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Time varying channel breaks the orthogonality between the subcarriers of Orthogonal Frequency Domain Multiplexing (OFDM). This introduces Intercarrier Interference (ICI). One of the ways to mitigate ICI is to first estimate the channel and then equalize it. In this paper we propose to estimate the channel using Discrete Proplate Spheroidal Sequences (DPS) using pilot carriers interleaved with data...
In this paper, we consider interference cancellation (IC) schemes for uplink orthogonal frequency division multiple-access (OFDMA) systems with carrier frequency offsets (CFOs). To improve the detection performance without increasing the computational complexity of the detector, we propose a low-complexity multi-stage interference cancellation (MIC) scheme based on a grouped minimum mean squared error...
Kolmogorov-Smirnov (K-S) test-a non-parametric method to measure the goodness of fit, is applied for automatic modulation classification (AMC) in this paper. The basic procedure involves computing the empirical cumulative distribution function (ECDF) of some decision statistic derived from the received signal, and comparing it with the CDFs of the signal under each candidate modulation format. The...
Turbo equalization schemes based on minimum mean square error (MMSE) criteria available in the literature for multiple-input multiple-output (MIMO) systems are computationally expensive as they require a relatively large matrix inversion. In this paper, we propose a low complexity turbo-equalization scheme with successive interference cancellation for the equalization of rapidly time varying multi-path...
As an alternative to the OFDM transceiver, single carrier frequency domain equalization (SC FDE) based transceiver has received much attention because of its simple implementation and low peak to average power ratio (PAPR). In this paper, a minimum mean square error (MMSE) FDE for single carrier block transmission is presented to effectively equalize the channels with high frequency selectivity such...
OFDM systems are known to outperform single-carrier systems in a multipath environment. However, multipath waves, whose delay times are longer than the guard interval, cause intersymbol interference, because of which the performance of the system degrades. The effectiveness of adaptive arrays in overcoming this problem has been investigated. This paper proposes the use of an adaptive array with eigenvector...
Record capacity transmission of 101.7-Tb/s (370×294-Gb/s) is performed over 3×55 km SSMF using PDM-128QAM-OFDM modulation and pilot-based phase noise mitigation. Achieved spectral efficiency of 11 bits/s/Hz is the highest reported to date for WDM transmission.
Femtocells that use co-channel allocation with macrocells can considerably increase wireless coverage and system capacity, especially for indoor and cell-edge users. However, the benefit is realized only when cross-tier interference between femtocells and macrocells is well managed. We propose a power allocation algorithm for femtocells in downlink OFDMA systems that effectively reduces cross-tier...
Inter-cell interference (ICI) is responsible for user throughput degradation and especially for users found near cell border which additionally experience serious path-losses. Efficient methods for ICI mitigation are ICI coordination (ICIC) schemes which allocate certain resources among users in different cells. In this paper we propose a decentralized ICIC scheme in order to mitigate the ICI and...
The CP-free MIMO-OFDM system is considered to be an alternative to improve the spectral efficiency of the CP-MIMO-OFDM system. In this paper, we investigate the performance of the CP-free ST-BC MIMO-OFDM system under the effects of non-linear distortion due to HPA in the transmitter, and IQ-imbalance in the receiver. We first show that with the ST-BC encoder the constraint of the CP-free MIMO-OFDM...
In this paper, we analyze the impact of carrier frequency offset (CFO) on the performance of orthogonal frequency division multiplexing (OFDM) transmission employing space-frequency coding over relay channels. The challenge in such systems lies in the difficulty of canceling the interference resulting from the different CFOs that correspond to the relays involved in the transmission. We first analyze...
This paper focuses on the coexistence problem of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems and current radio systems such as IEEE802.11a. Aiming at improving the performance of MB-OFDM UWB, we attempt to avoid interferences from IEEE802.11a systems. The cognitive radio (CR) technology is introduced to detect the distribution of co-channel interferences...
The focus of this paper is on the performance of an orthogonal frequency division multiplexing (OFDM) transmission system considering the combined influence of receiver noise, Rayleigh fading and the timing error due to imperfect slot synchronization at the receiver. Performance results are presented in terms of BER, BER improvement and BER-floor in presence of inter-channel interference (ICI) and...
To obtain both spatial multiplexing and diversity gains simultaneously, hybrid system was introduced in MIMO-OFDM system, which combines space time coding (STC) and spatial division multiplexing (SDM) schemes. Therefore, hybrid system achieve both multiplexing and diversity gains by reducing a little performance. Representative hybrid system is consisting as space time block coding (STBC) and spatial...
In this paper, we propose a sum rate maximizing ordering method for hard decision successive interference cancellation receiver of MIMO-OFDM systems. Compared with conventional ordering methods developed for open loop MIMO systems, the proposed scheme shows considerable improvement in throughput capacity. We propose two simplified methods with considerable complexity reduction and negligible performance...
This paper presents a novel adaptive multiuser detection scheme for MIMO OFDM, which we refer to as AMUD MIMO OFDM. It combines the adaptive minimum mean square error multiuser detection scheme with prior information of the channel and interference cancelation in the spatial domain. Simulation results show that joint channel parameters estimation has good performance compared to individual parameter...
In the frame of block pilot channel estimation, an ameliorated version of the Least Squares (LS) algorithm is here proposed for OFDM systems. Former studies use the fact that the cyclic prefix (CP) duration upper bounds the length of the channel impulse response (CIR) to cancel the estimation noise lying outside the CIR first taps, equal in number to the CP samples. However, if the channel is sparse,...
This paper proposes a novel approach of suppressing narrowband interference from a multi-subband convolutional coded orthogonal frequency division multiplexing (OFDM) system. In this system, the convolutional coded data symbols using different coding generators are transmitted in different subbands. By identifying and discarding the interfered subband(s), the interference level can be greatly reduced...
In this paper, a blind method to detect and suppress narrow-band interference (NBI) for multi-band orthogonal frequency-division multiplexing (MB-OFDM) based ultrawideband (UWB) communications is proposed. The method utilizes mean-square-error (MSE) statistics in the frequency domain to detect subcarriers damaged by NBI. Approximating the MSE statistics by a decision-feedback (DF) scheme creates a...
In this paper, a new space-frequency combination technique is proposed for Alamouti coded Orthogonal Frequency Division Multiplexing (OFDM) in the context of cooperative communications. Since cooperative antennas are distributed, there may exist multiple carrier frequency offsets (MCFOs) which cause problems for conventional space-frequency decoding. The proposed algorithm, taking cues from existing...
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