CChina is developing a new standardfor mobile radio — Professional Digi-tal Trunking (PDT) — that representsa significant global initiative. For thefirst time, an LMR standard hasemerged from China that will eventu-ally have a global presence. Thedevelopment represents Chinese orga-nizations working together to createnew technology standards designedfor the Chinese environment. Manyorganizations will be watching closelyto see how the standard emerges andhow it may pave the way for furtherChinese-based standards in the com-munications and technology industry.

PDT, driven by the Information andTelecommunication Bureau of the Chi-nese Ministry of Public Security(MPS), has a specific function. Origi-nally called the Police Digital Trunk-ing system, the standard is designed tomeet the specific needs of China’spublic-safety sector and seamlesslyinterface with the current police geo-graphic information system (GIS) dis-patching platform. In addition, it is

intended to provide features such asflexible networking, efficient dispatch-ing, high-quality voice and data trans-mission, and secure encryption.

The standard also offers a broadernational interest purpose. “PDT is theChinese standard for digital trunkingand has been implemented in such away to remain free from the constraintsof overseas patents,” said Ma XiaoDong, chief technology officer of theInformation and TelecommunicationBureau at MPS. “The invention ofPDT will greatly improve the develop-ment pace and strength of the Chinesepolice telecom industry. It will alsoprovide a solution that is more suitablefor Chinese police operation.”

Standards BodyThree radio technologies — con-

ventional analog, analog trunking(MPT 1327) and digital trunking(TETRA) — co-exist in the Chinesepolice mobile radio environment. Allthree systems are based on standardsdeveloped outside of China. For the

past 20 years, Chinese police usershave gained valuable experience andknowledge about trunked systems andtheir applications. New requirementshave been identified for mobile com-munications networks, and a set oftechnical standards are being devel-oped based on practical police needs,creating the technical route for PDTand providing the groundwork onwhich to develop the new standard.

In August 2008, the Chinese PoliceWireless Telecom Technology Spe-cialist Panel was established. Thepanel began working with local Chi-nese manufacturers to formulate thestandard for the next generation ofChinese digital trunking radio systems.

In accordance with Chinese lawand with the strong support of sixmajor branches in the Chinese govern-ment, a number of enterprises andinstitutions specializing in the devel-opment, production, marketing andoperation of special-use digital trunk-ing systems established the Profes-sional Digital Trunking System

32 Quarter 2 2012 RadioResource Internat ional www.RRImag.com

China’s Trunking StrategyThe Chinese government is developing a digital trunked technology that is poised to

facilitate the country’s evolution of existing analog networks.

By Trevor Laughton

Photo courtesy Tait Communications

Industry Association (PDTA). Theassociation expanded the originalmeaning of PDT from Police DigitalTrunking to Professional DigitalTrunking, and broadened the systemscope to make it applicable for otherprofessional users with similar needs.

PDTA has 23 corporate members,including 22 Chinese companies andone international member, Tait Com-munications. Other foreign companiesare negotiating to join the PDTA.

Tait Communications was invitedas the first international member inrecognition of the long-term relation-ship as a supporting partner of the Chi-nese police, providing the majority ofits private networks deployed to date.The company supports open-standardstechnology, and is a supplier of MPT1327, Project 25 (P25) and DigitalMobile Radio (DMR). Tait also is acontributor in the U.S. Telecommuni-cations Industry Association (TIA) andthe European TelecommunicationsStandards Institute (ETSI) committees

that develop and govern standards.The standards-based approach to

PDT is intended to develop an open,competitive marketplace to deliver thetechnology. The MPS and PDTA areexploring conformance interoperabilitytesting, again learning from what hasworked well elsewhere in the world.

“Although PDT is China’s stan-dard, it has not been developed in isolation,” said Tait China RegionalGeneral Manager Zeng Mianzhi. “Ithas strong parallels to the ETSI DMRtrunking standard, but combines theadvantages of other digital trunkingstandards plus unique local content tomeet the specific requirements of theChinese market.”

Core Requirements The PDT standard’s intentions are

to absorb the advantages of other stan-dards to deliver the following:

■ Spectrally efficient integratedvoice and data services;

■ High-quality voice communica-

tions with high immunity to back-ground noise;

■ Support for short messaging andsatellite-based positioning applications;

■ Effective and flexible networkmanagement and control through theconsolidation of signaling and userinformation; and

■ Encryption to ensure secure andconfidential communications. Theencryption is a key differentiator withthe requirement to support a Chineseproprietary digital encryption scheme.

At a basic level, PDT closelyresembles the ETSI standard for Tier 3DMR: trunking, two-slot TDMAapplied to 12.5-kilohertz channel spac-ing. The key benefit at this level is tohalve the spectrum used in legacy analog networks, doubling the spec-trum efficiency of the 12.5-kilohertzchannels administered by China’s StateRadio Regulatory Commission.

