Policies for Carbon Energy Footprint Reduction of Overhead Multiple-Input Multiple-Output High Voltage Broadband over Power Lines Networks

Transcription

1 Peer-Reviewed Article Trends in Renewable Energy OPEN ACCESS ISSN: futureenergysp.co/index.php/tre Policies for Carbon Energy Footprint Reduction of Overhead Multiple-Input Multiple-Output High Voltage Broadband over Power Lines Networks Athanasios G. Lazaropoulos * School of Electrical and Coputer Engineering, National Technical University of Athens (NTUA), 9 Iroon Polytechniou Street, Zografou, Athens, Greece Received April 11, 2015; Accepted May 12, 2015; Published May 15, 2015 The ipact of different environental policies on the broadband perforance of overhead ultiple-input ultiple-output high-voltage/broadband over power lines (MIMO/HV/BPL) networks is investigated in this paper. The exained environental policies focus on the carbon energy footprint reduction of overhead MIMO/HV/BPL networks while respecting their broadband character. The contribution of this paper is three-fold. First, the spectral and environental perforance of various configurations and topologies of overhead MIMO/HV/BPL networks is assessed with regard to respective spectral efficient (SE) and newly presented environental efficient (EE) etrics. Second, further insights regarding the perforance of overhead MIMO/HV/BPL networks highlight the better spectral and environental perforance of these networks against other today s overhead HV/BPL networks, such as single-input single-output (SISO), single-input ultiple-output (SIMO), or ultiple-input single-output (MISO) ones. Third, the definition of appropriate environental policies that optiize the coexistence of the three ain sectors of concern, which are the Quality of Service (QoS) requireents, protection of existing radioservices and prootion of environentally aware liits, is prooted. Towards that direction, the proposed SE/EE trade-off relation of this paper is expected to prove an extreely helpful SE/EE optiization technique. Keywords: Broadband over Power Lines (BPL) odeling; odal analysis; Power Line Counications (PLC); overhead High-Voltage (HV) power lines; capacity; green technology I. Introduction The deployent of broadband over power lines (BPL) networks across the entire transission and distribution grid i.e., high-voltage (HV), ediu-voltage (MV) and low-voltage (LV) grids ay critically facilitate the role of sensing, counications and control across the existing power grid [1]-[4]. On the basis of the odernization of today s power grid towards a sart power network with state-of-the-art counications capabilities, a plethora of potential sart grid (SG) applications, such as grid onitoring, protection and autoatic optiization of operations related to network interconnected eleents, can be available [5]-[11]. Until now, significant efforts have been ade to exploit the broadband potential of HV/BPL, MV/BPL and LV/BPL networks [12]-[30]. Apart fro the fervent interest towards the adoption of BPL technology in future s SG installations, new interest arises due to the recent developents regarding ultiple-input ultiple-output (MIMO) *Corresponding author: AGLazaropoulos@gail.co 87 Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

2 transission technology for BPL networks and the interoperability of the BPL technology with other already established broadband technologies intended to be installed in upcoing SG installations [31]-[33]. Since today's single-input single-output (SISO) HV/BPL systes lack of providing adequate transission rates so as to cover future SG application requireents in a trustworthy way, the deployent of MIMO configuration schees in overhead HV/BPL networks, which is firstly presented in [14], [32], [34]-[41], is iinent. Nevertheless, a ajor disadvantage of overhead HV/BPL systes either SISO or single-input ultiple-output (SIMO) or ultiple-input single-output (MISO) or MIMO schee configurations is their high energy consuption with regards to their spectral perforance. At the sae tie, carbon energy footprint reduction in inforation and counications technology (ICT) becoes a growing concern for providers in order not only to reduce their environental effect [42] but also to enhance their profitability [7], [43], [44]. Actually, the strong interest of teleco and energy regulatory authorities towards the reduction of ICT carbon energy footprint including carbon and energy use ebodied in the ICT infrastructure encourages technological innovations so that environental efficient (EE) iproveents can be achieved without significantly affecting the quality of service (QoS) [7], [45]-[52]. In fact, a possible reduction of energy consuption through appropriate techniques ay also entail the carbon energy footprint reduction. To define an environental high-bitrate MIMO/HV/BPL network design, the coexistence of injected power spectral density ask (IPSDM) liits, which assure electroagnetic interference (EMI) protection to priary wireless services that operate at the sae frequency bands with BPL systes [17], [19], with environental policies, which regulate carbon energy footprint and the energy consuption of MIMO/HV/BPL systes, needs to be exained in this paper. On the basis of [7], a odification to the fixed IPSDM liits through the insertion of an appropriate green factor is proposed so that the three ain sectors of concern, which are the Quality of Service (QoS) requireents, protection of the existing radioservices and prootion of environentally aware liits, can be coproised. To assess the spectral and environental perforance of overhead HV/BPL networks, the well-established hybrid ethod that is usually eployed to exaine the behavior of BPL transission channels installed on HV ulticonductor transission line (MTL) structures is also used in this paper. The hybrid ethod is based on: (i) a botto-up approach consisting of an appropriate cobination of the siilarity transforation and MTL theory [12], [16], [21]-[23], [31], [53]-[63]; and (ii) a top-down approach consisting of the exact version of ultidiensional chain scattering atrix ethod [5]-[7], [16]-[23], [53], [58], [59]. Through the botto-up approach, the odes that ay be supported by an overhead HV/BPL configuration are deterined concerning their propagation constants and their characteristic ipedances whereas, through the top-down approach, the end-to-end attenuation of overhead HV/BPL channels is defined. With reference to the nuerical results of the aforeentioned hybrid ethod, the perforance of overhead MIMO/HV/BPL networks is assessed using appropriate transission, spectral efficient (SE) and EE etrics [5], [16]-[20], [41], [52], [64]-[68]. Extending the energy efficient etrics of [7] to the EE etrics of this paper, the proposed trade-offs between spectral and environental perforance highlight a novel wiser coproise aong throughput perforance, EMI regulations and environental awareness. Further insights, such as how to iprove the occurred trade-off curves Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

