A Power Line-delivered and Lamp-based Broadband Mobile Communication System

Tang Youxi Shao Shihai

（National key Lab of Communications， UESTC，Chengdu 610054， China）

Abstra c t:A new mobile communications network architecture is p roposed to so lve four existing bottlenecks that restrict the rap id development of m obile comm unications,as well as to meet the developm ent demands of future b roadband m obile communications.The architec ture introduces the Inform ation Lamp（IL）,a nove l device carrying out transceiver function,as the access point,besides p rovid ing light.It fulfills inform ation interaction between the access points and rad io access network through the power line（or fiber）.The new system,supported by core technolog ies such as multi-antenna based d istributed space-time signal p rocessing and d istributed rad io resource management,integ rates the w ired and wireless networks to p rovide high-speed and high-quality m obile communication services.

T hemobile communication technology develops fastest among communication technologies.Any b reakthrough in concep tor technology in themobile communication field would lead to a leap in engineering and bring greateconom ic benefits[1].The introduc tion of the“cellular”concep t initiated the first generationmobile communication system[2]；thematurity ofd igitalsignal p rocessing technologies and devices p romoted the flourishing of the second generationmobile communication system rep resented by GlobalSystem for Mobile Communication（GSM）；the commercialapp lication ofWideband Code Division Multip le Access（WCDMA）and the p roposalofmultimedia technologies satisfied the func tion requirements for the Third Generation（3G）mobile communication system[3].

To enab le larger capacity in the future mobile communication system,the multi-antenna technologies,such as Multip le InputMultip le Output（MIMO）,have become one of the hot research sub jects in the w ireless communication field[4-5].

Compared w ith 3Gmobile communication systems,the next generation system is notonly required to deliver faster transm ission rates,bigger system capacity,higherspectrum efficiency and lower power consum p tion,but italso has to dealw ith amore com p licated network environmentwhere various communication networks co-exist.As a result,the follow ing four bottlenecks in the developmentofmobile communication have to be thoroughly solved:

（1）Difficulty in Base Station（BS）add ress selection

The installation location ofa BShas always been a p rob lem for the telecom operator due to two reasons:one is that the land owners ofsome old BSs are rec laim ing theirusage of the lands,and the other is thata p roper location fora new BS is d ifficult tofind.Nowadays,the rooftops of the non-residentialbuild ings in the urban areas have already been occup ied w ith various kinds of BSs.However,the installation ofa BSon the rooftop ofa residentialbuild ing is almost impossib le for the sake of the residents'health.

（2）Large transm itting powerof mobile phone The average transm itting powerofa GSM phone is 1W[6-7]and thatofa CDMA phone is 0.01W-1W[7-8].In trad itional cellular cells,mobile phonesmay be far away from BS,so they should have enough transm itting power tomake sure communication reliability.However,the large transm itting powergives rise to strong radiation,and does harm to the user's health.

（3）Strong radiation around BS A traditionalBS often takes charge of the cellular cellsw ithin a radius of 100m-1 000m,so the transm itting powerof its b roadcastchannelhas to be large enough tomeet the cell-w ide coverage requirement.However,ata location near the BS,where only a small power is necessary,the strong radiation arising from the large transm itting power is harm ful to the user's health.Itis for this reason thatmost residents ob ject to installing a BS in their residentialarea.

▲Figure 1. An indoor scenario of IL-based wireless access.

（4）Expensive rad io spectrum resources under5 GHz

The availab le spectrums under5GHz are quite scarce and have become so expensive that the users can no longer bear.Meanwhile,the license-free spectrum s（i.e.,the Industrial,Scientific and Medical（ISM）bands）,such as the 2.4GHz,are now suffering c rowdedness.（TheWireless LocalArea Network（WLAN）and Bluetooth use ISM bands.）

To solve the above fourbottlenecks,and tomeet the requirements for the futuremobile communication system concerning capacity and transm ission rate,this paper p roposes an Information Lam p（IL）based,new mobile communication system framework,which adop ts themulti-antenna signal p rocessing technology as its core technology.Italso d iscusses the typ ical scenarios for indoorand outdooraccess,as wellas the technologies involved in the IL-based network.

