01 System Principle

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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Table of Contents

Huawei Technologies Proprietary

i

Table of Contents

Chapter 1 Getting Started............................................................................................................. 1-1

Chapter 2 Common Subsystem................................................................................................... 2-1

2.1 Overview............................................................................................................................ 2-1

2.2 TMU ................................................................................................................................... 2-1

2.2.1 Overview ................................................................................................................. 2-1

2.2.2 Architecture and Principle ....................................................................................... 2-1

2.3 TDU.................................................................................................................................... 2-4

2.3.1 Overview ................................................................................................................. 2-4

2.3.2 Functions................................................................................................................. 2-4

2.4 ASU.................................................................................................................................... 2-5

2.4.1 Overview ................................................................................................................. 2-5

2.4.2 Functions................................................................................................................. 2-5

2.4.3 Interfaces................................................................................................................. 2-5

2.5 PAT .................................................................................................................................... 2-6

2.5.1 Overview ................................................................................................................. 2-6

2.5.2 Functions................................................................................................................. 2-6

2.5.3 Interfaces................................................................................................................. 2-6

2.6 TES.................................................................................................................................... 2-6

2.6.1 Overview ................................................................................................................. 2-6

2.6.2 Functions................................................................................................................. 2-7


2.7 ABB.................................................................................................................................... 2-8

2.7.1 Overview ................................................................................................................. 2-8

2.7.2 Functions................................................................................................................. 2-8

2.7.3 Board Location........................................................................................................ 2-9

2.8 ABA.................................................................................................................................... 2-9

2.9 PSU.................................................................................................................................... 2-9

2.9.1 Overview ................................................................................................................. 2-9

2.9.2 AC/DC Module ...................................................................................................... 2-10

2.9.3 DC/DC Module ...................................................................................................... 2-10

2.10 PMU............................................................................................................................... 2-11

2.10.1 Overview ............................................................................................................. 2-11

2.10.2 Functions............................................................................................................. 2-11

2.11 FMU ............................................................................................................................... 2-12

2.11.1 Overview ............................................................................................................. 2-12

2.11.2 Functions............................................................................................................. 2-12


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Chapter 3 Signal Processing Subsystem ................................................................................... 3-1

3.1 Overview............................................................................................................................ 3-1

3.2 TRX.................................................................................................................................... 3-3

3.2.1 Overview ................................................................................................................. 3-33.2.2 Architecture and Principle ....................................................................................... 3-3

3.3 EDGE Transceiver (ETR) .................................................................................................. 3-6

3.3.1 Overview ................................................................................................................. 3-6

3.3.2 Principle of Structure............................................................................................... 3-7

3.4 PBU.................................................................................................................................. 3-10

3.4.1 Overview ............................................................................................................... 3-10

3.4.2 Architecture and Principle ..................................................................................... 3-10

3.5 CDU ................................................................................................................................. 3-11

3.5.1 Overview ............................................................................................................... 3-11


3.6 ECDU............................................................................................................................... 3-13

3.7 EDU ................................................................................................................................. 3-13

3.7.1 Overview ............................................................................................................... 3-13


3.8 MDU................................................................................................................................. 3-14

3.8.1 Overview ............................................................................................................... 3-14


3.9 RCDU...............................................................................................................................3-15

3.10 REDU............................................................................................................................. 3-153.11 SCU ............................................................................................................................... 3-16

3.11.1 Overview ............................................................................................................. 3-16

3.11.2 Architecture and Principle ................................................................................... 3-16

3.12 ESCU............................................................................................................................. 3-16

Chapter 4 Antenna & Feeder Subsystem.................................................................................... 4-1

4.1 Overview............................................................................................................................ 4-1

4.2 Antenna.............................................................................................................................. 4-2

4.2.1 Classification........................................................................................................... 4-2

4.2.2 Gain......................................................................................................................... 4-2

4.2.3 Directional Diagram................................................................................................. 4-2

4.2.4 Polarization.............................................................................................................. 4-2

4.2.5 Diversity Technology............................................................................................... 4-3

4.2.6 Antennas Isolation................................................................................................... 4-3

4.3 Feeder................................................................................................................................ 4-3

4.4 Lightning Arrester .............................................................................................................. 4-3

4.5 TTA .................................................................................................................................... 4-4

4.5.1 Overview ................................................................................................................. 4-4


4.5.3 Functions................................................................................................................. 4-5


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Chapter 5 System Bus Structure................................................................................................. 5-1

5.1 Bus Classification............................................................................................................... 5-1

5.2 Bus Structure ..................................................................................................................... 5-1

5.3 DBUS................................................................................................................................. 5-35.4 CBUS................................................................................................................................. 5-4

5.4.1 CBUS1 .................................................................................................................... 5-4

5.4.2 CBUS2 .................................................................................................................... 5-5

5.4.3 CBUS3 .................................................................................................................... 5-5

5.5 Clock Bus........................................................................................................................... 5-6

5.6 FHBUS............................................................................................................................... 5-8


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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Chapter 1 Getting Started


1-1

Chapter 1 Getting Started

The BTS3X is composed of:

Common subsystem

Signal processing subsystem

Antenna & feeder subsystem

Each unit of the common subsystem and the signal processing subsystem is shown in

Table 1-1.

Table 1-1 Units of the common subsystem and the signal processing subsystem

SubsystemUnit

(abbreviation)Unit (full name) Remarks

TMU Timing/Transmission and ManagementUnit

TDUTime Distribution Unit

In BTS3006A andBTS3012A, TCU replacesTDU

ASUAccess network SDH transmission Unit

BTS3006A and BTS3012Ado not support ASU

PAT Passive Transmission Board BTS3006A and BTS3012Ado not support PAT

TES Transmission Extension Power SupplyUnit

BTS3006A and BTS3012Ado not support TES

ABB Abis Bypass Board

ABAAbis Bypass Assistant Board

BTS3006A and BTS3012Ado not support ABA

PSU Power Supply Unit

PMU Power Monitor Unit

FMU Fan Monitor Unit

TCUTemperature Control Unit

BTS30 and BTS312 do notsupport TCU

TEUTransmission Extension Unit

BTS3006A and BTS3012Ado not support TEU

Commonsubsystem

EMU Environment Monitor Unit

TRX Transceiver UnitSignalprocessing

ETR EDGE Transceiver


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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Chapter 1 Getting Started


1-2

SubsystemUnit

(abbreviation)Unit (full name) Remarks

PBU Power Boost Unit

CDU Combining and Distribution Unit

ECDU Enhanced Combining and DistributionUnit

EDU Enhanced Duplexer Unit

MDU Multi-channel Combining andDistribution Unit

RCDU Railway Combining and DistributionUnit

Supports GSM-R

REDU Railway Enhanced Duplexer Unit Supports GSM-R

SCU Simple Combining Unit

subsystem

ESCU Enhanced Simple Combining Unit


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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Chapter 2 Common Subsystem


2-1

Chapter 2 Common Subsystem

2.1 Overview

The common subsystem, by providing reference clock, power supply, transmission

interface, maintenance interface and external alarm collecting interface, realizes the

management of the BTS. This chapter introduces the working principle of the boards in

the common subsystem.

2.2 TMU

2.2.1 Overview

The timing/transmission and management unit (TMU) is the entity in charge of BTS

timing, transmission and management. It has the following functions:

Supporting multi-channel multiplexing, which furthers the utilization of the limited

transmission resources;

Supporting flexible networking modes, including star networking, tree networking

and chain networking of BTS;

Providing MMI and O&M link, and realizing software downloading, fault

management, configuration management, performance management and security

management;

Providing the centralized provisioning and hot backup of the clock;

Providing the input port for external alarm signal and collecting the external alarm.

2.2.2 Architecture and Principle

The system architecture of TMU includes such modules as BIU, OMU, MCK and EAC,

as shown in Figure 2-1.


