Yuan Ouyang

Low-complexity selected mapping schemes for peak-to-average power ratio reduction in OFDM systems

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitters output signal. The selected mapping (SLM) approach provides good performance for PAPR reduction, but it requires a bank of inverse fast Fourier transforms (IFFTs) to generate a set of candidate transmission signals, and this requirement usually results in high computational complexity. In this paper, we propose a kind of low-complexity conversions to replace the IFFT blocks in the conventional SLM method. Based on the proposed conversions, we develop two novel SLM schemes with much lower complexity than the conventional one; the first method uses only one IFFT block to generate the set of candidate signals, while the second one uses two IFFT blocks. Computer simulation results show that, as compared to the conventional SLM scheme, the first proposed approach has slightly worse PAPR reduction performance and the second proposed one reaches almost the same PAPR reduction performance.

A low-complexity peak-to-average power ratio reduction technique for OFDM systems

One major drawback of orthogonal frequency division multiplexing is the high peak-to-average power ratio (PAPR). The selective mapping (SLM) approach provides good performance for PAPR reduction, but it may suffer from the high computational complexity of the bank of inverse fast Fourier transforms (IFFTs). We propose two low-complexity conversions to replace half of the IFFTs in the SLM method. Computer simulation results and complexity analyses show that, with the two proposed conversions, we can reduce about half of the computational complexity of the SLM approach and get better performance for PAPR reduction.

A low-complexity peak-to-average power ratio reduction technique for OFDM-based systems

One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the output signal. To reduce the PAPR, some methods use the reserved tones to produce the clipping signal. However, this kind of method usually needs complicated computations. In this paper, we propose a simple and effective algorithm to iteratively determine the values of the reserved tones. For practical applications, such as the IEEE 802.11a wireless LAN and the digital video broadcasting system, we can choose some of the unused subcarriers or tones defined in the standards as the reserved tones to avoid lowering the transmission rate. Computer simulation results show that the transmitted signal processed by the proposed method has a better PAPR distribution and meets the transmit spectrum mask defined in the standards. The proposed method induces no in-band distortion and out-of-band radiation. As compared to the selected mapping and partial transmit sequences schemes, it does not need any side information and reaches comparable performance with much lower complexity.

A new carrier recovery loop for high-order quadrature amplitude modulation

In this paper, we present a new all-digital carrier recovery loop for high-order quadrature amplitude modulation (QAM) signal constellations. The proposed approach is a blind phase-frequency detector structure that consists of a phase detector, a phase offset estimator, a frequency offset estimator, and a digital control oscillator. As compared with previous related approaches, the proposed algorithm provides a wider acquisition range of /spl plusmn/400 kHz and a more accurate estimation of frequency and phase offsets. These features are demonstrated by simulation results of the DOCSIS (Data-Over-Cable Service Interface Specifications) cable modem system.

A Low-Complexity Peak-to-Average Power Ratio Reduction Technique for OFDM Systems Using Guided Scrambling Coding

One major drawback of orthogonal frequency division multiplexing schemes is the high peak-to-average power ratio (PAPR) of the output signal. Selected mapping (SLM) and partial transmit sequences (PTS) are two important techniques for reducing PAPR, but they need to transmit side information to indicate how the transmitter generates the signals. Guided scrambling (GS) SLM and GS-PTS techniques use augmenting bits to set the scramblers initial condition. With different patterns of the augmenting bits, different candidate signals can be generated. GS-SLM and GS-PTS do not require the transmission of side information, but they still need a bank of inverse fast Fourier transforms (IFFTs), i.e., involving high computational complexity. In this paper, we focus on reducing the high computational complexity of the GS-SLM and GS-PTS methods. We separate the operations of the augmented data word into the operations of the augmenting bits and the operations of the source data word. Different augmenting bits are processed in advance and the results are saved into a read-only memory (ROM). The proposed methods only need one IFFT, few adders, and a ROM and thus significantly reduce the computational complexity of the original GS-SLM and GS-PTS methods. The simulation results also show that the proposed GS-SLM and GS-PTS methods have almost the same PAPR reduction performance as the original ones.

A peak-to-average power ratio reduction technique for the IEEE 802.11a wireless LAN

In this paper, we propose a simple and effective peak-to-average power ratio (PAPR) reduction method for the IEEE 802.11a wireless local area network. Usually some unused subcarriers defined in the IEEE 802.11a standard are set to zero to prevent out-of-band radiation. However, without violating the transmit spectrum mask in the standard, it is shown that we can transmit nonzero values on some of these unused subcarriers. We propose an algorithm to reduce the PAPR of the transmitted signal by setting appropriate values to some of these unused subcarriers. Computer simulation results show that the transmitted signal processed by the proposed method has a better PAPR distribution and meets the transmit spectrum mask defined in the IEEE 802.11a standard.

A low-complexity selected mapping scheme for peak-to-average power ratio reduction in OFDM systems

One major problem associated with orthogonal frequency division multiplexing is the high peak-to-average power ratio (PAPR) of the output signal. The selected mapping (SLM) approach provides good performance for PAPR reduction, but it may suffer from the high computational complexity of a bank of inverse fast Fourier transforms (IFFTs). We propose a kind of low-complexity conversion to replace the IFFTs in the SLM method. Using the proposed conversions, we develop a novel SLM scheme with much lower complexity than the conventional SLM approach. Computer simulation results show that both of the SLM schemes have almost the same PAPR reduction performance.

A new symbol time estimator for orthogonal frequency division multiplexing systems

We propose a new symbol time estimator utilizing a specifically designed pilot symbol for orthogonal frequency division multiplexing systems. The proposed estimator consists of two stages of estimation (coarse-to-fine). In the stage of coarse estimation, the redundant information contained within the cyclic prefix is used for rough symbol time estimation. In the stage of fine estimation, the merit of the designed pilot symbol structure is utilized to generate a fine symbol time estimate. Computer simulation results show that, although the new estimator has a slightly larger variance than a recently described method by H. Minn et al. (see IEEE Commun. Lett., vol.4, p.242-4, 2000) for additive white Gaussian noise channels, it has a significantly smaller variance and a smaller bias (i.e., the mean of the estimation error) for intersymbol interference channels. The new method also involves less computational complexity than previous related approaches.