| 1. |
- Bilstrup, Katrin, et al.
(författare)
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Evaluation of the IEEE 802.11p MAC method for vehicle-to-vehicle communication
- 2008
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Ingår i: 68th IEEE Vehicular Technology Conference, 2008. VTC 2008-Fall. - Piscataway, N.J. : IEEE Press. - 9781424417216 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper the medium access control (MAC) method of the upcoming vehicular communication standard IEEE 802.11p has been simulated in a highway scenario with periodic broadcast of time-critical packets (so-called heartbeat messages) in a vehicle-to-vehicle situation. The 802.11p MAC method is based on carrier sense multiple access (CSMA) where nodes listen to the wireless channel before sending. If the channel is busy, the node must defer its access and during high utilization periods this could lead to unbounded delays. This well-known property of CSMA is undesirable for time critical communications. The simulation results reveal that a specific node/vehicle is forced to drop over 80% of its heartbeat messages because no channel access was possible before the next message was generated. To overcome this problem, we propose to use self-organizing time division multiple access (STDMA) for real-time data traffic between vehicles. This MAC method is already successfully applied in commercial surveillance applications for ships (AIS) and airplanes (VDL mode 4). Our initial results indicate that STDMA outperforms CSMA for time-critical traffic safety applications in ad hoc vehicular networks.
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| 2. |
- Nilsson, Dennis, 1980, et al.
(författare)
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Efficient In-Vehicle Delayed Data Authentication Based on Compound Message Authentication Codes
- 2008
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424417223
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Konferensbidrag (refereegranskat)abstract
- Modern vehicles contain an in-vehicle network consisting of a number of electronic control units (ECUs). These ECUs are responsible for most of the functionality in the vehicle, including vehicle control and maneuverability. To date, no security features exist in this network since it has been isolated. However, an upcoming trend among automobile manufacturers is to establish a wireless connection to the vehicle to provide remote diagnostics and software updates. As a consequence, the in-vehicle network is exposed to external communication, and a potential entry point for attackers is introduced. Messages sent on the in-vehicle network lack integrity protection and data authentication; thus, the network is vulnerable to injection and modification attacks. Due to the real-time constraints and the limited resources in the ECUs, achieving data authentication is a challenge. In this paper, we propose an efficient delayed data authentication using compound message authentication codes. A message authentication code is calculated on a compound of successive messages and sent together with the subsequent messages, resulting in a delayed authentication. This data authentication could be used to detect and possibly recover from injection and modification attacks in the in-vehicle network.
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| 3. |
- 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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| 4. |
- Verendel, Vilhelm, 1980, et al.
(författare)
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An Approach to using Honeypots in In-Vehicle Networks
- 2008
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Ingår i: 68th Semi-Annual IEEE Vehicular Technology, VTC 2008-Fall, Conference; Calgary, AB; Canada; 21 September 2008 through 24 September 2008. - 1550-2252. - 9781424417223
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Konferensbidrag (refereegranskat)abstract
- An emerging trend among automobile manufacturers is to introduce wireless technology in the vehicles. By allowing wireless communication, real-time information exchange between vehicles as well as between infrastructure and vehicles becomes a reality. This communication allows for road condition reporting, decision making, and remote diagnostics and firmware updates over-the-air, creating a complex critical infrastructure involving vehicles, road-side equipment, and firmware issuers. Allowing external parties wireless access to the vehicle creates a potential entry-point for cyber attacks. Since the safety of the driver depends on correct vehicle operation it is of utmost importance that the in-vehicle network is sufficiently protected against attacks. If we can learn the attackers' preferences, techniques, and weaknesses in existing systems, we can use this information to design security solutions for the in-vehicle network. In this paper, we present and discuss the use of honeypots as a means of collecting such attacker information. We show how to design a vehicle honeypot, how to gather data from attackers, and discuss how to process and analyze the gathered data. Furthermore, we provide a discussion where we highlight important issues related to using honeypots in vehicles.
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| 5. |
- Almers, Peter, et al.
