per formance enhancement of mimo-ofdm technology for high data rate wireless networks

8/22/2019 Per formance Enhancement of MIMO-OFDM Technology for High Data Rate Wireless Networks

1/7

International Journal of Computer Science and Application Issue 2010 ISSN 0974-0767

122

Performance Enhancement of MIMO-OFDMTechnology for High Data Rate WirelessNetworks

Nirmalendu Bikas Sinha, Makar Chand Snai, M. Mitra

Abstract- The use of mult iple antennas at both transmit terand receiver t o form mult ip le input and mult ip le ou tput(MIMO) channels cur rent ly hold the potential to drasticallyimprove wireless links spectrum e? ciency or robustness,in cr easin g cap acity an d the ab ility to in cr ease th et ransmission speed in future wireless communica tionssystem. For broadband communica tions, OFDM turns afrequency selectivechannel into a set ofp arallel flat channels,which significantly reduces the receiver complexity. In thispaper, we expand t he idea of spreading t he t ransmit tedsymbols in OFDM systems by applying Space-Time CodedMult ip le- Input Mult ip le-Outpu t OFDM (STC /MR C-MIMO-OFDM) systems. In the proposed systems, a multi-dimensional diversity, including time, frequency, space andmodulation diversit ies, can be used, result ing in better biterror performance in AWGN channel for with and withoutpadding as well as for with and without convolution coding.The exper imenta l resu lt s have been ver ified using t heMATLAB simulation, the results of simulat ion have beenverified with thevarious works being carried out in this areaand the results conferred to be correct . . Finally, the paperaddr esses the curr ent questions regarding the integration ofSTC/MRC-MIMO-OFDM system in pract ica l wirelesssystems and standards.Keywords-BER , PER, OFDM , STC /MRC , M IMO, GPS, 3Gand4G.

I. INTRODUCTION

The growth of mobile communications, wireless Internetaccess and multimedia applications has produced a strongdemand for advanced wireless techniques. The challengesfor wireless communication designs come from thedetrimental characteristics of wireless environments, suchas multipath fading, Doppler Effect, co-channelinterference, and intentional jamming in military

communications and ITS. The objective of our paper is toprovide new approaches to solve the problems mentionedabove and enhance the transmission speed to 100 Mbps bymeansof OFDM-MIMO (MRC/STC) system.

We are proceeding towards a broadband age both for thecommunication as well as remotesensing. There is a risingneed for high data rate [1] [2] [3] [4] [5] [6] [7] [8] [9] [10],wireless communication. As user's demands exceed thecapacity of wireless networks, operators are forced to findways to improve the network capacity and throughput inorder to provide an acceptable level of service. There is

tremendous technological growth towards exploiting thebandwidth of a system. Particularly, in the wirelessdomain, 60 GHz RF band has lots of promise which canoffer a bandwidth of 5 GHz. On the other hand, theWCDMA3G mobile system has lots of growth in terms of

better data rate, better interference rejection, better multi-path exploitation etc. Now we are thinking of a systemwhich can serve the purpose of communication in ITS

application. A Communication model is based on theprinciple that any change in the signal after transmission iseliminated to recover the original signal at receiver andavaila reliablecommunication.

The approaching Fourth generation (4G) mobilecommunication systems are projected to solve still-remaining problems of 3G (third generation) systems andto provide a wide variety of new services, from high-quality voice to high-definition video to high-data-ratewireless channels. The term 4G is used broadly to includeseveral typesof broadbandwirelessaccess communicationsystems, not only cellular telephone systems. 4G wirelesswas originally conceived by the Defense Advanced

Research Projects Agency (DARPA), the sameorganization that developed the wired Internet. 4G is anetwork of networks with which user will be in control.They will be decide the system even the right terminal foreach application and for each environment (mobility &coverage).So 4G is MAGICMobile multimedia,anytime anywhere, Global mobility support, integratedwireless solution, and customized personal service [11].The expected data rate for high mobility100Mbps andforNomadic1Gbps [12].As a promise for thefuture, 4Gsystems, that is, cellular broadband wireless accesssystems have been attracting much interest in the mobilecommunication arena. The 4G systems not only willsupport thenext generation of mobile service, but also will

support thefixedwirelessnetworks. This paperpresentsanoverall vision of the 4G features, framework, andintegration of mobile communication. The features of 4Gsystemsmight be summarized withone word-integration.

There are actually three major objectives which the 4Gtechnologies to fulfill-Continuous connectivity, Datarateof 100 MBPS at user terminal and Other services like ITSto deploy. CALM [13], continuos communication forvehicles, is a new World Standard for ITS operation. Itincludes Millimeter wave radar, GPS, 2G air interface tosupport ITSactivities.


