The concatenated code consists of an outer Reed-Solomon (RS) and an inner convolution code, and the coding and modulatio
IJRIT International Journal of Research in Information Technology, Volume 2, Issue 4, April 2014, Pg: 239- 243
International Journal of Research in Information Technology (IJRIT) www.ijrit.com
ISSN 2001-5569
Special Coding Techniques for Turbo and Trellis for UWB-IR Systems 1
2
Shabad Santosh Reddy1 and .S.Murugaveni2 M.Tech, Department of Telecommunication Engineering, SRM University, Kattankulathur – 603203, Chennai.
Project Guide, Assistant Professor, Department of Telecommunication Engineering, SRM University, Kattankulathur – 603203, Chennai. Email:
[email protected];
[email protected]
ABSTRACT- An efficient hybrid modulation scheme for a mixed phase-shift (PSK/PPM) for heterogeneous networks employing ultra wideband impulse radio (UWB-IR). The proposed scheme can support both coherent and non-coherent reception and is compatible with the IEEE 802.15.4a standard. Conventional hybrid modulation schemes for heterogeneous networks are generally constructed with a super-orthogonal coding (SOC) technique with which coherent receivers can get an additional performance improvement by encoding the phase bits. However, with the proposed modulation scheme, a coherent receiver can achieve performance improvement by displaying its best capability on phase detection. There are special coding techniques introduced in this paper such as turbo and trellis coding.
Index terms- UWB-IR, PPM, PSK, Turbo, Trellis. I.
INTRODUCTION
UWB-IR communication systems developed for wireless personal area networks (WPAN) offer great flexibility of performance, data rate, range, power and quality-of-service (QoS) by user preference. It is thus very desirable for UWBIR communication systems to enable heterogeneous network structures where users can flexibly choose the type of receiver such as a low-cost non-coherent energy detector (ED) and a high performance coherent rake receiver sufficient to achieve their specific requirements. Likewise, various hybrid modulation schemes are also required, which make non-coherent EDs and coherent rake receivers simultaneously receive the signal with their own best quality. To this end, PPM and PSK are generally employed to construct a hybrid modulation for the heterogeneous network including EDs and coherent receivers due to their simplicity and high-performance, respectively. However, when a coherent receiver operates with a hybrid PPM and PSK modulation (henceforth, HM-PPM/PSK), it cannot display its best performance on phase detection compared to when operating with the unitary PSK modulation. This is because the coherent receivers have no accurate knowledge on the locations or modulation slots of the received pulses due to the combined PPM signalling .Hence, the receivers need to use the averaged correlation outputs taken over all PPM modulation slots for phase detection, leading to performance decrease by an increased noise floor from the no-signal modulation slots. Therefore, in order to enhance the phase detection performance in coherent receivers, coding combined modulation schemes, especially with a SOC technique is used for heterogeneous networks. HM-PPM/PSK combined with SOC modulates the phase of the transmitted pulses with the encoded phase bits, so coherent receivers can get an additional coding gain by decoding the redundant phase bits. For instance, the IEEE 802.15.4a standard adopts a mixed binary PPM and binary PSK modulation combined with a systematically convolution coding (henceforth, SC-BPPM/BPSK) which is one of the SOC schemes. Non-coherent detectors are able to detect the PPM modulated data bits but not the PSK modulated parity ones, resulting from the
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application of a systematic convolution code, whereas coherent receivers can detect the entire encoded sequence including the phase sequence achieving a coding gain. However, the hardware and power consumption used in the maximum likelihood sequence detection (MLSD) for decoding the phase bits becomes a considerable burden for UWB-IR systems which are developed for low-power and low-cost communications. II.
