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ISSN 2229-5518

R.F. Pollution Reduction in Cellular

Communication

Sumit Katiyar , Prof. R. K. Jain, Prof. N. K. Agrawal

Abs tractR. F. pollution has been recognized as health hazard in India in the prevailing circumstances. There is lot of hue and cry against cellular tow ers installed in residential area. Recently high court in India has issued an order not to install tow ers in residential areas. For meeting the exponential demand of cellular communication in India th is w ill be a set back f or f uture grow th. An appropr iate solution has to be developed f or meeting demand as w ell as RF pollution concern of the society. This paper deals w ith the installation of low pow er base stations in residential areas instead of high pow er macro cell base stations. Macro stations are p roposed to be used f or f ast traff ic, low pow er micro cell f or a slow traff ic / pedestrian and pico cell / f emto cell f or indoor use. These cells w ill be in hierarchic al structure along w ith adaptive f requency allocation techniques and A -SDMA approach.

Inde x TermsR.F. Pollut ion, Smart / Adaptive Antenna, Hierarchical Cellular Structure, A-SDMA, Macrocell, Microcell, Picocell

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1 INTRODUCTION

F pollution has been consider ed as health hazar d for man kind. Ther e w er e two opinions in this matter. As per first opinion, ther e is no scientific evidence for harmful effects
of RF pollution at these RF levels which ar e being spr ead in the envir onment by cellular base stations. Lot of r esearch has been conducted in this connection by differ ent concerned d e- partments and harmless levels w er e also pr edicted. As per other opinion, R.F. radiation is harmful to mankind and can cause neur ological, cardiac, r espiratory, ophthalmological, dermatological and other conditions ranging in sever ity fr om headaches, fatigue and add to pneumonia, psychosis and strokes. In India w e didn’t b other for R.F. pollution and devel- oped our cellular netw or k in r esidential ar ea also as per sys- tem r equir ement completely ignoring this aspect. R ecently this issue has been raised by media, social activists and med ical experts loudly. As a r esult high court issued an or der to stop installation of cellular tow er in r esidential ar ea in U.P. (India). In view of above, it is the need of hour to develop a cellular networ k which may not raise the R.F. level beyond har mless levels. At the same time this networ k should meet the i n- cr eased demand raised due to exponential gr owth of cellular communication. Obviously solution lies w ith the use of low pow er tr ansmitter s in the netw or k. This paper explains the ways and means for enhancement of spectr al density and r e- duction of pow er consumption as w ell as R.F. pollution too. Hier archical str uctur e could be the answ er of this pr oblem if it is developed with the help of low power tr ansmitters. This paper pr esents the four layers hier archical cellular networ k consists of macr o cell for fast tr affic (less than 10 W ), micr o

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Sumit Katiyar is currently pursuing PhD degree program in electronics engineering from Singhania University, India, E-mail: sumitka- tiyar@gmail.com

Prof. R. K. Jain is currently pursuing PhD degree program in electronics

engineering from Singhania University, India, E-mail:

rkjain_iti@rediffmail.com

Prof. N. K. Agra wa l is a senior member of IEEE and life member of ISTE

a nd ISCEE. E-mail: agrawalnawal@gmail.com
cells (less than 1W ) for slow tr affic / pedestrians and pico cell (less than 200 mW ) / femto cell (less than 100 mW ) for indoor ar eas. Adaptive fr equency allocation and A-SDMA appr oach has been incorpor ated in the system to taking car e of optimum r esour ce utilization.
Instead of proper cell planning, vendors in India ar e using
high power micr o cells for penetrating signal inside the b uild- ing which is consuming mor e power and incr easing level of pollution. In this paper, w e have suggested simple technol o- gies with pr oper planning of networ king for meeting multiple r equir ements.

