| 1. |
- Vlastaras, Dimitrios, et al.
(författare)
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Vehicle Detection through Wireless Vehicular Communication
- 2014
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Ingår i: Eurasip Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; 2014:1, s. 146-153
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Tidskriftsartikel (refereegranskat)abstract
- Vehicles in the future are anticipated to have the ability to communicate and exchange useful information in order to avoid collisions. However, for this cooperation to be possible, all vehicles will have to be equipped with compatible wireless modules, based on, e.g. IEEE 802.11p (used in ITS-G5 or WAVE), which implements intelligent transport systems operating in the 5 GHz frequency band. During the implementation phase of the system, there will be many older vehicles without such equipment that can cause hazard as information about them will not be available to vehicles equipped with IEEE 802.11p modules. In this paper, we present a system to be used as a roadside unit (RSU), developed explicitly for infrastructure-to-vehicle (I2V) communication that can solve the aforementioned traffic safety problems. The system consists of a universal medium-range radar (UMRR) and an IEEE 802.11p modem integrated together to detect vehicles, with or without communication capabilities, and forward their position and speed vectors to vehicles, with IEEE 802.11p modules installed, for collision avoidance. Tests have been performed by using our system in parallel with vehicles in which IEEE 802.11p modules are installed and comparing the content in the Cooperative Awareness Messages obtained from both systems. Accuracy tests have been performed in order to verify the system, and Kalman filtering is applied on the radar data to improve the accuracy of the system further.
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| 2. |
- Hammarberg, Peter, et al.
(författare)
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Iterative receivers with channel estimation for multi-user MIMO-OFDM: complexity and performance
- 2012
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Ingår i: Eurasip Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; , s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedA family of iterative receivers is evaluated in terms of complexity and performance for the case of an uplink multi-user (MU) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. The transmission over block fading channels is considered. The analyzed class of receivers is performing channel estimation inside the iterative detection loop, which has been shown to improve estimation performance. As part of our results we illustrate the ability of this type of receiver to reduce the required amount of pilot symbols. A remaining question to ask is which combinations of estimation and detection algorithms that provide the best trade-off between performance and complexity. We address this issue by considering MU detectors and channel estimators, with varying algorithm complexity. For MU detection, two algorithms based on parallel interference cancellation (PIC) are considered and compared with the optimal symbol-wise maximum a-posteriori probability (MAP) detector. For channel estimation, an algorithm performing joint minimum-mean-square-error (MMSE) estimation is considered along with a low complexity replica making use of a Krylov subspace method. An estimator based on the space alternating generalized expectation-maximization (SAGE) algorithm is also considered. Our results show that low-complexity algorithms provide the best tradeoff, even though more receiver iterations are needed to reach a desired performance.
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| 3. |
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| 4. |
- Apelfröjd, Rikke, et al.
(författare)
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Design and measurement based evaluations of coherent JT CoMP : a study of precoding, user grouping and resource allocation using predicted CSI
- 2014
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; , s. 100-
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Tidskriftsartikel (refereegranskat)abstract
- Coordinated multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent joint transmission (JT) to multiple users. However, this requires accurate channel state information at the transmitter (CSIT) and also user groups with spatially compatible users. The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques. We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (> 20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities. A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding. Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.
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| 5. |
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| 6. |
- Chatzinotas, Symeon, et al.
(författare)
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Interference mitigation techniques for clustered multicell joint decoding systems
- 2011
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - Springer : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; 132:1
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Tidskriftsartikel (refereegranskat)abstract
- Multicell joint processing has originated from information-theoretic principles as a means of reaching the fundamental capacity limits of cellular networks. However, global multicell joint decoding is highly complex and in practice clusters of cooperating Base Stations constitute a more realistic scenario. In this direction, the mitigation of intercluster interference rises as a critical factor towards achieving the promised throughput gains. In this paper, two intercluster interference mitigation techniques are investigated and compared, namely interference alignment and resource division multiple access. The cases of global multicell joint processing and cochannel interference allowance are also considered as an upper and lower bound to the interference alignment scheme, respectively. Each case is modelled and analyzed using the per-cell ergodic sum-rate throughput as a figure of merit. In this process, the asymptotic eigenvalue distribution of the channel covariance matrices is analytically derived based on free-probabilistic arguments in order to quantify the sum-rate throughput. Using numerical results, it is established that resource division multiple access is preferable for dense cellular systems, while cochannel interference allowance is advantageous for highly sparse cellular systems. Interference alignment provides superior performance for average to sparse cellular systems on the expense of higher complexity.
