01 System Principle BTS312

8/13/2019 01 System Principle BTS312

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Huawei Technologies Proprietary

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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........................................................................................................ 2-8

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

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

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

2.9.2 AC/DC Module ........................................................................................................ 2-9

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

Table of Contents

Technical Manual System PrincipleM900/M1800 BTS312 Base Transceiver Station Table of Contents


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

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

3.2 TRX.................................................................................................................................... 3-2

3.2.1 Overview ................................................................................................................. 3-23.2.2 Architecture and Principle ....................................................................................... 3-3

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

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

3.3.2 Principle of Structure............................................................................................... 3-6

3.4 PBU.................................................................................................................................... 3-9

3.4.1 Overview ................................................................................................................. 3-9

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

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

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


3.6 ECDU............................................................................................................................... 3-12

3.7 TEDU ............................................................................................................................... 3-13

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


3.8 TMDU...............................................................................................................................3-14

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

Technical Manual System PrincipleM900/M1800 BTS312 Base Transceiver Station Table of Contents


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Technical Manual System PrincipleM900/M1800 BTS312 Base Transceiver Station Chapter 1 Getting Started


1-1

Chapter 1 Getting Started

The BTS312 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

Subsystem Unit (abbreviation) Unit (full name)

TMU Timing/Transmission and Management Unit

TDU Time Distribution Unit

ASU Access network SDH transmission Unit

PAT Passive Transmission Board

TES Transmission Extension Power Supply Unit

ABB Abis Bypass Board

ABA Abis Bypass Assistant Board

PSU Power Supply Unit

PMU Power Monitor Unit

FMU Fan Monitor Unit

TEU Transmission Extension Unit

Common

subsystem

EMU Environment Monitor Unit

TRX Transceiver Unit

ETR EDGE TransceiverPBU Power Boost Unit

CDU Combining and Distribution Unit

ECDU Enhanced Combining and Distribution Unit

TMDU Trunk Multiple combination and Distribution Unit

TEDU Trunk Enhanced Duplexer Unit

SCU Simple Combining Unit

Signalprocessingsubsystem

ESCU Enhanced Simple Combining Unit


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Technical Manual System PrincipleM900/M1800 BTS312 Base Transceiver Station Chapter 2 Common Subsystem


2-1

Chapter 2 Common Subsystem

2.1 Overview

The common subsystem manages the BTS. It provides reference clock, power supply,

transmission interface, maintenance interface and external alarm collecting interface.

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 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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2-3

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, to centralize the

downloading and saving of the software loaded to various units, and to support the

connection to the MMI at a PC.

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 through O&M Link (OML).

The new 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.

III. 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


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2-4

IV. EAC

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

2.3 TDU

2.3.1 Overview

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.

2.3.2 Functions

TDU has the following major function:

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

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 through the

120-ohm E1 interface on the cabinet top, and then transferred to TMU through TMU.

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. 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

Apart from E1 transmission, BTS312 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

1 P2P user RS232 interface


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2-6

NM interface: Ethernet/RS232

2.5 PAT

2.5.1 Overview

In addition to E1 transmission, BTS312 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.

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

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 a

bridge for TEU to report messages to TMU.


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2-7

2.6.2 Functions

The TES has the following functions:

One TES can provide power supply and communication transference to at mosttwo 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.

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.


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2-8

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 through 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 transmission

trunk. 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.

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. BTS312 has two TEU

slots, but ABB can only select slot 0 that hosts the TEU.


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2-9

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 throughCBUS3. But the slot of ABB does not provide the connection with CBUS3. Therefore,

ABA is used to provide the connection between them. Through 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.

II. Board Location

ABA shares the slot with TES in BTS312 cabinet. Therefore, the size of the board and

the interface definition are consistent with those of the TES.

2.9 PSU

2.9.1 Overview

The power supply unit (PSU) is a built-in power supply module. BTS312 supports

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

accordingly. Different power supply modes can be configured for BTS312 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


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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.

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


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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 analogvariable 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.)

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)

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.


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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:

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.

Controlling the fan speed

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.

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 BTS312 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, TMDU, TEDU, 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.

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 acell 4.

ESCU CDU slot

Can be used with PBU, CDU, ECDU, EDU, TMDU,and TEDU.

This condition shall be satisfied: number of TRXs in a

cell 4.

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 through

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.


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3-3

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 Processor

CUI: 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

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


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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 through 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 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

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.

II. RPU

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


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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 fortransmitting 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 is

necessary 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,

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


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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 through base band unit, and automaticallycloses 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 RFprocessing unit. ETR receives signal from MS through 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

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).


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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 BasebandProcessing 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.

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 through CUI.


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

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 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 and under-power alarm signal.

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


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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 transmittinglocal 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 through 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.

3.4 PBU

3.4.1 Overview

The power boost unit (PBU) is the TRX output power amplifier. It increases the effective

radiation power (EPR) of the antenna and extends the coverage of BTS. The maximum

output power: 49 !1 dBm.

PBU consists of PA synthesizing module, alarm management module and power

supply module.


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

Coupling and delay filter

Range and phasecontrol

60W PA

Power

synthesizing

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 managementmodule. 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),

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.


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The range and phase adjusting of coupling channel signal necessary for power

synthesizing 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 powersynthesizing, 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, PA

output 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

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 receiving

tributary.

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.


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GSM1800

GSM1900


3.7 TEDU

3.7.1 Overview

Trunk enhanced duplex unit (TEDU) is designed for wide coverage and low loss. It

realizes the following functions:

Transceiving duplex of two TRXs

Filtering the transmitting signal and the receiving signal

Low-noise amplification and division

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.

TEDU supports the frequency range of 806 MHz821 MHz (uplink) and 851 MHz866

MHz (downlink).



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

TA

feeder

Divider

Duplexer

Alarm and control

unit

Transmitting

input

Receiving

output Low noise amplifier

TEDU

Test

coupler

TA

feeder

Divider

Duplexer

Receivingoutput

Transmitting

input

Low noise amplifier

Test

coupler

Figure 3-7 TEDU architecture

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

functions for alarm test:


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

standing wave exceeds the preset threshold of 2.5:1, the TEDU gives

corresponding alarm and indication.

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

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

a certain range or no current is detected.

Control function: The TEDU 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 TMDU

TMDU is used in the site with S3 configuration of S3 or above. It can support 4-channel

signal combining.

For the architecture and principle of TMDU, see Figure 3-6.


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Technical Manual System PrincipleM900/M1800 BTS312 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 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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4.2.5 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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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. BTS312 adopts the latter one. The arrester of BTS312 isusually installed near the 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 occurs

along the feeder. This helps improve the receiving sensibility of the BTS system and theuplink 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 feederBy pass

Low noiseamplifier

Receiving

filter

Receiving

filter

Figure 4-2 Triplex TTA functional architecture


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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.

01 System Principle BTS312

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