2 E FFECT O F R.F. POLLUTION O N H UM AN H EALTH

Studies have shown that human beings ar e bio electr ical sys- tems. The heart and the brain ar e r egulated by internal bi o- electrical signals. Envir onmental exposur es to EMF can int e- ract w ith fundamental biological pr ocesses in the human body and in some cases this may cause discomfort
1. Modulation signals ar e one important component in the
delivery of EMF signals to w hich cells, tissues, or gans and
individuals can r espond biologically. Modulating signals have a specific beat defined by how the signal varies p e- r iodically over time. Modulation signals may inter fer e with normal, nonlinear biological functions.
2. Ther e have been gr owing public concer n of possible a d-
verse health effects due to EMF Radiation. The ar ea of
concern is the r adiation emitted by the fixed infr astr uctur e used in mobile telephony such as base stations and their antennas, w hich pr ovide the link to and fr om mobile phones.

3. Ther e ar e two distinct possibilities by which the Radio

Fr equency Radiation (RFR) exposur e may cause biological
effects. Ther e ar e thermal effects caused by holding m o- bile phones close to the body. Secondly, ther e could be possible non-thermal effects fr om both phones and base stations.

a) Thermal Effects:- One effect of micr owave radiation is

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dielectr ic heating, in which any dielectr ic mater ial, (such as living tissue) is heated by r otation of polar molecules induced by the electromagnetic field. The thermal effect has been lar gely r eferr ed to the heat that is gener ated due to absorption of EMF r adiation. In the case of a person using a cell phone, most of the heating effect occurs at the sur- face of the head, causing its temper atur e to incr ease by a fr action of a degr ee. The brain blood cir culation is capable of disposing the excess heat by incr easing the local blood flow. How ever , the cornea of the ey e does not have this temperatur e r egulation mechanism. The Thermal effect leads to incr ease in body temperatur e.

b) Non-Thermal Effects: - The communication pr otocols

used by mobile phone often r esult low fr equency pulsing
of the car eer signal. The non-thermal effect is r einter- pr eted as the normal cellular r esponse to an incr ease in temperatur e. The Non-thermal effects ar e attr ibuted to the induced electr omagnetic effects inside the biological cells of the body which is possibly mor e harmful. People who
ar e chr onically exposed to low level w ir eless antenna
emissions and users of mobile handsets have r eported feeling several unspecific symptoms during and after its use, r anging fr om burning and tingling sensation in the skin of the head, fatigue, sleep disturbance, dizziness, lack of concentration, ringing in the ear s, r eaction time, loss of memory, headache, disturbance in digestive system and heart palpitation etc. Ther e ar e r eports indicating adver se health effects of cell phones w hich emit electr o-magnetic radiation, with a maximum value of 50% of their ener gy being deposited when held close to the head.
4. Member Scientist, ICMR has indicated that the hot tr op i-
cal climate of the country, low body mass index (BMI),
low fat content of an average Indian as compar ed to Eu- r opean countr ies and high envir onmental concentr ation of radio fr equency radiation may place Indians under r isk of radio fr equency r adiation adverse effect [1].

3 EM F EXP OSURE LIM ITS FROM M OBILE B AS E

STATIONS

Some countr ies in the w or ld have specified for their ow n r adi- ation level keeping in view the envir onmental and physiologi- cal factor s. In order to pr otect the population living ar ound base st ations and user s of mobile handsets, established new, low intensity based exposur e standar ds. The new exp osur e guidelines ar e hundr eds or thousands of times lower than those of Institute of Electr ical & Electr onics Engineer s (IEEE), USA and ICNIRP. The exposur e limit for RF field of some of the countries including countr ies that have low er ed their limit, in cell phone fr equency range of 900 MHz and 1800 MHz for example ar e as given under [1] :-

Table – 1: International Exposure Standards

Follow ing ar e the r efer ence levels based on inter national and
national guidelines [1].

