Comparatve Analyss of Reuse and 3 n ular Network Based On IR Dstrbuton and Rate Chandra Thapa M.Tech. II, DEC V College of Engneerng & Technology R.V.. Nagar, Chttoor-5727, A.P. Inda Emal: chandra2thapa@gmal.com Abstract-gnal to nterference rato (IR) s always an mportant measure for analyss of qualty of connecton of forward as well as reverse lnk n any wreless cellular network. And mportance of cellular concept s that t provdes optmum use of resources. We can calculate network parameters as coverage probablty and rate (ndvdual user as well as network) from IR metrcs usually gnal to Interference Plus Nose (INR), for dfferent frequency reuse schemes. Thus, IR has promnent mportance and here n ths paper, IR dstrbuton n cellular envronment for downlnk channel s plotted for frequency reuse and 3 along wth per user rate and ther comparatve analyss s undertaken. base statons and ther channel groups throughout a market, the avalable channels are dstrbuted throughout the geographc regon and may be reused as many tmes as necessary so long as the nterference between co-channel statons s kept below acceptable levels []. Index Terms- IR, Frequency Reuse, ular Concept. I. INTRODUCTION The problem of spectral congeston and user capacty s solved by ntroducton of cellular concept. It offers very hgh capacty n a lmted spectrum allocaton wthout any major technologcal changes []. Frequency plannng and frequency reuse comes along wth cellular concept. Thus mportant factor that always makes senses n cellular system s nterference from adjacent as well as co-channel cells. To tackle ths factor we take gnal to nterference plus nose (INR) factor under consderaton and accordng to ts value we can analyze the performance of cellular network for dfferent frequency plannng schemes (here frequency reuse and 3). Fg.. Dagram of cellular concept and cellular frequency reuse. wth the same letter use the same set of frequences. The reuse shown here s for cluster sze of N=7. The cellular concept s a system-level dea whch calls for replacng a sngle, hgh power transmtter (large cell) wth many low power transmtters (small cells), each provdng coverage to only a small porton of the servce area. Each base staton s allocated a porton of the total number of channels avalable to the entre system, and nearby base statons are assgned dfferent groups of channels so that all the avalable channels are assgned to a relatvely small number of neghborng base statons. Neghborng base statons are assgned dfferent groups of channels so that the nterference between base statons (and the moble users under ther control) s mnmzed. By systematcally spacng II. FREQUENCY ALLOCATION CHEME The cellular frequency reuse concept s llustrated n Fg., each cellular base staton s allocated a group of rado channels to be used wthn a small geographc area called a cell. Base statons n adjacent cells are assgned channel groups whch contan completely dfferent channels than neghborng cells. The base staton antennas are desgned to acheve the desred coverage wthn the partcular cell. By lmtng the coverage area to wthn the boundares of a cell, the same group of channels may be used to cover dfferent cells that are separated from one another by dstances large enough to keep nterference levels wthn tolerable lmts. Advances n Computng, Communcaton, Electrcal & Network Technologes (), Vol 3, PP.80-85
8 Chandra Thapa The desgn process of selectng and allocatng channel groups for all of the cellular base statons wthn a system s called frequency reuse or frequency plannng []. 3,5,7 Power 7 2 3 A. Frequency Reuse of Ths s smplest form of reuse where all frequency channels are allocated to each cell. Ths ncreases the number of channels per user area but at same tme due to the decrease n dstance between co-channels cells (here t wll be adjacent cell) faces huge nterference. Ths concept of reuse to ncrease of system capacty s employed n 3 rd generaton partnershp project (3GPP) Long Term Evoluton (LTE) 4G OFDMA base cellular network. Thus ths s analyzed here. 2,4,6 Frequency Fg.3. Frequences reuse rato 3. 6 5 4 Power 3,5,7 7 2 3 III. YTEM MODEL AND INR CALCULATION 2,4,6 Frequency Fg.2. Frequences reuse rato. 6 5 4 Here we are assumng homogenous dstrbuton of load (.e. load n all cell are equal and statc). mlarly Hexagonal shape s taken and ts geometry s carefully appled for INR calculaton. The hexagon geometry for reuse showng ts nterferng cells (adjacent cells) s shown n Fg. 4. The dots poston s consdered as Base taton poston.e. center excted cellular coverage. mlarly for reuse 3 we can be draw postons of nterferng cells. B. Frequency Reuse of 3 In Re-use 3, the system bandwdth s dvded nto 3 equal sub-bands, each of these sub-bands are allocated to cells n a manner that no other surroundng cell s usng the same subband, ths s llustrated n Fg.3. Thus, the dstance of cochannel cells are ncreased and thereby co-channel nterference s decreased. Wth use of more cluster sze and area of cell, nter-cell nterference can be mtgated but ths s at the expense of huge loss n system capacty. If we consder cell A as cell under consderaton to calculate INR then B and C (actually 6 adjacent cell Base tatons) are nterferng base statons. If we consder A as (0,0) as ts co-ordnate then co-ordnate for nterferng base staton can be found by usng hexagonal geometry as shown n above Fg 4. The co-channels cells are those cells that use the same set of frequences. By smply ncreasng transmtted power we can t ncrease INR value because t ncreases the nterference to neghborng co-channel cells. Thus, smple soluton s co-channel should be separated by certan dstance.