(författare)
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Effect of random walk phase noise on MIMO measurements
- 2005
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Ingår i: [Host publication title missing]. - 1550-2252. ; 61:1, s. 141-145
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Konferensbidrag (refereegranskat)abstract
- In this paper we study the influence of phase noise from free-running local oscillators on SAGE signal parameter estimation. Phase noise is here modeled as a random-walk process. We present phase noise estimates from our LUND RUSK MIMO channel sounder, and draw conclusions on requirements on local oscillators' phase noise in terms of the Allan variance. We investigate an error propagation effect in SAGE, and finally, we present random-walk phase noise effect on channel capacity.
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| 6. |
- Aronsson, Daniel, et al.
(författare)
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Performance Evaluation of Memory-less and Kalman-based Channel Estimation for OFDMA
- 2009
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Ingår i: VTC Spring 2009 - IEEE 69th Vehicular Technology Conference; Barcelona; Spain; 26 April 2009 through 29 April 2009. - 1550-2252. - 9781424425174 ; , s. Art. no. 5073788-
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Konferensbidrag (refereegranskat)abstract
- The next generation wireless systems based onOrthogonal Frequency Division Multiple Access (OFDMA) needto operate in widely different deployment and usage scenarios. Thus, support for flexible resource allocation is important. In this paper we investigate the performance of different memory-less and memory-based channel estimators with different OFDMA subcarrier allocation schemes and different pilot patterns. We evaluate the performance in various fading environments and for different user terminal velocities. The results show that channel estimation can perform well enough for time-frequency localized resources as small as 22 channel symbols with two pilots in many important scenarios. The results provided can be used to identify appropriate subcarrier allocations for the next generation OFDMA based wireless systems.
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| 7. |
- Deumal, M., et al.
(författare)
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Constrained clipping for peak power reduction of multicarrier systems by tone reservation
- 2007
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 1424402662 ; , s. 2195-2199
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Konferensbidrag (refereegranskat)abstract
- In this paper we introduce a new method to limit the peak factor of a multicarrier signal based on tone reservation. A peak-reducing signal is computed by clipping the original OFDM symbol. The peak-reducing signal is forced to have the constraints of tone reservation, so that when added to the original signal, the peak factor is reduced without increasing the BER and the out-of-band radiation. The proposed method has low computational complexity requirements and is fast-converging. Moreover, simulation results show that it has higher PAPR-reduction capabilities than other PAPR-reducing methods based on TR in the literature. © 2007 IEEE.
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| 8. |
- Gunnarsson, Fredrik, et al.
(författare)
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Downtilted Base Station Antennas - A Simulation Model Proposal and Impact on HSPA and LTE Performance
- 2008
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Ingår i: Proceedings of the 68th IEEE Vehicular Technology Conference. - 9781424417223 - 9781424417216 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a low-complexity model for vertical antenna radiation patterns, e.g. for inclusion in system- level simulations. They can be seen as extensions to the horizontal radiation pattern model used in 3GPP simulation scenarios. The model is verified against and compared to predicted and measured data from real networks. The impact on system-level performance is also investigated. It is seen that using the proposed model, simulated geometry distributions and soft handover statistics closely matching those of real networks may be achieved. The analysis also concludes that many real networks have better cell isolation than what is modeled by the 3GPP antenna model. As a consequence, the horizontal radiation pattern model significantly under-estimates the system level performance in such networks. Furthermore, the proposed model is used to assess the LTE and HSPA system-level performance for realistic scenarios.
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| 9. |
- Harrysson, Fredrik, et al.
(författare)
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Dual antenna terminals in an indoor scenario
- 2006
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Ingår i: [Host publication title missing]. - 1550-2252. ; 6, s. 2737-2741
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Konferensbidrag (refereegranskat)abstract
- The performance of two different dual antenna hand-held test mobile terminals has been investigated in a realistic indoor office environment and scenario, with respect to antenna performance, diversity combining and Shannon MIMO channel capacity. Measurements of a 2times2 MIMO channel at 1877.5 MHz (narrowband) were performed using a dual-polarized base station antenna. Analyses show that diversity gains, using ideal selection combining and maximum ratio combining, between 0.7 and 4.6 dB was achieved at the 10% outage probability level. Ideal dual-side beamforming (single branch) gives up to 3.3 dB capacity gain compared to single antenna systems at SNR less than 10 dB, however, decreases with rising SNR. Dual branch MIMO capacity gain is only significant at higher SNR above 10 dB. In addition, horizontal polarization at the base station was found to outperform vertical polarization in this scenario
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| 10. |
- Harrysson, Fredrik, et al.
