Telecommunication Principles - Assignment Example

Telecommunication Principles L02.3: Q1 a) Factors affecting the maximum data rate The bandwidth available: this is the measure of the bit rate per second; that is, the data consumed in a communication expressed in bits per second. The bandwidth that be transmitted depends upon the system or medium of transmission. It has been established that the data rate of a network is highly influenced by the bandwidth of that channel. Since a bandwidth acts like a highway through which the data travels through, its size significantly determines the speed of data being transmitted. The wider the bandwidth, the higher the data rate; from the example of a free highway, when the lanes are many, more traffic can flow through; similar to the bandwidth(Carr). The level of signal used: a signal represents the electromagnetic waves in data transmission. In telecommunication, signals are generated by a transmitter and then promulgated by a transmitter. An effective bandwidth has been described as one in which the most of signal energy is concentrated. Signals are transmitted in two forms: digital and analogue signals. Data transmission using analogue signals is slower that when using digital signals. This is because transmission in analogue becomes slower due to weakening of the analogue signals over time or long distances. Also, it has been established that the strength of the signal determines the data rate of a system. High signal quality results in a higher data rate(Leven). The quality of channel or the level of noise: some systems result in erroneous transmission due to distortion of data. Distortions such as noise have been identified to affect the transmission rate of data in a system. Such distortions are associated with analogue signals. Continuous distortions affect the performance of a system; particularly the data rate. This means that when the noise generate rate in the transmission system is higher, the bit rate per second is reduced. Signal sharing: wireless networks allow multiple users to use the signals simultaneously. This means the more devices have to be in connection with the network signal at the same time. The access point has to delegate its resources to each of the users. As users` number rises, the performance of the system gets lowered. With few users, the data rate is higher and reduces as users increase(Carr). Network range and distance between devices: as explained earlier, signal strength reduces with an increase in distance. This means that the transmission speed will also reduce as the signal strength drops. If the two devices are located in distant places, this could mean that the data rate will be impaired. Similarly, short distances denote a strong network signal. With a strong signal, higher data transmission speeds will be experienced. Obstruction: obstacles to networks signals have been found to impair the data rates of the system. Walls, hills and other solid objects occurring in the way of transmission signals impair the speed of transmission. They slow down the signal and therefore reduce the transmission speed. Other obstacles may make it impossible for signals to penetrate, another setback to data rates. b) The Nyquist theorem: it is based on the assumption that noise is free. Nyquist provides the upper bound for the bit rate of a transmission system by determining the bit rate straight from the number of bits in a symbol and the bandwidth of the transmission system (assumption: 2 symbols/per cycle and first harmonic). In conclusion, it can be deducted that doubling the bandwidth doubles the data rate if only all other factors are equal. Shannon’s Theorem, on the other hand tries to determine the relationship between noise, data rate and error rate. This theorem is used to determine the capacity of a signal transmission system in where noise is present. The variation between the two theorems is that when the Shannon theorem gives us the upper limit, the Nyquest theorem tells us how many signal levels we require. (i) The theoretical highest bit rate C = B log2 (1 + SNR) 3000 log2 (1 + 35) = (ii) The applicable bit rate and number of signal levels First we determine the highest bit rate C = B log2 (1 + SNR) = 106 log2 (1+ 63) = 6 Mbps This is the upper limit in accordance with the Shannon formula. For higher performance and efficiency, we will use a lower value, let us say 4Mbps. The Nyquest formula will give us the levels of signal as follows 4 Mbps = 2 × 1 MHz × log2 L L = 4 L02.4 Q 2: impairments and their effects Path loss This is described as the loss in signal strength as the network signals are transmitted through space. Path loss has been identified as a major channel impairment that springs from wave expansion in the free space as a result of increased sphere. Factors that contribute to path loss include: Reflection: this is described as the change in direction of waves as a result of interaction with another surface. The result of reflection is that the wave goes back to the transmitting device (source of transmission). Refraction: this is the change in the direction of a wave front as a result of change in the medium through which the waves are being transmitted. In refraction, the direction of the wave changes by the velocity and frequency of the wave remains unchanged. Absorption: this is the way electromagnetic waves are taken in by another matter and transformed into another form, mostly heat energy. Path loss may also be experienced in another form called multipath. This is where electromagnetic waves from a similar transmission source travel along different paths to the receiver. Upon arrival at the receiver, they are perceived as different types. The receiver will therefore treat them differently thereby distorting the original transmission. Fading is another form of path loss that is closely related to multipath. As waves travel from the transmission source to the receiver, multiple transmission paths of the same waves may occur. Waves following different paths may experience differently delays, attenuations or phase shifts as they travel to the receiver. This may result in constructive or destructive interference of the waves. Strong interference results in deep fading. Path loss generally causes poor performance of a communication system as it can lead to a loss in signal power without necessarily reducing the power of the noise. Path loss is associated with distortion and impairment of