Koçak, T

Morris, KA

Woodward, G

Xu, R

English

Various techniques, such as bidirectional search, have been employed in sequential decoding to reduce the decoding delay. In this paper, a idirectional Fano algorithm (BFA) is proposed, in which a forward decoder (FD) and a backward decoder (BD) search in the opposite direction simultaneously. It is shown that the proposed BFA can reduce the average decoding delay by at least 50% compared to the unidirectional Fano algorithm (UFA). Due to the reduction in the variability of the computational effort by using bidirectional search, there is even higher decoding throughput improvement at low signal-to-noise ratio (SNR). For example at Eb/No=3dB, there is 300% throughput improvement by using the BFA decoding compared to the conventional UFA decoding. The proposed BFA decoding technique can be employed in very high throughput wireless communication systems with low hardware complexity and power consumption.Various techniques, such as bidirectional search, have been employed in sequential decoding to reduce the decoding delay. In this paper, a bidirectional Fano algorithm (BFA) is proposed, in which a forward decoder (FD) and a backward decoder (BD) search in the opposite direction simultaneously. It is shown that the proposed BFA can reduce the average decoding delay by at least 50% compared to the unidirectional Fano algorithm (UFA). Due to the reduction in the variability of the computational effort by using bidirectional search, there is even higher decoding throughput improvement at low signal-to-noise-ratio (SNR). For example at Eb/No=3dB, there is 300% throughput improvement by using the BFA decoding compared to the conventional UFA decoding. The proposed BFA decoding technique can be employed in very high throughput wireless communication systems with low hardware complexity and power consumption

