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According to the cost and power consumption of wireless communication receiver under high-precision quantization, this paper discusses the effect on the performance of channel estimation for OFDM systems with low-precision quantization. Theoretical analysis and simulation results show that the low-precision quantization degrades the system performance. However, the optimized channel estimation algorithm...
In this paper, a new trend of Space Time Block codes-Orthogonal Frequency Division Multiplexing (STBC-OFDM) with Convolutional and Turbo codes. The applied method is based on Alamouti's scheme. We examine the performance of two, three and four transmitters with one receiver over Nakagami-m fading channel using convolutional and turbo codes using different types of modulation such as BPSK and 64-QAM...
The advance of wireless communications brings in various schemes of wireless digital communication technology. In the field of digital radio broadcasting, several specifications have been proposed, such as Eureka-147 and DRM (Digital Radio Mondiale). These systems require new spectrum assignment, which is a huge cost due to depletion of the available spectrum. Therefore, the IBOC (In-Band On-Channel)...
A new cross-layer design taking advantage of OFDMA in ad hoc networks is presented. OFDMA technology is exploited at the physical layer to improve data rate through multiuser diversity and to enhance channel throughput by enabling multiple concurrent transmissions over orthogonal subchannels, each consisting of a group of tones or subcarriers. The proposed Subchannel Selection Algorithm (SSA) addresses...
In adaptive modulation systems, the receiver should identify the modulation employed at the transmitter. This paper presents a new modulation classification method based on amplitude moments and correlation between subcarriers in Orthogonal Frequency Division Multiplexing (OFDM) systems. In the OFDM systems, a frequency offset causes inter-carrier interference (ICI), and the amplitude moments of received...
The mobile WiMAX standard (802.16e) uses multiple-input multiple-output (MIMO) limited feedback linear precoding to exploit the channel state information at the transmitter. Although the performance of limited feedback linear precoding in relation to traditional open-loop MIMO-OFDM has been extensively studied in the literature, these studies commonly assume perfect channel estimation at the receiver...
Within the context of high-data rate transmissions over time varying multipath fading channels, this article presents a new receiver design for orthogonal frequency division multiplexing (OFDM) systems. The received signal is processed jointly in time and frequency domains. A Discrete Wavelet Transform is applied to the received signal before equalization which is based on the minimum mean square...
Orthogonal Frequency Division Multiplexing (OFDM) can provide a flexible usage of the spectrum by controlling individual sub carriers. Sets of sub carriers can be zero-modulated to avoid interfering narrowband primary users, making OFDM a strong candidate for Cognitive Radio implementations. This paper presents the design and implementation of a non-contiguous OFDM physical layer (PHY) capable of...
It is well known that the realization of enormous capacity of multiple-input multiple-output (MIMO) channels depends greatly on the accuracy of channel estimation at the receiver. And the problem of pilot or training design is crucial to channel estimation. In this paper, the optimal pilot sequences and the optimal length of pilot-OFDM symbols are discussed. The optimizing process of pilot design...
When high power amplifiers are in OFDM transmitters employed in the area of their nonlinear characteristics, the transmitters became more energy efficient and their consumption decreases. However, transmitted signal is nonlinearly amplified and therefore subject to nonlinear distortion. When assuming perfect channel state information present at the receiver, only data symbols are nonlinearly distorted,...
This paper proposes an advanced OFDM-MIMO reconfigurable architecture that uses an adaptive switching algorithm between diversity and spatial multiplexing. The transmitter blocs' specifications such as the MIMO technique and the modulation scheme are adjusted according to the channel state, which gives a practical cognitive radio strategy. The system cost- efficiency is performed by the application...
A Doppler estimation system using a maximum likelihood criterion is presented in the context of underwater acoustic communications between moving transmitter/receiver. We simulate the method for the estimation of the Doppler effect induced by an underwater acoustic channel (UWA) using Zero Padded-Orthogonal Frequency Division Multiplexing (ZP-OFDM). Among the wide range of physical processes that...
In OFDMA multiple access wireless communication systems, carrier frequency offsets between the transmitter and the receiver tend to destroy the orthogonality among subcarriers, and hence, introduces intercarrier interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users...
Receivers for horizontally encoded LTE based MIMO-OFDM systems are considered in this paper. Adaptive modulation and coding (AMC) is used as well as precoding. The linear minimum mean square error (LMMSE), successive interference cancellation (SIC) and K-best list sphere detectors (LSD) are compared. The receivers were designed and implemented for 2??2 and 4??4 antenna systems and meet the decoding...
In this paper, we describe a novel design of a Peak-to-Average-Power-Ratio (PAPR) reducing system, which exploits the relative temporal sparsity of Orthogonal Frequency Division Multiplexed (OFDM) signals to detect the positions and amplitudes of clipped peaks, by partial observation of their frequency content at the receiver. This approach uses recent advances in reconstruction of sparse signals...
Subspace based blind channel estimation for OFDM systems has received considerable attention. Existing schemes mainly exploit inherent redundancy such as cyclic prefix and virtual subcarriers or artificial redundancy generated by pre-coding. In this paper, OFDM and multicarrier CDMA systems are considered. Frequency-domain oversampling is used at the receiver to perform detection and channel estimation...
This contribution addresses the potential of N-continuous OFDM signals in systems where the receiver is unaware of the transmitter precoder operation. First, we present a memoryless precoder rendering N-continuous signals. Second, we evaluate the effect on the magnitude of the emitted signal's error-vector. Third, we present three ad hoc precoders designed under a hard constraint on the allowed EVM...
In this paper, we propose a new blind SLM scheme with low complexity using m-sequence as a phase sequence in OFDM. The proposed scheme significantly reduces the computational complexity for searching the side information of the phase sequence and decoding the alternative symbol sequence at the receiver. After generating alternative symbol sequences using a set of phase sequences, the side information...
A well-known problem of OFDM signals is their high peak-to-average power ratio, which can cause the clipping of peaks in the transmitted signal due to the limited linear range of high power amplifiers. Operating the amplifier solely in the linear region, i.e., with a large output back-off, results in an undistorted transmitted signal, but at the expense of a low SNR at the receiver. Driving the amplifier...
We propose a novel adaptive interleaving scheme for orthogonal frequency division multiplexing (OFDM) systems. Based on the channel state information, the approach selects one interleaver from a pool of candidate interleavers. As the selected one is expected to have larger minimum Euclidean distance (MED) at receiver, the technique can significantly improve the decoding error rate performance. Compared...
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