| 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 ; , 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. |
- Alegria, Juan Vidal, et al.
(författare)
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Decentralized equalizer construction for large intelligent surfaces
- 2019
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Ingår i: 2019 IEEE 90th Vehicular Technology Conference, VTC 2019 Fall - Proceedings. - 1550-2252. - 9781728112206 ; 2019-September
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Konferensbidrag (refereegranskat)abstract
- In this paper we present fully decentralized methods for calculating an approximate zero- forzing (ZF) equalizer in a large intelligent surface (LIS). A LIS is intended for wireless communication and facilitates unprecedented MU- MIMO performance, far superior to that of Massive MIMO. Antenna modules in the grid connect to their neighbors to exchange messages of information needed for interference cancellation in a fully- decentralized fashion, making the system scalable. By a careful design of how the messages are routed, we show that the proposed method is able to cancel inter-user interference sufficiently well without any centralized coordination, opening the door for the realization of this type of structures.
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| 3. |
- 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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| 4. |
- Ang, Lay-Hong, et al.
(författare)
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Modification of SOVA-based Algorithms for Efficient Hardware Implementation
- 2010
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Ingår i: IEEE 71st Vehicular Technology Conference (VTC 2010-Spring), 2010. - 1550-2252. ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper, a modified soft-output Viterbi algorithm (SOVA) is presented to enable efficient hardware implementation. The forward-only processing of the SOVA has an inherent lower latency than forward-backward algorithms such as BCJR and its offspring, which are commonly used in iterative decoders. Thus, SOVA-based architectures require less parallelization and therefore hardware for the same data throughput. A simplification is proposed to the Battail rule ( BR) SOVA to approximate the concurrent path reliability values with the corresponding metric differences. This simplified BR-SOVA (SB-SOVA) performs close to max-log-MAP. Furthermore, a novel hybrid decoding architecture is proposed that combines the simplicity of the original Hagenauer rule and the performance-preserving properties of the SB-SOVA to trade implementation complexity for decoding performance. The hybrid approach is evaluated with practical link-level simulations of the downlink data channel in LTE Rel-8.
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| 5. |
- 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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| 6. |
- Bernadó, Laura, et al.
(författare)
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In-tunnel vehicular radio channel characterization
- 2011
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Ingår i: [Host publication title missing]. - 1550-2252. - 9781424483327
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedInside a tunnel, electromagnetic wave propagation differs strongly from the well understood "open-air" situation. The characterization of the tunnel environment is crucial for deploying vehicular communication systems. In this paper we evaluate vehicle-to-vehicle (V2V) radio channel measurements inside a tunnel. We estimate the time-varying root mean square (rms) delay and Doppler spreads, as well as the excess delay and the maximum Doppler dispersion. The fading process in V2V communications is inherently non-stationary. Hence, we characterize the stationarity time, for which we can consider the fading process to be wide sense stationary. We show that the spreads, excess delay, and maximum Doppler dispersion are larger on average when both vehicles are inside the tunnel compared to the "open-air" situation. The temporal evolution of the stationarity time is highly influenced by the strength of time-varying multipath components and the distance between vehicles. Furthermore, we show the good fit of the rms delay and Doppler spreads to a lognormal distribution, as well as for the stationarity time. From our analysis we can conclude that the IEEE 802.11p standard will be robust towards inter-symbol and inter-carrier interference inside a tunnel.
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| 7. |
- 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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| 8. |
- Botella Mascarell, Carmen, 1979, et al.
(författare)
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On the performance of joint processing schemes over the cluster area
- 2010
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Ingår i: IEEE Vehicular Technology Conference Spring, Taipei, Taiwan, May 2010. - 1550-2252. - 9781424425181 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper, three joint processing schemes for the downlink are characterized and compared within a cluster of base stations. The motivation of this study is to analyze the performance of these schemes over the cluster area, as a first step towards designing an adaptive joint processing scheme supporting dynamic usage scenarios. Each one of the analyzed schemes, the centralized, partial and distributed joint processing approaches, requires a different amount of available channel knowledge at the transmitter side, inter-base information exchange and feedback from the users. In addition, these schemes show varying capabilities to serve the users depending on their location in the cluster area. Therefore, in a real scenario, an adaptive joint processing scheme encompassing the three schemes could be used by the cluster of base stations. Simulation results show that, assuming coherent transmission, the centralized joint processing scheme outperforms with 25% the partial joint processing scheme and with 50% the distributed joint processing approach in the cell edge when a backhaul-load weighted average sum-rate per cell metric is taken into account.
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| 9. |
- Chen, Jingjing, 1982, et al.
(författare)
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Demonstration of analog millimeter-wave fronthaul for 64-QAM LTE transmission
- 2015
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252.
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Konferensbidrag (refereegranskat)abstract
- Centralized baseband architecture is believed to be cost efficient and to offer high network performance. The fronthaul network, connecting the centralized baseband to distributed remote radios, requires high capacity and low latency transport links, due to the stringent specifications of the data interface, known as common public radio interface (CPRI). Today, fronthaul links are mostly based on digital CPRI over fibers, although it is possible to realize CPRI over wireless technology with the drawback of poor bandwidth efficiency. In this paper, we propose an analog wireless fronthaul concept to enable bandwidth efficient and scalable fronthaul networks. The basic idea is to transport narrow band analog radio signals over millimeter-wave bands instead of multi-gigabit digital signals. The phase and frequency impairments introduced by high frequency carriers are effectively reduced using an analog pilot-based mitigation technique. As a proof-of-concept demonstration, an analog fronthaul link is implemented, and the link performance is verified for 20 MHz 64-QAM LTE transmission over 70/80 GHz (E-band). The measured error vector magnitude (EVM) is about 3% with 10% pilot bandwidth overhead.
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| 10. |
- Chen, Jingjing, 1982, et al.
(författare)
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Experimental demonstration of RF-pilot-based phase noise mitigation for millimeter-wave systems
- 2014
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781479944491 ; , s. Art. no. 6965978-
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Konferensbidrag (refereegranskat)abstract
- Millimeter-wave bands are gaining popularity for high data rate wireless communication systems due to the wide available bandwidth. However, oscillator phase noise also increases as the carrier frequency increases. Methods of phase noise mitigation are therefore crucial for future millimeter-wave systems. In this work, we propose to adopt analog phase noise mitigation using an RF-pilot tone, which reduces both phase and frequency impairments of an arbitrary millimeter-wave signal at the expense of reduced spectral efficiency. The method is verified experimentally at carrier frequency of 28 GHz and E-band 73 GHz showing a 20 dB noise reduction up to 100 kHz offset. Since the method relaxes phase noise requirement it is attractive for phase noise sensitive technologies at high carrier frequency, such as OFDM used in LTE. As indicated by the simulation results, the reduced phase noise enables a LTE signal on a millimeter-wave carrier with marginal performance impact.
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