| 1. |
- Li, Jingya, 1986, et al.
(författare)
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Optimal Design of Energy-Efficient HetNets: Joint Precoding and Load Balancing
- 2015
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Ingår i: IEEE International Conference on Communications. - : IEEE. - 1550-3607. - 9781467364324 ; 2015-September, s. 4664-4669
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Konferensbidrag (refereegranskat)abstract
- This paper considers the downlink of a heterogeneous network, where multiple base stations (BSs) can serve the users by non-coherent multiflow beamforming. We assume imperfect channel state information at both BSs and users. The objective is to jointly optimize the precoding, load balancing, and BS operation mode (active or sleep) for improving the energy efficiency of the network. The considered problem is to minimize the weighted total power consumption (both circuit power and dynamic transmit power), while satisfying per-user quality of service constraints and per-BS transmit power constraints. This problem is non-convex, but we prove that for each combination of BS modes, the considered problem has a hidden convexity structure. Thus, the global optimal solution is obtained by an exhaustive search over all possible BS mode combinations. Furthermore, by iterative convex approximations of the non-convex power consumption functions, a heuristic algorithm is proposed to obtain a local optimal solution with low complexity. Simulation results illustrate that our proposed algorithms significantly reduce the total power consumption, compared to the scheme where all BSs are continuously active. This implies that putting a BS into sleep mode by proper load balancing is an important solution for energy savings in heterogeneous networks.
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| 2. |
- Jamaly, Nima, 1979, et al.
(författare)
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Analysis and Measurement of Multiple Antenna Systems for Fading Channel Prediction in Moving Relays
- 2014
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Ingår i: 2014 8TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). - 2164-3342. - 9788890701849 ; , s. 2015-2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The performance of wireless data transmission to mobile vehicles is improved if channel state information is available at the transmitter but movement of vehicles causes outdating of channel estimates. The concept of a predictor antenna has recently been proposed, where an antenna is placed in front of other antennas on the roof of the vehicle to sense the radio environment in advance. This can comparatively provide an order-of-magnitude improvement in channel prediction performance. A potential problem with this idea is that closely placed antennas will experience mutual electromagnetic couplings. These may reduce the efficiency of the predictor antenna concept if they are not taken into account. In this paper, we discuss about how to treat the forgoing issue and eventually evaluate a promising candidate on measured channels. We argue that only open-circuit voltage method would be realistic for the present application. The usefulness of the proposed decoupling method is demonstrated on field measurements obtained in downtown Dresden, Germany. We also partly address the sensitivity of the open-circuit decoupling method to the accuracy of the utilized network parameters.
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| 3. |
- Jungnickel, Volker, et al.
(författare)
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The role of small cells, coordinated multi-point and massive MIMO in 5G
- 2014
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Ingår i: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 52:5, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- 5G will have to support a multitude of new applications with a wide variety of requirements, including higher peak and user data rates, reduced latency, enhanced indoor coverage, increased number of devices, and so on. The expected traffic growth in 10 or more years from now can be satisfied by the combined use of more spectrum, higher spectral efficiency, and densification of cells. The focus of the present article is on advanced techniques for higher spectral efficiency and improved coverage for cell edge users. We propose a smart combination of small cells, joint transmission coordinated multipoint (JT CoMP), and massive MIMO to enhance the spectral efficiency with affordable complexity. We review recent achievements in the transition from theoretical to practical concepts and note future research directions. We show in measurements with macro-plus-small-cell scenarios that spectral efficiency can be improved by flexible clustering and efficient user selection, and that adaptive feedback compression is beneficial to reduce the overhead significantly. Moreover, we show in measurements that fast feedback reporting combined with advanced channel prediction are able to mitigate the impairment effects of JT CoMP.
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| 4. |
- Klockar, Annika, et al.
(författare)
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Utility as a User Selection Criterion for Coordinated Multi-Point Systems
- 2013
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Ingår i: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC). - London : IEEE conference proceedings. ; , s. 3123-3128, s. 3123-3128
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Konferensbidrag (refereegranskat)abstract
- Coordinated multipoint (CoMP) transmission and reception techniques have been proposed to combat inter-cell interference in cellular systems and, hence, to increase the data rates. Due to the overhead introduced, not all users may be served with CoMP. In this paper, we focus on how to select users for joint processing CoMP under limited backhaul capacity. The evaluated user selection schemes take user experience into account, quantified by the utility of Internet application types. We propose a heuristic algorithm utility based user selection that has low computational complexity. Utility based user selection and maximize utility, which maximizes the sum utilities, are compared to maximize rate, which maximizes the sum data rates. A range of traffic mixes and user locations are evaluated. The simulation results indicate that resources required for CoMP are more efficiently used if the user selection is based on utility rather than on maximizing the total data rate. If utility is taken into account a higher total utility can in many cases be achieved for the same limited backhaul capacity.
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| 5. |
- Klockar, Annika, et al.
(författare)
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Utility of Joint Processing Schemes
- 2010
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Ingår i: 2010 7th International Symposium on Wireless Communication Systems (ISWCS 2010). - : IEEE Communications Society. - 9781424463152 ; , s. 76-80, s. 76-80
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Konferensbidrag (refereegranskat)abstract
- Joint processing between base stations has been shown as an efficient technique to mitigate inter-cell interference and increase data rates, in particular at the cell edges. In this paper, we evaluate the utility of Internet applications in a joint processing enabled cluster of base stations. Utility is used to quantify system performance as experienced by the end user. In particular, the utility of three joint processing schemes for the downlink is characterized and compared within the cluster area. The qualitative results indicate that joint processing can significantly improve the utility of hard real-time and adaptive applications. For elastic applications, joint processing is not worthwhile, since almost as high utility is achieved also with conventional single base station assignment
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| 6. |
- Li, Jingya, 1986, et al.
