| 1. |
- Bohge, Mathias, et al.
(författare)
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Optimal Power Masking in Soft Frequency Reuse based OFDMA Networks
- 2009
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Konferensbidrag (refereegranskat)abstract
- Soft frequency reuse is a strong tool for co-channel interference mitigation in cellular OFDMAILTE networks. The performance of such networks significantly depends on the configuration of the power masks that implement the soft frequency reuse patterns. In this paper, we investigate the performance of different power mask configurations against the optimal case, in which a central entity optimally distributes power and resource blocks among the users of the network. It is shown that large differences exist between the performance of different mask types and the optimal case in both, the overall cell throughput, as well as the cell-edge user performance.
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| 2. |
- Bohge, Mathias, et al.
(författare)
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A New Optimization Model for Dynamic Power and Sub-Carrier Allocations in Packet-Centric OFDMA Cells
- 2007
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Ingår i: Frequenz. - : FACHVERLAG SCHIELE SCHON. - 0016-1136 .- 2191-6349. ; 61:1-2, s. 35-38
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that applying dynamic resource allocation to down-link transmissions of OFDMAsystems provides a significant performance increase, by taking advantage of diversity effects. In order toquantify the maximum possible gain achievable by applying dynamic mechanisms, several optimizationproblems have been suggested for studying a dynamic system's optimal behaviour. However, so far theseoptimization approaches do not take sophisticated system requirements into account, as there are differentpacket-arrival processes, buffering constraints, scheduling policies, as well as QoS requirements per serviceclass. In this paper we present a new optimization model that is based on a packet-centric system view andincludes the system requirements mentioned above. We compare the performance results of the conventionaland the new approach and study the impact of dynamic power allocation in both cases.
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| 3. |
- Bohge, Mathias, et al.
(författare)
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Dynamic Resource Allocation in OFDM Systems : An Overview of Cross-Layer Optimization Principles and Techniques
- 2007
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Ingår i: IEEE Network. - : IEEE Communications Society. - 0890-8044 .- 1558-156X. ; 21:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a lot of research effort has been spent on cross-layer system design. It has been shown that cross-layer mechanisms (i.e., policies) potentially provide significant performance gains for various systems. In this article we review several aspects of cross-layer system optimization regarding wireless OFDM systems. We discuss basic optimization models and present selected heuristic approaches realizing cross-layer policies by means of dynamic resource allocation. Two specific areas are treated separately: models and dynamic approaches for single transmitter/receiver pairs (i.e., a point-to-point communication scenario) as well as models and approaches for point-to-multipoint communication scenarios (e.g., the downlink of a wireless cell). This article provides basic knowledge in order to investigate future OFDM cross-layer-optimization issues.
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| 4. |
- Bohge, Mathias, et al.
(författare)
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Optimal Soft Frequency Reuse and Dynamic Sub-carrier Assignments in Cellular OFDMA Networks
- 2010
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Ingår i: European transactions on telecommunications. - : Wiley. - 1124-318X .- 2161-3915. ; 21:8, s. 704-713
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Tidskriftsartikel (refereegranskat)abstract
- Soft frequency reuse (SFR) is a common technique for co-channel interference (CCI) mitigation in cellular OFDMA networks. The performance of such networks significantly depends on the configuration of the power profiles that implement the soft frequency reuse patterns. In this paper, we investigate the performance of static soft frequency reuse by comparing it against the optimal case, in which a central entity optimally distributes power among the users of the network. It is shown that there is a significant performance gap between both approaches, which needs to be filled by adaptive SFR mechanisms. Moreover, we show that the achievable gain of static SFR is small in a system that is able to optimally decide on terminal/sub-carrier assignments.
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| 5. |
- Bohge, Mathias, et al.
(författare)
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The Potential of Dynamic Power and Sub-carrier Assignments in Multi-User OFDM-FDMA Cell
- 2005
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Ingår i: Global Telecommunications Conference, 2005. GLOBECOM '05. IEEE (Volume 5 ). - : IEEE conference proceedings. - 0780394143 ; , s. 2932-2936
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Konferensbidrag (refereegranskat)abstract
- OFDM systems are known to overcome the impairment of the wireless channel by splitting the given system bandwidth into parallel sub-carriers, on which data symbols can be transmitted simultaneously. This enables the possibility of enhancing the system's performance by deploying adaptive (dynamic) mechanisms, namely power and modulation adaption and dynamic sub-carrier assignments. In multi-user communication systems (OFDM-FDMA), these mechanisms can be used to achieve a level of system fairness ensuring that each terminal receives at least an environment-specific minimum amount of data per down-link phase. However, it has been doubted by multiple previous investigations that dynamic power adaption provides enough performance gain in order to be applied in such systems, as it increases the computational load significantly. In this study we discuss the performance gain due to the different approaches and show that in specific communication scenarios enabling a dynamic power distribution provides a significant performance increase compared to dynamic schemes without power adaption.
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| 6. |
- Bohge, Mathias, et al.
(författare)
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The use of guard bands to mitigate multiple access interference in the OFDMA uplink
- 2008
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Ingår i: Proceedings of the 13th International OFDM-Workshop (InOWo). ; , s. 75-79
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Konferensbidrag (refereegranskat)abstract
- The usual approach to mitigate multiple access interference (MAI) in the uplink of cellular OFDMA based systems is to use relatively large cyclic prefixes as time domain guard periods. In this paper, we suggest to use a combination of short time domain guard periods and frequency domain guard bands to protect against MAI instead. Guard bands can be added and removed as necessary and, thus, increase the MAI protection flexibility. We show that, if optimally applied, the use of guard bands can significantly increase the system’s uplink capacity or minimum capacity per user.
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| 7. |
- Willkomm, Daniel, et al.
(författare)
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Double Hopping : A new Approach for Dynamic Frequency Hopping in Cognitive Radio Networks
- 2008
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Ingår i: IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008. - : IEEE conference proceedings. - 9781424426447 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- One of the major challenges in designing cellular cognitive radio (CR) networks is the avoidance of secondary user (SU) interference to so called primary users (PUs) operating in the licensed bands. Usually, SU operation has to be interrupted periodically in order to detect PU activity and avoid the respective frequencies. Recently, dynamic frequency hopping (DFH) mechanisms have been suggested to enable reliable PU detection and continuous SU operation at the same time. Applying DFH in a multi-cell environment adds the challenge of mitigating co-channel interference (CCI). In this paper, we introduce a new DFH approach for cellular CR networks to allow reliable PU detection and continuous SU operation while avoiding CCI: double hopping (DH). We present a distributed frequency assignment heuristic for DH and compare it to the optimal assignment. We show that the performance of the sub-optimal distributed assignment is only slightly worse than the optimal performance, and, thus, outperforms existing distributed approaches by far.
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