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2-2

MCK

OMU

BIU

EAC

DBUS

CBUSMMI

BSC

MCK

Active TMU

Environment

monitoring instrument

Abis

TCU

Standby TMU

BIU

TBUS,CBUS,DBUS

Local Maintenance

Console

RS485

External clock

BSC: Base Station Controller TMU: Timing/Transmission and Management Unit

BIU: BTS Interface Unit OMU: Operation and Maintenance UnitTCU: Temperature Control Unit EAC: External Alarm Collection ModuleMCK: Main Clock Module DBUS: Internal Data BusCBUS: Internal Control Bus TBUS: Internal Timing Bus

Figure 2-1 TMU functional architecture

1) BIU

The BIU has the following functions:

Realizing the conversion and reverse conversion from digital signal (on BTS

internal HW) to HDB3 code (on E1 transmission link);

Exchanging the timeslots on HW to realize the flexible configuration of timeslots;

Extracting clock signals from the upper level, supporting the input of external clock,

outputting accurate clock through phase-locking and frequency dividing;

synchronizing data transmission of the internal bus, generating free run clock in

case of no upper-level clock available due to the failure in E1 or BSC,

synchronizing the data transmission of internal bus, and generating alarms to be

reported to OMU;

A BIU can provide up to four channels of E1. In a single cabinet, the BIUs of two

TMUs are the extension of each other. Eight channels of mutually extended E1

data can realize full exchange.

The interfaces of E1 cable on BIU can be used to connect BSC or BTS at the

upper or lower level. It supports star, tree, chain and ring connections of BTS.

2) OMU

The OMU is the core control and processing unit of TMU. It can be used to configure

the performance parameters of various units of BIU and MCK, receive fault alarms, and

implement alarm management. With the internal control bus and the communication

between TRX, CDU, PMU and TES), it is possible to realize the O&M operation on the

entire system, centralize the downloading and saving of the software loaded to various

units, and support the connection to the MMI at a PC.


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2-3

The Flash Memory of OMU can store two different versions of BTS software. One is

under current use. The OMU can load one of the two versions to each board according

to the request of BSC as the current operation software. If the software of BTS is to be

upgraded, BSC can load the new software to OMU for saving via O&M Link (OML). Thenew software is used as the substitute of the previous version. At the same time, the

previous version is also backed up in OMU in case of upgrading failure.

3) MCK

The MCK has an OCXO complying with the AAA standard and a phase-locked

frequency dividing circuit. The OCXO output standard 13 MHz system reference clock.

According to the system configuration, the MCK can work in free run mode or software

phase-locking mode. Through the frequency dividing of the reference clock, it can

output the reference clock (SREF) with the stability higher than 5 % 10-8

ppm, and

provides the frame clock (FCLK), 1/8 bit clock (OBCLK) and frame number (FN), etc.

The clock is the "calendar" and "pulse" of TDMA system. Therefore, its reliability is very

crucial. The clock source of a synchronous cell is provided by the MCK on TMU in the

main cabinet. The MCKs of two boards are the hot backup of each other. When the

main board is faulty, the switchover will be implemented to activate the standard board,

and report it to OMU.

The frequency, period and duty ratio of various system clocks are listed below:

13 M: 13 MHz, duty ratio: 50%;

SREF: 13 MHz/4 = 3.25 MHz, period: 307.7 ns, duty ratio: 50%;

OBCLK: 13 MHz/6 = 2.167 MHz, period: 461.5 ns, duty ratio: 50%;

FCLK: 13 MHz/6/10000 = 216.7 Hz, period 4.615 ms, duty ratio: 50%;

The FN increases by 1 after each frame clock period.

The time sequence of clock signal is shown in Figure 2-2.

13MHz

OBCLK

FCLK

D31 D30FN

Figure 2-2 Time sequence of clock signal

4) EAC

This module collects the external alarm signals, and reports the signals to OMU.


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2-4

2.3 TDU

2.3.1 Overview

BTS3006A and BTS3012A do not support TDU.

The major function of the timing distribution unit (TDU) is to receive the clock signals

from TMU: SREF (3.25 MHz), OBCLK (2.16 MHz), FCLK (216.7 Hz) and FN, and

transfer them to each TRX in the cabinet and each unit in other cabinets. TDU also

transfers other signals, such as alarm signal.

In the BTS3006A and BTS3012A, the clock of extension cabinet is driven by TCU

(Temperature Control Unit). For the detailed theory, refer to M900/M1800 BTS3012A

Base Transceiver Station Technical Manual Auxiliary System.

2.3.2 Functions

TDU has the following major function:

1) Providing the clock signal channel in a synchronous cell

Each cabinet is configured with a TDU. The clock signals generated from the main

cabinet (SREF, OBCLK, FCLK and FN) is sent to the TDU in each cabinet. After driving

the clock signal, TDU sends the signal to the TRX in the local cabinet. Figure 2-3shows

the transmission structure of clock signal.

Figure 2-3 Transmission structure of clock signal

2) Transferring the 120-ohm E1 signal for the local cabinet

TMU provides eight trunk signal interfaces, including four E1 interfaces and the four E1

interfaces available from the standby TMU. The interfaces are connected to the cabinet

top through coaxial cables. The data signal from BSC is sent to TDU via the 120-ohm

E1 interface on the cabinet top, and then transferred to TMU via TMU.

3) Providing alarm channels


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2-5

TDU provides 24 channels of Boolean value alarm input, 8 channels of analog variable

input and 8 channels of control variable output signal. It also supports the connection

between RS_485 bus and external equipment, such as environment monitoring

equipment.4) Providing bus connections

TDU provides inter-cabinet data bus DBUS (DBUS1 and DBUS2) in a synchronous cell

and the connection between control bus CBUS (CBUS1, CBUS2 and CBUS3) and

frequency hopping bus FHBUS. The signals from uplink cabinet are transferred by TDU

through the signal bus to each TRX in the cabinets.

2.4 ASU

2.4.1 Overview

BTS3006A and BTS3012A do not support ASU.

Apart from E1 transmission, BTS30/312 also provides the built-in transmission system

that supports external optical transmission interfaces, such as the 155 M SDH optical

interface and PON optical interface. The SDH transmission mode is realized with

Huawei's OptiX 155/622 access SDH unit (ASU).

2.4.2 Functions

The ASU has the following functions:

Providing photoelectric conversion function

It can be configured as a terminal mulitplexer (TM), add/drop multiplexer (ADM) or

regenerator (REG) according to networking demands.

It can be configured as a ring network, chain network and point-to-point (P2P)

network topology. With OptiX 155/622H and OptiX 155/622B, it can also be

configured as one of the following complex network structures, such as star,

tangent ring, dual ring or chain in ring.

Providing the 64 kbit/s sub-rate crossing function for the first four inter-E1.

Providing four E1 interfaces with the re-timing function

2.4.3 Interfaces

The external interfaces of the ASU include:

2 line optical interfaces: interface type, SC/PC

4 to 8 2-Mbit/s electrical interfaces: interface type, E1

1 order wire interface

1 Ethernet interface


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1 P2P user RS232 interface

NM interface: Ethernet/RS232

2.5 PAT

2.5.1 Overview

In addition to E1 transmission, BTS30/312 also provides the built-in transmission

system that supports external optical transmission interfaces, such as the 155 M SDH

optical interface, and PON optical interface. The PON transmission mode is realized

with PAT, a type of Huawei access network product.

BTS3006A and BTS3012A shall be configured with external optical transmission

equipment. It does not support PAT.

2.5.2 Functions

The PAT has the following functions:

Realizing order wire communication together with local transmission equipment.

Realizing the far end photoelectric conversion, multiplexing and de-multiplexing of

data and 1 to 4 channels of 2 Mbit/s services, including free upload or download,

processing and reporting of order wire.

