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In this paper, we deal with channel estimation and intercarrier interference mitigation for very high mobility OFDM systems, the communication is between a BS and a train traveling at a speed of 500km/hr. The scheme proposed here uses piece-wise polynomial expansion to approximate time-variations of multipath channels. Two adjacent symbols are utilized to estimate the first and second-order parameters...
In this paper, we develop a general reduced-rate orthogonal frequency division multiplexing (OFDM) transmission scheme for inter-subchannel interference (ICI) mitigation in a high-mobility environment. By transmit and receive preprocessing, we transform the original N-subcarrier OFDM system into an equivalent K-subcarrier one with significantly reduced ICI. In particular, we develop a general structure...
We study a cyclic prefix (CP) assisted method used for the uplink of code division multiple access (CDMA) systems in which the code despreading is performed in front of the frequency domain equalizer (FDE). The main advantage of the new despreading scheme is that the required points of discrete Fourier transform in the FDE are significantly reduced compared to the conventional CDMA scheme. Although...
In OFDMA-based Cognitive Radio (CR) systems, how to deal with the time-varying nature of avaliliable spectrum resources has become a hotspot and challenging problem in resource allocation. Traditional resource allocation algorithm can not guarantee proportional rates among non-real-time CR user (CRU) because the number of available subchannels is smaller than the number of CRUs in some OFDM symbol...
In this paper, the blind and semiblind channel estimation and equalization are investigated for zero-padding single-carrier block transmission (ZP-SCBT) systems using second-order statistics. Unlike the conventional channel estimation techniques, the proposed approach focuses on identifying the inverse of the channel impulse response rather than the channel response itself by skillfully exploiting...
In this paper, we are interested in blind and semi-blind identification of multiple-input multiple-output (MIMO) channel for orthogonal frequency division multiplexing (OFDM) systems. Using the sparsity property of wireless channel impulse response, we propose an iterative method which minimizes a cost function to result from the combination of blind or semi-blind criterion and the lp norm. This norm...
In this paper, we obtain approximations for the optimal Log-Likelihood Ratio (LLR) decision rule in cooperative detection when local energy detectors are assumed. Considering conditional independence, we also show under which bandwidth and sampling frequency regimes these approximations hold best. Furthermore, we present simulations where the performance of the approximated LLR decision rule is compared...
We consider the allocation of spectral and power resources every subframe (1~ms) on the uplink of the Long Term Evolution (LTE) wideband orthogonal frequency division multiple access (OFDMA) cellular network. System bandwidth is divided into multiple sub-bands. The fractional power control to manage interference is allowed to be a function of the sub-band. Moreover, the channel gains from the base-station...
Limited feedback precoding is part of the LTE standard. Despite standardization, important fundamental questions, especially relating to the performance due to the use of codebooks and receiver processing techniques, remain to be explored. In order to understand these questions, we consider a single user in a single cell employing single or multi-stream transmission using a variety of codebooks and...
In this paper, we propose subcarrier suppressed transmission for OFDMA (Orthogonal Frequency Division Multiple Access) in order to improve frequency utilization efficiency of STICS (Satellite/Terrestrial Integrated Mobile Communication System), which shares the same frequency band between satellite and land mobile systems. In OFDMA introducing channel rotation scheme, the proposed scheme can achieve...
A novel carrier sensing method with self-cancelation of the inter-carrier emission inevitably existent in OFDMA-based coexisting systems is proposed. Different from the conventional energy-based carrier detector, which directly compares the carrier energy with some predefined thresholds without considering such inter-carrier emissions, our proposed method can remove them before making decision, thus...
In this paper, the impact of double-sided signal clipping on optical wireless communication (OWC) systems employing asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) is investigated. Time domain signal clipping is introduced due to biasing issues or physical limitations of the front-ends. These include insufficient forward biasing of the emitter and the maximum driving...
We address the problem of designing efficient resource allocation schemes for an OFDMA based multiuser cooperative communication system that uses amplify and forward relaying. With a two-phase relaying protocol, we assume that both source and the relay have fixed power constraints and that the source employs a selective relaying mechanism. That is, the source adaptively decides on which frequency...
Confidentiality of the communication is extremely important in wireless networks due to the broadcast nature of the radio channel. The secrecy of the communication can be achieved via secure PHY layers or by using crypto techniques which need a pre-shared secret between the sender and the legal receiver. A technique has been proposed in literature to avoid preshared secrets based on the noise-pattern...
Recently, the OFDM-based Spectrum-sliced Elastic Optical Path (SLICE) network attracts significant interests due to its elastic band-width allocation. The OFDM technology, on one hand, enables both sub-wavelength and super-wavelength traffic accommodation by allocating appropriate number of sub-carriers. On the other hand, it can provide high signal quality by overcoming various impairments. In SLICE...
N-continuous OFDM is a modulation technique that produces a lower sidelobe than the original OFDM as a result of the continuous connection with its higher-order derivatives between the OFDM symbols. However, when there are low data channels, N-continuous OFDM has a high symbol error rate. In this paper, the authors propose a method for improving the symbol error rate of N-continuous OFDM using SLM...
The use of distributed space-time codes in cooperative communications promises to increase the rate and reliability of data transmission. These gains were mostly demonstrated for ideal scenarios, where all nodes are perfectly synchronized. Considering a cooperative uplink scenario with asynchronous nodes, the system suffers from two effects: timing errors and individual carrier frequency offsets....
The advantage of using channel feedback information to determine the optimal pilot placement is examined for amplify-and-forward OFDM relay links. This work extends upon the previously proposed feedback-aided pilot placement scheme to systems that employ subcarrier pairing at the relay. With channel feedback, the pilot subcarriers can be properly chosen to reduce the channel estimation error and increase...
This paper is concerned with the efficient feedback of the channel state information (CSI) in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. A hybrid transform coding (HTC) scheme is proposed by exploiting the frequency and time correlation of CSI. An upper bound for the overhead-distortion performance of HTC is derived. Numerical results show that,...
A novel preamble design is proposed for orthogonal frequency division multiplexing systems, which exploits the variable distance between a pair of training sequences for the transmission parameter signalling. Compared to the existing P1-symbol based preamble for the second generation digital terrestrial television broadcasting standard, the proposed design maintains the high performance and robustness...
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