Secret key establishment technique using channel state information driven phase randomisation in multiple‐input multiple‐output orthogonal frequency division multiplexing

Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform generation in wideband transmission. it's a superior technology for the high-speed rate of wired and wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G networks & tactical communication. The OFDM has many advantages over other techniques like its high capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping (SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLMPTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate (BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the proposed scheme is more complex than the prevailing techniques.

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.

To meet the growing demand for multimedia services, Multimedia Broadcast/Multicast Service (MBMS) was proposed to enhance bandwidth efficiency in wireless communication systems. Although MBMS supports multimedia streams with several resolutions, streams with different resolutions are treated as separate services and transmitted upon independent radio resources, resulting in inefficient resource utilization. At the receiver, some valuable information embedded in the higher-resolution channels is not utilized to enhance the reception of the data stream in a lower resolution channel. In this work, we propose a multilevel coupling modulation (MCM) scheme aimed to improve the overall system throughput and to extend the service coverage of the multi-resolution MBMS in orthogonal frequency division multiplexing (OFDM) systems. The proposed MCM scheme can fully utilize all the usable information conveyed in different channels, thereby improving the receiving performance. In addition, we derive the symbol error rates of the proposed MCM scheme, in the AWGN and frequency-selective fading channels, for performance evaluation. The analytical and simulation results demonstrate that the proposed MCM scheme can substantially enhance the receiving performance, service accessibility and overall system throughput of multi-resolution MBMS in OFDM systems.

This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity. Space time coded OFDM systems, which can provide transmit diversity, require perfect channel estimation to improve communication quality. In actual OFDM systems, training sequences are usually used for channel estimation. The authors propose a training based channel estimation strategy suitable for space time coded OFDM systems. This novel strategy provides enhanced performance, high spectrum efficiency and relatively low computation complexity.

ABSTRACTWhile inter-symbol interference is not of concern, inter-carrier interference that is caused by carrier frequency offset (CFO) is more concerned in orthogonal frequency division multiplexing (OFDM) systems. The estimation of channel impulse response (CIR) is another important parameter of interest in the system. Recently, a number of approaches for the joint estimation of CFO and CIR in OFDM systems have been proposed in the literature, and most of them are traditional maximum-likelihood-based approaches. In this paper, we propose a number of mixture cost-reference particle filtering (CRPF) approaches for joint estimation of CIR and CFO, and a couple of them can be applied without the knowledge of both state and measurement noise statistics. Conventional least mean squares algorithm or recursive least squares algorithm is jointly employed with recently developed CRPF for nonlinear and multiple parameters estimation in OFDM systems. The computer simulation results show that mixture CRPFs are more robust against particle impoverishment (PI) problem than standard mixture particle filtering (PF) and mixture regularized PF (RPF) approaches although RPF was particularly developed to tackle the PI problem. In this paper, we investigate a number of mixture PF approaches including ones that do not need the information of noise statistics for the joint estimation of CFO and channel in OFDM systems.

Security issues of the physical layer in wireless communications have attracted extensive attention in recent years. Meanwhile, the key space and encryption mechanisms have great impact on the security performance. This paper proposes a novel physical layer encryption scheme based on multi-fold chaotic maps in orthogonal frequency-division multiplexing(OFDM) systems. High security is achieved by performing the chaotic maps on the phase and amplitude of quadrature amplitude modulation(QAM) symbols, and the transmitted subcarrier. The initial conditions of the chaotic maps serve as the secret keys. Mathematical analysis indicates that the proposed scheme can provide a huge key space of 1.5 × 1098, which is much larger than that of the existing solutions. In addition, the transmission performance is evaluated over both AWGN channels and Rayleigh fading channels. The theoretical analysis and simulation results reveal that the proposed scheme significantly outperforms the existing solutions in terms of security. Meanwhile, it can achieve similar transmission performance over different channels.

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.

A three-dimensional (3D) orthogonal frequency division multiplexing (OFDM) system with peak-to-average power ratio (PAPR) reduction method for the wireless sensor networks (WSNs) is presented. The transmit power of wireless nodes in an ad hoc network is strictly limited. Thus, high PAPR of the 3D OFDM system is a possible drawback when it is considered as a physical layer transmission scheme for the WSNs. Here, we propose an improved partial transmit sequence (PTS) technique to reduce PAPR of the OFDM system with 3D modulation formats. In the proposed algorithm, the components of 3D signals are assigned to different subblocks using a diagonal rule (DR), increasing randomness of the signals in the disjoint subblocks forcibly. As a result, the proposed method reduces PAPR of the 3D OFDM system significantly without increase in computational complexity. Hence, the proposed algorithm makes the 3D OFDM system be a possible candidate for a physical layer transmission scheme in future WSNs.

