Imad Barhumi - Academia.edu (original) (raw)

Papers by Imad Barhumi

IEEE Internet of Things Journal

IEEE Transactions on Green Communications and Networking

Journal of Communications

We propose a combinatorial auction-based subcarrier assignment algorithm for single-relay Amplify... more We propose a combinatorial auction-based subcarrier assignment algorithm for single-relay Amplify-and-Forward (AF) Orthogonal-Frequency-Division-Multiple-Access (OFDMA) relaying systems. The proposed algorithm is based on a one-shot multiple-item auction, where each user submits bundles of subcarriers and their corresponding bids. Bundles are generated based on the Shapley and the pair-wise Synergy-Shapley values computed for the user's data rate. After receiving all bids, the Winner-Determination-Problem (WDP) is solved using the structured search algorithm to allocate the subcarriers, then the power is allocated optimally at the source and relay nodes to maximize the sum rate. The effect of the number of submitted bundles/bids on the throughput and fairness indices is investigated. The proposed combinatorial auction outperforms in the throughput and fairness indices an auction algorithm without bundling strategies even though for the case where users are allowed to bid for few bundles in addition to the singleton bid. Numerical results are used to show the advantages of the proposed algorithm.

ABSTRACT We develop an auction-based algorithm for joint allocation of resources, namely power pr... more ABSTRACT We develop an auction-based algorithm for joint allocation of resources, namely power profiles at the source and relay nodes and subcarrier assignment profile for multiple users amplify and forward (AF) orthogonal frequency division multiple access (OFDMA) system. The proposed algorithm is based on sequential single item auction, where each user submits a bid based on either the marginal increase or the relative marginal increase of the data rate after using that subcarrier with optimal power profiles at the source and relay nodes. The first bidding strategy maximizes the sum data rate, whereas the second bidding strategy maximizes the fairness index. In both cases, the subcarrier is assigned to the user who submits the highest bid. The algorithm proceeds in a sequential fashion until all subcarriers are assigned. The system throughput and fairness indices are used to evaluate the performance of the proposed algorithm. Numerical results are used to show the merits of the proposed algorithm.

2005 13th European Signal Processing Conference, Sep 1, 2005

In this paper, we propose an estimation technique for rapidly time-varying channels. We approxima... more In this paper, we propose an estimation technique for rapidly time-varying channels. We approximate the time-varying channel using the basis expansion model (BEM). The BEM coefficients of the channel are needed to design channel equalizers. We rely on pilot symbol assisted modulation (PSAM) to estimate the channel (or the BEM coefficients of the channel). We first derive the optimal minimum mean-square error (MMSE) interpolation based channel estimation technique. We then derive the BEM channel estimation, where only the BEM coefficients are estimated. We consider a BEM with a critically sampled Doppler spectrum, as well as a BEM with an oversampled Doppler spectrum. It has been shown that, while the first suffers from an error floor due to a modeling error, the latter is sensitive to noise. A robust channel estimation can then be obtained by combining the MMSE interpolation based channel estimation and the BEM channel estimation technique. Through computer simulations, it is shown that the resulting algorithm provides a significant gain when an oversampled Doppler spectrum is used (an oversampling rate equal to 2 appears to be sufficient), while only a slight improvement is obtained when the critically sampled Doppler spectrum is used.

... Through simulations it is shown that the optimal pilot-tone based training sequences as deriv... more ... Through simulations it is shown that the optimal pilot-tone based training sequences as derived in this paper signifi-cantly outperform full ... A technique of special interest is OFDM (Or-thogonal Frequency Division Modulation) which is a multi-carrier modulation technique. ...

