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| 3. |
- Falahati, Sorour, 1971, et al.
(författare)
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Future improvements to wideband CDMA
- 1999
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Ingår i: Proceedings Radiovetenskap och Kommunikation, Karlskona, Sweden. ; , s. 470-475
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Konferensbidrag (refereegranskat)
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| 4. |
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| 5. |
- Johansson, Ann-Louise, 1968
(författare)
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Group-wise successive interference cancellation in multirate CDMA systems
- 1999
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Ingår i: Proceedings IEEE Vehicular Technology Conference, Houston, Texas. ; , s. 1435-1439
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Konferensbidrag (refereegranskat)abstract
- In this paper, the performance of variable processing gains (VPG) and multicode (MC) systems employing a group-wise successive interference canceller (GSIC) is analysed. The GSIC is an interference canceller performing group-wise signal estimation using matched filters and successive cancellation between the groups. The results for long random codes show that the systems converge to similar performance. Before convergence, the two schemes have however different performance. For the first few stages the MC scheme performs better than the VPG scheme, while the VPG scheme obtains the lowest minimum BER.
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| 6. |
- Johansson, Ann-Louise, 1968
(författare)
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Interference Cancellation for DS/CDMA Systems in Flat Fading Channels
- 1996
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates interference cancellation in direct-sequence codedivision multiple access (DS/CDMA) systems that support multiple data rates.Two approaches for implementing multiple data rates are considered. Oneis the use of mixed modulation. The second is the use of parallel channels.With mixed modulation we denote that each user chooses a modulation format,e.g., BPSK, QPSK (4-QAM) or 16-QAM, according to the desired data rate.Parallel channels are realized by assigning several spreading codes toeach user. This enables the transmission of several parallel data streamsthat are mutually synchronous.We introduce and analyse a novel approach that combines the above describedmultiple data rate systems with interference cancellation (IC). The cancellationin the receiver is performed successively on each user, starting with theuser received with the highest power. This procedure can in turn be iterated,forming a multistage scheme, with the number of iterations set as a designparameter. We will evaluate the performance of these two multiple datarate schemes when used in combination with IC and compare them to the performanceof systems employing conventional detectors.We first analyse IC for M-ary rectangular QAM systems and then applythe results to mixed modulation systems and systems employing parallelchannels. Our analysis employs a Gaussian approximation for the distributionof the interference, and it includes both the AWGN and the flat Rayleighfading channel. The systems ate also evaluated via computer simulations.Our analysis and simulations indicate that the IC schemes used in mixedmodulation or parallel channel systems yield a performance close to thesingle BPSK user bound and, consequently, give a prospect of a considerableimprovement in performance compared to systems employing a conventionaldetector.
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| 8. |
- Johansson, Ann-Louise, 1968, et al.
(författare)
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Linear group-wise successive interference cancellation in CDMA
- 1998
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Ingår i: Proceedings IEEE International Symposium on Spread Spectrum Techniques and Applications, Sun City, South Africa, 2-4 Sep 1998. ; 1, s. 121-126
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider a matrix-algebraic approach to linear group-wise successive interference cancellation. As for both successive and parallel cancellation, it is shown that the general linear group-wise scheme corresponds to a one-shot linear matrix filtering. Furthermore, it is shown that if the general structure converges, it converges to the decorrelator. Four structures are considered for the group detector, namely the matched filter, the parallel canceller, the decorrelator and the MMSE detector, and the equivalent one-shot filters are derived. Conditions for convergence related to the grouping are studied and it is shown that group detection with a decorrelator, which has conventional successive interference cancellation as a special case, always converges. Through numerical examples, it is illustrated that the performance for all the structures behaves like the performance for the linear successive canceller where a minimum BER is reached before convergence to the performance of the decorrelator occurs. The matched filter group canceller achieves the lowest minimum BER but also has the slowest convergence.
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| 15. |
- Johansson, Ann-Louise, 1968
(författare)
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Successive Interference Cancellation in DS-CDMA Systems
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is every indication that direct-sequence code division multiple access (DS-CDMA) will be one of the multiple access schemes for the third generation wireless mobile systems. CDMA is a flexible multiple access method suitable for supporting many new services (speech, data, video, etc), which are becoming increasingly important for mobile communications. Besides supporting multiple data rates, future systems also have to meet enhanced performance and capacity demands. A CDMA system employing conventional receiver techniques is limited in capacity, since its performance can be significantly degraded by multiple access interference and the near-far effect. These problems can, however, be combated with multiuser detection. The multiuser detector studied in this thesis is the successive interference canceller (SIC), chosen because of its relatively low complexity and suitability for hardware implementation. Additionally, this thesis analyses interference cancellation (IC) in combination with variable data rate systems. The initial study analyses the single- and multistage SIC for asynchronous, multirate DS-CDMA systems. Two multirate schemes are considered, which are based on mixed (or multiple) modulation formats and multicode. These schemes are compared for the additive white Gaussian noise (AWGN) and the Rayleigh fading channels. A conventional linear SIC is used for the single-path channel, but the corresponding SIC adapted to the multipath channel includes both linear and non-linear SIC together with RAKE combining. The results indicate that it is possible to achieve a performance close to the single-user bound for both multirate schemes in systems with fairly high load. Furthermore, the multi-stage SIC is analysed using a matrix-algebraic approach, leading to the description of the SIC as a linear matrix filtering. Using this representation, an analytical expression for the bit error rate is derived, and the convergence behaviour of the SIC is studied. A group-wise successive interference canceller (GSIC) is also analysed and a general analytical expression for the performance of the GSIC scheme with any linear group detector is given. Four structures are considered for the group detector: the matched filter, the decorrelator, the parallel interference canceller and the MMSE detector. Convergence characteristics, the effect of the grouping and the performance of systems with and without weighted cancellation are analysed. Finally, the matrix-algebraic approach is applied to multirate systems employing the GSIC based on the matched filter group detector, and the multirate systems based on variable processing gain and multicode schemes are compared.
