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Adaptive bit-loading algorithms can improve the performance of OFDM systems significantly. The tradeoff between the algorithms performance (optimum solution) and the computational complexity is essential for implementation of loading algorithms. In this paper, we present a low complexity non-iterative discrete bit-loading algorithm to maximize the data rate subject to specified target BER and uniform...
In this paper, we propose a novel two-stage detection framework to facilitate the coexistence detection for OFDM-based 60-GHz millimeter-wave (MMW) WLAN/WPAN. Either blind or non-blind detection scheme can be employed at both stages regarding practical concerns. Here, the “non-blind” only refers to the case that relies on the prior knowledge of the noise variance. On the other hand, the blind detection...
In this paper, we consider multicarrier systems with multiple transmit antennas under a power-balancing constraint. Applying transmit antenna selection and discrete rate-adaptive modulation using M-ary quadrature-amplitude modulation (QAM) according to the channel variation per subcarrier, we develop an optimal transmit antenna selection scheme in terms of the maximum spectral efficiency, where all...
Existing feedback schemes of Channel State Information (CSI) in OFDMA systems can be mainly sorted into two categories as follows: 1) sounding channel feedback, and 2) precoder matrix indicator (PMI) feedback. However, both these two categories have some performance drawbacks and limitation of usage. In this paper, two Sounding-based Phase Feedback (SPF) schemes, namely, Type_1 SPF and Type_2 SPF,...
This paper proposes a transmit power and bit allocation algorithm with constraint on allocated bit number. Transmit power and bit allocation algorithms help improve performance of OFDM systems, however the existing algorithms can't fully satisfy the need of baseband data modulation methods, which only map a certain number of input bits into a data symbol. The presented approach aims at maximization...
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...
A bit loading algorithm is presented for orthogonal frequency division multiplexing (OFDM) systems to minimize bit error rate (BER), where quadrature amplitude modulation (QAM) is employed. The target data bits are loaded onto selected subcarriers that have largest remaining signal-to-noise ratio (SNRrem) values on a group-by-group basis. The number of iterations is determined by the maximum size...
The optimal detector for CP (Cyclic Prefix)-OFDM (Orthogonal Frequency Division Multiplexing) signal with inherent periodic pilots in low signal to noise ratio environments relies on perfect time synchronization. In this paper, we modify the optimal detector and propose a new suboptimal sensing scheme based on pilots estimation (SSS-BPE). In the proposed SSS-BPE, the likelihood criterion and periodicity...
This paper is concerned with the challenging and timely problem of channel estimation for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. In OFDM systems operating over rapidly time-varying channels, the orthogonality between subcarriers is destroyed leading to inter-carrier interference (ICI) and resulting in...
This paper was proposed a modified blind OFDM system parameters estimation method. The method was based on the periodicity of mobile autocorrelation function, and it estimated the OFDM symbol duration by using of the cyclic frequency test. Moreover, it limited the searching range of cyclic frequency which reduced the computational complexity. Simulation results show that the proposed time-parameter...
For single-carrier systems with frequency domain equalization, decision feedback equalization (DFE) performs better than linear equalization, and has a lower complexity and computational costs than optimum equalizers. The main challenge in DFE is the feedback symbol selection rule. In this paper, we give a theoretical framework for a simple, sparsity based thresholding algorithm. We feedback multiple...
Equispaced and equipowered pilot tones have been proved the optimal pilot design for conventional orthogonal frequency division multiplexing (OFDM) systems, but it does not hold true for non-contiguous OFDM (NC-OFDM) systems. In this paper, the optimal pilot design is derived for NC-OFDM systems with available but non-contiguously distributed spectrum fragments. Based on minimizing the average mean...
In order to increase the accuracy of timing estimation in frequency selective fading (FSF) channels and reduce the computational complexity, in this paper an adaptive symbol synchronization of OFDM blind channel estimation is proposed. First, by the ML algorithm used in flat fading channels, we give a rough estimated time position dML, then choose Δd, and give the maximum d1 of the measure function...
In this paper we propose a novel multicarrier (MC) architecture to address the energy saving problem in WLAN applications. We refer to this scheme as hybrid filtered multitone (H-FMT). Depending on the channel condition, H-FMT wisely switches between Filtered Multitone Modulation (FMT) with orthogonal pulses and adaptive orthogonal frequency division multiplexing (A-OFDM). We show that H-FMT provides...
In this paper, we consider multi-carrier systems with multiple transmit antennas under a power balancing constraint. Applying transmit antenna selection and discrete rate adaptive modulation using M-ary quadrature amplitude modulation (QAM) according to the channel variation per subcarrier, we develop an optimal antenna selection scheme in terms of maximum spectral efficiency where all the possible...
Novel subspace-based channel estimation is proposed for single-input multiple-output (SIMO) zero-padded orthogonal frequency-division multiplexing (ZP-OFDM) systems. By stacking all the received OFDM symbols, the stacked channel matrix is of block Toeplitz. The block matrix scheme is then presented such that a group of subvectors are formed from the stacked OFDM signal and the number of equivalent...
The power control problem is considered with the CR user QoS requirement and the interference to primary user under the threshold which the primary user can tolerate. We model the power control as a optimize problem which each CR user SINR must not less than minimum SINR requirement and the total interference must less than predefined threshold. Firstly we consider the network can satisfy the CR user...
Adaptive HF OFDM system can improve the transmission performance by bit and power loading based on the characteristic of subchannel. Greedy algorithm is the optimal method for finite granularity bit allocation, but it has high computational complexity. A new improved bit and power loading algorithm is proposed for HF OFDM systems in this paper, some bits is pre-allocated to some subchannels based...
Transmit diversity is an effective technique for combating fading in mobile wireless channels and improving the capacity of wireless networks. On the other hand, to cope with frequency selective fading channels, OFDM systems can be applied to transform the channels into multiple flat fading channels and solve the multipath induced ISI problem. Therefore, combining OFDM with transmit diversity can...
Adaptive coded modulation (ACM) is a key technique to increase spectral as well as power efficiency for orthogonal frequency division multiplexing (OFDM) systems. In this paper, an efficient rate adaptive low density parity check (LDPC) coded modulation (RALCM) algorithm is proposed, which maximizes the payload rate for OFDM systems under the constraint of the given transmit power and the target bit...
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