OPTIMUM MEDIUM ACCESS TECHNIQUE FOR NEXT GENERATION WIRELESS SYSTEMS

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1 9 th Febuay. Vol. 3 No. 5 - JATIT & LLS. All ights eseved. ISSN: E-ISSN: OPTIMUM MEDIUM ACCESS TECHNIQUE FOR NEXT GENERATION WIRELESS SYSTEMS N.AMUTHA PRABHA, V.MANIANDAN VIT UNIVERSITY, Velloe, TamilNadu Coimbatoe Institute of Technology, Coimbatoe, TamilNadu namuthapabha@gmail.com, maniandan@cit.edu.in ABSTRACT This pape poposes a Multi-Code Multi-Caie CDMA, best suited fo multi-ate sevices using multicode schemes and multi-caie sevices used fo high ate tansmission as equied fo the Univesal Telecommunication Mobile Systems (UMTS) Long Tem Evolution (LTE). The system pefomance has been analyzed and evaluated by means of signal-to-noise plus intefeence atio and bit eo ate unde a selective fading channel. The thoughput of the system signifies moe supeio than the conventional CDMA, Multi-Code CDMA and Multi-Caie CDMA It has been widely adopted due to its high pefomance ate and low sensitive to impulse noise and multipath channels. eywods: Multi-Code Multi-Caie CDMA, Univesal Telecommunication Mobile Systems, Long Tem Evolution, Multiple Access Intefeence.. INTRODUCTION In mobile wieless communications, system pefomance is seveely degaded due to apidly time-vaiant multipath fading. Taditional communication systems designed fo the wostcase channel conditions use a fixed lin magin to maintain acceptable pefomance when the channel quality is poo. The tansmitte and the eceive ae not optimized fo the cuent channel condition. As a esult, thee is a need to ceate new tansmission techniques that can efficiently utilize the capacity of the multipath fading channel encounteed in mobile communications. This poposed system povides highe pefomance, obustness to selective fading channel model and moe pominent in handling multiple data ates. The system pefomance in diffeent fading channel was analyzed in [] fo Multi-Code CDMA and in [] about Mutli-Caie CDMA. With a single caie in a fading channel about Multi-Code Multi-Caie was investigated in liteatue. System pefomance impovement of Mutli-Caie system using divesity techniques was discussed in [5].. SYSTEM MODEL The poposed MC-MC-CDMA system consists of the multi-code pat and the multi-caie pat. The multi-code pat convets seial input data into paallel sub steams, speads each paallel sub steam with othogonal codes to poduce code division multiplexed bits. And, now all the sub steams ae summed to poduce a supe-steam B (t) []. In the multi-caie section, the supesteam is Seial-to-Paallel (S/P) conveted again, spead with a use specified Pseudo-andom Noise (PN) sequence, and modulated with othogonal i q caies. The data d d jd has duation T and symbol ate RM/T, assuming R codes and M caies, whee d i (t) and d q (t) epesent the in-phase (I) and quadatue (Q) data symbols espectively, whee subscipt denote the th use. If the system is BPS modulated, only the in-phase data symbol is pesent. Afte S/P convesion and othogonal code modulation the esulting output is B R ( t ) d ( t ) a ( t ) (.) Whee d (t) is an input sub steam and a is an othogonal code set fo the th sub steam given by 79