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                          Xu, R., Koçak, T., Woodward, G., & Morris, K. A. (2009). Bidirectionalfano algorithm for high throughput sequential decoding. In IEEE 20thPersonal, Indoor and Mobile Radio Communication Conference 2009(PIMRC2009), Tokyo, Japan. (pp. 1809 - 1813). Institute of Electrical andElectronics Engineers (IEEE). 10.1109/PIMRC.2009.5450140Link to published version (if available):10.1109/PIMRC.2009.5450140Link to publication record in Explore Bristol ResearchPDF-documentUniversity of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only the publishedversion using the reference above. Full terms of use are available:http://www.bristol.ac.uk/pure/about/ebr-terms.htmlTake down policyExplore Bristol Research is a digital archive and the intention is that deposited content should not beremoved. However, if you believe that this version of the work breaches copyright law please contactopen-access@bristol.ac.uk and include the following information in your message:• Your contact details• Bibliographic details for the item, including a URL• An outline of the nature of the complaintOn receipt of your message the Open Access Team will immediately investigate your claim, make aninitial judgement of the validity of the claim and, where appropriate, withdraw the item in questionfrom public view.Centre for Communications ResearchBidirectional Fano Algorithm for High Throughput Sequential DecodingRan Xu*, Taskin Kocak*, Graeme Woodward†, Kevin Morris* and Craig Dolwin†*Centre for Communications Research, Merchant Venturers Building, University of Bristol, Bristol, UK†Toshiba Research Europe Limited, Telecommunications Research Laboratory, Queens Square, Bristol, UKAbstract IntroductionØIn this paper, a bidirectional Fano algorithm (BFA) is proposed, in which a forward decoder (FD) and a backward decoder (BD) search in the opposite direction simultaneously.ØIt is shown that the proposed BFA can reduce the average decoding delay by at least 50% compared to the unidirectional Fano algorithm (UFA). Due to the reduction in the variability of computational effort by using bidirectional search, there is even higher decoding throughput improvement at low signal-to-noise-ratio (SNR). For example at Eb/No=3dB, there is 300% throughput improvement by using the BFA decoding compared to the conventional UFA decoding.ØThe proposed BFA decoding technique can be employed in very high throughput wireless communication systems with low hardware complexity and power consumption.ØThere is a forward decoder (FD) and a backward decoder (BD) in the bidirectional Fano algorithm. Both of them start decoding from the known state zero and perform decoding in the forward and backward direction in parallel. The decoding will finish if the FD and the BD merge somewhere in the code tree. Otherwise, if the FD and the BD cannot merge, the decoding will finish when either of them reaches the other end of the code tree in its own direction.ØBoth of the FD and the BD decode the same codeword in the opposite direction according to the flow chart in Fig. 3, which is similar to the conventional unidirectional Fano algorithm (UFA)[1][2], except that a merging check is carried out after a forward movement is made.≥≥( )?FD BD FDS P L K l== + −( )?BD FD BDS P L K l== + −≤Figure 1. Illustration of bidirectional Fano decoding,where L is the information length and K is theconstraint length of the convolutional codeFigure 2. Illustration of the more rigorous mergingcheck in the proposed BFA, in which there are morethan one merged states and the overlapped lengthshould be not less than 1Figure 3. Flow chart of the FD or the BD with a bidirectionalFano algorithmcentre forcommunicationsresearchccrResults ConclusionsReferences20 40 60 80 100 120 140 160 180 20000.0050.010.0150.020.025Merging depthProbability of mergingMerging depth distribution  3dB4dB5dB6dB3 3.5 4 4.5 5 5.5 610-610-510-410-310-210-1Eb/No(dB)BERBER comparison between BFA, UFA and VA  BFAUFAVA10210310410510610-410-310-210-1100Prob(C>X)Total NoIPareto distribution at Eb/No=4.1dB  BFAUFAVABFAUFAVA3 4 5 60%  50% 100%150%200%250%300%Eb/No(dB)Throughput improvementThroughput improvement by using the BFA  Merged states=1Merged states=5Merged states=103 3.5 4 4.5 5 5.5 610-610-510-410-310-210-1Eb/No(dB)BERBER performance improvement by using more rigorous merging check  Merged states=1Merged states=5Merged states=10VAØSimulation setup-Code rate is R=1/3-Generator polynomials are g0={133}8, g1={171}8 and g2={165}8-Constraint length is K=7-Threshold increment value in the Fano algorithm is ∆=2-Metric calculation is based on the Fano metric which is considered to be optimal for sequential decoding-Output of the demodulator is 1-bit hard decision-Modulation is BPSK-AWGN channelØIn this paper, a bidirectional Fano decoding algorithm for convolutional codes was proposed.ØThe proposed BFA can reduce the decoding delay by applying a forward decoder and a backward decoder to search in the opposite direction simultaneously. The average decoding delay can be reduced by at least 50% compared to the unidirectional Fano decoding and there is higher throughput improvement at low SNR.ØMore rigorous merging check condition can be applied to make a trade-off between error rate performance and decoding throughput.ØAlternative decoding techniques for convolutional codes are of interest in high throughput systems due to the high power consumption and large silicon area of Viterbi decoders. The proposed bidirectional Fano decoding technique is very attractive for high throughput wireless communication systems, such as the WirelessHD system[3][4], due to its low hardware complexity, low power consumption and ability to decode very long constraint length convolutional codes[5][6].[1] S. Lin and D. J. Costello, Jr., Error Control Coding: Fundamentals and Applications. Englewood Cliffs, NJ: Prentice-Hall, 1983.[2] R. M. Fano, “A heuristic discussion of probabilistic decoding,” IEEE Transactions on Information Theory, vol. IT-9, no. 2, pp. 64-74, Apr. 1963.[3] “Wireless High-Definition (WirelessHD)”; http://www. wirelesshd.org/[4] H. Singh, J. Oh, C. Kweon, X. Qin, H.-R. Shao and C.Ngo. “A 60 GHz wireless network for enabling uncompressed video communication,” IEEE Communications Magazine, vol. 46, no. 12, pp. 71-78, 2008.[5] R. O. Ozdag and P. A. Beerel, “An asynchronous low-power high-performance sequential decoder implemented with QDI templates,” IEEE Transactions on Very Large Scale Integration (VLSI) Systems, vol. 14, no. 9, pp. 975-985, Sep. 2006.[6] M. Benaissa and Y. Zhu, “Reconfigurable hardware architectures for sequential and hybrid decoding,” IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 54, no. 3, pp. 555-565, Mar. 2007.Figure 4. Merging depth distribution of theBFAFigure 5. BER performance comparisonbetween the VA, the UFA and the BFAFigure 6. Pareto distribution of the BFA,the UFA and the VAFigure 7. Throughput improvement by using theBFA with respect to the UFA for differentnumber of merged statesFigure 8. BER performance improvementby using more rigorous merging check

A heuristic discussion of probabilistic decoding,”

An asynchronous low-power high-performance sequential decoder implemented with QDI templates,”

Error Control Coding: Fundamentals and Applications. Englewood Cliffs,

Reconfigurable hardware architectures for sequential and hybrid decoding,” IEEE Transactions on Circuits and Systems I: Regular Papers,

Shao and C.Ngo. “A 60 GHz wireless network for enabling uncompressed video communication,”

Bidirectional fano algorithm for high throughput sequential decoding

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Bidirectional Fano algorithm for high throughput sequential decoding

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Bidirectional fano algorithm for high throughput sequential decoding

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