bts3900.docx

System Architecture of the BTS3900The BTS3900 consists of the BBU3900, RFUs, and indoor macro cabinet. The BBU3900 and RFUs are installed in the indoor macro cabinet.

Figure 1 shows the BTS3900 system.

Figure 1 BTS3900 system

NOTE:

The RFUs are of two types: DRFUs and GRFUs.

The BTS3900 mainly consists of the following components:

The BBU3900 is used for baseband processing and enables interaction between the BTS and the BSC.

The RFU is an RF filtering unit, which performs modulation, demodulation, data processing, and combining and dividing for baseband signals and RF signals.

The indoor macro cabinet houses the BBU3900 and RFUs. In addition, the indoor macro cabinet provides the functions such as power distribution, heat dissipation, and surge protection.

Parent topic: BTS3900 GSM Technical Description

Logical Structure of the BTS3900The BTS3900 mainly consists of the BBU and RFUs. The logical structure of the BTS3900 consists of the RF subsystem, control subsystem, power subsystem, and antenna subsystem.

Figure 1 shows the logical structure of the BTS3900.

Figure 1 Logical structure of the BTS3900

NOTE:

In Figure 1, the power subrack (DC/DC) is configured in only the +24 V DC cabinet; the power subrack (AC/DC) is configured in only the 220 V AC cabinet.

If the TMA is configured, the GATM and the Bias-Tee must be configured.

The logical subsystems of the BTS3900 are as follows:

RF subsystem, implemented by the RFUs Control subsystem whose functions are implemented by the BBU Power subsystem whose functions are implemented by the following modules:

o DCDU–01 in the BTS3900 cabinet (-48 V DC)o DCDU–01 and Power subrack (DC/DC) in the BTS3900 cabinet (+24 V DC)o DCDU–01 and Power subrack (AC/DC) in the BTS3900 cabinet (220 V AC)

Antenna subsystem whose functions are implemented by the following modules:o Antenna

o Bais-Teeo GATMo TMA

BTS3900 Monitoring SystemThe BTS3900 monitoring system enables the power monitoring, fan monitoring, and environment monitoring.

BBU Monitoring Ports

Figure 1 shows the monitoring ports of the BBU.

Figure 1 Monitoring ports of the BBU

The BBU provides a maximum of two RS485 buses and 16 Boolean signals. The modules on RS485 bus 0 cannot be interchanged with the modules on RS485 bus 1. When two PMUs are configured, they cannot be connected to the same bus if the settings

of the DIP switches on the two PMUs are the same.

Components of the Monitoring System

Figure 2 shows the components of the BTS3900 monitoring system.

Figure 2 Components of the monitoring system

NOTE:

The RS485 bus 0 is indicated by bus0. The RS485 bus 1 is indicated by bus1.

Table 1 describes the monitoring modules of the BTS3900.

Table 1 Monitoring modules of the BTS3900

Module Address Bus Pin Description

PMU bus0 - Configured only in the BTS3900 cabinet (220 V AC)

FAN1 bus0 - Mandatory

FAN2 bus0 - Configured when two cabinets are stacked

GATM2 bus0 - Optional

GATM1 bus1 - Optional

EMU bus1 - Optional

Power subrack (DC/DC)

Boolean Pin 3 and pin 6 Configured only in the BTS3900 cabinet (+24 V DC)

Functions of the BTS3900 Monitoring System

Table 2 describes the functions of the BTS3900 monitoring system.

Table 2 Functions of the BTS3900 monitoring system

Module Monitoring Function

FAN Fan fault detection Adjusting rotation speed of the fans Detecting temperature and rotation

speed of the fans

GATM Reporting the RET control alarm signals

EMU Communicating with the central processing unit through the two RS485 ports

Detecting the input voltage Providing the independent sensor port

for detecting humidity and temperature (12 V DC/24 V DC current type)

Providing the port for detecting the Boolean input signals in dry contact mode and in OC mode

Providing six external Boolean output control ports of the relay node type

PMU Communicating with the central processing unit through the RS232/RS422 serial port

