GSM BTS Overview

GSM BTS & CELL OPERATIONS

By- Deepak Garg (BSS CM)

General Basics about Ericsson RBS

1RBS = 3 CELLS 1RBS OR 1BTS can handle up to 12 TRXs (1TRX means 1 frequency) An MO is a logical representation of HW unit and SW of the BTS

in the BSC One TG handles can handle only on RBS (BTS Cabinet) One TG can have different channel groups,each channel group

can consist up to a maximum of 16 frequencies TRU (RBS2000) or TRX (RBS200) stands for transceiver group, 1

TRU handles one frequency, which consist of 8 timeslots, each timeslot needs 16kbps bandwidth

AXE BSC : RL… commands used for cell handling RX… commands used for managed object handling

Managed objects Block Diagram

9702373

RX

TX

TS0 TS

7

TRXC0

RX

TX

TS0 TS

7

TRXC15

IS ( UP TO 16 TRXCs)

CF TF

8 TS

8 TS

DP

CON

9702380

Managed object block diagram RBS2000 (G12)

Managed object block diagram RBS200 (G01)

1.Transceiver Group (TG)2.Central Function (CF)3.Digital Path (DP)4.Concentrator (CON)5.Transceiver Controller (TRX)6.Transmitter (TX)7.Receiver (RX)8.Interface Switch (IS)9.Timing Function (TF)10.Time Slots (TS)

RBS

2000200

Macro Micro Pico

Indoor Outdoor

2202 DXU-11

2101 2102 DXU-11 2302 Maxite 900 & 1800 2401

TRU 6(12) 2(4) 6(12) 2(6) 2(6) 2

P [W] 28 28 28 1,6 20 0,08BatteryBackup 0-12h 0-2h 3min

(2.5h) 2h n/a

RBS 2000 Family

EoS(End of Support)

2014

2012

2014

2014

2014

2012

2014

5 min

¦ ¦¦ ¦¦ ¦V V

3000

RBS 2000 family

The BTS controls the radio interface to the MS. The BTScomprises the radio equipment such as transceivers and

antennaswhich are needed to serve each cell in the network. A group

ofBTSs are controlled by a BSC.

• Radio resources

• Signaling link management

• Synchronization

• Local maintenance handling

Functions of RBS

RBS 2000 HardwareRBS 2000 Hardware

The RBS 2000 series is based on standardized hardware units called Replaceable Units (RU).The major RU’s are:

(1) Distribution switch Unit (DXU) (2)Configuation Switch unit (CXU) (3) Transceiver Unit (TRU) (4) Combining and Distribution Unit (CDU) (5) Power Supply Unit (PSU) (6) Energy Control Unit (ECU)

RBS 2206 Hardware overview

DXU-21 Distribution Switch Unit

DXU

Central control unit for RBS

Flashcard makes it possible to change a faulty DXU card, without the need for loading RBS software from the BSC

OMT is the RBS configuration tool. All the RBS configuration data and the software stored in flash memory card (size: 32Mb). Configuration file: ldb.dbb.

Distribution Switch Unit Functions

CF Central Function: the control part of a TG. The BSC communicates with the CF using layer 2 LAPD, address: TEI = 62.

CON LAPD concentration for RBS 2000.

IS Interworking Switch: system interface to the 2 Mbit/s link, connects time slots to transceivers.

TF Timing Function, synchronization with PCM link and generates a timing reference for the RBS.

DP Digital Path, Layer 1, each of the PCM systems terminating in TG has an associated supervision object, the DP.

DTRU – double Transceiver Unit

Contains 2 TRXs for transmission and reception of carriers.

built-in combiner with the possibility of combining two TX signals into one output.

Prepared for RX diversity

dTRU - Transceiver Unit functions

TRXC The transceiver controller is controlling all the functions for signal processing, Radio receiving and Radio Transmitting.

RX The receiver provides the radio frequency reception functionality for one transceiver.

TX The transmitter provides the radio frequency transmission functionality on a time slot basis for eight TSs using different time slot numbers.