(författare)
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The composite channel method : Efficient experimental evaluation of a realistic MIMO terminal in the presence of a human body
- 2008
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Ingår i: 2008 IEEE 67th Vehicular Technology Conference-Spring, VTC. - 1550-2252. - 9781424416455 ; , s. 473-477
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Konferensbidrag (refereegranskat)abstract
- The immediate environment of the transmit (TX) and receive (RX) antennas, including the antenna casings and the users holding the antennas, has a strong impact on the propagation channel and thus on wireless systems. In this paper we experimentally evaluate a method that synthetically combines double-directional measurements of the propagation channel (without the user influence) with measured antenna patterns of antennas-plus-users, by comparing obtained sample results with direct measurements in the same environment. The measurements are done for a static microcell 8×4 MIMO scenario at 2.6 GHz. A realistic user phantom was used together with a test terminal prototype with four antenna elements, and a number of different configurations and orientations of the phantom were tested. In average over all test cases, the mean signal power deviation between composite channel method and measurements was well within 1 dB. The composite method shows 6% higher terminal antenna correlation but similar statistical distributions as the measured. The differences between the model and measurements for the strongest eigenvalue (relevant for MRC combining) was found to be within 1 dB above 10% outage level. Relative deviations in the ergodic MIMO capacity were smaller than 10%.
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| 11. |
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| 12. |
- Johansson, Anders J, et al.
(författare)
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MIMO channel measurements for personal area networks
- 2005
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Ingår i: [Host publication title missing]. - 1550-2252. - 0780388879 ; 61:1, s. 171-176
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Konferensbidrag (refereegranskat)abstract
- This paper analyzes MIMO propagation channels for personal area networks. Such channels show important differences to propagation channels in wide-area networks, due to the different environments in which the systems are operated, as well as due to different mobility models, ranges, and presence of humans in the environment, and the impact of the antenna arrangement. We present results from a recent measurement campaign for this type of channel. We first analyze the requirements for measurement setups, especially in terms of different positions and orientations of the antenna arrays, to obtain meaningful results. We then analyze the measured data and present results for path loss, power delay profiles, spatial correlation and temporal correlation.
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| 13. |
- Karout, Johnny, 1985, et al.
(författare)
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Performance Trade-off Investigation of B-IFDMA
- 2009
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424425143 ; 1-4, s. 368-372
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Konferensbidrag (refereegranskat)abstract
- A performance trade-off investigation is carried out between different possible uplink multiple access schemes, that are based on Orthogonal Frequency Division Multiplexing (OFDM), for International Mobile Telecommunication (IMT) Advanced systems. Between the Discrete Fourier Transform (DFT) precoded systems with different subcarrier allocation mappings and systems lacking DFT-precoders, Block Interleaved Frequency Division Multiple Access (B-IFDMA) is shown to provide a good trade-off between the frequency diversity collected, envelope properties achieved, and channel estimation performance compared to the other mapping schemes. The schemes are analyzed in the presence of the different possible modules which include equalizers, modulators, interleavers, and channel codes. In particular, robust codes such as Turbo codes are able to collect the diversity provided by such schemes, and B-IFDMA systems is shown to be able to beat the other systems in bit error rate (BER) performance terms.
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| 14. |
- Kåredal, Johan, et al.
(författare)
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Shadowing effects in MIMO channels for personal area networks
- 2006
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Ingår i: [Host publication title missing]. - 1550-2252. ; , s. 173-177
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Konferensbidrag (refereegranskat)abstract
- In this paper we analyze the effects of body shadowing in multiple-input-multiple-output (MIMO) channels used for personal area networks (PANs). We give physical reasoning to why PANs may experience two different types of shadowing, and to support our argument, we present results from a measurement campaign for three different PAN channels with human influence. The campaign is performed using different types of multi-element antenna devices; an access point, a body-worn device and two hand-held devices, conducted over a series of distances between 1-10 m. For each distance, a number of channel realizations are obtained by moving the antenna devices over a small area, and by rotating the persons holding the devices. The results show that it is suitable to distinguish between body shadowing (due to the rotation of the person holding the device) and shadowing due to surrounding objects (lateral movement). We also present a statistical model where the two types of shadowing are described as separate log-normal processes. Furthermore, we find that body shadowing has a big influence on the capacity of the investigated PAN channels. © 2006 IEEE.
