| 1. |
- Berggren, F., et al.
(author)
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Joint power control and intracell scheduling of DS-CDMA nonreal time data
- 2001
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In: IEEE Journal on Selected Areas in Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 19:10, s. 1860-1870
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Journal article (peer-reviewed)abstract
- The performance of DS-CDMA systems depends on the success in managing interference arising from both intercell and intracell transmissions. Interference management in terms of power control for real time data services like voice has been widely studied and shown to be a crucial component for the functionality of such systems. In this work we consider the problem of supporting downlink nonreal time data services, where in addition to power control, there is also the possibility of controlling the interference by means of transmission scheduling. One such decentralized schedule is to use time division so that users transmit in a one-by-one fashion within each cell. We show that this has merits in terms of saving energy and increasing system capacity. We combine this form of intracell scheduling with a suggested distributed power control algorithm for the intercell interference management. We address its rate of convergence and show that the algorithm converges to a power allocation that supports the nonreal time data users, using the minimum required power while meeting requirements on average data rate. Numerical results indicate a big potential of increased capacity and that a significant amount of energy can be saved with the proposed transmission scheme.
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| 2. |
- Eriksson, Magnus
(author)
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Dynamic Single Frequency Networks
- 2001
-
In: IEEE Journal on Selected Areas in Communications. - New York : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 19:10, s. 1905-1914
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Journal article (peer-reviewed)abstract
- Wireless asymmetric Internet access with a downlink peak bit rate of 10 to 30 Mb/s can be achieved by using the terrestrial digital video broadcasting system (DVB-T) as a supplemental downlink together with today's cellular systems. This paper is a study of dynamic radio resource management on a packet-by-packet basis for this broadband downlink. The dynamic single frequency networks (DSFN) scheme is evaluated. It exploits the macrodiversity capability of the OFDM modulation scheme. The transmitters are dynamically divided into groups of transmitters that send the same information at the same channel frequency simultaneously. The fairly shared spectrum efficiency (FSSE), in bits per second per Hertz per site, which is a combined measurement of maximum throughput and fairness, is evaluated for best-effort traffic. DSFN improves the FSSE by 100% to 370%, for a certain set of test cases, in comparison to the dynamic packet assignment (DPA) scheme, which combines packet scheduling with dynamic channel assignment (DCA).
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| 3. |
- Gunnarsson, Fredrik, et al.
(author)
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Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled DS-CDMA
- 2001
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In: IEEE Journal on Selected Areas in Communications. - Linköping : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 19:1, s. 141-151
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Journal article (peer-reviewed)abstract
- Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.
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| 4. |
- Hokfelt, Johan, et al.
(author)
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On the Theory and Performance of Trellis Termination Methods for Turbo Codes
- 2001
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In: IEEE Journal on Selected Areas in Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0008 .- 0733-8716. ; 19:5, s. 838-847
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Journal article (peer-reviewed)abstract
- The performance of a turbo code can be severely degraded if no trellis termination is employed. This paper investigates the implications of the choice of trellis termination method for turbo codes, and explains the origin of the performance degradation often experienced without trellis termination. An efficient method to derive the distance spectrum of turbo codes for different trellis termination methods is presented. Further, we present interleaver design rules that are tailored to each termination method. Using interleavers designed with these restrictions, we demonstrate that the performance difference between various termination methods is very small, including no trellis termination at all. For example, we demonstrate a turbo code with a 500-bit interleaver that exhibits no sign of an error floor for frame error rates as low as 10-8, even though no trellis termination is employed
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| 5. |
- Janssen, Gerard J. M., et al.
(author)
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Symbol error probability analysis of a multiuser detector for M-PSK signals based on successive Cancellation
- 2002
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In: IEEE Journal on Selected Areas in Communications. - New York : IEEE. - 0733-8716 .- 1558-0008. ; 20:2, s. 330-338
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Journal article (peer-reviewed)abstract
- A narrow-band multiuser receiver based on successive signal detection and subtraction, is considered in this paper. The symbol error probability (SEP) for M-PSK modulated signals is evaluated and analytical approximations for the SEP of the individual signals are presented and compared with results obtained from simulations. For geometrically related signal amplitudes, a constant minimum distance can be guaranteed independent of the number of signals. The required amplitude ratio is shown to be related to and the number of co-channel signals. Optimizing the transmitted power for the different signals while ensuring the same SEP is then addressed and closed-form expressions of the signal amplitude ratios are derived. The effect of inaccurately estimated signal parameters due to noise is also analyzed. SEP results are presented for synchronous signals in an additive white Gaussian noise environment.