2 9 th Febuay. Vol. 3 No. 5 - JATIT & LLS. All ights eseved. ISSN: E-ISSN: Na n n a ( t ) a P T N ( t nt N a) (.) Whee N a is the code length of the othogonal codes, TNa is the chip duation, a n is the n th value of a, with chip ate/t Na M Na / T. In ode to maintain othogonality, the maximum T numbe of the sub steams is limited to 3. PERFORMANCE ANALYSIS a N a M T N a The analytical famewo is fomulated and system pefomance is evaluated by means of signal-to-noise plus intefeence atio and bit eo ate unde a slowly fading channel [, ]. In ode to calculate the vaiance of the noise and intefeence tems, we assume that all tems ae zeo mean, statistically independent andom vaiables. We examine the SNIR and the BER pefomance of MC/MC-CDMA system compaed to the conventional CDMA, the Multi- Code CDMA, and the Multi-Caie CDMA 3. SNIR Pefomance Analysis Hee we assume that all tems ae zeo mean statistically independent andom vaiables. We find the value of Multipath Intefeence, Inte-Sub steam Intefeence, Inte Caie Intefeence, Multi-Use Intefeence and AWGN. Total intefeence and noise vaiance ae obtained. Numbe of multi path, Numbe of sub steams, Numbe of caies, Numbe of uses, Local mean powe and Multipath decay facto ae chosen 3. BER Pefomance Analysis BER of MC-MC-CDMA system with the existing systems was compaed. Pefomance of MC-MC-CDMA is expected to be supeio to any othe conventional system. 3.3 Compaisons with othe Appoaches CDMA s Rate Detemination Algoithm (RDA) is designed to select Rate (9. bps) fo speech and Rate / (. bps) fo non-speech. Unfotunately, impaiments such as bacgound noise and acoustic echo ae often misintepeted by the RDA as voice, consuming unnecessay netwo bandwidth [].When deployed, Ditech s CDMA Capacity solution pevents noise and acoustic echo fom enteing the RDA, educing the aveage fowad-lin data ate geneated by the vocode by an aveage of % in noisy conditions. The powe consumption of a minimum mean squae eo (MMSE) multicaie CDMA eceive implemented in digital hadwae is consideed in []. Simulations using data consistent with typical pefomance of a multi-caie CDMA eceive indicate that the bloc based appoach can poduce a powe eduction of aound 5%. The pefomance enhancement due to such nea optimal ate and powe adaptation deceases with divesity ode with incease in capacity. In ou appoach the bit eo ate of the system is analytically deived in fequency selective fading, with Gaussian noise and multiple access intefeence. The esults show that the poposed MC-MC-CDMA system clealy outpefoms both single-code multi-caie CDMA (MC-CDMA) and single-caie multi-code CDMA in a fixed bandwidth allocation. This indicates that MC- MC-CDMA should be seiously consideed fo next geneation cellula 3.3. Pefomance degadation due to multiple access intefeence CDMA tansmittes shae the same channel. Timing, fequency and phasing of all the uses ae identical. The mean squae of the cosscoelation between the diffeent speading codes=/q whee thee ae Q chips pe peiod T. The SINR seen by the modem includes both the eceive noise and multiple access intefeence. The degadation depends upon the opeating E b /N o, the numbe of uses and the speading facto Q. Degadation (db) Pefomance degadation due to multiple access intefeence /q=.5 /q=.5 /q=.75 /q= Eb/No (db) Figue.3. Pefomance degadation due to multiple access intefeence

3 9 th Febuay. Vol. 3 No. 5 - JATIT & LLS. All ights eseved. ISSN: E-ISSN: Powe contol In conventional systems, tansmittes that euse the same channel ae sepaated such that thei mutual intefeence is sufficiently attenuated. In MC/MC CDMA system, the intent is to euse the same fequency channel within the same aea. The SINR of the fist use is given by SINR Whee, D ' g y Y E (3.) N E (3.) E Q b b Eb ' D (3.3) g N E b Q N (3.) The tem Eb / N in Eq. (3.3) is the SNR in the absence of multiple access intefeence. The facto D g is the degadation due to multiple access intefeence. Compaing D g with D g we see that the eceived enegy fo the desied signal is now α E b instead of E b. The othe, moe impotant, diffeence is that the denominato D g includes the facto (3.5) The tem in Eq. (3.5) is a multiplie applied to the multiple access intefeence. If all tansmitted signals ae eceived with equal powe, then this tem is unity. Howeve, if any of the signal stengths is significantly geate than the desied signal (i.e., α >> α ), then thee will be a significant incease in the multiple access intefeence. This phenomenon is nown as the nea fa poblem. That is, signals coming fom the tansmittes significantly close to the eceive can cause excessive intefeence with the desied signal. To illustate the poblem, we plot the degadation in pefomance with CDMA fo = uses in Figue. 3.. One solution to the nea-fa poblem is powe contol, in which each use s tansmitted powe is adjusted individually such that the eceived powe α E b is constant and thus independent of. Powe contol impoves intefeence management significantly. We plot the degadation in pefomance with CDMA fo the case of = uses. The degadation of the fist use is plotted against elative powe of the second use. Pefomance degadation of fist of two uses as a function of elative powe and pocessing gain 5 Eb/No= db Eb/No=3 db Eb/No= db Eb/No=9 db Degadation (db) a/a (db) Figue. 3. Pefomance degadation of fist of two uses as a function of elative powe and pocessing gain Degadation due to multiple access intefeence with & without FEC We plot the degadation in pefomance with CDMA fo diffeent values of /Q and is plotted against the loading /Q fo uncoded situation and calculated fo diffeent values of E b /N. Degadation (db) Degadation due to multiple access intefeence with & without FEC uncoded coded Loading (/Q) Figue.3.3 Degadation due to multiple access intefeence with & without FEC 3.3. MC-MC CDMA in cellula envionment One of the advantages of CDMA is that intefeence caused by anothe CDMA signal appeas to be appoximately equivalent to additive white Gaussian noise. This popety is used advantageously in cellula The multiple