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| 15. |
- Lau, Buon Kiong, et al.
(författare)
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Capacity analysis for compact MIMO systems
- 2005
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Ingår i: IEEE 61st Vehicular Technology Conference, VTC 2005-Spring. - 1550-2252. - 0780388879 ; 61:1, s. 165-170
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Konferensbidrag (refereegranskat)abstract
- We analyze the impact of mutual coupling on the capacity of MEMO systems with compact antenna arrays. Existing studies present conflicting views on the effect of mutual coupling. This is, in part, due to their different scopes and underlying assumptions of the system setups. In this paper, we aim to give a comprehensive picture by first examining the impact of mutual coupling on three capacity-related performance measures: antenna correlation, efficiency and bandwidth. While the first two aspects have received significant attention, antenna bandwidth with mutual coupling is a relatively uncharted territory. We show that while implementing a good matching network can drastically improve the system capacity for narrowband systems in the presence of strong mutual coupling, the same conclusions may not necessarily apply to wideband cases. To exemplify this, we carry out capacity simulations for an end-to-end MIMO system, where a recently proposed S-parameter approach is used in conjunction with the 3GPP-3GPP2 channel model to model realistic wideband channel and antenna effects at both transmit and receive ends.
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| 16. |
- Riback, Mathias, et al.
(författare)
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Carrier frequency effects on path loss
- 2006
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Ingår i: [Host publication title missing]. - 1550-2252. ; 6, s. 2717-2721
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Konferensbidrag (refereegranskat)abstract
- To study the carrier frequency effects on path loss, measurements have been conducted at four discrete frequencies in the range 460-5100 MHz. The transmitter was placed on the roof of a 36 meters tall building and the receive antennas were placed on the roof of a van. Both urban and suburban areas were included in the measurement campaign. The results show that there is a frequency dependency, in addition to the well known free-space dependency 20 log10(f), in most of the areas included in the measurements. In non line of sight conditions, the excess path loss is clearly larger at the higher frequencies than at the lower. A model capturing these effects is presented
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| 17. |
- Santos, Telmo, et al.
(författare)
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Scatterer detection by successive cancellation for UWB - method and experimental verification
- 2008
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Ingår i: [Host publication title missing]. - 1550-2252. - 9781424416448 ; , s. 445-449
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Konferensbidrag (refereegranskat)abstract
- We present a new high delay resolution method to detect ultra-wideband (UWB) scatterers when using frequency domain measurements. Our approach makes use of the impulse response envelope amplitudes and delays measured over a distance that is larger than the region of stationarity, and detects the 2D coordinates of the channel scatterers, assuming that only single-scattering (single-interaction) processes occur. The identification methodology is based on multiple application of interference cancellation: at every step, we detect the strongest scatterer from an array of measurements, save its information, cancel it from the channel and search for the next strongest scatterer. To precisely define the strength of each scatterer, we present a method to define its birth and death locations along the measurement array. Finally, we verify the method by applying it to measurement results in an outdoor environment; the scatterer locations identified from the measurements show excellent agreement with the physically present objects like walls and columns.
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| 18. |
- Tian, Ruiyuan, et al.
(författare)
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Uncoupled antenna matching for performance optimization in compact MIMO systems using unbalanced load impedance
- 2008
-
Ingår i: IEEE Vehicular Technology Conference, VTC Spring 2008.. - 1550-2252. - 9781424416448 ; , s. 299-303
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Konferensbidrag (refereegranskat)abstract
- Some MIMO applications require antennas to be closely spaced, which result in mutual coupling among antennas and high spatial correlation for signals. In order to compensate for the performance degradation due to correlation and coupling, impedance matching networks may be used. Recently, it was shown that uncoupled matching networks could be optimized against a given performance metric with the constraint of similar matching impedance for all antennas, i.e., balanced matching. In this paper, we investigate the use of uncoupled matching networks with both balanced and unbalanced load impedances, where either the received power or the channel capacity is optimized. For two- and three-element dipole arrays, we show numerically that a significant performance improvement can be achieved by introducing unbalanced matching. Observations suggest that the achieved improvement varies with array geometry and propagation environment. For example, a large capacity gain of up to 23% is realized when matching a uniform linear array to propagation environments that are asymmetrical about the array broadside, whereas the symmetrical environments do not benefit as much from unbalanced matching.
