International Journal of Emerging Trends & Technology in Computer Science (IJETTCS) Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 3, Issue 2, March – April 2014 ISSN 2278-6856

Signal Attenuation in Powerline Communication Channel Dipashree Duche, Prof.Vidya Gogate Shah And Anchor Kutchhi Engineering College Mumbai University W.T. Patil Marg , Next to Dukes Co., Chembur, Mumbai, Maharashtra 400088, India.

Abstract: Power line communications (PLC) is a favorable technique for many smart grid applications. By transmitting information over the existing power line infrastructure, PLC has the benefit of low deployment cost. However, due to low transmit power, limited bandwidth, and harsh channel conditions, reliable long distance and high-capacity PLC is challenging. This paper presents the effect of network topology, multipath signal propagation, cluster index (transmission distance) and frequency on signal transmission capacity of power line network. Cable losses also attenuate the signal and thus reduce signal carrying capacity of power line network. Study of these parameters help to find out the losses in PLC network which later use to built the PLC model

Keywords: Powerline communication, network topology, cluster index, cable losses, attenuation.

1. INTRODUCTION The powerline network differs considerably in topology, structure, and physical properties from conventional media such as twisted pair, coaxial, or fiber-optic cables. Therefore PLC systems have to encounter rather hostile properties [2]. For computer simulations oriented to appropriate system design, models of the transfer characteristics of the mains network are of major interest. Only in the case of very simple topologies, such as a cable with a single branch, the physical reasons for the observed results (cable loss, reflection, and transmission factors) can be easily identified. In real network topologies—which are always more complicated—a backtracing of measurement results to physical reasons will generally turn out to be impossible. The proposed model will nevertheless describe the frequency response with sufficient precision. The parameters, however, cannot be directly derived from physical properties of the network. The smart grid (SG) uses two-way electricity and information flow to create a widely distributed and automated energy delivery network in order to meet the efficiency and reliability requirements of the modern society. Data communications is the key technology in SG for information exchange. In SG applications, the data communications needs to ensure reliability and broad coverage, guarantee security and privacy, and support quality of service (QoS) [1]. Among all communication architectures, power line communications (PLC) [2] utilizes the existing powerline infrastructure to transmit information alongside the electric power, and provide a solution with many advantages including cost-effectiveness effectiveness and broad coverage in the SG. The Volume 3, Issue 2 March – April 2014

communication can reach anywhere a powerline exists, especially places where radio signal cannot propagate through, e.g., underground, underwater, and rooms with metal walls. In recent years, several PLC-enabled applications have been deployed or proposed. The utility companies around the world have been using narrowband (NB) PLC (3–500 kHz) for automation and control applications. The broadband (BB) PLC systems which operate in the high frequency band (2–30 MHz) with data rates up to a few hundred Mbps have been advocated to provide Internet access for residential customers and facilitate local area networking within home/office [3]. PLC is believed to play a significant role in future SG [4]. However, as the powerline is originally designed for electrical energy delivery but not for communication purposes, direct-link communications over the powerline has limited capacity and transmission distance. the signal attenuation is severe for long distance and high frequency signal propagation, resulting in limited bandwidth .In terrestrial wireless environments, relay communications have been shown to enhance reliability and extend communication range . Thus relay-aided (RA-) PLC is an attractive option for long-range PLC.

2. POWER-LINE COMMUNICATION Communication using power line network cost effective solution as it utilizes the existing infrastructure. Today most of the powerline grids are smart grids and at high bandwidth (2-30 MHz) communication signal passes through the powerline helps to transfer data at faster rate. Various factors like network topology, multipath signal propagation, cable loss affects the channel capacity to carry the communication signal. Also parameters like frequency and signal transmission distance causes attenuation in signal.

3. FACTORS

AFFECTING COMMUNICATION

THE

POWERLINE

3.1 Topology of the Mains Network Opposite to the telephone copper loop, the powerline “local loop access network” does not consist of point-topoint connections between substations and customer’s premises, but represents a line bus. A typical access link between a substation and a customer consists of the distributor cable, or a series connection of distributor cables, and the branching house connection cables, both with real valued characteristic impedance ZL. The house service cable ends at a house connection box, followed by Page 123

International Journal of Emerging Trends & Technology in Computer Science (IJETTCS) Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 3, Issue 2, March – April 2014 ISSN 2278-6856 the indoor wiring, which can be modeled from the point of view of the access network by a complex termination impedance ZH (f) .The impedance of the house connection point is usually low due to numerous branching in-house cables. Moreover, ZH (f) appears very stationary, since the low impedance point hides impedance variations within the indoor network. Numerous reflections are caused by the joints of the house service cables, house connection boxes, and the joints at series connections of cables with different characteristic impedance.

