13 GHz/11GHz MICROWAVE RADIO STATION - TRANSMISSION MEDIA-MICROWAVE

TRANSMISSION MEDIA-MICROWAVE

13 GHz/11GHz MICROWAVE RADIO STATION

INTRODUCTION

The 13GHz/ 11GHz microwave radio station equipment is one of the

series of digital microwave equipments currently in production line of ITI. It

specifically caters for medium capacity digital transmission interconnection

local exchange in a city. The equipment operates in the frequency band of

12.750 GHz to 13.250 GHz and is designed to carry 480 PCM voice channel

data on a single radio frequency bearer channel. Simultaneously, a maximum

of 8 radio frequency channels consisting of 7 working and one protection

channel can be equipped.

SALIENT FEATURES FO THE EQUIPMENT

Capable of transmitting and receiving simultaneously,

1. 480 PCM voice channel data traffic corresponding to 34.368 Mb/s HDB-3

coded data.

2. Two omnibus / express orderwire (analog) channels with selective

calling facilities for link maintenance.

3. Extensive remote supervisory system.

4. Switching information.

Automatic switch over for 7 working and one protection channel.

The equipment is fully solidstate and employs microwave integrated

circuits, dielectric resonators, oscillators and high speed digital

integrated circuits for high reliability.

Radio transmission with QPSK modulation.

Operates from a station supply of 48v DC with positive terminal

grounded.

Space diversity receiver with IF combiner as a counter measures

against the deep flat fading over the hop.

Transversal equalizers as a counter measure against in band amplitude

and delay distortion caused by frequency selective fading.

BRIFE DISCRIPTION

The block schematic of 13GHz/11GHz (1+1) frequency diversity

Microwave radio station configuration expandable upto (7+1) configuration

is as shown:

TRANSMITTING END

The 34.368 Mb/s data in HDB# format from external multiplex

equipment is applied to switch over (SWO) module where the signal is

attenuated by approximately 3 db and is then divided into 2 routes

respectively to be supplied to transmitter digital processor (TX DPU)

module of regular (REG) and protection (PROT) channels. The TX DPU

facilitates Bi-polar to uni-polar (B-U) conversion, serial to parallel (S_P)

conversion, insertion of frame pattern, parity check information and switch

signals into two transmitting data streams of 19.332Mb/s each. The data

stream is scrambled and sent to the phase modulator (PH MOD) module of

transmitter (TX) unit.

In the PH MOD module, each of the two 19.338 Mb/s data streams are

differentially encoded and low pass filtered for shaping the pulse stream.

The pulse streams thus shaped are applied to two 0-pi modulators. A 70

MHz IF carrier is generated at the 70 MHz oscillator and split into the two

carriers for each 0-pi modulators. The phase difference between the two 70

MHz carrier is pi/2 radians. In each 0-pi modulator, the phase of carrier 70

MHz is modulated to a 0 phase or a pi phase by input pulse streams. The

output of the two 0-pi modulators are thus combined for four phase

assignment onto a 70 MHz carrier and IF amplifier and sent to the

transmitter radio frequency (TX RF) module of the TX unit at an output

level of 3 dbm.

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Main antenna

BR CKT

W/G

T X

T X

SWO

DISP

A L M MS /

BR CKT

250 mm

SW O

TRX

PS

P D U

RS

TEL

SC

MS / RS

NFB

P D U

R X

B B

B B

P S

P D U

R X

B B

B B

P S

P D U

50

mm

SY ST E M B A SE P L A T E

480 mm

In the TX RF module, the modulated IF signal is mixed with an RF local

signal from VCO to produce the transmitting frequency and is pass

through a 5-section band pass filter (5 BPF)

which allows only the

desired RF signal. The RF signal from 5 BPF is amplified upto the specified

value by GaAs FET amplifier in the FET AMP module and the signal thus

amplified is sent through the respective branching circuit. The FET AMP is

provided with an ALC circuit to stabilize the transmit output signal by

compensating for the variations of the signal due to temperature etc.

RECEIVING END

The RF input signal coming from the associated branching circuit

is applied to the receiver radio frequency (RX RF) module of receiver(RX) unit,

which also consist of delay equalizer (DEL EQL), receiver intermediate

frequency (RX IF) and transversal equalizer (TRSV EQL) (optional) modules. In

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the RXRF module the received RF signal is amplified by a GaAs FET low noise

RF pre-amplifier, which has a low noise figure of max. 4.5 db and is mixed

with an RF signal of the local oscillator and converted into a 70 MHz band IF

signal and the local IF signal is amplified by the pre-amplifier to the required

level.

In the case of space diversity receiver (SD RX) which consist of space

diversity radio frequency (SD RX RF) and IF combiner (IF COMB) modules ,

the RF is input signal applied from the associated SD branching circuits to

the SD RX RF , is mixed with an SD local signal from the main RX. Then the

RF input signal with an SD local signal from the main is converted into a 70

MHz band IF signal. After amplification it is applied to IF COMB. The IF

COMB monitors the phase difference between the main and SD IF signals.

And when detects a phase difference between the 2, the local signal phase

of the SD receiver is shifted by the endless phase shifter (EPS) of the SD

RX FREQ CONV module to make the two phase coincide. The voltage sum

of IF signal from the main receiver are combined in-phase by an IF hybrid.

