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

comunications

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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 ś3 dbm.

126


IDB


TRANSMISSION MEDIA-MICROWAVE

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  passé


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

127



TRANSMISSION MEDIA-MICROWAVE

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 ś3dbm

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  ckt‘s  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

128


TRANSMISSION MEDIA-MICROWAVE

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  śconsisting  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.

129


TRANSMISSION MEDIA-MICROWAVE

·    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 ś

48v DC supply with positive grounded.



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