of the battery pack — and therefore decreasing portability.

The other option is to decrease transmit power, which is by far the most energy-intensive
function of two-way radio. But this means decreasing transmission range and increasing
the potential for interference from other devices — an unacceptable tradeoff in
professional situations.

Two-slot TDMA provides another, very effective option. Since each call uses only one of the
two slots, it requires only half of the transmitter’s capacity. The transmitter is idle half the
time — that is, whenever it’s the unused time-slot’s “turn.”

For example, in a typical duty cycle of 5 percent transmit, 5 percent receive, and 90
percent idle, the transmit time accounts for roughly 80 percent of the total current drain
on the radio’s battery. By cutting the effective transmit time in half, two-slot TDMA can
thus enable an up to 40 percent reduction in current battery drain, or an up to 40 percent
improvement in talk time. As a result, overall battery consumption per call is dramatically
reduced, enabling much longer usage time in the field between recharges. Modern digital
devices also include sleep and power-management technologies that increase battery life
even further.

The Right Choice for Professional
Two-Way Digital Radio: TDMA
For professional users, digital two-way radio in licensed bands is the wave of the future.
Whether they’re using analog radio today, or looking to implement their first two-way radio
system, business organizations of all kinds will soon be choosing their first digital two-
way radio solutions. The advantages and opportunities are simply too great to ignore — in
transportation, education, construction, manufacturing, energy and utilities, private security,
small municipalities and many other industries.

For most enterprises in these professions, TDMA provides the best method for achieving
6.25 kHz equivalent efficiency in licensed 12.5 kHz channels:
• TDMA is being leveraged in European and U.S. standards initiatives aimed at providing
greater spectral efficiency for the land mobile radio market.
• Unlike FDMA methods of rebanding existing channels into discrete 6.25 kHz channels,
properly designed
two-slot TDMA systems fit cleanly into existing channel structures, with no rebanding or
relicensing necessary.
• TDMA improves capacity today, while offering a path to compliance with further channel
efficiency requirements that may be mandated in the future.
• Because it increases capacity without the need for additional repeaters and other
infrastructure, TDMA can lower the overall costs of implementing digital two-way radio.
• TDMA offers the performance and flexibility to support the functional requirements of
mobile professionals in virtually any industry.

11 TDMA Technology

Motorola’s Next Generation TDMA-based Professional
Digital Two-Way Radio
Motorola invented the first portable two-way radio, and has more than 65 years of experience delivering wireless
communications systems for government and industry. Motorola has emerged as the recognized leader in digital
two-way radio technology, with proven solutions in the mission critical, professional, and unlicensed tiers.

Now Motorola is enabling innovative solutions for licensed professional tier. MOTOTRBO™ Professional Digital
Two-way Radio System is a digital communications platform that combines the best of two-way radio with digital
technology based on TDMA to deliver increased capacity and spectral efficiency, integrated data applications and
enhanced voice communications. MOTOTRBO is specifically designed to meet the requirements of professional
organizations that need a customizable business critical communication solution using licensed spectrum.

MOTOTRBO is a private system that can be tailored to meet the unique coverage and feature needs of group-
oriented and dispatch environments. And, MOTOTRBO provides a return on investment requiring only a small
up-front investment with no recurring fees, and will typically pay for itself in less than 18 months compared with
cellular or public carrier solutions.

For more information on the MOTOTRBO Professional Digital Two-Way Radio System visit
www.motorola.com/mototrbo.

Motorola, Inc.
1303 E. Algonquin Road
Schaumburg, Illinois 60196 U.S.A.
www.motorola.com

MOTOROLA and the Stylized M Logo are registered in the U.S. Patent and
Trademark Office. All other product or service names are the property of their
registered owners. © Motorola, Inc. 2006

Tdma technology

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