BASE STATION CONTROL METHODS

(Source: Motorola, author unknown)

TONE REMOTE CONTROL
Tone Remote Control (TRC) is a Motorola control sequence used in keying transmitters. The TRC sequence comprises three basic elements: High Level Guard Tone (HLGT), Function Tone (FT), and Low Level Guard Tone (LLGT). The TRC sequence follows an audio level convention whereby FT is 10 dB below HLGT and LLGT is 30 dB below HLGT. The relative audio levels of HLGT, FT, and LLGT are usually referenced to a system Test Tone level. Test tone is defined as a 1000 Hz signal sent from the controller at the system operating level by which the transmitters are aligned to produce nominal analog transmit deviation. Relative to Test Tone, HLGT is 5 dB above Test Tone, FT is 5 dB below Test tone and LLGT is 25 dB below Test tone. Figure 2 graphically illustrates the control sequence.

Paging uses a Tone Remote Control sequence called PURC TRC. PURC is an acronym for Paging Universal Remote Control, trademarked by Motorola. The TRC sequence was modified and redefined to allow a transmitter to be keyed on a specific frequency channel and to place the transmitter in the proper mode of operation (analog or binary). The mode of transmitter operation is determined by the information that follows the TRC sequence. The analog mode is assumed when the normal TRC sequence of HLGT, FT, and LLGT is sent. The binary mode of operation is assumed when no LLGT follows the FT, and instead a gap or pause of silence occurs followed by paging modem tones. Often due to noisy wireline environments, this pause gets detected as a signal and thus causes mode switches from analog to binary to not take place. Consequently the binary page goes out in the analog mode and the pager is not alerted.

HLGT is a 2175 Hz frequency tone that indicates the start of a TRC control sequence. Function Tone is used to tell the transmitter on what frequency channel to key or is used to disable a transmitter when sector paging is used. FT values range from 750 Hz to 2350 Hz in 100 Hz steps (excluding 2150 Hz and 2250 Hz). The 1950 Hz function tone is the standard key on channel 1 frequency. LLGT is a 2175 Hz tone used to tell the base station that the controller has access to the channel in the analog mode. A loss of LLGT and activity by the base station for more than 350 milliseconds will cause the transmitter to drop off the air. For more in depth timing information on the operation of PURC TRC consult the PURC Simulcast System Controller and Paging Station Controller instruction manual, part number 6881063E15.

Non-Simulcast Function Tone Key Commands for PURC 5000 stations. This option requires special TRC software and the transmitter needs to be programmed for multiple frequency operation.

2050 - Monitor

1950 - Key on Channel 1

1850 - Key on Channel 2

1350 - Key on Channel 3

1250 - Key on Channel 4

1150 - Key on Channel 5

1050 - Key on Channel 6

950 - Key on Channel 7

750 - Key on Channel 8

Simulcast Station Function Tone Key Commands Standard PURC 5000 station TRC.

1950 - Key on Channel 1

850 - Key on Channel 2

2350 - Key on Channel 3

FIGURE 2. PURC Tone Remote Control Audio Flow Diagram

DIGITAL REMOTE CONTROL
Digital Remote Control (DRC) is a Motorola developed MSK, Minimum Shift Keying, communications control scheme. The digital signaling scheme uses Cyclical Redundancy Checking (CRC) and convolutional coding. This provides excellent error detection and forward error correction in the presence of fading, noise, and multi-path distortion in the outbound (control) and inbound (diagnostic) RF channel. The code was developed by the Motorola Data Communications group and therefore it is referred to as MDC. The signaling scheme used for Paging DRC control is a 1200 baud scheme, MDC 1200. The signaling scheme is transmitted via 1200 and 1800 Hz modem tones for distribution through phone line and RF mediums. An MDC 1200 mess
age used for paging control is approximately 233 milliseconds in duration.

Unlike TRC, which had limited control functionality, DRC is able to transfer much more information in each transmitted packet of MDC 1200. Due to error detection and correction, DRC offers substantially improved performance reliability over TRC in noise environments. Unlike TRC, which relied on "pauses" and "gaps" of silence to force mode switches, DRC simply sends a specific message identifying the desired mode of operation. DRC is therefore referred to as a positive control scheme. See Figure 3 and 4 below, which illustrate Analog and Binary DRC keying sequences. The sequences shown are for single key and dekey modes. If multiple and alternating key requests were present the dekey message would be substituted with the appropriate MDC keying message. HLGT does not need to be present since the link will remain keyed on activity.

