Search

This paper introduces a new method for estimating the maximum Doppler shift using decision feedback channel estimation (DFCE). In highly mobile environments, which are expected to be covered beyond 5G and 6G systems, the relative movement between the transmitter and receiver causes Doppler shifts. This leads to inter-carrier interference (ICI), significantly degrading communication quality. To mitigate this effect, systems that estimate the maximum Doppler shift and adaptively adjust communication parameters have been extensively studied. One of the most promising methods for maximum Doppler shift estimation involves inserting pilot signals at both the beginning and end of the packet. Although this method achieves high estimation accuracy, it introduces significant latency due to the insertion of the pilot signal at the packet's end. To address this issue, this paper proposes a new method for rapid estimation using DFCE. The proposed approach compensates for faded signals using channel state information obtained from decision feedback. By treating the compensated signal as a reference, the Doppler shift can be accurately estimated without the need for pilot signals at the end of the packet. This method not only maintains high estimation accuracy but also significantly reduces the latency associated with conventional techniques, making it well-suited for the requirements of next-generation communication systems. [ABSTRACT FROM AUTHOR]

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technology is widely used in integrated radar and communication systems (IRCSs). Moreover, index modulation (IM) is a reliable OFDM transmission scheme in the field of communication, which transmits information by arranging several distinguishable constellations. In this paper, we propose a sparse reconstruction-based joint signal processing scheme for integrated MIMO-OFDM-IM systems. Combining the advantages of MIMO and OFDM-IM technologies, the integrated MIMO-OFDM-IM signal design is realized through the reasonable allocation of bits and subcarriers, resulting in better intercarrier interference (ICI) resistance and a higher transmission efficiency. Taking advantage of the sparseness of OFDM-IM, an improved target parameter estimation method based on sparse signal reconstruction is explored to eliminate the influence of empty subcarriers on the matched filtering at the receiver side. In addition, an improved sequential Monte Carlo signal detection method is introduced to realize the efficient detection of communication signals. The simulation results show that the proposed integrated system is 5 dB lower in the peak sidelobe ratio (PSLR) and 1.5 × 10 5 lower in the number of complex multiplications than the latest MIMO-OFDM system and can achieve almost the same parameter estimation performance. With the same spectral efficiency, it has a lower bit error rate (BER) than existing methods. [ABSTRACT FROM AUTHOR]

Orthogonal frequency-division multiplexing (OFDM) chirp waveforms are an attractive candidate to be a dual-function signal scheme for the joint radar and communication systems. OFDM chirp signals can not only be employed to transmit communication data through classic phase modulation, but also can perform radar detection by applying linear frequency modulation for subcarriers. However, the performance of the OFDM chirp communication system under the phase noise environment still remains uninvestigated. This paper tries to discuss the influence of phase noise on OFDM chirp communication systems and proposes effective phase noise estimation and compensation methods. We find that the phase noise effect on OFDM chirp communication systems consists of a common phase error (CPE) and an inter-carrier interference (ICI). If not compensated, the performance of the dual-function systems can be seriously degraded. In particular, an exact expression for the signal-plus-interference to noise ratio (SINR) for the OFDM chirp communication system is derived and some critical parameters are analyzed to exhibit the phase noise effects on system performance. Moreover, two low-complexity estimation approaches, maximum likelihood (ML) and linear minimum mean square error (LMMSE), as well as two compensation approaches, the de-correlation and cancellation algorithms, are respectively utilized to eliminate the phase noise impairment. Finally, the phase noise effects and the effectiveness of the compensation approach are verified by extensive numerical results. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) has a paramount role in industrial implementations, especially for better energy efficiency, high speed-data rates, and low susceptibility to interference. However, since studies on VLC for industrial implementations are in scarcity, areas concerning illumination optimisation and communication performances demand further investigation. As such, this paper presents a new modelling of light fixture distribution for a warehouse model to provide acceptable illumination and communication performances. The proposed model was evaluated based on various semi-angles at half power (SAAHP) and different height levels for several parameters, including received power, signal to noise ratio (SNR), and bit error rate (BER). The results revealed improvement in terms of received power and SNR with 30 Mbps data rate. Various modulations were studied to improve the link quality, whereby better average BER values of 5.55 x 10-15 and 1.06 x 10-10 had been achieved with 4 PAM and 8 PPM, respectively. The simulation outcomes are indeed viable for the practical warehouse model. [ABSTRACT FROM AUTHOR]

