Mw presentation 1

MW Basic Knowledge

• Microwave Microwave is kind of electromagnetic wave. In a broad sense, the

microwave frequency range is from 300MHz to 300GHz. But in microwave communication, the frequency range is generally from 3GHz to 30GHz.

According to the characteristics of microwave propagation, microwave can be considered as plane wave.

The plane wave has no electric field and magnetic field longitudinal components along the propagation direction. The electric field and magnetic field components are vertical to the propagation direction. Therefore, it is called transverse electromagnetic wave and TEM wave for short

MW Basic Knowledge• Microwave Frequency• 2 GHz (1.7-1.9GHz; 1.9-2.3GHz; 2.4GHz; 2.49-2.69Ghz)• 4/5 GHz (3.4-3.8GHz; 3.8-4.2GHz; 4.4-5.0GHz; 5.8GHz)• 6 GHz (5.925-6.425GHz;6.430-7.110GHz)• 7 GHz (7.125-7.425GHz;7.425-7.725GHz)• 8 GHz (7.725-8.275GHz;8.275-8.5GHz;8.50-8.75GHz)

• 11/13 GHz (10.7-11.7GHz; 12.75-13.25GHz)

• 15/18 GHz (14.50-15.35GHz; 17.7-19.7GHz)

• 23GHz; 26GHz; 32GHz; 38GHz;

MW Basic Knowledge• Microwave Links Capacity PDH TDM: (4E1/8E1/16E1/32E1/48E1,Super PDH 75E1);

Ethernet: (20M/40M/75M);

SDH TDM: N STM-1 (1≤N≤14)

Ethernet: N 138M/150M/170M (1≤N≤14) Split MW SDH (1+1 STM-1—3+1 STM-1) Truck MW SDH (7+1 STM-1; 2*(7+1) STM-1)

Microwave Radio Link

TX/Rx

Hop NO.1

OrTX/Rx

Hop NO.2

Hop No.n

TX/Rx TX/Rx

Distance between the transmitter and the receiver, a few km < D < 100km

Availability and quality depends on the distance recommended by ITU-R.

TerminalStation

Cable

Relay station(Passive)

TerminalStation

Relay station(Active)

CableRadio Link

MW Basic Knowledge

Radio Wave Propagation （ 1）The radio link propagation follows the line of sight: it requires a perfect clearing between transmitting and receiving antennas. The propagation medium is made of the lower layers of the atmosphere (a few meters to a few hundred of meters above ground)

The non homogeneity of the atmosphere influences the waves propagation:1. Path curvature2. Reflecting, diverging, focusing intermittent events

Free space loss (Lfs)=92.4+20×log(f×d) (dB) f:GHz, d:km

MW Basic Knowledge

Radio Wave Propagation （ 2）

AbsorptionPartial reflection

Almost horizontal

DiffusionRefraction

Atmosphere influence

i.1

i.2

n1

n2

n1

n2

Diffusion volume

500km

n1×sin i.1 = n2×sin i.2

Gaz and water vapor

Freq. < 15GHz : insignificant20 GHz : 0.1 dB / km

Rain

Freq. > 10GHz

MW Basic Knowledge

Radio Wave Propagation （ 3）Ground influenceGround influence

ReflectionDiffraction

Spherical diffraction

Diffraction on a ridge

MW Basic Knowledge

Radio Wave Propagation （ 4）

An imaginary earth with the radius of 8500km, allows to simplify analysis on Refraction propagation of radio wave.

RImaginary EarthReal Earth

Ro

Standard atmosphere N = - 39 N km

K = R/Ro = 4/3h

h

N : Gradient of air refraction index

N may reach more extreme values than + 250 or - 350, during short percentage of time

N = 315 N units

Air refraction index at sea level: n = 1.000 315

N

MW Basic Knowledge

MW Basic Knowledge• Microwave Transmission Characteristic• —Loss Characteristic

The Rules of Loss changing: A: Higher Frequency; Longer Distance; Worse Loss. B: Day better than Night; Winter better than Summer; C: Cloudy, Windy more stable than Sunny day D: Over water is worse than Over land; E: Over Hill/Mountain is better than Over Plain;

The reason is the reflection index of electric wave is changing with different time, location and height

MW Basic Knowledge

• Microwave Transmission Characteristic

When there is loss in the link, not only with worse SNR (Signal Noise Ratio), but also the deep loss will break off the link; To get a better performance and reliability in MW transmission, we need to consider some methods to avoid the loss, such as Diversity.