2006 14th European Signal Processing Conference, Sep 1, 2006

ABSTRACT In this paper we propose a frequency-domain IQ-imbalance and carrier frequency offset (C... more ABSTRACT In this paper we propose a frequency-domain IQ-imbalance and carrier frequency offset (CFO) compensation and equalization for OFDM transmission over doubly selective channels. IQ-imbalance and CFO arise due to imperfections in the receiver and/or transmit-ter analog front-end, whereas user mobility and CFO give rise to channel time-variation. In addition to IQ-imbalance and the chan-nel time-variation, the cyclic prefix (CP) length may be shorter than the channel impulse response length, which in turn gives rise to inter-block interference (IBI). While IQ-imbalance results in a mir-roring effect, the channel time-variation results in inter-carrier in-terference (ICI). The frequency-domain equalizer is proposed to compensate for the IQ-imbalance taking into account ICI and IBI. The frequency-domain equalizer is obtained by transferring a time-domain equalizer to the frequency-domain resulting in the so-called per-tone equalizer (PTEQ).

Ieee Transactions on Signal Processing, Apr 1, 2006

In this paper, we propose a time-domain as well as a frequency-domain per-tone equalization for o... more In this paper, we propose a time-domain as well as a frequency-domain per-tone equalization for orthogonal frequency-division multiplexing (OFDM) over doubly selective channels. We consider the most general case, where the channel delay spread is larger than the cyclic prefix (CP), which results in interblock interference (IBI). IBI in conjunction with the Doppler effect destroys the orthogonality between subcarriers and, hence, results in severe intercarrier interference (ICI). In this paper, we propose a time-varying finite-impulse-response (TV-FIR) time-domain equalizer (TEQ) to restore the orthogonality between subcarriers, and hence to eliminate ICI/IBI. Due to the fact that the TEQ optimizes the performance over all subcarriers in a joint fashion, it has a poor performance. An optimal frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency domain. Through computer simulations, we demonstrate the performance of the proposed equalization techniques. Index Terms-Basis expansion model (BEM), doubly selective channels, orthogonal frequency-division multiplexing (OFDM), per-tone equalization (PTEQ), time-domain equalization (TEQ).

2014 Ieee 79th Vehicular Technology Conference, May 18, 2014

ABSTRACT A low complexity algorithm is proposed for joint allocation of power profiles at the sou... more ABSTRACT A low complexity algorithm is proposed for joint allocation of power profiles at the source and relay nodes and subcarrier assignment for single user amplify and forward (AF) cooperative communication using orthogonal frequency division multiplexing (OFDM) system. The relay uses AF cooperative relaying to transmit messages on a set of available subcarriers with diversity. The remaining subcarriers are used for direct transmission without diversity. The objective is to allocate the resources to maximize the sum rate subject to individual power constraint on each node. We formulate such a problem as subcarrier based resource allocation that seeks joint optimization of subcarrier assignment and power profiles at the source and relay nodes. The algorithm is based on an ordering of the channel gain’s ratio and splitting them into two partitions, then searching for the partition that maximizes the sum rate. Simulation results demonstrate the merit of the proposed algorithm.

This paper describes a channel estimation and tracking scheme for OFDM MIMO systems based on pilo... more This paper describes a channel estimation and tracking scheme for OFDM MIMO systems based on pilot tones. The mean square error of the proposed scheme is de- rived, and through this we derive optimal training sequences and placement of the pilot tones. It is shown in this pa- per that minimum mean square (MMSE) channel estimation is obtained with equipowered, equispaced, orthogonal and phase shift orthogonal training sequences. Through simula- tions it is shown that the optimal pilot-tone based training sequences as derived in this paper significantly outperform full-block training sequences in rapidly time varying chan- nels. Additionally, we show that by satisfying all conditio ns of optimality, our training sequences outperform orthogonal and random sequences, which both appear to be sub-optimal for channel identification.