This paper examines the performance of orthogonal frequency division multiplexing (OFDM) systems for vehicle-to-vehicle (V2V) communication channels. More specifically, a doubly selective channel under high intercarrier interference (ICI) is considered. Current solutions involve complex detection and/or reduced spectral efficiency receivers. This paper proposes the use of virtual carriers (VC) in an OFDM system with a low-complexity maximal ratio combining (MRC) detector to improve the bit error rate (BER) performance. The results show that VC provides diversity in received data, resulting in a ≥5 dB gain compared to previous OFDM systems with conventional linear/nonlinear detectors used as a reference. The detector presented in this paper has linear complexity, making it a suitable solution for real-time V2V communication systems. [ABSTRACT FROM AUTHOR]

The Multiple-Input Multiple-Output (MIMO) scheme uses multiple antenna configurations to achieve high throughput data transmission in current communication systems. The new generation wireless communication system considers using generalised frequency division multiplexing (GFDM) due to its advantages such as lower out-of-band (OOB) emission and peak-to-average power ratio (PAPR), etc. However, inter-symbol interference (ISI) and inter-carrier interference (ICI) occur due to GFDM utilises the pulse shaping filter. This paper proposes a low-complexity joint minimum mean square error (MMSE) receiver to suppress ISI, ICI, and multi-user interference (MUI) for multi-user MIMO-GFDM (MU-MIMO-GFDM) system. The conventional approach is to design the equalisation and the GFDM demodulation separately. This paper jointly designs the equalisation and demodulation process that significantly reduces the complexity and enhances the error rate performance. This paper also analyzes the closed-form expression and two low-complexity methods for the proposed receiver. The simulations demonstrate the effectiveness of the proposed low-complexity multi-user MIMO-GFDM receivers. [ABSTRACT FROM AUTHOR]

Multiple‐Input Multiple‐Output Orthogonal Frequency Division Multiplexing (MIMO‐OFDM) is an essential technology in the wireless communication system. However, its performance is significantly affected by Carrier Frequency Offset (CFO), which leads to inter‐carrier interference (ICI). The CFO estimation and compensation techniques are used to mitigate the Doppler effect. In addition, the confidentiality of data is a key factor of the system. This paper proposes a Turbo‐based encryption and coding scheme to improve reliability and security for the MIMO‐OFDM wireless communication systems affected by the Doppler frequency offset. In our proposed scheme, the secret key is produced from channel parameters between legitimate users and it is used as a seed for generating a pseudo‐random bit sequence using an Advanced Encryption Standard (AES) generator with variable key lengths. The Turbo code's puncturing mechanism is controlled by this pseudo‐random bit sequence. The proposed method is applied to the system with different modulation schemes through the Rayleigh channel. The simulation results show that the system affected by the Doppler effect would obtain the best performance when using the highest key length of the AES generator, the BPSK, and a great number of receive antennas. Furthermore, the proposed solution outperforms several previous approaches for the MIMO‐OFDM systems. [ABSTRACT FROM AUTHOR]

Summary: The dimming control feature of light‐emitting diode (LED) makes it a viable candidate for indoor lighting applications. In this study, the performance of variable pulse position modulation (VPPM) based visible light communication (VLC) system is investigated in detail for an office room of 5 × 5 × 3‐m3 dimensions. A total of four LED lamps having Lambertian radiation patterns are mounted over the ceiling of the room. Several receiver locations are chosen over the three different trajectories to evaluate the error performance of the proposed system. The height of the receiver plane is also varied to find the optimum height where error‐free data reception is achieved. Moreover, an effort is made to optimize the dimming percentage of the transmitted signal using VPPM in terms of bit error rate (BER), where the illumination requirements over the receiver plane are also as per the International Standards of Organization (ISO). The results show that the duty cycle of 50% is optimum for efficient system performance. Furthermore, a colored image is transmitted through the proposed system and the computed results reveal that satisfactory BER performance and good quality of the image is received at receiver heights ranging from 0.85 to 1.7 m, that is, approximately 2.75 to 5.6 ft above the ground plane. [ABSTRACT FROM AUTHOR]

