Seung-Hee Han

An overview of peak-to-average power ratio reduction techniques for multicarrier transmission

High peak-to-average power ratio of the transmit signal is a major drawback of multicarrier transmission such as OFDM or DMT. This article describes some of the important PAPR reduction techniques for multicarrier transmission including amplitude clipping and filtering, coding, partial transmit sequence, selected mapping, interleaving, tone reservation, tone injection, and active constellation extension. Also, we make some remarks on the criteria for PAPR reduction technique selection and briefly address the problem of PAPR reduction in OFDMA and MIMO-OFDM.

PAPR reduction of OFDM signals using a reduced complexity PTS technique

A major drawback of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of OFDM signals. In the PTS technique, the data block to be transmitted is partitioned into disjoint subblocks and the subblocks are combined using phase factors to minimize PAPR. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of subblocks. In the proposed technique, a gradient descent search is performed to find the phase factors. It is shown that the proposed technique achieves significant reduction in search complexity with little performance degradation.

Modified selected mapping technique for PAPR reduction of coded OFDM signal

High peak-to-average power ratio (PAPR) of the transmitted signal is a major drawback of orthogonal frequency division multiplexing (OFDM). In this paper, we propose a modified selective mapping (SLM) technique for PAPR reduction of coded OFDM signal. In this technique, we embed the phase sequence, which is used to lower the PAPR of the data block, in the check symbols of the coded OFDM data block. It is shown that we can achieve both PAPR reduction from the SLM technique as well as error performance improvement from the channel coding with no loss in data rate from the transmission of side information. In addition, approximate expression for the complementary cumulative distribution function (CCDF) of the PAPR of the modified SLM technique is derived and compared with the simulation results.

IFN‐γ‐STAT1 signal regulates the differentiation of inducible Treg: Potential role for ROS‐mediated apoptosis

Regulatory CD4+ T cells are important for the homeostasis of immune cells, and their absence correlates with autoimmune disorders. However, how the immune system regulates Treg homeostasis remains unclear. We found that IFN‐γ‐deficient‐mice had more forkhead box P3 (FOXP3+) cells than WT mice in all secondary lymphoid organs except the thymus. However, T‐bet‐ or IL‐4Rα‐deficient mice did not show a similar increase. In vitro differentiation studies showed that conversion of naïve T cells into FOXP3+ cells (neo‐generated inducible Treg (iTreg)) by TGF‐β was significantly inhibited by IFN‐γ in a STAT‐1‐dependent manner. Moreover, an in vivo adoptive transfer study showed that inhibition of FOXP3+ iTreg generation by IFN‐γ was a T‐cell autocrine effect. This inhibitory effect of IFN‐γ on iTreg generation was significantly abrogated after N‐acetyl‐L‐cysteine treatment both in vitro and in vivo, indicating that IFN‐γ regulation of iTreg generation is dependent on ROS‐mediated apoptosis. Therefore, our results suggest that autocrine IFN‐γ can negatively regulate the neo‐generation of FOXP3+ iTreg through ROS‐mediated apoptosis in the periphery.

Tone injection with hexagonal constellation for peak-to-average power ratio reduction in OFDM

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the OFDM signal. Tone injection (TI) technique is a promising candidate for the reduction of the PAPR of an OFDM signal. But this technique requires the increase of the transmit signal power because of the injected signal. In this paper, we propose the use of hexagonal constellation as a method to achieve PAPR reduction without increasing signal power in the TI technique

Selected mapping technique with novel phase sequences for PAPR reduction of an OFDM signal

High peak-to-average power ratio (PAPR) of the transmitted signal is a major drawback of orthogonal frequency division multiplexing (OFDM). The selected mapping (SLM) technique is one of the promising PAPR reduction techniques for OFDM. In the SLM technique, some statistically independent data blocks are generated from an OFDM data block using a set of phase sequences and the one with the lowest PAPR is chosen and transmitted. In this paper, we propose an SLM technique with novel phase sequences. In the proposed SLM technique, it is not required to exchange side information between transmitter and receiver, which is usually required in the ordinary SLM technique. It is shown that we can achieve comparable PAPR reduction performance to the ordinary SLM technique with no data rate loss and a small increase in transmitted signal power.

On the Use of Hexagonal Constellation for Peak-to-Average Power Ratio Reduction of an ODFM Signal

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the OFDM signal. In this paper, we propose the use of hexagonal constellation for PAPR reduction of an OFDM signal. Because hexagonal constellation is the densest packing of regularly spaced points in two dimensions, we can have more signal points in a given area with hexagonal constellation than with quadrature amplitude modulation (QAM) constellation. We can exploit these extra degrees of freedom provided by the hexagonal constellation for PAPR reduction of an OFDM signal. We will apply the proposed technique to eliminate data rate loss due to the side information in partial transmit sequence (PTS) technique and selected mapping (SLM) technique.

Peak-to-average power ratio reduction of an OFDM signal by signal set expansion

A major drawback of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted signal. In this paper, we propose a novel technique to reduce PAPR in an OFDM signal. Proposed technique is based on signal set expansion. Each point in the original signal set is associated with two or more points in the expanded signal set. Each symbol in an OFDM data block is mapped into a point among associated points in the expanded signal set so as to achieve PAPR reduction. The proposed technique is very simple and does not require any side information to be transmitted from the transmitter to the receiver.

CD40-targeted recombinant adenovirus significantly enhances the efficacy of antitumor vaccines based on dendritic cells and B cells.

Despite the advantages of using adenoviral vectors for specific antigenic gene delivery in the development of antigen-presenting cell (APC)-based vaccines, the lack of the coxsackievirus-adenovirus receptor (CAR) on APCs limits the use of adenoviral vectors for in vitro gene delivery. In this study, we used a recombinant adapter protein, CFm40L, which consists of the ectodomain of CAR genetically fused to the ectodomain of CD40 ligand (CD40L) via a trimerization motif, to target Her-2/neu- or human papillomavirus 16 (HPV16) E6/E7-encoding adenoviruses to CD40 on dendritic cells (DCs) and B cells. Targeting CD40 enabled the enhancement of tumor antigen delivery and simultaneous activation of APCs via the CD40-CD40L interaction. We found that these transduced DCs and B cells substantially enhanced the CTL response against human Her-2/neu- and HPV16 E6/E7-expressing tumors, resulting in significant inhibition of tumor growth in a murine tumor model. In addition, the use of the CFm40L adapter protein in combination with gemcitabine treatment allowed for a successful immune response against a self-tumor antigen, murine Her-2/neu. Our results suggest that targeting adenovirus to APCs via CD40, using CFm40L, represents a great improvement in anticancer cellular vaccines.

Multi-stage partial PIC receivers for multi-rate DS-CDMA system with multiple modulation

In a multi-rate DS-CDMA system with multiple modulation, modulation format is adjusted according to the data rate of each user while symbol duration is fixed for all users. In this paper, two types of multi-stage partial parallel interference cancellation (PIC) receivers are considered for multi-rate DS-CDMA system with multiple modulation: multi-stage PIC receiver with partial cancellation factors and multi-stage PIC receiver with decision thresholds. Performance of the receivers is evaluated by simulation in a Rayleigh fading channel. It is shown that the multi-stage PIC receiver with partial cancellation factors achieves significant performance improvement over the matched filter (MF) receiver and has much lower symbol error rate (SER) than multi-stage PIC receiver for multi-rate DS-CDMA system with multiple modulation in a Rayleigh fading channel.