Managing the power system and the battery charging and discharging

Detecting power distribution and reporting alarms

Power subrack (DC/DC) Detecting module fault alarms (overvoltage output, no output, and fan fault)

Detecting module protection alarms (overtemperature protection, and overvoltage and undervoltage protection) and AC power failure alarms

Signal Flow of the BTS3900/BTS3900A

The signal flow of the BTS3900/BTS3900A consists of the traffic signal flow and the signaling flow of the BTS. The BTS3900/BTS3900A signal flow is classified into the DL traffic signal flow, UL traffic signal flow, and signaling flow. The BTS3900/BTS3900A supports three types of transmission mode: TDM, HDLC, and IP. The following sections describe the signal flow of the BTS3900/BTS3900A in three transmission modes respectively.

TDM Transmission

DL Traffic Signal Flow

The DL traffic signal flow is transmitted from the BSC to the MS through the BTS3900/BTS3900A. In the BTS3900/BTS3900A, the BBU and RFUs work together to process the DL traffic signals. Figure 1 shows the DL traffic signal flow.

Figure 1 DL traffic signal flow

The DL traffic signal flow is as follows:

1. The E1 signals from the BSC are transmitted to the BBU through the E1 cable.2. After receiving the E1 signals, the BBU processes the E1 signals as follows:

a. Extracts clock signals from the E1 signalsb. Configures the BTS system based on the data configuration on the OMLc. Encapsulates the E1 data in the format of the CPRI frame, and then transmits the

data to the RFU through the CPRI signal cable3. After receiving the signals, the RFU processes them as follows:

a. Decapsulates the high-speed CPRI frames to obtain the baseband signalsb. Transmits the baseband signals to the relevant operation units for encryption and

interleavingc. Converts the digital signals into the analog signals and modulates the analog

signals into RF signalsd. Combines or divides the RF signals based on its own configuratione. Transmits the combined or divided signals through the feeder and antenna

UL Traffic Signal Flow

Compared to the DL traffic signal flow, the UL traffic signal flow is transmitted from the MS to the BSC through the BTS3900/BTS3900A. In the BTS3900/BTS3900A, the BBU and RFUs work together to process the UL traffic signals. Figure 2 shows the UL traffic signal flow.

Figure 2 UL traffic signal flow

The UL traffic signal flow is as follows:

1. The antenna receives the signals sent from the MS. If the TMA is configured, the received signals are amplified by the TMA and then transmitted to the RFU through the feeder.

2. After receiving the UL signals, the RFU processes the signals as follows:a. Divides the UL signals from the antenna or diversity RX portb. Converts the divided analog signals into the digital signals to obtain the baseband

signalsc. Transmits the baseband signals to the relevant operation units for decryption and

de-interleavingd. Encapsulates the processed data in the format of the CPRI frame, and then

transmits the data to the BBU through the CPRI signal cable3. After receiving the signals, the BBU processes the signals as follows:

a. Decapsulates the high-speed CPRI frames to obtain the baseband signalsb. Encapsulates the baseband signals in the format of the E1 frame, and then

transmits the signals to the BSC through the E1 cable

Signaling Flow

The BTS3900/BTS3900A signaling flow refers to the signaling on the Abis interface. The BBU serves as the control unit and works with the RFUs to process the signaling. Figure 3 shows the signaling flow.

Figure 3 Signaling flow

The signaling flow is as follows:

1. The signaling data received from the BSC is transmitted to the BBU through the Abis interface.

2. The BBU encapsulates the signaling data in the format of the CPRI frame, and then transmits the signaling data to the RFU through the CPRI signal cable.

3. The RFU decapsulates the CPRI signals into the baseband signals, and then transmits the baseband signals to the relevant operation units for processing.

4. The RFU encapsulates the data of its own status in the format of the CPRI frame, and then transmits the data to the BBU through the CPRI signal cable.

5. The BBU decapsulates the received CPRI signals to obtain the baseband signals.6. The BBU analyzes and processes the baseband signals to obtain the BTS status, and then

sends the status data to the BSC on the Abis interface.

