| 1. |
- Wei, Xinning, et al.
(författare)
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Joint Transmission with Significant CSI in the Downlink of Distributed Antenna Systems
- 2009
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Ingår i: 2009 IEEE International Conference on Communications, ICC 2009; Dresden; Germany; 14 June 2009 through 18 June 2009. - 0536-1486. - 9781424434350 ; , s. Art. no. 5199124-
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Konferensbidrag (refereegranskat)abstract
- Interference management is required for improving the performance of future mobile radio communication systems. In the downlink (DL) of cellular systems with base stations (BSs) located in the cell centers and equipped with omnidirectional antennas, transmission strategies such as matched filtering (MF) can’t achieve good system performance, and zero forcing (ZF) with full channel state information (CSI) of the whole system imposes a high computational cost and requires a substantial amount of feedback. In this paper, an intelligent signal processing technique with moderate complexity, i.e., ZF joint transmission (JT) with significant CSI, based on distributed antenna systems (DASs) with BSs located at three vertices of each cell and equipped with sector antennas is proposed. From numerical results, it is shown that our proposal is a good combination of BS antenna layout and signal processing technique for inter- ference management. The proposed intelligent signal processing technique can significantly benefit from the proposed smart BS antenna layout.
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| 2. |
- Alvarado, Alex, 1982, et al.
(författare)
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Correcting Suboptimal Metrics in Iterative Decoders
- 2009
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Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781424434350
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Konferensbidrag (refereegranskat)abstract
- In this paper the issue of improving the performance of iterative decoders based on sub-optimal calculation of the messages exchanged during iterations (L-values) is addressed. It is well known in the literature that a simple---yet very effective---way to improve the performance of suboptimal iterative decoders is based on applying a scaling factor to the L-values. In this paper, starting with a theoretical model based on the so-called consistency condition of a random variable, we propose a methodology for correcting the L-values that relies only on the distribution of the soft information exchanged in the iterative process. This methodology gives a clear explanation of why the well-known linear scaling factor provides a very good performance. Additionally, the proposed methodology allows us to avoid the exhaustive search required otherwise. Numerical simulations show that for turbo codes the scaling factors found closely follow the optimum values, which translates to a close-to-optimal BER performance. Moreover, for LDPC codes, the proposed methodology produces a better BER performance compared with the known method in the literature.
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| 3. |
- Alvarado, Alex, 1982, et al.
(författare)
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Unequal Error Protection in BICM with QAM Constellations: Interleaver and Code Design
- 2009
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Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781424434350
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a general methodology for the interleaver and code design for QAM-based BICM transmissions. We develop analytical bounds on the bit error rate and we use them to predict the performance of BICM when unequal error protection (UEP) is introduced by the constellation labeling. Based on these bounds, the optimum design of interleaver and code is presented. The improvements obtained reached 2~dB for the analyzed cases, and are obtained without complexity increase. Although previous works noted the influence of the interleaver design and the UEP, to the best of our knowledge, this paper is the first to analyze formally this problem for BICM transmissions.
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| 4. |
- Aulin, Jocelyn, 1964, et al.
(författare)
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Performance Bounds for MLSD Reception of OFDM Signals in Fast Fading
- 2008
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Ingår i: IEEE International Conference on Communications, ICC 2008; Beijing; China; 19 May 2008 through 23 May 2008. - 0536-1486. - 9781424420742 ; , s. 4626 - 4633
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Konferensbidrag (refereegranskat)abstract
- For OFDM systems in fast fading, it is difficult to obtain a closed form expression for the OFDM symbol error probability. Thus, tight analytical bounds on actual performance are extremely useful for performance prediction and verification. Additionally, the structure of the bound provides insight into system behavior. A new expurgated 2-dimensional union bound is proposed and applied to an OFDM system in fast fading. This bound becomes extremely tight as the rate of fading $L$ increases. Performance comparison of the new bound to a lower bound on a known expurgated union bound demonstrates a gain of up to 1.5 dB at $P(\epsilon)=10^{-2}$ for channel implicit diversity order of $L=4$. A new simulated upper bound that uses a reduced state vector in a modified trellis search algorithm and a simulated lower bound that assumes limited knowledge of the ICI are also presented.Both bounds are derived from a "time-varying" finite state machine model of the received signal. Performance results for these bounds are extremely tight for small to large values of $N$, where $N$ is the number of OFDM signal tones. Also, the reduction in computational complexity achieved for $N=512$ is from $2^{512}$ to $2^{6}$ for both bounds.
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| 5. |
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| 6. |
- Gao, Yuehong, et al.
