| 1. |
- Arias, Marvin, et al.
(författare)
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Time Domain Cluster PDF and Its Application in Geometry-Based Statistical Channel Models
- 2007
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Ingår i: Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2007). - 9781424411443 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- This paper presents an approach to derivate the Time of Arrival (TOA) power density function (PDF) and its application in geometry-based statistical channel models for urban environments. The cluster PDF derived can be used to simulate temporal dispersion of the multipath signal grouped in clusters in a variety of urban propagation conditions to quantify second order statistics, i.e., delay spread for a given elliptical shape of the cluster. We propose a clustering approach channel model, and employ it to derive the PDF of TOA of the multipath signal. In order to evaluate the theoretical clusters PDF in time domain proposed, we make computer simulations for the geometry-based channel model proposed and compared it with experimental results published in the open literature. The comparison with experimental results shows good agreement.
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| 2. |
- Ghosh, A. K., et al.
(författare)
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Sender side intelligence for TCP throughput enhancement in wired-cum-wireless network
- 2007
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Ingår i: 2007 IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications. - 1424411440 - 9781424411443 ; , s. 4394381-
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Konferensbidrag (refereegranskat)abstract
- Performance of the TCP Congestion Control Algorithm has been the focus of research over the last decade. In this paper we propose modifications to TCP Congestion Control to improve its performance in wired-cum-wireless networks The key idea to determine the Optimal Congestion Window for a TCP Sender, in a particular network scenario (that corresponds to the fair share of that connection) and keep this congestion window a constant to a point where the fair share in the network has changed considerably from the instance of the calculation of the size of the last window. At this point, the TCP Congestion Window is recalculated according to the nature of new scenario. The proposed mechanism is particularly effective over wireless links, which have an inherently loss-prone nature, as Modified TCP's congestion window being independent of packet losses (be it corruption losses or it congestion losses), keeps transmitting at the same rate at before.
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| 3. |
- Paier, Alexander, et al.
(författare)
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First results from car-to-car and car-to-infrastructure radio channel measurements at 5.2GHZ
- 2007
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Ingår i: [Host publication title missing]. - 9781424411443 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Car-to-car and car-to-infrastructure (henceforth called C2X) communications are constantly gaining importance for road-safety and other applications. In order to design efficient C2X systems, an understanding of realistic C2X propagation channels is required, but currently, only few measurements have been published. This paper presents a description of an extensive measurement campaign recently conducted in an urban scenario, a rural scenario, and on a highway. We focused on 4 ÿ 4 multiple-input multiple-output (MIMO) measurements at a center frequency of 5.2 GHz with high Doppler resolution. As first results from evaluating the measurement data we present the power-delay profile and the delay-Doppler spectrum from a selected, especially interesting measurement run from an urban measurement route. We observe dispersed Doppler contributions between zero and the Doppler shift corresponding to the relative speed of the cars, and very concentrated (in the Doppler domain), contributions from double reflections. Surprisingly, we also found paths with larger delays and zero Doppler shifts.
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| 4. |
- Rusek, Fredrik, et al.
(författare)
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Optimal time-frequency occupancy of finite packet OFDM
- 2007
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Ingår i: 2007 IEEE 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, vols 1-9. - 9781424411443 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider the least time--frequency product necessary to transmit a small finite symbol packet such that the symbols can be independently detected. The system model assumed is offset QAM-OFDM, based on a finite duration pulse shape. The outcome is that the optimal pulse shape is of very short duration and that the optimal symbol allocation strategy is often to use as many subcarriers as there are symbols to transmit. Symbol packets up to 150 symbols are considered.
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| 5. |
- Shin, Eun-Hee, et al.
(författare)
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On the Asymptotic Sum-Rate in 2xNx2 Dual-Hop Relaying with Quality based Channel Reporting and Relay Selection
- 2007
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Ingår i: 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9. - : IEEE. - 9781424411443 ; , s. 2508-2512
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Konferensbidrag (refereegranskat)abstract
- In this paper, we prove the asymptotic sum-rate growth like 2 log log N can be achieved in 2 times N times 2 dual-hop relaying systems with 2 transmit antennas at a base station (or a source), N > 2 single receive/transmit antenna relays and 2 destination users with a single antenna. The capacity is achieved when the base station transmits with zero-forcing beamforming and the relays that actively transmit are selected with semi-orthogonal relay selection principle. Since the base station should know the channel information to the relays, the feedback load grows prohibitively large if N rarr infin. To reduce the feedback load from the relays to the base station, we use quality-based channel state reporting (QBR). Numerical results show that the sum-rate achieved by N relays gets close to its multiuser counterpart if the amplifying gain at the relay is large. We also show how QBR is effective in reducing the feedback load when N is large.
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| 6. |
- Song, Young-Keum, et al.
(författare)
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Setting Up/Down Step-Size in Open Loop Power Control for Wibro Reverse Link
- 2007
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Ingår i: 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9. - : IEEE. - 9781424411443 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper, we describe how to set up/down step-size in open loop power control for WiBro reverse link. Since open loop power control does not use feedback information, it is difficult to efficiently use wireless resource with accurate power control. We also provide a method of estimating levels of noise and interference. With numerical investigation, asymmetric up/down power-control step-size is shown to be promising to achieve high sector throughput as well as low error rate.
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| 7. |
- Timus, Bogdan, et al.
(författare)
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Performance analysis of an amplify and forward relaying scheme with pre-coding
- 2007
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Ingår i: 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9. - : IEEE. - 9781424411443 ; , s. 2834-2838
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Konferensbidrag (refereegranskat)abstract
- Cooperative diversity can combat fading on multipath channels by exploiting space diversity available through cooperative relays. Half-duplex relaying is quite simple to implement but it is useful only when the direct link is weak. By allowing the source to transmit continuously, full-rate relay channels can be obtained. However, the performance of such a full-rate scheme is still limited by the direct link. In this paper1 we consider pre-coding at the transmitter as a way of improving the performance of full-rate relay channels. The obtained results show that, with a proper selection of the pre-coding parameters, better system capacity can be obtained.
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| 8. |
- Wu, Di, 1979-, et al.
(författare)
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Lattice-Reduction Aided Multi-User STBC Decoding with Resource Constraints
- 2007
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Ingår i: 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS. - : IEEE. - 9781424411436 - 9781424411443 ; , s. 192-196
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Konferensbidrag (refereegranskat)abstract
- Recently lattice-reduction aided decoders have been proposed in MIMO system to achieve near Maximum Likelihood decoder performance while maintaining reasonable complexity. This paper studies the implementation of lattice-reduction aided linear decoders on a programmable device for multi-user space-time block coding (MU-STBC). By reloading software, the device can be configured to use different decoding schemes according to the amount of resources available, which is an important feature of cognitive radio. In this paper, two different lattice-reduction aided linear decoding methods namely SQRD-LR and AQRD-LR for MU-STBC are evaluated based on their BER performance and computational complexity. Furthermore, the effect of deadline constraint on LR is evaluated and based on the evaluation, a new method namely adaptive decoding is proposed by us to allow mode-switching of the decoder according to the environment parameters, so that the best decoder performance can always be achieved while fulfiling the resource constraints.
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