Performance of visible light communication systems which is encoded using turbo product codes is studied in this article. It is the first time to show the effect of turbo product codes in these systems. We chose ceiling bounce model since its accuracy with the practical measurements is proved. Our simulations are carried out in two different link distance and two different data rates. Encoder parameters are selected according to the code rate. This way, meaningful comparison can be made among the results considering distance, data rate, and code rate. Our investigations infer that using turbo product codes, higher data rate is achieved where link distance is the same. Similarly, it can be reached higher link distance when data rate is set to a constant value. [ABSTRACT FROM AUTHOR]

This paper designs and analyzes the bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) framework under color-shift-keying (CSK) modulation to achieve spectrally efficient transmissions in visible light communication (VLC) systems. Specifically, we investigate the protograph low-density parity-check (LDPC) codes, bit-to-symbol mapping schemes, and constellation labeling rules in higher-order CSK-aided VLC systems. To fully explore the BICM-ID benefit, we propose an irregular CSK mapping, in which an $M$ -ary standardized constellation (called “Standard constellation”) and a new $M$ -ary constellation (called “Target constellation”) are separately applied to modulate two different coded sub-blocks in a codeword to optimize the error performance of the CSK-aided VLC systems. Furthermore, using a modified protograph extrinsic information transfer (PEXIT) algorithm, we construct two types of protograph LDPC codes (i.e., unpunctured and punctured protograph LDPC codes) that outperform the conventional protograph LDPC codes. Both analytical and simulation results show that the proposed irregular-CSK-mapped BICM-ID employing the new protograph LDPC codes and Target constellation is capable of achieving outstanding performance, and is a promising transmission solution for high-speed VLC applications. [ABSTRACT FROM AUTHOR]

Impulsive noise significantly deteriorates the performance of orthogonal frequency-division multiplexing (OFDM)-based underwater acoustic (UWA) communication systems. The pulse blanking (PB) based approach can mitigate the impulsive noise. However, it causes inter-carrier interference (ICI) and signal attenuation to the receiver. In this work, we first show that the ICI introduces pronounced non-Gaussianity to the receiver chain and leads to significant performance degradation. We then propose a non-Gaussianity-aware iterative ICI cancelation scheme to mitigate the adverse impacts of PB. A companding transformation scheme is incorporated into the soft symbol computation to alleviate the non-Gaussianity of the log-likelihood ratios (LLRs) caused by the residual ICI and impulsive noise. Simulation results illustrate that the proposed non-Gaussianity-aware iterative receiver achieves significant performance gains over the conventional non-Gaussianity-agnostic one with even lower computational complexity. [ABSTRACT FROM AUTHOR]

Under-Water Acoustic (UWA) communication networks are commonly formed by associating various independent UWA vehicles and transceivers connected to the bottom of the sea with battery-operated power modems. Orthogonal Frequency Division Multiplexing (OFDM) is one of the most vital innovations for UWA communications, having improved data rates and the ability to transform fading channels into flat fading. Moreover, OFDM is more robust on Inter- Symbol and Inter-Carrier Interferences (ISI and ICI respectively). However, OFDM technology suffers from a high Peak to Average Power Ratio (PAPR), resulting in nonlinear distortions and higher Bit Error Rates (BERs). Saving power of battery deployed modems is an important necessity for sustainable underwater communications. This paper studies PAPR in UWA OFDM communications, employing Selective Mapping (SLM) as a tool to mitigate PAPR. The proposed SLM with the oversampling factor method proves to be less complex and more efficient. Simulation results indicate that SLM is a promising PAPR reduction method for UWA OFDM communications reducing BER. [ABSTRACT FROM AUTHOR]

