Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

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Capacity Improvement of Cellular SystemUsing Fractional Frequency Reuse (FFR)

1Gyan Prakash Pal, 2Sadhana Pal1M.E. Scholar, ECE Department, NITTTR, Chandigarh, India

2Assistant Professor, ECE Department, VGI, Greater Noida, India

Abstract:- Today wireless communication is mostly usedrather than wired communication, due to remote locationreach ability, less fault occurrence, less time to commissioningand low cost etc. But wireless network has less frequencyspectrum to cover the whole world. To improve the capacityof cellular system in a limited spectrum without majortechnological changes, frequency is reused in cells. But itoffers interferences mostly for cell edge users. To solve theproblem of spectral congestion and user capacity, fractionalfrequency reuse is used. This paper gives idea about differentfrequency reuse factors, fractional frequency reuse and supercell with sectoring to improve the capacity of cellular system.

Keywords: Frequency reuse factor, Frequency reuse ratio,Interference, Co-channel interference, Adjacent channelinterference, Fractional frequency reuse, Signal-to-interferenceratio

I.INTRODUCTIONEnable a fix number of channels to serve an arbitrarilylarge number of users by reusing the channel throughoutthe coverage region. Effective reuse of resources canhighly enhance the system capacity. Frequency reuse factor(FRF) N defines frequency reuse pattern= + + (1)Where i and j are non-negative integers.

Figure 1: Cell arrangements with reuse factor

With a smaller frequency reuse factor (FRF), N moreavailable bandwidth can be obtained by each cell. With theusage of FRF-1, the most user terminals (UTs) are afflictedwith heavy Inter-cell interference (ICI). Especially near thecell edge. The conventional method to figure out thisproblem is by increasing the FRF which mitigate the ICIefficiently but decrease on available bandwidth in a cell.The most representative approaches improving cell-edgeperformance while retaining spectrum efficiency byFractional Frequency Reuse (FFR).

Figure 2: Interference for cell edge users

II. LITERATURE SURVEYThe initial search procedure in WCDMA is used to identifythe scrambling code used by the base station that has thelowest path loss coefficient of the received signal amongall the other base stations. The timing relationship betweenbase stations is asynchronous in W-CDMA system. So thethree-step cell search algorithm is introduced in 3GPPprotocols in order to fast identify the special base station.The second step, Secondary Synchronous Channel(S-SCH)acquisition, is much critical. We have focused on thesecond step of the initial search procedure: framesynchronization and code-group identification. We proposepartial correlation method, which extremely reduces thehardware complexity. This method minimizes theacquiring time of the scrambling code group further usedfor identify the scrambling code of the selected basestation. [7]Wireless Sensor Network (WSN) has specific constraintsand stringent requirements in contrast to traditional wiredand wireless computer networks. Due to the wide potentialapplications of wireless sensor networks, this topic hasattracted great attention. The strict energy constraints ofsensor nodes result in great challenges for energyefficiency. Because of limitation in energy and selection ofbest route, for the purpose of increasing network remainingenergy a node with most energy level will be used fortransmission of data. The most part of energy in nodes iswasted on radio transmission, thus decreasing number oftransferred packets in the network will result in increase innode and network lifetimes.This paper proposes an energy-efficient organizationmethod. The organization of wireless sensor networks isformulated for target tracking. The destination route isachieved by collaborative sensing with multi-sensor fusion.The sensor nodes implement sensing tasks are awakened ina distributed manner. Thus, by using this we can be

Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

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minimized energy consumption in wireless sensor network.[8][10]The network developed after integrating the variouswireless technologies is called heterogeneous network.This growth of available broadband access technology hasbrought enormous challenges for operators wanting toensure seamless mobility to its customer in heterogeneousenvironment. In this paper, we proposed a possible UMTS-WIMAX internetworking architecture and the VHOprotocol based on MIH (IEEE 802.21 standard) for UMTSand WIMAX heterogeneous network for seamless inter-system handover, services continuity with low handoverlatency, system throughput and packet loss. The handoverprocedure is based on the media independent handoverfunction (MIHF) which is guided by MIIS server. [9]This paper presents the features of the WorldwideInteroperability for Microwave Access (WiMAX)technology and future applications of WiMAX. Adiscussion is given by comparing WIMAX with DSL(Digital subscriber line) & Cable and Wireless Fidelity(Wi-Fi). Several references have been included at the endof this paper for those willing to know in detail aboutcertain specific topics. [11] [12]5G technologies will change the way most high-bandwidthusers access their phones. With 5G pushed over a VOIP-enabled device, people will experience a level of callvolume and data transmission never experienced before.5Gtechnology is offering the services in Product Engg.,Documentation, supporting electronic transactions (e-Payments, e-transactions) etc. As the customer becomesmore and more aware of the mobile phone technology, heor she will look for a decent package all together, includingall the advanced features a cellular phone can have. Hencethe search for new technology is always the main motiveof the leading cell phone giants to out innovate theircompetitors. The ultimate goal of 5G is to design a realwireless world that is free from obstacles of the earliergenerations. This requires an integration of networks. [16]