1 Overall System Structure

As the indoorand outdoor lighting lamps sp read over the urban areas,a user,at any location,can be very c lose to a lighting lamp.Therefore,an IL can be assemb led,by integ rating the w ireless Access Point（AP）into the lighting lam p,to send and receive signals.In the up link ofan IL-based communication system,the signals received by the w ireless APs w illbe sent to the centralsignal p rocessor via the power line for necessary p rocessing.While in the downlink,the p rocessed signalswillbe transm itted from the centralp rocessor to the w ireless receiving device（e.g.,mobile station）via the power line and the w ireless APs in the information lam ps.

▲Figure 2. An outdoor scenario of IL-based wireless access.

1.1 Typical Indoor/Outdoor Scenario

Figure 1 is an indoorscenario ofan IL-based w ireless access.With the APs integrated into the indoor lighting lamps,the w ireless term inal（e.g.,notebook PC,PDA and mobile phone）can setup connection（s）with one ormore APs simultaneously.If the term inalhas severalantennas,a d istributed MIMO system structurew illbe formed.

The AP in the information lam p perform s some signalp rocessing functions,and communicatesw ith the centralsignalp rocessorvia the power line.After the rad io signals are separated from,and up loaded onto the power line by the signalseparatoror coup ler,they w illbe transm itted to the centralsignal p rocessor via the power line（orvia other media such as op tical fiberafter the signals are converted）.At the central p rocessor,the power line-delivered signals and some d istributed space-time signalsw illbe p rocessed.

Figure 2 is an outdoor scenario of IL-based w ireless access where the street lamps are used aswireless APs.Themobile term inal,or vehic lemounted station,accesses the communication network via the APs around it.These APs are connected to the centralsignal p rocessorw ith the power lines,op tical fiber cab les or coaxial cab les.In this way,the term inalcommunicates w ith the backbone network.

1.2 Network Hierarchy Model

Figure 3 gives a network hierarchy model for the IL-based mobile communication system.Accord ing to thismodel,there are threemain layers from the userend to the core network:access layer,signalp rocessing layerand management layer.The signal p rocessing layer is furtherdivided into three sub layers:w ireless conversion,power line conversion,and p rocessing.The functions ofeach layerare desc ribed as follows:

（1）Access Layer

The Access Layermainly consists of userdevices and information lam ps.A userdevice can communicate w ith severalinformation lam ps at the same time toform a d istributed MIMO structure.The interface between the user device and the information lamp is air interface（w ired interfacemay be p rovided for specialuserdevice）.The user devices here refer to allkinds of term inals supported by the network and have access demands likemobile phone,notebook PC,vehic lemounted station and GPS equipment,for instance.

（2）SignalProcessing Layer

The SignalProcessing Layer converts w ireless signals into power line（or op ticalfiber）signals or vice versa,and p rocesses some d istributed space-time signals.Itis further divided into three sub layers:

·Wireless conversion sub layer,which converts the physicalformatofair interface w ireless signals into thatof power line（orop tical fiber）communication signals.

·Power line conversion sub layer,which connects the p rocessing sub layer and the power line（orop ticalfiber）communicationmodule,and converts the format from power line（orop tical fiber）communication signals intow ireless signals.·Processing sub layer,which processes some d istributed signals.（3）Management Layer The Management Layermanages the distributed signals,and d irectly interchanges its information w ith the core network.

▲Figure 3. Network hierarchy model for the IL-based mobile communication system.

2 Advantages and Challenges

Using themulti-antenna distributed signalp rocessing technology as its core technology,and managing the distributed ILs w ith the d istributed rad io resourcemanagement technology,the IL-based communication system is advantageous in structure,and suggests a good solution for the fourexisting basic p rob lem s ofmobile communications.

