GoTa Digital Trunking Services and Their Operating Modes

As a digital trunking system derived from the CDMA2000 technology, the GoTa system has many features and advantages of a CDMA system. Basically a GoTa system can be used in two fields: the private mobile radio system that includes the dispatching system, government Integrated Emergency Response System (IERS) and vehicle location report system, and the public mobile radio system that consists of the cellular mobile phone, radio paging system and cordless phone.
  Equipped with positioning equipment such as the Mobile Position Center (MPC) and Position Determining Entity (PDE), a GoTa system can implement a high-efficient location function.

The trunking communication system is an important branch of mobile communication systems. ZTE Corporation has launched CDMA-based GoTa (Global Open Trunking Architecture) digital trunking system with its proprietary intellectual property rights[1]. Compared with TDMA-based trunking systems[2], GoTa system has a higher frequency efficiency and greater capacity due to advanced CDMA technologies. 

  Besides basic trunking dispatch services, a GoTa system can offer mature and perfect services of traditional mobile networks, including basic telecom services, complementary services, short message service and high-speed
(153.6 kb/s) data services.

1 GoTa Services

1.1 Trunking Dispatch Services
  Trunking dispatch services include:
  (1) One-to-One Private Calls
  One-to-one private calls are point-to-point communication between terminal equipment such as mobile stations, fixed stations and dispatch stations. They are divided into one-to-one private calls within a group and one-to-one private calls between groups. Flexible numbering schemes help implement private communication within a group through dialing short numbers.

  (2) One-to-Many Group Calls
  For one-to-many group calls, each group has a unique group icon to implement group calls, i.e. one-to-many half duplex communication. Any members of a group can initiate a group call by inputting the group icon and then pressing Push-to-Talk (PTT) button.

  (3) Dynamic Regrouping
  No matter in idle status or during calling, the group administrator can add or delete group members via mobile methods. The system will send a confirmation signal to notify the administrator the success of addition or deleting. Moreover, the administrator can set user priorities and conversation time limits.

  (4) Forced Release and Forced Insertion
  A user with a higher priority can get the communication right of a lower-priority user. By forcing the release of the user with the lowest priority, this function helps avoid the failure of emergency calls due to system congestion, when the system resource is short or emergency happens.

  (5) Late Entry
  A call cannot reach the object mobile station if it is off or out of the PTT service area during calling. However, the function of Late Entry can, without any manual operation, implement the automatic group calling to this object later once it is on or in the PTT service area.

  (6) Call Display
  For a group call, the group number is displayed on the terminal of the called party, while, for a private call, it is the number of the calling party that is displayed.

  (7) Talk Prompt
  There is a talk prompt ring when a group member gets the right to talk.

  (8) Call Forward of GoTa User Groups
  For GoTa users, functions of call forward when busy and call forward with no conditions are available.

  (9) Group VPN (Virtual Private Network)
  Trunking VPN can be implemented on the GoTa network. End users can manage equipment configurations of their terminal users, including opening accounts, adding new services, changing private dispatch numbers, group numbers and phone numbers, regrouping and obtaining detailed calling history lists and statistics as their like. Meanwhile, making use of CDMA network resources, VPN services of the intelligent network may provide some enterprises or groups with a logically dedicated network on which these enterprises and groups can offer services to their CDMA clients. These services are allowed to support internal calling with short numbers of the dedicated network. Besides, for these services, calls between VPN users enjoy some favored charges.

  (10)  Other Functions
  End-to-end encryption and the trunking dispatch station are also available.

1.2 Basic Voice Services
  (1) Phone Services
  Fully automatic phone services with both users of the Public Switched Telephone Network (PSTN) and those of digital mobile phone networks are offered. Various special service calls are available, including all sorts of inquiries and application services. In addition, manual and automatic wireless paging services are provided.

  (2) Emergency Call Services
  These services are applied when users call to public networks via special service calling.

  (3) Complementary Services
  The GoTa system supports users to register, activate/inactivate and delete information about a certain complementary service through calling a special character number. It also supports operators to change users’ information about various complementary services via the service application station. The complementary services include call forwarding, call waiting, three-party calling, meeting calling, call transfer, number identification, Personal Identification Number (PIN) code access, PIN code interception, voice information pick-up, message waiting notification, no disturbance, calling via passwords, and so on.

1.3 Wireless Data Services
  (1) Packet Data Services
  The GoTa system provides a two-way data channel with a rate of 153.6 kb/s. The channel helps develop diversified data service. For example:

• The channel can be used for visiting the Internet, File Transfer Protocol (FTP) download, Voice on Demand (VoD) and so on.
• It meets demands on images and video data, and can be applied in such fields as public security, transportation, news media and hydraulic works construction.
• It provides video monitoring function, and can be applied in public security, transportation and estate management.
• It can implement wireless data applications, so is fit for industries with demands on wireless data transmission such as the electric power industry, environment protection units, weather service providers, railway departments, oil fields and finance industry.