(författare)
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Performance evaluation of coordinated multi-point transmission schemes with predicted CSI
- 2012
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Ingår i: IEEE Conference on Personal, Indoor and Mobile Radio Communications, PIMRC, Sydney, Australien. - 9781467325691 ; , s. 1055-1060
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Konferensbidrag (refereegranskat)abstract
- Coordinated multi-point (CoMP) transmission is considered as an efficient technique to improve cell-edge performance as well as system spectrum efficiency. In CoMP-enabled systems, a cluster of coordinated base stations (BSs) are typically assumed to be connected to a control unit (CU) via backhaul links, and the provided performance gain relies heavily on the quality of the channel state information (CSI) available at the CU side. In this paper, we consider the downlink of a CoMP cluster and compare three different CoMP transmission schemes: zero-forcing coherent joint transmission, non-coherent joint transmission and coordinated scheduling. Moreover, for each of the analyzed schemes, the performance in terms of average sum rate of the CoMP cluster is studied with predicted CSI, considering the effects of the feedback and backhaul latency, as well as the user mobility. Compared to zero-forcing coherent joint transmission, we show that non-coherent joint transmission and coordinated scheduling are more robust to channel uncertainty. In addition, depending on the latency, user mobility and user locations, different schemes would achieve the highest average sum rate performance. Hence, a system could switch between the transmission schemes to improve the sum rate.
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| 7. |
- Phan-Huy, Dinh-Thuy, et al.
(författare)
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Making 5G Adaptive Antennas Work for Very Fast Moving Vehicles
- 2015
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Ingår i: IEEE Intelligent Transportation Systems Magazine. - 1939-1390 .- 1941-1197. ; 7:2, s. 71-84
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Tidskriftsartikel (refereegranskat)abstract
- Wireless systems increasingly rely on the accurate knowledge at the transmitter side of the transmitter-to-receiver propagation channel, to optimize the transmission adaptively. Some candidate techniques for 5th generation networks need the channel knowledge for tens of antennas to perform adaptive beamforming from the base station towards the mobile terminal. These techniques reduce the radiated power and the energy consumption of the base station. Unfortunately, they fail to deliver the targeted quality of service to fast moving terminals such as connected vehicles. Indeed, due to the movement of the vehicle during the delay between channel estimation and data transmission, the channel estimate is outdated. In this paper, we propose three new schemes that exploit the "Predictor Antenna" concept. This recent concept is based on the observation that the position occupied by one antenna at the front of the vehicle, will later on be occupied by another antenna at the back. Estimating the channel of the "front" antenna can therefore later help beamforming towards the "back" antenna. Simulations show that our proposed schemes make adaptive beamforming work for vehicles moving at speeds up to 300 km/h.
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| 8. |
- Popovsk, Petar, et al.
(författare)
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EU FP7 INFSO-ICT-317669 METIS, D1.1 Scenarios, requirements and KPIs for 5G mobile and wireless system
- 2013
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This deliverable introduces generic scenarios based on fundamental challenges, and the specific problem description of test cases that will be relevant for beyond future radio access. Specific characteristics of each scenario and each test case include the key assumptions regarding requirements and key performance indicators. In order not to constrain the potential solutions, the requirements are specified from an end-user perspective. The deliverable will not only serve as the guideline for the technical work and system concept design in METIS, but also can serve in external research communities to help to harmonize the work towards the future radio access system including the new generation system of 5G
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| 9. |
- Sternad, Mikael, et al.
(författare)
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Resource allocation and control signaling in the WINNER flexible MAC concept
- 2008
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Ingår i: 68TH IEEE VEHICULAR TECHNOLOGY CONFERENCE, FALL 2008. - 9781424417216 ; , s. 1553-1557, s. Art. no. 4657161-
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Konferensbidrag (refereegranskat)abstract
- The EU WINNER projects have studied OFDM-based packet data systems beyond 3G that use adaptivity on all time-scales to obtain high flexibility and performance. The adaptive transmission in both downlink and uplink is scheduled and controlled at base stations and relay nodes and requires frequent transmission of control information over the downlink. The use of scheduling, adaptive modulation and coding, with fine granularity in both time and space, could potentially result in unrealistic bandwidth demands for such downlink control signaling. The present paper describes how this problem has been handled within WINNER in two cases: Frequency-adaptive transmission, which allows individual link adaptation within time-frequency resource units and non-frequency adaptive transmission, which averages over the channel variations in the frequency domain. An important tool for limiting the associated control information is to broadcast only a small essential set of control data to all user terminals, using a safe but therefore bandwidth-demanding code rate. The remaining control information is multicast to groups of users with different signal to interference and noise ratios (SINRs). The modulation and code rates of these transmissions are adjusted to the SINRs of these groups. The over-all coded data rate of the control transmission can thereby be reduced to acceptable levels.
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| 10. |
- Sternad, Mikael, et al.
(författare)
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Towards systems beyond 3G based on adaptive OFDMA transmission
- 2007
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Ingår i: Proceedings of the IEEE. - 0018-9219 .- 1558-2256. ; 95:12, s. 2432-2455
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Forskningsöversikt (refereegranskat)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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