CDU

Combining and Distribution Unit (CDU)

Interface between the transceivers (TRU) and the antenna system.

Signals are filtered before transmission and after reception with bandpass filters.

RBS 2206 maximum 3 CDU CDU-F used for high capacity solutions (Baseband hopping) CDU-G is the most common used, it can be configured

either for high capacity or high coverage. It supports synthesizer hopping

Different Modes of CDUs

CDU Uncombining modeMost straightforward configurationTrx connected to own antenna port No combination lossesAlso called coverage mode.

CDU combining modeOut-put power is 3.5 db lower than uncombined modeReduces no of antennaUsed for high capacity coverage in dense areasAlso called capacity modeHybrid combined (ex: CDU-G) and Filter combined (ex: CDU-F)

2xTX/RX TX/RX and RX

• dTRU used in uncombined mode with CDU-G• One CDU-G is fully occupied by one dTRU• Max 3 dTRUs in one cabinet (3x2)

Maximum Range Standard High Capacity

• dTRU used in combined mode with CDU-G• One CDU-G is fully occupied by two dTRUs• Max 6 dTRUs in in one cabinet

• dTRU used in uncombined mode with CDU-F• One CDU-F is fully occupied by two dTRUs• Max 6 dTRUs in one cabinet.

Basic Rules for Product Packages

CDU-G CDU-F

• Product Packages are always described as maximum configurations (maximum TRX-s)• Necessary TX and RX cables for the maximum configuration are always delivered (inside the cabinet), i.e. to add a TRU within the maximum configuration will not require additional cables.• Cables for extension configurations, e.g. next CDU, are not included.

2xTX/RX

CDU-G

Dummy

Light gray TRU is optional

Uncombined CDU-G Product Packages

1x2 2x2 3x22xTX/RX

2xTX/RX 2xTX/RX 2xTX/RX

2xTX/RX

2xTX/RX

Always equippedwith 1 dTRU

Always equippedwith 2 dTRUs

Always equippedwith 3 dTRUs

Only TX-cables shown

Combined CDU-G Product Package (1-sector)

1x4 1x8 1x122xTX/RX

TX/RX and TX TX/RX and TX TX/RX and TX TX/RX and TX

2xTX

Can be equippedwith 1-2 dTRUs




CDU-F Product Package (1-sector)

1x4 1x8 1x122xTX/RX




TX/RX and RX 2xTX/RX


Configuration Switch Unit (CXU)

Distributes the RX signal from CDU to dTRUs Built up SW controlled switches Makes it possible to reconfigure a cabinet without cable

moving Only one set of RX cables to cover all configurations Only one type of CXU to cover all configurations with CDU-

F,CDU-G

Energy Control Unit (ECU)Energy Control Unit (ECU) The ECU controls and supervises the power The ECU controls and supervises the power equipment aequipment aregulates the environmental conditions inside the regulates the environmental conditions inside the cabinet.cabinet.

Internal Distribution Module (IDM). Actually IDM consists of many MCBs.These Actually IDM consists of many MCBs.These MCBs are used to protect all replaceable units from MCBs are used to protect all replaceable units from severe sudden voltage fluctuations.severe sudden voltage fluctuations.

IDB, OMT and OMT over IP

• IDB stands for Installation Database• That tells the DXU what RUs are installed in what type of

cabinet and in what way they are installed• RBS 2206• Using E1• GSM 900 & 1800• Combined mode• No TMA• etc.

• An IDB can be viewed/created/installed using OMT

What is IDB?

The OMT, Operation and Maintenance Terminal, is a powerful application providing efficient aid for the operation and maintenance of RBS 2000 base stations. The OMT supports all RBSs in the RBS 2000 family.

The OMT comes in three different versions:

• OMT (or Local OMT)Is a PC application and can be connected to the

RBS through a serial cable• Remote OMT

Same functionality as Local OMT. The Remote OMT utilizes the regular site transmission via the BSC for communication with the RBS.

• Remote OMT over IPSame functionality as Local OMT. The Remote OMT over IPcan connect to any RBS 2000 in the network from any remote location with IP access to the serving BSC.