III. INTERFERENCEInterference is the major limiting factor in the performanceof cellular radio systems. Interference on voice channelscauses crosstalk and on control channels, interference leadsto missed and blocked calls due to errors in the digitalsignaling.Two major cellular interferences are:

1. Co-channel interference2. Adjacent channel interference

1. Co-channel InterferenceFrequency reuse pattern give the coverage area withseveral cell that use the same set of frequencies. Thesecells are called co-channel cells, and the interferencebetween signals from these cells is called co-channelinterference. To reduce co-channel interference, co-channel cells must be physically separated by a minimumdistance to provide sufficient isolation due to propagation.When the size of the each cell is approximately the sameand the base stations transmit the same power, the co-channel interference ratio is independent of the transmittedpower and becomes a function of the radius of the cell (R)and the distance between centers of the nearest co-channelcells (D). By increasing the ratio of D/R, the spatial

separation between co-channel cells relative to thecoverage distance of a cell is increased. Thus interferenceis reduced from improved isolation of RF energy from theco-channel cell. The parameter Q, called the co-channelreuse ratio, is related to the cluster size. For a hexagonalgeometry

(2)

A small value of Q provides larger capacity since thecluster size N is small, whereas a large value of Qimproves the transmission quality, due to a smaller level ofco-channel interference. A trade-off must be made betweenthese two objectives in actual cellular design.

Table 1: Co-channel reuse ratio and SIR for some value ofN

Cluster Size(N)

Co-channel Reuseratio (Q)

I = 1, j = 1 3 3I = 1, j = 2 7 4.58I = 2, j = 2 12 6

Let io be the number of co-channel interfering cells. Thesignal-to-interference ratio (SIR) for a mobile receiver canbe expressed as= ∑ (3)

Considering only the first layer of interfering cells, if allthe interfering base stations are equidistant from thedesired base station and if this distance is equal to thedistance D between cell centers, then equation (3)simplifies to= ( / ) = √

(4)

S: the desired signal power from the desired base stationIi: interference power caused by the ith interfering co-channel cell base stationSignal-to-interference ratio for the worst case can be= ( ) ( ) (5)

Or = ( ) ( ) (6)

2. Adjacent Channel InterferenceInterference resulting from signals which are adjacent infrequency to the desired signal is called adjacent channelinterference. Adjacent channel interfere results fromimperfect receiver filters allow nearby frequencies to leakinto the pass band. Adjacent channel interference can beminimized through careful filtering and channelassignment. Keep the frequency separation between eachchannel in a given cell as large as possible. A channelseparation greater than six is needed to bring the adjacentchannel interference to an acceptable level.

NR

DQ 3

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Figure 3: Adjacent channel interference

IV. POWER CONTROL FOR REDUCINGINTERFERENCE

In practical cellular radio and personal communicationsystems, the power levels transmitted by every subscriberunit are under constant control by serving base stations.Ensure each mobile transmits the smallest power necessaryto maintain a good quality link on the reverse channelPower control helps on: long battery life

decrease SIR

solve the near-far problem

V. IMPROVING CAPACITY IN CELLULARSYSTEMS

Methods for improving capacity in cellular systems are: Cell Splitting: subdividing a congested cell into

smaller cells. Reduce transmission power.

Sectoring: directional antennas to control theinterference and frequency reuse.

