mai cancellation in an overloaded cdma system (2) (1)
TRANSCRIPT
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MULTIPLE ACCESS MULTIPLE ACCESS INTERFERENCE CANCELLATION INTERFERENCE CANCELLATION
IN AN OVERLOADED CDMA IN AN OVERLOADED CDMA SYSTEM SYSTEM
PROJECT GUIDE:
Mr G.Vairavel
71806106042 - Muthusathiyapriya.B
71806106047 - Nithia .D
71806106304 - Naghamanickam .N.J
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ABSTRACTABSTRACT
CDMA- To accommodate more number of users.
Overloading - to extend capacity limitation of multiple access techniques.
Two sets of orthogonal signal waveforms.
MAI- Inability to maintain complete orthogonality.
MAI CANCELLATION – using Weighted Linear Parallel Interference Canceller.
BER Performance comparison of WLPIC with CLPIC and MF Detector.
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INTRODUCTIONINTRODUCTION
FDMA – splitted into frequency bands and allocated to each user.
TDMA- full spectral occupancy but only for short duration of time.
CDMA- unique digital codes are used to differentiate subscribers.
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DRAWBACKS OF TDMA AND DRAWBACKS OF TDMA AND FDMAFDMA
Only one subscriber at a time.
Voice data –burst- takes much time.
Limits the capacity.
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ADVANTAGES OF CDMAADVANTAGES OF CDMA
No hard handoffNo guard timeLess fadingGreater capacityNo equalizer neededImproved security and privacyFewer dropped calls
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PROCESSING GAINPROCESSING GAIN
Processing gain - ratio of the spreading rate to the information rate.
Expressed in decibels (dB).
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PSEUDO SEQUENCESPSEUDO SEQUENCES
Noise like pseudo-random codes. Identification codes - balanced not to correlate to other
codes of itself. The most commonly used sequences
1. Maximal length sequences
2. Gold codes
3. Walsh codes
4. Hadamard codes Gold codes- better correlation property, more number of
codes can be generated.
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NEAR FAR EFFECTNEAR FAR EFFECT
Users close to the base station – stronger signal.
Cross correlation between 2 PN codes is not zero.
To combat this effect - Power control.
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SCRAMBLINGSCRAMBLING
To split the interference power evenly over the in-phase and quadrature components.
Two types
1.Periodic scrambling
2.Complex scrambling
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MULTIPLE ACCESS MULTIPLE ACCESS INTERFERENCE INTERFERENCE CANCELLATIONCANCELLATION
The most common interferences 1. Multiple Access Interference (MAI) 2. Inter Modulation Interference (IMI) Inter Modulation Interference - undesired combining
of several signals.
MAI- inability to maintain complete orthogonality Cancellation of MAI is done.
Using MATLAB 7.0.1.
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CANCELLATION METHODSCANCELLATION METHODS
1. Successive Interference Canceller
2. Parallel Interference Canceller
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SUCCESSIVE INTERFERENCE SUCCESSIVE INTERFERENCE CANCELLERCANCELLER
Order of subtractions given by the relative strength of the users.
Ranking the signal strengths.
Strongest signal is cancelled out first.
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PARALLEL INTERFERENCE PARALLEL INTERFERENCE CANCELLERCANCELLER
All the Interferences are cancelled parallely. Block diagram of PIC
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CANCELLATION METHODS CANCELLATION METHODS USING PICUSING PIC
Matched Filter Detector Conventional LPIC Weighted LPIC
Cancellation of MAI is done using WLPIC and it’s performance is compared with MF detector and CLPIC.
