| 1. |
- Du, J, et al.
(författare)
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Estimation of Performance Loss Due to Delay in Channel Feedback in MIMO Systems
- 2004
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Ingår i: 2004 IEEE 60th Vehicular Technology Conference, 2004. VTC2004-Fall.. - 0780385217 ; 3, s. 1619-1622
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Konferensbidrag (refereegranskat)abstract
- Latency of available channel state information (CSI) at the transmitter in time-varying channels greatly affects the performance of multiple-input multiple-output (MIMO) systems. We have derived a simple algorithm to calculate an approximation of the expected performance loss based on the most recent channel feedback. The proposed algorithm can be used to determine the maximum tolerable channel feedback delay for each particular channel realization.
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| 2. |
- Hultell, Johan, et al.
(författare)
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Business models and resource management for shared wireless networks
- 2004
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Ingår i: VTC2004-FALL. - NEW YORK : IEEE. - 0780385217 ; , s. 3393-3397
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Konferensbidrag (refereegranskat)abstract
- In this paper we analyze main use cases for sharing wireless access networks between multiple operators and service providers. Network sharing has been proposed as a metho l to lower roll-out costs for 3G operators in Europe, and is widely used in WLAN systems where local access providers offer wireless access to service providers. A similar structure also exist in cellular networks where Mobile Virtual Network Operators (MVNO) provide mobile services without having a mobile network of their own. The development points at a further fragmentation of wireless access networks into specialized service providers that connect to local service and access providers, possibly via an inter-connection provider serving with core network functionality. In this context, we propose a framework for how radio resources could be managed using Service Level Agreements (SLA) and analyze key differences between the SLA for different types of service and network providers.
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| 3. |
- Kjellander, Per, et al.
(författare)
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Correlated fading and antenna directionality in multiuser detection
- 2004
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Ingår i: VTC2004-FALL. - NEW YORK : IEEE. - 0780385217 ; , s. 1909-1913
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Konferensbidrag (refereegranskat)abstract
- We investigate detection of multiple users at a base station array of antennas, isotropic or directional, with overlapping beam patterns. The question is whether the increased diversity obtainable by isotropic antennas can compensate for the loss of antenna gain. We also account for limited angle spread of the arriving signals, which correlates the gains and reduces diversity. We consider the multiuser detection algorithm to be maximum likelihood and present new expressions for the resulting symbol error rate in correlated fading. Among other features, they show that each user's performance depends on the angle spreads of all users. We also demonstrate that a circular array of directional antennas with overlapping beams can achieve the same level of diversity as a circular array of isotropic antennas.
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| 4. |
- Kåredal, Johan, et al.
(författare)
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Statistical analysis of the UWB channel in an industrial environment
- 2004
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Ingår i: [Host publication title missing]. - 0780385217 ; , s. 81-85
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a statistical model for the ultra-wideband (UWB) channel in an industrial environment. Based on a set of measurements in a factory hall, we find that the abundance of metallic scatterers causes dense multipath scattering. This can be seen to produce mostly a Rayleigh distributed small-scale fading signal, with only a few paths exhibiting Nakagami distributions. For the power delay profile, we suggest a generalization of the Saleh-Valenzuela model where clusters with different excess delays have different ray power decay constants; the decay constants follow a linear dependence on the delay. This model provides an excellent fit to the measured data. We also note that for non-line-of-sight scenarios at larger distances, several hundred multipath components need to be collected to capture 50% of the available energy
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| 5. |
- Lee, Chae Y., et al.
(författare)
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Call admission control for real time multimedia services with variable bit rate in WCDMA systems
- 2004
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Ingår i: VTC2004-FALL. - : IEEE. - 0780385217 ; , s. 2559-2563
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Konferensbidrag (refereegranskat)abstract
- Call admission control for real time multimedia services with variable bit rate (VBR) is considered in this paper. In the WCDMA system, one of the most prevailing services will be real time multimedia in which the data rate changes dynamically. In this paper, we propose two call admission schemes that effectively reflect features of VBR multimedia services and well satisfy the objectives. The proposed schemes are based on the signal to interference ratio (SIR) of the system. Especially, they anticipate the fluctuation of SIR due to the data rate change of each multimedia service and make an admission decision based on prediction of future SIR rather than the current SIR value. The proposed schemes are compared with an admission policy whose admission decision depends only on the current SIR value.
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| 6. |
- Lundevall, Magnus, et al.
(författare)
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Streaming Applications Over HSDPA in Mixed Service Scenarios
- 2004
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Ingår i: Proceedings of the 60th IEEE Vehicular Technology Conference. - 0780385217 ; , s. 841-845
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Konferensbidrag (refereegranskat)abstract
- High-speed downlink packet access (HSDPA) is included in release 5 of the WCDMA specifications to increase downlink capacity and bitrates. This paper considers performance aspects of streaming applications over HSDPA in a mixed streaming and best-effort service scenario. Different scheduling algorithms are evaluated with the aim of providing sufficient quality-of-service for streaming. The simulation results show that reasonable streaming performance can be achieved without service differentiation if a somewhat fair scheduler is used, and that a streaming-aware scheduler further can protect streaming quality-of-service in high load conditions.