Realizing far end delay control and ranging. Providing various loopback functions. There are two segments of loopbacks: E1

loopback and 2M loopback. Each segment of loopback has two directions: near

end loopback and far end loopback.

2.5.3 Interfaces

The external interfaces of PAT include:

Four 2-Mbit/s electric interfaces: interface type, E1

1 order wire interface

1 P2P user RS232 interface

1 maintenance serial port

1 print serial port

2.6 TES

2.6.1 Overview

BTS3006A do not support TES.


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The transmission extended power supply unit (TES) provides various working power

and communication transference for TEU. The power supply provided includes +5 V

DC, 5 V DC and 75 V AC ringing current to ensure the normal operations of TEU and

the built-in transmission of BTS. TES can communicate with TEU and TMU. It is abridge for TEU to report messages to TMU.

2.6.2 Functions

The TES has the following functions:

One TES can provide power supply and communication transference to at most

two TEUs.

Providing DC power supply to TEU, including +5 V DC and 5 V DC

Realizing the communication between TMU and TEU

Providing ringing current to TEU. The ringing signal is a type of 75 V AC/25 Hz

sinusoidal waveAC signal.


Figure 2-4shows the functional architecture of TES.

To TEU communication serial port

To TMU communication serial port

Communicationmodule

Power supplymodule

+24 V DC input

1st +5 V DC output

75 V AC ringing current output

-5 V DC output

For first TEU

For second TEU

For both TEUs

2nd +5 V DC output

For both TEUs

TES

Figure 2-4 TES functional architecture

I. Power Supply Module

The power supply module of TES includes DC/DC conversion circuit and DC/AC

conversion circuit. The DC/DC conversion circuit converts the +24 V DC to 2 channels

of +5 V DC power and 1 channel of 5 V DC power. The DC/AC conversion circuit

converts the +24 V DC power to 1 channel of 75 V AC ringing signal.


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II. Communication Module

The communication module realizes the communication between TES and TMU, and

the communication between TES and TEU. It also obtains the PCB version No. of TES

and cabinet No.

The serial port communication between TES and TMU conforms to RS485 standard. It

is connected to the CBUS3 of TMU. TES is connected to CBUS via the level conversion

circuit. The parallel communication mode between TES and TEU adopts the P2P mode.

The parallel level is TTL.

2.7 ABB

2.7.1 Overview

In practice, chain networking is usually adopted at BSS. This networking mode features

simple structure and lower cost. However, when power failure occurs at a site, all

services of the downstream sites are interrupted. The Abis transmission bypass board

(ABB) provides the Abis interface bypass function as a solution to the problem above.

2.7.2 Functions

ABB is applied in the BTS chain networking. It is in charge of the BTS transmissiontrunk. When power failure occurs at a certain level (middle level) of BTS in the chain

networking, ABB bypasses the Abis transmission line off this site, and directly connect

it to the downstream BTS. In this way, even if power failure occurs at a middle-level site

in the chain networking, the services of the downstream site will not be affected. See

Figure 2-5.

BSCABB

TMU

ABB

TMU

ABB

TMU

Site1 Site2 Site3

Figure 2-5ABB working principle

ABB can also perform loopback at the transmission line, so that ABB can loopback the

E1 signal for BSC to detect the quality of the entire transmission link in the case of

power failure at the end-level BTS.


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2-9

2.7.3 Board Location

The ABB shares the same slot as that of the TEU. Therefore, the size of the board and

the interface definition of ABB are consistent with those of TEU. Because BTS30 hasonly one TEU slot, ABB is to take the slot of TEU. BTS312 has two TEU slots, but ABB

can only select slot 0 that hosts the TEU. In BTS3012A, there is a fixed slot for the ABB.

Warning:

For the links configured with ABB board, if the ABB board powers off or is replaced, the

E1 link is interrupted.

2.8 ABA

I. Overview

The Abis bypass assistant board (ABA) realizes the communication between ABB and

TMU, so it shall be used to cooperate with ABB. ABB communicates with TMU via

CBUS3. But the slot of ABB does not provide the connection with CBUS3. Therefore,

ABA is used to provide the connection between them. Via ABA, part of the signals from

ABB (e.g. the signals indicating that the ABA is in position) can be transmitted to

CBUS3 on the backplane of the common resource frame.

BTS3006A and BTS3012A do not support ABA

II. Board Location

ABA shares the slot with TES both in BTS30 and BTS312 cabinet. Therefore, the size

of the board and the interface definition are consistent with those of the TES.

This method of bus communication is unfit for BTS3006A and BTS3012A, so there is

no need to configure ABA on BTS3006A and BTS3012A.

2.9 PSU

2.9.1 Overview

The power supply unit (PSU) is a built-in power supply module. BTS3X supports

multiple power input modes, so PSU is divided into AC/DC unit and DC/DC unit


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accordingly. Different power supply modes can be configured for BTS3X according to

different power supply module:

In the 220 V AC power mode, the AC/DC unit is configured.

In the -48V V DC power mode, the DC/DC unit is configured. In the +24 V DC power mode, there is no need to configure a PSU.

One PSU provides power supply for two TRXs. The configuration of power supply

module adopts N +1 current equalizing hot backup.

2.9.2 AC/DC Module

The input power of the AC/DC unit is 220 V AC, and the output power is +26 V DC

The 220 V AC power is input through AC lightning protection board, and then to the AC

EMI filter at the cabinet top. The power cable is led along the cabling trough to the 220

V AC input bus bar on the motherboard. Figure 2-6shows the principle framework of

AC/DC power supply system.

AC input anti-lightning power distribution

unit

PSU PSU PSU PSU

220VAC InputInput busbar

Output busbar

26VDC Output

DC distribution copper bar

PMU

Figure 2-6 Power distribution of AC/DC power supply module

2.9.3 DC/DC Module

The input power of the DC/DC module is 48 V, and the output power is +26 V.

The 48 V DC power is input through the AC EMI filter at the cabinet top. The power

cable is led along the cabling trough to the -48 V DC input bus bar on the motherboard.

Figure 2-7shows the principle framework of AC/DC power supply.


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2-11

PSU PSU PSU PSU

-48V DCinputInput busbar

Output busbar

26V DCoutput

DC distribution copper bar

PMU

Figure 2-7 Power distribution of DC/DC power supply module

2.10 PMU

2.10.1 Overview

The power supply management unit (PMU) is close to the power supply module group.

The PMU mainly performs power supply management and alarm collection. If the

AC/DC unit is configured for PSU, the PMU supports the power supply management

function. If the DC/DC unit is configured, it is necessary to set the capacity of PMU

battery to 0, that is, the battery management function is not used.

2.10.2 Functions

The PMU monitors the control variable signal, Boolean value, current, voltage analog

variable in real-time.

1) Control variable signal

Even and float charging management and current limited control of battery

Control over the switching of the protection load for batteries

2) Boolean value signal

AC mains signal and over/under voltage signal (12 V DC/10 mA)

N %AC/DC module(s) provides N %fault status variables (12 V DC/10 mA) for

PMU. (N is the number of PSU configured. For example, if four PSUs are

configured for BTS30, then four fault status variables will be provided for PMU.)

Fan monitoring status variable (normally 12 V DC/10 mA)

Cabinet internal smoke detection (alarm: 24 V/10 mA), water proof (alarm: 12 V/10

mA), access control (normal; 12 V/10 mA)


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Switching status variable of the battery fuse (0.3 V DC < normal voltage

difference < 0.3 V DC)

3) Current and voltage analog variable signal

Battery group current (A) Total load current (A)

Main bar voltage (V)

4) Environment variable analog signal

Cabinet internal temperature (with a sensor) (C)

Cabinet internal humidity (with a sensor) (RH%)

Figure 2-8shows the monitoring principle of PMU.

