| 11. |
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| 12. |
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| 13. |
- Seifi, Nima, 1981, et al.
(author)
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Downlink performance and capacity of distributed antenna systems based on realistic channel model
- 2008
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In: WSA 2008. International ITG Workshop on Smart Antennas, Damstdart, Germany. ; , s. 249-253
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Conference paper (peer-reviewed)abstract
- Recent academic studies of distributed antenna system (DAS) using a frequency-flat fading channel model show that DAS outperforms standard systems, where the base-station (BS) antenna elements are centralized at one location. In this paper the performance of a DAS under time-varying frequency-selective fading based on a realistic channel model is investigated. Specifically, we show that if we shift the hexagonal cellular layout in the conventional system and use sectorized antennas instead of omnidirectional antennas at each BS, the performance in terms of outage probability and outage capacity will improve by a large extent without a need for additional BS towers. The results show that with the same total transmit power and bandwidth DAS can reduce the inter-cell interference (ICI) in a multicell environment and improve the outage capacity especially near the cell boundary.
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| 14. |
- Seifi, Nima, 1981, et al.
(author)
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Performance Analysis of Distributed versus Co-located MIMO-OFDM
- 2008
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In: 1st COST2100 Workshop on MIMO and Cooperative Communications, Trondheim, Norway..
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Conference paper (peer-reviewed)abstract
- The predicted capacity gain of a traditional colocatedmultiple-input multiple-output (MIMO) system is oftenseverely limited in realistic propagation scenarios, especially inthe presence of interference. One remedy proposed recently, is toemploy a generalized form of MIMO systems called distributedMIMO. In this paper, we compare the downlink performance ofa wireless orthogonal frequency-division multiplexing (OFDM)-based distributed MIMO system to that of a co-located MIMO system using a realistic channel model. In addition, the presence of co-channel interference is considered.We show that distributed MIMO-OFDM outperforms the traditional co-located MIMO-OFDM in terms of outage capacity and eigenvalue distribution owing to the inherent macro-diversity
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| 15. |
- Sternad, Mikael, et al.
(author)
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Towards systems beyond 3G based on adaptive OFDMA transmission
- 2007
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In: Proceedings of the IEEE. - 0018-9219 .- 1558-2256. ; 95:12, s. 2432-2455
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Research review (peer-reviewed)abstract
- High data rates, high spectral efficiency, flexibility, and low delays over the air interface will be important features in next-generation wireless systems. The overall challenge will be packet scheduling and adaptive radio transmission for multiple users, via multiple antennas and over frequency-selective wideband channels. This problem needs to be structured to obtain feasible solutions. The basic simplifying assumptions used here are clustering of antennas into cells, orthogonal transmission by use of cyclic-prefix orthogonal frequency-division multiplexing (OFDM) and a time-scale separation view of the total link adaptation, scheduling and intercell coordination problem. Based on these assumptions, we survey techniques that adapt the transmission to the temporal, frequency, and spatial channel properties. We provide a systematic overview of the design problems, such as the dimensioning of the allocated time-frequency resources, the influence of duplexing schemes, adaptation control issues for downlinks and uplinks, timing issues, and their relation to the required performance of channel predictors. Specific design choices are illustrated by recent research within the Swedish Wireless IP program and the EU IST-WINNER project. The presented results indicate that high-performance adaptive OFDM transmission systems are indeed feasible, also for challenging scenarios that involve vehicular velocities, high carrier frequencies, and high bandwidths
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| 16. |
- Wang, Wei, 1965, et al.
(author)
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Evaluations of a 4G Uplink System Based on Adaptive Single-Carrier TDMA
- 2005
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In: Proceedings IEEE Vehicular Technology Conference Fall, Dallas, Texas, USA. - 1550-2252. - 0780391527 ; 3, s. 1667-1671
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Conference paper (peer-reviewed)abstract
- © 2005 IEEE. Recent research has shown that a single-carrier system with frequency domain equalization can be a potential alternative to an OFDM-based system in a single user case. In this paper we propose and evaluate an adaptive single-carrier TDMA uplink with scheduling for broadband cellular packet data systems. Frequency division duplex (FDD) is assumed. Multiuser channel estimation and channel prediction are considered. The adaptive modulation scheme is optimized to maximize the throughput including also the ARQ part of the transmission. Frequency domain equalization is employed to combat the inter-symbol-interference (ISI). With the proposed design, the simulation results show that the multiuser diversity gain in spectral efficiency is limited in a wideband system, which indicates that an OFDM based system might be a more favorable candidate.
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| 17. |
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| 18. |
- Wolfgang, Andreas, 1977, et al.
(author)
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Resource allocation and linear precoding for relay assisted multiuser MIMO systems
- 2008
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In: WSA 2008. International ITG Workshop on Smart Antennas, Damstdart, Germany. ; , s. 162-168
-
Conference paper (peer-reviewed)abstract
- In this paper we investigate the use of infrastructure half-duplex amplify-and-forward (AF) relays in the downlink of a multi-user (MU) multiple-input multiple-output (MIMO) system, which uses linear precoding based on block-diagonalization. Owing to the half-duplex mode of the relay, the communication is divided into two time-slots. During the first time-slot the relay nodes are treated as an additional mobile station (MS), while during the second time-slot the base-station (BS) and the relays form a distributed, virtual antenna array. In contrast to many relay applications, the purpose of the proposed scheme is not to increase diversity, but rather to increase the system throughput at the borders of a communication cell or in areas with a high user density. The performance of the proposed architecture is investigated by examining the sum-capacity of the system as well as the distribution of the capacity over the cell-area.
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| 19. |
- Zhao, Hongxia, 1971, et al.
(author)
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Performance of a Decorrelator in Convolutionally Coded WCDMA Systems
- 2005
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Reports (other academic/artistic)abstract
- The objective of this paper is to study the performance of a linear multiuser detector (a decorrelator) in a convolutionally encoded wideband code-division multiple-access (WCDMA) system. The study, which is valid for a traditional detection scheme, where the decorrelator and the channel decoder work separately, shows that the single-user detector (the Rake receiver) performs better than the decorrelator at low signal-to-noise ratios (SNRs). The SNR range, in which the Rake receiver outperforms the decorrelator, is influenced by the error correction capability of the channel code and the load of the system. In particular, a WCDMA speech service is evaluated. Simulations show that the Rake receiver is superior to the decorrelator when targeting a required bit-error rate (BER) of 10^{-3}.
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