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In this paper, we propose an efficient carrier frequency offset (CFO) estimation technique based on the space alternating generalized expectation-maximization (SAGE) for uplink orthogonal frequency division multiple access (OFDMA) systems. In general, the SAGE method transforms a multidimensional search problem into a sequence of one-dimensional searches, which greatly simplifies the estimation procedure...
OFDM is playing a more and more important role in wireless communication systems. Unfortunately, it is not trivial to conduct a performance analysis of OFDM systems. Therefore, it is highly desired to develop an analytical design and performance analysis framework for OFDM channels. In this paper, we consider a unified performance metric for OFDM channels, which we shall refer to as outage exponent...
In this paper, the optimal number of pilot symbols for orthogonal frequency division multiplexing (OFDM) systems is determined based on the criterion of minimizing the loss in mean capacity, and the simulation results that verify the analysis are presented.
In this paper, the outage performance is investigated for orthogonal frequency division multiplexing (OFDM)-based selective amplify-and-forward cooperative networks over independent but not identically distributed (i.n.i.d.) Nakagami-m fading channels, with integer values of parameter m. A unified closed-form expression for the outage probability is derived for three selective relaying schemes. The...
In this paper, a new opportunistic feedback protocol for orthogonal frequency division multiple access (OFDMA) systems with mixed realtime (RT) and non-realtime (NRT) traffic is proposed and analysed. Based on the proposed feedback mechanism, a dedicated feedback channel is allocated for each RT user, while shared feedback channels are available for all NRT users. NRT users have to compete to send...
This paper proposes a differential codebook-based method to reduce the feedback overhead for closed-loop MIMO-OFDM systems. With the assumed multimode transmit precoding, both the number of data streams (rank) and the index of precoding matrix are fed back to the transmitter at each sub-band. By exploiting the channel correlation in frequency domain, an enhanced differential codebook (a subset of...
We investigate the outage probability for amplify-and-forward (AF) and decode-and-forward (DF) relaying in OFDM-based cooperative networks. To minimize the outage probability, the relay which has the maximum received SNR is selected as the cooperative relay. Based on the relay selection, the problems of optimal power allocation and placing relays in the optimal position are discussed. And the expressions...
Abstract-The problem of optimizing the AGC reference level for OFDM-based telecommunication systems is studied in this paper. We first give a statistical model of the OFDM signal envelop, then derive the power of granular noise and clipping distortion introduced by the analog-to-digital converter. The overall distortion which is related to AGC reference level is discussed and closed form expression...
Frequency synchronization plays a critical role in acquiring cooperative diversity for cooperative OFDM systems. However, the superposition of different carrier frequency offsets (CFOs) among each relay and destination makes the estimation difficult. In this paper, a novel multiple CFOs estimation algorithm is proposed. With this algorithm, the CFO corresponding to each relay can be accurately estimated...
Orthogonal Frequency Division Multiplexing (OFDM) is predicted to be implemented in future broadcasting and Wireless Local Area Network (WLAN) systems due to its robustness in transmitting a high data rate. Some examples of current applications using OFDM include ETSI BRAN in Europe, IEEE802.11 in United States, and ARIB MMAC in Japan have adopted the OFDM transmission technology as a physical layer...
Semi-blind joint CFO, channel estimation and data detection for OFDM systems over doubly selective channels (DSCs) is investigated in this work. A joint iterative algorithm is developed based on the maximum a posteriori expectation-maximization (MAP-EM) algorithm. In addition, a novel algorithm is also proposed to obtain the initial estimates of CFO and channels. Simulation results show that the performance...
This paper analyzes the performance of space-time block coded orthogonal frequency division multiplexing (OFDM) systems. In our analysis, we abandon the usually made assumption of quasi-static channel conditions. Instead of this, we consider the more general and realistic case that the channel envelope changes during two consecutive transmission time slots. In addition, we take the spatial correlation...
Orthogonal frequency division multiplexing (OFDM) technique has a major problem due to the impact of the flat fading channel. Many channel estimation techniques addressed this problem. This paper presents a technique named trend analysis pilot aided (TAPA) channel estimation, which is dynamic technique minimizes the required training data. Simulation results show that the proposed technique exhibits...
In this paper, we propose a general expression of the peak-to-average power ratio (PAPR) distribution in orthogonal frequency division multiplexing (OFDM) systems with unequal power allocation strategy, which is based on the extreme value theory for Chi-squared-2 process. The proposed general distribution of the PAPR depends on the number of the subcarriers, distribution of the power allocation and...
An efficient IQ imbalance estimation and compensation scheme for MIMO-OFDM systems is proposed. The scheme exploits the inherent data structure imposed by space frequency block code (SFBC), for lowering the implementation complexity. As such, no further requirements are laid on the preamble design. The proposed algorithm can be easily extended to the MIMO-OFDM systems using STBC or with frequency-selective...
Inter-cell Interference (ICI) is a key issue in orthogonal frequency-division multiple access (OFDMA) systems. Since OFDMA was proposed to be used in next generation networks several schemes have been investigated for mitigating the ICI. One of the techniques that promises improvement in reducing ICI is partial frequency reuse (PFR). In this paper we investigate a flexible bandwidth allocation (FBA)...
In this paper, we propose an RNS arithmetic based FH pattern design approach that is well suited and easy to implement for practical OFDMA systems. The proposed RNS aided FH scheme not only guarantees orthogonality among intra-cell users but also randomizes inter-cell interference. We present detailed construction procedures and performance analysis for both independent and cluster hopping scenarios...
In this paper, a joint channel estimation and data detection algorithm is proposed for OFDM systems under doubly selective channels (DSCs). After representing the DSC using Karhunen-Loe??ve basis expansion model (K-L BEM), the proposed algorithm is developed based on the expectation-maximization (EM) algorithm. Basically, it is an iterative algorithm including two steps at each iteration. In the first...
A method for estimating the Doppler spread in mobile orthogonal frequency division multiplexing (OFDM) systems is described. The estimation is based on phase message of time domain channel estimation over several OFDM symbols. In OFDM systems, channel estimation is popularly performed in frequency domain. Channel frequency response estimates are affected by noise and inter-carrier interference (ICI)...
Multiuser diversity can significantly improve wireless system performance by exploiting the feedback information that conveys the channel quality. In multiple input-multiple output and orthogonal frequency division multiplexing (MIMO-OFDM) systems, the per subcarrier on per antenna feedback induces a substantial amount of feedback overload and requires high computational complexity. This paper addresses...
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