AC power supply

AC/DC AC/DC AC/DC AC/DC

Load

FMUPMU

SmokeTemprature& Humidity

WaterloggingAccess

Batteries

FUSE

External alarm collection

Figure 2-8 PMU monitoring

2.11 FMU

2.11.1 Overview

The fan monitoring unit (FMU) is located in the fan box. It manages and controls the

fans in the fan box to guarantee satisfactory heat dissipation of the BTS.

2.11.2 Functions

The FMU has the following functions:

1) Feeding fans

This part of circuit consists of two parts: power supply filter and voltage reduction. It

processes the working power needed from system power supply to fan, and provides

the feeding to the fan.

2) Controlling the fan speed


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The voltage-controlled mode is used to control the fan speed, so that the fan will

maintain the rotation at a constant speed within the variation range of voltage to satisfy

the needs of heat dissipation of the system.

3) Alarm monitoring

There are two types of fan failure: stalled and short circuited. The symptom of these two

cases is that the fan stops running. The FMU monitors the speed of the fan to decide

the working status of the fan. If the fan is faulty, the alarm signal is sent to PMU.


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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Chapter 3 Signal Processing Subsystem


3-1

Chapter 3 Signal Processing Subsystem

3.1 Overview

The signal processing subsystem includes such boards as TRX, PBU, CDU, ECDU,

EDU, MDU, RCDU, REDU, SCU, and ESCU. The system realizes the conversion from

digital signal to RF signal, including:

Baseband processing

RF processing

Signal combining before transmitting

Signal dividing after receiving

Figure 3-1shows the signal transmit process of the BTS.

TMU TRX AntennaCDUAbis

Figure 3-1 Signal transmit process of BTS

Figure 3-2shows the signal receive process of BTS.

TMU TRX AntennaCDUAbis

Figure 3-2 Signal receive process of BTS

There are many optional boards in signal processing subsystem. For the functions and

slots of each board, see Table 3-1.

Table 3-1 Functions of optional boards

Optionalboard

Slot Feature of configuration

ETR TRX slotTo support the EDGE function, the ETR shall beconfigured.


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3-2

Optionalboard

Slot Feature of configuration

PBU TRX slot

For increasing the transmitting power;

It is possible to configure PBU to TRX.

One PBU can amplify the power of only one TRX.The PBU only supports the power amplification of a40W TRX at GSM900, GSM1800, EGSM and RGSMfrequency bands.

BTS supports the configuration of PBU to someTRXs.

EDU CDU slot

For enlarging coverage and lowering combining loss;

The following conditions shall be satisfied:

Number of TRXs in each sector 2

No need for large capacity upgrading

ECDU CDU slotMeets the requirements in combining and dividingwhen configured with PBU

MDU CDU slot

Used together with EDU capacity expansion;

Supports smooth capacity expansion from 1 TRX to8 TRXs.

RCDU CDU slotWhen the BTS works in the EGSM band, the RCDUis optional.

REDU CDU slot

For the BTS working in the EGSM band andrequiring lower combining loss, the REDU isoptional.

The following conditions shall be satisfied:

Number of TRXs in each sector 2

No need for large capacity upgrading

SCU CDU slot

For lowering the consumption of feeders when thereare too many TRXs configured for a cell.

This condition shall be satisfied: number of TRXs in a

cell 4.

ESCU CDU slot

Can be used with PBU, CDU, ECDU, EDU, RCDU,and REDU.

This condition shall be satisfied: number of TRXs in a

cell 4.


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3-3

3.2 TRX

3.2.1 Overview

The transceiver unit (TRX) adopts a modularized structure. It includes base band

processing unit and RF processing unit. The TRX receives signals from an MS via the

antenna, and then demodulates the signals received into signaling information and

voice information for sending forward. The downlink signaling information and voice

information are sent to the antenna after being processed by the TRX, and then are

transmitted to the MS.

The TRX also receives various management and configuration information from TMU,

and reports its own status and alarm information to TMU.


Figure 3-3shows the functional architecture of TRX, which includes a baseband signal

processing unit (TBPU) and a RF signal processing unit (RPU).

SCP DSP CUI

TDP PAU

RCU

RPU

DBUSFH_BUS

CBUS

TIMING_BUS

TBPU

Transmitting

Main receiving

Diversity receiving

Clock processing part

SCP: Signaling Processing Part DSP: Digital Signal ProcessorCUI: Carrier Unit Interface Controller TDP: Transmitter Driver and PLL unitPAU: Power Amplifier Unit RCU: Receiver UnitTBPU: Transceiver Baseband Processing Unit RPU: Radio frequency Process UnitDBUS: Data bus CBUS: Control busFHBUS: Frequency Hopping bus TBUS: Clock bus

Figure 3-3 TRX logical structure


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3-4

I. TBPU

The TBPU includes the following parts:

Signaling processing part (SCP) Digital signal processor(DSP)

Carrier unit interface controller (CUI)

Because the GSM adopts the TDM system, the operation of TRX relies on various

clocks. This is the purpose of clock processing part in TRX.

1) SCP

The SCP processes the signaling protocols of various interfaces of BTS, including:

L2 protocol LAPDm between BTS and MS

L2 protocol LAPD between BTS and BSC

L2 protocol DCL between BTS and OMU

The SCP also processes the L3 non-transparent messages. SCP also loads programs

to DSP and processes the alarms from the entire TRX module.

2) DSP

The DSP realizes the following functions:

Signal coding

Signal decoding

Interleaving

De-interleaving Voice/data communication with TRAU of BSC

The DSP sends the signaling from the MS to SCP, receives the signaling from SCP, and

implements the corresponding coding/decoding according to the relative protocol. The

downlink data are sent to RF signal processing unit RPU via CUI.

3) CUI

The CUI is the interface module between DSP and RPU. It is used to realize the FH

function of TRX. FH by CUI can be decided in the system configuration. If the system is

operating under RF FH mode, CUI operates under non-FH mode, and FH is

implemented by RPU; if system operating under base band FH mode, FH will beimplemented by CUI. In addition, CUI also samples and filters the uplink intermediate

frequency signals from RPU, and then sends them to DSP for demodulation and

diversity combining.

4) Clock Processing Part

The clock of TRX is from the clock bus of TMU. To ensure high reliability, the clock bus

operates in active/standby mode. These clocks include frame clock, 1/8-bit clock and

FN. The clock processing part of TRX first selects the active or standby clock, and then

generates the TS NO. and bit clock necessary for TRX through frequency dividing

counter.


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3-5

II. RPU

RPU includes the receiver unit (RCU), transmitter driver and PLL unit (TDP) and power

amplifier unit (PAU).

1) RCU

The RCU provides the diversity receiving function. The receiver consists of two

channels of fully independent paths. The input signal of the two channels mainly comes

from the antenna in the main and diversity modes. When the signals received from one

channel is in poor quality due to complicated radio transmission condition, there will be

different signal qualities if the other channel receives signals from other paths. BTS

receives signals from two channels: main set and diversity. It is possible to provide 3 dB

to 5 dB of diversity gain to improve communication quality after demodulation with

combining algorithm.

Each channel of receiving path is made up of a primary down-conversion circuit. The

receiving signal is sent to frequency mixer to generate an intermediate-frequency (IF)

signal. After being amplified to a certain level, the IF signal is sent to the base band part

for digital demodulation.

2) TDP

The TDP includes the transmitting excitation unit, frequency synthesizer and loop test

unit.

