Complementary M ‐ary orthogonal spreading OFDM architecture for HF communication link

Quadrature amplitude modulation (QAM) constellation and Golay complementary sequences (GCSs) are usually applied in orthogonal frequency division multiplexing (OFDM) systems to obtain a higher data rate and a lower peak-to-mean envelope power ratio (PMEPR). In this paper, after a sufficient search of the literature, it was found that increasing the family size is an effective way to improve the data rate, and the family size is mainly determined by the number of offsets in the general structure of QAM GCSs. Under the guidance of this idea, we propose a new construction for -QAM GCSs through generalized Boolean functions (GBFs) based on a new description of a -QAM constellation, which aims to enlarge the family size of GCSs and obtain a low PMEPR. Furthermore, a previous construction of -QAM GCSs presented by Li has been proved to be a special case of the new one, and the family size of new sequences is much larger than those previously mentioned, which means that there was a great improvement in the data rate. On the other hand, a previous construction of 16-QAM GCSs presented by Zeng is also a special case of the new one in this paper, when . In the meantime, the proposed sequences have the same PMEPR upper bound as the previously mentioned sequences presented by Li when applied in OFDM systems, which increase the data rate without degrading the PMEPR performance. The theoretical analysis and simulation results show that the proposed new sequences can achieve a higher data rate and a low PMEPR.

This paper considers waveform design of orthogonal frequency division multiplexing (OFDM) signal for radar applications, which aims at mitigating the envelope fluctuation in OFDM. A novel method is proposed to reduce the peak-to-mean envelope power ratio (PMEPR), which is commonly used to evaluate the fluctuation. The proposed method is based on the tone reservation approach, in which some bits or subcarriers of OFDM are allocated for decreasing PMEPR. We introduce the coefficient of variation of envelopes (CVE) as the cost function for waveform optimization, and develop an iterative least squares algorithm. Minimizing CVE leads to distinct PMEPR reduction, and it is guaranteed that the cost function monotonically decreases by applying the iterative algorithm. Simulations demonstrate that the envelope fluctuation is significantly smoothed by the proposed method.

This letter considers waveform design of orthogonal frequency division multiplexing (OFDM) signal for radar applications, and aims at mitigating the envelope fluctuation in OFDM. A novel method is proposed to reduce the peak-to-mean envelope power ratio (PMEPR), which is commonly used to evaluate the fluctuation. The proposed method is based on the tone reservation approach, in which some bits or subcarriers of OFDM are allocated for decreasing PMEPR. We introduce the coefficient of variation of envelopes (CVE) as the cost function for waveform optimization, and develop an iterative least squares algorithm. Minimizing CVE leads to distinct PMEPR reduction, and it is guaranteed that the cost function monotonically decreases by applying the iterative algorithm. Simulations demonstrate that the envelope is significantly smoothed by the proposed method.

The peak-to-mean envelope power ratio (PMEPR) of a code employed in\northogonal frequency-division multiplexing (OFDM) systems can be reduced by\npermuting its coordinates and by rotating each coordinate by a fixed phase\nshift. Motivated by some previous designs of phase shifts using suboptimal\nmethods, the following question is considered in this paper. For a given binary\ncode, how much PMEPR reduction can be achieved when the phase shifts are taken\nfrom a 2^h-ary phase-shift keying (2^h-PSK) constellation? A lower bound on the\nachievable PMEPR is established, which is related to the covering radius of the\nbinary code. Generally speaking, the achievable region of the PMEPR shrinks as\nthe covering radius of the binary code decreases. The bound is then applied to\nsome well understood codes, including nonredundant BPSK signaling, BCH codes\nand their duals, Reed-Muller codes, and convolutional codes. It is demonstrated\nthat most (presumably not optimal) phase-shift designs from the literature\nattain or approach our bound.\n

Clipping is a popular method to overcome large peak-to-mean envelope power ratios (PMEPRs) in orthogonal frequency-division multiplexing (OFDM) systems, but it results in nonlinear distortion, which degrades signal detection performance. In this paper, clipping effects on signal detection with a simple channel estimation in OFDM are investigated, signal-to-noise and distortion ratio (SNDR) results of detected signals are derived, and symbol error rates (SERs) of clipped OFDM in frequency selective Rayleigh fading channels are evaluated. The evaluated SER results are supported by simulations.

Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio (PMEPR), which can result in significant distortion when transmitted through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the bit error rate, and the PMEPR. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.

The design of waveforms play an important role in the performance of radar systems. Multicarrier complementary phase-coded signal has been a field of interest for many researchers due to its prominent properties. This paper aims to reduce the Peak-to-Mean Envelope Power Ratio (PMEPR) of a Multicarrier Complementary Phase-Coded (MCPC) signal consisting of P subcarriers which are phase modulated by P phase sequences. The carriers are equally separated in terms of frequency. The carrier separation is equal to the reciprocal of t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , which is equal to the span of each phase element, forming Orthogonal Frequency Division Multiplexing (OFDM). In this paper we propose a new approach to generate MCPC signal using Complementary Block Coding (CBC) method which has lower value of PMEPR in comparison with the conventional method.