3 through proper environental policies and how to tune the operation points of overhead MIMO/HV/BPL networks at the trade-off curves to balance the aforeentioned coproise, are expected to influence the practical syste design of future s overhead MIMO/HV/BPL networks [42], [45], [66]. Moreover, the strategic turn of countries towards cleaner energy sources is studied through the lens of the proposed trade-off curves. Consequently, this paper introduces a ultidisciplinary approach towards a greener sustainable developent of overhead MIMO/HV/BPL networks by appropriately cobining a wide range of research areas, such as counications and electrical engineering, econoic anageent and environental planning. The rest of the paper is organized as follows: In Section II, the overhead HV configuration adopted in this paper is deonstrated. Section III highlights the ain features of MIMO/HV/BPL transission that are MTL theory, eigenvalue decoposition (EVD), singular value decoposition (SVD) odal analyses and hybrid ethod. Section IV ephasizes to the electroagnetic copatibility (EMC) of overhead HV/BPL systes with other already licensed radioservices, the proposed green odification of existing IPSDM liits, the HV/BPL syste power consuption and carbon energy footprint. Section V provides a description of the transission, SE and EE etrics applied in this paper for the MIMO/HV/BPL network analysis. In Section VI, nuerical results and conclusions are presented, aiing at arking out how the various EMI regulations, EE policies and MIMO schee configurations influence overhead MIMO/HV/BPL transission, SE and EE etrics. On the basis of the proposed SE/EE trade-off curves, appropriate EE high-bitrate policies are proposed. Section VII concludes the paper. II. Overhead HV Transission Power Networks The overhead HV power grid differs considerably fro transission via twisted-pair, coaxial, or fiber-optic cables due to the significant differences of the network structure and the physical properties of the power transission cables used [5], [6], [16], [18], [22], [23], [25], [54], [69]-[75]. Overhead 400kV double-circuit overhead HV transission phase lines with kv radii r 400 kv =15.3 hang at typical heights h 400 equal to 20 above ground p i.e., conductors 1, 2, 3, 4, 5, and 6. These six phase conductors are divided into three bundles; the phase conductors of each bundle are connected by non-conducting spacers 400kV 400kV and are separated by equal to 400, whereas bundles are spaced by equal p1 to 10. Moreover, two parallel neutral conductors with radii equal to 12 hang at heights 400kV n p kv r 400 n =9 spaced by kv h 400 n equal to 23.7 i.e., conductors 7 and kV This double-circuit eight-conductor ( n 8 ) overhead HV distribution line configuration is considered in the present work consisting of ACSR conductors see Fig. 1 [5], [6], [23], [73]-[80]. p2 Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

4 Figure 1. Typical overhead 400kV double-circuit HV ulticonductor structures [1], [76]-[80]. The ground is considered as the reference conductor. The conductivity of the ground is assued g =5S/ and its relative perittivity rg =13, which is a realistic scenario [5], [6], [16], [17], [23], [54], [72]. The ipact of iperfect ground on signal propagation via overhead power lines was analyzed in [16], [17], [54], [72], [81]-[84]. Contrary to other available odels for overhead power lines [85]-[88], this forulation is suitable for transission at high frequencies [5], [6], [7], [16]-[20], [23]. III. An Overview of the Modal Analysis of Overhead MIMO/HV/BPL Systes Through a atrix approach, the standard TL analysis can be extended to the MTL case which involves ore than two conductors. Copared to a two-conductor line supporting one forward- and one backward-traveling wave, an MTL structure with eight plus one conductors parallel to the z axis as depicted in Fig. 1 ay support eight pairs of forward- and backward-traveling waves with corresponding propagation constants. These waves ay be described by a coupled set of sixteen first-order partial V i z, t, i 1,, 8 to the line currents differential equations relating the line voltages Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