Transmitting excitation unit

The transmitting process is in direct modulation mode. The transmitting excitation unit

modulates the I and Q signals sent from TBPU into the RF signals needed for

transmitting with the quadrature modulator. The modulated signal provides PAU with a

certain power level. Transmitting excitation unit also provides the dynamic and static

power control for BTS. The static power control is defined during network planning to

decide the maximum transmitting power of BTS. Dynamic power control is

implemented during the process of communication. The static power levels are Level 0

to 9, among which, Level 0 is 46 dBm, and the decrease step is 2 dBm. The levels of

dynamic power control are Level 0 to 15, and the decrease step is 2 dBm. To lower the

noise level in radio environment, and improve network capacity and QoS, it isnecessary to lower the transmitting power of BTS as much as possible without harming

the QoS, so that each TCH is at the lowest dynamic power level, and the transmitting

power of idle channels is closed. Transmitting excitation unit also supports PA

over-power alarm signal. An alarm will be generated when the output power of PA

exceeds the set level by 3 dB.

Frequency synthesizer

The frequency synthesizer is crucial to the entire transceiver. It generates various local

oscillation of transceiving up/down-conversion, such as transmitting oscillation,


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3-6

receiving oscillation and loop test local oscillation. Both transmitting local oscillation

and receiving local oscillation have two loops for FH loop switching.

Loop test unit

Loop test unit is designed for TRX loop test. It attenuates part of the signals coupled at

the output terminal of PAU to the receiving band, and then sends them to the receiver

after coupling. Its major function is to test the operation of TRX transmitting channel

and receiving channel.

3) PAU

The PAU amplifies RF signals. TRX supports two kinds of PAU. Their maximum output

power levels are 46 dBm and 47 dBm respectively. The PAU also provides the

feedback sampling signals controlled by transmitting APC and the following alarm

signals:

Over temperature alarm:When the temperature of PA is over 85 C, the PAU

reports the over temperature alarm via base band unit, and automatically closes

the PAU.

Over-standing wave alarm:When the output standing wave exceeds 3.5, the

PAU reports this alarm to base band unit.

3.3 EDGE Transceiver (ETR)

3.3.1 Overview

ETR adopts modularized structure. It includes base band processing unit and RF

processing unit. ETR receives signal from MS via antenna, and then demodulates the

signal received into signaling information and voice information for sending forward.

The downlink signaling information and voice information is sent to antenna after ETR

processing, and then transmitted to MS.

ETR also receives various management and configuration information issued from

TMU, and reports its own status and alarm information to TMU.

The ETR supports multiple frequency bands:

GSM850

GSM900/EGSM/RGSM

GSM1800

GSM1900


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3-7

3.3.2 Principle of Structure

Figure 3-4 shows the structure of ETR, including EDGE Baseband Radio-frequency

Unit (EBRU), Edge Power Amplifier Unit (EPAU) and Edge ETR Power Supply Unit(ETPS).

SCP DSP CUI

TDP EPAU

RCU

DBUS

FH _ BUS

CBUS

TIMING_BUS

Clockprocessing unit

Transmitting

Main receiving

Diversity receiving

EBPU

SCP: Signaling Processing Part DSP: Digital Signal ProcessorCUI: Carrier Unit Interface Controller TDP: Transmitter Driver and PLL unitEPAU: EDGE Power Amplifier Unit RCU: Receiver UnitTBPU: Transceiver Baseband

Processing Unit

RPU: Radio frequency Process Unit

DBUS: Data bus CBUS: Control busFHBUS: Frequency Hopping bus EBRU: EDGE Baseband Radio-frequency Unit

Figure 3-4 ETR logical structure

EBRU includes signaling processing part (SCP), digital signal processor(DSP), carrier

unit interface controller (CUI), receiver unit (RCU) and transmitter driver and PLL unit

(TDP). Since GSM adopts TDM system, the operation of ETR relies on various clocks.

This is the purpose of the presence of the clock processing part in ETR.

I. SCP

SCP processes the signaling protocols of various interfaces of BTS, including the L2

protocol LAPDm between BTS and MS, L2 protocol LAPD between BTS and BSC and

L2 protocol DCL between BTS and OMU. It also processes the L3 non-transparent

messages. SCP also loads programs to DSP and processes the alarms from the entire

ETR module.


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3-8

II. DSP

DSP realizes the functions such as signal coding/decoding, interleaving/de-interleaving,

and voice/data communication with TRAU of BSC. It sends the signaling from the MS to

SCP, receives the signaling from SCP, and implements the corresponding

coding/decoding according to the relative protocol. The downlink data are sent to RF

signal processing unit RPU via CUI.

III. CUI

CUI is the interface module between DSP and RPU. It is used to realize the FH function

of ETR. FH by CUI can be decided in the system configuration. If the system is

operating under RF FH mode, CUI operates under non-FH mode, and FH is

implemented by RPU. If system operating under base band FH mode, FH will be

implemented by CUI. In addition, CUI also samples and filters the uplink intermediate

frequency signals from RPU, and then sends them to DSP for demodulation and

main/diversity combining.

IV. RCU

RCU provides main/diversity receiving function. The receiver consists of two channels

of full-independent paths. The input signal of the two channels mainly comes from main

set and diversity antenna. When the signal received from one channel is in poor quality

due to complicated radio transmission condition, there will be different signal qualities if

the other channel receives signals from other paths. BTS receives signals from two

channels: main set and diversity. It is possible to provide 3~5 dB of diversity gain to

improve communication quality after demodulation with combining algorithm.

Each channel of receiving path is made up of a primary down-conversion circuit. The

receiving signal is sent to frequency mixer to generate a mid-frequency signal. After

being amplified to a certain level, it is sent to the base band part for digital

demodulation.

V. TDP

TDP includes transmitting excitation unit, frequency synthesizer and loop test unit.

Transmitting excitation unit

Transmitting is in direct modulation mode. Transmitting excitation unit modulates the I

and Q signals sent from TBPU into the RF signals needed for transmitting with the

quadrature modulator. The modulated signal provides PAU with a certain power level.

Transmitting excitation unit also provides the dynamic and static power control for BTS.

The static power control is defined during network planning to decide the maximum

transmitting power of BTS. Dynamic power control is implemented during the process


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3-9

of communication. The static power levels are Level 0~9, among which, Level 0 is 46

dBm, and the decrease step is 2 dBm. The levels of dynamic power control are Level 0

~ 15, and the decrease step is 2 dBm. To lower the noise level in radio environment,

and improve network capacity and QoS, it is necessary to lower the transmitting powerof BTS as much as possible without harming the QoS, so that each TCH is at the lowest

dynamic power level, and the transmitting power of idle channels is closed.

Transmitting excitation unit also supports PA over-power and under-power alarm signal.

An alarm will be generated when the output power of PA exceeds the set level by 3 dB.

Frequency synthesizer

Frequency synthesizer is crucial to the entire transceiver. It generates various local

oscillation of transceiving up/down-conversion and some oscillation reference, such as

transmitting oscillation, receiving oscillation, loop test local oscillation. Both transmitting

local oscillation and receiving local oscillation have two loops for FH loop switching. Loop test unit

Loop test unit is designed for ETR loop test. It attenuates part of the signals coupled at

the output terminal of PAU to the receiving band, and then sends them to the receiver

after coupling. Its major function is to test the operation of ETR transmitting channel

and receiving channel.

VI. Clock Processing Part

Clocks of the ETR are derived from the clock bus of the TMU. To ensure higher

reliability, clock bus adopts active/standby work mode. The clocks include frame clocks,

1/8 bit clocks and FN. The clock processing part in the ETR first selects master clocks

or slave clocks, and then generates the timeslot number and bit clocks required by the

ETR through frequency divider counting.

VII. EPAU

EPAU amplifies RF signals. Its maximum output power level is 47.8 dBm when the ETR

works in the GSMK mode. Its maximum output power level is 46 dBm when the ETR

works in the 8PSK mode. It also provides the feedback sampling signals controlled by

transmitting APC and the following alarm signals:

Over-heat alarm: when the temperature of PA is over 85 C, PAU reports the

over-heat alarm via base band unit, and automatically closes PAU.