Compared with the TETRA net-works deployed in China to date, the

www.RRImag.com RadioResource Internat ional Quarter 2 2012 33

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new standard will offer two keyimprovements:

■ Compatibility with the significantnumber of existing MPT systems usedfor police communications to ensure asmooth digital migration; and

■ Delivery of wide-area coverage atminimum cost with increased coveragecompared with analog and superiorvoice quality to the edge of range.

These two factors are significant.TETRA networks are deployed inChina’s largest cities, yet the countryis incredibly vast with analog conven-tional and MPT 1327 trunked technol-ogy public-safety networks. The needto digitize is clear — the current spectrum is consumed — but thegeography of China means that furtherdigitization is needed for maximumcoverage and cost effectiveness.

Current StatusThree aspects of the standard, the

encryption scheme, the speech vocoder

and the approach to non-Chinesepatents, are still being refined.

Encryption is an essential elementof the PDT standard. Both software-and hardware-based encryption technology and the encryption man-agement tools are being developed andwill eventually be supplied by MPS-designated agencies.

PDTA vocoder trials and technicalstudies have narrowed the speechvocoder choice to the United States-sourced vocoder used in DMR andP25, a Russian vocoder, and a localChinese vocoder developed byTsinghua University. There is a strongdesire to adopt local technology, butultimately the choice will be based oncost and performance.

With respect to the vocoder andother elements, the PDTA looked atbest practices based on a number ofinternational radio standards, in partic-ular the DMR standard. For both costand security reasons, the PDT stan-dard approach has been to develop

alternative methods to ensure non-infringement with patents held byinternational companies. Althoughwhere possible, the PDTA is alsolooking to negotiate suitable terms forthe use of these patents.

Given the current status of the stan-dard, there is a long way to go beforegenuine open-standard PDT systemscan be deployed. However the processitself provides interesting commentaryon other international standards. Thedesire for PDT to take the best of otherstandards is a bold challenge and wor-thy of global attention. Certainly theglobal intentions for the standard havebeen signaled with the formation of thePDTA. ■

Trevor Laughton is the chief technical officer

(CTO) at Tait Communications. Laughton,

who has 30 years of experience, is involved

in standards bodies around the globe and is

a strong proponent of open standards and

vendor interoperability. Email comments to

editor@RRMediaGroup.com.

34 Quarter 2 2012 RadioResource Internat ional www.RRImag.com

Hytera Communications executives

said the company has deployed sev-

eral Professional Digital Trunking (PDT)

systems in China, and they envision a

future with PDT systems deployed in coun-

tries worldwide.

In China, Hytera installed a system to

support the recent University games in

Shenzhen and a multisite PDT trunking

system for the Shenzhen Bay Custom and

Immigration checkpoint. Hong Kong Cus-

toms is also using a Hytera PDT trunked

system, along with the Guizhou Minority

Civil Games and the Harbin Police. One of

China’s largest oil fields adopted a PDT

trunked system.

“Outside of China, we have deployed

a PDT trunking system in Guatemala,”

said G. S. Kok, vice president of research

and development (R&D) for Hytera.

“We have multisite test systems currently

being set up in Thailand, Cambodia,

Indonesia and Vietnam. We also have

several enquiries from Europe, Latin

America and the Middle East wishing to

have PDT demonstration systems.”

Kok said the company plans to support

the strong market growth by relocating its

manufacturing to the Longgang district in

Shenzhen. “The new manufacturing facility

has 10 times our current manufacturing

floor space,” he said.

The technology is inexpensive, and that

is the main catalyst for growth, he said.

“PDT is an open Chinese digital trunking

standard that is extremely cost competitive

because the manufacturers pay only token

fees for the low-rate sine excitation linear

prediction (SELP) vocoder developed by

China Tsinghua University and no intellec-

tual property rights (IPR) fees for the mem-

bers,” Kok said.

Hytera provides PDT portables,

mobiles, repeaters, simulcasting and trunk-

ing solutions. The Chinese firm also has a

team developing applications software for

the products.

Executives said the PDT standard is

“loosely” based on the Digital Mobile Radio

(DMR) standard. Hytera also supplies

DMR equipment. The fundamentals of

PDT and DMR are the same; they are both

TDMA, two-slot and four-level FSK modu-

lation technologies.

“PDT is based loosely on DMR with the

same 30-millisecond time slots,” said Kok.

“The differentiator is because PDT is devel-

oped in China, it is easier to implement.

The main differences are in areas of DMR

Tier 3, which are yet to be proposed.”

Kok said one example is the GPS data

handling, which is not defined in DMR Tier

3, but is already part of the PDT standard.

PDT also defined the Air Interface Encryp-

tion (AIE) protocol, which may take a few

years to define for DMR Tier 3.

“Minor differences can be seen where

the DMR Tier 3 standards are still pending

definitions,” he said. “Hytera will follow the

ETSI standards through software upgrades

once these missing portions are defined.” ■

Sandra Wendelken is editor of Radio-

Resource International magazine. Contact

her at swendelken@RRMediaGroup.com.

China’s Hytera Sees Strong Global Growth for PDTBy Sandra Wendelken