5 I i z, t, i 1,, 8. Each pair of forward- and backward-traveling waves is referred to as a ode [5]-[7], [16]-[23], [60], [61]. Consequently, in the case of overhead HV transission lines involving eight conductors over lossy plane ground, eight odes ay be supported, naely: Coon ode of overhead BPL transission (CM) with propagation constant. Its spectral behavior is thoroughly investigated in [1], [5], [6]. CM 1 Differential odes of overhead BPL transission ( DM, i 1,, 7 ) with i corresponding propagation constants DM, i 1,, 7. Their spectral i i1 behavior is thoroughly investigated in [1], [5], [6]. The EVD odal voltages z V1 z V8 z currents z I T 1 z I8 z V z V z V and z I z I Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre V and the EVD odal I ay be related to the respective line quantities transforations T 1 8 z V I T T 1 8 z I via the siilarity z z z z T V V (1) T I I (2) where T denotes the transpose of a atrix, T and T V I are 8 8 atrices depending on the overhead power grid type, the frequency, the physical properties of the cables and the geoetry of the MTL configuration [1], [5], [6], [16], [18], [23], [53], [60], [61], [76]-[95]. On the basis of eqs (1) and (2), the line voltages and currents are expressed as appropriate superpositions of the respective EVD odal quantities, naely: 1 0 T V0 V V (3) The TM2 ethod, which is odule of the top-down approach of the hybrid ethod, is based on the scattering atrix theory and is presented analytically in V i z, 1,, 8 V 0, j 1,, 8 [7], odels the spectral relationship between i and j proposing operators H i, j, i, j 1,, 8 so that V H V 0 where H is the 8 H i, j, i, j 1,, 8 with j while those H, i, j 1,, 8 with j z (4) 8 EVD odal transfer function atrix whose eleents i are the EVD odal co-channel (CC) transfer functions, i, j i are the EVD odal cross-channel (XC) transfer functions and H denotes the eleent of atrix H in row i of colun j i, j [5]-[7], [16]-[23], [55], [91]. Cobining eqs. (1) and (4), the 8 8 transfer function atrix H of overhead HV/BPL transission network relating V z with V 0 through Vz HV 0 (5) is deterined fro T H T 1 H V V (6) Since in overhead MIMO/HV/BPL networks, the nuber of active transit ports n ay vary fro one to eight, through a siilar atrix expression n T and receive ports R

6 to eq. (6), n, in T n R parallel and independent SISO/HV/BPL channels ay occur, appropriately decoposing channel transfer function atrix H using the SVD transforation [32], [35]-[37], [39], [96], [97]: ~ ~ H ~ H TV H T I (7) where H ij, if i nt and j n R H ij i, j 1,,8 (8) 0,otherwise denotes the eleent of atrix H in row i of colun j. Fro eqs. (7) and (8), ij atrix operator whose eleents H ~ i, i 1,,in n T, n R H and, at the sae tie, the SVD odal transfer functions, x, y H is the 8 8 extended channel transfer function atrix whose eleents H, i, j 1,, 8 are the extended channel transfer functions, H ~ is a diagonal sallest value between x and y, n T and are the singular values of in returns the n R are the active transit port and the active receive port sets, respectively, H denotes the Heritian conjugate of a atrix, and T ~ V and T ~ I are 8 8 unitary atrices [36], [39], [98]. Cobining eqs. (6)-(8), SVD odal transfer function atrix function atrix H. H ~ ay be deterined given EVD odal transfer IV. Brief Description of Overhead MIMO/HV/BPL Channels A. Power Constraints due to EMI and Environental Constraints A critical issue related to the operation of overhead MIMO/HV/BPL networks has to do with the power constraints (i.e., IPSDM liits) that should be iposed in order to ensure their successful coexistence with other already existing wireless and telecounication services at the sae frequency band of operation [17], [19], [26], [99]. Aong regulatory bodies that have established proposals concerning the safe EMI BPL operation, the ost iportant are those of FCC Part 15, Geran Reg TP NB30, the Norwegian Proposal and the BBC/NATO Proposal [71], [100]-[102]. Especially, the IPSDM liits proposed by Ofco for copliance with FCC Part 15 that are presented in [71], [100]-[102] are the ost cited due to their proneness towards the deployent of high-bitrate BPL networks. More specifically, for overhead HV/BPL networks, according to Ofco, in the MHz frequency range, axiu levels 60 db/hz constitute appropriate IPSDM liits p f providing presuption of copliance with the current FCC Part 15 liits [17], [19], [103], [104]. To extend the capacity analysis in the 30-88MHz range, axiu IPSDM liits p f that are equal to 77dB/Hz for overhead HV/BPL networks are assued to provide a presuption of copliance in this frequency range [17], [19], [103], [104]. Note that as it regards the above power constraints of overhead MIMO/HV/BPL schee configurations, to extend the analysis in the MHz range, coon IPSDM liits p f between HV/BPL and MV/BPL systes have been assued exploiting the significant siilarities regarding overhead HV/BPL and MV/BPL transission without Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

