Cellular networks with base station cooperation

Energy ingestion of communicating engineerings is of great involvement late for both environmental and economical grounds. Coordinated Multi Point ( CoMP ) is a promising engineering to extenuate and even exploit intervention through signal articulation processing, response and transmittal at the Base Stations ( BSs ) and has the possible to hike spectral efficiency every bit good as to supply more homogenous user informations rate distribution. However, CoMP requires extra infrastructural cost, low latency backhaul links between BSs, signalling operating expenses and hence, increased signal processing at the transceivers end. The energy efficiency appraisal of auspicious engineerings like CoMP will function as a utile tool to look into the tradeoff between the possible additions in throughput and the energy ingestion in future cellular webs.

This research investigates the farther executions needed for BS co-operation and evaluates the extra power that will be dissipated at Base Stations due to the new constituents. This undertaking aims at developing a mathematical power ingestion theoretical account which will depict the extra power needed for BS cooperation in cellular systems and interpret the several parametric quantities harmonizing to the LTE/LTE-A cellular criterions.

The planetary information and communicating engineering ( ICT ) industry is a fast turning subscriber to the universe broad nursery gas emanations. The whole Information and Communication Technology ( ICT ) sector has been estimated to stand for about 2 % of planetary CO2 emanations and about 1.3 % of planetary CO2 equivalent ( CO2e ) emanations in 2007. The survey in estimations that the nomadic webs represent 0.2 % and 0.4 % of the planetary CO2e emanations in 2007 and 2020, severally. Within ICT, the nomadic communications sector today has a instead little portion, but a important addition can be expected in the close hereafter. Merely late, the European Union Commission called on ICT industry to escalate their aspirations to cut down its C footmark by about 20 % already by 2015 and to better energy efficiency of the webs. The chief subscriber to greenhouse gas emanations caused by wireless webs originates from the wireless entree web, more exactly from the base Stationss. There are in chief two ways to cut down energy cachexia: by energy cognizant constituents in the base Stationss and by energy cognizant web deployment schemes, efficaciously minimising idle capacity of base Stationss.

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As per, RAN operation dominates the planetary C footmark of planetary Mobile communications today, and it will still be responsible for about tierce of the C footmark in 2020. The survey presented in this papers suggests that nomadic traffic volume will lift by a factor of 100 to 150 and the figure of BS sites will approximately double between 2010 and 2020. Parallel to that, the overall RAN energy ingestion will lift by approximately 40 % . The survey besides posits that the overall C footmark of nomadic communications will about treble between 2007 and 2020 if no extra agencies for decrease are taken. The EARTH undertaking focuses on RAN operation and is expected to hold major impact on the energy ingestion ( and therefore the C footmark ) of new base Stationss. RAN energy ingestion could be decreased by agencies of a co-ordinated attempt to recognize both component and system-level energy efficiency betterments.

Despite the strong connexion of increasing informations rates and higher energy ingestion, scientific and technological advancement managed to maintain gait with the addition, a fact that is besides observed for the last decennary of 3G developments. In that period, possible information rates and existent informations traffic increased by a factor of one hundred while the energy ingestion of base Stationss dropped five times per provided channel capacity harmonizing to Ericsson. This tendency could go on as the EARTH undertaking keeps working on energy efficiency in nomadic webs.

LTE and coordinated multi-point

The 3GPP Long Term Evolution ( LTE ) and LTE-Advanced are extremely flexible wireless interface and one of the ends of this development is to make and even excel the demands on IMT-Advanced, as presently being defined by ITU-R. These demands will include farther important sweetenings in footings of public presentation and capableness compared to current cellular systems, including the first release of LTE. In order to make the demand of LTE Advanced, coordinated multi-point transmission/reception ( CoMP ) is used as a method to increase the cell norm and cell edge user throughput in the both uplink and downlink. When coordination is employed, inter-cell intervention is mitigated so that the links can run in the high signal/noise ratio ratio government and hence increases the spectral efficiency which is a major design end for future radio webs.