In this paper, an integrated Orthogonal Frequency Division Multiplexing (OFDM) system is developed to improve Bit Error Rate (BER) performance of communication systems in order to meet the requirements of advanced communication systems like long term evaluation advanced (LTE –A). The proposed OFDM system consists of channel estimation using comb type pilot arrangement and convolution encoder with the best known Coding Bounds and Maximum A Posteriori (MAP) decoder. Using pilot symbols, the channel quality is estimated. The BER performance of OFDM system is improved using pilot carriers, channel estimation schemes and MAP decoder at the best known coding bounds. The system performance is analyzed with recursive systematic and non-systematic convolution codes, ML and MAP decoders. From the results, it is evident that the proposed OFDM system with channel estimation and MAP decoder at the best known coding bounds improves the system performance significantly.

Golay sequences have been introduced to construct 16-QAM (quaternary amplitude modulation) code for the orthogonal frequency division multiplexing (OFDM), reducing the peak-to-mean envelope power ratio (PMEPR). As an alternative way to construct Golay sequences, the construction of 16- QAM using Rudin-Shapiro polynomials (RSP) was also reported recently in several literatures. In this paper, we develop a simple efficient construction of 16-QAM using generalized RSP, which provides high code rate and large Hamming distance while tightly controlling the PMEPR.

We propose a multiple-subcarrier (MS) optical communication system with subcarrier signal point sequence (SSPS). We use the SSPS having the large minimum value and the large Euclidean distances, so that the required d.c. bias is minimized and the error rate performance is improved. Note that in the proposed systems, the signal points having the larger minimum value are selected, while the signal points having lower peak to mean envelope power ratio (PMEPR) are selected in orthogonal frequency division multiplexing (OFDM) systems. Therefore, the signal point sequences good for OFDM with phase shifting by /spl pi/ radian are not necessarily good ones for MS optical communication systems. We show that the normalized power requirement and normalized bandwidth requirement of the MS-SSPS are smaller than those of the conventional MS systems.

In this paper, we consider out-of-band radiations caused by high sidelobes in orthogonal frequency division multiplexing (OFDM) system. Suppression of sidelobes in OFDM system allows higher spectral efficiency and less interference with existing legacy systems in OFDM based overlay system. We combine different sidelobe suppression techniques to suppress the sidelobes in OFDM system. The multiple-choice sequence (MCS) is combined with cancellation carriers (CCs) and also MCS is combined with subcarrier weighting (SW) technique. MCS is applied prior to CCs or SW techniques. Simulation results show that combining MCS with CCs and MCS with SW techniques the sidelobes in OFDM system can be significantly reduced, which allow a successful co-existance between OFDM overlay system and an existing legacy system.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the promising contendents in the race of very high data rate delivery, for 4G wireless systems. The conventional OFDM systems, so far deployed make use of Fast Fourier Transform (FFT) as their basic building block. Besides the numerous advantages, the restriction over the data rate imposed by the FFT in the form of cyclic prefix may be intolerable for the next generation OFDM systems. So, researches are on the way to replace FFT with a more suitable transform which is redundant free. DWT OFDM is one such system in which FFT in the conventional OFDM is replaced with Discrete Wavelet Transform (DWT). Using simulations, already it has been established that in ideal conditions, the performance of DWT OFDM is better than that of FFT OFDM. As phase noise can be considered as the major RF impairment and one of the leading performance limiting factors of the wireless systems, this paper analyses the Bit Error Rate (BER) performance of the DWT OFDM in presence of phase noise. BER performances of both DWT OFDM and FFT OFDM are analysed and compared in presence of phase noise. For this, Matlab Simulink model have been developed for both types of OFDM, and simulation is carried over in presence of phase noise for different modulation schemes. In all cases the BER performances of DWT OFDM is found to be fairly ahead that of FFT OFDM.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

Based on the sampling-concatenating operation with any integer interval, a large number of orthogonal subsets are designed for M-ary spread spectrum (MSS) communications with orthogonal frequency division multiplexing (OFDM) modulation. Any two sequences in the designed subset are orthogonal to each other, that is, the in-phase cross-correlation (IPCC) between them is equal to zero. Compared with the previous researches, the designed multiple subsets may possess more sequences at the cost of the peak-to-mean envelope power ratio (PMEPR) and inter-subset IPCC, which will be suitable for MSS-OFDM communications where the larger number of sequences means higher data rate. We provide a simple example to show how the designed algorithm works, and the corresponding performance of PMEPR and IPCC is analyzed.

Orthogonal frequency division multiplexing (OFDM) systems suffer from high sidelobes level. In some applications, as cognitive radios, this phenomenon can be a serious matter. This paper proposes Minimum shift keying (MSK)-OFDM to address this problem. The proposed method is an OFDM system using MSK modulation in each subcarrier. The corresponding transmitter and receiver are introduced. The method doesn't entail great changes in the main parts of OFDM. Like OFDM systems, the transceiver can be implemented using DFT/IDFT. Simulation results show great reduction in out of band radiation in comparison with conventional OFDM.