Fig 2 the Cross-Section of a Four Conductor Power Cable, with three live connections (L1, L2 and L3) and one neutral connection (N). The scalar a represents the space between two adjacent conductors which is filled by PVC. Scalar is the radius from geometry centre to the outer edge of the conductor. Table 1: Cable Geometry Properties [5] Cable Properties NAYY150 (mm) a (Space between two conductor)

Figure 1 A Practical In-door PLC Topology In-door and wide area network uses T type topology of the PLC network. A randomly generated networks topology is used in the signal propagation behavior characteristics of a large number of real PLC network. Series arrangement of branches is connected to backbone cables. According to the impedance carry-back [11] method all the subbranches can be merged into the corresponding connected branch. Thus the PLC network can be considered equivalent to the topology shown in Fig. 1 which consists of backbone cables and first order branches. The components and configuration of the network topology are described as follows: In the typical network topology NAYY35 and NAYY150 types of cables are used for indoor power distribution, outlet-outlet and inter-junction connections respectively. The cables, outlet (circles) and junctions (rectangular) build a PLC network .The junctions can be a derivation box in practice. The outlets can be an open circuit power socket or a socket plugged with an appliance. Reflection signals occur at terminals with open sockets or mismatched appliances. Figure 2 [5] shows the structure of a power cable which is used in [2], Table 1 and Table 2 show the geometric parameters and the electromagnetic parameters of NAYY150 and NAYY35 cables. The insulator between conductors is PVC. When feeding signals into two adjacent conductors, most of the electric field is concentrated between these two conductors. The lumped parameters of the cable can be calculated by the geometric dimensions and material electrical properties.

Figure 2 Cable Structures Volume 3, Issue 2 March – April 2014

r (Scalar radius)

NAYY35 (mm)

1.8

1.2

6.909 9

5.9161

Table 2: Cable Electric Properties [5] 58 x 106 Conductivity of Copper k S/m Dissipation of PVC

0.025

Relative Permittivity of PVC

4

Free Space Permittivity

8.5419 x 10-12 F/m

Relative Permeability of Cooper

1

Free Space Permeability

1.2566 x 10-6 (H/m)

In power line networks, the branch density may vary from scenario. As an example scenario, ρ is set to 5 which indicate an average of 5 branches per 100 m of cable. . For each connection type, the Probability Density Function (PDF) of branch length is given as function of the side length of the cell in building. In this dissertation, the branch length is generated according the PDFs in [11] with a maximum side length of up to 20m. To approach a realistic scenario, half of the terminals are randomly set to open circuit. For the remaining sockets, the impedance is randomly allocated a discrete value between 5 ohms to 200 ohms with a 5 ohm interval. 3.2 Multipath Signal Propagation Signal propagation does not only take place along a direct line-of-sight path between transmitter and receiver, but additional paths (echoes) must also be considered. The result is a multipath scenario with frequency selective fading. Multipath signal propagation is studied by a simple example which can be easily analyzed (Fig. 3). The link has only one branch and consists of the segments (1), (2), and (3) with the lengths l1, l2 , l3 and and the characteristic impedances ZL1, ZL2, ZL3. Page 124

International Journal of Emerging Trends & Technology in Computer Science (IJETTCS) Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 3, Issue 2, March – April 2014 ISSN 2278-6856

Figure 3 Multipath Signal Propagation In order to simplify the considerations, A and C are assumed to be matched, which means ZA = ZL1 and ZC.= ZL2 The remaining points for reflections are B and D , with the reflection factors denoted as r1B,r3D,r3B , and the transmission factors denoted as , .With these assumptions, an infinite number of propagation paths is possible in principle, due to multiple reflections (i.e. ABC , . ABDBC, and so on). Each path has a weighting factor gi , representing the product of the reflection and transmission factors along the path. All reflection and transmission factors at powerlines are basically less or equal to one. This is due to the fact that transmission occurs only at joints, where the load of a parallel connection of two or more cables leads to resulting impedance being lower than the characteristic impedance of the feeding cable. Hence, the weighting factor gi a product of transmission and reflection factors is also less or equal to one, i.e. The more transitions and reflections occur along a path, the smaller the weighting factor gi will be. Furthermore, longer paths exhibit higher attenuation, so that they contribute less to the overall signal at the receiving point. Due to these facts, it is reasonable to approximate the basically infinite number of paths by only N dominant paths, and to make N as small as possible.

3.3 Transmission Line Theory At high frequencies, the wavelength is much smaller than the circuit size, resulting in different phases at different locations in the circuit. Quasi-static circuit theory cannot be applied. We need to use transmission line theory. A transmission line is a two-port network connecting a generator circuit at the sending end to a load at the receiving end. At high, dielectric loss is caused when the insulating material inside the transmission line absorb energy from a.c. electric field and convert it to heat [7] Unlike in circuit theory, the length of a transmission line is of utmost importance in transmission line analysis. Using KVL and KCL circuit theorems, we can derive the following differential equations for this section of transmission line.