Coordinated multi-point transmission/reception is a concerted transmittal and response engineering, which can be easy deployed in a semi-distributed communicating system with distributed aerials but centralized control functionality. Several transmittal points are linked to one eNodeB, whereas each transmittal point may incorporate one or multiple antenna elements. Multiple UEs ( User Equipment ) can be served at the same time by one or multiple transmittal points of the same or different eNodeBs. The co-ordinated cardinal accountants retrieve information from distributed transmittal points and allocate resources to fulfill the QoS demands of the UEs while maximising the web public presentation.

Uplink CoMP

Uplink CoMP implies a possibility for joint processing of signals being received at multiple, geographically detached points. In general, a UE does non necessitate to be cognizant of at what points its transmittal is being received and what processing is carried out on the corresponding standard signals, either at these points or, instead, at a cardinal accountant. Two uplink CoMP articulation processing strategies are listed below:

Joint processing before decrypting

In this strategy, users transmit signals to all receive points and receive points will send on the signals they received to the joint point before decrypting it. Using this scheme really small information is lost, and hence higher CoMP addition can be achieved. But new interfaces between receive points and joint point are needed in this instance.

Joint processing after decrypting

In this strategy, users transmit signals to all receive points and receive points will send on the signal they received to the joint point after decrypting it. Using this strategy more information is lost compared to the old strategy, and hence lower CoMP addition will be achieved. But this strategy can be achieved easy by utilizing bing X2 or S1 interfaces.

Downlink CoMP

Downlink CoMP implies dynamic coordination between downlink transmittals from multiple geographically separated transmittal points. In conventional cellular systems, each base station transmits signals intended for users within its cell coverage. Depending on the users ' channel conditions, intervention caused by neighbouring cell transmittals can aggressively degrade the standard signal quality. Therefore, the downlink capacity of cellular radio webs is limited by inter-cell intervention. Since the base Stationss can be connected via a high-velocity anchor, there is an chance to organize the base aerial transmittals so as to extenuate inter-cell intervention, and therefore better spectral efficiency. The chief rule of CoMP that UE could be jointly served by multiple points over the same wireless resource is the footing to increase the spectrum efficiency while keeping the macro diverseness and/or spacial multiplexing addition. In the general sense, the downlink CoMP is chiefly characterized into two categories:

Coordinated scheduling and/or beam-forming ( CS-BF )

In the category of CS-BF, `` information to individual UE is outright transmitted from one of the transmittal points while the programming determinations are coordinated to command the intervention generated in a set of co-ordinated BSs '' . In other words, the informations intended for a peculiar UE is non shared while some information related to the channels are shared among different BSs.

Joint treating / transmittal ( JP )

In the category of JP, `` information to individual UE is at the same time transmitted from multiple transmittal points to better the standard signal quality and/or natural actively intervention for other UEs '' . In this instance, informations intended for a peculiar UE is shared among different BSs and is jointly processed at these BSs.

General power model

In order to quantify additions achieved by using energy cognizant techniques in web planning, an appropriate energy efficiency metric must be defined. One of import figure of virtue is the energy ingestion of a web. In the hereafter, base Stationss will go more energy efficient. The points with the highest impact on a base station 's power ingestion are the undermentioned: use of distant wireless caputs or ordinary power amplifiers with matching feeder losingss, different sorts of chilling ( air conditioning, air circulation, or free chilling ) , site sharing ( particularly sing substructure ) , and figure of bearer frequences. It can be expected that the mean power ingestion demand per spot lessenings in the undermentioned old ages due to new engineerings. Major power devouring constituents involved in cellular webs are listed below:

Power Amplifier: The power amplifier ( PA ) is expected to work in a province in which the extremum value of the signal corresponds with the possible peak power of the PA. Thus, the efficiency can be maximized. Doherty and Gallium nitride ( GaN ) PAs have the potency to better the efficiency. They are particularly suited for LTE with its high crest factor compared to GSM, where a changeless envelope transition technique is employed ( Gaussian Minimum Shift Keying: GMSK ) .

Signal Processing: UMTS signals are much more complex than GSM signals sing the signal processing on sender and receiver side, whereas LTE signals are even more complex. Therefore, the signal processing per nexus is well increased.