Multicarrier code‐division multiple access (MC‐CDMA) is an efficient method for high‐speed data transmission. MC‐CDMA systems are mostly affected with high peak‐to‐average power ratio (PAPR) and this may reduce the spectral efficiency of the system. This paper presented the PAPR reduction of a MC‐CDMA using partial transmit sequence (PTS) method via whale optimization algorithm (WOA) and modified brain storm optimization (MBSO). For quadrature phase‐shift keying (QPSK) modulation, our proposed method uses pseudorandom sequence (PRS) at dissimilar amount of active users. MBSO algorithm optimizes time delay and carrier frequency offset (CFO), and thus, we can minimizes the intercarrier interference from the carrier signal. Thus, we can achieve high‐speed data transmission in MC‐CDMA with PTS system. The results show that 64‐bit QPSK has superior performances in case of bit error rate, PAPR, spectral efficiency, maximum likelihood sequence estimation, normalized mean square error, minimum mean square error, CFO, and mean square error. Hence, the performance variations for the abovementioned parameters are 60%, 23%, 12%, 15%, 40%, 5%, 14%, and 3%, respectively. These all the outcomes are taken for dissimilar modulation and the different channels. [ABSTRACT FROM AUTHOR]

The revolution of the solid-state lighting technology and the looming radio frequency (RF) spectrum crisis enabled the rapid evolution of visible light communication (VLC) in the recent times. To furnish contemporaneous illumination and communication, VLC relies on white light emitting diodes (WLEDs). However, the limited modulation bandwidth of WLEDs poses a threat to VLC as the achievable data rates are drastically minimized. Eventually, to enhance the achievable throughput, the pre-eminent way is to apply orthogonal frequency division multiplexing (OFDM) to a VLC system. Furthermore, a VLC system can also exploit non-orthogonal multiple access (NOMA) scheme to bestow with seamless services to the multiple users. However, much similar to the RF-based OFDM system, the OFDM-VLC system also inherits one of the serious disadvantages like the high peak to average power ratio (PAPR). In addition, the rapid fluctuations of the continuous time-domain signal amplitude in DC-biased optical OFDM (DCO-OFDM) results in much complicated design of the LED driver circuitry for driving the LED. Thus, to overcome such drawbacks, we incorporate delta-sigma modulators (DSM) to the NOMA-VLC system which is making use of DCO-OFDM, and we analyze its performance over VLC channel environment. The stunning advantage imparted by the proposed DSM-based DCO-OFDM-NOMA-VLC system is that the continuous amplitude of the time-domain transmitted signal is converted into two levels for driving the LED. Additionally, with the major goal to maximize the sum throughput of the proposed multiuser VLC system by taking into consideration both the user fairness as well as the intensity constraints, we derived the optimal values for the power allocation coefficients corresponding to the fair power allocation algorithm. Furthermore, the dynamically varying fair power allocation algorithm is compared with the fixed/static power allocation algorithm. The major contribution of this work is of two-fold: firstly, the proposed DCO-OFDM-NOMA-VLC system which is making use of DSM exhibits a remarkable reduction in PAPR when compared with the conventional system without the application of DSM, where the proposed system demonstrates a significant gain of 4.78 dB in terms of PAPR reduction. Secondly, from the simulated results it can affirmed that the proposed system not only achieves enhanced sum rates and better outage performance but also imparts a better bit error ratio (BER) performance corresponding to the far user. • For reducing the PAPR in OFDM-NOMA-VLC systems, we applied the concept of DSM. • The DSM-DCO-OFDM-NOMA-VLC system can convert the continuous amplitude of the time-domain signal into 2 levels for driving the LED. • For maximizing the sum throughput, we derived the optimal values for the power allocation coefficients. • DSM-DCO-OFDM-NOMA-VLC system demonstrates a significant gain of 4.78 dB in terms of PAPR reduction. • The DSM-DCO-OFDM-NOMA-VLC system improves the BER performance of the far user. [ABSTRACT FROM AUTHOR]