7 haring the generality of the following MIMO analysis [17], [19], [54], [72], [103]-[105]. Different IPSDM liits ay provide to the authorities the necessary alternative options in protecting services and, at the sae tie, peritting energy efficient high-bitrate MIMO/HV/BPL syste operation. In accordance with [7], power spectral regulation through the insertion of a suitable green ultiplicative factor 1 f to the existing IPSDM liits (in db/hz) ay offer significant flexibility options; since existing IPSDM liits receive negative values, new IPSDM liits p f p f 1 f can assure both BPL copatibility with other wireless services and the required energy efficiency. Note that the green factor f that ay be defined by both regulatory bodies and network operators can take only positive values in order to aintain the necessary EMC of overhead HV/BPL networks. The factors that deterine the iposed green factor depend on the required degree of energy consuption (carbon energy footprint saving), the local traffic, the type of services delivered and QoS threshold criterion iposed. Since lower energy consuption iplies higher carbon energy footprint savings, the higher the value of the green factor f, the higher the influence of EE policies is. In contrast, when the green factor is equal to 0, no concern for EE policies is taken. Without affecting the generality of the following analysis, only the class of continuous EE policies will be taken into consideration; this class contains all the EE policies where a constant value of green factor f across the entire MHz frequency range is assued [7]. B. Noise Characteristics According to [17], [19], [25], [54], [72], [106], [107], two types of noise are doinant in overhead HV/BPL channels: Colored background noise: This type of noise is doinant in BPL channels. It is the environental noise that depends on weather conditions, huidity, geographical location, height of cables above the ground, etc. Corona discharge is a ajor source of colored background noise, especially under huid and severe weather conditions [54], [72], [82], [101], [108], [109]. Narrowband noise: This type of noise is the result of the narrowband interferences fro other wireless services operating at the sae frequency bands with overhead HV/BPL networks. This kind of noise exhibits local variations and is tie-dependent [17], [19], [72], [108], [109]. As it regards the noise properties of overhead MIMO/HV/BPL schee configurations, to extend this analysis in the MHz range, unifor additive white Gaussian noise (AWGN) PSD level N f will be assued [17], [19], [54], [72], [103]-[105], [110]. In detail, to evaluate the capacity of overhead MIMO/HV/BPL systes, a unifor AWGN/PSD level is assued equal to 105dB/Hz [17], [19], [54], [72]. The noise AWGN/PSD of each power grid type is assued coon to all MIMO channels of the MTL configuration. Note that as it regards the above noise features of overhead MIMO/HV/BPL schee configurations, to extend the analysis in the MHz frequency range, coon AWGN PSD level N f between HV/BPL and MV/BPL systes has been assued exploiting the significant siilarities regarding Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

8 overhead HV/BPL and MV/BPL transission without haring the generality of MIMO analysis. C. Power Consuption According to [66], [111]-[114], two types of power consuption occur in overhead MIMO/HV/BPL systes, naely: Power Consuption due to Power Aplifiers. Power aplifiers are the ain power consuption blocks in any advanced counication syste due to their needed high RF power aplifier efficiency. This class of power consuption depends ainly on the iposed EE policy [66], [112]. Power Consuption due to all other Circuit Blocks. Apart fro power aplifiers, overhead MIMO/HV/BPL systes consist of the Digital-to-Analog Converter (DAC), the ixer, the active filters at the transitting end, the frequency synthesizer, the low-noise aplifier (LNA), the interediate frequency aplifier (IFA), the active filters at the receiver side and the Analog-to-Digital Converter (ADC). This type of power consuption is related to all these circuit blocks and depends on the nuber of active transit and receive ports of MIMO/HV/BPL systes [66], [112]. The total average power consuption P tot of overhead MIMO/HV/BPL systes is given by the su of the aforeentioned two types of power consuption. Based on the related circuit and syste paraeters, which are detailed in [66], [111]-[114], an approxiation of the actual MIMO/HV/BPL syste power consuption is coputed. D. Carbon Eissions The carbon energy footprint of an overhead MIMO/HV/BPL network depends on its power consuption and on the origin of the electricity production [115]. A etric of carbon energy footprint, which is subject to each country s energy sources, is given by converting power consuption into gr of CO2 per each kwh of energy consuption. For anthracite electricity production and gas electricity production of this paper, the carbon energy footprint of an overhead MIMO/HV/BPL syste is coputed according to CO K P X (9) CO2 where K is expressed in tons of CO2 per year and X is the conversion etric that is equal to 870grCO2/kWh and 360grCO2/kWh for anthracite electricity production and gas electricity production, respectively [115], [116]. tot V. SE and EE Metrics of Overhead MIMO/HV/BPL Networks To assess the spectral and environental perforance of overhead MIMO/HV/BPL networks, respective SE and EE etrics are used. SE etrics describe how efficiently BPL networks exploit their allocated frequency band whereas EE etrics correspond each bit per second (bps) to a carbon energy footprint. In this Section, several useful SE and EE etrics are introduced in order to exaine the properties of the overhead MIMO/HV/BPL networks, naely: a. Capacity. Capacity is the axiu achievable transission rate in bps over a BPL channel and depends on the applied configuration of MIMO/HV/BPL Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