Table – 2: Reference levels for the general public at 900 &

1800 MHz

International Exposure limits for RF fields (1800 MHz)

12 W /m2

USA, Canada and Japan

9.2 W /m2

ICNIRP and EU r ecommendation 1998 –

Adopted in India

9 W /m2

Exposur e limit in Austr alia

2.4 W /m2

Exposur e limit in Belgium

1.0 W /m2

Exposur e limit in Italy, Israel

0.5 W /m2

Exposur e limit in Auckland, New Zea l-

and

0.45 W /m2

Exposur e limit in Luxembour g

0.4 W /m2

Exposur e limit in China

0.2 W /m2

Exposur e limit in Russia (since 1970),

Bulgar ia

0.1 W /m2

Exposur e limit in Poland, Par is, Hungary

0.1 W /m2

Exposur e limit in Italy in sensitive ar eas

0.095 W/m2

Exposur e limit in Switzer land, Italy

0.09 W /m2

ECOLOG 1998 (Germany) Pr ecaution

recommendation only

0.001 W/m2

Exposur e limit in Austr ia

4 SMART / ADAPTIV E ANTENNA

The concept of using multiple antennas and innovative signal pr ocessing to serve cells mor e intelligently has existed for many year s. In fact, var ying degr ees of r elatively costly smart antenna systems have alr eady been applied in defense sys- tems. Until r ecent years, cost barriers have pr evented their use in commer cial systems. The advent of pow er ful low-cost digi-

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tal signal pr ocessors (DSPs), general-pur pose pr ocessors (and ASICs), as well as innovative software-based signal-pr ocessing techniques (algor ithms) have made intelligent antennas pra c- tical for cellular communications systems (fig 1). Today, when spectrally efficient solutions ar e incr easingly a business im- perative, these systems ar e pr oviding gr eater cover age ar ea for each cell site, higher r ej ection of inter fer ence, and substantial capacity impr ovements [2].

Fig. 1. Smart Antenna System

4.1 Merits of Smart Antenna

Smart antennas at base stations can be used to enhance mobile communication systems in sever al ways:
• Incr eased BS r ange
• Less inter fer ence w ithin the cell
• Less inter fer ence in neighb or ing cells
• Incr eased capacity b y mea ns of SFIR or SDMA / A-SDMA

5 ADAP TIV E SPATIAL D IVISION MULTIP LE ACCESS


A-SDMA is based on the exploitation of the spatial dimension which has so far not been used for parallelism. Using adaptive arr ay antennas at the base station sites, multiple independent beams can be formed with which several users can be served simultaneously on the same radio channel. This appr oach is an extension of the system wher e adaptive arrays ar e used for inter fer ence r eduction, without exploiting the potential of sp a- tial par allelism. This is illustr ated in fig 2. Benefits of A-SDMA ar e pr oven and have been demonstr ated in [4]. The benefits of adaptive antenna ar e also pr oven and can be easily impl e- mented [3]. In essence, the scheme can adapt the frequency alloca- tions to where the most users are located.

Beca use SDMA e mploys s pa tia lly se le ctive tra ns miss ion, a n SDMA base s ta tion ra dia tes much les s tota l powe r tha n a conve n- tiona l base s ta tion. One res ult is a re duction in ne twork-wide RF pollution. Anothe r is a re duction in power a mplifie r s ize . First, the powe r is divide d among the e leme nts , a nd the n the power to each e le ment is re duce d beca use the e nergy is be ing de live re d dire c- tiona lly. W ith a te n-e leme nt a rray, the a mplifie rs a t ea ch e le ment nee d only tra ns mit o ne -hundre dth the power tha t would be tra nsmitte d from the corres ponding s ingle a nte nna s ys tem [5].