HDLC Transmission





1. The BSC encapsulates the service data in the format of the HDLC data packet, and then transmits the data to the BBU through the E1 cable.

2. After receiving the E1 signals, the BBU processes the E1 signals as follows:a. Extracts the clock signals from the E1 signalb. Resolves the data packet in the HDLC format from the E1 timeslot signals bound

to the HDLC channel, and then configures the BTS system based on the ESL and OML data resolved from the data packet

c. Encapsulates the HDLC service data in the format of the CPRI frame, and then transmits the data to the RFU through the CPRI signal cable

3. After receiving the signals, the RFU processes the signals as follows:a. Decapsulates the high-speed CPRI frames and HDLC packets to obtain the

baseband signalsb. Transmits the baseband signals to the relevant operation units for encryption and










de-interleavingd. Encapsulates the processed signal in the format of the CPRI frame, and then

transmits the signal to the BBU through the CPRI signal cable3. After receiving the signals, the BBU processes the signals as follows:

a. Decapsulates the high-speed CPRI frames to obtain the data in the format of the HDLC frame

b. Finds the HDLC transmission channel corresponding to this HDLC data packet, and then transmits the data in the format of the E1 frame to the BSC through the E1 cable

Signaling Flow

The BTS3900/BTS3900A signaling flow refers to the signaling on the Abis interface. The BBU serves as the control unit and works with the RFUs to process the signaling. Figure 6 shows the signal flow of signaling processing.

Figure 6 Signaling flow of signaling processing


1. The BBU receives the signaling data from the BSC through the E1 cable.2. The BBU receives the relevant signaling data and processes the signaling data as

required.3. The BBU encapsulates the signaling data to be processed by the RFU in the format of the

CPRI frame, and then transmits the signaling data to the RFU through the CPRI signal cable.

4. The RFU decapsulates the received CPRI signals and processes the signals as required.5. The RFU encapsulates the data of its own status in the format of the CPRI frame, and

then transmits the data to the BBU through the CPRI signal cable.6. The BBU decapsulates the received CPRI signals to obtain the data of the RFU status.7. The BBU analyzes and processes the baseband signals to obtain the BTS status, and then

sends the status data to the BSC on the Abis interface.

IP Transmission





1. The BSC encapsulates the service data in the UDP payload, and then transmits the IP packet to the BBU through FE transmission.

2. After receiving the IP packet, the BBU processes the packet as follows:a. If the current clock mode is configured to the IP clock, the clock packet is

identified from the IP packet. The clock information is resolved from the clock packet for clock synchronization.

b. Identifies the packet on the ESL and OML and configures the BTS system based on the resolved data.

c. Identifies the service packet and deletes the UDP/IP header of the service packet. Encapsulates the service data in HDLC format and transmits the data to the RFU in the format of the CPRI frame.

3. After receiving the signals, the RFU processes the signals as follows:a. Decapsulates the high-speed CPRI frames and HDLC packets to obtain the

baseband signalsb. Transmits the baseband signals to the relevant operation units for encryption and










de-interleavingd. Encapsulates the processed signal in the format of the HDLC frame and then in

the format of the CPRI frame, and then transmits the signal to the BBU through the CPRI signal cable

3. After receiving the signals, the BBU processes the signals as follows:a. Decapsulates the high-speed CPRI frames to obtain the data in the format of the

HDLC frameb. Obtains the UDP/IP header information corresponding to the HDLC data packet

in the configuration data, and then encapsulates the HDLC frame payload in the UDP/IP format. Then, the BBU checks the ARP table, finds the destination MAC address, encapsulates the packets in the MAC format, and transmits the packets to the BSC through FE transmission.

Signaling Flow

The BTS3900/BTS3900A signaling flow refers to the signaling on the Abis interface. The BBU serves as the control unit and works with the RFUs to process the signaling. Figure 9 shows the signal flow of signaling processing.

Figure 9 Signaling flow of signaling processing


1. The BBU receives the signaling data encapsulated in the UDP/IP format from the BSC through FE transmission.

2. After decapsulating the signaling data, the BBU receives the relevant signaling data and processes the data as required.