9 network, the syste features, the iposed EE policy and the noise characteristics. In this paper, capacity is the considered QoS criterion. More specifically, the capacity of the SISO/HV/BPL syste fro transit port j to receive port i is given by [7], [17], [19] where K 1 s q0 SISO 2 C ij f log 2 1 SNR qfs H ij, q, i, j 1,, 8 (10) f 1 f p f N f L SNR / (11) is the BPL signal-to-noise ratio (SNR), is an operator that converts db/hz L into a linear power ratio (W/Hz), K is the nuber of subchannels in the BPL f signal frequency range of interest and s is the flat-fading subchannel frequency spacing [17], [19], [99]. As it concerns the characterization of overhead SISO/HV/BPL systes, the eleents L C, i, j 1,, 8 with i j and i j characterize SISO/CC HV/BPL and SISO/XC HV/BPL syste capacities, respectively. Siilarly, the capacity of the 1 n R SIMO HV/BPL systes fro the transit port j with n R receive ports ranging fro two to eight is given by K 1 SIMO 2 C j f slog 2 1 SNRqfs H ij qfs (12) q0 in R In the case of n T 1 MISO HV/BPL syste, the capacity to the receiving port i with n T transit ports ranging fro two to eight is given by [7], [64], [117] K 1 MISO SNR qf 2 s Ci f slog 2 1 H ij qfs (13) q0 nt jn T Finally, in the general case of nt nr MIMO/HV/BPL systes with n T and n R ranging both fro two to eight, the capacity is deterined by [7], [32], [36], [37], [39], [40], [64], [117] K 1 inn R, nt 2 MIMO SNR qfs ~ C f s log2 1 H i qfs (14) q 0 i 1 nt Note that both eqs. (13) and (14) are based on equal power uncorrelated sources as the coon case is adopted where the transitting end does not have channel state inforation (CSI). According to the different SISO, SIMO, MISO and MIMO schee configurations, the resulting single- and ulti-port diversities ay be classified into two ajor classes: Pure Schee Configuration Class. This class contains the eleentary single- and ulti-port ipleentations, naely: 8 8 MIMO, 1 8 SIMO, 8 1 MISO, and all SISO systes either SISO/CCs or SISO/XCs. Mixed Schee Configuration Class. This class contains all the other ulti-port ipleentations that ay be deployed, naely: n MIMO systes with 1 n, n 8. T n R T SISO ij R Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

10 b. The EE capacity. It denotes the axiu achievable transission rate of Mbps that the syste can deliver per ugr of CO2 eitted fro it. This EE capacity etric is obtained as the ratio of the capacity to the carbon energy footprint for given EE policy, circuit/syste paraeters and country s energy sources for electricity production. This EE capacity etric provides a acroscopic qualitative estiate of the role of EE policies and syste power consuption during BPL syste operation. VI. Nuerical Results and Discussion The siulation results of various configurations of overhead MIMO/HV/BPL networks ai at investigating: (a) their broadband perforance; (b) how the applied SE and EE capacity etrics are influenced by the ipleentation of various MIMO/HV/BPL schee configurations; and (c) the occurred SE/EE dynaic equilibria due to the different EE policies. As entioned in Section III, since the odes supported by the overhead HV/BPL configurations ay be exained separately, it is assued for siplicity that the BPL signal is injected directly into the EVD odes [5]-[7], [16]-[23], [53]-[56], [58]-[62], [72], [117]. For the nuerical coputations, the 400kV double-circuit overhead HV transission line configuration, depicted in Fig. 1, has been considered. The siple overhead topology of Fig. 2(a), having N branches, has been assued. In order to siplify the following analysis without affecting its generality, the branching cables are assued identical to the transission cables and the interconnections between the transission and branch conductors are fully activated. With reference to Fig. 2(b), the transitting and the receiving ends are assued atched to the characteristic ipedance of the odal channels supported, whereas the branch terinations Z bk, k 1,2,, N are assued open circuit [5]-[8], [16]-[19], [54], [76]-[79], [92]. With reference to Fig. 2(b), four indicative overhead HV topologies concerning end-to-end connections of average lengths equal to 25k are exained. These topologies are [5]-[8], [22]-[24], [69], [73], [74], [76]-[79], [92], [118]-[120]: (1) A typical urban topology (urban case) with N=3 branches (L1=1.15k, L2=12.125k, L3=8.425k, L4=3.3k, Lb1=27.6k, Lb2=17.2k, Lb3=33.1k). (2) A typical suburban topology (suburban case) with N=2 branches (L1=9.025k, L2=12.75k, L3=3.225k, Lb1=46.8k, Lb2=13.4 k). (3) A typical rural topology (rural case) with only N=1 branch (L1=3.75k, L2=21.25k, Lb1=21.1k). (4) The LOS transission along the average end-to-end distance L=L1+ +LN+1=25k when no branches are encountered. This topology corresponds to Line-of-Sight transission in wireless channels. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

11 Figure 2. (a) End-to-end overhead HV/BPL connection with N branches. (b) An indicative HV/BPL topology considered as a cascade of N+1 odules corresponding to N branches [5]-[7], [16], [17], [19]-[23]. As it concerns the MIMO transission schee assuptions, in the coon case, the transitter does not have CSI as it has already entioned whereas the channel is perfectly known to the receiver (i.e., channel knowledge at the receiver can be aintained via training and tracking). The flat-fading subchannel frequency spacing is assued equal to f s 10 khz. The proposed MIMO/HV/BPL syste analysis, which is outlined in Section III, is used in the rest of this paper. As it has already been entioned in Section IV, to evaluate the capacity of overhead MIMO/HV/BPL networks, a unifor AWGN PSD level is assued equal to 105dB/Hz [17], [19], [54], [72]. As it concerns the power consuption of overhead MIMO/HV/BPL systes, the related circuit and syste paraeters are detailed in [66], [111]-[114] providing a satisfactory approxiation towards the actual HV/BPL syste power consuption. A. Effect of HV Grid Topology and MIMO Schee Configuration on Overhead MIMO/HV/BPL Capacity Perforance The spectral perforance in ters of capacity in the 3-88MHz frequency band is evaluated based on the application of FCC Part 15 under the assuption of Ofco/IPSDM liits when different overhead HV/BPL network configurations occur. In this subsection, it is assued that only the highest values (upper bound) of capacity of each MIMO/HV/BPL configuration of the sae class for each of the aforeentioned indicative overhead HV/BPL topologies are going to be presented. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