  (2) Message Services
  Message services include:

• Point-to-point short message service. Both short message sending within the GoTa network and that between the GoTa network and other Public Land Mobile Networks (PLMN) are supported.
• Missed call prompt service.
• Trash message monitoring service.
• Cell broadcasting and greetings to roaming users.

  (3) Location Services
  The location services implement all sorts of service applications related to location by using wireless positioning technologies.

  Such services include:

• Positioning functions based on Cell ID and AFLT (Advanced Forward Link Trilateration) positioning. GoTa terminals generally support these functions.
• GPS (Global Positioning System) function of terminals, which transfers location information of the terminals via packet data networks.
• GPS-based positioning with high precision.
• Other location-related services such as location inquiry, goods tracing, vehicles dispatching, children guarding and navigation.

  In addition, GoTa also offers WAP-based services, IN-based services and other additional services.

2 Service Operation Modes
Based on digital trunking dispatch services, GoTa offers diversified wireless mobile services.

  GoTa applications in 4 typical trunking application fields are analyzed in the following.

  (1) Public Security Departments, Fire Departments and Army
  Public security departments, fire departments and army ask for the trunking calls with high priorities. Moreover, they want solid terminals with easy and convenient operation.

  Service modes of GoTa at these departments mainly include:

• Group calls with quick access and high access success rates.
• Good secrecy. The system and terminals should have end-to-end encryption.
• Packet data services with functions of image and video data transmission, data inquiry and video watch.
• Positioning. The dispatch/control station can inquiry and gain the geographic location of groups via the third party.

  (2) Popular Users
  Popular users are mainly such user groups as students, family members, friends, individual users, members of various associations.

  Their service modes mainly have:

• Basic trunking functions. The private call is a point-to-point call between groups. The charge of a group call is lower than that of a basic voice service, so the private call can save the cost of a call. Group calls can be made between both fixed groups and temporary groups.
• Group sending of short messages within a group. The system implements the group sending of short messages within a group to meet demands of popular users. A terminal of a group sends out a short message by the group number, and then all the group members can receive the message. This function is often used for meeting notification and greetings between group members.
• Positioning function. Location of children and the aged can be watched through short messages and online inquiry.

  Instant messages. Applied into the trunking system, instant messages can implement convenient and quick communication between friends in a group.

  (3) Transportation Departments
  Mobility is the characteristic of users at transportation departments. GoTa services can provide vehicle drivers and dispatch administrators with trunking dispatching to meet industrial demands on routine vehicle management,
real-time communication and so on. Meanwhile, users enjoy positioning service via their trunking terminals.

  (4) Building Industry, Hotels and Urban Administration Departments
  Users at the building industry, hotels and urban administration departments are low-end users. They are either potential or mature trunking service user groups. They usually use basic trunking functions and should be given priority to develop. Basic voice services and intelligent network services are necessary, and favorite or low charge strategies are attractive.

3 Billing Strategies
  According to the characteristics of the GoTa digital trunking system, its bill strategies mainly include billing according to talk time, conversation time, successful calls, traffic and monthly fixed pay of user groups respectively. In general, billing strategies should differentiate calls between users, calls between groups, group calls and private calls.

  The service charges of a GoTa system mainly include the trunking dispatch service charge, basic voice service charge, wireless data service charge and short message service charge. Billing schemes of trunking dispatch services are suggested here:

• Users of groups pay a fixed amount per month to user private calling and group calling without any limitation on call times and talk time.
• A group pays a fixed amount per month. The group is regarded as a whole, and the monthly charge is made according to the user number of the group.
• A user pays a fixed amount per month according to either call times or talk time of group calls and private calls.
• Private calls and group calls are separated to charge. The former is charged according to call times and talk time, while the latter adopts a fixed monthly pay.
• Group calls (according to the group size) of group users and private calls are charged by call times.
• Billing according to actual call times and talk time.
• Billing according to the calling party.

  In real operation, an operator can, according to their strengths and need, adopt one of the schemes mentioned above or combinations of several schemes. Moreover, combining billing of basic voice services, wireless data services and short message services, the billing of trunking dispatch service can provide different user groups with different charge sets.

4 Conclusions
The Public Mobile Radio (PMR) trunking network is a main development trend of future digital trunking communication systems, which has strengths of common frequencies and channels sharing, coverage sharing, communication service sharing and cost sharing. The design of the GoTa system has taken the characteristics of a common trunking network into full consideration.

  Facing mobile operators, it paid full attention to various demands of mobile commercial users. Only one GoTa terminal integrates multiple communication services such as trunking dispatch services, basic voice services and wireless data services into one network, so GoTa users can make full use of great advantages of the wireless world.

References
[1] YDC 031-2004 General Specification Requirements on CDMA-Based Digital Trunking System [S].
[2] SJ/T11228-2000 Digital Trunking Mobile Communication System Structure [S].

Manuscript received: 2004-11-16