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| 19. |
- Wang, Wei, 1965, et al.
(författare)
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Evaluations of a 4G Uplink System Based on Adaptive Single-Carrier TDMA
- 2005
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Ingår i: Proceedings IEEE Vehicular Technology Conference Fall, Dallas, Texas, USA. - 1550-2252. - 0780391527 ; 3, s. 1667-1671
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Konferensbidrag (refereegranskat)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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| 20. |
- Wyne, Shurjeel, et al.
(författare)
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A cluster-based analysis of outdoor-to-indoor office MIMO measurements at 5.2 GHz
- 2006
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Ingår i: [Host publication title missing]. - 1550-2252. ; , s. 22-26
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a cluster based analysis of an outdoor-to-indoor Multiple-Input Multiple-Output (MIMO) measurement campaign, and extract model parameters for the COST273 channel model. The measurements were performed at 5.2 GHz for 159 measurement locations in an office building. Multipath component (MPC) parameters have been extracted for these positions using a high-resolution algorithm. We analyze the clustering of MPCs, i.e., grouping together of MPCs with similar DOAs, DODs, and delays. We compare cluster identification by visual inspection to automatic identification by the recently proposed algorithm of Czink et al. In the paper we include results on the intercluster properties such as the distribution of the number of clusters and the cluster powers, as well as intracluster properties such as the angle and delay spreads within the clusters. In particular, we extract parameters for the COST 273 channel model, a standardized generic model for MIMO propagation channels. © 2006 IEEE.
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| 21. |
- Xiaoyu, Wei, et al.
(författare)
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A Joint Power and Rate Control Algorithm and Fairness Enhancement for Multiuser OFDM System
- 2008
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Ingår i: 68TH IEEE VEHICULAR TECHNOLOGY CONFERENCE, FALL 2008. - 9781424417223 ; , s. 1872-1876
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Konferensbidrag (refereegranskat)abstract
- A joint adaptive power and adaptive rate (APAR) control algorithm for OFDM systems that aims at sum-rate maximization, subject to certain power and rate constraints, is presented in this paper. In the basic optimization framework, the overall system throughput is the main objective, but as such it lacks user fairness consideration. Two scheduling schemes that allow adjusting the trade-off between fairness and throughput are proposed and combined with the APAR scheme for fairness enhancement. Simulation results show that enhanced system performance and balanced efficiency-fairness trade-off can be achieved by the proposed schemes in downlink.
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| 22. |
- Zander, Roland, et al.
(författare)
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Analysis of prediction-oriented features in dynamic bandwidth reservation schemes
- 2006
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. ; , s. 2439-2443
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Konferensbidrag (refereegranskat)abstract
- Out of Quality of Service reasons, higher priority shall in cellular networks be assigned to ongoing connections than to new call attempts. This can be accomplished through reserving a portion of the bandwidth assigned to a cell exclusively for high priority connections. A low priority call is only admitted to a cell if the unoccupied bandwidth in the cell following the acceptance of the call exceeds or is equal to the reserved bandwidth. In order to improve the efficiency of the bandwidth reservation scheme, the amount of bandwidth to reserve can be made time-varying and adaptive towards the momentary network conditions. Subscriber movement predictions can be applied to obtain handover arrival rate estimations, which can be used as input to the bandwidth reservation allocation procedure. The subscribers can for instance be grouped according to speed and previous cells. In this paper, a Markovian analysis of such prediction-oriented grouping features will be performed. The probability for a new call attempt to be blocked and the probability for a handover attempt to fail, due to channel occupancies, will be calculated for a bandwidth reservation scheme with and without grouping features. The obtained analytical results will be validated using computer simulations. © 2006 IEEE.
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