12 In Figs. 3(a)-(d), the capacity of the overhead MIMO networks for the aforeentioned indicative overhead topologies is plotted with respect to the active transit and receive ports of different MIMO schee configurations. Moreover, the relative capacity gain concerning each MIMO schee configuration in relation with the corresponding SISO one for the aforeentioned indicative overhead topologies is also deonstrated. Fro Figs. 3(a)-(d), it is observed that: The high IPSDM liits of FCC Part 15, cobined with the relatively low end-to-end channel attenuation and the low noise characteristics of overhead MIMO/HV/BPL networks, reveal their significant broadband potential. Regardless of the high average end-to-end transission distances occurred in overhead HV grids, capacity and relative capacity gain aintain sufficient high values for all the future s SG applications. Observing capacity and relative capacity gain results, SIMO/HV/BPL networks present better results than the corresponding ones of MISO/HV/BPL networks regardless of the topology and the MIMO configuration schee. This is due to the fact that, in the SIMO cases, all the transitted power is concentrated at one transit port and collected fro ultiple receive ports whereas, in the MISO cases without CSI, the transitted power is equally allocated aong the available transit ports and collected fro one receive port [121]. Due to the coon bus-bar syste topology [7], [40], [122], in overhead BPL networks, end-to-end channel attenuation curves between CCs and XCs present siilarities indicating the strong coupling aong the individual MIMO channels. However, the XC channels present significantly higher end-to-end channel attenuation than CC ones regardless of the network topology [35], [37], [50]. The increase of the available transit ports in MISO systes entails higher influence of XC channels in the occurred capacity results and, consequently, lower capacity results in coparison with the upper bound of SISO systes. When the nuber of transit n T and receive n R ports increases, the capacity differences aong nt nr and nr nt MIMO networks tend to be itigated. MIMO configuration schees provide draatic iproveent in the capacity results rendering their installation preferable in coparison with the other available SISO, SIMO and MISO alternatives. Due to their siilar capacity behavior, only one overhead HV topology, say LOS case, will be exained hereafter. B. Ipact of EE Policies on SE and EE Metrics Until now, MIMO/BPL research has ainly focused on deterining the optiu nuber of transit and receive ports, which succeeds the best coproise aong syste coplexity, capacity and syste availability [35], [123]-[125]. However, the recent growing counications concern is not only to axiize the spectral efficiency Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

13 Figure 3. Capacity and relative capacity gain of overhead MIMO/HV/BPL networks for the four indicative topologies (IPSDM liits of the FCC Part 15 liits are applied and the subchannel frequency spacing is equal to 10kHz). (a) Urban case. (b) Suburban case. (c) Rural case. (d) LOS case. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

14 of networks and systes but also to increase profitability through energy consuption savings while protecting the environent [42]. Towards that direction, different MIMO/HV/BPL networks arrangeents are investigated in this paper when different EE policies are adopted. In the rest of this paper, it is assued that only the axiu values of all possible SIMO, MISO and MIMO syste capacities will be studied in the 3-88MHz frequency band. As it has already been analyzed in Fig. 3(d), the capacity and relative capacity gain of overhead MIMO/HV/BPL LOS case have been plotted for various MIMO schee configurations when FCC Part 15 is applied. These results define the optiu capacity case when no environental concern is taken into account (EE1 policy). Apart fro EE1 policy, other five indicative EE policies given in Table 1 have been applied in order to exaine how their application affect the SE and EE etrics of this paper (i.e., capacity, carbon energy footprint and EE capacity). Note that as the nuber x of EEx policy increases so does the environental awareness. In Table 1, green factor Φ of each EE policy is also reported. To exaine the ipact of EE policies on spectral perforance of overhead MIMO/HV/BPL networks, in Figs. 4(a)-(g), the capacity and the relative capacity gain of overhead MIMO/HV/BPL networks for the LOS case are plotted with respect to the active transit and receive ports of different MIMO schee configurations when the six indicative EE policies of Table 1 are applied, respectively. The influence of EE policies on the EE perforance of overhead MIMO/HV/BPL networks is exained in Figs. 5(a)-(g) where the corresponding carbon energy footprint is plotted for the above six indicative EE policies, respectively. The interaction between SE and EE etrics can be exained through the use of suitable cobined SE/EE etrics such as EE capacity. In Figs. 6(a)-(g), the corresponding EE capacity and relative EE capacity gain are given for the above six indicative EE policies, respectively. Note that as it regards the carbon eissions of overhead MIMO/HV/BPL schee configurations, in Figs. 5(a)-(f) and 6(a)-(f), only anthracite electricity production is assued. Fro Figs. 4(a)-(f), 5(a)-(f) and 6(a)-(f), several interesting conclusions ay be drawn as follows. Capacity and carbon energy footprint of overhead MIMO/HV/BPL networks are very sensitive to IPSDM liit changes as these are iposed by the applied EE policy [17], [19]. However, the strategic choice of the countries to achieve significant carbon eission reductions pushes towards the adoption of EE policies that can diinish the broadband perspectives of overhead MIMO/HV/BPL networks. On the other hand, EE policies that are not environentally oriented lead to waste of energy since the capacity iproveent becoes arginal above a capacity threshold. Therefore, ecologically aware EE policies should be prooted that can lead to energy savings and reduction of carbon eissions while their corresponding capacity results ay be carefully adjusted so as to satisfy certain capacity requireents. In fact, it can be seen that by reducing the IPSDM liits by 5% see EE2 in Table 1 and in Figs. 4(a) and 4(b), the capacity reduction of overhead MIMO/HV/BPL networks Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

