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In cooperative relay systems, relayed signals propagate through different channels and are received at the destination node with distinct timing and carrier frequency offsets (CFOs). This feature makes synchronization a rather challenging task as compared with centralized multiple-input multiple-output systems. Unlike conventional preamble designs with good correlation properties only in time domain...
In this paper, an iterative interference suppression algorithm based on energy spreading transform (EST) is proposed. The performance of interference suppression can be significantly improved by our proposed iteration scheme between demodulator and parameter estimator. The energy of residual interference after initial narrowband interference (NBI) suppression is spread over the whole band by EST,...
A novel chaotic FH-OFDM communication system based on OFDM (Orthogonal Frequency Division Multiplexing) and FH (Frequency Hopping) is presented. The carriers frequency of OFDM are controlled by chaotic pseudo random sequences. In every iteration period, the method adopts the different keys. It analyzes the balance, the distance and the maximum Hamming correlation of this FH sequences in theory and...
This paper investigates the sidelobe suppression techniques of orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) systems. We firstly argue that the existing sidelobe suppression algorithms cannot satisfy the special requirements of CR systems. Then we formulate the interference suppression problem of CR systems into two algorithms from capacity perspective, namely, average...
This paper investigates the problem of resource allocation in spatial multiuser access cognitive OFDM (orthogonal frequency division multiplexing) systems. The objective is to maximize the cognitive users' weighted rate sum, which is constrained by the licensed users' (LU) interference temperatures. The spatial multiuser access using singular value decomposition (MU-SVD) model is introduced to the...
A new method is proposed to construct space-frequency (SF) codes for multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems undergoing frequency-selective fading. The new design exploits the geometric relationship of coherent and noncoherent SF codes, and each codeword is constructed as a product of a noncoherent SF codeword and an information-bearing square...
In this paper, we propose a noncoherent space-frequency (SF) code for multiple-input-multiple-output (MIMO) orthogonal-frequency-division-multiplexing (OFDM) systems for broadband wireless communications. The proposed noncoherent SF code matrix is constructed as a combination of a noncoherent SF code matrix and a differential modulation matrix. Comparing to noncoherent SF codes and differential SF...
Due to the nonlinear effect caused by the high power amplifier (HPA), wireless communication system suffers from the in-band distortion and out-band spectrum regrowth. For orthogonal frequency division multiplexing (OFDM) systems, the high peak to average power ratio (PAPR) would lead to HPA nonlinearity or inefficiency. Compared to traditional PAPR reduction methods, the tone reservation with null...
In this paper, we focus on noncoherent space-frequency (SF) coded multiple-input-multiple-output orthogonal-frequency-division-multiplexing (MIMO-OFDM) systems. Based on OFDM subcarrier grouping, a group-based unitary space- frequency code is proposed and the effect of grouping on system performance is studied. Comparing to the coding scheme without grouping, which implements SF coding among all the...
In this paper, we propose a space-time coding and carrier block spreading based multiple-input-multiple-output (MIMO) orthogonal-frequency-division-multiplexing (OFDM) system. The proposed system exploits the potential spatial and frequency diversity of MIMO systems in frequency-selective fading environments through a two-stage procedure. In the first stage, we use space-time coding to exploit the...
Partial transmit sequence (PTS) is a promising technique for reducing the high peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. In PTS, multiple candidate signals are generated and the optimal signal with the lowest PAPR is selected for transmission. One drawback of PTS is that parts of the candidate signals are strongly correlated so as to degrade the...
The main problem of orthogonal frequency-division multiplexing (OFDM) system is the large peak-to-average power ratio (PAPR). In this paper, we investigate two conventional PAPR reduction methods-clipping and partial transmit sequence (PTS), and analyze the computational complexity of each method. Furthermore, based on the conventional methods, a novel PAPR reduction method is proposed to make a tradeoff...
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