2/7

2.1 MIMO SYSTEM MODELThe input /output a relation of a narrow band single-userMIMO wireless link is modulated by a complex basebandvectornotation:Y= HX+ n ..(1). Where H isthe channelmatrixandn is theadditive white Gaussian noise (AWGN)

vectorat a given instant in time channel noise.

Furthermore, as a commonly used structure for the MIMOsystem, V-BLAST shares some basic modules with ourgeneral multipleantennas.

Y= y1

The time-varying channel impulse response betwen thej-th (j = 1.2..........M) transmit antenna and the i-th

(j= 1.2 ........N) receive antenna is denoted as hi.j(,t) Thisis the response at time t-. The composite MIMO channelresponseisgivenbytheNxMmatrisH(,t)with

Thevector

referred to as the spatio-temporal signature induced by thej-th transmitantennaacross the receiveatenna.

Furthermore,given that thesignal sj(t) is launchedfrom thej-th transmit antenna, the signal received at thei-th receive antenna isgivenby

Where * denotes the convolution operator and is

additive noise in the receiver. For transmit/receive beam

forming with the diversity of order M N, is considered asfull diversity. Ontheotherhandthe antenna gain is

Max={M,N}antennagainMN

2.2 MIMOsystemchannelCapacityMultipath propagation has long been regarded asimpairment because it causes signal fading. To mitigatethis problem, diversity techniques were developed.Antenna diversity is a widespread form of diversity.Information theory has shown that with multipath

propagation, multiple antennas at both transmittre and

n (t)i

123

II. OFDM-MIMO IN WIRELESS COMMUNICATION

Increasing thenumber of MIMOtransmittersand receivershowever holds even greater potential. By using multipleantennas both at transmitter and receiver it boost the datatransmission rate and quality of wireless signals. In doing

so MIMO takes the advantages of the various reflectionsseen by the receiver. STC/MRC is one of the techniquesused in MIMO, which spatially multiplexes multipleindependent data streams transferred simultaneouslywithin one spectral channel of bandwidth. OFDM-MIMO(STC/MRC) can significantly increase data throughput asthenumber of resolvedspatial data streams is increased.

A MIMO channel is a wireless link between M transmitsand N receive antennas. It consists of MN elements thatrepresent the MIMO channel coefficients. The multipletransmit andreceive antennas could belong to a singleusermodem or it could be distributed among different users.

The later configuration is called distributed MIMO andcooperative communications. Statistical MIMO channelmodels offer flexibility in selecting the channel

parameters, temporal and spatial correlations. MIMOchannel simulation tools are implemented based on thesemodels. Several statistical MIMO channel models were

proposed in [8] and [9].Both models introduced spatialcorrelation by multiplying a matrix of uncorrelatedrandom variables by a square root of a covariance matrixandboth arebasedon similar assumptions.However, theydiffer in their approach. In [10], the authors validate thestatistical model of [8] based on measurements inmicrocells and microcells. They showed that the eigenvalue distr ibution of the model matches themeasurements. Fig.1(a), (b), (c)and (d)showsconceptualdiagram of existing technology, smart antenna system andMIMOchannels respectively.

M

Scatterer

TX

1

2

N

RX

1

2

Fig. 1(d) A MIMO wireless channel

Fig. 1 (a) Existing technology, (b) & (c) Smart antenna system

yi(t) = Nitntsth iM

J

jji ,,2,1),()(*),(1

, L=+=

..(7)



3/7

124

CSHANNON= B. log2 [1+SNR]

ZHBPS .....(15)

CSHANNON= B. log2 [1+SNR . |H|2 ]

ZHBPS ....(16)

Fig.3 Shanons capacity for SISO system

eceiverchannels that operate simultaneously, on the samefrequency band at the same total radiated power. Antennacorrelation variesdrastically as a function of thescatteringenvironment, the distance between transmitter and

receiver, the antenna configurations, and the Dopplerspread. Recent research has shown that multipath

propagationcan in fact contribute to capacity.

Channel capacity is themaximuminformation rate that canbe transmittedand receivedwitharbitrarilylow probabilityof error at the receiver. A common representation of thechannel capacity is within a unit bandwidth of the channeland canbe expressedin bps/Hz.This representation isalsoknown as spectral (bandwidth) efficiency. MIMO channelcapacity depends heavily on the statistical properties andantenna element correlations of the channel. Representingthe input and output of a memory less channel with therandom variables X and Y respectively, the channel

capacity is defined as the maximum of the mutualinformationbetween X andY:

receiver can establish essentially multiple parallel

A channel is said to memory less if the probabilitydistribution of the output depends only on the input at thattime and is conditionally independent of previous channelinputs or outputs. p(x) is the probability distributionfunction(pdf)of theinputsymbolsX.