3. The BBU encapsulates the signaling data to be processed by the RFU in the format of the CPRI frame, and then transmits the signaling data to the RFU through the CPRI signal cable.

4. The RFU decapsulates the received CPRI signals and processes the signals as required.5. The RFU encapsulates the data of its own status in the format of the CPRI frame, and

then transmits the data to the BBU through the CPRI signal cable.6. The BBU decapsulates the received CPRI signals to obtain the data of the RFU status.7. The BBU analyzes and processes the baseband signals to obtain the BTS status, and then

sends the status data encapsulated in the UDP/IP format to the BSC through FE transmission.

Topologies of the BTSThe topologies of the BTS include the TDM networking, IP networking, and HDLC networking. In practice, these topologies can be combined. Optimum utilization of the topologies can improve the quality of service and lower the investment on the transmission equipment.

TDM Networking

The E1/T1 transmission is used between the BSC and the BTS, and the TDM transmission is used on the Abis interface. The TDM networking can be classified into the star topology, chain topology, tree topology, and ring topology.

Figure 1 shows the star topology.

Figure 1 Star topology

Figure 2 shows the chain topology.Figure 2 Chain topology

Figure 3 shows the tree topology.Figure 3 Tree topology

Figure 4 shows the ring topology.

Figure 4 Ring topology

Table 1 compares the topologies.

Table 1 Comparison of topologies

Topology Application Scenario Advantage

Star topology Applies to common areas, especially densely populated areas, such as cities.

Simple networking Easy engineering construction Convenient maintenance Flexible capacity expansion High network reliability

Chain topology Applies to sparsely populated areas in strip-like terrain, such as areas along highways and railway tracks.

Reduces costs in transmission equipment, construction, and transmission link lease.

Tree topology Applies to areas where network structures, site distribution, and subscriber distribution are complicated, for example, an area where large-scale coverage overlaps hot spot or small-scale coverage.

Requires fewer transmission cables compared with the star topology.

Ring topology Applies to common scenarios. Due to its strong self-healing capability, the ring topology is preferred, if permitted by the routing.

If there is a breaking point in the ring, the ring breaks into two chains at the breaking point automatically. In this way, the BTSs preceding and following the breaking point can work normally despite the breaking point, thus improving the robustness of the system. For example, BTS0, BTS1, and BTS2 are sequentially connected to form a ring (clockwise). When a failure occurs at B, BTS0, the BTS topology preceding B, remains unchanged, and BTS2 and BTS1, the BTSs following B form a chain (anticlockwise), as shown in Figure 5.

Figure 5 Regrouping for disconnection in the ring topology

IP Networking

The FE transmission is used between the BSC and the BTS, and the IP transmission is used on the Abis interface. The IP networking consists of the layer-2 networking topology and layer-3 networking topology.

Figure 6 shows the layer-2 networking topology.Figure 6 Layer-2 networking topology

Figure 7 shows the layer-3 networking topology.Figure 7 Layer-3 networking topology

HDLC Networking

The E1/T1 transmission is used between the BSC and the BTS, and the HDLC transmission is used on the Abis interface. The HDLC networking can be classified into the star topology, chain topology, and ring topology.

Figure 8 shows the star topology.

Figure 8 Star topology

Figure 9 shows the chain topology. The upper-level BTS transparently transmits the signals of the lower-level BTS.

Figure 9 Chain topology

Figure 10 shows the ring topology.

Figure 10 Ring topology

BTS3900/BTS3900A Configuration Principles

The BTS3900/BTS3900A is configured with the antenna system, RFUs, and BBU.

Basic Configuration Principles

If multiple hardware configurations meet the requirements for the RNP parameter settings, the configuration mode that supports smooth upgrades is preferred.

The DRFU is applicable to small- and middle-capacity scenarios; the GRFU is applicable to large-capacity scenarios. The DRFU and GRFU can be configured in the same cabinet or cell to support flexible capacity expansion.