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| 20. |
- Rasmussen, Lars K., et al.
(författare)
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Convergence of linear successive interference cancellation in CDMA
- 1997
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Ingår i: Proceedings Workshop on Multiaccess, Mobility and Teletraffic for Personal Communication, Melbourne, Australia. - Boston, MA : Springer US. ; , s. 13-27
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider a matrix-algebraic approach to linear successive interference cancellation (SIC). It has been shown that both single- and multi-stage linear SIC schemes correspond to a one-shot linear matrix filtering. Eigenvalue conditions on the resulting linear filter for convergence of the multistage scheme are considered and the concept of e-convergence is introduced for determining the number of stages necessary for practical convergence. It is observed that the BER for the users does not generally reach its minimum when the scheme converges, hence, optimal performance is achieved after a limited number of cancellation stages, which does not have to be the same for different users.
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| 22. |
- Rasmussen, Lars K., et al.
(författare)
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One-shot filtering equivalence for linear successive interference cancellation in CDMA
- 1997
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Ingår i: Proceedings IEEE Vehicular Technology Conference, Phoenix, Arizona, May 04-07. ; , s. 2163-2167
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Konferensbidrag (refereegranskat)abstract
- We consider a matrix-algebraic approach to linear successive interference cancellation (SIC). It is shown that both single- and multi-stage linear SIC schemes correspond to a one-shot linear matrix filtering that can be performed directly on the received chip-matched filtered received vector without explicitly performing the interference cancellation. This description allows for determining the bit error rate analytically. Also eigenvalue conditions for convergence of the multi-stage scheme are derived and the concept of ε-convergence introduced for determining the number of stages necessary for practical convergence.
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| 25. |
- Wållberg-Jonsson, Solveig, 1953-, et al.
(författare)
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Extent of inflammation predicts cardiovascular disease and overall mortality in seropositive rheumatoid arthritis : A retrospective cohort study from disease onset
- 1999
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Ingår i: Journal of Rheumatology. - Toronto, Canada : University of Toronto Publishing. - 0315-162X .- 1499-2752. ; 26:12, s. 2562-2571
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To identify predictors for cardiovascular disease (CVD) and for overall survival in patients with rheumatoid arthritis (RA) followed from disease onset. METHODS: A retrospective cohort of patients with seropositive RA and disease onset between 1974 and 1978 (n = 211) was followed up at the end of 1995. Potential predictors for CVD, as measured by "the first cardiovascular event," and for overall survival were registered. The predictors were identified by extended Cox regression models. RESULTS: In simple Cox regression analysis, male sex, higher age at disease onset, HLA-B27, high disease activity, corticosteroid treatment early in disease, and hypertension significantly increased risk of cardiovascular event. Higher educational level, extensive disease modifying antirheumatic drug (DMARD) treatment, and corticosteroids > or =1 yr before event decreased the risk. In multiple Cox regression analysis, male sex, high age at disease onset, hypertension, higher haptoglobin level at disease onset, and corticosteroid treatment early in disease increased risk of CVD. In a multiple model comprising only patients with CVD, corticosteroids delayed the event. A high last registered erythrocyte sedimentation rate (ESR) value before event increased CVD risk, in particular when early in disease progression. Decreased life span was predicted by higher age at disease onset, male sex, low education level, high disease activity, hypertension, and CVD. HLA-B27 was associated with decreased life span, as was early, but not extensive corticosteroid treatment. DMARD treatment was associated with decreased mortality risk, as was the presence of joint prosthesis. In multiple regression, male sex, higher age at disease onset, atlantoaxial subluxation early in disease, hypertension, and cardiovascular event increased mortality. A high last registered ESR value before event or death added to that risk. CONCLUSION: The study emphasizes the importance of inflammation as an important risk indicator for CVD and mortality in RA. The positive impact of disease activity reducing treatment on CVD risk and survival is suggested.
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| 26. |
- Österlund, Lars, 1967, et al.
(författare)
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Model studies of NOx storage
- 1999
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Ingår i: 8th European Conference on Applications of Surface and Interface Analysis (ECASIA’99) in Sevilla, Spain, October, 4-8, 1999.
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Konferensbidrag (refereegranskat)
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