15 Table 1. EE Policies Used EE Policy EE1 EE2 EE3 EE4 EE5 EE6 (type) Green factor Φ is ranging fro 14.05% to 21.45% while carbon eissions decrease and EE capacity increase are ranging fro 44.85%-48.99% and 42.44%-64.59%, respectively. Siilar results for the other EE policies reveal the iportance of the selection of proper IPSDM liits, capacity threshold and carbon eissions reduction goal. Carbon eissions depend drastically on the IPSDM liits that are iposed by the applied EE policy as well as the applied MIMO configuration schee. The traditional belief that MIMO networks are always ore energy-efficient and, subsequently, ore environentally friendly in coparison with SISO, MISO and SIMO ones ay be isleading when the carbon eissions of overhead MIMO/HV/BPL networks are considered [64], [66], [111], [112]. More specifically, depending on the MIMO configuration schee, applied EE policy, and SE and EE thresholds iposed, various trade-offs aong SE and EE etrics ay occur, naely: (i) in approxiately 85% of the cases exained, given the nuber of transit n T and receive n R ports, overhead nt nr MIMO/HV/BPL networks with nt nr present better EE capacity values in coparison with other equivalent pure and ixed configurations, i.e. i j MIMO networks with 1 i nt, 1 j nr ; and (ii) Siilarly to capacity results, in all the cases exained, overhead 1 nr SIMO/HV/BPL networks deonstrate a ore environentally friendly behavior rather than equivalent n R 1 MISO/HV/BPL networks. However, in general, by adopting suitable EE policies, the superiority of MIMO systes in ters of EE etrics ay be further enhanced [64], [66], [111], [112]. On the basis of capacity and EE capacity, the exact knowledge of the trade-off relation aong IPSDM liits, EE policies and MIMO schee configurations is essential for the overhead MIMO/HV/BPL network design. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

16 Figure 4. Capacity and relative capacity gain of overhead MIMO/HV/BPL LOS case networks for the EE policies of Table 1 (the subchannel frequency spacing is equal to 10kHz). (a) EE1. (b) EE2. (c) EE3. (d) EE4. (e) EE5. (f) EE6. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

17 Figure 5. Carbon eissions of overhead MIMO/HV/BPL LOS case networks for the EE policies of Table 1 (the subchannel frequency spacing is equal to 10kHz). (a) EE1. (b) EE2. (c) EE3. (d) EE4. (e) EE5. (f) EE6. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

18 Figure 6. EE capacity and relative EE capacity gain of overhead MIMO/HV/BPL LOS case networks for the EE policies of Table 1 (the subchannel frequency spacing is equal to 10kHz). (a) EE1. (b) EE2. (c) EE3. (d) EE4. (e) EE5. (f) EE6. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

19 Carbon eissions savings in overhead MHMO/HV/BPL networks can be adjusted by appropriately regulating the capacity threshold requireents. Carbon eissions savings decrease as the capacity threshold increases. Therefore, at lower capacity thresholds, MIMO configuration schees of lower cardinality can be used. As the capacity threshold increases, MIMO configuration schees of higher cardinality are encouraged to be deployed [67]. C. Capacity and EE Capacity Trade-Off Curves The aforeentioned analysis has focused on the behavior of SE and EE etrics as well as their interaction through the lens of the carbon energy footprint. In fact, the relation between capacity and EE capacity in overhead MIMO/HV/BPL networks has been investigated for different MIMO configuration schees and EE policies. Their interaction is iportant for designing greener overhead MIMO/HV/BPL networks since a better balance between spectral perforance and environental awareness can be achieved. In the rest of this paper, it is assued that only the axiu values of pure schee configurations (8 8 MIMO, 1 8 SIMO, 8 1 MISO, and SISO systes either SISO/CCs or SISO/XCs ) of overhead MIMO/HV/BPL LOS case networks are going to be studied in the 3-88MHz frequency band. Until now, the proposal of suitable IPSDM liits has derived fro the coproise between BPL technology prootion and the protection of existing radioservices. Hence, during the proposal of today s IPSDM liits, environental issues have not seriously been addressed. Nowadays, since the adoption of environental initiatives becoes urgent, the proposed green factor f aids towards that direction during the proposal of future s IPSDM liits in overhead MIMO/HV/BPL networks. Actually, EE1 see Figs. 4(a) and 6(a) and EE6 see Figs. 4(f) and 6(f) policies define two extree state conditions of an interesting SE/EE trade-off. To highlight this interesting SE/EE trade-off, in Fig. 7(a), the EE capacity of pure schee configurations of the overhead MIMO/HV/BPL LOS case network is plotted versus the corresponding capacity for all continuous EE policies when anthracite electricity production is used. The SE/EE trade-off behavior of the above EE policies is copared against respective results of EE policies whose IPSDM liits range fro 100 db/hz to 0 db/hz with step 0.1dB/Hz (denoted as SISO/CC, SISO/XC, 1 8 SIMO, 8 1 MISO, and 8 8 MIMO curves). Siilarly to Fig. 7(a), in Fig. 7(b), curves are drawn in the case of gas electricity production. Cobining Figs. 7(a) and 7(b) with the previous figures, several interesting conclusions ay be given: The type of the electricity production, say either anthracite or gas electricity production of this paper, has strong effect on the carbon energy footprint. Siilarly to the vintage trade-off between energy-efficient and SE etrics presented in the literature [7], [68], [126], the trade-off between EE capacity/capacity is also expected to be a quasiconcave function deterining a dynaic equilibriu that depends on the EE policy, MIMO configuration schee and the type of electricity production. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