（1）The BS add ress selection p rob lem is avoided.With the AP installed in the lighting lam p,the BS add ress selection is no longera p rob lem.Besides,the AP is hidden in the lam p and is thus,good-looking.

（2）The low powermobile phone is possib le.

Asmentioned above,the average transm itting powerofa GSM phone is 1W,and thatofa CDMA phone ranges from 0.01W to 1W.Suppose the average d istance between the IL-based APand mobile phone is 10m,the average distance between the GSM or CDMABSand mobile phone is 250m（a conservative value）,and the interference allowances of the distributed APand the receiverof traditionalGSM/CDMA BS are the same.Basing on the fad ing law of electromagnetic wave p ropagation in free space,the calculation ind icates that the transm itting powerof themobile phone using IL-based access w illbe 28 dB less than thatof the GSM/CDMA phone.Therefore,the short-distance,d istributed IL-based access solution makes the extremely low powermobile phone possib le.

（3）The transm itting powerofBS is greatly lowered.

Generally,the average transm itting powerofa CDMA base station w ith a coverage rad ius of100m-500m is 0.25W.From the assum p tions above,the distributed IL-based AP can lower the transm itting powerof the b roadcast channelby amaximum of10 000 times.

（4）The use ofhigherband spectrum is possib le.

In the IL-based w ireless access,the Line-of-Sight（LOS）channelis likely to occur.Aswe know,the fading of short-d istance LOS channelis insensitive to carrier frequency.So,it is possib le for such a system to use a frequency band higher than 5GHz.

（5）Itis safe and good-looking.

The integration of the w ireless AP into the lighting lamp can betterp rotec t the AP from fires orother damages and make itmore beautifulin appearance.

（6）Itenab les easy,flexib le and controllab le access.

In an indoorenvironment,the APs can be installed or turned on/offby the user in the same way as the lighting lam p or in a way he likes.Therefore,the operation of the APs becomes quite sim p le and convenient.Besides,the users w illnot interfere w ith each otherwhen using the APs respec tively.

As a future-oriented,new w ireless communication architec ture,the IL-based d istributed mobile communication system is stillchallenged in the core technologies,either for the d istributed signalp rocessing in the physical layeror for the d istributed signal managementin the p rotocollayer.Many initiative researches have to be done regard ing the core technologies.Follow ing are some criticalp rob lems that have to be solved:

（1）Integ ration ofAP and lighting lam p

The integration ofAPs and lighting lamps,which should notbe a sim p le put-together,buta perfectmerging,is the p rimary p rob lem for IL-based access.

（2）Conversion between w ireless and wired communications

In indooraccess environments like homes and offices for instance,the information lamp is connected w ith the power line and uses it to deliver information.As a result,the physical formats of the information have to be converted forw ireless and w ired communication respectively,and the high capability p rocessing chip willbe required.

（3）Information security

The power line is a typ ical information-sharing transm issionmed ia.Therefore,the information security on the power line is stillan open issue.At p resent,standard ization organizations forpower line use the Data Encryp tion Standard（DES）as a temporary solution,which have been detailed ly discussed in references[9]and[10].

（4）Resourcemanagementof distributed signals

Although the IL-based AP is sim ilar to the trad itionalBSw ith regard to access function,its large numberand irregulargeographic distribution are d ifficult to be dealtw ith using traditional radio resourcemanagementmethods.As a result,a distributed signal managementmethod should be developed,inc lud ing its concep t,way of thinking and operation.

（5）Modeling based on short-distance channelcharacteristics

The app lication environmentof information lam p determ ines thatits access d istance willdecrease d ramatically com pared to the traditional mobile communication system s.Therefore,it is necessary to accurately measure the MIMO channel for short-d istance access,and then setup a p roper p ropagationmodelbased on the channel's characteristics.