6 HIERARCHICAL STRUCTURE

Cellular networ ks ar e becoming incr easingly heter ogeneous due to the co-deployment of many disparate infr astr uctur e elements, including micr o, pico and femtocells, and distr i- buted antennas. A flexible, accur ate and tractable model for a general downlink HCN consisting of K tiers of r andomly l o- cated BSs, wher e each tier may differ in ter ms of average transmit pow er, supported data rate, a nd BS density. Assum- ing 1) a mobile connects to the str ongest BS, 2) the tar get Si g- nal to- Inter fer ence-Ratio (SIR) is gr eater than 0 dB, and 3) r e- ceived pow er is subj ect to Rayleigh fading and path loss. Ex- pr essions for the average r ate achievable by differ ent mobile users ar e der ived. This model r einforces the usefulness of r an- dom spatial models in the analysis and r esear ch of cellular networ ks. This is a baseline tr actable HCN model with poss i- ble futur e extensions being the inclusion of antenna sector ing, fr equency r euse, power contr ol and inter fer ence avoidance/ cancellation [6]. To overcome handoff pr oblem in hier archical cell str uctur e, efficient use of radio r esour ces is very impor- tant. All r esources have to be optimally utilized. How ever , in or der to adapt to changes of traffic, it is necessary to consider adaptive radio r esour ce management.
The ability of hierar chical cellular structur e (Fig 3) with inter-

layer r euse to incr ease the capacity of a mobile communication radio netw or k by applying Total Fr equency Hopping (T-FH) and Adaptive Fr equency Allocation (AFA) as a strategy to r euse the macro- and micr o cell r esources without fr equency planning in indoor picocells / femtocells have been discussed [7].

Fig. 2. Typical scenario f or A-SDMA application

Fig.3. Hierarchical Cellular Structure

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6.1 Macro Cell

A conventional base station w ith 20W power and range is about 1 km to 20 km. Macr o cell in hierar chical structur e takes car e of roaming mobiles.

6.2 Micro Cell

A conventional base station w ith 1W to 5W power and r ange is about 500 m to 2 km. Micr o cells and pico cells takes car e of slow tr affic (pedestr ian and in-building subscriber s). Micr o cells can be classified as the follow ing:
1) Hot Spots: These ar e ser vice ar eas w ith a higher tele-traffic density or ar eas that ar e poor ly cover ed. A hot spot is typically isolated and embedded in a cluster of lar ger cells.
2) Downtown Cluster ed Micr o cells: These occur in a dense, contiguous ar ea that serves pedestr ians and mobiles. They ar e typically found in an “urban maze ofstr eet canyons,” w ith antennas located far below building height.
3) In-Building. 3-D Cells: These serve office buildings and pe- destr ians (fig 4). This envir onment is highly clutter dominated,
with an extr emely high density and r elatively slow user m o- tion and a str ong concer n for the pow er consumption of the portable units.

6.4 Femto Cell

A femtocell is a smaller base station, typically designed for use in home or small business. In telecommunications, a femtocell is a small cellular base station, typically designed for use in a home or small business. It connects to the service pr ovider ’s networ k via br oadband (such as DSL or cable).

7 PROP OS ED N ETWORK

7.1 Evolu tion Path


For meeting the r equir ement of RF pollution l evels the evolution path is given in fig 4 [4] -

Fig.5. Evo lution Path

6.3 Pico Cell

Fig.4. M icrocell Installation Concep t

7.2 Network


Pr oposed netw or k (Fig 4 & 5) is based on simple handoff algo- r ithm discussed in [8] and hierar chical cellular str uctur es w ith inter-layer r euse in an enhance GSM radio netw or k is sug- gested [9]. A design of Macr o-Micr o CDMA Cellular Overlays in the Existing Big Urban Ar eas is suggested [10]. It is also as- sumed that the MS is equipped with a Rake r eceiver capable of per forming “maximal ratio combining” of the signals it r ec e- ives fr om the transmitting BSs [11]. The following cellular structur e will be used for dense urban ar eas [12]:
The picocells ar e small versions of base stations, ranging in
size fr om a laptop computer to a suitcase. Besides plugging
coverage holes, picocells ar e fr equently used to add voice and
data capacity, something that r epeater and distributed antenna cannot do.
Adding capacity in dense ar ea, splitting cells ar e expensive,
time consuming and occasionally impossible in dense urban envir onment wher e r oom for a full size base station often is expensive or unviable. Compact size picocells makes them a good fit for the places needing enhanced capacity, they can get.
Picocells ar e designed to serve very small ar ea such as part of
a building, a str eet corner , malls, r ailway station etc. These ar e used to extend coverage to indoor ar ea wher e outdoor signals do not r each w ell or to add netw or k capacity in ar eas w ith very dense uses.