Due to the spectrum scarcity in the space information networks, non-orthogonal multiple access (NOMA) is envisioned as a promising technique in satellite-terrestrial communications networks as its improved system capacity and spectral efficiency. In this paper, to further improve the spectrum utilization efficiency in satellite-terrestrial networks, bandwidth compression (BC) design is embedded in the NOMA scheme, which contributes to the non-orthogonality both in power and frequency domains, named BC-NOMA. However, with such advantages provided by BC-NOMA, the inter-carrier interference (ICI) and the intra-group interference (IGI) are severe, which degrade the reliability and the capacity. Therefore, the impacts of BC and power domain multiplexing on the system capacity are first investigated. To cancel the mixed internal interference, an iterative and successive interference cancellation (ISIC) approach is proposed. Secondly, the symmetrical coding (SC) is designed with BC-NOMA to avoid the error propagation when using ISIC, which benefits much for the low power user (LUE). Furthermore, the closed-form expression of error probability for SCNOMA is derived and the system and individual capacities are also analyzed. Results show that the BC-NOMA system can achieve a quasi-optimal performance compared with the orthogonal subcarrier NOMA (ONOMA) system and balance the fairness. [ABSTRACT FROM AUTHOR]

High mobility and multipath propagation induce Doppler and delay dispersion, respectively. When both phenomena affect the transmitted signal, the communication channel is known as a doubly selective channel (DSC). In multicarrier systems under this scenario, intersymbol interference (ISI) and intercarrier interference (ICI) are ineluctably present, severely degrading the system's performance. Therefore, much effort has been invested in researching convenient waveforms that enable the receiver self-interference cancellation, while making use of the available space, time, and frequency diversity. In this paper, a multicarrier multiple-input multiple-output (MIMO) system for communication in DSCs is presented. By using the virtual trajectory (VT) representation of the MIMO channel, direct conversion of Doppler diversity into additional virtual antennas in the receiver is achieved. This concept is developed for a coherent system with one-tap channel estimation (CE) and equalization algorithms of low complexity as well as for incoherent detection using differential space-frequency block codes (DSFBCs), where pilot signals are not used. For both systems, runtime cancellation and/or inversion of complex interference channel matrices is avoided. Diversity of the doubly selective MIMO channel is exploited without sacrificing compatibility with current multicarrier MIMO systems. The presented system offers robustness in DSCs with minimal extra complexity when compared to conventional approaches. The results demonstrate that MIMO orthogonal frequency division modulation (MIMO-OFDM) can be still implemented in extremely high Doppler scenarios if VT reception is incorporated. [ABSTRACT FROM AUTHOR]

Visible light communications (VLCs) using light-emitting-diodes (LEDs) as communication devices have developed rapidly with the widespread deployment of solid-state illumination. However, the modulation bandwidth of LEDs is one of the dominant issues that limit the VLC system efficiency. Although plenty of techniques have been investigated to deal with this restriction, few people pay attention to the theoretical analysis of LED illumination process. The light-conversion concept shows significant influence on the white LED transmission modeling and receiving technologies. We propose an LED response modeling approach based on the white light generation process and its spectral characteristics, as well as the corresponding signal receiving methods. A dual-pole zero-forcing equalizer (ZFE) is designed, and the analytical signal-to-noise ratios (SNRs) of the output signal with different receiving processes are derived. Simulation results show that SNR is effectively improved by adopting the proposed ZFE, and the dual-pole equalizer can effectively improve system bit error rate performance with different transmission rate. Under the practical lighting scenario, transmission rate can reach up to 70 Mbps over a 1.5 m line-of-sight link. Meanwhile, a minimum data rate of 30 Mbps can be supported within a coverage area of 3 m in diameter. [ABSTRACT FROM AUTHOR]

