Adaptive OFDM for wideband radio channels

Czylwik, Andreas

doi:10.1109/glocom.1996.594454

Cited by 215 publications

(108 citation statements)

References 4 publications

(2 reference statements)

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“…Although the problem of optimal real-time subcarrier allocation has been extensively studied (see [4]- [14] and references therein), our work is philosophically different from most of literature: Often, in subcarrier allocation, an "instantaneous throughput" is maximized while assuming infinitely backlogged buffers; the algorithms are run periodically, to allow updates regarding channel variations and varying number of data streams. The problem with these techniques is that the scheduler fails to anticipate the impact of its allocation decision on the future state of the system.…”

Section: Introductionmentioning

confidence: 99%

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Resource Allocation in OFDMA with Time-Varying Channel and Bursty Arrivals

Javidi

2007

IEEE Commun. Lett.

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Abstract-This paper considers the issue of delay optimal subcarrier allocation in OFDMA wireless networks when the arrivals and channels are stochastic. Our objective is to minimize the longterm average packet delay over multiple time epochs. In previous studies, we have shown that the optimal policy is complicated and unknown. However, based on the insights learned from a simple On-Off channel model, we provide heuristic policies that use different degrees of channel and queue state information. More importantly, these examples show how the significance of queue vs. channel state information varies with the traffic load. This is of extreme practical interest when one considers the overhead associated with channel estimation and feedback.

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Section: Introductionmentioning

confidence: 99%

“…each subcarrier receives equal power) instead of the optimal power spectrum [4]. The channel gain h ij can be mapped to the number of packets per time slot, c ij , that subcarrier i can potentially transmit for user j as [4]:…”

Section: A Numerical Comparisons and Simulationmentioning

confidence: 99%

Resource Allocation in OFDMA with Time-Varying Channel and Bursty Arrivals

Javidi

2007

IEEE Commun. Lett.

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“…The choice of the target BER has obviously quite an impact, as a lower target BER leads to higher SNR switching points per modulation type (and therefore to a lower physical layer throughput). Refer to [21] for an detailed discussion of the performance difference between adaptive modulation and bit loading.…”

Section: Dynamic Single-user Ofdmmentioning

confidence: 99%

“…One particular simple but still very efficient dynamic scheme is adaptive modulation, where the transmit power per sub-carrier is fixed and only the modulation type per sub-carrier is varied according to the SNR. In fact, in [21] it has been shown that adapting the modulation while keeping the transmit power fixed provides a large performance boost which is only marginally improved by also adapting the transmit power.…”

Section: Introductionmentioning

confidence: 99%

Enhancing IEEE 802.11a/n with dynamic single-user OFDM adaptation

Gross

Emmelmann

Punal

et al. 2009

Performance Evaluation

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Earlier paper have demonstrated that the achievable throughput of OFDM systems can benefit significantly from individual modulation/transmit power selection on a per sub-carrier basis according to the actual gain of individual sub-carriers (so called dynamic OFDM scheme). Usage of such approach requires, however, providing support for additional functionalities like: acquisition of the sub-carrier gains, signaling of the used modulation types between sender and receiver, etc. Therefore dynamic OFDM is actively pursued for future radio interfaces, rather than considered as extension of existing OFDM based standards. In this paper we introduce a proposal how the widely accepted IEEE 802.11a/g systems as well as the emerging IEEE 802.11n system might be extended to support the dynamic OFDM in a single-user (point-to-point) setting. The presented approach guarantees backward compatibility to legacy devices. We address these issues by presenting a) a set of protocol modifications required to incorporate dynamic OFDM in 802.11a/g/n; and b) a performance evaluation of the suggested extension (referred further on to as single-user 802.11 DYN mode). Although 802.11n already includes advanced MAC and PHY features, i.e., frame aggregation and MIMO transmissions, our performance evaluation demonstrates that a further improvement is achievable by incorporating dynamic OFDM.

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“…Many researchers have studied the performance and have proposed possible solutions under imperfect CSI at the transmitter. Bit and power loading algorithms were pursued in [7][8][9][10][11][12][13][14], where partial CSI was utilized to adapt the constellation size and/or the power, adhering to a certain target bit error rate (BER) http://jwcn.eurasipjournals.com/content/2012/1/208 per subcarrier. However, the authors did not consider the effect of ICI.…”

Section: Introductionmentioning

confidence: 99%

Effect of power and rate adaptation on the spectral efficiency of MQAM/OFDM system under very fast fading channels

Dong

Fan

Panayırcı

et al. 2012

J Wireless Com Network

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In this article, the effect of power and rate adaptation on the spectral efficiency of orthogonal frequency division multiplexing (OFDM) systems using M-ary quadrature amplitude modulation (MQAM) is investigated in the presence of frequency selective and very rapidly time-varying fading channels, under power and instantaneous bit error rate (BER) constraints. Lower bounds on the maximum spectral efficiency of adaptive OFDM/MQAM systems with perfect and imperfect channel state information (CSI) are obtained, together with a closed-form expression for the average spectral efficiency of adaptive OFDM systems. The delay between the channel estimation and the actual transmission is also considered in this article. The theoretical and numerical results show that the adaptive MQAM/OFDM systems under fast fading channels have substantial gains in spectral efficiency over the non-adaptive counterparts with perfect CSI or moderate imperfect CSI. The theoretical and numerical results also show that a good way to deal with the delay CSI under very rapidly time-varying channels is to increase the subcarrier bandwidth of the OFDM system while ignoring the impact of the cyclic prefix.

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Adaptive OFDM for wideband radio channels

Cited by 215 publications

References 4 publications

Resource Allocation in OFDMA with Time-Varying Channel and Bursty Arrivals

Resource Allocation in OFDMA with Time-Varying Channel and Bursty Arrivals

Enhancing IEEE 802.11a/n with dynamic single-user OFDM adaptation

Effect of power and rate adaptation on the spectral efficiency of MQAM/OFDM system under very fast fading channels

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