This paper proposes a partial transmit sequence (PTS) scheme with applying a stochastic optimization technique for peak-to-average power ratio (PAPR) reduction in the orthogonal frequency division multiplexing (OFDM) system. PTS technique combining can improve the PAPR statistics of an OFDM signals, but the considerable computational complexity for the required search through a high-dimensional vector space is a potential problem for implementation in the practical systems. Differential evolution (DE) is an efficient and powerful population-based stochastic search technique for solving optimization problems over continuous space, which has been widely applied in many scientific and engineering fields. Thus, to reduce the complexity for searching phase weight vector and to improve the PAPR statistics, we introduce the DE, an effective algorithm that solves various combinatorial optimization problems, to search the optimal phase weight factors. The simulation results show that the proposed DE-based PTS obtains the excellent PAPR performance with a low computational complexity.

Orthogonal Frequency Division Multiplexing (OFDM) is transmission multi-carrier method used in wireless communication systems. OFDM has a lot of advantages, including a high spectral density and a resistance to channel fading. The primary objective is to accomplish a low or zero-bit error Rate (BER) when employing OFDM in a wireless communication system. However, contemporary challenges include the complexity of OFDM design and the demand and selection of an appropriate modulation mechanism. As a result, this work develops two OFDM based system designs to examine the working presentation of the OFDM in wireless communication. Communication schemes necessitate a system with high baud rates, minimum inter-carrier interference, and minimum inter-symbol interference. OFDM is particularly important in 4G communication systems such as fixed Wi-Fi, fixed WiMAX, mobile WiMAX, and Long-Term- Evolution (LTE). In this research, the influence of altering design factors on OFDM systems will be investigated by simulating several OFDM systems with different modulation strategies using MATLAB / Simulink.

This paper focuses on multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with channel order larger than the cyclic prefix (CP) length. Writing the demodulating fast Fourier transform (FFT) as a sliding FFT followed by a downsampling operation, we show in this paper that by swapping the filtering operations of the MIMO channel and the sliding FFT, the data model for the temporally smoothened received signal of each individual tone of the MIMO OFDM system is very similar to the data model for the temporally smoothened received signal of a MIMO single-carrier (SC) system. As a result, to recover the data symbol vectors, the conventional equalization approach for MIMO SC systems can be applied to each individual tone of the MIMO OFDM system. This so-called per-tone equalization (PTEQ) approach for MIMO OFDM systems is an attractive alternative to the recently developed time-domain equalization (TEQ) approach for MIMO OFDM systems. In the second part of this paper, we focus on direct per-tone equalizer design and adapt an existing semi-blind equalizer design method for space-time block coding (STBC) SC systems to the corresponding semi-blind per-tone equalizer design method for STBC OFDM systems.

Signal-to-noise ratio (SNR) is an important parameter for adaptive orthogonal frequency division multiplexing (OFDM) systems as it serves as a standard measure of signal quality. In this work, we present a novel SNR per subcarrier estimation scheme for wireless OFDM systems in frequency selective channels. The novel scheme can operate both in time and frequency, requiring only one previously known OFDM symbol. Firstly the noise variance per subcarrier estimate is obtained using the estimated channel coefficients and a novel analysis of its estimation error is provided. The noise variance per subcarrier estimate is used to obtain the SNR per subcarrier estimate. The estimation scheme takes under consideration the frequency selectivity of the channel and the variation of the noise statistics across the OFDM subcarrier index. The estimator's performance, in means of normalized mean square error (NMSE), is evaluated through simulations on a variety of channel models and is compared with another estimation scheme. The NMSE of the proposed scheme demonstrates its ability to identify the local statistics of the noise efficiently resulting into a reliable estimator in contrast with other similar approaches.

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.

Orthogonal frequency division multiplexing (OFDM) systems work well if the subcarriers are orthogonal to each other. However, the orthogonality among subcarriers may not exist and result in inter-carrier interference (ICI) at the receiver. This may cause by residual carrier frequency offset, time variations due to Doppler shift or phase noise. Further developing the parallel cancellation (PC) scheme to mitigate the ICI of OFDM systems, we expand this OFDM symbol-based PC scheme into a space-frequency (SF) coded system. This new simple space- frequency parallel cancellation (SFPC) scheme is a technique that combines the SF and PC schemes together. Computer simulations indicate that OFDM systems using the SFPC scheme outperform the regular PC and SF systems in slow and fast frequency selective fading channels, specifically at a high signal-noise-ratio (SNR). Furthermore, the error floor of the SFPC-OFDM system is significantly lower than that of the PC and SF systems without increasing computational load. Additionally, the SFPC scheme is a simple multiple input and multiple output (MIMO) system.

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.