82 Comparatve Analyss of Reuse and 3 B ( 3 2 R, 3 2 R) ) A 30 C ( 3R,0) (0,0) Fg. 4. Hexagonal cell geometry wth neghbor cells. When the sze of each cell s approxmately the same and the base statons transmt the same power, the co-channel nterference rato s ndependent of the transmtted power and become a functon of radus of the cell (R) and the dstance between centers of the nearest co-channel cells (D). The parameter Q, called the co-channel reuse rato, s related to the cluster sze. For a hexagonal geometry, Q= D = 3N () R A small value of Q provdes larger capacty snce the cluster sze N s small, whereas a large value of Q mproves the transmsson qualty, due to a smaller level of co-channel When the transmt power of base staton s equal and the path loss exponent s the same throughout the coverage area, /I for a moble can be approxmated as, = R -n I 0 (D ) -n Consderng only the frst layer of nterferng cells, f all the nterferng base statons are equdstant from the desred (3) nterference. A trade-off must be made between these two objectves n actual cellular desgn. The sgnal to nterference rato (/I or IR) for a moble whch montors can be expressed as, = I 0 I Where, 0 s the number of co-channel nterferng cells. s the desred sgnal power from desred base staton. I s the nterference power caused by the th nterferng cochannel cell base staton. base staton and f the dstance s equal to the dstance D between cell centers, then equaton (3) can be, = (D/R) -n I 0 (2) = ( 3N) n (4) 0 Durng smulaton n Matlab, nose s not consdered for smplcty. And approxmated equaton for worst case scenaro s,
83 Chandra Thapa R -n IR= (5) 2(D-R) -n +2(D+R) -n +2D -n To calculate rate we use hannon s model for capacty as, C=B* log 2 (+IR) (6) Where, B s Bandwdth of Channel (Hz). IR s gnal to nterference rato per user not n db. C s rate per user (bts/hz). IV. IMULATION AND REULT We are consderng Hexagonal geometry havng Radus R=500m. Mobles are taken randomly wthn n cell coverng almost all poston nsde hexagonal cell. Frequency reuse of rato and 3 s consdered and CDF of IR for respectve reuse rato s plotted and compared. Nose s not consdered. From Fg. 5 t s clear that the degradaton n sgnal-tonterference rato (IR) for reuse relatve to reuse 3, whch s approxmately 0dB. Thus frequency reuse 3 s seems to be better than reuse but ths s at the expense of decrease n capacty due to dvson of avalable spectrum among cells. o, tradeoff should be done n between nterference and capacty. If we consder the hannon Channel Rate ( C ) whch s always upper bound, then the hstogram for rate for reuse and reuse 3 for Bandwdth of 20MHZ s llustrated n Fg.6 and Fg.7. If we consder the hannon Channel Rate (C) whch s always upper bound, then the hstogram for rate for reuse and reuse 3 for Bandwdth of 20 MHZ s llustrated n Fgure 6 and Fgure 7. It s clear from hstogram of rate dstrbuton (one sample) that for frequency reuse.e. Fgure 6.6a, 2*0^4 users can acheve at least rate of ~50*0^7 bps and 0.*0^4 users can acheve at least rate of ~2.5*0^8 bps wth the overall mean rate of 70.86995*0^6 bps. mlarly, consderng frequency reuse 3.e. Fgure 6.6b, 2*0^4 users can acheve at least rate of ~3.5*0^7 bps and 0.*0^4 users can acheve at least rate of ~0*0^7 bps wth the overall mean rate of 46.026026*0^6 bps. V. CONCLUION IR has huge sgnfcance n network qualty analyss and t s not lmted to 2G or 3G but also has mportance n 4G cellular networks. Here n ths paper we had analyzed IR dstrbuton for Reuse and Reuse 3. We found that Reuse 3 had better IR and lower mean per user rate than Reuse. But, ths s clear that Reuse has hgh throughput as number of channels avalable per cell s hgh whle n Reuse 3, total spectrum s dvded nto 3 groups and used n dfferent cells provded for same cellular coverage area. Therefore, there should have tradeoff between these two parameters: throughput and IR, for better channel qualty and coverage. REFERENCE [] T.. Rappaport, Wreless Communcatons, Prentce Hall, Upper addle Rver, NJ, 2002. [2] Mustafa M.M. El.Tantawy, Mohamed Aboul Dahab, Hesham El-Badawy Performance Evaluaton of Frequency Reuse chemes n LTE Based Network 8 th telecommuncatons forum TELFOR 200. [3] Andrea Goldsmth, Wreless communcaton, 2005 Cambrdge Unversty Press
84 Comparatve Analyss of Reuse and Reuse 3 Emprcal CDF 0.9 0.8 Reuse= Reuse=3 0.7 0.6 F(x) 0.5 0.4 0.3 0.2 0. 0-0 -5 0 5 0 5 20 25 30 35 40 45 50 IR Dstrbuton (db) Fg.5. INR dstrbuton for a network wth Reuse and Reuse 3 (500m cell). Fg.6. Hstogram of rate per user for Frequency Reuse. Fg.7. Hstogram of rate per user for Frequency Reuse