FIGURE 3. Analog and Binary keying sequence for Non-Advanced Control DRC Paging Stations

Figure 3 illustrates the order of control information as well as relative level differences in the information. As shown above, HLGT is only required for an RF control system where it keys link transmitters and repeaters. The duration of HLGT is dependent on the number of repeaters and if Digital Private Line (DPL) is used or not. When in use, DPL is a coded identification that is included in the TRC message intended to key a certain link transmitter to insure private use. The MDC DRC messages are sent at the same level as HLGT. LLGT is sent only during an analog page to identify operation in the analog mode. The base station looks for LLGT and will drop off the air if LLGT is not detected for more than 6 seconds and no audio activity exists. This is required as a fail safe method in the event of a control channel impairment to the station (i.e., receiver, link transmitter, or link repeater failure) prior to decoding an MDC dekey message. Without this fail safe method the station could remain keyed indefinitely with dead or offset carrier. LLGT is transmitted 30 dB down from HLGT and MDC audio level. The base station will reduce the LLGT signal another 30-40 dB via a notch filter to prevent the tone from mixing with a voice page and degrading the audio quality. For an Analog transmission the audio is sent at 5 dB down from HLGT and MDC audio level. For a binary page LLGT is not sent. After a binary key message, FSK modem tones are sent until no more binary pages exist. The station senses FSK audio and will drop off the air if FSK audio is not detected for more than 6 seconds. This check of incoming FSK audio is a fail safe method to prevent a transmitter from being keyed indefinitely if the control channel to the station is impaired (from receiver, link transmitter, or link repeater failure) prior to decoding an MDC dekey message. The FSK modem tones are sent 5 dB down from HLGT and MDC audio level.

ADVANCED CONTROL DRC INFORMATION FLOW AND RELATIVE LEVEL DIFFERENCES

FIGURE 4. Analog and Binary keying sequence for Advanced Control DRC Paging Stations

Advanced Control Paging Stations are designed with a different hardware and software architecture than non-advanced control paging stations. This architecture difference imposes operating differences in the MDC audio level required for optimal station MDC decoding. The only difference between Figure 3 and Figure 4 is the MDC message level relative to HLGT and paging information audio. MDC audio is 5 dB below HLGT. MDC audio level now is at the same level as either analog or binary paging information. In the event a DDC controller is used with Advanced Control Paging Stations, the MDC audio level from the Digital Diagnostic Controller (DDC) should be decreased by 5 dB. This 5 dB reduction in level gives the station additional audio level capability. Non-advanced control stations working under this audio level protocol will be more susceptible to falsing low deviation alarms since the alarm trip point is fixed in hardware and will alarm when MDC is received at 6 dB below the HLGT level. This only gives the channel 1 dB of margin as opposed to 6 dB.

DRC MESSAGE STRUCTURE AND FORMAT TYPES
DRC signaling allows for information transfer between the controller and transmitter as well as providing keying control. This added level of communications allows for remote individual transmitter access for diagnostics as well as configuring or reprogramming various station operating parameters. As with any communications protocol, the data is formatted and interpreted from a data set, which is defined by the Product Group. DRC has two completely different data sets commonly referred to as DRC 1 and DRC 2. Due to the limited amount of communications provided by DRC 1, DRC 2 was created to add expanded communications capability beyond that provided by DRC 1.

DRC 1
DRC 1 is the communications protocol used by the Digital Diagnostic Controller (DDC), Advanced Simulcast Controller 1000 (ASC 1000), PURC 5000 DRC transmitters (JLB models) and MICOR PURC DRC transmitters (non-Advanced Control). Advanced Control transmitters can support both DRC 1and DRC 2 messaging, however full feature capability of the Advanced Control will only be realized when DRC 2 messaging is used.

To better understand DRC 1 communications for key control and diagnostic messaging the following three DRC parameters must be discussed: the System ID, the Group ID, and the Individual Station ID. The System ID uniquely associates a paging transmitter with a DRC controller. It has 255 possible values, ranging from 0 to 254. The controller and paging transmitter must be programmed with matching System ID's if they are to communicate. Key control for paging is based on the System ID alone.

The Group ID is another ID used to differentiate the controller from the base station. The Group ID has 1024 possible values, ranging from 0 to 1023. The Group ID was implemented early on in the DRC development program for potential future expansion, however it has never been utilized. The Group ID is set by hardware jumpers on the DRC CPB board, unlike the System ID which is programmed in EEPROM non-volatile memory. A peculiarity between the Group ID and DDC controller does exist however. During diagnostic messaging, the station responses include the status of the CPB board Group ID. If the Group ID does not match the Group ID programmed in the DDC, then the message is ignored. This often creates a problem when someone accidentally changes the DDC Group ID value and then cannot figure out why the station keys and sends diagnostic messages but the controller reports a 'No Response' alarm. The CPB board ships from the factory with a Group ID of 0 and should never be changed. For the Advanced Control, ASC 1000, and ASC 1500 product, the Group ID is not a changeable value and defaults to zero (0). The Group ID concept has been cancelled in these new products. When upgrading system equipment be sure the paging transmitters have group ID's of zero (0) so that diagnostic messaging is possible with these new products.