Fig.6. The Umbrella Cell Ap p roach

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system based on pr oved simple, easily implementable technologies which better r eflects the r equir ements of po- tential clients.
II. Our basic model is a hybrid networ k wh ich includes hie-
rar chical str uctur e (umbr ella structur e), A-SDMA ap-
pr oach along with adaptive fr equency allocation and i n- telligent micr ocell technologies (such as in -building com- munication, coverage under the gr ound, coverage along winding r oads, cover age along city str eets and simple hand-off technologies).
III. Our model will enhance spectral density and quality of
service. RF pollution reduction, cost reduction and power consumption reduction will be the added requirements problem. This is the first 4-tier model that we have seen and it includes macrocell.

Fig.7. Hier archical Structure

1) Macr o cell will be mar ked for fast traffic and micr o cell will be mar ked for slow traffic in hierarch ical structur e. The RF r esour ces will be dynamically allocated betw een macr o and micro cells on the b asis of velocity estimation using adaptive arr ay antennas [13].

2) Pico cell will be mar ked for hotspots. An adaptive fr equen-

cy allocation will be applied as str ategy to r euse the macr o and micro cell r esour ces without fr equency planning in indoor picocells [9].

3) Femto cell w ill be mar ked as home base stations - which ar e data access points installed by home users to get better indoor voice and data cover age. Femtocells enable a r educed transmit pow er , while maintaining good indoor cover age. Penetration losses insulate the femtocell fr om surr ounding femtocell transmissions. As femtocells serve only ar ound 1-4 user s, they can devote a lar ger portion of their r esources (transmit power

& bandw idth) to each subscr iber. A macr o / micr o cell, on the
other hand, has a lar ger coverage ar ea (500m-20 km radius),
and a lar ger number of users; pr oviding Quality of Service (QoS) for data user s is mor e difficult. Deploying femtocell w ill enable mor e efficient uses of pr ecious power and fr equency r esour ces [14].
The above pr oposed str uctur e w ill undoubtedly enhance the
spectral density w ith the help of diversity and adaptive a p-
pr oach thr ough rake r eceiver and adaptive antenna r espectiv e- ly. The induction of pico and femto cell w ill r euse the RF r e- sour ces of over laid macr o / micr o structur es which will en- hance spectr al density manifold. The simple technologies su g- gested by William C Y Lee for deployment along city str eets, deployment along binding r oads, deployment under the gr ound (subway coverage) and in -building designs etc. will also be consider ed in pr oposed hier archical structur e [15].

8 CONTRIBUTIONS

I. We pr esent a new optimization model for the hierar ch ical networ k design micr ocell, picocell and femtocell selection. It is a capacity maximization model, for existing 2G / 2.5G

9 CONCLUSION

Intelligence has been pr ovided in four layer s (macr o / micr o / pico / Femto cell layers) w ith the help of A-SDMA appr oach and adaptive fr equency allocation along w ith total fr equency hopping techniques. Application of intelligent micr o cell, pico cell, Femto cell and adaptive antenna makes this hier archical structur e spectr um efficient. In addition to it power consum p- tion is r educed substantially w ith the application of adaptive antennas. Low power base stations w ill r esult in r eduction of inter fer ence and R. F. pollution substantially. This has been pr oved beyond doubt thr ough simulations and pra ctically too by r esear cher s [16] – [18]. Pr oposed networ k is not only spec- tr um efficient but also it w ill r educe power consumption and R. F. pollution dr astically. This will help in achieving our goal of spectr al efficiency and r eduction of R.F. poll ution which is the dir e need of hour in India in the pr evailing cir cumstances.

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