Course: Digital Communications, Advanced Course (ETTN01

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Study period Ht-2 2010.

Course: Digital Communications, Advanced Course (ETTN01)

Aim

The aim of this course is to give very good knowledge of advanced digital

communication methods.

The course gives a broad and deep understanding such that many of the communication

methods used today, as well as many future methods, can be understood.

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Digital Communications, Advanced Course (ETTN01)

Examples of previous project works :

• Mobile telephony (GSM, 3G, 4G)

• Digital Radio & TV

• Modem (e.g., ADSL)

• WLAN (Wireless Local Area Network)

• Future communication methods/systems (4G, 5G,…)

• MIMO systems (multiple antenna systems)

• UWB (Ultra Wide Band, “Impulse Radio”)

• GPS (Global Positioning System)

• Bluetooth

• Home electronics (CD, DVD, remote controls, etc. )

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How good can we do concerning bit rate & bit

error probability?

C=W*log2(1+SNR), Claude Shannon 1948

Practical consequences?

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Remember!

Thinking in the frequency domain is necessary to be able to

understand communication methods and systems.

Problem 2.26a (M-ary PSK)!!

Problem 2.26b (M-ary QAM)!!

Problem 2.30 (Peak value of R(f); Radiation aspects (EMC),

standards)!!

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A practical implementation is therefore:

General bandpass:

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Example 3.1:

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In 3G mobile telephony systems all users use the same

time-interval and the same frequency-interval simultaneously!

CDMA is used instead of TDMA and FDMA.

Each user has a unique code.

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AM: The information is in the envelope.

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A VCO is also useful to generate FSK and GSM signals!

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FM

• Assume that the input signal a(t) gives the

FM-signal v(t).

• Assume now that the input signal is

doubled, i.e. =2a(t).

What is now the FM-signal?

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Interpretation in the frequency domain:

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Common challenge in both Wireless and Wireline applications!

Remember the training bits in GSM!

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This will cause overlapping signals unless Tb is increased to 3 s!

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Sent:

Received:

How do we handle this situation?

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All frequencies are equally disturbed.

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Gaussian probability

distribution:

What is the probability that the output noise is above a critical level A (“bit-error”)?

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Very useful

tables!

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Q(x) versus x

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Sent:

Received:

How can we find the sent information bits?

Pb=?

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(The same definition as in (2.12))

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Sent message (k bits): Decided

message:

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How is your decision strategy?

The disturbed image on the black-board: Is it a house or a boat?

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Optimal decision strategy!

How is your decision strategy?

The disturbed image on the black-board: Is it a house or a boat?

Since the decided message must be 0,1,2,3,…,(M-2) or (M-1)

we test all cases in equation (4.13).

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Furthermore, we can quite easy implement the optimal receiver!

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Probability of “false alarm”: “0” is sent but the receiver decides “1”.

Probability of a “miss” : “1” is sent but the receiver decides “0”.

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This receiver is optimal if the signal alternatives are equally likely.

The received signal is compared with all noise-free signal alternatives.

That is why the channel must be known to the receiver!

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“Correlation receiver”:

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