New Techniques to Reduce Sidelobes in OFDM System

Ahmed, Saleem; Rehman, Razi Ur; Hwang, Humor

doi:10.1109/iccit.2008.157

Cited by 17 publications

(13 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, the active interference cancellation approach in [14] inserts cancelling tones adaptively at the edges, which enables deeper spectrum notches at the expense of high computational complexity at the transmitter. Similarly, subcarrier weighting [15], multiple-choice sequence [16], and selected mapping [17] all suppress OOB radiation based on the transmitted data. However, these approaches are not applicable to the multiuser case since they inevitably introduce dependency among different users.…”

Section: Introductionmentioning

confidence: 99%

Multiuser Spectral Precoding for OFDM-Based Cognitive Radio Systems

Zhou

2013

IEEE J. Select. Areas Commun.

View full text Add to dashboard Cite

Orthogonal frequency-division multiplexing (OFDM) is an ideal transmission technique for cognitive radio (CR) systems because of its flexible nature to support dynamic spectrum access. However, the out-of-band (OOB) radiation of OFDM signals from different CR users must be strictly controlled to protect licensed users operating in the adjacent frequency bands. In this paper, we propose a spectral precoding approach for multiple OFDM-based CR users to reduce OOB leakage and enhance spectrum compactness. By constructing individual precoders to render selected spectrum nulls, our approach suppresses the overall OOB radiation without sacrificing biterror rate performance of CR users. The proposed approach also ensures user independence thus with low encoding and decoding complexities. Furthermore, our approach can improve bandwidth efficiency by carefully selecting notched frequencies. As a comprehensive application of the proposed approach, two simplified multiuser spectral precoding schemes are provided to reduce the computational complexity. Simulation results demonstrate that our spectral precoding schemes effectively limit OOB radiation and enable efficient spectrum sharing.Index Terms-Cognitive radio, dynamic spectrum access, orthogonal frequency-division multiplexing, out-of-band radiation, spectral precoding.

show abstract

Section: Introductionmentioning

confidence: 99%

Multiuser Spectral Precoding for OFDM-Based Cognitive Radio Systems

Zhou

2013

IEEE J. Select. Areas Commun.

View full text Add to dashboard Cite

show abstract

“…In (12), · ∞ denotes the sup-norm. That is, we wish to ensure that the power-per-sub-carrier for the reserved sub-carriers never exceeds a constant factor of the power-per-sub-carrier of the data sub-carriers.…”

Section: Power Constrained N -Continuous Ofdmmentioning

confidence: 99%

“…These large side-lobes are the result of the summation of the spectra for each of the modulated sub-carriers, which extend infinitely in the form of a sinc function and introduce high out-of-band power (OBP), that can interfere with users of neighbouring bands. There are a number of techniques for reducing these side-lobes including windowing the signal [4], increasing the bandwidth of the guard-bands between subcarriers [2], inserting cancellation carriers at the edges of the spectrum [5], multiple-choice sequences (MCS) [6], phaseadjusted OFDM [7], N -continuous OFDM [8], algorithms which jointly optimize the PAPR problem [9]- [11], and techniques which combine multiple approaches [12], [13].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the reserved sub-carrier approach to achieving N-continuity for side-lobe reduction in OFDM

Haber-Kucharsk¹,

Alian

Mitran

2013

2013 13th Canadian Workshop on Information Theory

View full text Add to dashboard Cite

Orthogonal frequency division multiplexing (OFDM) is a popular modulation scheme used in a variety of applications. One significant problem associated with OFDM is the possibility of large side-lobes in its spectrum. In this paper, we consider the so-called N -continuous method for reducing the side-lobes. We first consider one implementation approach, whereby certain sub-carriers are reserved for the purpose of adjusting the spectrum of an OFDM symbol. We find that significant side-lobe reduction is possible, although at the cost of injecting very large power in the reserved sub-carriers that results in unacceptable spectrum overshoot. In order to achieve reasonable power levels, at least 20 % of all sub-carriers must be reserved for weighting. As a solution to the problem of spectrum overshoot, we propose an alternative approach whereby the power of the reserved sub-carriers is constrained. Numerical results show that reasonable power levels are achieved at the cost of significant performance loss in the N -continuous OFDM technique for side-lobe reduction. We thus find that the performance cost of eliminating the spectrum overshoot reduces the side-lobes reduction to less than 5 dB in cases of interest.

show abstract

“…As the OFDM edge subcarriers possess the strongest influence on the OOB radiation, only those subcarriers are altered. Another variant of the MCS method involves its merging with other spectrum shaping algorithms, e.g., in [18] the authors combined the MCS method with both SW and CCs method.…”

Section: State-of-art Techniques For Oob Radiation Reductionmentioning

confidence: 99%

Protection of primary users in dynamically varying radio environment: practical solutions and challenges

Kryszkiewicz

Bogucka

Wyglinski

2012

J Wireless Com Network

View full text Add to dashboard Cite

One of the primary objectives of deploying cognitive radio (CR) within a dynamic spectrum access (DSA) network is to ensure that the legacy rights of incumbent licensed (primary) transmissions are protected with respect to interference mitigation when unlicensed (secondary) communications are simultaneously operating within the same spectral vicinity. In this article, we present non-contiguous orthogonal frequency division multiplexing (NC-OFDM) as a promising and practical approach for achieving spectrally agile wireless data transmission that is suitable for secondary users (SUs) to access fragmented spectral opportunities more efficiently. Furthermore, a review of the current state-of-the-art is conducted with respect to methods specifically designed to protect the transmissions of the primary users (PUs) from possible interference caused by nearby SU transceivers employing NC-OFDM. These methods focus on the suppression of out-of-band (OOB) emissions resulting from the use of NC-OFDM transmission. To achieve the required OOB suppression, we present two practical approaches that can be employed in NC-OFDM, namely, the insertion of cancellation carriers and windowing. In addition to the theoretical development and proposed improvements of these approaches the computer simulation results of their performance are presented. Several real-world scenarios regarding the coexistence of both PU and SU signals are also studied using actual wireless experiments based on software-defined radio. These simulation and experimental results indicate that OOB suppression can be achieved under real-world conditions, making NC-OFDM transmission a viable option for CR usage in DSA networks.

show abstract

New Techniques to Reduce Sidelobes in OFDM System

Cited by 17 publications

References 9 publications

Multiuser Spectral Precoding for OFDM-Based Cognitive Radio Systems

Multiuser Spectral Precoding for OFDM-Based Cognitive Radio Systems

On the reserved sub-carrier approach to achieving N-continuity for side-lobe reduction in OFDM

Protection of primary users in dynamically varying radio environment: practical solutions and challenges

Contact Info

Product

Resources

About