Over-standing wave alarm: when the output standing wave exceeds 3.5, PAU

reports this alarm to base band unit.


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3-10

3.4 PBU

3.4.1 Overview

The power boost unit (PBU) is the TRX output power amplifier designed for wide

coverage. The PBU can increase the effective radiation power of the antenna and the

coverage of BTS. The maximum output power is 49 ! 1 dBm. It consists of PA

synthesizing module, alarm management module and power supply module. It can

amplify one channel output power of 40 W TRX working at GSM900, GSM1800, EGSM

and RGSM frequency bands.


Figure 3-5shows the functional architecture of the PBU.

Coupling and delay filter

Range and phasecontrol

60W PA

Powersynthesizing

and test

PA Synthiesizing Module

Alarm collectionand output

PA control signalgenerating

Alarm Management Module

26V

26V

8V

8V

Alarm collectionPA control

Alarm output

26V

RF signal input

PBU

Power

supply

module

RF signal

output

Figure 3-5 PBU functional architecture

The PBU couples the 40 W power signal output from TRX as main channel signal and

coupling channel signal. The main channel signal is input into power synthesizing unit

after delay filtering, and the coupling channel signal is input into power synthesizing unit

after 60 W PA. To get the final synthesizing signal, it is necessary to control the range

and phase of these two channels of input synthesizing signals. The generation of

control signal and collection/reporting of alarm are implemented by alarm management

module. The coupling, control and synthesizing of power signal is implemented by the

network.

1) PA synthesizing module

Under the control of alarm collection and management module, the PA synthesizing

module amplifies the TRX output signal. It also provides PA control and alarm

information (positive input power and positive output power demodulation signal),


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3-11

alarm signal (over-temperature, over-standing wave alarm) to alarm collection and

management module so that it can perform PA test and alarm reporting.

The PA synthesizing module includes:

Input coupling

Delay filter/range/phase control

60 W PA

Power synthesizing and test

The input coupling and delay filter will couple the 40 W signal output from TRX as main

channel signal and coupling channel signal (main channel signal counts for most part of

the energy). The main channel signal is sent to an entrance of power synthesizing and

test unit after adjusting delay processing at the filter.

The range and phase adjusting of coupling channel signal necessary for powersynthesizing is done by alarm collection and management module, and then is

amplified to 60 W to be sent to another entrance of the power synthesizing and test unit.

The two channels of input signals can obtain the final PBU output power after power

synthesizing, and is ready for output.

2) Alarm management module

The alarm management module receives the PA control (positive input power and

positive output power demodulation signal) and alarm signal (over-temperature and

over-standing wave alarm) to test PA and control the phase and range of the PA

synthesized network, as well as reports the alarms of positive output power too low, PAoutput standing wave and PA over-temperature.

3) Power supply module

This module provides the power supply signals for PA and synthesized network, alarm

collection and management module.

3.5 CDU

3.5.1 Overview

The combiner and divider unit (CDU) realizes the following functions:

Combining and filtering of transceiving duplex

Transmitting signal

Filtering of receiving signals

Low-noise amplification

Dividing of receiving signals

Provides TTA feeding.


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3-12

The CDU uses the bridge combiner (broadband combiner) at 3 dB power loss to enable

multiple transmitting signals and receiving signals to share the same antenna unit. In

practice, the mode of transmitting 2-in-1 or receiving dual channel 1-into-4 (or single

channel 1-into-8) can be adopted. In addition, CDU also has a diversity receivingtributary.

The CDU supports the GSM900, GSM1800, GSM1900, and GSM850 frequency bands.

The maximum input power of its single port is 60 W.


Figure 3-6shows the functional architecture of CDU.

Test coupler TA feeder

Divider

Duplexer

Low noise amplifier Receiving fiter

Alarm and control unit

Combiner

Transmitting input

Receiving output

Divider

Receiving output

Low noise amplifier

TA feeder

CDU

Figure 3-6 CDU functional architecture

Besides the basic combining and dividing function, the CDU also has the following

functions for alarm test:

1) Standing wave test: monitors the status of the antenna and feeder system.

When finding that the standing wave exceeds the preset threshold 1.5:1, the CDU

reports a minor alarm, and the corresponding indicator on the front panel is in the

ON" status.

When finding that the standing wave exceeds the preset threshold of 2.5:1, the

CDU reports a critical alarm, and the corresponding indicator on the front panel is

in the ON" status, then the transmitting signal will be closed one minute later.

2) Low-noise amplifier faulty alarm: The fault signal is from the power supply current

of low-noise amplifier. The alarm is generated when the current exceeds a certain

range or no current detected.

3) TTA alarm: When TTA is operating, CDU judges the working status of TTA

according to its working current. The alarm is generated when the current exceeds

a certain range or no current is detected.

4) Control function: The CDU performs power attenuation control of the main

receiving channel and diversity receiving channel (dynamic range: 15 dB, step: 1


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3-13

dB). It realizes the function of TTA feeding switch, which automatically closes TTA

feeding upon TTA alarm.

3.6 ECDU

The functions and external interfaces (including dimensions) of ECDU are the same as

those of CDU. It implements combination of transmitted signals, dividing of received

signals, and duplex functions.

The ECDU supports multiple frequency bands:

GSM850

GSM900

GSM1800

GSM1900


3.7 EDU

3.7.1 Overview

The enhanced duplex unit (EDU) is designed for wide coverage and low loss. It realizes

the following functions:

Combining and filtering of transceiving duplex and transmitting signal

Filtering of receiving signals

Low-noise amplification

Dividing of receiving signal for TRXs

It also provides TTA feeding. Each TRX uses independent antenna, and transmitting

combiner is not needed. The receiving mode is 1-into-2.

EDU supports the following frequency bands:

GSM850

GSM900

GSM1800

GSM1900



Figure 3-7shows the functional architecture of the EDU.


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3-14

TA

feeder

Divider

Duplexer

Alarm and control

unit

Transmitting

input

Receiving

output Low noise amplifier

EDU

Test

coupler

TA

feeder

Divider

Duplexer

Receiving

output

Transmitting

input

Low noise amplifier

Test

coupler

Figure 3-7 EDU functional architecture

Besides the basic combining and dividing function, CDU also has the following

functions for alarm test:

Standing wave test: monitors the status of antenna feeder. When finding that the

standing wave exceeds the preset threshold of 2.5:1, the CDU reports minor alarm,

and the corresponding indicator on the front panel is on.

Low-noise amplifier faulty alarm: Fault signal is from the power supply current of

low-noise amplifier. The alarm is generated when the current exceeds a certain

range or no current is detected.

TTA alarm: When TTA is operating, the CDU judges the working status of TTAaccording to its working current. The alarm is generated when the current exceeds

a certain range or no current is detected.

Control function: The EDU performs power attenuation control of the main

receiving channel and diversity receiving channel (dynamic range: 15 dB, step: 1

dB). It realizes the function of TTA feeding switch, which automatically closes TTA

feeding upon TTA alarm.

3.8 MDU

3.8.1 Overview

The MDU is a multi-channel combining and distribution unit to realize smooth capacity

expansion from 1 TRX to 8 TRX even when the EDU is configured. The MDU is a

passive component, supporting the following frequency bands:

GSM850

GSM900 (RGSM)

GSM1800

GSM1900


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3-15

RGSM



Figure 3-8shows the functional architecture of MDU.