Wide coverage is preferred. The DRFU supports the PBT, TX diversity, and 4-way RX diversity mode. Therefore, the DRFU can be applied to wide-coverage scenarios.

Antenna Configuration Principles

One dual-polarized antenna can serve a maximum of two RFUs. By default, RX diversity is adopted on the GSM network. That is, two feeders connected

to two single-polarized antennas or one dual-polarized antenna must be configured in a cell.

Each sector of the BTS must be configured with the minimum number of antennas. For the 2-way RX diversity, each sector has two antenna channels; for the 4-way RX

diversity, each sector has four antenna channels.

RF Cable Connections of the DRFUsOne end of the RF jumper is connected to the RF port on the DRFU, and the other end is connected to the feeder. You can determine the appropriate RF ports based on the actual networking modes.

RF Cable Connections

The TX/RX mode and Sending Receiving Mode described in the following list are set on the BSC side.

The RF cables differ from each other in colors. Figure 1 shows the mapping between the RF signal cables and their colors.

Figure 1 Mapping between the RF cables and their colors

S1 with Transmit Independency or Combining, S1 with Transmit Diversity, and S2 with Transmit Independency or Combining

The S1 with Transmit Independency or Combining, S1 with transmit diversity, and S2 with Transmit Independency or Combining use the configuration of one DRFU and one dual-polarized antenna. Table 1 describes the related configurations.

Table 1 Configuration description (1)

Networking Configuration

Transmit mode Sending Receiving Mode

Hardware Configuration

S1, Transmit Independency or Combining

Transmit Independency or Combining

Double Feeder (2TX + 2RX)

One DRFU One dual-

polarized antenna

S1, Transmit Diversity Transmit Diversity Double Feeder (2TX + 2RX)




Figure 2 shows cable connections.

Figure 2 RF cable connections of S1 (Transmit Independency or Combining/transmit diversity)/S2 (Transmit Independency or Combining)

The other available Sending Receiving Mode for the DRFU with Transmit Independency or Combining are Single Feeder (1TX + 1RX), Double Feeder (1TX + 1RX), and Double Feeder (1TX + 2RX). The transmit mode is Transmit Independency or Combining. Figure 3 shows cable connections.

Figure 3 RF cable connections of the DRFU with Transmit Independency or Combining

S2 with PBT, S3 with Transmit Independency or Combining, and S4 with Transmit Independency or Combining

The S2 with PBT, S3 with Transmit Independency or Combining, and S4 with Transmit Independency or Combining use the configuration of two DRFUs and one dual-polarized antenna. Table 2 describes the related configurations.





S2, PBT PBT Single Feeder (1TX + 2RX)

Two DRFUs One dual-

polarized antennaS3, Transmit

Independency or Combining


Single Feeder (1TX + 2RX)





Figure 4 RF cable connections of S2 (PBT)/S3 (Transmit Independency or Combining)/S4 (Transmit Independency or Combining)

The S3/3 with Transmit Independency or Combining uses three DRFUs and two dual-polarized antennas. Table 3 describes the related configurations.





S3/3, Transmit Independency or Combining


DRFU0: Single Feeder (1TX + 2RX)

DRFU1: Double Feeder

Three DRFUs Two dual-

polarized antennas





(2TX + 4RX) DRFU2: Single

Feeder (1TX + 2RX)


Figure 5 RF cable connections of S3/3 configured with three DRFUs

S2 with 4-Way RX Diversity

The S2 with 4-way RX diversity uses two DRFUs and two dual-polarized antennas. The typical configurations are as follows:

Set the receive mode to 4-Way Receive Diversity. Set the sending receiving mode to Double Feeder (2TX + 4RX).


Figure 6 RF cable connections of S2 with 4-way RX diversity

S2 with Transmit Diversity and S4 with Transmit Independency

The S2 with transmit diversity and S4 with transmit independency use the configuration of two DRFUs and two dual-polarized antennas. Table 4 describes the related configurations.