2.3 Capacity of Single-Input-Single-Output (SISO)System:According to Shannon capacityof wirelesschannels,given

a single channel corrupted by an additive white Gaussiannoiseat a levelofSNR, thecapacityis:

where:C is theShannon limitson channel capacity, SNRis signal-to-noiseratio, B is bandwidthof channel. In theractical case of time-varying and randomly fadingwirelesschannel,the capacitycanbe written as:

Where: H is the 1x1 unit-power complex matrix Gaussianamplitude of the channel. Moreover, it has been noticedthat thecapacityis very smalldueto fadingevents [15].

From the above expression it is clear that theoreticallycapacity increase as the bandwidth is increased whichshown in Fig.3. C increases 1 bits/sec/Hz for every 3dB ofSNR. Thus by using multiple antennas we can increase thethroughput. Using MIMO architecture the throughput can

be increased with a much reduced transmission powerusing STC/MRC code helps to fulfill the high throughput

potential of OFDM-MIMO system in a highly efficientmanner. Using wider bandwidth with OFDM offerssignificant advantages when maximizing performancewider bandwidth channels are cost effective and easilyaccomplished with moderate increases in digital signal

processing(DSP).

III. EXPERIMENTAL SETUP FOR OFDM-MIMO(MRC/STC) SYSTEMS:

Block diagram of OFDM-MIMO (MRC/STC) transmitterand receiver system is dipicted in Fig. 4(a) and Fig 4(b).

OFDM is a multicarrier transmission technique, whichdivides theavailable spectruminto many carriers,eachone

being modulated by a low data rate stream. Each sub-carrier is orthogonal to each other, meaning that cross-talk

between the sub-channels is eliminated and inter-carrierguard bands are not required which significantly reducesthe receivercomplexity.

In current 802.11 systems without MIMO (Multiple InputMultiple Output) there is a single RF (Radio Frequency)chain on the wireless device. Multiple antennas use thesame hardware to process the radio signal. So only oneantenna cantransmit or receive at a time asallradiosignalsneed to go through the single RF chain. In MIMO there

can be a separate RF chain for each antenna allowingmultipleRFchains to coexist.

The various parameters on which the simulation followedby analysis for Fig.4(a)and Fig 4(b)are:

Modulation techniques: BPSK, QPSK. Number of FFTpoints: 256 and 1024 (with and without interleaving),Convolution code rates: R1/2 and R3/4, Channel Models:AWGN.

IV. SIMULATION AND PERFORMANCE ANALYSISOF OFDM-MIMO (STC/MRC) SYSTEMS:

Performance analysis has been done for the proposedsystem based on MATLAB simulation. In communicationsystems, information bits are typically grouped into aframe or packet format and transmitted to a receiver. Thereceived packets may be lost or include errors because of anoisy channel for transmitting the data. The packet errorrate (PER) is the percentage of received packets thatinclude an error. PER in a coded system depends on theratio of thebitenergy to noise spectrum density (SNR), theFEC code rate, ARQ scheme and the packet size.Bit ErrorRate(BER) is the fundamental parameter to access the



4/7

125

Fig.4(a): Block diagram of OFDM-MIMO (MRC/STC) Transmitter System.

Fig.4(b): Block diagram of OFDM-MIMO (MRC/STC) Receiver System.

DETECTION &

DECODING

Contains: MIMO

detection, Phase

drift Correction,

demapping,

deinterleaving and

decoding

RX1FFT Remove

Cyclic

Prefix

FFT Remove

Cyclic

Prefix

Synchronization

Channel estimation

RXN

Binary

O/P data

quality of any digital transmission and qualitymeasurement of recovered data. Using FFT approach asthe number of subcarrier increases the better is accuracydue to higher number of points. Hence data rate will alsoincrease.i) In comparison with three modulation schemes by

varying receiver elements and keeping the transmitterelements initiallyfixed, forthe case ofwith andwithout

padding for BPSK and QPSK modulation, as SNRincreases BER and PER improves. So data rateincreases as shown in fig. 4, which is mainly due to itsreceivingdiversitytechnique.

0 5 10 15 20 25 3010

-6

10-4

10-2

100

SNR [dB]

BER/PE

R

Modulation: BPSK Number of Data Carriers: 256

BER

PER

BER

PER

010

-210

-410

-610

Fig.4: Performance of a BPSK modulation for withoutpadding and without coding. Parameters: No. of FFTpoints= 256; Modulation = BPSK; Channel = AWGN, Txelements=2 andRxelement=2.