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| 6. |
- Jäntti, Riku, et al.
(author)
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Second-Order Power Control with Asymptotically Fast Convergence
- 2000
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In: IEEE Journal on Selected Areas in Communications. - New York : IEEE. - 0733-8716 .- 1558-0008. ; 18:3, s. 447-457
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Journal article (peer-reviewed)abstract
- This paper proposes a distributed power control algorithm that uses power levels of both current and previous iterations for power update. The algorithm is developed by applying the successive overrelaxation method to the power control problem. The gain from such a second-order algorithm is in faster convergence. Convergence analysis of the algorithm in case of feasible systems is provided in this paper. Using the distributed constrained power control (DCPC) as a reference algorithm, we carried out computational experiments on a DS-CDMA system. The results indicate that our algorithm significantly enhances the convergence speed of power control. A practical version of the proposed algorithm is provided and compared with the bang-bang type algorithm used in the IS-95 and the WCDMA systems. The results show that our algorithm also has a high potential for increasing the radio network capacity. Our analysis assumes that the system is feasible in the sense that we can support every active user by an optimal power control. When the system becomes infeasible because of high traffic load, it calls for other actions such as transmitter removal, which is beyond the scope of the present paper.
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| 7. |
- Nilsson, Rickard, et al.
(author)
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Autonomous synchronization of a DMT-VDSL system in unbundled networks
- 2002
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In: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 20:5, s. 1055-1063
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Journal article (peer-reviewed)abstract
- We present an algorithm that autonomously synchronizes all DMT-Zipper based VDSL modems in an unbundled access network, solving the problem with nonorthogonal NEXT that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL-modem in the central office or in the street cabinet. We determine the other modems ' relative frame offsets by exploiting their NEXT signal using the inherent cyclic redundancy found in DMT signals. By estimating the relative frame offsets of the other users, we can adjust a given user's own frame-timing relative to the mean of the others. With our method all modems in the network will be synchronized to within a small fraction of the total DMT frame-length, suppressing the nonorthogonal NEXT to a level far below the background noise-floor. This means that we can achieve the same performance in an unbundled access network without any master clock reference as in a system where all modems are perfectly synchronized using a master clock. Index Terms-Discrete multitone, frame synchronization, subscriber loops.
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| 8. |
- Skoglund, Mikael, et al.
(author)
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On the capacity of a multiple-antenna communication link with channel side information
- 2003
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In: IEEE Journal on Selected Areas in Communications. - : IEEE Communications Society. - 0733-8716 .- 1558-0008. ; 21:3, s. 395-405
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Journal article (peer-reviewed)abstract
- We investigate the capacity of a system with multiple transmit and receive antennas, assuming that the transmitter and receiver both have access to (possibly defective) channel-state information. Two different special cases of a general system are studied in detail. Our main results are capacity expressions for these cases and a general conclusion that the encoder can be split into separate space-time coding and direction weighting or beamforming, without capacity loss. We also present numerical results illustrating the dependence of capacity on the parameters of a quantization scheme providing channel-state information to the transmitter from the receiver. These results have high practical value since the assumptions behind them are closely related to the ones of the closed-loop mode in the UMTS/WCDMA standard.
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| 9. |
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| 10. |
- Carlemalm, C, et al.
(author)
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Suppression of multiple narrowband interferers in a spread-spectrum communication system
- 2000
-
In: IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0733-8716. ; 18:8, s. 1365-1374
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Journal article (peer-reviewed)abstract
- We consider the problem of estimating and suppressing many unknown independent and time-varying interferers in a spread-spectrum communication system. The interferers are assumed to be present in a wide frequency range. In order to detect, estimate, and t
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