What is OMT?

The ability to perform OMT operations remotely yields a number of benefits:

• Limited presence at site is needed.• Faster site configuration.• Easier site surveillance.

Remote OMT Benefits

OMT Main Window

TG sync & Cascade mode

TG sync: More than 1 cabinet in one cell Master / Slave mode used (RXMOI: TFMODE

parameter) TFCOMPNEG is the distribution delay

between the master and slave TG , value depends on the cablelenght. OMT able to calculate.

Cascade mode used when only 1 PCM available for 2 RBSs

1 PCM Cascade mode

2 PCMs no cascade mode

RBS0 RBS1 RBS0 RBS1TFMODE M S M STEI 62 61 62 62TFCOMPOSS OMT OMT OMT OMT

2 RBS in cascade mode with TG sync

Calculate required channel number on E1

In our case we have 3 x 4 configuration, and two T1 links connected to PCM1 and PCM3 slots (from RXCDP and RXAPP printout).

We have 8 TS / frequency, this means 3 x 4 x 8 = 96 timeslots. 1 frequency is used for BCCH on each channel (no signaling needed

between BTS and BSC for BCCH), so we have 96-3=93 timeslots. Other 1 SDDCCH per cell is reserved for signaling purposes, this

means 93- 3 =90 timeslots for voice call on the whole site. 1 voice call = 16 kbit/s , this means one 64 kbit/s PCM timeslot

can carry 4 voice calls, so we need 90/4 = 23 timeslots for the voice calls on the PCM link.

We also need signaling, one 64kb/s channel for each frequencies, but we have LAPD concentration with CONFACT=4 (RXMOP:MO=RXOTG-204), this means 3 PCM channel is enough for signaling.

We needs 26 PCM time slots for voice calls and signaling.

3 cells x 4 freq x 8 timeslot = 96 TSs96 TS - 3 BCCH - 3 SDCCH - = 90TSs without BCCH and SDCCH90/4=22.5 -> 23 TSs needed for voice traffic on the PCM23 + (12/4) = 26 timeslots needed for voice calls and signaling

Frequency Hopping types

In baseband hopping each transmitter is assigned with a fixed frequency.

At transmission all burst jumping from one transmitter to the other independently of the connection

The number of the frequencies can be used for hopping = The number of transmitters

Narrow-band combiners can handle 12 (16) transmitters.

In synthesizer hopping one transmitter handles all frequencies belongs to the same connection

The number of frequencies can be used for hopping is independent from the number of transmitters

Each TRX is configured to hop over a large amount of frequencies (20 for example)

Frequency hopping definitions Random hopping sequence - > pseudo-random sequence 63 independent sequences, parameter HSN specifies which sequence will be used Length of sequence ~ 6 minutes

Each transceiver in the same channel group in the same cell will be assigned with the same HSN (they hop in the same way).

Avoid interference -> using an offset in the hopping sequence, called Mobil Allocation Index Offset (MAIO).

CHGR: a group of frequencies handled in the same way within one cell. Channel group 0 contains the Broadcast Control Channel (BCCH) and is automatically defined at cell definition.

________________________________... , f 1 , f 4 , f 4 , f 3 , f 1 , f 2 , f 4 , f 1 , f 3 ,

f 3 , f 2 , ...

... , f 4 , f 3 , f 1 , f 2 , f 4 , f 1 , f 3 , f 3 , f 2 , f 2 , f 1 , ...

... , f 1 , f 2 , f 4 , f 1 , f 3 , f 3 , f 2 , f 2 , f 1 , f 4 , f 3 , ...

... , f 4 , f 1 , f 3 , f 3 , f 2 , f 2 , f 1 , f 4 , f 3 , f 1 , f 2 , ...

________________________________

BCCH: CHGR 0TCH: CHGR 1 Frequency 104-123MAIO: A=(0,2,4), B=(6,8,10), C=(12,14,16)HSN: A=10, B=10, C=10

A valid GSM900 configuration with 20 hopping frequencies

Hopping sequences

GSM BTS Overview

Documents

Transcript of GSM BTS Overview