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| 7. |
- Martin, Cristoff, et al.
(författare)
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File based mobile satellite broadcast systems : Error rate computation and QoS based design
- 2004
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Ingår i: VTC2004-FALL. - NEW YORK : IEEE. - 0780385217 ; , s. 4017-4021
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Konferensbidrag (refereegranskat)abstract
- Mobile satellite broadcast systems have the potential of delivering entertainment, information and other data services with outstanding coverage and reliability. However, the long signal interruptions due to obstacles in the terminal environment that characterizes the land mobile satellite channel make the design of efficient air interfaces challenging. In this paper, a file based mobile satellite broadcast system is studied where, to overcome the signal blockages, packet time diversity is applied. Based on some simple assumptions, an analytical expression for the file error rate of the system is derived. Using this result, a design scheme is proposed that, for a given channel and file, minimizes the total number of transmitted symbols required to satisfy quality of service (QoS) constraints in terms of acceptable delay and file receive probability. The results can also be used to estimate the reduction in bandwidth requirements that can be achieved if users in demanding environments can be served using terrestrial repeaters or other means.
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| 8. |
- Martin, Cristoff, et al.
(författare)
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Spectrally efficient mobile satellite real-time broadcast with transmit diversity
- 2004
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Ingår i: VTC2004-FALL. - NEW YORK : IEEE. - 0780385217 ; , s. 4079-4083
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Konferensbidrag (refereegranskat)abstract
- Mobile broadcast services from satellites require the terminals to constantly be in near line of sight conditions with the transmitting satellite in order to efficiently provide real-time services. To satisfy this constraint in practice, satellite diversity as well as terrestrial repeaters are used. By separating the various transmissions in frequency, exploiting this spatial diversity at the receiver is straightforward. However, transmitting the same information at different frequencies also reduces the limited and expensive spectrum available for these types of services. By configuring the different transmissions as a single frequency network. in principle a more efficient usage of the spectrum can be achieved. Due to the vast distances involved in satellite diversity systems, practical design of such a system is challenging. In this paper we propose the use of a small adaptive antenna at the receiver in order to separate the different transmissions and improve the spectral efficiency. System architectures are outlined, an example illustrates the potential gain and implementation issues are discussed.
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| 9. |
- Medbo, Jonas, et al.
(författare)
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Temporal radio channel variations with stationary terminal
- 2004
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Ingår i: [Host publication title missing]. - 1090-3038. - 0780385217 ; 1, s. 91-95
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Konferensbidrag (refereegranskat)abstract
- In wireless communications, stationary terminal scenarios are becoming increasingly important as bitrates goes up. Consequently, the need to improve the knowledge about the channel behavior and to develop realistic channel models for these scenarios is also increasing. The present work comprises both measurements and modeling of the radio channel when the terminal is stationary. The measurements were performed at 5 GHz in indoor scenarios using a vector network analyzer. The measured channel was essentially static most of the time. Only about 1% of the time did it show substantial channel variations. An important finding is that the dominant cause for temporal channel variations in the measurements was the movement of persons in the vicinity of either antenna. This is also supported by a simple model, based on a single moving scatterer, which shows good agreement with measurements.
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| 10. |
- Mehta, N B, et al.
(författare)
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Rate of MIMO Systems with CSI at Transmitter and Receiver from Pilot-Aided Estimation
- 2004
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Ingår i: IEEE 60th Vehicular Technology Conference, VTC 2004-Fall.. - 1090-3038. - 0780385217 ; 3, s. 1575-1579
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Konferensbidrag (refereegranskat)abstract
- We consider realistic multiple input multiple output antenna systems operating over spatially colored channels with instantaneous, albeit imperfect, channel state information at the receiver and only covariance knowledge available at the transmitter. We focus on pilot-aided channel estimation in which the receiver uses minimum mean square error channel estimation. For such a setup, our goal is then to design both the pilot and data sequences optimally to maximize the information rates achievable over the channel. We first demonstrate that the estimation error cannot be modeled as additive white Gaussian noise. We adopt a lower bound on channel capacity with imperfect channel knowledge and show that an optimum design leads to a matching of the eigenspaces of the pilots and of the data to the eigenspace of the channel. Furthermore, the ranks of the pilot and data covariance matrices need to be equal, and the optimal training duration need only equal the above rank. The assignment of powers to the different modes of transmission can then be obtained numerically. The paper, in essence, extends the results in the literature that assume perfect channel knowledge at the receiver, and shows that fully exploiting covariance knowledge leads to a visible improvement in capacity when compared to schemes that assume no channel knowledge, whatsoever, at the transmitter.
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