The IF signal is then applied to the DEL EQL module, which equalizes

group delay caused by the branching filters. The equalized IF signal is

filtered by RX IF module and amplified to a constant output level of 3dbm

by automatic gain control(AGC) ckt. The IF signal then passes

The phase demodulator (PH DEM) modules consist of four phase

demodulator circuit where the input IF signal is split into two paths and the

applied to has detector ckts where information is detected by coherent

detection. The HDB3 signal from receiver digital processor (RX DPU) is

then, fed to SWO modules, where one of REG and PROT is selected by the

control signal for passing on to external multiplex equipment.

The pilot generator/ pilot detector (PG/PD) consists of PG/PD

circuits. The pilot generator generates a 34.368 MHz signal and encodes a

pilot signal pattern. The PG section consist of TX PROT access switch over ckt

that selects either transmitting protection access signal or pilot signal by TX P

access switch over control signal. The PD converts the receiving bipolar pilot

signal into a uni-polar signal and decodes the signal to detect a pilot signal

pattern. The PD section is composed of RX PROT access switch over ckt,

which leads the receiver pilot signal to a PD ckt and the receiving protection

access signal to the output terminal by switch over operation.

The Alarm Control (ALM CONT) module outputs the alarm and control

signalsto the external equipments. Alarm signals, monitored in each

respective module and control signals are gathered at the AMT CONT

module for concentrated processing according to use.

SUPERVISORY AND CONTROL SYSTEM

The service channels (SC) unit for 34 Mb/s digital microwave radio

system provides the following facilities through analog service occupying

the band 0.3 to 12 KHz.

a) Remote supervision and control (4.3 to 7.4 KHz band)

b) Omnibus orderwire telephone circuit (0.3 to 3.4 KHz band)

c) Express orderwire telephone circuit (8.3 to 11.4 KHz band)

To ensure satisfactory maintenance operation of radio relay communication

system, the sc UNIT is classified into the following three types:

1) SC/MS: Service channel unit equipped with supervisory and control Master

Station facility

2) SC/ RS: Service channel unit equipped with supervisory and control

Remote Station facility

3) SC: Service channel unit without supervisory and control facility.

A 4 wire operation telephone panel (TEL) is mounted on SC unit for

two channel use with a channel selection switch, a hand set and selective

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calling facility. The in band DTMF (dual tone multi frequency) system is used

for selective calling facility.

The SC unit includes remote supervisory and control facility, which

employs microprocessor control logic circuit design. The remote station

module can report upto 32

Supervisory items & can receive upto 8 remote control items. The master

station module

Can monitor and control upto 8 station consisting of 7remote stations and

master station it self-by the polling method. The supervisory control Signal is

transmitted using FSK signal, which is assigned in 4.3 to 7.4 KHZ band of

Analog service channel.

The Analog Service Channel (ASC) signal occupying the 0.3 to 12 KHZ

band is inserted to both the regular and protection channels. The drop of ASC

is normally made from the regular channel and if it become faulty, the drop

will be switched to

the protection channel.

SWITCHOVER CONTROL SYSTEM:

The Switchover control system (NAL) which has a capability of

switching up to 7+1 systems, provides automatic and manual control function

to prevent the traffic from interruption hen one of the regular channels fail due

to out of frame, bit error rate (BER) degradation or loss of signal etc. it

provides the switchover control function for RX switching. A switchover

control signal arranged in digital service channel is transmitted together with

main signal stream.

Automatic switchover to the protection channel is carried out when

any one of the regular channels fails. Automatic switching operation is

initiated from the NAL at the receiving end of the switching section. The radio

equipment at receiving end informs NAL of its channel according to the

following sequence:

1. A fault in the regular channel is detected at the receiving end. The

protection channel must be ready for service.

2. The faulty channel switching control signal is transmitted from the

receiving end to the transmitted end.

3. The above control signal is decoded at the transmitting end and the

transmitting end switch (TX SW) is controlled to the disconnect the

line drive (radio pilot pattern) signal from the protection channel

and transmit the incoming regular channels signal on both the

regular and protection channels.

4. The protection channel does not receive the line drive signal and in

frame condition of regular channel signal transmitted over the

protection channel is detected at the receiving end.

5. RX switching from the regular channel to the protection channel is

performed.

The Automatic switching mentioned above, however, automatically

restores to the original state upon recovery of the defective channel. if two or

more regular channels fail at the same time , this equipment controls the

highest priority regular channel and it will be switched over to the protection

channel. This switching priority can be arranged simply by setting priority

switch.

MECHANICAL CONSTRUCTION:

The equipment is built in a slim rack of dimension 120mm (W) x

225mm (D) x 2500mm (H) to utilize minimum floor space. Each radio

transmitter receiver is built in one rack, switch over control equipment is built

in one rack and supervisory equipment along with antenna port , Wave guide

& input power switch(NFB)are equipped in one rack. Thus a (1+1) system is

equipped in four slim racks.

ASSOCIATED EQUIPMENTS:

13 GHz 34 Mbs radio Relay System Works in conjunction with the

following equipments.

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Antenna: 13 GHz high performance antenna with dual Linear polarized

feed. The size of the antennas is decided by the route engineering &

vary from 1.2meter to 2.4 meter.

Waveguide run: Elliptical waveguide with UBR 120 flange is used as a

feeder waveguide.

Digital PCM MUX: Digital PCM MUX to CCITT specs consisting of 2Mb/s,

8Mb/s and 34Mb/s data from voice frequency.

Station battery supply: the13GHz 34Mb/s equipment operates from

48v DC supply with positive grounded.