A/D Converter: This constituent consumes less than 5 % of a macro base station 's input power. Therefore, it is non regarded and assumed to be included in the signal processing portion.

Antenna Gain and Feeder Loss: Normally included in the Link Budget.

Power Supply and Battery Backup: The loss within these two constituents is typically between 10 % and 15 % and depends chiefly on the employed engineering. By utilizing 10 % , an optimistic value is assumed.

Cooling: Cooling is chiefly dependent on environmental conditions. Valuess between nothing ( free chilling ) and 40 % can be found.

Analysis/enhancements on power models

Energy consumption of cellular base stations

Power model # 1

A simple theoretical account of the long term base station energy ingestion is given in . Another power theoretical account capturing backhauling energy is modelled in as followers:

PBS = a * Ptx + B * Psp + c * Pbh,

where PBS, Ptx, Psp and Pbh denote the norm consumed energy per base station, the radiated power per base station, the signal processing power per base station, and the power due to backhauling, severally. The coefficients a, B, and hundred theoretical account effects that scale with the matching power type such as amplifier and feeder losingss, chilling, or battery backup. A brief overview of three power types has been given below:

Transmission

Transmit power effects the overall base station power ingestion through the efficiency of the power amplifier, the chilling equipment every bit good as battery backup required for operation. The mean transmit power per base station graduated tables with the inter site distance D harmonizing to the way loss theoretical account as

10 log ( Ptx ) = 10 log Pmin + 10 log K + 10 * I» log D/2

where Pmin is the needed minimal receive power at the Mobile and the term 10 log K + 10 log D2 is the path loss at the cell border in dubnium for a given inter site distance D. For power calculation we require coverage of 95 % and presume the base Stationss are centered at their cell countries. Average values of K have been taken with regard to shadowing and LOS chances as per LTE criterions.

Signal Processing

Base set digital signal processing is performed in all cellular base Stationss. The complexness of the operations and the energy ingestion depends amongst others on the employed air interface every bit good as the sum of cooperation between base Stationss. In the LTE-Advanced testbed execution about 10 % of the overall parallel and digital processing power are due to uplink channel appraisal and approximately 3 % are due to uplink and downlink MIMO processing. The former graduated tables linearly with Nc due to the increasing figure of estimated links. Assuming an MMSE filter operation, the latter requires Nc3 operations, nevertheless, the calculation is performed merely one time per cooperation bunch such that mean MIMO processing per base station merely scales quadratically with Nc. With a basal value of psp the signal processing power per sector as a map of different cooperation sizes graduated tables as

Psp = psp * 0.87 + 0.1Nc + 0.03Nc2

Backhauling

Reflecting the state-of-the-art in most cellular webs, we model backhaul as a aggregation of radio micro wave links of 100 Mbit per 2nd capacity and a power dissipation of 50 W each. Therefore for a given norm backhaul demand per base station cbh, the extra backhaul power computes as

Pbh = ( cbh/100Mbit/s ) * 50W.

The above mentioned is the power theoretical account proposed in.

Power model # 2

In this subdivision, the power theoretical account in [ 9 ] has been discussed. First, the power ingestion of the base Stationss has been evaluated. Based on this rating, the power ingestion of the base station to the radio coverage scope has The base Stationss are placed out-of-door and indoor residential scenario for the nomadic Stationss are the premises made in this work.

Power ingestion of a base station

In this subdivision, the power ingestion of base Stationss in wireless entree webs has been detailed. In a basal station we typically find several power devouring constituents. We define a base station as the equipment needed to pass on with the nomadic Stationss and with the backhaul web. A basal station contains equipment that occurs per sector ( so nsector times for all sectors ) such as digital signal processing ( responsible for system processing and cryptography ) , power amplifier, transceiver ( responsible for having and directing of signals to the nomadic Stationss ) , signal generator, AC-DC convertor. Furthermore a base station contains equipment that occurs merely one time such as the air conditioning and the microwave nexus ( responsible for communicating with the backhaul web ) . In the figure below, the equipment of the base station and the different notations for the power ingestion Pel of the different parts are indicated:

Once the power ingestion of the different constituents of the base Stationss is known, the power ingestion Pel of the full base station ( in Watt ) can be calculated as follows:

Pel = nsector ( nTx _ Pel/amp + Pel/trans + Pel/proc +Pel/conv + Pel/gen ) + Pel=micro + Pel=airco with nsector the figure of sectors in the cell, Pel/amp, Pel/trans, Pel/proc, Pel/conv, Pel/gen, Pel/micro and Pel/airco are the power ingestions of the power amplifier, the transceiver, the digital signal processing, the AC-DC convertor, the generator, the microwave nexus and the air conditioning, severally. Table below shows the values that we consider here for the power ingestion of this equipment for the considered engineerings. These values are retrieved from informations sheets of assorted makers of web equipment.

In the above probe, cells have been considered with three sectors ( therefore nsector is 3 ) . Furthermore, nTx is the figure of conveying antennas per sector. In the most simple state of affairs, which is called a SISO ( Single Input Single Output ) system, the base station uses merely one aerial for transmittal and the nomadic station uses merely one aerial for having. In this instance the parametric quantity nTx is 1. When a MIMO ( Multiple Input Multiple Output ) system is considered where the base station uses two conveying aerials and the nomadic station one or two having aerials, the nTx parametric quantity is 2. For each conveying aerial of the base station we need one power amplifier. So we have to take the power ingestion of the power amplifier into history several times harmonizing to the figure of conveying aerials that are used in one sector. The power ingestion of each portion of the base station is a changeless value ( in Watt ) , except for the power amplifier. The power ingestion of the power amplifier depends on the required input power of the aerial. To pattern the power ingestion of the power amplifier we need to specify the efficiency _ of the power amplifier. The efficiency of the power amplifier is the ratio of RF end product power Pout/amp ( in Watt ) to the electrical input power Pel=amp of the power amplifier ( in Watt ) .

Calculation of scope R

In this subdivision, the power ingestion Pel of the base station has been related to the radio scope R. For this, a nexus budget has been set-up. A nexus budget takes all of the additions and losingss of the sender through the medium to the receiving system into history. First, the maximal way loss PLmax ( in dubnium ) has been calculated to which a familial signal can be subjected while still being noticeable at the receiving system. The way loss is the ratio of the radiated power to the standard power of the signal. Table below gives an overview of all the additions and losingss that occur. It is of import to observe that PLmax is dependent of the input power PTx of the aerial and therefore dependant of the end product power of the power amplifier which is Pel/amp.

Once the maximal way loss PLmax is known, the scope R ( in meters ) can be determined by utilizing a way loss theoretical account. A general way loss PLmed map is given as:

PLmed = g ( d| degree Fahrenheit, hemoglobin, hectometer )

PLmed is a map g ( : ) of the distance vitamin D ( in meters ) , the frequence degree Fahrenheit, the height hemoglobin of the base station and the height hectometer of the nomadic station. The measure before the | is a variable and varies over a uninterrupted interval while the measures after the | are parametric quantities which take merely one discrete know value. The map g ( : ) depends on the used way loss theoretical account e.g. , the HATA theoretical account and the Erceg theoretical account. Erceg C theoretical account has been used here.

To find the distance d the upside-down map of equation above has been considered:

500 = g-1 ( PLmed| f, hemoglobin, hectometer )

Based on equation above the maximal scope R ( in meters ) that can be reached with the base station of a certain engineering has been estimated as follows:

R = g-1 ( PLmax- SM | degree Fahrenheit, hemoglobin, hectometer )

with SM the shadowing border which depends on the standard divergence of the way loss theoretical account, the coverage per centum and the out-of-door standard divergence. Here we consider a coverage per centum of 90 % .

Power Model # 3

A elaborate and updated power theoretical account for LTE baseline system has besides been studied in, one of the plants of EARTH undertaking enterprise, which will be an country of survey.

Backhauling propositions

From the comparing of Power Model # 1 and Power Model # 2, it is evident that the power ingestion of Microwave nexus has been underestimated in the former one by 60 % . As microwave nexus has a major function in the power ingestion theoretical account, it is indispensable to hold a more power efficient backhaul option.

