Analog Communication Model Exam

ANALOG COMMUNICATION

Model Exam Answer Key (2015)

1. Non linearity in vge vs freq chara, amounts to harmonic distortion, no amplitude limiting.

2. IF is 455kHz in AM. Always lower than RF. So easier and less expensive to construct high gain stable amplifiers. Most of the receiver’s gain and selectivity is achieved in IF stage.

3. Balanced slope detector.

Disadvantages:

• Poor Linearity

• Difficulty in tuning

• Lack of provisions in limiting

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Stability of the crystal is very high and produce constant frequency.

7. fo= fs+ fi ; fsi= fs+2fi= f0+fi ; IFRR= (1+Q2ρ2)1/2

8. The probability density function of the Rayleigh distribution is

where is the scale parameter of the distribution. The cumulative distribution function is[1]

for

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a) Gaussian (Normal) Distribution

b)

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b)

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18. Refer Telecommunication and switching networks by Thyagararaja Viswanath

19. There are 2 types of signaling:

In-Band: signals are carried over the same circuit that carries formation during the session. ·        Has drawbacks, such as fraud; toll thieves are able to defeat automatic message accounting systems by using devices that emulate signaling tones.

Out-of-Band: uses a separate network to carry the signals. Two examples:·        D channel of ISDN (see Chapter 32 for elaboration)·        Signaling System 7 (SS7)- separate common channel signaling network; this eliminates toll fraud.

Signals can be grouped into four functions:·        Supervising - monitoring the status of a line or circuit to determine if it is busy, idle, or isrequesting service.·        Alerting - indicates to the addressee the arrival of an incoming call; audible bells and tones or visual lights.·        Call Progress Tones - informs the user of the status of the call setup process; eg.: busy signal.·        Addressing - the process of transmitting route and destination signals over the network; such as dial pulses, tone pulses, or data pulses over loops, trunks, and signaling networks.

Differences Between In-Band and Out-Band Signaling

In-Band Signaling

·        Line busy or idle; Central Office (CO) monitors constantly the status·        When you lift receiver, it signals CO intent to make a call·        CO marks the line busy and sends back a dial tone·        Caller dials the number and CO transmits the dual-tone multi-frequency (DTMF) or dial pulses·        System translates digits and sends them to the terminating end thus producing a ring·        The process of setting up the talking path determines whether the path is operative since audible signals are passed over the channel that will be used for talking.·        Are limited to transferring call setup and supervision information, and are therefore incapable of supporting virtual voice networks.·        Call setup consumes circuit time (takes several seconds to setup), which is important because it represents a direct expense in the access charges paid to the LECs.

Common Channel Signaling (Out of Band)

Replaces the In-Band Signaling and uses a separate data communications network to exchange signals and route the calls.·        SS7 is the international common channel signaling system.

The Architecture of OUt of Band Signaling

·        Service switching points (SSPs): Software applications running in the central offices, and are linked via data circuits to ·        Signal transfer points (STPs): Network nodes that act as hubs for signaling messages. ·        STPs are linked to service control points (SCPs), which contain a database of network information that can be accessed by the network nodes.·        Each stage of the call, ringing, connect, and disconnect, is signaled with a data message.·        It is so fast, the circuit connection can wait until the called party answers, further increasing circuit

utilization.·        Important to the LECs’ market strategies; enables them to receive more revenue from CLASS.·        Custom Local Area Signaling Services (CLASS): Uses a separate packet-switched network to pass call setup, charging, and supervision information.·        Can access the carrier’s database to obtain account information, such as features and points served, on a virtual network.·        Is required for local number portability - take your previous phone number to your new location.

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