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Vector Coding (VC) is a transmission scheme that can obtain path diversity gain while orthogonalizing multiple symbols. It has been shown that VC can provide good bit error rate (BER) performance compared to orthogonal frequency division multiplexing (OFDM). In addition VC has been proven to be the optimal partition of time domain channel. However, In VC, the eigenvectors of the channel matrix must...
The performance of opportunistic forwarding in the multi-hop cognitive radio networks (CRN) is dependent on the efficient detection of spectrum opportunities and the diversity of relay links. To find appropriate spectrum opportunities, effective spectrum sensing is essential in a CRN, especially under highly dynamic channel conditions. In this paper, a novel channel metric is proposed to determine...
Transmitted-reference (TR) modulation schemes have generated interest in the context of ultrawide bandwidth (UWB) communications in order to avoid complex channel estimation and synchronization. In these schemes, the length of the integration interval must be carefully chosen to achieve optimal performance. Difficulties arise since this parameter is related to the channel characteristics and to the...
This paper presents novel channel estimation techniques for wideband continuous phase modulation (CPM). It is shown that relatively simple basis functions can be used to estimate the frequency selective channel for CPM with single carrier frequency domain equalisation. Simulation results show that a robust estimate of the channel is formed using B-splines allowing CPM to be considered as an excellent...
Recently, a progressive receiver has been proposed to mitigate the intercarrier interference (ICI) in orthogonal-frequency-division-multiplexing (OFDM) transmissions over underwater acoustic (UWA) channels, where the ICI span gradually increases during the receiver iterations. Operating on a block-by-block basis, the progressive receiver is initialized by measurements on pilot subcarriers inserted...
Channel estimation is important for coherent detection in orthogonal frequency-division multiplexing (OFDM) systems. Current time-domain Kalman filtering (TDKF) method has a good performance in estimating the channel responses, but is impractical since it requires the knowledge of multipath delays. In this paper, we propose a new scheme to relax such requirement by combining the recent methodology...
In this paper, we do research about Expectation Maximization (EM) Algorithm for MIMO-OFDM systems (Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing). The EM algorithm is analyzed and used to channel estimating and channel tracking. It is shown that EM is an efficient iterative algorithm which can adapt to the fading channel for MIMO-OFDM system.
In this paper, a novel rapid varying doubly-selective channel estimator for OFDM systems has been proposed, in which channel is modeled by basis expansion model (BEM). Unlike traditional BEM channel estimation algorithms, in which the comb-pilot is used and the large path delay is not considered, the proposed algorithm uses firstly block-type pilot to estimate the BEM coefficients of fast-varying...
In this paper, a cognitive system for link adaptation of Wi-Max physical layer is presented. The proposed cognitive system makes the Wi-Max physical layer adaptive to the wireless channel. It monitors the wireless channel as well as the system performance and then by choosing optimal transmission parameters adapts the physical layer thus maximizing the latter. The cognitive system is based on Support...
In this paper, we analyze the effective capacity gains of opportunistic spectrum-sharing with imperfect channel information. We consider that a secondary user may access the spectrum allocated to a primary user as long as the average interference power, inflicted at the primary's receiver as an effect of the transmission of the secondary user, remains below predefined power limits. We consider partial...
Channel assignment has been extensively researched for multi-radio wireless mesh networks, but it is still very challenging when it comes to its implementation. In this paper we propose a semi-dynamic and distributed channel assignment mechanism called SICA that uses game theory. To the best of our knowledge this is the first game formulation of channel assignment which takes the co-channel interference...
MIMO-OFDM technology make full use of space and spectrum resources, it can exponentially increase the channel capacity, so it is one of the core technology of next generation mobile communication systems. In order to estimate the time domain (or frequency domain) response of MIMO-OFDM systems fast and accurately, the traditional SVD estimator is modified in this paper. To reduce the time to compute...
A verification of delay and angular parameters of a deterministic ray tracing MIMO channel model requires dedicated high-resolution wide-band directional propagation channel measurements to estimate according channel parameters and is rarely done. This contribution presents such an analysis in the 2.53 GHz range through simulations and measurements in a real MIMO urban outdoor cellular environment...
Future communication systems for car-to-x (C2X) applications have to meet stringent requirements regarding reliability issues. Channel estimation (CE) - as one of the key tasks that affect the system performance - has to be able to cope with the rapidly changing channel conditions. Applying a Wiener filter (WF) is one very efficient method to reduce the estimation error of any channel estimation approach...
The use of MIMO (Multiple Input Multiple Output) in current and future mobile communications relies on accurate channel estimates. In OFDM based systems such as LTE (Long Term Evolution), the channel estimation can be successfully designed with processing in a transform domain, both for uplink and downlink. One such popular transform is to use the IDFT (Inverse Discrete Fourier Transform), window...
In a typical wireless communication environment, radio channels need to be estimated for systems employing coherent detection. For implementation simplicity, Pilot-Assisted Channel Estimation (PACE) techniques have been widely used. An efficient interpolation method helps to estimate the channel fading coefficients between consecutive pilots with minimised pilot overhead. The simple linear interpolation...
In SFN (Single Frequency Network) broadcasting systems the equivalent CIR (Channel Impulse Response) can be very long but typically it has a sparse nature. This means that the equivalent CIR has several clusters of paths, each one associated to the CIR between a given transmitter and the receiver. These clusters have several multipath components and are typically well separated in time. In this paper...
This paper deals with the symbol timing issue of an OFDM system in frequency selective fading scenarios. A modified symbol timing offset estimator based on an energy transition metric is proposed. This metric can also be applied to estimate the maximum channel delay spread. Benefiting from the knowledge of the maximum channel delay spread, the modified estimator shows its advantage in a relatively...
This paper presents a novel time-variant ML channel estimator for mobile radio navigation receivers. Our novel ML channel estimator enables the coherent noise averaging over several hundred codewords for time-variant channel phasors. Compared to the conventional incoherent summation of log-likelihood functions or compared to the conventional time-invariant log-likelihood functions, we avoid the squaring...
Channel estimation techniques for Multi Input Multi Output Orthogonal Frequency Division Multiplex (MIMO-OFDM) systems based on a pilot arrangement are investigated. Training based Channel estimation with a block type pilot arrangement is studied through an algorithm for determination of efficient number of pilot symbols in an OFDM symbol by adding a feedback branch and employment of the Maximal Ratio...
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