S2, Transmit Diversity Transmit Diversity Double Feeder (2TX + 2RX)

Two DRFUs Two dual-

polarized antennasS4, Transmit

IndependencyTransmit Independency or Combining



Figure 7 RF cable connections of S2 (transmit diversity)/S4 (transmit independency)

S5 with Transmit Independency or Combining and S6 with Transmit Independency or Combining

The S5 with Transmit Independency or Combining and S6 with Transmit Independency or Combining use the configuration of three DRFUs and two dual-polarized antennas. Table 5 describes the related configurations.









DRFU2: Double Feeder (2TX + 2RX)

Three DRFUs Two dual-

polarized antennas





DRFU2: Double Feeder (2TX + 2RX)


Figure 8 RF cable connections of S5 (Transmit Independency or Combining)/S6 (Transmit Independency or Combining)

S7 with Transmit Independency or Combining and S8 with Transmit Independency or Combining

The S7 with Transmit Independency or Combining and S8 with Transmit Independency or Combining use the configuration of four DRFUs and two dual-polarized antennas. Table 6 describes the related configurations.





S7, Transmit Transmit Single Feeder (1TX + Four DRFUs







2RX) Two dual-polarized antennas





Figure 9 RF cable connections of S7 (Transmit Independency or Combining)/S8 (Transmit Independency or Combining)

RF Cable Connections of the GRFUsOne end of the RF jumper is connected to the RF port on the GRFU, and the other end is connected to the feeder. You can determine the appropriate RF ports based on the actual networking modes.



Figure 1 Mapping between the RF signal cables and their colors

The Sending Receiving Mode of the GRFU is set on the BSC side. Table 1 describes the typical configurations of the Sending Receiving Mode for the GRFU.

Table 1 Typical configurations of the sending receiving mode

GRFU Configuration Sending Receiving Mode

Single module Double Feeder (1TX + 2RX)

Two interconnected modules Single Feeder (1TX + 2RX)

The other available Sending Receiving Mode for the GRFU are Single Feeder (1TX + 1RX) and Double Feeder (1TX + 1RX). Figure 2 shows cable connections.

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Figure 2 RF cable connections (1)

Cell Configuration with a Single GRFU

When a dual-polarized antenna is configured, one TX channel and two RX channels are used. The ANT_RXB and ANT_TX/RXA ports receive the signals from the antenna to achieve RX diversity.




Cell Configuration with Two GRFUs

The ANT_TX/RXA port on each GRFU supports the receiving and transmitting of signals. Two GRFUs provide RX signals for each other through the RF interconnection ports. Thus, the RX diversity is implemented.




RF Cable Connections for the Coexistence of the DRFUs and GRFUsOne end of the RF jumper is connected to the RF port on the RFU, and the other end is connected to the feeder. You can determine the appropriate RF ports based on the actual networking modes.



Figure 1 Mapping between the RF cables and their colors

Single Antenna System Configured With One DRFU and One GRFU

When a DRFU and a GRFU share a dual-polarized antenna, the typical configuration of the Sending Receiving Mode for the DRFU and GRFU is as follows:

The DRFU is configured with Single Feeder (1TX + 2RX). The GRFU is configured with Single Feeder (1TX + 2RX).



Double Antenna Systems Configured with One DRFU and One GRFU

When a DRFU and a GRFU share two dual-polarized antennas, the typical configuration of the Sending Receiving Mode for the DRFU and GRFU is as follows:

The DRFU is configured with Double Feeder (2TX + 2RX). The GRFU is configured with Double Feeder (1TX + 2RX).



Double Antenna Systems Configured with Two DRFUs and One GRFU

When two DRFUs and a GRFU share two dual-polarized antennas, the typical configuration of the Sending Receiving Mode for the DRFUs and GRFU is as follows:

The DRFUs are configured with Single Feeder (1TX + 2RX). The GRFU is configured with Double Feeder (1TX + 2RX).



CPRI Cable Connections of the RFUsThe RFUs support two types of topology: star and chain.

Figure 1 shows the typical topology of the DRFUs.

Figure 1 Typical topology of the DRFUs

Figure 2 shows the typical topology of the GRFUs.



Figure 2 Typical topology of the GRFUs

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