Gaussian pulse shape replaces the square pulses with gaussian pulse
Q1. Identify a contemporary digital communication system giving an overview of function and capacity. Then describe how access, switching, routing and multiplexing is undertaken.
Internetworking (internet) is one of the best examples to be discussed in the category of contemporary digital communication system. TCP/IP which is abbreviated form of standard internet protocol suite is used to interconnect computer networks globally is called internet. It serves millions and billions of users globally. In this network which is a network of networks consists of billions of official, business, research, academic, public and private networks. Linked by a wide arrangement of electronic, optical and wireless circuitry technology, it has local to global ambit. (Internet Wikipedia, 2011).
LAN operates in a baseband model, which means that a given wire is carrying one data at one time. Various apparatus use the medium turn wise. If each medium allows only one data course, data communication having relatively great extent in space is difficult to put in and carry on and as a result would be ineffectual. Thus two or more data courses are supported by broadband media and it is called WAN or Wide Area Network. Thus multiplexing is used to enable more than one data streams to distribute a towering bandwidth intermediate. (Alex Peeters- Delivering data through internetworks, n.d).
In the statistical time division multiplexing there is uneven distribution of time slots to different data streams as some data courses are given more while other may get less time slots. In the figure the channel d which is an ideal channel is allocated no slot. The device is thus called stat-mux. (Alex Peeters- Delivering data through internetworks, n.d).
Switching Data:
When two apparatus starts communication, a path is formed between the two devices which is called circuit and this circuit has a dedicated bandwidth for it.
This circuit is used to transfer all data between these devices. But a case may arise in which bandwidth may be wasted if data flow uses less than the dedicated magnitude. Circuit needs to be reconfigured if less busy paths in the network has to be utilised. Here the role of circuit switching comes where it doesn't mean that there is a continuous and fixed physical pathway between the apparatus. Multiplexing of message streams with each other may take place in a broadband network.
Routing:
ANS:
It allows different terminus associated to the same multiple point transfer medium to transfer over it and divide its range. Examples of such physical apparatus are hub networks, wireless circuit, ring circuit, bus circuit and half-duplex point-to-point links.
A route-access scheme is based on a multitudinous method in which same communication apparatus allows several data token. Here, physical layer provides multiplexing. Point to note is that multitudinous is also used in full-duplex point-to-point communication between terminals in a switched circuit, which can not be believed as multi accesses.
Mainly two types of data compression are there- lossless data compression and lossy data compression.
Statistical superfluous is used in algorithms of lossless compression so as to show the sender's information briefly and with accuracy. Most information that is used in real world has statistical superfluous which makes lossless condensation (compression) possible. On the other hand, storage capacity in digital cameras is increased with minimum decadence of the quality of picture by the help of lossy image compression. Non-hearable or less hearable parts of the token in audios are removed by the help of psychoacoustics in lossy audio compression. (Data Compression Wikipedia, 2011).
A finite number of frequencies are used in frequency-shift keying which is abbreviated as FSK.
A finite number of amplitudes are used in amplitude-shift keying which is abbreviated as ASK.
Figure 7: Example of 11011000100 in Manchester Coding (Wikipedia, 2011)
In the deregulation of a digitally regulated conveyance or to a digital bit stream are the cases where FEC course in a receiver is used. For the first one, FEC is the main part of the initial analog-to-digital change in a receptor. Soft-decision algorithm is applied by Viterbi decoder to demodulate digital information from an analog token adulterated by noise. In order to fine-tune the analog receiving electronics, BER (bit-error rate) signal is generated by FEC decoders. It is a fact that various FEC codes are useful in various situations because the maximum part of inaccuracy or missing information that is to be corrected is determined by the design of FEC code. (Forward Error Correction Wikipedia, 2011).
Physical Transmission Channel:
The bodily or logical component that connects a data originator to a data terminator in a communication system.
For members to connect in an Internet Relay Chat (IRC) network. (Channel-Communication, Wikipedia, 2011)
Figure 10: Band pass filtering method for demodulation of a binary FSK signal (Bob Watson, WJ communication Inc, n.d)
Effect of Band Pass filtering:
In Figure "Simplified frequency spectrum" above it is shown that there is two times energy in the space tone sis within a within a bandwidth equal to twice the baudrate, centred about the mark and space frequencies, respectively.
Figure 13: Simplified demodulation spectrum for “matched filter” type FSK demodulation (Bob Watson, WJ communication Inc, n.d).
Because non-coherent FSK is so much more common than coherent FSK, it is necessary to have a type of demodulator that does not depend on phase information. Optimum demodulation of non-coherent FSK can be achieved by envelope detection of the signal filter outputs in a filter-type demodulator. The outputs of the mark and space filters are envelope-detected and then compared to determine which has greater magnitude. Note that phase information is not required. With the “right” filter shape, performance of this type of demodulator approaches the theoretical optimum for non-coherent FSK (Bob Watson, WJ communication Inc, n.d).
Q4. Explain the benefit of shaping the baseband pulse, as used in Gaussian filtered minimum shift keying (GMSK). Your answer should include a description of the BT product and its relationship with inter-symbol interference. Word length max 500 words (can include citations in this word count)
Figure 15: Time domain pulses shaped by Gaussian pulses (Charan Langton-Guide to principles of communication, 2005).
Quantity Bb is signal bandwidth. BT factor is equal to this number times the symbol time T.
Figure 19: Spectral Densities for MSK and GMSK (MX.com- Practical GMSK data Transmission, Inc. 1998).
