| 1. |
- Lakshmana, Tilak Rajesh, 1980, et al.
(författare)
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Partial joint processing for frequency selective channels
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424435746
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider a static cluster of base stations where joint processing is allowed in the downlink. The partial joint processing scheme is a user-centric approach where subclusters or active sets of base stations are dynamically defined for each user in the cluster. In frequency selective channels, the definition of the subclusters or active set thresholding of base stations can be frequency adaptive (per resource block) or non-adaptive (averaged over all the resource blocks). Frequency adaptive thresholding improves the average sum-rate of the cluster, but at the cost of an increased user data interbase information exchange with respect to the non-adaptive frequency thresholding case. On the other hand, the channel state information available at the transmitter side to design the beamforming matrix is very limited and rank deficiency problems arise for low values of active set thresholding and users located close to the base station. To solve this problem, an algorithm is proposed that defines a cooperation area over the cluster where the partial joint processing scheme can be performed, frequency adaptive or non-adaptive, for a given active set threshold value.
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| 2. |
- Makki, Behrooz, 1980, et al.
(författare)
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Data Transmission in the Presence of Channel State Feedback and Outage Probability Constraint
- 2010
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Ingår i: IEEE 72nd Vehicular Technology Conference. - 1550-2252. - 9781424435746
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Konferensbidrag (refereegranskat)abstract
- Recently, substantial attention has been paid to increase the achievable rates of wireless networks using different kinds of limited channel state information (CSI) feedback. This paper aims to investigate the effect of limited CSI feedback on the achievable rates of power-limited block fading channels constrained to have limited outage probability. Considering different power allocation strategies and various fading conditions, the results are obtained for different outage probabilities and are compared with the case where there is no outage limitation. Simulation results show that 1) although the outage probability constraint reduces the channel average rate, its influence diminishes as the channel state information feedback or the input power increases, 2) the effect of the outage probability constraint decreases as the channel fading severity is reduced.
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| 3. |
- Soltani Tehrani, Ali, 1982, et al.
(författare)
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Successive Cancellation of Power Amplifier Distortion for Multiuser Detection
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424435746
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Konferensbidrag (refereegranskat)abstract
- This paper presents an iterative interference suppression technique to cancel power amplifier (PA) distortion at the receiver. The focus is mainly on single carrier frequency division multiple access systems, and on removing the distortion created by adjacent users' power amplifier. It is assumed that the receiver has perfect knowledge of all the users' transmitter power amplifier nonlinearities.By relaxing the requirement on PA linearity at the mobile terminals, the PA power efficiency can be improved. The simulations show that by utilizing the successive interference cancelation technique, the require signal to noise ratio required to achieve 10^-3 symbol error rate is decreased by 3 - 4 dB. By using a clipped communication signal instead of backing off the power in the transmitter PA, we are able to improve the power added efficiency by 8 percentage points.
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| 4. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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A Low-Complexity Semi-Analytical Approximation to the Block Error Rate in Nakagami-m Block Fading Channels
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424435746
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Konferensbidrag (refereegranskat)abstract
- There are few analytical formulas that can be usedfor calculating the block error rate (BLER) in block fadingchannels. Thus, an estimate of the BLER is often obtained usingnumerical methods. One such method is the threshold methodwhich assigns 0 or 1 to the instantaneous BLER given the signalto noise ratio (SNR) level. It has been shown that utilizing sucha method results in an accurate approximation of the BLER inNakagami-m block fading channels for a wide range of m.In this work, we consider a recently proposed simple method ofobtaining the threshold and study the effect of adopting differentphysical layer and channel parameters on that threshold. Weshow that, while the value of this threshold depends on themodulation, coding, and block size, it is almost unaffected bythe m parameter of Nakagami-m channels for a wide range ofpractical values. In addition, for a given modulation and codingmethod, the threshold is shown to be a simple function of blocksize. As a result, the computational complexity required to obtainthe threshold can be significantly reduced.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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