20 Figure 7. EE capacity and capacity trade-off curves of various single- and ulti-port syste ipleentations for the overhead HV/BPL LOS case when different EE policies are applied. (a) SISO, 1 8 SIMO, 8 1 MISO, and 8 8 MIMO trade-off curves when anthracite electricity production occurs. (b) SISO/CC, SISO/XC, 1 8 SIMO, 8 1 MISO and 8 8 MIMO trade-off curves when gas electricity production occurs. To achieve the best coproise aong the different interests of SE- and EE-oriented lobbies, the best proposal is the operation of overhead MIMO/HV/BPL systes near the absolute axia of trade-off curves presented in Figs. 7(a) and 7(b). Since operation points of today s overhead MIMO/HV/BPL systes are far fro the best coproise see EE1 points of Figs. 7(a) and 7(d), iinent IPSDM liits corrections through the proposed greener EE policies are required. In contrast, although very strict IPSDM liits see EE5 and EE6 points of Figs. 7(a) and 7(d) facilitate the EMC of BPL networks, the corresponding IPSDM liits push overhead MIMO/HV/BPL networks to operate with poor SE and EE perforances. Therefore, observing all the cases exained, regardless of the MIMO configuration schee and the electricity generation type, EE4 policy offers the best coproise results since its operation points are located at absolute axia of trade-off curves. The countries strategic fraeworks towards cleaner energy sources further iprove the SE/EE trade-off curves of overhead MIMO/HV/BPL networks. By interchanging fro anthracite electricity production to gas one, EE capacity values get iproved by a factor of 2.5 for given EE policy. Moreover, the choice of providers towards distributed energy sources, sart grid solutions and renewable sources tailored to the needs of their countries ay, at the sae tie, skyrocket the EE perforance of overhead MIMO/HV/BPL networks. Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

21 The application of well-tuned EE policies cobined with the use of adaptive green factor to regulate BPL operation in certain frequency segents according to carbon eission and capacity requireents ay provide flexibility in authorities and providers so that the power consuption of overhead MIMO/HV/BPL networks gets reduced with slight deterioration of their capacity. The spectral selectivity is the ain advantage of adaptive EE policies against continuous ones. Before overhead MIMO/HV/BPL systes interoperate with other broadband technologies wired, such as fiber and DSL, and wireless, such as WiFi and WiMax, the overhead HV/BPL systes need to intraoperate with other overhead and underground MV/BPL and LV/BPL that already are installed [5]-[7], [17], [19], [20], [22], [23]. Apart fro copatible frequencies, equipent and signaling, BPL standardization and adequate IPSDM liits [26], scalable capacity ust be assured taking into account the specific features of MIMO technology, overhead and underground HV/BPL, MV/BPL and LV/BPL transission and EE issues. Eerging green technology considerations aid towards this direction by introducing suitable EE policies that both respect capacity requireents and ecological awareness. Sustainable developent and growth is an iportant issue for countries that historically have been dependent on the exploitation of their natural resources (i.e., forestry, agriculture, ining and fishing) as their econoic base [127]. Nowadays, through the pris of the green econoy, countries can still coercialize their natural resources in order to financially stiulate their econoies [128]. This odern resource harvest can be achieved through icrogrids that are owned by the local counities. Microgrids include energy storage systes, distributed generation sources, like icroturbines and fuel cell units, renewable energy sources, such as wind turbines and photovoltaic systes and controllable loads [9], [10]. Except for their environental effect, the operation of icrogrids can also significantly iprove the SE/EE trade-off curves of overhead MIMO/HV/BPL networks at a local basis. Hence, the future research is going to focus on: (i) the developent of new ad-hoc SE/EE trade-off curves of overhead MIMO/HV/BPL networks at a local and daily basis that can cobine electricity supply/deand odels with the energy source ix of the power grid and the icrogrids [129], [130], [131]; and (ii) the stabilization of SE/EE trade-off curves when fluctuations of the energy production in the energy source ix occurs either in the power grid or in icrogrids [11], [132]-[134]. VII. Conclusions This paper has focused on the assessent of the broadband perforance of overhead MIMO/HV/BPL networks when environental policies are adopted. Using suitable SE and EE etrics, ajor features of today s BPL networks have been reviewed for use in future s greener overhead MIMO/HV/BPL networks. In the light of the inforation theory, the capacity values of all the considered overhead MIMO/HV/BPL networks revealed that these networks can operate both as a robust broadband platfor for SG applications across the transission power grid and as a green counications solution. In the eanwhile, exploiting the proposed SE/EE trade-offs that deterine dynaic equilibriu between capacity and EE capacity of the different overhead MIMO/HV/BPL configurations, a wiser coproise aong Tr Ren Energy, 2015, Vol.1, No.2, doi: /tre

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