| 1. |
- Uhlemann, Elisabeth
(författare)
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Adaptive Concatenated Coding for Wireless Real-Time Communications
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this thesis is to improve the performance of real-time communication overa wireless channel, by means of specifically tailored channel coding. The deadlinedependent coding (DDC) communication protocol presented here lets the timeliness and thereliability of the delivered information constitute quality of service (QoS) parametersrequested by the application. The values of these QoS parameters are transformed intoactions taken by the link layer protocol in terms of adaptive coding strategies.Incremental redundancy hybrid automatic repeat request (IR-HARQ) schemes usingrate compatible punctured codes are appealing since no repetition of previously transmittedbits is made. Typically, IR-HARQ schemes treat the packet lengths as fixed and maximizethe throughput by optimizing the puncturing pattern, i.e. the order in which the coded bitsare transmitted. In contrast, we define an IR strategy as the maximum number of allowedtransmissions and the number of code bits to include in each transmission. An approach isthen suggested to find the optimal IR strategy that maximizes the average code rate, i.e., theoptimal partitioning of n-kparity bits over at most M transmissions, assuming a givenpuncturing pattern. Concatenated coding used in IR-HARQ schemes provides a new arrayof possibilities for adaptability in terms of decoding complexity and communication timeversus reliability. Hence, critical reliability and timing constraints can be readily evaluatedas a function of available system resources. This in turn enables quantifiable QoS and thusnegotiable QoS. Multiple concatenated single parity check codes are chosen as examplecodes due to their very low decoding complexity. Specific puncturing patterns for thesecomponent codes are obtained using union bounds based on uniform interleavers. Thepuncturing pattern that has the best performance in terms of frame error rate (FER) at a lowsignal-to-noise ratio (SNR) is chosen. Further, using extrinsic information transfer (EXIT)analysis, rate compatible puncturing ratios for the constituent component code are found.The puncturing ratios are chosen to minimize the SNR required for convergence.The applications targeted in this thesis are not necessarily replacement of cables inexisting wired systems. Instead the motivation lies in the new services that wireless real-time communication enables. Hence, communication within and between cooperatingembedded systems is typically the focus. The resulting IR-HARQ-DDC protocol presentedhere is an efficient and fault tolerant link layer protocol foundation using adaptiveconcatenated coding intended specifically for wireless real-time communications.
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| 2. |
- Uhlemann, Elisabeth, et al.
(författare)
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Concatenated hybrid ARQ - a flexible scheme for wireless real-time communication
- 2002
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Ingår i: Eighth IEEE Real-Time and Embedded Technology and Applications Symposium. - Los Alamitos, Calif. : IEEE Computer Society Press. - 0769517390 ; , s. 35-44
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Konferensbidrag (refereegranskat)abstract
- The concept of deadline dependent coding (DDC) has previously been suggested by the authors for maximizing the probability of delivering the required information before a given deadline in a wireless communication system.. In this paper, these principles are further developed using concatenated codes with iterative decoding, providing a new level of flexibility and robustness for DDC protocols. The strategy of DDC is to combine different coding and decoding methods with automatic repeat request (ARQ) techniques in order to fulfill the application requirements within a wireless realtime communication system. These requirements are formulated as two quality of service (QoS) parameters: deadline (tDL) and probability of correct delivery before the deadline (Pd), leading to a probabilistic view of realtime communication. An application can negotiate these QoS parameters with the DDC protocol, thus creating a flexible and fault-tolerant scheme.
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| 3. |
- Uhlemann, Elisabeth, et al.
(författare)
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Deadline dependent coding-a framework for wireless real-time communication
- 2000
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Ingår i: Seventh International Conference on Real-Time Computing Systems and Applications. - Piscataway, NJ : IEEE. - 0769509304 ; , s. 135-142, s. 135-142
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Konferensbidrag (refereegranskat)abstract
- A framework for real-time communication over a wireless channel is proposed. The concept of deadline dependent coding (DDC), previously suggested by the authors, is further developed using soft decision decoding of block codes to maximize the probability of delivering information before a given deadline. The strategy of DDC is to combine different coding and decoding methods with automatic repeat request (ARQ) in order to fulfil the application requirements. These requirements are formulated as two Quality of Service (QoS) parameters: deadline (t_DL) and probability of correct delivery before the deadline (P_d), leading to a probabilistic view of real-time communication. An application can negotiate these QoS parameters with the DDC protocol, thus creating a flexible and dependable scheme.
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| 4. |
- Uhlemann, Elisabeth, et al.
(författare)
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Hybrid ARQ based on serially concatenated block codes using iterative detection for real-time communication
- 2002
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A protocol for real-time communication over a wireless channel, based on concatenated codes using iterative decoding is proposed. The concept of deadline dependent coding (DDC), previously suggested by the authors, to maximize the probability of delivering the information before a given deadline, is further developed to include concatenated codes. The strategy of DDC is to combine different coding and decoding methods with automatic repeat request (ARQ) in order to fulfill the application requirements. These requirements are formulated as two Quality of Service (QoS) parameters: deadline (t_DL) and probability of correct delivery before the deadline (P_d), leading to a probabilistic view of real-time communication. An application can negotiate these QoS parameters with the DDC protocol, thus creating a flexible and reliable scheme.