Combiner

Divider

DividerIN1

IN2

COM

3

RX5

RX6

RX7

RX8

RX1

RX2

RX3

RX4

RXIN1

RXIN2

CombinerTX1

TX2

COM

1

CombinerTX3

TX4

COM2

Figure 3-8 MDU functional architecture

3.9 RCDU

The RCDU is the same as ECDU in terms of structure, functions, peripheral interfaces,

peripheral interface dimensions, and maximum input power. It can also combine

transmitted RF signals, divide received RF signals and implement reception and

transmission duplex. The difference between RCDU and ECDU lies in the bands

supported. The bands supported by RCDU ranges from 876 MHz to 901 MHz (uplink)

and 921 MHz to 946 MHz (downlink). For the BTS working at the EGSM band with the

frequency range of 880 MHz to 890 MHz (uplink) and 925 MHz to 935 MHz (downlink),

The RCDU is optional.

3.10 REDU

The REDU is the same as EDU in terms of structure, functions, peripheral interfaces,

peripheral interface dimensions, and maximum input power. It can also implement

1-to-2 division of received signals and implement reception and transmission duplex.


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3-16

The difference between REDU and EDU lies in the bands supported. The band

supported by REDU ranges from 876 MHz to 901 MHz (uplink) and 921 MHz to 946

MHz (downlink). If the BTS works in the EGSM band with the frequency range as 880

MHz to 890 MHz (uplink) and 925 MHz to 935 MHz (downlink) and it is required toachieve low loss, REDU is optional.

3.11 SCU

3.11.1 Overview

The simple combiner unit (SCU) is a transmitting unit of four carriers in one (4-in-1). It

realizes broadband combining with 3 dB power loss bridge. The cooperation of SCU

and CDU can realize the combining transmitting of multi-carriers, thus realizing numberof CDUs and lowering cost.

The SCU supports the following frequency bands:

GSM900

GSM1800



Figure 3-9shows the functional architecture of SCU.

Transmitting input

SCU

Transmitting output

1

2Combiner

3

4Combiner

Combiner

Figure 3-9 SCU functional architecture

3.12 ESCU

The ESCU is the same as SCU in terms of structure, functions, peripheral interfaces

and peripheral interface dimensions. It can also implement 4-in-1 combination of

transmitted signals. The differences between ESCU and SCU lie in:


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3-17

Bands supported: The band supported by ESCU ranges from 921 MHz to 960

MHz (900M ESCU) and 1805 MHz to 1880 MHz (1800M ESCU).

Maximum input power supported at a single port: The single port of ESCU

supports the maximum input power of 100 W. The 900M ESCU can be used with 900M CDU, ECDU, EDU, RCDU and REDU,

while the 1800M ESCU can be used with 1800M CDU, ECDU and EDU. When

ESCU works with the ECDU, it can implement more than four carriers, which thus

improves the BTS transmit power and effective radiated power of antenna ports

and enlarges the coverage of BTS.


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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Chapter 4 Antenna & Feeder Subsystem


4-1

Chapter 4 Antenna & Feeder Subsystem

4.1 Overview

The antenna & feeder subsystem includes:

Antenna

Feeder

Jumpers

Lightning arrester

Tower top amplifier (TTA)

Figure 4-1shows the cable connections between these parts.

Antenna

TTA

Antennasupport

Jumper fromantenna to TTA

Jumper fromTTA to feeder

Feeder

Lightningarrester

Jumper fromlightning arrester

to cabinet top

BTS3X

cabinet

Figure 4-1 Cable connections of antenna & feeder subsystem

The antenna & feeder subsystem transmits the modulated RF signals, and receives the

signals from MSs.


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4-2

4.2 Antenna

The antenna is the originating point of transmission and the terminating point of

receiving. The type, gain, directional diagram and front-to-rear ratio of the antennahave great effect on system performance. These elements shall be planned on the

basis of subscriber number and coverage. The following will detail on the key indices of

antenna.

4.2.1 Classification

Antennas can be classified into the omni-directional antenna, unipolarized directional

antenna and dual polarized directional antenna. The dual polarized directional antenna

is usually used to substitute unipolarized directional antenna to reduce the number of

antennas. A dual polarized directional antenna equals to two unipolarized directional

antennas.

4.2.2 Gain

Gain of an antenna indicates the capability of the antenna in focusing and radiating the

power to a certain direction. Usually the higher the gain of the antenna is, the stronger

the field strength will be along the wave radiation direction and the wider the antenna

will cover. But there may be blind spot nearby.

4.2.3 Directional Diagram

The directional diagram of antenna describes the radiation strength on different

directions. In the telecom field, it is normally described with horizontal azimuth angle

and declination angle as the coordinate. BTS antenna is described with azimuth angle.

Usually there are situations: omni-directional antenna and directional antenna. The

coverage of omni-directional antenna is horizontal round coverage. The main lobe

width of directional antenna is 120, 90, or 65. The declination angle of antenna is

normally realized with mechanical or electrical adjusting. The currently applied

declination angles for BTS directional antenna are 0 and 2, etc. It is possible to realize

large scale angle adjustment with pitch controller (such as 0 to 10).

4.2.4 Polarization

Polarization is used to describe the direction of the electric field radiated by the antenna.

Antennas used in mobile communication system include unitpolarized antennas and

dual polarization antennas. The two polarization directions of the dual polarization

antenna are vertical to each other. The dual polarization antenna can reduce the

number of antennas hoisted.


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4-3

4.2.5 Diversity Technology

The electric wave transmission in a city has the following features:

1) The strength mid-value slightly varies with the change of place and time. The ruleof changing conforms to lognormal distribution, which is called slow fading.

2) Due to multi-path transmission, the instantaneous value of field strength features

selective fading along transmission path. The fading rule conforms to Rayleigh

distribution, which is called fast fading.

Both fast and slow fading has negative effect on mobile communication quality. In some

cases, they may even cause communication interruption. Diversity technology is a

measure to settle the problem of fading. If the correlation between two channels of

fading signals is low, the suitable diversity receiving and combining technology can be

adopted to eliminate the fading effect of signal transmission. Diversity can be classifiedinto polarization diversity and space diversity, etc.

Two antennas are used at BTS to realize diversity receiving. Two directional antennas

or two unipolarized directional antennas can be used to realize space diversity

receiving. One dual polarized directional antenna can realize polarization diversity

receiving.

4.2.6 Antennas Isolation

To avoid the negative effect of transmitter on receiver, different antennas shall beproperly isolated and the two polarization directions of dual polarized antenna shall be

properly isolated. In GSM system, the antenna isolation shall be more than 30 dB.

4.3 Feeder

A transceiving path is mainly made up of one feeder. There are two selections: 7/8"

feeder and 5/4" feeder. A unipolarized directional antenna or omni-directional antenna

needs a feeder. A dual polarized directional antenna needs two feeders.

Since feeder insertion loss has a great impact on the noise factor of receiver and thetransmitting power of BTS, it is required to reduce the insertion loss of feeder as much

as possible. The low loss RF feeder is usually adopted for BTS. If the length of the

feeder is smaller than 60 m, the 7/8" feeder can be used. If the length is greater than 60

m, 5/4" shall be considered to lower the feeder loss.

4.4 Lightning Arrester

Lightning arrester is used to avoid damaging the equipment caused by the influence

current through the conductor in the feeder. A feeder shall be configured with a lightning


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4-4

arrester. There are usually two types of arrester: one directs the current to the ground

according to microwave principle, and the one is discharge tube arrester, which will

become a conductor when the voltage between both ends of the discharge tube

reaches a certain value. BTS3X adopts the latter one. The arrester of BTS30 and thatof BTS312 are usually installed near the cabinet, while that of BTS3012A and that of

BTS3006A are installed in the cable inlet of the auxiliary equipment cabinet

4.5 TTA

4.5.1 Overview

The tower top amplifier (TTA) is a low-noise amplification module installed on the tower.

Its function is to amplify the uplink signal from MS before the transmission loss occursalong the feeder. This helps improve the receiving sensibility of the BTS system and the

uplink coverage of the system while lowering the transmitting power of MS and

improving the session quality.

