CS431 - Wireless Communication

@zaasmi thank you so much sir

Answer to Q#1
Modern transponders can carry many different types of communications traffic. They can also receive signals from multiple ground stations, combining (multiplexing) or splitting (de-multiplexing) them for onwards transmission to other multiple ground stations. This method, by which many users share a common satellite resource, is called Multiple Access. There are several schemes for accomplishing this, each with its benefits and drawbacks.

TDMA (Time Division Multiple Access) allocates a time slot to the user in a repetitive time frame. The signal is digitized and the data bits are stored in a buffer in a compressed time frame until their allocated time slot comes around when they are transmitted during their allocated time. At the receiver end of the link the bits are rearranged, spreading them out to reassemble the original digital signal and converted back to analogue form. The signal occupies the entire transponder bandwidth, but only during its allocated time slot. The rest of the time the bandwidth is available to other users. Digital signals typically have better noise immunity than analogue signals.

FDMA (Frequency Division Multiple Access) shares the bandwidth between the users, with each user allocated a unique, narrower section of the available bandwidth. It works with analogue signals and all users have uninterrupted use of their own narrow frequency band or channel with all users occupying the available bandwidth simultaneously, each within their own narrow channel. The sender’s signal, called the baseband signal, is frequency shifted into the allocated frequency band for transmission and the receiver restores it back to the baseband.

CDMA (Code Division Multiple Access) also known a Spread Spectrum, modulates the user’s signal with a pseudorandom code so that it occupies the full available spectrum, appearing as noise. The receiver uses the same pseudorandom code in an auto correlator device, which only recognizes a signal modulated with the same auto code and thus separates it from the noise. CDMA is more complex but has better noise immunity and provides greater security than the other two systems.

Answer to Q#2
• Mobile Service Satellites (MSS)
• Example: Satellite Phones

Answer to Q#1

A transponder is a wireless communications, monitoring, or control device that picks up and automatically responds to an incoming signal.
Transponders are microwave repeaters located at intermediate points in a communications link, which are used to compensate for the signal attenuation along the route to extend the range of the link. They receive the very weak signals from a sender at one end of the link, amplify them, and re-transmit them at much higher power to the receiver at the other end of the link. The whole purpose of a communications satellite system is to place a transponder in position, to keep it there and to keep it powered up. Because of the very high launch costs, for satellite systems to be economically justified, the transponder should be able to carry high traffic volumes including television channels as well as dozens of multiplexed voice communications and other data links. It should also be small and light.

Questions: Marks 10

Question # 1 Marks 10
An organization has its satellite-based network that it provides direct broadcast services. This organization comes across signal attenuation problem due to the long distance communication links, which results in the poor service.
As a network engineer, what you will advise to that organization to compensate this attenuation?

Answer to Q#1

A transponder is a wireless communications, monitoring, or control device that picks up and automatically responds to an incoming signal.
Transponders are microwave repeaters located at intermediate points in a communications link, which are used to compensate for the signal attenuation along the route to extend the range of the link. They receive the very weak signals from a sender at one end of the link, amplify them, and re-transmit them at much higher power to the receiver at the other end of the link. The whole purpose of a communications satellite system is to place a transponder in position, to keep it there and to keep it powered up. Because of the very high launch costs, for satellite systems to be economically justified, the transponder should be able to carry high traffic volumes including television channels as well as dozens of multiplexed voice communications and other data links. It should also be small and light.

Answer to Q#2
Being a networking engineer, he should suggest the use of polynomial codes to the organization for desired objective.
The benefits of using polynomial codes is that it produces short codes. For example, here a 6-bit pattern is replaced by 3 terms.
In polynomial codes, the degree is 1 less than the number of bits in the binary pattern. The degree of polynomial is the highest power in polynomial. For example as shown in fig degree of polynomial x5 +x2 + 1 are 5. The bit pattern in this case is 6.
A pattern of Os and 1s can be represented as a polynomial with coefficient of o and 1.
Here, the power of each term shows the position of the bit and the coefficient shows the values of the bit.
For example, if binary pattern is 100101, its corresponding polynomial representation is x5 + x2 + 1. Figure shows the polynomial where all the terms with zero coefficient are removed and x J is replaced by x and XO by 1.

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