3,452 research outputs found
Multicarrier-signal design with low peaks and low out-of-band power
Projecte fet en col.laboració amb el Department of Electrical and Information Technology. Lund UniversityThe high peak-to-average power ratio (PAPR) and the high out-of-band power
(OBP) are two major drawbacks of multicarrier communication systems. Many
PAPR reduction and OBP supression techniques have been proposed in the literature
whereas not much has been proposed regarding the jointly reduction performance.
This thesis focuses on joint reducing time-domain peaks and out-of-band
leakage of OFDM signals. The resulting algorithm combines the bene ts of both
methods and yields better results than each method does separately
Multicarrier-signal design with low peaks and low out-of-band power
Projecte fet en col.laboració amb el Department of Electrical and Information Technology. Lund UniversityThe high peak-to-average power ratio (PAPR) and the high out-of-band power
(OBP) are two major drawbacks of multicarrier communication systems. Many
PAPR reduction and OBP supression techniques have been proposed in the literature
whereas not much has been proposed regarding the jointly reduction performance.
This thesis focuses on joint reducing time-domain peaks and out-of-band
leakage of OFDM signals. The resulting algorithm combines the bene ts of both
methods and yields better results than each method does separately
PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink
We investigate an orthogonal frequency-division multiplexing (OFDM)-based
downlink transmission scheme for large-scale multi-user (MU) multiple-input
multiple-output (MIMO) wireless systems. The use of OFDM causes a high
peak-to-average (power) ratio (PAR), which necessitates expensive and
power-inefficient radio-frequency (RF) components at the base station. In this
paper, we present a novel downlink transmission scheme, which exploits the
massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to
achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM
modulation, and PAR reduction by solving a convex optimization problem. We
develop a corresponding fast iterative truncation algorithm (FITRA) and show
numerical results to demonstrate tremendous PAR-reduction capabilities. The
significantly reduced linearity requirements eventually enable the use of
low-cost RF components for the large-scale MU-MIMO-OFDM downlink.Comment: To appear in IEEE Journal on Selected Areas in Communication
Peak to average power ratio reduction in NC–OFDM systems
Non contiguous orthogonal frequency division multiplexing (NC-OFDM) is an efficient and adaptable multicarrier modulation scheme to be used in cognitive radio communications. However like OFDM, NC-OFDM also suffers from the main drawback of high peak to average power ratio (PAPR). In this paper PAPR has been reduced by employing three different trigonometric transforms. Discrete cosine transform (DCT), discrete sine transform (DST) and fractional fourier transform (FRFT) has been combined with conventional selected level mapping (SLM) technique to reduce the PAPR of both OFDM and NC-OFDM based systems. The method combines all the transforms with SLM in different ways. Transforms DCT, DST and FRFT have been applied before the SLM block or inside the SLM block before IFFT. Simulation results show the comparative analysis of all the transforms using SLM in case of both OFDM and NC-OFDM based systems
Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems
Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER
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