(författare)
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System Spectral Efficiency and Stability of 3G Networks : A Comparative Study
- 2009
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Ingår i: 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8. - : IEEE Press. - 9781424434350 ; , s. 5398-5403
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Konferensbidrag (refereegranskat)abstract
- CDMA2000, WCDMA and WiMAX are three widely used 3G technologies. Since they share the same goal, which is to provide broader coverage and higher throughput in 3G networks, an impartial comparison of their performance is indispensable. However, they are based on different design principles and methodologies, which make the comparison challenging. This paper presents a comparative study of these technologies, with focus on system spectral efficiency and stability in 3G networks. Specifically, the paper presents a framework for the comparison based on the common set of configurations adopted by these technologies, which include channel models, system parameters and key algorithms. Through extensive simulations, the system spectral efficiency and stability of CDMA2000 1x EV-DO Rev.A, WCDMA HSDPA/HSUPA and Mobile WiMAX are compared. It is found that while WiMAX can provide highest throughput, the two CDMA-based technologies achieve higher system spectral efficiency, especially on the downlink. Regarding system stability, it is observed that CDMA2000 1x EV-DO Rev.A can operate under higher interference levels than WCDMA HSDPA/HSUPA and Mobile WiMAX. In addition, the comparison on system spectral efficiency between CDMA2000, WCDMA and WiMAX is also conducted when relevant enhanced technologies, i.e., MIMO and interference cancelation, are adopted. We believe that our work will serve as a cornerstone for a fair comparison between the various technologies for prospective 3G networks.
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| 7. |
- Nilsson, Dennis, 1980, et al.
(författare)
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Secure Firmware Updates over the Air in Intelligent Vehicles
- 2008
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Ingår i: ICC 2008 - 2008 IEEE International Conference on Communications Workshops; Beijing; China; 19 May 2008 through 23 May 2008. - 0536-1486. - 9781424420513 ; , s. 380-384
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Konferensbidrag (refereegranskat)abstract
- Modern intelligent vehicles have electronic control units containing firmware that enables various functions in the vehicle. New firmware versions are constantly developed to remove bugs and improve functionality. Automobile manufacturers have traditionally performed firmware updates over cables but in the near future they are aiming at conducting firmware updates over the air, which would allow faster updates and improved safety for the driver.In this paper, we present a protocol for secure firmware updates over the air. The protocol provides data integrity, data authentication, data confidentiality, and freshness. In our protocol, a hash chain is created of the firmware, and the first packet is signed by a trusted source, thus authenticating the whole chain. Moreover, the packets are encrypted using symmetric keys. We discuss the practical considerations that exist for implementing our protocol and show that the protocol is computationally efficient, has low memory overhead, and is suitable for wireless communication. Therefore, it is well suited to the limited hardware resources in the wireless vehicle environment.
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| 8. |
- Shi, L., et al.
(författare)
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Loop-free forwarding table updates with minimal link overflow
- 2009
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Ingår i: ICIEA. - 9781424434350 ; , s. 3960-3963
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Konferensbidrag (refereegranskat)abstract
- The forwarding paths in an IP network may change due to a link failure, network equipment maintenance, or reconfiguration of link weights. The forwarding tables in the routers need then to be updated. These updates may cause transient loops and link overflow, if they are not performed in an appropriate order. While existing proposals achieve loop-free updates, transient link overflow is still a problem during the updating process. In this paper, we present a method that compares the initial and final forwarding paths, and obtains the updatable nodes that do not cause any transient loop or link overflow. However, this goal is not always achievable, therefore, we propose an algorithm to update the forwarding tables that will refrain the link overflows to a minimal level. The performance study on a real topology with two setups confirms that our approach achieves smaller link overflow than by using a previously proposed approach.
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| 9. |
- Stranne, André, et al.
(författare)
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Energy-based throughput analysis of packet radio networks
- 2004
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Ingår i: IEEE International Conference on Communications. - 0536-1486. ; 6, s. 3718-3722
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Konferensbidrag (refereegranskat)abstract
- The increasing use of wireless technology utilizing unlicensed frequency bands calls for more in-depth analysis of interference and coexistence between systems. In this paper a framework is presented for detailed analysis of the performance of coexisting networks in shared frequency bands. The framework allows for multiple packet lengths to be used by the communicating devices and the analysis is performed with respect to the received interfering energy, which in effect leads to a link budget analysis on a packet basis. A system of interfering Bluetooth piconets is analyzed to illustrate the use of the framework and the conceptual difference in basing the analysis on link budgets, rather than on packet collisions. Furthermore, some indications on throughput saturation in the analyzed Bluetooth system are presented.
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| 10. |
- Szczecinski, Leszek, 1970, et al.
(författare)
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Probability Density Functions of Reliability Metrics for 16-QAM-Based BICM Transmission in Rayleigh Channel
- 2007
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Ingår i: IEEE International Conference on Communications ICC 2007. - 0536-1486. - 1424403537 ; , s. 1012-1017
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Konferensbidrag (refereegranskat)abstract
- In bit interleaved coded modulation (BICM), the probabilitydensity function (PDF) of the reliability metrics (L-values) fully defines the BICM transmission and may be used to analyze it from an information-theoretic point of view. In this paper, the closed-form expressions for the PDF of the L-values in Rayleigh fading channels for 16-QAM with Gray mapping are derived and contrasted with histograms of the L-values obtained via numerical simulations. The obtained closed-forms show that the PDF is either a sum of exponentials or is bounded by such a sum.
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