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| 7. |
- Chen, Lei, 1981-, et al.
(författare)
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Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks
- 2012
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- For broadband cellular access based on orthogonal frequency divisionmultiple access (OFDMA), fractional frequency reuse (FFR) is one ofthe key concepts for mitigating inter-cell interference and therebyoptimizing cell-edge performance. In standard FFR, the number of OFDMAsub-bands and the reuse factor are both fixed. Whereas this works wellfor an idealized cell pattern, it is neither directly applicable noradequate for real-life networks with very irregular cell layouts. Inthis paper, we generalize the standard FFR to allow for flexibilities inthe total number of sub-bands as well as the number of sub-bands ineach cell-edge zone, enabling network-adaptive FFR. Two powerassignment strategies that use fixed power per sub-band prior tosub-band allocation and apply cell-specific power derived from thenumber of sub-bands allocated to each cell-edge zone, respectively,are investigated. Optimization algorithms based on local search aredeveloped for sub-band allocation to maximize the cell-edgethroughput. Evaluations using networks with realistic radiopropagation conditions demonstrate the applicability of the generalizedand optimized FFR in performance engineering of OFDMA networks.
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| 8. |
- Christopoulos, Dimitrios, et al.
(författare)
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Linear and nonlinear techniques for multibeam joint processing in satellite communications
- 2012
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; , s. 162-
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Tidskriftsartikel (refereegranskat)abstract
- Existing satellite communication standards such as DVB-S2, operate under highly-efficient adaptive coding and modulation schemes thus making significant progress in improving the spectral efficiencies of digital satellite broadcast systems. However, the constantly increasing demand for broadband and interactive satellite links emanates the need to apply novel interference mitigation techniques, striving towards Terabit throughput. In this direction, the objective of the present contribution is to investigate joint multiuser processing techniques for multibeam satellite systems. In the forward link, the performance of linear precoding is investigated with optimal nonlinear precoding (i.e., dirty article coding) acting as the upper performance limit. To this end, the resulting power and precoder design problems are approached through optimization methods. Similarly, in the return link the concept of linear filtering (i.e., linear minimum mean square error) is studied with the optimal successive interference cancelation acting as the performance limit. The derived capacity curves for both scenarios are compared to conventional satellite systems where beams are processed independently and interbeam interference is mitigated through a four color frequency reuse scheme, in order to quantify the potential gain of the proposed techniques.
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| 9. |
- Dely, Peter, 1982-, et al.
(författare)
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Optimization of WLAN associations considering handover costs
- 2012
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer. - 1687-1472 .- 1687-1499. ; 255
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Tidskriftsartikel (refereegranskat)abstract
- In Wireless Local Area Network (WLAN) hotspots the coverage areas of Access Points (APs) often overlap considerably. Current state of the art optimization models find the optimal AP for each user station by balancing the load across the network. Recent studies have shown that in typical commercial WLAN hotspots the median connection duration is short. In such dynamic network settings the mentioned optimization models might cause many handovers between APs to accommodate for user arrivals or mobility. We introduce a new mixed integer linear optimization problem that allows to optimize handovers but takes into account the costs of handovers such as signaling and communication interruption. Using our model and extensive numeric simulations we show that disregarding the handover costs leads to low performance. Based on this insight we design a new optimization scheme that uses estimates of future station arrivals and mobility patterns. We show that our scheme outperforms current optimization mechanisms and is robust against estimation errors
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| 10. |
- Gholami, Mohammad Reza, 1976, et al.
(författare)
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Wireless network positioning as a convex feasibility problem
- 2011
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Ingår i: Eurasip Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1499 .- 1687-1472. ; 2011:1
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Tidskriftsartikel (refereegranskat)abstract
- In this semi-tutorial paper, the positioning problem is formulated as a convexfeasibility problem (CFP). To solve the CFP for non-cooperative networks, we con-sider the well-known projection onto convex sets (POCS) technique, and study itsproperties for positioning. We also study outer-approximation (OA) methods tosolve CFP problems. We then show how the POCS estimate can be upper boundedby solving a non-convex optimization problem. Moreover, we introduce two tech-niques based on OA and POCS to solve the CFP for cooperative networks andobtain two new distributed algorithms. Simulation results show that the proposedalgorithms are robust against non-line-of-sight conditions.
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