TTA is optional. Usually, the triplex TTA is configured. It is installed close to the antenna.

This type of TTA consists of triplex filter, low-noise amplifier and feeder. The triplex filter

is actually the combination of two duplex filters. The signal from the antenna is first

filtered off the external interference at the triplex filter, and then is amplified by the

low-noise amplifier, and finally sent to the indoor unit.


Figure 4-2shows the functional architecture of a triplex TTA.

DC

BTS

Triplex TTA

Transmitting filter

TTA feeder

By pass

Low noiseamplifier

Receiving

filter

Receiving

filter

Figure 4-2 Triplex TTA functional architecture


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4-5

4.5.3 Functions

The TTA has the following functions:

The noise factor of TTA is very low. TTA has a wide dynamic range, which is full adaptable to the change of strength of

signal received by antenna caused by different distance between MS and BTS.

TTA has the alarm bypass function.

TTA is fed with feeder, so it has the feeding detection device.

TTA adopts strict water-proof sealing and is adaptable to a wide range of working

temperature (40C to 70C).

TTA can sustain strong lightning strikes.


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Technical Manual System PrincipleM900/M1800 BTS3X Series Base Transceiver Station Chapter 5 System Bus Structure


5-1

Chapter 5 System Bus Structure

5.1 Bus Classification

BTS3X adopts the advanced bus management mode to allocate the resources for BTS

so that the cooperative efficiency between boards and components can be higher. The

inter-cabinet bus is used to transmit the following signals:

Clock signal

Control signal

Data signal

Status signal between cabinets

Logically, BTS buses include the following types:

Data bus

Control bus

Clock bus

FH bus

Physically, there are only two types of bus cables:

Clock cable: has 25 PIN DB connectors. It contains clock bus and CBUS1.

Data cable: has 37 PIN DB connectors. It contains CBUS2, CBUS3, DBUS1,

DBUS2 and FHBUS.

5.2 Bus Structure

Figure 5-1shows the bus connection of BTS30.


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5-2

Clock bus

CBUS1

CBUS2

DBUS1,2

FHBUS

CBUS3

TMU0

TRX0 TRX17

CDU

0~ 8

PMU

0~2

TES

Clock bus

CBUS1

CBUS2

DBUS1,2

FHBUS

CBUS3

TMU0

TRX0 TRX17

CDU

0~ 8

PMU

0~2

TES

BTS30 main cabinet group

(1)

TMU1 TMU0

TRX0 TRX17

CDU

0~ 8

PMU

0~2

BTS30 extension cabinet group

TMU0

TRX0 TRX17

CDU

0~ 8

PMU

0~2

CBUS2

DBUS1,2

FHBUS

CBUS3

CBUS2

DBUS1,2

FHBUS

CBUS3

BTS30 extension cabinet groupBTS30 main cabinet group

(1)

TMU1 TMU0

TRX0 TRX17

CDU

0~ 8

PMU

0~2


TMU0

TRX0 TRX17

CDU

0~ 8

PMU

0~2

CBUS2

DBUS1,2

FHBUS

CBUS3

CBUS2

DBUS1,2

FHBUS

CBUS3


(1) Environmental monitoring instrument

Figure 5-1 BTS30 system bus connection

Figure 5-2shows the bus connection of BTS312.

Clock bus

CBUS1

CBUS2

DBUS1,2

FHBUS

CBUS3

TMU0

TRX0 TRX23

CDU

0~ 11

PMU

0~1

TES

BTS312 main cabinet group

(1)

TMU1 TMU0

TRX0 TRX23

CDU

0~ 11

PMU

0~1


TMU0

TRX0 TRX23

CDU

0~ 11PMU

0~1

CBUS2

DBUS1,2

FHBUS

CBUS3

CBUS2

DBUS1,2

FHBUS

CBUS3


(1) Environmental monitoring unit

Figure 5-2 BTS312 system bus connection

Figure 5-3shows the bus connection of BTS3012A.


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5-3

TMU

TRX0 TRX11

CDU

0~ 2PMU

Clock bus

CBUS1

CBUS2

DBUS1,2

FHBUS

CBUS3

BTS3012A cabinet

Figure 5-3 BTS3012A system bus connection

The following section takes BTS30 as an example to introduce various buses in detail.

The principle of data buses of BTS312 is similar to that of BTS30 and BTS3012A. The

buses of BTS3012 are connected through their backplanes instead of TDUs.

5.3 DBUS

The data bus (DBUS) is for the data connection between TMU and TRX. Each TMU

provides 2 full duplex DBUS link and TRX connection, called DBUS1 and DBUS2.

The physical feature of DBUS is differential RS485, TDMA synchronous bus and

distribution of 32 timeslots is similar to that of PCM.

The active TMU has DBUS connections to each TRX in the same cabinet. The active

and standby links are led from the main cabinet to the 18 TRXs in the local cabinet

group. There is no DBUS connection between cabinet groups. For BTS3012A, DBUS

connection only exists between TMU and TRX in a single cabinet.

Figure 5-4shows the signal connection between BTS30 cabinets.


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5-4

Figure 5-4 DBUS connection between BTS30 cabinets

Figure 5-5shows the intra-cabinet signal connection of BTS30.

Upper cabinetTDU

JP6

TDU

JP5

Cabletransfer

Inner cabledistribution

CMB J25

(connect with TMU)


TRB

JC3

TRB

JC1

TDU

JP7

TDU

JP8


Cabletransfer

Lower cabinet

Inner cabledistribution(connect with 6 TRXs)

Figure 5-5 DBUS connection flow

For the cabinet at the uppermost level, JP6 shall be configured with connector. For the

cabinet at the lowermost level, JP8 shall be configured with connector.

5.4 CBUS

5.4.1 CBUS1

The control bus 1 (CBUS1) is for the communication between the TMUs of this same

site. It adopts RS485 semi-duplex bus and asynchronous transmission. The link layerconforms to HDLC protocol. The bus rate is 256 kbit/s.

Because only the PCM link in main cabinet group has the operation and maintenance

signaling of BTS, the master TMU in main cabinet group is to send the operation and

maintenance signaling to the slave TMUs in the two extension cabinet groups, as

shown in Figure 5-6.


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5-5

Figure 5-6 CBUS1 connection between BTS30 cabinets

Figure 5-7shows the connection of the intra-cabinet signal of BTS30.

Upper cabinetTDU

JP3

Cabletransfer TDU

JP2


CMB J24

(connect with TMU)

TDU

JP4

TDU

JP2

CMB

J24


Cabletransfer

Lower cabinet

Figure 5-7 CBUS1 connection flow

5.4.2 CBUS2

The CBUS2 is for the control link between TMU and TRX.

Physically, it conforms to the differential RS485 interface and semi-duplex bus. The link

layer conforms to the HDLC protocol. The bus rate is 2 M. The 2 M clock of DBUS is

used as the clock of CBUS2. There is no CBUS2 connection between cabinet groups.

The connection between CBUS2 cabinet groups and the connection paths are similar

to that of DBUS.

5.4.3 CBUS3

CBUS3 is for the connection between TMU and some low rate control parts, such as

CDU, PMU and environmental monitoring units.

Physically, it conforms to the differential RS485 interface. The link layer conforms to the

DLC protocol, differential transmission and master/slave communication. The bus rate

is 9.6 kbit/s. There is no CBUS3 connection between cabinet groups.


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5-6

Figure 5-8 CBUS3 connection between BTS30 cabinets

Figure 5-9shows the connection of the intra-cabinet signal of BTS30.

Upper cabinet TDUJP6

TDUJP18

TDUJP5

Cabletransfer

Cabletransfer

Alarm

box

CMB J25(connect with TMU and PMU)

TRBJC3


TRBJP1

Documents

01 System Principle