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What Is BER MER For Digital Headend System

BER MER

Introduction Of BER MER

BER MER are the two parameters generally used in Digital Headend system for the characterization of digitally Modulated signal.

In Other Words,

BER MER are two factors which are responsible for proper delivery of signal.

If you are a Headend Engineer then these two parameters plays very important role in the maintenance of Digital Headend System. Troubleshooting with these two parameters you will not get any major problem in field also. So we need to maintain these two parameters from our Digital Headend to field for proper signal reception.

What Is BER

BER is abbreviation for Bit Error Rate. BER also known as Bit Error Ratio. Digital Signal meter or QAM analyzers are used in the measurement of BER.

If bits are transmitted from one side and these are receiving at the other side then there will losses in the bits which are denoted by BER. To understand more about it follow the diagram below,

BER explanation

As shown above in the figure a cable modem is transmitting the bits to CMTS (Cable Modem Termination System). These transmitted bits are 010101. But at the receiving end the CMTS received 010001 bits. So there is loss of 1 bit at receiving side.So this bit is called Errored Bit.

Thus BER is the ratio of Number Of Errored Bit to the Total Number Of bits sent.

bit error ratio ber

For Example,

We are sending 1,000,000 bits from the transmitter and at the receiving end we get 3 errored bits. So BER will be

BER = 4/1000000 = 0.000004 =  4×10-6

It can be expressed as 4.0E-06

So the efficient value for the BER is 1×10-8 or 1.0E-08

A QAM analyzer shows two types of BER

(A) Pre BER

(B) Post BER

Pre BER is known as Pre-FEC BER (Pre-Forward Error Correction BER). It means it is showing BER before applying Reed Solomon Encoding. While Post BER is also known as Post-FEC BER.It means it is showing the BER after applying Reed Solomon Encoding.

Now its obvious that value of Pre-FEC BER will be greater than Post-FEC BER because after applying RS Encoding the number of Error Bit would be less.

For Example,

A BER reading of QAM Analyzer is

Pre-FEC BER = 5.6E-5

Post-FEC BER = 1.4E-7

Reasons For Degradation Of BER

(1) Incorrect Signal Level

(2) Laser Clipping

(3) Interference Of Channels

(4) Sweep Transmitter Interference

(5) Loose Connections

What Is MER

MER is abbreviation for Modulation Error Ratio. Modulation Error Ratio is the difference between Transmitted Symbol  and the Targeted Symbol.

In other words,

MER is the vector difference between Transmitted Symbol Vector and Ideal Symbol Vector.

MER = 10log10 (Average Symbol Power / Average Error Power)

modulation error ratio mer

MER is measured in dB. We need to keep MER 3 to 6 dB above from the unequalized MER value for proper receiving of signal. The unequalized MER value is different for different modulation i.e.

QPSK ∼ 18 dB

16 QAM  ∼ 24 dB

64 QAM ∼ 27 dB

256 QAM ∼ 31 dB

Try to maintain high MER for proper signal receiving.

Reasons For Degradation Of MER

(1) Incorrect Signal Level

(2) Collision Of Data

(3) Low quality Modulation

(4) Low C/N Ratio Or Carrier To Noise Ratio

Conclusion

BER MER are two essential parameters when the things comes in terms of maintenance of digital data transmission for proper signal reception.

We need to maintain low value of BER as much we can and also keep high the value of MER as much we can maintain. If we are maintaing these two parameters in Digital Headend as well as in the field then we can better services to our subscribers.

Know More About   What Is CBR And VBR In Digital Headend

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Comments

  1. KAMAL BERA says:

    THANK YOU SIR

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