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MATCHED FILTER DETECTORMATCHED FILTER DETECTOR
MF- detect each user in parallel . The MF output of Kth user is given by
where A is the amplitude
b is the bit transmitted
ρ is the cross correlation coefficient
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MAI CANCELLATION USING MAI CANCELLATION USING CLPICCLPIC
Optimum weight is 1 for all the users. Estimate of MAI is subtracted from the received signal. The mth stage output of CLPIC is given by
Where
ρ is the cross correlation coefficient
y is the received signal
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MAI CANCELLATION USING MAI CANCELLATION USING WLPICWLPIC
MAI estimate is weighted by a factor before cancellation. Mth stage output of a desired user is given by,
where yk is the received signal
ρk is the cross correlation coefficient
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EXPRESSIONS TO OBTAIN EXPRESSIONS TO OBTAIN OPTIMUM WEIGHTSOPTIMUM WEIGHTS
Where Pk,opt is the optimum weight for the kth user A is the amplitude ρij is the cross correlation between ith and jth user
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SIMULATION RESULTSSIMULATION RESULTS
BER PERFORMANCE BER PERFORMANCE COMPARISONCOMPARISON
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USING RANDOMLY USING RANDOMLY GENERATED PN SEQUENCESGENERATED PN SEQUENCES
WITHOUT OVERLOADING
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Comparision of MF o/p of single Comparision of MF o/p of single user with multiuseruser with multiuser
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Comparison of MF o/p of single Comparison of MF o/p of single user with MF and CLPIC o/p of user with MF and CLPIC o/p of
multiusermultiuser
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Comparison of MF o/p of single Comparison of MF o/p of single user with MF and WLPIC o/p of user with MF and WLPIC o/p of
multiusermultiuser
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Comparison of MF o/p of single Comparison of MF o/p of single user with MF,CLPIC and WLPIC user with MF,CLPIC and WLPIC
o/p of multiusero/p of multiuser
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC without scrambling MF and WLPIC without scrambling
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC with scrambling MF and WLPIC with scrambling
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No.of users Vs BER – without Near-No.of users Vs BER – without Near-Far effectFar effect
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No. of users Vs BER – with Near-No. of users Vs BER – with Near-Far effectFar effect
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USING RANDOMLY USING RANDOMLY GENERATED PN SEQUENCESGENERATED PN SEQUENCES
WITH OVERLOADING
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC with scrambling MF and WLPIC with scrambling
and 50% overloading and 50% overloading
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC with scrambling MF and WLPIC with scrambling
and 75% overloading and 75% overloading
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USING GOLD CODES(Single USING GOLD CODES(Single set) AS PN SEQUENCESset) AS PN SEQUENCES
WITH OVERLOADING
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Comparision of BER performance Comparision of BER performance of MF and WLPIC with scrambling of MF and WLPIC with scrambling
and 50% overloading and 50% overloading
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USING GOLD CODES(2 sets) USING GOLD CODES(2 sets) AS PN SEQUENCESAS PN SEQUENCES
WITH OVERLOADING
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC without scrambling MF and WLPIC without scrambling
and with 50% overloadingand with 50% overloading
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC with scrambling MF and WLPIC with scrambling
and 50% overloading and 50% overloading
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Comparison of BER performance of Comparison of BER performance of MF and WLPIC with scrambling MF and WLPIC with scrambling
and 75% overloading and 75% overloading
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PERFORMANCE ANALYSISPERFORMANCE ANALYSIS
WLPIC performs better for two sets of gold codes.
WLPIC performs better than the MF Detector as well as CLPIC.
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CONCLUSIONCONCLUSION
WLPIC performs better than CLPIC and MF.
WLPIC performs better for two sets of gold codes.
Works well under near far as well as non near far conditions also.
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REFERENCESREFERENCES[1]Preetam Kumar and Saswat Chakrabarti ,”OCDMA/OCDMA overloading
scheme for cellular ds-cdma using orthogonal gold codes And Complex Scrambling ,” G S Sanyal School of Telecommunications ,IIT kharagpur,India,received on May 5,
2008 ;Revised and accepted on June 27,2008.
[2]V.Tikiya, S.Manohar and A.Chockalingam, “SIR Optimized Weighted Linear Parallel Interference Canceller on Fading Channels,“ IEEE transactions on wireless communications ,vol. 5,No. 8, August 2006 .
[3]F.Vanhaverbeke ,M.Moeneclaey and H.Sari ,”DS/CDMA with two sets of orthogonal sequences and Iterative-Detection ,“ IEEE Communication Lettters, vol.4 , pp.289-291,September 2000 .
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[4]Preetam Kumar and Saswat Chakrabarti,” Overloading Scheme for Cellular DS-CDMA using Quasi Orthogonal Sequences and Iterative Interference Cancellation Receiver”.
[5]K. Yang, Y. K. Kim, and P. V. Kumar, “Quasi-orthogonal sequences for code-division multiple-access systems,”IEEE Transactions on Information Theory, Vol. 46, pp.982–993, May 2000.
[6]Elmustafa Erwa and Jeffery Andrews,”Performance comparison of Successive and Parallel Interference Canceller”, Dec 9, 2003.
[7]John Proakis, “Digital Communications”.
[8]Theodore S. Rappaport, “Wireless Communications Principles and Practice”, second edition.