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Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-7599-4367
2011 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 10, no 7, 2069-2074 p.Article in journal (Refereed) Published
Abstract [en]

We consider the optimization of power in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes when the maximum number of(re)transmissions is fixed. We formulate two optimization problems:(i) minimizing the packet drop probability (PDP) undera total average transmit power constraint, and (ii) minimizingthe average transmit power under a fixed PDP constraint.We consider in detail the special case of only two allowed transmissions, and we prove that the two optimization problems are equivalent. For this special case, we also provide a sub-optimal root- finding solution and compare its performance with the optimal solution obtained through an exhaustive search.The results show that the optimal power allocation can provide significant gains over the equal power solution in terms of average transmit power spent. The performance of the proposed root-finding solution is practically the same as that of the optimal solution.

Place, publisher, year, edition, pages
IEEE , 2011. Vol. 10, no 7, 2069-2074 p.
Keyword [en]
Hybrid ARQ, incremental redundancy, optimal power allocation, outage probability.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-67132DOI: 10.1109/TWC.2011.041311.101978ISI: 000293685400010OAI: oai:DiVA.org:liu-67132DiVA: diva2:407596
Note
Funding Agencies|Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||ELLIIT||Knut and Alice Wallenberg Foundation||Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Improved Techniques for Retransmission and Relaying in Wireless Systems
Open this publication in new window or tab >>Improved Techniques for Retransmission and Relaying in Wireless Systems
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The last three decades have seen significant advances in the wireless communication field. As the data rates of wireless systems are increasing, the demand for mobile services also is increasing rapidly. Like other natural resources, radio spectrum suitable for mobile wireless communications is also limited. In order to keep up with this ever increasing demand, there is a requirement of new signal processing algorithms.

Diversity is a technique used in wireless systems to combat the effects of fading and thereby improve reliability of data transfer. There are many ways in which algorithms can exploit diversity in wireless channels. Hybrid-automatic repeat request (H-ARQ) schemes and relaying mechanisms are two such diversity extracting techniques. Even though these diversity achieving techniques have been well understood in theory, there are many ways in which one can optimize these techniques for specific application scenarios.In this thesis, we focus on improving the performance of retransmission schemes and relaying systems.

In the first part of the thesis, we improve the performance of H-ARQ schemes in the 3GPP- long term evolution (LTE) system by improving the performance of feedback signaling. We employ complex-field coding to extract the inherent frequency diversity available in the resources. Next, we provide a sub-optimal solution to the outage-optimal power allocation problem in incremental redundancy based H-ARQ system, whose performance is practically the same as that of the optimal solution.

In the later part of the thesis, we propose a retransmission scheme based on superposition coding (SPC) for the symmetric relaying scenario. We provide packet error probability (PEP) expressions and solutions for the optimal fraction of power allocated for the partners' data. Finally, we study the optimal bits-to-symbol mappings for SPC and its effect on an H-ARQ scheme and the symmetric relaying scenario using SPC.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 19 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1494
Keyword
Hybrid-ARQ, relaying schemes, superposition coding, 3GPP- LTE
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68289 (URN)978-91-7393-144-1 (ISBN)
Presentation
2011-06-17, Visionen, Hus B, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2011-05-27 Created: 2011-05-17 Last updated: 2016-08-31Bibliographically approved
2. HARQ Systems: Resource Allocation, Feedback Error Protection, and Bits-to-Symbol Mappings
Open this publication in new window or tab >>HARQ Systems: Resource Allocation, Feedback Error Protection, and Bits-to-Symbol Mappings
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reliability of data transmission is a fundamental problem in wireless communications. Fading in wireless channels causes the signal strength to vary at the receiver and this results in loss of data packets. To improve the reliability, automatic repeat request (ARQ) schemes were introduced. However these ARQ schemes suffer from a reduction in the throughput. To address the throughput reduction, conventional ARQ schemes were combined with forward error correction (FEC) schemes to develop hybrid-ARQ (HARQ) schemes. For improving the reliability of data transmission, HARQ schemes are included in the present wireless standards like LTE, LTE-Advanced and WiMAX.

Conventional HARQ systems use the same transmission power and the same number of channel uses in different ARQ rounds. However this is not optimal in terms of minimizing the average transmit power or the average energy spent for successful transmission of a data packet. We address this issue in the first part of the dissertation, where we consider optimal resource allocation in HARQ systems with a limit on the maximum number of allowed transmissions for a data packet. Specifically, we consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint or equivalently minimizing the average transmit power under a fixed PDP constraint. We consider both incremental redundancy (IR)-based and Chase combining (CC)-based HARQ systems in our work. For an IR-HARQ system, for the special case of two allowed transmissions for each packet, we provide a solution for the optimal number of channel uses and the optimal power to be used in each ARQ round. For a CC-HARQ system, we solve the problem of optimal power allocation in i.i.d. Rayleigh fading channels as well as correlated Rayleigh fading channels. For the CC-HARQ case, we also provide a low complexity geometric programming (GP) solution using an approximation of the outage probability expression.

HARQ systems conventionally use one bit acknowledgement (ACK)/negative ACK (NACK) feedback from the receiver to the transmitter. In the 3GPP-LTE systems, one method for sending these HARQ acknowledgement bits is to jointly code them with the other control signaling information using a specified Reed-Muller code consisting of 20 coded bits. Even though the resources used for sending this control signaling information can inherently provide a diversity gain, the Reed-Muller code with such a short block size is not good at extracting all of the available diversity. To address this issue, in the second part of this dissertation, we propose two new methods: i) based on complex-field coding (CFC), and ii) using repetition across frequency bands, to extract the inherent diversity available in the channel resources and improve the error protection for the HARQ acknowledgement bits along with the other control signaling information. In the second part of the dissertation, we also propose a new signal space diversity (SSD) scheme, which results in transmit signals having constant envelope (CE). The proposed CE-SSD scheme results in a better overall power efficiency due to the reduced back-off requirements on the radio frequency power amplifier. Moreover, the proposed CE-SSD technique can be useful for application scenarios involving transmission of small number of information bits, such as in the case of control signaling information transmission.

In conventional HARQ systems, during the retransmission phase, the channel resources are exclusively used for the retransmitted data packet. This is not optimal in terms of efficient resource utilization. For efficient utilization of channel resources during the retransmissions, a superposition coding (SPC) based HARQ scheme was proposed in the literature. In an SPC based HARQ system, an erroneous packet is transmitted together with a new data packet by superposition in the Euclidean space. In the final part of this dissertation, we study performance of different bits-to-symbol mappings for such an SPC based HARQ system.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 43 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1526
Keyword
HARQ Systems, Resource Allocation, Geometric Programming, 3GPP-LTE, PUCCH Format 2, Complex-field coding, Signal Space Diversity, Optimization, Superposition Coding
National Category
Communication Systems Telecommunications
Identifiers
urn:nbn:se:liu:diva-96021 (URN)978-91-7519-574-2 (print) (ISBN)
Public defence
2013-09-27, Visionen, Hus B, Campus Valla, Linköpings universitet, Linköping, 10:56 (English)
Opponent
Supervisors
Available from: 2013-09-11 Created: 2013-08-13 Last updated: 2016-08-31Bibliographically approved

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