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| 5. |
- Uhlemann, Elisabeth
(författare)
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Hybrid ARQ Using Serially Concatenated Block Codes for Real-Time Communication : An Iterative Decoding Approach
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ongoing wireless communication evolution offers improvements for industrial applications where traditional wireline solutions causes prohibitive problems in terms of cost and feasibility. Many of these new wireless applications are packet oriented and time-critical. The deadline dependent coding (DDC) communication protocol presented here is explicitly intended for wireless real-time applications. The objective of the work described in this thesis is therefore to develop the foundation for an efficient and reliable real-time communication protocol for critical deadline dependent communication over unreliable wireless channels. Since the communication is packet oriented, block codes are suitable for error control. Reed-Solomon codes are chosen and incorporated in a concatenated coding scheme using iterative detection with trellis based decoding algorithms. Performance bounds are given for parallel and serially concatenated Reed-Solomon codes using BPSK. The convergence behavior of the iterative decoding process for serially concatenated block codes is examined and two different stopping criteria are employed based on the log-likelihood ratio of the information bits. The stopping criteria are also used as a retransmission criterion, incorporating the serially concatenated block codes in a type-I hybrid ARQ (HARQ) protocol. Different packet combining techniques specifically adapted to the concatenated HARQ (CHARQ) scheme are used. The extrinsic information used in the iterative decoding process is saved and used when decoding after a retransmission. This technique can be seen as turbo code combining or concatenated code combining and is shown to improve performance. Saving the extrinsic information may also be seen as a doping criterion yielding faster convergence. As such, the extrinsic information can be used in conjunction with traditional diversity combining schemes. The performance in terms of bit error rate and convergence speed is improved with only negligible additional complexity. Consequently, CHARQ based on serially concatenated block codes using iterative detection creates a flexible and reliable scheme capable of meeting specified required realtime constraints.
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| 6. |
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| 7. |
- Uhlemann, Elisabeth, et al.
(författare)
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Optimal Incremental-redundancy strategy for type-II hybrid ARQ
- 2003
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Ingår i: ISIT 2003 Yokohama. - Piscataway, N.J. : IEEE. - 0780377281 ; , s. 448-, s. 448-
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Konferensbidrag (refereegranskat)abstract
- Given a type-II hybrid ARQ scheme, we propose a general solution to find the optimal partitioning of n-k parity bits over at most M transmissions. The solution is in terms of maximizing the average code rate for a given puncturing pattern.
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| 8. |
- Uhlemann, Elisabeth, et al.
(författare)
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Optimal type-II concatenated hybrid ARQ using single parity check codes
- 2003
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Ingår i: Proc. International Symposium on Turbo Codes & Related Topics, Brest, France, September 2003. ; , s. 587-590
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Konferensbidrag (refereegranskat)abstract
- We consider an incremental redundancy (IR) type-II hybrid ARQ scheme based on multidimensional single parity check (SPC) product codes. Random interleaving is applied between dimensions, resulting in equivalent systematic, parallel or serially concatenated SPC codes. This enables larger interleavers and a larger range of overall code rates. The puncturing pattern used for IR transmissions of the concatenated SPC codes is chosen specifically to reduce decoder complexity for the hybrid ARQ scheme, activating only those constituent decoders for which parity bits have been received. Given the proposed puncturing pattern and a maximum number of allowable transmissions, an approach for determining the optimal number of parity bits per IR transmission in terms of maximizing the overall code rate, is suggested. With this strategy, each data frame is accepted following the transmission of a minimum number of parity bits.
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| 9. |
- Uhlemann, Elisabeth, et al.
(författare)
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Packet combining and doping in concatenated hybrid ARQ schemes using iterative decoding
- 2003
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Ingår i: The IEEE Wireless Communications and Networking, 2003. WCNC 2003. 2003 IEEE. - Piscataway, NJ : IEEE. - 0780377001 ; , s. 849-854
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Konferensbidrag (refereegranskat)abstract
- We consider serially concatenated block codes in a hybrid ARQ scheme using iterative decoding. The extrinsic information generated in the iterative decoding process is saved and used when a retransmission is decoded. Two different strategies are examined; one using the extrinsic information only in the very first iteration, whereas the other uses it in all subsequent iterations until another retransmission arrives. The latter can be seen as turbo or concatenated code combining whereas the former, where the extrinsic information is used only once may be seen as code doping, providing an alternative perspective. The strategy of saving the extrinsic information is also compared to traditional type-III, equal gain diversity combining. Using the extrinsic information from previous retransmission is shown to improve performance not only in terms of bit error rate but also in terms of throughput and convergence speed and requires only negligible additional decoder complexity. The performance of this strategy is however not as good as simple equal gain combining. As a consequence, the investigated schemes are not competitive alternatives, however, the code doping procedure can be used in conjunction with traditional diversity combining schemes, improving further on convergence speed.
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