There is a demand for backhaul capacity to increase for nomadic broadband, informations entree, and picture services to prosecute the end-users every bit good as support cost in cheque. Radio-over-Fiber [ 11 ] as a solution has been turn toing how to administer broadband radio signals in entree webs, including dynamic allotment of resources. Radio-over-Fiber system ( RoF ) is the technique of modulating the wireless frequence ( RF ) sub-carrier onto an optical bearer for distribution over a fibre web. RoF technique has been considered a cost-efficient and dependable solution for the distribution of the hereafter radio entree webs by utilizing optical fibre with huge transmittal bandwidth capacity. RoF has the following chief characteristics: ( 1 ) it is crystalline to bandwidth or transition techniques. ( 2 ) Simple and little BSs. ( 3 ) Centralized operation is possible. New radio endorsers are subscribing up at an increasing demand of more capacity for ultra-high informations rate transportation at velocities of 1 Gbp/s and up sing, while the wireless spectrum is limited. This demand of more bandwidth allotment, topographic points heavy load on the current operating wireless spectrum and causes spectral congestion at lower microwave frequence. Millimeter Wave ( mm-Wave ) communicating system offers a alone manner to decide these jobs. Furthermore, to cut down the sum cost and serve as many users as possible, 60 GHz systems show first-class advantages for the future super-broadband informations services presenting in footings of information rate and power ingestion. Therefore, developing a cost effectual agencies of bring forthing optical millimeter-wave signals at frequences above 60 GHz is of great involvement.

Future Work

Existing Power Models needs to be studied in item and should be enhanced with the aid of EARTH undertaking enterprise.

Backhaul demands for LTE/LTE-A should be investigated as this one of the key demands for CoMP.

Specifically, Power Requirements for Fibre Optic backhaul systems needs to be investigated.

Most Energy Efficient Backhaul system should be recommended and included in the Power Model to heighten the same for better appraisal of Power Consumption.

If clip licenses, power theoretical accounts for Mobile Equipment ( ME ) presently in the market should be studied in item and most energy efficient power theoretical account should be estimated.

Undertaking aims

• Learn about Coordinated Multi-Point ( CoMP )
• Understand the construct of CoMP and why is it required?
• Learn about different sorts of CoMP involved in downlink and uplink.
• What is a Power Model and why is it required?
• Learn about LTE/LTE-A Cellular Standards
• Learn in item about LTE/LTE-A cellular webs
• Focus on the Base Station Subsystem as this is the portion which chiefly consumes power in cellular webs.
• Learn about Remote Radio Equipment introduced for LTE-A
• Develop a Power Model for the extra power needed for BS Co-operation in cellular systems
• Identify the Overhead required due to CoMP with specific concentration on Backhaul systems.
• Identify the LTE/LTE-A parametric quantities required to be mapped in the Power Model
• Develop/Recommend an enhanced energy efficient Power Model and interpret the several parametric quantities harmonizing to LTE/LTE-A cellular criterion.

Work Plan

A planned class of action for this undertaking is given below:

TASKS Jan-March April - May June July August

1. Task 1- Learn about Coordinated Multi Point and Generic Power Models.
2. Task 2- Learn about LTE/LTE-A Cellular Standards and Architecture.
3. Task 3- Investigate energy efficient Power Models and Backhaul demands
4. Task 4- Identify and Learn in item about the Overhead constituents required due to Coordinated Multi Point particularly Backhaul system and Enhance bing Power Models
5. Task 5- Design/Develop/Recommend an enhanced energy effcient Power Model and interpret the several parametric quantities harmonizing to LTE/LTE-A cellular criterion.

In a nutshell, the overall program of action can be summarized as followers:

• Build on bing literature on base station energy ingestion and constituents involved in it.
• Further executions needed for Base Station cooperation and rating of extra power that will be dissipated at Bases Stations will be investigated.
• A power theoretical account for power ingestion depicting the extra power needed for Base Station cooperation in cellular systems will be developed and translated to respective parametric quantities harmonizing to LTE/LTE-A cellular criterions.

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