5/7

126

SNR [dB]

0 5 10 15 20 25 3010

-6

10-4

10-2

100

SNR [dB]

BER/PER


BER

PER

BER

PER

010

-210

-410

-610

0 5 10 15 20 25 3010

-6

10-4

10-2

100

SNR [dB]

BER/P

ER


BER

PER

BER

PER

010

-210

-410

-610

Fig.5: Performance of a QPSK modulation for withpadding Parameters: No. of FFT points = 256; Modulation=QPSK; Channel = AWGN, Tx elements=2 and Rxelement =2,coderate=1/2.ii) For with coding OFDM-MIMO (STC/MRC) system

overall performance of all modulation techniques ismuch better than without coding. But the performance

of QPSK is better than BPSK for higher values of SNRand overall performance of code rate is better than

Fig.6: Performance of a BPSK modulation for withoutpadding Parameters: No. of FFT points = 256; Modulation= BPSK; Channel = AWGN, Tx elements=2 and Rxelement =2,coding rate=3/4.

Fig.7: Performance of a QPSK modulation for withoutpadding Parameters: No. of FFT points = 256; Modulation= QPSK; Channel = AWGN, Tx elements=2 and Rxelement =2,coding rate=3/4.

iii) The overall performance of BPSK for OFDM-MIMO(STC/MRC) system can improve for highervalues of FFT points but the performance of QPSKalmost remain constant .The overall performance for

both with coding ,without padding and with coding

,with padding1024 FFT points is better than 256 FFTpoints in case of QPSK modulation as depicted inFig.4,5 andFig.8- Fig.12.

Fig.8: Performance of a BPSK modulation for withoutpadding Parameters: No. of FFT points = 1024;Modulation = BPSK; Channel = AWGN, Tx elements=2andRx element =2.

Fig.9: Performance of a QPSK modulation for withoutpadding Parameters: No. of FFT points =256; Modulation= QPSK; Channel = AWGN, Tx elements=2 and Rxelement=2.

Fig.10: Performance of a QPSK modulation for withoutpadding Parameters: No. of FFT points = 1024;Modulation = QPSK; Channel = AWGN, Tx elements=2andRx element =2.



6/7

127

Fig.11: Performance of a QPSK modulation for withoutpadding Parameters: No. of FFT points = 1024;Modulation = QPSK; Channel = AWGN, Tx elements=2andRx element =2,Coderate =1/2.

Fig.12: Performance of a QPSK modulation for with

padding Parameters: No. of FFT points = 1024;Modulation= QPSK; Channel=AWGN,Tx elements=2andRx element =2,Coderate =1/2.

iv) If the TX elements are more than the receiverelements then overall performance of the systemsignificantly decreasesas showninfig.4andFig.13.

Fig.13: Performance of a BPSK modulation forwithoutpadding Parameters: No. of FFT points = 256;Modulation = BPSK; Channel = AWGN, Tx elements=4andRxelement=2.

V. CONCLUSION

The performance of the proposed OFDM-MIMO(STC/MRC) system for different antenna configurationsandpropagationconditions wasanalyzedbased on ourLabmodel. It has found that OFDM-MIMO system with

MRC/STC coding can get potentially higher spectralefficiency because no orthogonal transmitted signals andreceived co-channel signals are separatedby decorrelation(processing algorithm) due to multipath. It is understoodthat both MIMO technology and wider bandwidthchannels will be required to reliably satisfy the higherthroughput demands of next generation applications. Theresult shows that proposed system fare capable ofimproving bit rate and maximizing throughput efficiencywithout increasing total transmit power or required

bandwidthwithSTC/MRCprocessingat the receiver .

REFERENCES

[1] Y. Li and N. R. Sollenberger, Adaptive Antenna Arrays for OFDMsystems with Co-Channel Interference, IEEE Trans.Communications,vol. 47,no. 2,pp.217-229, February1999.

[2] G. J. Foschini, Layered space-time architecture for wirelesscommunication in a fading environment when using multi-elementantennas, Bell Labs.Tech. Journal, Vol. 1, No.2, autumn 1996, pp41-59.

[3] G. J. Foschini and M. J. Gans, On limits of wirelesscommunications in a fading environment when using multipleantennas, Wireless Personal Communications, Vol. 6, No. 3,March1998,pp 311-335.

[4] M. Jankiraman, Space time Codes andMIMO systems, publishedbArtechHouse,2004.

