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 หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : On Adjusting Vector Symbol Decoding for Many Different Nonbinary Convolutional Codes) ผู้เขียน: ดร.อุศนา ตัณฑุลเวศม์, รองศาสตราจารย์ ,  Chanothai Chaiwan สื่อสิ่งพิมพ์:pdf AbstractThe use of nonbinary convolutional codes with Vector Symbol Decoding (VSD) was proposed to correct long burst errors in high data rate wireless networks. VSD allows the symbol size to easily and arbitrarily increase as desired. Therefore, the same technique can be used for both the current data rate and any upcoming data rate of new wireless network standards. Convolutional VSD is more attractive than block VSD due to its lower complexity. Tables of convolutional codes with rate 2/3 and 3/4 are explicitly shown in the feedforward forms as required by VSD. The decoding performance was analyzed for several codes in an additive white Gaussian noise (AWGN) and a Rayleigh fading channel. The performance of VSD for different levels of decoder complexity was also tested. From the results, three design options that provide good performance were discussed including their advantages and disadvantages in terms of fl exibility, complexity and ease of implementation. |
หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Performance Investigation of Convolutional Vector Symbol Decoding with Larger than Two Choices and with Incomplete Second Choices) ผู้เขียน:ดร.อุศนา ตัณฑุลเวศม์, รองศาสตราจารย์, Auttaphud Seubnaung สื่อสิ่งพิมพ์:pdf AbstractVector Symbol Decoding (VSD) is a decoding technique for both block and convolutional nonbinary encoders. Convolutional VSD uses a convolutional encoder with nonbinary symbols at the encoder and VSD at the decoder. VSD can employ diversity quite easily to improve the performance and simplify the decoding because diversity provides alternative choices for the decoder. Previous work always assumed two complete choices for simplicity. This paper explores the performance of a convolutional VSD for the case of up to four complete choices and the case of two incomplete choices. The results showed that 1) although the second choice clearly improved the performance, the third and fourth choices do not provide ample improvement to justify the higher complexity of the hardware. 2) VSD can use incomplete second choices to improve performance. In summary, second choices should be applied whenever possible, but no more than two choices should be used. These results are very useful for hardware implementation. |
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หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Concatenated Reed-Solomon Inner and Convolutional Outer Codes for Mobile Channels with Soft Core Processor Implementation) ผู้เขียน:ดร.อุศนา ตัณฑุลเวศม์, รองศาสตราจารย์, วศิน สุขตลอดชีพ, จตุพล ท่นไชย สื่อสิ่งพิมพ์:pdf AbstractThe use of Reed-Solomon inner code in the Forney’s concatenated code structure was proposed to correct longer burst errors in high speed mobile communications without interleaving. Vector Symbol Decoding (VSD) was selected as the outer code decoding of the large sized outer symbols (greater than 100 bits per symbol). The complete concatenated coding system with VSD was analyzed for both Bose- Chaudhuri-Hocquenghem (BCH) and Reed-Solomon (RS) inner codes. The inner decoder for BCH was a combined list and soft Viterbi algorithm (VA) or a soft VA, while the inner decoder for RS was an algebraic decoder. Results were shown for the BCH inner only, the VSD only and for the complete system. In a Rician channel with a carrier frequency of 2.1 GHz at 80 km.hr-1 and a signal to noise ratio of 11 dB, the probability of decoding failure for the system with RS and hard decision was three magnitudes lower than the one with BCH and soft VA. For VSD only with no inner code, the larger sized symbols provided better performance in a burst error channel, while a smaller size was better in a random error channel. In addition, all the coding processes were implemented on a soft processor TSK 3000A and field programmable gate array boards to show that it was practical in terms of complexity. |