In underwater acoustic orthogonal frequency division multiplexing (OFDM) communication system, channel variations would introduce inter-carrier interference (ICI). This gets more severe as mobile speed, carrier frequency or OFDM symbol duration increases. In this paper, we propose a kind of parallel iterative ICI cancellation algorithm to combat that problem. The proposed method extracts channel variations from the adjacent OFDM symbols, and constantly improves the estimation accuracy of ICI through iteration. Finally, simulation and trial in real lake channel verify the availability and stability of the algorithm in the underwater acoustic time varying channel. In addition, this algorithm avoids the matrix inversion, reducing the complexity of the algorithm, and has the obvious advantage in accuracy and speed. [ABSTRACT FROM AUTHOR]

A fundamental drawback of the orthogonal frequency division multiplexing (OFDM), both in communication and radar, is its sensitivity to the Doppler effect. In this paper, we present a novel signal processing approach for OFDM radar and communication systems that overcomes the Doppler sensitivity of OFDM. We propose a scenario independent Doppler correction method that enables an intercarrier-interference free processing for OFDM. The Doppler robustness of the proposed approach opens new perspectives for system parameterization, enabling radar concepts not feasible before. We show in simulations that the proposed Doppler correction method is superior to the classical signal processing in many important aspects. Measurements with an OFDM-MIMO radar prototype are used to validate the proposed approach and to show its effectiveness in real-life applications. [ABSTRACT FROM AUTHOR]

Synchronization is an important issue for a communication system to decode the received symbols correctly. Basically, synchronization process includes the time and frequency offsets prediction and compensation. If there are Time Offset (TO) and Carrier Frequency Offset between the Transmitter (Tx) and Receiver (Rx), OFDM system will suffer the Inter-Symbol Interference and Inter-Carrier Interference that degrade the system performance dramatically. In this paper, we propose a low complexity time synchronization and sector identification (ID) method using the unique null sub-carrier feature of the Primary Synchronization Signal and the Second Synchronization Signal for the LTE system. Combined with the down-sampling technique, computer simulations and experimental results show that the proposed method can predict the TO and sector ID correctly and has the advantage of very low computational complexity. [ABSTRACT FROM AUTHOR]

• The main contribution of our work is that we introduce the concept of FR from the concept of time-frequency duality and propose a low-complexity FR scheme which can be applied in practical UWA OFDM communication systems for ICI mitigation. Orthogonal-frequency-division-multiplexing (OFDM) modulation has been intensively studied in underwater acoustic (UWA) communications recently for its ability to tackle large delay spread channels. Nevertheless, the inter-carrier interference (ICI) caused by Doppler spread of UWA channels degrades the system performance significantly. This paper proposes the concept of frequency reversal (FR) dual to time reversal (TR), as well as a feasible FR scheme. FR can compress the frequency spread caused by Doppler, and hence eliminate the ICI in OFDM communications. Furthermore, FR has similar advantages as TR: 1) low computational complexity and 2) robustness against complicated and changeable channels. Numerical simulation verifies the effectiveness of the proposed FR scheme as an ICI mitigation technique for UWA OFDM communications. [ABSTRACT FROM AUTHOR]

Wireless Body Area Network (WBAN) is the most convenient, cost-effective, accurate, and non-invasive technology for e-health monitoring. The performance of WBAN may be disturbed when coexisting with other wireless networks. Accordingly, this paper provides a comprehensive study and in-depth analysis of coexistence issues and interference mitigation solutions in WBAN technologies. A thorough survey of state-of-the art research in WBAN coexistence issues is conducted. The survey classified, discussed, and compared the studies according to the parameters used to analyze the coexistence problem. Solutions suggested by the studies are then classified according to the followed techniques and concomitant shortcomings are identified. Moreover, the coexistence problem in WBAN technologies is mathematically analyzed and formulas are derived for the probability of successful channel access for different wireless technologies with the coexistence of an interfering network. Finally, extensive simulations are conducted using OPNET with several real-life scenarios to evaluate the impact of coexistence interference on different WBAN technologies. In particular, three main WBAN wireless technologies are considered: IEEE 802.15.6, IEEE 802.15.4, and low-power WiFi. The mathematical analysis and the simulation results are discussed and the impact of interfering network on the different wireless technologies is compared and analyzed. The results show that an interfering network (e.g., standard WiFi) has an impact on the performance of WBAN and may disrupt its operation. In addition, using low-power WiFi for WBANs is investigated and proved to be a feasible option compared to other wireless technologies. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new method for inter-carrier interference (ICI) mitigation in orthogonal frequency-division multiplexing (OFDM) systems. The proposed approach views the signal reconstruction problem at the receiver end as an integer least squares (ILS) problem, and uses a recently developed spectral approach called sequential probabilistic ILS (SPILS) to solve it. The proposed approach outperforms other state-of-the-art approaches while having the same computational complexity. In addition, we present a novel extension to the SPILS scheme that allows the generation of soft decisions (for communication systems which use soft-decision decoding). The use of soft-decision decoding (naturally) brings significant improvement in the detection reliability, and we show that the proposed method again outperforms other state-of-the-art approaches. To better address the tradeoff between performance and complexity, we first suggest a novel method to reduce the number of matrix inversions required and hence, to reduce the implementation complexity without any degradation in performance. We also introduce a novel low complexity scheme termed Quick SPILS (QSPILS) in which we lose a little in detection reliability, but significantly reduce the implementation complexity. [ABSTRACT FROM PUBLISHER]