METHODOLOGY
This signalling scheme for heterogeneous ultra wideband communications networks that contain both coherent (rake) and transmitted-reference (TR) receivers. While coherent receivers are capable of receiving TR signals, they do so with a 3 dB penalty, because they cannot make use of the energy invested into the reference pulse. We propose a new signalling scheme that avoids this drawback, by encoding redundant information on the reference pulse. The resulting scheme does not affect the operation of a TR receiver, while recovering the 3 dB penalty and furthermore providing an additional 1.7 dB coding gain to a coherent encoded binary scheme. This can be explained by interpreting the scheme as a trellis-coded modulation. We also provide an alternative implementation that can be viewed as a recursive systematic convolution encoder. Combining this version further with a simple forward error correction encoder results in a concatenated code that can be decoded iteratively, providing a bit-error rate of 10-3 at 2.8 dB signal-to-noise ratio in additive white Gaussian noise. The convergence behaviour of this iterative code is analyzed by using extrinsic information transfer charts. “AWGN performance of super-orthogonal convolution codes” The bit error rate performance of super orthogonal convolution codes is examined for the AWGN channel with an emphasis on graphical error rate curves. The little-noticed generalization of the class of super orthogonal codes that allows for more parameter combinations is examined and found to have error rate performance than is primarily a function of constraint length and not code rate. Symbol puncturing of the codes is also briefly examined An ultra-wide bandwidth time-hopping spread-spectrum code division multiple-access system employing a binary PPM signalling has been introduced by Schultz (1993), and its performance was obtained based on a Gaussian distribution assumption for the multiple-access interference. In this paper, we begin first by proposing to use a practical low-rate error correcting code in the system without any further required bandwidth expansion. We then present a more precise performance analysis of the system for both coded and encoded schemes. Our analysis shows that the Gaussian assumption is not accurate for predicting bit error rates at high data transmission rates for the encoded scheme. Furthermore, it indicates that the proposed coded scheme outperforms the encoded scheme significantly, or more importantly, at a given bit error rate, the coding scheme increases the number of users by a factor which is logarithmic in the number of pulses used in time-hopping spread-spectrum systems. “Performance analysis of the IEEE 802.15.4aUWB systems” The recently approved IEEE 802.15.4a standard defines an ultra-wideband (UWB) based physical layer using concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM) and direct-sequence spreading with time hopping. The concatenated code consists of an outer Reed-Solomon (RS) and an inner convolution code, and the coding and modulation are combined such that both coherent and non-coherent receiver architectures are supported. In this paper, the error-rate performance of IEEE 802.15.4a compliant UWB radios is investigated. To this end, semi-analytical expressions for the bit-error rate (BER) and frame-error rate (FER) of the coded UWB system are derived. The presented framework is comprehensive in that (i) different methods for generating reliability information (i.e., decoding metrics), (ii) the effects of suboptimal multipath combining, and (iii) coherent and non-coherent reception methods are included. Furthermore, a particularly suited errors-and-erasures RS decoding scheme is devised. The evaluation of the error-rate expressions together with simulation results for realistic UWB channels show that (i) the error-rate approximations are tight over wide ranges of BER and FER, (ii) symbol-wise metrics are clearly advantageous over bit-wise metrics for decoding of the convolution code, (iii) combining the 5 to 10 strongest multipath components approaches the performance of full combining within 1-2 dB for residential and 3-5 dB for outdoor UWB environments.
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III.
RESULTS
Fig 2. Trellis using QAM BER vs. SNR
Fig 1. Trellis using gain vs. SNR
Fig 3 . Trellis using PSK modulation gain vs. SNR
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Fig 4 Trellis with PSK Gain vs. SNR
Fig 5 Turbo using BER vs. SNR IV.
Conclusion
This paper shows the results using special coding techniques such as turbo and trellis coding and achieved BER using both techniques are below 2.0dB for both turbo as well trellis techniques. V. References [1] M. Yamashita, R. Sakai, A. Tanaka, K. Imada, Y. Takahashi, T. Ida, N.Matsumoto, and N. Kato, “Image super-resolution and multiple videoplayback on TV sets using cell processor,” IEEE International Symposium on Consumer Electronics (ISCE2009), pp. 305-306, May 2009. [2] W. T. Freeman, T. R. Jones, and E. C. Paztor, “Example based super resolution, ”IEEE Computer Graphics and Applications, Vol. 22, No. 2,pp. 56-65, March/April 2002. [3] J. Sun, N. N. Zheng, H. Tao, and H. Y. Shum, “Image hallucination with primalsketch priors,” IEEE Computer Society Conference on Computer Vision andPattern Recognition (CVPR2003), Vol. 2, pp. 729-736, June 2003.
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[4] H. Cang, D. Y. Y Oung, and Y. Xiong, “Super-resolution through neighbor embedding,” IEEE Computer Society Conference on Computer Vision and Pattern Recognition (CVPR2004), Vol. 1, pp. 275-282, July 2004. [5] W. T. Freeman, E. C. Pasztor, and O. T. Carmichael, “Learning low level vision,” International Journal of Computer Vision, Vol. 40, No. 1,pp. 25-47, November 2004. [6] S. Dai, M. Han, W. Xu, Y. Wu, and Y. Gong, “Soft edge smoothness prior for alpha channel super resolution,” IEEE Computer Vision and Pattern Recognition (CVPR2007), pp. 1-8, June 2007. [7] J. Yang, J. Wright, Y. Ma, and T. Huang, “Image super-resolution asperse representation of raw image patches,” IEEE Computer Vision and Pattern Recognition (CVPR2008), pp. 1-8, August 2008.
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