| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Cho, Jeong-woo, 1978-, et al.
(författare)
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Infrastructure Support Increases the Capacity of Ad Hoc Wireless Networks
- 2005
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Ingår i: VTC2005-FALL: 2005 IEEE 62ND VEHICULAR TECHNOLOGY CONFERENCE, 1-4, PROCEEDINGS. - : IEEE Press. - 0780391527 ; , s. 2663-2668
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Konferensbidrag (refereegranskat)abstract
- In ad hoc wireless networks, one of the hottest research directions has been to increase the throughput capacity scaling with respect to the number of nodes n. Gupta and Kumar (2000) introduced a fixed random network model and showed that the throughput per source-destination pair is Theta(1/root nlogn) when the network is coordinated by a centralized entity. Grossglauser and Tse (2001) introduced a mobile random network model and showed that a source-destination pair acquires a constant throughput of Theta(1) assuming that delays incurred by mobile nodes with low mobility are tolerable.In this paper, we consider the capacity of ad hoc wireless networks with infrastructure support. Although Grossglauser-Tse mobile network model enables Theta(1) per-node throughput scaling, the mobility assumption may be too unrealistic to be accepted in some practical situations. One of the key observations we acquired is that the infrastructure support plays the same role played by the mobility in the Grossglauser-Tse model. We show that nodes can utilize the randomly located infrastructure support instead of mobility when nodes are nearly static. In this case, we show that the per-node throughput of Theta(1) is still achievable when the number of access points grows linearly with respect to the number of nodes. Furthermore., we show that there is additional per-node throughput improvement of Theta(1) when nodes are mobile.
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| 6. |
- 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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| 7. |
- Dimou, Konstantinos, et al.
(författare)
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Generic link layer : A solution for multi-radio transmission diversity in communication networks beyond 3G
- 2005
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Ingår i: VTC2005-FALL. - 0780391527 ; , s. 1672-1676
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Konferensbidrag (refereegranskat)abstract
- Communication systems beyond 3G (B3G) will consist of a mixture of radio access technologies. For such systems the challenge is to provide a multi-radio access architecture that facilitates the interconnection of heterogeneous radio access networks and supports efficiently the various services. Achieving this interconnection in a transparent way for users and services requires extensions at link layer level. The Generic Link Layer (GLL), as proposed in the context of the Ambient Networks (AN) project addresses this challenge. The principal role of GLL within the AN multi-radio access architecture is to integrate different Radio Access Technologies (RATs) at the link layer and to facilitate their efficient interworking. A feature that is enabled by the use of GLL is termed multi-radio transmission diversity (MRTD). It implies a well-defined split of a data-flow over the available RATs; the main benefits thereby are gain in user QoS, in spectral efficiency and in robustness. In this paper we give the system architecture and the GLL functions required for the realization of MRTD. Then, the specific scenario of cooperation between UMTS and IEEE 802.11 is discussed.
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| 8. |
- 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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| 9. |
- 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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| 10. |
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