By letting Δz→0, these lead to coupled equations:

Figure 4 Transmission Line in Power Circuit

The delay Ti of a path For sinusoidal varying voltages and currents, we can use phasor forms. can be calculated from the dielectric constant ɛr of the insulating material, the speed of light C0 , and the lengths di of the cables. The losses of cables cause an attenuation A(f, d),decreasing with length and frequency. The signal components of the individual paths have to be combined by superposition. Therefore, the frequency response from A to C can be expressed as

V(z) and I(z) are called phasors of v(z,t) and i(z,t). In terms of phasors, the coupled equations can be written as:

(2) Signal propagation in more complicated networks with more branches can be partitioned into appropriate paths in a similar way. Volume 3, Issue 2 March – April 2014

After decoupling,

Page 125

International Journal of Emerging Trends & Technology in Computer Science (IJETTCS) Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 3, Issue 2, March – April 2014 ISSN 2278-6856 of each segment in the above topology can be expressed by ABCD parameters which can be illustrated by the Two-Port network (2PN) in Fig. 6 [11]

Figure 6 ABCD Parameters The relations between the inputs and outputs of the 2PN in Fig. 6 can be formulated as: Figure 5 Circuit Layout is the complex propagation constant whose real part is the attenuation constant (Np/m) and whose imaginary part is the phase constant (rad/m).Generally, these quantities are functions of . For modeling purposes, any of the cable types described above is regarded as a twoconductor plus reference wire transmission line, with surrounding dielectric material of relative dielectric constant εr. Transmission line’s configuration specified above – parallel two-conductor plus reference wire cable, having solid conducting cores and being surrounded by the same dielectric material – gives the following distributed parameters: The lumped parameters such as capacitance (C), inductance (L), resistance (R) and conductance (G) per unit length can be calculated by applying the parameters.[7]

Where, Tf is called the transmission matrix. The definition of the ABCD parameters can be seen that A, B, C and D are functions of frequency. Then, the transfer function of this segment can be written as:

The transmission matrix of a shunt segment is:

Thus, the network above can be considered as a series of cascaded segments. After applying the Chain Rule (CR), the transmission matrix for the complete network can be calculated as:

The ABCD matrix for the transmission line with: Zc= characteristic impedance, γ =propagation constant and l =length can be calculated as,

3.4 Two Port Network and Transfer Function The power line model is considered as a black box described by transfer function, the method for modeling the transfer function of a power line channel uses the chain parameter matrices describing the relation between input and output voltage and current of two-port network. The voltage and current transfer characteristics Volume 3, Issue 2 March – April 2014

Where, Tif is the transmission matrix of the ith segment. Following the above steps are computed all the shunted segments. The Following Features of Indoor PLC Channel is based on the modeling result. Obvious frequency selective fading in the frequency domain and multipath signal propagation in the time domain. Frequency Selective fading: A coherence bandwidth of (it is a statistical measurement of the range of frequencies over which channel can be considered” flat”.) the channel is smaller than the bandwidth of the signal. • Higher attenuation at higher frequencies. Page 126

International Journal of Emerging Trends & Technology in Computer Science (IJETTCS) Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 3, Issue 2, March – April 2014 ISSN 2278-6856 • Attenuation increasing with the transmitter to receiver distance Above steps has been described channel transfer function for the frequency domain response in (1) is shown in Fig.7

real part of propagation constant and signal propagation distance. As propagation constant depends upon the frequency, cable losses are depends on frequency and propagation distance. [3] According to [3], the cable losses in the frequency domain of a powerline can be approximately written: [5]

as: a0 = (0.0002086*Dist) +0.0008739; a1 = (0.00002644*Dist) +0.00004644; k = (-0.00009098*Dist)-0.000001126; b0 = (-0.0006432*Dist)-0.000001126;

Figure 7 Transfer function of channel against frequency Above fig.7 indicating the effect of channel frequencies in MHZ versus magnitude (db) of different impedances .At low frequency, magnitude is maximum & high frequency Magnitude is low.There should be infinitely many paths in a single channel impulse response. In order to extract the path features, herein only paths with a magnitude which is larger than a certain threshold (20dB below the maximum peak Magnitude) is consider for analysis. [7]

i) ii) iii) iv) [5]

Where, a0, a1, k- the attenuation factor. a0, a1, b0 are linear functions of path propagation d for a given cable, (from equation i),ii),iii),iv)) Dist=d= path propagation distance. F=Frequency in MHZ and can be calculated by the cable parameters.

3.5 Cable Losses In Power line communication, cable has important role of carrying the signal from source to destination. The propagating signals are affected by attenuation increasing with length and frequency This cause loss in signal which is of main three types1. Resistive Loss 2. Dielectric Loss 3. Radiated Loss In power line power dissipated due to conductor and insulator properties of cable is called as cable losses. Resistive loss produces due to skin effect of conductor. It increases with increase in frequency. Dielectric loss which causes by voltage difference across the dielectric part of cable Radiated loss which are negligible .Cable parameters R,L,G,C can be roughly estimated by the geometric dimensions and some material properties which influences the losses. From equation (2) The Conductance per unit length G’ is mainly influenced by the dissipation factor of the dielectric material (usually PVC) and proportional to frequency. Where R’