EURASIP Journal on Wireless Communications and Networking, 2012

Performance analysis of an up-link cooperative diversity system is investigated; sharing of the t... more Performance analysis of an up-link cooperative diversity system is investigated; sharing of the two ordered best relays over Rayleigh flat fading channel is introduced to establish full diversity order for both users. The two users are competing for the same best relay, so assigning the best relay for one user, and the next-best relay for the other shows different diversity orders. The relays are ordered based on the end-to-end signal to noise ratio (SNR) of the source-relay-destination links. In this sense, relay selection is examined under different criteria. Mainly, the ordered best relay, the ordered next-best relay, and equally sharing the two best ordered relays. To this end, analytical expression, for the moment generating function (MGF) is derived, and used to find the probability density function (PDF), and the cumulative density function of the end-to-end SNR for decode and forward (DF) sharing scenario. Furthermore, the MGF of the upper bound of the end-to-end SNR for amplify and forward (AF) sharing scenario is also derived. Sharing the two ordered best relays shows better performance in the bit error probability (BEP) than using the next-best relay alone in DF relay systems, while exploiting the full diversity of the system. Sharing of the two ordered best relays in AF relay systems shows better BEP performance than using the best relay alone. Distributed space time block coding and distributed beamforming (BF) scenarios at the relays that utilize the bandwidth more efficiently are also explored. It is found that the BEP performance of the two ordered best relays distributed BF with equal power allocation for AF (at high SNR) and DF (for all SNRs) schemes outperforms the BEP performance of the best ordered relay alone. The BEP performance for the DF distributed BF scheme with equal power allocation approaches the BEP performance of the optimum power assignment under global power sum constraint. Numerical simulations are used to validate the analysis.

... and high mobility in future wireless communication systems introduces doubly-selective (time-... more ... and high mobility in future wireless communication systems introduces doubly-selective (time-and fre-quency-selective) channel effects. To combat these effects, equal-izers are needed. In this paper, we propose a serial equalization approach for doubly-selective channels. ...

Icc, Oct 15, 2003

... Partly supported by the Palestinian European Academic Cooperation in Education (PEACE) Progra... more ... Partly supported by the Palestinian European Academic Cooperation in Education (PEACE) Programme. ... In this paper, we propose a frequency-domain equalization approach for OFDM ... We consider the most general case, where the doubly-selective channel delay spread is ...

Ieee Transactions on Signal Processing, 2007

In this paper, we propose a frequency-domain equalization technique for orthogonal frequency divi... more In this paper, we propose a frequency-domain equalization technique for orthogonal frequency division multiplexing (OFDM) transmission over frequency-selective channels. We consider the case where the receiver analog front-end suffers from IQ-imbalance and the local oscillator suffers from carrier-frequency offset (CFO). While the IQ-imbalance results in a mirroring effect, the CFO induces inter-carrier interference (ICI). In addition to ICI, we consider the channel delay spread is larger than the cyclic prefix (CP). This means that inter-block interference (IBI) is present. The frequency-domain equalizer is obtained by transferring a time-domain equalizer (TEQ) to the frequency-domain resulting in a per-tone equalizer (PTEQ). Due to the presence of IQ-imbalance the conventional TEQ (where only one TEQ is applied to the received sequence) is not sufficient to cope with the mirroring effect. A sufficient TEQ consists of two time-domain filters; one applied to the received sequence and another applied to a conjugated version of the received sequence. For the case of IQ-imbalance and CFO, the TEQs are designed according the basis expansion model (BEM) which showed to be able to cope with the ICI problem. Finally, in addition to the frequency-domain PTEQ design procedure, a training-based RLS type initialization scheme for direct per-tone equalization is also proposed. Index Terms-Basis expansion model (BME), carrier-frequency offset (CFO), IQ-imbalance, orthogonal frequency-division multiplexing (OFDM), per-tone equalizer (PTEQ). I. INTRODUCTION O RTHOGONAL frequency-division multiplexing (OFDM) has been adopted for digital audio and video broadcasting [1] and chosen by the IEEE 802.11 standard [2], as well as by the HIPERLAN-2 standard [3] for wireless LAN (WLAN) transmission. This is due to its robustness against multipath fading and its relatively simple implementation. However,

Iwssip 2014 Proceedings, May 12, 2014

IEEE Transactions on Mobile Computing, 2015

2014 IEEE 25th Annual International Symposium on Personal, Indoor, and Mobile Radio Communication (PIMRC), 2014