4 9 th Febuay. Vol. 3 No. 5 - JATIT & LLS. All ights eseved. ISSN: E-ISSN: access intefeence (MAI) is diectly popotional to the channel loading. Fo a constant SINR, moving fom a noise limited system (Io/No= db) to an intefeence limited system (Io/No= db) inceases the channel loading. Fo a constant SINR, inceasing othe cell intefeence educes the pemissible channel loading. Reducing the SINR equied by the eceive significantly impoves the pemissible channel loading. 9 7 Maximum channel loading as a function of the othe cell intefeence facto f and the atio of intefeence noise density to that of eceive I/No= db, f=.5 I/No= db, f=.5 I/No= db, f=. I/No= db, f=. SNIR SNIR pefomance mc/mc cdma system Eb/No Figue.. SNIR pefomance atio fo MC-MC CDMA SINR (db) 5.3 BER Pefomance Analysis fo diffeent systems Loading (/Q) Figue.3. Maximum channel loading as a function of the othe cell intefeence facto and the atio of intefeence noise density to that of the eceive.. RESULTS AND ANALYSIS Fo a given system, the bit eo atio will be affected by both the data tansmission ate and the signal powe magin. Compaison of the BER fo conventional CDMA, multi caie CDMA, multi code CDMA and multi-code multi-caie CDMA system was calculated. The BER is obtained by aveaging the conditional pobability of eo P e. Figue. clealy states, MC-MC-CDMA system has the lowest BER pefomance of all the systems compaed and found be supeio than the othes. Fo a compaison we assume vaiables lie delay ange, bandwidth, powe and bit ate to be same fo all the In the case of delay ange, we used the same channel with the same popagation delay fo all systems compaed, especially, when intefeence fom seveal elements ae consideed.. Simulation Paametes Numbe of multipath: 3 Numbe of substeam: Numbe of uses: 3 Bit Rate: 9. SNIR Pefomance Analysis The SNIR of MC/MC CDMA is compaed with othe systems fo the equied paametes. The figue. illustates the pefomance of a MC/MC CDMA system. The system has highe SNIR compaed to multi code o multi caie CDMA BER - - Bit eo ate pefomance fo diffeent systems -3 MC/MC CDMA system multi-code CDMA system multi-caie CDMA system spead spectum CDMA system Eb/No (db) Figue.. Bit eo ate pefomance fo diffeent systems. BER Pefomance vs. Numbe of uses The figue.3 shows the pefomance as a function of the numbe of uses. Inceasing deceases E b /N o, and inceases BER pefomance. MC/MC CDMA system can be used moe effectively by moe uses compaed to the othe

5 9 th Febuay. Vol. 3 No. 5 - JATIT & LLS. All ights eseved. ISSN: E-ISSN: bit eo ate BER pefomance Vs numbe of uses mc cdma mc/mc cdma numbe of uses Figue..3 BER pefomance vs. numbe of uses 5. CONCLUSION We have poposed a novel appoach to implement multi-code multi-caie CDMA system. The analytical fame-wo is fomulated and system pefomance was evaluated unde a slow fading channel and analyzes was made. The pefomance is compaed to Multi-Caie CDMA, Multi-Code CDMA and conventional CDMA system. In all pefomance measue, it was found that the poposed MC/MC CDMA povided supeio pefomance. This access technique illustates the efficiency, which is expected to get moe and moe significance in the next geneation wieless system. Extensive simulation studies wee pefomed unde vaious cases and fom the simulation esults we conclude that the pefomance of MC/MC CDMA system is supeio to conventional In addition, this shows that data ate flexibility can be achieved in a multi-caie CDMA system without any sacifice in pefomance. Also we see that the degadation is vey less even fo lage numbe of uses eeping the speading facto high. FEC coding impoves pefomance ove the case without coding by.7 db. Maximum channel loading as a function of the othe cell intefeence facto and the atio of the intefeence noise density to that of the eceive was obtained. slow fequency hopping communications, IEEE SPAWC 5, pp [3] Jin Woo Lee, Oechuwu C. Ugweje and Chistian Madubata, Multi-Code Multi- Caie CDMA Systems fo G Wieless Communications, IEEE 5, pp. -. [] Taeyoon im, Jeffey G. Andews, Jaeweon im, and Theodoe S. Rappapot, Multicode Multicaie CDMA Pefomance Analysis IEEE Communications Society,, pp [5] D. Hsiung and J. Chang, Pefomance of multi-code CDMA in a multipath fading channei, IEE Commm. vol. 7, pp , Dec [] A. C. McComic, P. M. Gant, J. S. Thompson, T. Aslan and A. T. Edogan, A low powe MMSE eceive fo multi-caie CDMA [9] S. Manoha, V. Tiiya, R. Annavajjala, and A. Chocalingam, BER Analysis of Weighted Intefeence Cancellation in multi-caie DS- CDMA Systems, IEEE Communication Society,. REFERENCES: [] Alexanda Duel-Hallen, Ming Lei, Hans Hallen,(Mach ) Reliable adaptive modulation and intefeence mitigation in mobile adio slow fequency hopping channels, IEEE Tansaction on communication vol.5,pp [] Alexanda Duel-Hallen, Ming Lei, Hans Hallen,(June 5) Enabling adaptive modulation and intefeence mitigation fo 3