Introduction to Digital Microwave Communication

EquipmentChapter 3

Outlines

• Microwave Equipment Category• Split-Mount Microwave Equipment• Microwave Antenna• Antenna Adjustment• Split-Mount Microwave Equipment – ODU• Split-Mount Microwave Equipment – IDU

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Microwave Equipment Category

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Trunk Microwave Equipment

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All Outdoor Microwave Equipment

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Split-Mount Microwave Equipment (1)

• The RF unit is an Outdoor Unit (ODU)– The IF, signal processing,

and MUX/DEMUX units are integrated in the Indoor Unit (IDU)

– The ODU and IDU are connected through an IF cable

• The ODU can either be directly mounted onto the antenna

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Split-Mount Microwave Equipment (2)

• It’s the most widely used microwave equipment– Although the capacity is smaller than the trunk, due to the easy

installation and maintenance, and fast network construction• Unit Functions

– Antenna: Focuses the RF signals transmitted by ODUs and increases the signal gain

– ODU: RF processing, conversion of IF/RF signals– IF cable: Transmitting of IF signal, management signal and power

supply of ODU– IDU: Performs access, dispatch, multiplex/demultiplex, and

modulation/demodulation for services

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Split-Mount MicrowaveEquipment – Installation

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Microwave Antenna (1)

• Antennas are used to send and receive microwave signals

• Parabolic antennas is common type of microwave antennas

• Microwave antenna diameters includes: 0.3m, 0.6m, 1.2m, 1.8m,2.0m, 2.4m, 3.0m, 3.2m

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Microwave Antenna (2)

• Different frequency channels in same frequency band can share one antenna

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Antenna Adjustment (1)

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Antenna Adjustment (2)

• During antenna adjustment, change the direction vertically or horizontally. – Use a multimeter to test the RSSI (Received

Signal Strength Indication) at the receiving end– The voltage wave will be displayed as shown

in the lower right corner. – The peak point of the voltage wave indicates

the main lobe position in the vertical or horizontal direction

– Large-scope adjustment is unnecessary– Perform fine adjustment on the antenna to

the peak voltage point

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Antenna Adjustment (3)

• When antennas are poorly aligned, a small voltage may be detected in one direction– Perform coarse adjustment on the

antennas at both ends, so that the antennas are roughly aligned

• The antennas at both ends that are well aligned face a little bit upward– Though 1–2 dB is lost

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Antenna Adjustment (4)

• During antenna adjustment, the two wrong adjustment cases are show here– One antenna is aligned to

another antenna through the side lobe

– The RSSI cannot meet the requirements

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Split-Mount Microwave Equipment – Antenna (1)

• Antenna gain– Ratio of the input power of an isotropic antenna Pio to the input

power of a parabolic antenna Pi when the electric field at a point is the same for the isotropic antenna and the parabolic antenna

• Half-power angle– The given antenna specifications contain the gain in the largest

radiation (main lobe) direction (denoted by dBi)– The half-power point, or the –3 dB point is the point which is

deviated from the central line of the main lobe and where the power is decreased by half

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Split-Mount Microwave Equipment – Antenna (2)

• Cross polarization discrimination• Suppression ratio of the antenna receiving heteropolarizing

waves, usually, larger than 30 dB– XdB＝ 10lgPo/Px– Po: Receiving power of normal polarized wave– Px: Receiving power of abnormal polarized wave

• Antenna protection ratio– Attenuation degree of the receiving capability in a direction of

an antenna compared with that in the main lobe direction– An antenna protection ratio of 180° is called front-to-back ratio

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Split-Mount Microwave Equipment – ODU (1)

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Split-Mount Microwave Equipment – ODU (2)

• Specifications of Transmitter– Working frequency band – Generally, trunk radios use 6, 7, and

8 GHz frequency bands• 11, 13 GHz and higher frequency bands are used in the access

layer (e.g. BTS access)– Output power - The power at the output port of a transmitter

• Generally, the output power is 15 to 30 dBm

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Split-Mount Microwave Equipment – ODU (3)

– Local frequency stability• If the working frequency of the transmitter is unstable, the

demodulated effective signal ratio will be decreased and the bit error ratio will be increased

• The value range of the local frequency stability is 3 to 10 ppm– Transmit Frequency Spectrum Frame

• The frequency spectrum of the transmitted signal must meet specified requirements

– To avoid occupying too much bandwidth and thus causing too much interference to adjacent channels

• The limitations to frequency spectrum is called transmit frequency spectrum frame

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Split-Mount Microwave Equipment – ODU (4)

• Specifications of Receiver– Working frequency band

• Receivers work together with transmitters• The receiving frequency on the local station is the transmitting

frequency of the same channel on the opposite station– Local frequency stability

• The same as that of transmitters: 3 to 10 ppm– Noise figure

• The noise figure of digital microwave receivers is 2.5 dB to 5 dB

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Split-Mount Microwave Equipment – ODU (5)

– Passband• The passband and amplitude frequency characteristics should be

properly chosen to effectively suppress interference and achieve the best transmission quality

• The receiver passband characteristics depend on the IF filter– Selectivity

• Ability of receivers of suppressing the various interferences outside the passband

– Especially the interference from adjacent channels, image interference and the interference between transmitted and received signals

– Automatic gain control (AGC) range• Automatic control of receiver gain

– With this function, input RF signals change within a certain range and the IF signal level remains unchanges

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Split-Mount Microwave Equipment – ODU (6)

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Split-Mount Microwave Equipment – IDU (1)

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Split-Mount Microwave Equipment – IDU (2)

• IDU functions– Service access– Service scheduling– Multiplexing– Modulation and demodulation

• If an IF board is equal to the line board of optical network equipment– IDU is similar to the box-shape equipment of optical network

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Split-Mount Microwave Equipment – IDU (3)

• Common IDU Specifications

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Split-Mount Microwave Equipment – IDU (4)

• Common IDU Specifications (cont..)

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