Diversity has the following types: Space diversity, Frequency diversity,

Polarization diversity, Angle diversity and Multiply diversity.

MW Basic Knowledge

• Microwave Transmission Characteristic —Overcome Loss

1. Space Diversity Signals have different multi-path effect over different paths and thus have

different fading characteristics. Accordingly, two or more suites of antennas at different altitude levels to receive the signals at the same frequency which are composed or selected. This work mode is called space diversity. If there are n pairs of antennas, it is called n-fold diversity.

Advantages: The frequency resources are saved; Disadvantages: The equipments is complicated, as two or more suites of

antennas are required; Antenna distance: As per experience, the distance between the diversity

antennas is 100 to 200 times the wavelength in the frequency used frequency bands, and normally we choose 5/10 meters, also we can calculation by;

MW Basic Knowledge• Microwave Transmission Characteristic

—Overcome Loss 1. Space Diversity

d= (100~200)λ= (100~200)ν/F

Where v=3*108

MW Basic Knowledge

• Microwave Transmission Characteristic —Overcome Loss

2. Frequency Diversity Signals at different frequencies have different fading characteristics.

Accordingly two and more microwave frequencies with certain frequency spacing to transmit and receive the same information which is then selected or composed, to reduce the influence of fading. This work mode called frequency diversity

Advantages: The effort is obvious. Only one antenna is required;

Disadvantages: The utilization ratio of frequency bands is low;

MW Basic Knowledge

• Microwave Transmission Characteristic —Overcome Loss

3. Polarization Diversity When using polarization diversity, utilizing the same aerial on different

polarizations and scrambling polynomials have to be different for both signals send the same signal.

4. Angle Diversity The efficiency of angle diversity is based on the antennas uncorrelated radiation

pattern (resultant signals are different). One antenna and two feedersTwo antennas (are located close to each other, space diversity effect is achieved if

antennas are far a way from each other) and the other antenna has been tilted

MW Basic Knowledge• Microwave Transmission Characteristic Advantage: 1. Can be rapidly installed; 2. Can use the existing network infrastructure repeatedly (digital radio uses the

infrastructure of the analogue radio) 3. Can cross complicated terrains (rivers, lakes and mountains) 4. Can use point-to-point radio transmission structure in the remote mountains 5. Can rapidly restore the communication after the natural disasters 6. Can protect hybrid multiple transmission media

Those advantages not only apply to the fixed nodes or temporary nodes and feeder routes in the urban areas, but also apply to very long long-

distance routes.

MW Basic Knowledge

• Microwave Transmission Characteristic Disadvantage:

1. Line of sight transmission conditions should be ensured;

2. Transmission distance between two stations should be not too long;

3. Frequencies need to be applied for;

4. Communication quality is greatly affected by the environment;

5. Communication capacity is limited.

Microwave Equipment Application

Ethernet Application

Mobile Network Application

Cellular Network Application

Application/Solution

Application/Solution

Point to Point Digital Microwave transmission system

MUX

Satellite

Fiber optic cable

Microwave link

Coaxial cable

MUX

Mobile Network Application

BSC

MSCPSTNBSC

.....

MSC

SDH

BSC

BSC

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BTSBTS

BTS BTS

BTS

BTS

BTS

BTS

BTS PDH

PDH

BTS

PDHBTS

BTS

BTS

BTS

BTS

BTS

SDH

SDH

SDH

SDH

PDH

PDH

PDH

PDH

PDH

PDH

PDH

SDH SDH

SDH Microwave

PDH Microwave

PSTN: Public Switched Telephone NetworkMSC: Mobile Switching CenterBSC: Base Station ControllerBTS: Base Transceiver Station

Cellular Network Application （ 1）

UMTS: Universal Mobile Telecommunication System

21

Difficult Areas for Microwave Links

• In areas with lots of rain, use the lowest frequency band allowed for the project.

• Microwave hops over or in the vicinity of the large water surfaces and flat land areas can cause severe multipath fading. Reflections may be avoided by selecting sites that are shielded from the reflected rays.

• Hot and humid coastal areas