Fractional frequency Reuse (FFR)

VI. FRACTIONAL FREQUENCY REUSE (FFR)There are different methods to use fractional frequencyreuse:

i. Frequency reuse factor 1 Same frequency is reused by each sector High spectral efficiency Large inter-cell interference Cell edge users can rarely retain connection

Figure 4: Frequency Reuse Factor 1

ii. Frequency reuse factor 3 Same frequency is reuse every 3 sectors Low spectral efficiency

Low inter-cell interference Cell edge users have fairly good connection

quality

Figure 5: Frequency Reuse Factor 3

iii. Different frequency reuse factor in one sector Sector edge band using frequency reuse 3,

allocated to the cell edge users Sector center band using frequency reuse 1,

allocated to the users in the center of thesector

Figure 6: Frequency Reuse Factor 1 and 3

iv. Soft Fractional Frequency Reuse To compensate the spectral efficiency loss

due to fractional frequency reuse The reserved band at each sector is allocated

for center users with restricted power

Figure 7: Soft Fractional Frequency Reuse

v. Dynamic Fractional Frequency Reuse Dynamic fractional frequency reuse The ratio of sector center and sector edge

bands is adaptive to traffic load, userdistribution, etc.

desired signal

receiving filterresponse

desired signalinterference

interference

signal on adjacent channelsignal on adjacent channel

FILTER

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Figure 8: Dynamic Fractional Frequency Reuse

VII. SIMULATION RESULTS

Fig. 9: Comparison of dynamic and soft FFR schemes

Fig. 10: Performance improvement of cell edge users

VIII. CONCLUSIONFractional frequency reuse (FFR) scheme should besupported to improve average and cell-edge userthroughput. The ratio of different frequency reuse factorand the corresponding power level are optimized oradjusted adaptively according to the traffic load and userdistribution, etc., to trade of between spectral efficiencyand average/cell-edge user throughput enhancement.

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Vehicular Technology Conference, 1983, vol. 33, pp. 322 – 327, May2010.[4] Zohreh Mohades, Vahid Tabataba Vakili, S. Mohammad

Razavizadeh, Dariush Abbasi-Moghadam, “Dynamic FractionalFrequency Reuse (DFFR) with AMC and Random Access in WiMAXSystem”, Wireless Pers Commun, Springer Science+Business Media,LLC. 2012[5] Andreas Dotzler, Wolfgang Utschick, Guido Dietl, “Fractional ReusePartitioning for MIMO Networks”, IEEE Globecom 2010 proceedings.[6] S. Shamai and B. M. Zaidel, “Enhancing the cellular downlinkcapacity via co-processing at the transmitting end,” IEEE VTS 53rdVehicular Technology Conference, VTC 2001 Spring, vol. 3, pp. 1745–1749, 2001.[7] Mridula S. Korde, Abhay S. Gandhi, “An Improved Method forSecondary Code Synchronization in WCDMA” IJSRET Volume 1 Issue3, pp-1-6, June 2012[8] Anuj Kumar, Dr. Ashish Chaturvedi, “Organization of EnergyEfficiency in Wireless Sensor Network”, IJSRET Volume 1 Issue 3, pp-22-25, June 2012[9] Gurpartap Singh, Garima Saini, “Development of Vertical Handover(VHO) Protocol Based on MIH (IEEE 802.21 standard) In UMTS-WIMAX Heterogeneous Network”, IJSRET Volume 1 Issue 2, pp-27-34,May 2012[10] Anuj Kumar, Neeraj Shukla, Dr. Ashish Chaturvedi, “Formulation ofEnergy Consumption in Wireless Sensor Network”, IJSRET Volume 1Issue 2, pp-35-39, May 2012[11] Gyan Prakash, Sadhana Pal, “WIMAX TECHNOLOGY AND ITSAPPLICATIONS”, IJERA, Vol. 1, Issue 2, pp.327-336, July-Aug 2011[12] Abdul Rehman, Tauheed Khan, Sunil Kumar Chaudhry, “Study ofWiMAX Physical Layer under Adaptive modulation Technique usingSimulink”, IJSRET Volume 1 Issue 5, pp- 5-11 August 2012[13] Ruchin Mangla, Maninder Singh, “MIMO-Orthogonal FrequencyDivision Multiplexing System over Rayleigh Fading Channel withSimulink”, IJSRET Volume 1 Issue 5, pp- 53-58, August 2012[14] Nalini Tyagi, Rahul Gupta, Ruchi Singh, “Parent Cluster Head withXML usage in Wireless Network”, IJSRET Volume 1 Issue 5, pp- 41-44,August 2012[15] Sakshi Srivastava, Kushal Johari, “A Survey on Reputation and TrustManagement in Wireless Sensor Network”, IJSRET Volume 1 Issue 5,pp- 139-149, August 2012[16] Sapana Singh, Pratap Singh, “Key Concepts and NetworkArchitecture for 5G Mobile Technology”, IJSRET Volume 1 Issue 5, pp-165-170, August 2012