communication channels. Communication systems have been designed to cope with fading over time but fading can occur at a faster rate that the stipulated rate causing communication problems. Interference In telecommunication, interference is described anything that tampers with the transmitted waves in their path to the receiver. These interferences may alter, modify or disrupt the electromagnetic waves as they travel to the receiver. Generally, this term is used to denote addition on unwanted electromagnetic signals to the originally transmitted signals. Electromagnetic interference (EMI): this is a form of communication channel impairment that tampers with the electric circuit due to electromagnetic induction or radiation emissions from an outside source. This affects the communication channel; that is, it may lead to communication data degradation and data loss some instances. This form of impairment is commonly used in jamming radio and other communication systems. Adjacent interference: this a form and peripheral power source from an adjacent channel. It is also caused by insufficient filtering of unwanted frequencies or improper tuning. Broadcast regulators always filter the frequencies to avoid overlapping of waves between different radio stations. Crosstalk: this is a situation where a signal from one channel causes an undesired outcome in another channel. It is normally caused by unwanted inductive, capacitive or conductive coupling on one channel or circuit to another. In communication, is evident in leakage of speeches from other people. The effect of this channel impairment is reception of undesired messages on the system. Signal distortion: this refers to those impairments that widen the width I pulses leading to inter-symbol interferences (ISI). The ISI in turn limits the data rate of the system. L03.1: Q 3. Need for modulation and modulation schemes in analogue (a) Modulation is the way of varying various properties of a periodic wave referred to as a carrier wave which is a high frequency signal, using a modulating signal that normally contains information or data that is to be transmitted. In telecommunications, modulation is described as the process of relaying a message signal, for instance, an analog audio signal, in another signal which can be transmitted physically. Modulation of a sine waveform converts a baseband message signal into a pass-band signal. Radio waves contain sound. According to science, sound does not travel over long distances because it has low frequency. For the radio waves to reach distant places, it should be modulated to reach space satellites that amplify the waves and transmit them further. In radio wave transmission, the waves are modulated in two forms; that is, the Frequency Modulation (FM) and Amplitude Modulation (AM). (i) Frequency Modulation: in radio wave processing and telecommunication, Frequency modulation is used to refer to the encoding of data or information through a carrier wave by changing the instantaneous frequency of the wave. When it comes to analogue signal applications, the distinction between instantaneous frequency and base frequency of a carrier wave is directly proportional to the instant value of the amplitude of the input signal. Mathematically, FM is expressed as follows: Where:  is the amplitude   denotes the angular frequency of carrier signal.  represents the time. and fe is the linear frequency FM in the audio frequency range can generate very rich spectra from just two sinusoidal oscillators, and also the spectra can be evolved with time. Mathematically, FM expression is developed from its properties as a wave. (ii) Amplitude Modulation (AM): this is a commonly used form of modulation in transmitting radio carrier waves. It functions through variation of the amplitude (strength) of the carrier in proportion with the waves being transmitted. Mathematically, is expressed as follows: Vt = Vp sin (ωt ±θ0) Where: Vt is the voltage at any point in time, Vp is the peak voltage, Ωrepresents radians per second and θ0 represents the phase shift per second. (b) v = 5 (1 + 0.6 cos 6280 t) sin 211 × 104 t volts (i) minimum amplitude = = Ec – mEc = 5 − 0.6 × 5 = 2 V Maximum amplitude =Ec + mEc = 5 + 0.6 × 5 = 8 V (ii) frequency components fc-fs Fc fc + fs 335 336 337 Amplitudes of the three components are: Ec 1.5 V 5V 1.5 V L03.2: Q 4: Modulation methods in digital wave transmission (i) Amplitude-shift keying (ASK): this is a type of AM which is a representation of digital data changes in the carrier wave’s amplitude. In this type of system, the binary digit 1 is denoted by conveying a fixed frequency and amplitude for a bit period of T seconds. The signal is only transmitted when the signal value is 1. All digital signal modulations use a finite number for definite signal to represent digital data. The simplest type of ASK functions as a switch that uses the existence of a carrier wave to designate a binary one and its nonappearance to show a binary zero. This mode of modulation is termed as on-off keying, and is used with radio frequencies to transmit Morse code; which is called continuous wave operation. (ii) Frequency Shift Keying (FSK): this is one of the modulation schemes through which digital data can be transmitted through variation of frequency in the carrier wave. In the figure below, logic 1 is called the mark frequency whereas logic 0 is called the space frequency. This is the simplest form called the Binary FSK which uses discrete values 0 and 1to transmit binary information. (iii) Phase shift keying (PSK): this is yet another digital modulation scheme where information is transmitted by modulation of the Phase of the carrier signal. Digital data always have a finite number representing the information being sent. PSK employs finite number of phases with unique patterns of binary digits. Normally, every phase encodes a similar number of bits. Each of patterns of bits creates the symbol that is signified by the particular phase. The demodulator that is designed precisely for the symbol-set used by the modulatorgoverns the phase of the received signal and traces it back to the symbol it represents. Hence the original data is recovered.A receiver is required for comparing the part of the received signal to a signal in reference. This kind of system is called coherent. L03.3: Q 5: Digital modulation methods and typical applications The commonly used modulation methods include: Pulse Amplitude Modulation (PAM): this represents a type of signal modulation where the data is coded in amplitude of a sequence of signal pulses. This is an analogue pulse modulation scheme through which amplitudes of a pulse train are changed in accordance to the sample value of the message signal. Demodulation is done by identifying the amplitude level of the carrier in each symbol period. Pulse Width Modulation (PWM): Pulse duration modulation is a methodology used to control pulse width, which is typically the pulse duration using the modulator signal information. It allows control of power circulated in electrical systems. Pulse modulation systems denote a message-bearing signal using a train of pulses. Three types of PWM can be identified: a) The pulse center can be permanent at the center of the time window and both ends of pulse moved to expand or expand the width. b) The lead end may be held at the lead end of the window and the tail end modulated. c) The tail end may be static and the lead end modulated. The subsequent spectra from the above three cases are analogous. Each of them contains a dc component, a base sideband with the modulating signal and phase modulated carriers at every harmonic of the frequency of the pulse. Amplitudes of the harmonic sets are constrained by a sin x /x cover which is spread to infinity. Figure: Three types of PWM signals (blue): leading end modulation , trailing end modulation and centered pulses. The green lines are the saw tooth wave; in the first two cases and a triangle wave in the third case, used to produce the PWM wave based on the intersective method. In telecommunications, PWM represents signal modulation in which the widths of the pulses match to specific data values coded at one end and then decoded at the other end. Pulses of different lengths will be transmitted at consistent intervals. L03.4: Q 6: Multiplexing This is technique of transmitting many signals by combining them into one transmission circuit. The multiplexed signal is conveyed over a communication channel through a physical transmission medium for instance, a cable. The multiplexing splits the ability of the high-level communication channel into many low-level logical channels, one for every data stream to be conveyed. Multiplexing reduces the number of electrical connection in a communication channel. Multiplexing is an economic strategy employed where the users share communication resources. When sending five different signals using the Multiplexer, multiplexer assigns precisely equal time slot to every device at all times. For instance, Time slot A, is assigned to device A only and cannot be allocated to any other device. Then every time its allocated time slot pops up, a device has the chance to send a portion of its data.Whether a device has to transmit data or does not have data to convey, its time slot remains unoccupied. Wave forms in TDM L04.1 and L04.2:Q7 circuit switched network and a packet switched network (i) Circuit Switched Networks: they were designed to send telephone calls. During a call, this channel cannot be used until the end of the call. Messages are not broken, they arrive at their destination in the order they were sent. Information is passed through various switches before the call is connected. Once connected, no other device can use the switches (Leven). During operation, service is dedicated to one user at a time hence no sharing. With the use of this network, there is a guaranteed full bandwidth in the call duration. However, this network has been discredited for it takes long to set up the circuit. It is efficient in transmitting non voice data. (ii) Packet Switched Networks: In packet-based networks, the information to be sent is broken into small constituent data packets. These packets are then transmitted out from the device and they move around the system seeking the most appropriate and efficient route to follow. They do not have to follow the same route, they may split; with each of the data sets following its own route. Each of the packets has an assigned address and details of how many other packets were sent altogether. The recipient computer is able to determine how many packets should be received (Leven). If the recipient computer fails to receive all the sent packets, information is sent to the source computer asking for the missing packets. This type of network is designed for bursty data transmission and in voice data transmission. It is a secure method of transmitting data; if one packet is compromised, the others remain secure. The bandwidth is fully utilized when using this type of network.In case the network is overtasked, like when there is heavy traffic, there is likely to be delay. Data packets may also get corrupted before reaching the receiver device. Some of the packets may also be lost during transmission(Leven). The two circuits can be illustrated by the diagram below L04.3 Q8: mathematical formulae a) (i) Erlangs: this is a general purpose runtime system and programing language. It was designed to enable distribution, soft-real-time, fault-tolerant nonstop application. With this technology, you can hot swap for code changing without stopping systems. It is a unit denting traffic intensity (Leven). (ii) Grade of Service (GOS): this is the term used in telecommunication in determining the quality of service. It is used to show the probability that a call will be delayed or will be blocked; taking more time than the stipulated time. It is expressed as a fraction of a decimal. (iii) Busy Hour Traffic (BHT): this is described as the busiest 60 minutes of the day in communication channel. It is that one single hour where the most number of calls are recorded. It is represent as the average number of calls per hour in a day (Carr). b) Blocking rate 2% = 0.02 Earlings = 10 The number of lines required = 17 (c) Average calls per second= 650/1800 Ϡ = 0.36 Ts = 150 seconds M= 34 Traffic intensity u = 0.36*150 = 54 Agent occupancy, p = 54/34 = 1.59 Probability of waiting Ec (u,m) = 0.14 = 14 % Average speed of answer, Tw = average waiting time Ec (m,u). Ts /m.(1-p) = 4.6 seconds Level of service: percentage of calls will be answered within 20 seconds Wt = 1-e (m,u). e = 92.8% Work Cited Carr, Joseph J. The Technician's Radio Receiver Handbook: Wireless and Telecommunication Technology. Boston: Newnes, 2001. Internet resource Leven, Andrew A. Telecommunication Circuits and Technology. Oxford: Butterworth Heinemann, 2000. Internet resource. Read More