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Unique word (UW) OFDM is a new multicarrier technique that was first introduced in [1]. In this technique, the guard interval is a part of the inverse FFT (IFFT) output, and is filled with known symbols. To be able to construct — by using an IFFT — a time domain signal containing a block of known samples, it is necessary to sacrifice a number of carriers. These carriers are called redundant carriers...
In sub-band ultra-wideband (SUWB) systems, the use of spreading codes in conjunction with sub-banding enables energy efficient reduced sampling rate receiver designs. In this work, the orthogonal frequency division multiplexing (OFDM) technique is proposed for SUWB systems as a means to mitigate the multipath fading effects of the channel. The OFDM demodulation performed at the sub-sampled rate with...
In this paper, we propose the use of constellation rotated vector OFDM (CRV-OFDM) to combat a fast fading channel, which accompanies with carrier frequency offset (CFO) and Doppler frequency spread (DFS). Employing Gaussian approximation of interference, we give pair-wise error probability bounds of CRV-OFDM in terms of the CFO and DFS. The theoretical analysis indicates that robustness of CRV-OFDM...
This paper presents indoor experimental results on an implemented real-time downlink multiuser multiple-input multiple-output (DL-MU-MIMO) transceiver for next generation wireless LAN systems. In the transceiver, channel state information (CSI) is estimated at each station (STA) and fed back to an access point (AP) on a real-time basis. At the AP, transmit beamforming weight for DL-MU-MIMO transmission...
In this paper, a resource allocation problem for downlink multiple input-single output orthogonal frequency division multiple access (MISO-OFDMA) systems is investigated. The problem is defined as maximizing the minimum user rate with the constraints of total power and bit error rate (BER). Since it is difficult to obtain the optimal solution to this problem, a suboptimal but efficient solution is...
The reduction of spurious emission is an important issue in future OFDM-based systems, especially in the context of cognitive radio, when the primary users must be protected from the interference. In this paper, flexible quasi-systematic precoder is presented for non-contiguous OFDM transmitter, which has the effect of relatively small distortion of the data symbols modulating the subcarriers. We...
This paper proposes a novel clipping and filtering method employing transmit power control to improve the bit error rate (BER) performance in MIMO-OFDM transmission. The feature of the proposed approach is to perform the transmit power control before clipping and filtering to alleviate the BER degradation caused by clipping and filtering. Since the transmit power control to satisfy maximum signal-to-noise-plus-distortion...
Distributed space-time block coding with orthogonal frequency division multiplexing (DSTBC-OFDM) and distributed space-frequency block coding with orthogonal frequency division multiplexing (DSFBC-OFDM) are introduced in this paper. Unlike the original DSTBC scheme which was designed for networks with a fixed number of relays operating in frequency-nonselective channels with insignificant Doppler...
This paper proposes a novel recursive approach for orthogonal frequency division multiplexing (OFDM) channel estimation over highly mobile channels without any priori channel statistics. The key idea is to decompose each objective channel into the known component and the rest for estimation. The known component is the output of the prior iteration except that the first one is attained in linear time-varying...
This paper addresses the problem of fractional timing offset and channel estimation in Multiple input Multiple output orthogonal frequency division multiplexing (MIMO OFDM) systems. The estimators have been derived assuming a flat fading channel and using the maximum likelihood criterion. Closed form Cramer Rao bound (CRB) expressions for fractional timing offset and channel response are also derived...
In this paper, the truncated singular value decomposition expectation-maximization (TSVD-EM) based channel estimation on single transmit antenna transmission is extended to transmit diversity transmission. Particular attention is given to Long Term Evolution (LTE) systems. In order to obtain the received symbols for each transmit antenna, an approximation is proposed by using the soft symbols and...
Deliberate clipping is a simple solution to high Peak-to-Average Power Ratio problem of OFDM signal. In Amplify-and-Forward OFDM relay networks, due to the limited resource, deliberate clipping is also suggested. However, clipping is a nonlinear process and may cause significant performance degradation. Based on Bussgang Linearization Theory, we provide a linear system model for Amplify-and-Forward...
This paper considers the resource allocation problem for a Multiple Access Relay Channel (MARC). A transmission scheme with OFDMA and Amplify-and-Forward (AF) relaying is assumed. To maximise the sum rate a joint allocation of transmit power and subcarriers has to be done. This problem is known to be NP-hard and can only be solved by an exhaustive search which is not feasible for practical problem...
In this paper, we propose a new technique to reduce the interference caused by high OFDM sidelobes to the primary users in MIMO-OFDM cognitive systems. The proposed technique does not affect the rate of the system and has very low complexity. We also analyze the performance of the technique for a class of flat fading channels and show that the analytical results agree with simulations. Furthermore,...
This paper considers the resources allocation problem in decode-and-forward (DF) relayed OFDM based cognitive radio (CR) system. The subcarrier matching and power allocation are optimized jointly under the individual power constraints in source and relay so that the sum rate is maximized while the interference induced to the primary system is kept below a pre-specified interference temperature limit...
This paper investigates the resource allocation problem in a relay-aided cognitive radio (CR) system under the orthogonal frequency division multiplexing (OFDM) transmission. Different from the conventional CR resource allocation problem, the relay node here is capable of performing subcarrier permutation over two hops such that the signal received over a particular subcarrier is forwarded on a different...
Detection of cyclostationary primary user (PU) signals in colored Gaussian noise for cognitive radio systems is considered based on looking for a cycle frequency at a particular time lag in the cyclic autocorrelation function (CAF) of the noisy PU signal. We explicitly exploit the knowledge that under the null hypothesis of PU signal absent, the measurements originate from colored Gaussian noise with...
Wireless Local Area Networks (WLAN) and Wireless Personal Area Networks (WPAN) such as the Bluetooth are designed to operate in 2.4 GHz ISM band. Since both IEEE 802.15 based Bluetooth and IEEE 802.11 WLAN devices, among various others, use the same frequency band, interference may lead to significant performance degradation. Hence, Cognitive Radio (CR) technology has been considered for coordinating...
This paper presents a machine learning approach for link adaptation in orthogonal frequency-division multiplexing systems through adaptive modulation and coding. Although machine learning techniques have attracted attention for link adaptation, most of the the schemes proposed so far are based on off-line training algorithms, which make them not well suited for real time operation. The proposed solution,...
In this paper we study the effect of phase noise (PHN) in a single carrier cyclic prefix (SCCP) system operating with a known cyclic prefix. The PHN process is a limiting factor in high throughput communication systems as higher-order constellations are extremely sensitive to it. In this paper we propose a robust and non-iterative scheme to enhance both the estimation of, and compensation for, the...
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