Multiple-access interference (MAI) and intercarrier interference (ICI) due to a carrier frequency offset are two major factors that deteriorate the performance of multicarrier code-division multiple access (MC-CDMA) in wireless communications. This paper presents a new mathematical analysis for the spectral efficiency of asynchronous MC-CDMA communication systems over a frequency-selective Rayleigh fading environment. It employs accurate statistical models for MAI and ICI that account for the correlation between adjacent subcarriers to derive a new simple expression. An approximate expression for the spectral efficiency is also provided, which reduces complexity. [ABSTRACT FROM AUTHOR]

Summary: With wireless communications in high‐mobility environment becoming popular, this poses a big challenge for communication systems based on the comb‐pilot OFDM, such as IEEE 802.11p, since it has not the enough pilots to estimate the time‐ and frequency‐selective channel accurately. In this paper, several comb‐pilot schemes and three comb‐pilot design rules are proposed to meet the Nyquist criterion for sampling the vehicle‐to‐vehicle (V2V) channel and the requirements of second‐order statistic of V2V channel. Based on the proposed pilot schemes, an iterative channel estimation method from the CE‐BEM model is proposed, together with three ICI cancellation methods. After thorough simulation, the effectiveness of the comb‐pilot design rules, the proposed channel estimation method, and intercarrier interference (ICI) cancellation methods is verified. Compared with other channel estimation methods, the proposed method performs better. The simulation results also reveal that the channel order L+1 has a great impact on the performance of the comb‐pilot OFDM system. [ABSTRACT FROM AUTHOR]

Spatial Modulation Technologies (SMTs) are schemes that reduce inter-carrier interference (ICI), inter-channel interference, inter-antenna synchronization (IAS), and system complexity for multiple-input multiple-output (MIMO) communication systems. Moreover, high spectral and energy efficiency have rendered SMTs attractive to underwater acoustic (UWA) MIMO communication systems. Consequently, this paper focuses on SMTs such as spatial modulation (SM), generalized spatial modulation (GSM), and fully generalized spatial modulation (FGSM) in which one constant number and one multiple number of antennas are active to transmit data symbols in any time interval for underwater acoustic communication (UWAC). In SMTs, the receiver requires perfect channel state information (P-CSI) for accurate data detection. However, it is impractical that the perfect channel knowledge is available at the receiver. Therefore, channel estimation is of critical importance to obtain the CSI. This paper proposes the pilot-based recursive least-square (RLS) adaptive channel estimation method over the underwater time-varying MIMO channel. Furthermore, maximum likelihood (ML) decoder is used to detect the transmitted data and antennas indices from the received signal and the estimated UWA-MIMO channel. The numerical computation of mean square error (MSE) and bit error rate (BER) performance are computed for different SMTs like SM, GSM and FSGM using Monte Carlo iterations. Simulation results demonstrate that the RLS channel estimation method achieves the nearly same BER performance as P-CSI. [ABSTRACT FROM AUTHOR]