Individual Station ID is uniquely assigned to each paging transmitter enabling communication with the controller. The Individual Station ID has 1024 values, ranging from 0 to 1023. The ID is set locally at the paging transmitter during installation. Care must be taken not to assign two stations with the same Individual Station ID since diagnostic messaging will not be possible for both transmitters. The Individual Station ID has no bearing on paging key-ups, only diagnostic or individual station testing key-ups.

The DRC 1 format has provisions for transmitters to key up on 4 frequencies and 254 sectors for both the analog and binary paging modes and transmitter test modes. The DRC 1 message format supports the following paging transmitter diagnostic messaging: forward and reflected power readings, delay line setting, station audio gain and inversion, station frequency adjust, wildcard input reads, wildcard output writes, and level 1 alarm information. Level 1 alarms are specific to the PURC 5000 paging transmitter alarm set and include, TX fault, PA fault, synthesizer out of lock, low deviation, battery revert, system timer, external 1, and external 2 alarms. For MICOR DRC stations all diagnostic messaging and alarms apply except for the station frequency adjust capability and PA fault alarm.

DRC 2
DRC 2 is the communications protocol used by the Advanced Simulcast Controller 1500 (ASC 1500) and base stations equipped with Advanced Control (JQB model transmitters, JLB models retrofitted with Advanced Control, or MICOR stations retrofit with Advanced Control). Advanced Control Paging Transmitters are unique in the sense that they can decode both DRC 1 and DRC 2 messaging. This makes the base station compatible with any system currently in use. The station operating language, DRC 1 or DRC 2, is therefore dependent on the controller.

To better understand DRC 2 communications for key control and diagnostic messaging the following two DRC parameters must be discussed: the System ID and the Individual Station ID. The System ID has 16 possible values, ranging from 0 to 15. The System ID uniquely associates a paging transmitter with an ASC 1500 DRC controller. The controller and paging transmitter must be programmed with matching System ID's if they are to communicate. Key control for paging is based on the System ID alone. As mentioned in the DRC 1 section, the Group ID parameter has been cancelled for DRC 2 messaging. When converting a system from DDC or ASC 1000 controller operation to ASC 1500 controller, the System ID must be within the 0 to 15 range. Use the original controller to change the station System ID to a value between 0 and 15.

The Individual Station ID is uniquely assigned to each paging transmitter enabling individual communication with the controller. The Individual Station ID has 1024 values, ranging from 0 to 1023. The ID is set locally at the paging transmitter during installation. Care must be taken not to assign two stations with the same Individual Station ID since diagnostic messaging will not be possible for both transmitters. The Individual Station ID has no bearing on paging key-ups, only diagnostic or individual station testing key-ups.

The DRC 2 format has provisions for transmitters to key up on 4 frequencies and 254 sectors, for both the analog and binary paging modes and transmitter test modes. The DRC 2 message format can support all alarm and diagnostic information provided by DRC 1 messaging however it is communicated in a much more efficient manner. The DRC 2 format enables new messaging required for Advanced Control and ASC 1500 systems, which could not be, implemented with the DRC 1 format.

KEY ON DATA
Key on Data is a fixed operating configuration of the transmitter rather than a specialized control scheme. When equipped with the proper software and hardware, the transmitter will key and transmit in the binary mode upon detection of paging data. Depending on the system application either the internal station paging modem or an external source of binary data can be used. This capability allows a Motorola transmitter to operate in a competitor's binary only system. For this type of operation the customer will need an external alarm reporting system to monitor the transmitter if remote diagnostics is required. The station may or may not require external data delay compensation for the transmitter when operating in a simulcast system. This is largely dependent on the transmitter model (JLB or JQB), station hardware and software, and the information channel type (analog or digital). Key on data can also be used as a temporary control method for binary only systems when the customer does not purchase the appropriate infrastructure and is willing to forfeit remote transmitter diagnostics.

DIRECT DIGITAL CONTROL
Direct Digital Control describes the method of information transfer not the content of the information. Direct Digital Control is based on DRC messages however the messages are in digital form (a bit stream of ones and zeros) rather than in analog form (MDC modem tones of 1200 and 1800 Hz). With this mode of operation the paging data is also transferred to the base station in the digital form, as opposed to being converted to analog form, 1200 and 2200 Hz modem tones.

Direct Digital Control is currently used for digital satellite distribution channels. The ASC 1500 and Advanced Control paging stations are required for this type of system operation. The ASC transmits MDC in digital form at 1200 baud and then passes or generates paging terminal data in the digital form as well. In this mode the ASC1500 expects data from the terminal at RS232 levels and outputs the data at RS232 levels. Pass through digital transmissions are restricted to baud rates of 300, 600, 1200 and 2400 baud. The ASC when used with an MBPS 2000 terminal can be configured to generate the paging information. In this manner the ASC acts like the terminal output card. Paging data is user selectable for TTL or RS232 output levels. The ASC also provides handshake signals such as Request-To-Send (RT.) and Clear-To-Send (CTS), to be used for interface with the external Digital transmission equipment for the satellite uplink.