[5] B.Vucetic& J.Yuan, 'SpaceTimeCoding', publishedby John Wiley&SonsInc.,2003.

[6] A. J. Paulraj and T. Kailath, Increasing capacity in wirelessbroadcast systems using distributed transmission/d irectionalreception,"U. S. Patent, no.5,345,599,1994

[7] G.G. Raleighand J.M. Cioffi, Spatio-temporalcoding forwirelesscommunication," IEEE Trans. Commun., vol. 46, no. 3, pp. 357-366,1998.

[8] H. B olcskei, D. Gesbert, and A. J. Paulraj, On the capacity ofOFDM-based spatial multiplexing systems," IEEE Trans.Commun.,vol. 50,no. 2,pp.225-234, Feb.2002.

[9] I.E. Telatar, Capacity of multi-antenna Gaussian channels, Eur.Trans.Telecomm,vol.10, no.6, pp.585595, 1999.

[10] H.BolcskeiandA. J. Paulraj,The Communications Handbook, 2nded. CRC Press, 2002, Multiple-input multiple-output (MIMO)Wirelesssystems,pp. 90.1 90.14.

[11] W. W. Lu, Defining China's Fourth Generation Mobilecommunications, ITU Telecom World, Hong Kong, December2006.

[12] Beyond 3G / 4G RadioAccess Technologies (RATs) and StandardsRoadmaps, e-Mobility Technology Platform Whitepaper by DidierBourseAND RahimTafazolliin December2007.

[13] www.calm.hu

[14] Abdul Aziz, M.K., Fletcher, P.N. and Nix, A.R., 'Performanceanalysis of IEEE802.11n solutionscombining MIMOarchitectureswith iterative decoding and sub-optimal ML detection via MMSEandZero forcing GISsolutions', WCNC,March 2004.

[15] Bonek, E., zcelik, H.O., Herdin, M., Weichselberger, W. andWallace, J., Deficiencies of a popular stochastic MIMO radiochannel model, International Symposium on Wireless PersonalMultimedia Communications, WPMC, Yokosuka, Japan, October,2003.

[16] Doufexi,A.,Armour, S.,Butler,M.,Nix,A. andBull,D.,'AStudyof



7/7

128

the Performance of HIPERLAN/2 and IEEE 802.11a PhysicalLayers',VTC Spring,May, 2001.

[17] Kermoal, J., Schumacher, L., Pedersen, K., Mogensen, P. andFrederiksen, F., A stochastic MIMO radio channel model withexperimental validation, IEEE Journal on Selected Areas inCommunications, vol.20, pp.12111226,Aug.2002.

[18] Draft 802.11n Revealed: Part 1 - The Real Story on Throughput vs.Range by Tim Higgins at http://www. tomsnetworking.com/2006/06/01/draft_11n_revealed_part1/index.html.

[19]IEEE P802.11n/D1.0, March, 2006.

Prof. Nirmalendu Bikas Sinhareceived the B.Sc (Honours inPhysics), B. Tech, M. Tech degreesin Radio-Physics and Electronicsf rom C.U, Calcutta , India ,i n 1 9 9 6 , 1 9 9 9 a n d 2 0 0 1 ,respectively.

Heiscurrentlyworking towards thePh.Ddegree with the specialization

of Wireless Communication and RADAR. Since 2003,he has been associated with the C.E.M.K ,W.B, India,where he is currently an Asst.Professor is with thedepartment ofECE & EIE.Hiscurrent research Interestsare in the area of Microwave /Millimeter wave basedBroadband Wireless Mobile/4G Communication,semiconductor Devices, Remote Sensing, Digital RadarandRCSImaging.

He has published large number of papers in differentinternational Conference, proceedings and journals.Heis presently the editor and reviewers in different

international journals.

M a k a r C h a n d Sn a i ispu rs uing B. Tech in th eDepartment of Electronics &Communication Engineeringat College of Engineering andManagement, Kolaghat ,under WBUT in 2011, WestBengal, India. His areas ofinterest are in Microwave/Mil l imeter wave basedBroadband Wireless Mobile

Communication and digital electronics. He has

published some papers in different internationaljournals.

Dr. Monojit Mitr a is an Asst.Professor in the Department of E.T. C.of BESU, Shibpur. He obtained hisB.Tech, M.Tech& Ph.D .degrees fromC.U. His research areas are in the fieldof Microwave & Microelectronics,especially in the fabrication of highfrequency solid state devices likeIMPATT. He has published large

number of papers in different national and internationaljournals. He has handled sponsored research projects ofDOE andDRDO.


per formance enhancement of mimo-ofdm technology for high data rate wireless networks

Documents