| 1. |
- Lioliou, Panagiota, 1982, et al.
(author)
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Efficient Channel Estimation Techniques for Amplify and Forward Relaying Systems
- 2012
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In: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 60:11, s. 3150-3155
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Journal article (peer-reviewed)abstract
- In this paper, we present a channel estimation scheme for Amplify-and-Forward (AF) relaying systems, using measurements at the destination only. A Least-Squares (LS) based channel estimation algorithm is developed, that provides the destination with full knowledge of all channel responses involved in the transmission. To investigate the algorithm performance, the Cramer-Rao lower bound (CRB) is analytically computed and compared with the asymptotic covariance of the proposed estimator. Since the existing estimator does not reach the CRB, we also propose and analyze an improved algorithm by taking into account the noise characteristics via weighted LS (WLS). The improved algorithm is asymptotically efficient, since it attains the CRB as the SNR tends to infinity.
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| 2. |
- Lioliou, Panagiota, 1982, et al.
(author)
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Self-Interference Suppression in Full-Duplex MIMO Relays
- 2010
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In: 44th Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781424497218 ; , s. 658-662
-
Conference paper (peer-reviewed)abstract
- Full-duplex relays can provide cost-effective cover-age extension and throughput enhancement. However, the main limiting factor is the resulting self-interference signal which deteriorates the relay performance. In this paper, we propose a novel technique for self-interference suppression in full-duplex Multiple-Input Multiple-Output (MIMO) relays. The relay employs transmit and receive weight filters for suppressing the self-interference signal. Unlike existing techniques that are based on zero forcing of self-interference, we aim at maximizing the ratio between the power of the useful signal to the self-interference power at the relay reception and transmission. Our simulation results show that the proposed algorithm outperforms the existing schemes since it can suppress interference substantially with less impact on the useful signal.
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| 3. |
- Seifi, Nima, 1981, et al.
(author)
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An Efficient Signaling for Multi-mode Transmission in Multi-user MIMO
- 2010
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In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781424442966 ; , s. 3402-3405
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Conference paper (peer-reviewed)abstract
- In this paper the downlink of a multi-user MIMO (MUMIMO)system with multi-mode transmission is considered.We propose a low-complexity algorithm for selecting usersand the corresponding number of data streams to each user,denoted as user transmission mode (UTM). The selectionis only based on the average received signal-to-noise ratio(SNR) from the base station (BS) for each user. This reducesthe overall amount of feedback for scheduling, as opposedto techniques that assume perfect instantaneous channelstate information (CSI) from all users. Analytical averagethroughput approximations are derived for each user at different UTMs. Simulation results demonstrate that the proposed algorithm provides performance close to dirty paper coding (DPC) with considerably reduced feedback.
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| 4. |
- Seifi, Nima, 1981, et al.
(author)
-
Coordinated Single-Cell vs Multi-Cell Transmission with Limited-Capacity Backhaul
- 2010
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In: IEEE Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove, CA, Nov. 2010. - 1058-6393. - 9781424497218 ; , s. 1217-1221
-
Conference paper (peer-reviewed)abstract
- Base station coordination is an efficient techniqueto transcend the limits on spectral efficiency imposed by intercellinterference. In this paper, we compare the performance ofdifferent coordination strategies with different amount of channelstate information (CSI) and data sharing among the coordinatingbase stations. We focus on the effect of limited backhaul capacityin a two-cell network. Contrary to the common belief, we showthat coordination strategies with no data and only limited CSIsharing is preferred to those with full data and CSI sharing whenthe backhaul capacity is relatively low and the edge SNR is high.
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| 5. |
- Seifi, Nima, 1981, et al.
(author)
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Impact of base station antenna tilt on the performance of network MIMO systems
- 2012
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In: IEEE Vehicular Technology Conference. - 1550-2252. - 9781467309905 ; , s. Art. no. 6239994-
-
Conference paper (peer-reviewed)abstract
- We study the downlink of a multicell MIMO system where clusters of multi-antenna base stations jointly serve multiple single-antenna users, commonly referred to as a network MIMO system. Most of the previous studies on network MIMO have only considered the azimuth pattern of the antenna, while ignoring the elevation pattern. In this paper, we consider both the azimuth and the elevation patterns and investigate the impact of the elevation angle tuning parameter, denoted as the antenna tilt, on the performance of such systems. Using system simulations, it is shown that the promised performance gains of network MIMO systems over conventional non-coordinated systems, crucially depend on the choice of the right tilt setting including the tilt type, i.e., mechanical or electrical, and the tilt angle. In particular, for tilt angles smaller than the optimum, network MIMO with intra-site coordination performs almost as well as the conventional system; while for tilt angles larger than the optimum, the performance of network MIMO with intra-site is similar to that of network MIMO with inter-site coordination.
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| 6. |
- Seifi, Nima, 1981, et al.
(author)
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Multimode Transmission in Network MIMO Downlink with Incomplete CSI
- 2011
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In: Eurasip Journal on Advances in Signal Processing. - : Springer Science and Business Media LLC. - 1687-6172 .- 1687-6180. ; 2011, s. Art. no. 743916-
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Journal article (peer-reviewed)abstract
- We consider a cooperative multi-cell MIMO (a.k.a network MIMO) downlink system with multiantennabase stations (BSs), which are connected to a central unit and communicate with multi-antennausers. In such a network, obtaining perfect channel state information (CSI) of all users at the central unitto exploit opportunistic scheduling requires a substantial amount of feedback and backhaul signaling.In this paper, we propose a scheduling algorithm based only on the knowledge of the average receivedSNR at each user from all the cooperating BSs, denoted as incomplete CSI. Multi-mode transmission isapplied that is able to adaptively adjust the number of data streams transmitted to each user. Utilizingthe results of random matrix theory, an analytical framework is proposed to approximate the ergodicrate of each user with different number of data streams. Using these approximate ergodic rates, a jointuser and mode selection algorithm is proposed, where only the scheduled users need to feed backinstantaneous CSI. Simulation results demonstrate that the developed analytical framework providesa good approximation for a practical number of antennas. While substantially reducing the feedbackoverhead, it is shown that the proposed scheduling algorithm performs closely to the opportunisticscheduling algorithm that requires instantaneous CSI feedback from all users.
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| 7. |
- Seifi, Nima, 1981, et al.
(author)
-
Throughput Optimization for MISO Interference Channels via Coordinated User-Specific Tilting
- 2012
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In: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2558 .- 1089-7798. ; 16:8, s. 1248-1251
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Journal article (peer-reviewed)abstract
- In this letter, we propose a novel framework to enhance the throughput in multiple-input single-output (MISO) mutually interfering channels via selecting the tilt angles at all base stations (BSs) in a coordinated fashion. In the proposed framework, multiple BSs adjust their tilt angles jointly to maximize the sum throughput of the scheduled users, denoted as coordinated user-specific tilting. Assuming the availability of location information of the scheduled users at all BSs, accurate analytical expression for user ergodic rate is provided, which enables a decentralized deployment of the proposed framework at each BS. Simulation results show that the proposed coordinated user-specific tilting scheme outperforms the conventional schemes employing a fixed tilt angle at each BS.
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