| 1. |
- Helmersson, Anders, 1957-, et al.
(författare)
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Uplink D-MIMO with Decentralized Subset Combining
- 2022
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Ingår i: ICC 2022 - IEEE International Conference on Communications. - : IEEE. - 9781538683484 - 9781538683477 ; , s. 5134-5139
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Konferensbidrag (refereegranskat)abstract
- We propose decentralized processing and combining in the uplink for a distributed MIMO (D-MIMO) network by a subset method. A subset that consists of a partial number of access points (APs) that are connected to a CPU is defined for each UE. A subset that consists of only one AP turns a D-MIMO network into “small cell” network; a subset that consists of all APs connected to the CPU give the same performance as a fully centralized method. The paper also shows that the subset method provides a very scalable trade-off between complexity and performance. It is simpler to realize as the processing can be distributed and parallelized. In the studied simulation scenarios, we show that it is possible to reach 85% of the performance upper bound by including only 20% of total APs in the subset, and to reach 95% of the performance upper bound by including 40% of APs in the subset.
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| 2. |
- Wang Helmersson, Ke, 1960-, et al.
(författare)
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Robust precoding weights for downlink D-MIMO in 6G Communications
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Point-to-point MIMO and massive MIMO techniques have played significantroles in the success of 4G and 5G radio networks, and in 6G we believethat distributed MIMO will play a similar critical role. The performanceof downlink phase coherent distributed MIMO transmission relies on tightphase alignment between the serving access points (APs) in the system.In realistic scenarios, there will always be some level of phasemisalignment between APs due to e.g., differences in the local clocksof the APs, which can severely degrade the performance.One main contribution of this paper is that we propose the use of aLinear Quadratic Regulator (LQR) based solution for calculating downlinkprecoding weights in D-MIMO systems. The optimal LQR based precodingsolution is numerically stable and computationally efficient, and it caneasily utilise parallel computing in distributed or centralised hardwareprocessors. Furthermore, we also show how the LQR based solution can bemodified to include differently sized subsets of serving APs for each UE,which enables a scalable tradeoff between performance and complexity.Another main contribution of the paper is that we identify a new phasemisalignment problem in D-MIMO. The proposed LQR-based precoding methodis the first solution that takes not only the channel estimation phaseerrors, but also the relative phase errors between serving APs intoaccount when designing the downlink D-MIMO transmission precoder. By this,some of the performance lost due to different causes of phase misalignmentcan be regained. In the scenarios studied in this paper we observe 20-70%performance increase of the proposed method compared to a reference casewhere residual phase errors are ignored when determining the downlinkprecoding weights.
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| 3. |
- Wang Helmersson, Ke, 1960-, et al.
(författare)
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Uplink D-MIMO Processing and Combining Using Kalman Filter
- 2022
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Ingår i: Globecom 2022. - : IEEE. - 9781665435406 - 9781665435413 ; , s. 1703-1708
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Konferensbidrag (refereegranskat)abstract
- We propose a decentralized subset method for optimal processing and combining of uplink signals in a distributed MIMO (D-MIMO) network. We further propose the use of Kalman filters with the square-root implementation to estimate the received uplink signals. This square-root implementation is shown to be numerically stable when inverting the covariance matrix, as it always assures the covariance matrix to be symmetric and positive semi-definite. In the paper we also analyze the computational complexity and cost with different combining methods. We show that the Kalman filter implementation provides the same result as the MMSE method in terms of the spectral efficiencies and equivalent SINR. However, the Kalman filter implementation is shown to be very efficient as it provides the possibility to fully utilize parallel computing of distributed hardware processors. Moreover, the processing can be decentralized and the estimates can be aggregated from local estimates to as many access points (APs) as needed to reach the desired performance target. A Kalman filter implementation has the flexibility to aggregate signals in different ways, allowing the fronthaul architecture to support connectivity of individual APs in any combination of parallel or serial manners.
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| 4. |
- Axell, Erik, et al.
(författare)
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Coexistence of Speech and Best Effort Services in Enhanced Uplink WCDMA
- 2005
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Ingår i: in Proc. of Radiovetenskap och Kommunikation (RVK).
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Konferensbidrag (refereegranskat)abstract
- An evaluation of the performance of coexistent voice and best effort data users in Enhanced Uplink WCDMA is studied in this paper. The main focus is on deriving the capacity regions and compare with previous WCDMA releases. It is shown that the Enhanced Uplink yields a large capacity gain in many aspects for all fractions of voice users compared to previous WCDMA releases. It is also shown, by the cumulative distribution functions of noise rise at the capacity limits, that the best effort data users experience bad quality at lower noise rise than voice users. This means that the capacity is in fact limited by the best effort users.
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| 5. |
- Sang, Shaowei, et al.
(författare)
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The epidemiological characteristics of dengue in high-risk areas of China, 2013-2016
- 2021
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Ingår i: PLoS Neglected Tropical Diseases. - : Public Library of Science. - 1935-2727 .- 1935-2735. ; 15:12
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Dengue has become a more serious human health concern in China, with increased incidence and expanded outbreak regions. The knowledge of the cross-sectional and longitudinal epidemiological characteristics and the evolutionary dynamics of dengue in high-risk areas of China is limited.Methods: Records of dengue cases from 2013 to 2016 were obtained from the China Notifiable Disease Surveillance System. Full envelope gene sequences of dengue viruses detected from the high-risk areas of China were collected. Maximum Likelihood tree and haplotype network analyses were conducted to explore the phylogenetic relationship of viruses from high-risk areas of China.Results: A total of 56,520 cases was reported in China from 2013 to 2016. During this time, Yunnan, Guangdong and Fujian provinces were the high-risk areas. Imported cases occurred almost year-round, and were mainly introduced from Southeast Asia. The first indigenous case usually occurred in June to August, and the last one occurred before December in Yunnan and Fujian provinces but in December in Guangdong Province. Seven genotypes of DENV 1-3 were detected in the high-risk areas, with DENV 1-I the main genotype and DENV 2-Cosmopolitan the secondary one. The Maximum Likelihood trees show that almost all the indigenous viruses separated into different clusters. DENV 1-I viruses were found to be clustered in Guangdong Province, but not in Fujian and Yunnan, from 2013 to 2015. The ancestors of the Guangdong viruses in the cluster in 2013 and 2014 were most closely related to strains from Thailand or Singapore, and the Guangdong virus in 2015 was most closely related to the Guangdong virus of 2014. Based on closest phylogenetic relationships, viruses from Myanmar possibly initiated further indigenous cases in Yunnan, those from Indonesia in Fujian, while viruses from Thailand, Malaysia, Singapore and Indonesia were predominant in Guangdong Province.Conclusions: Dengue is still an imported disease in China, although some genotypes continued to circulate in successive years. Viral phylogenies based on the envelope gene suggested periodic introductions of dengue strains into China, primarily from Southeast Asia, with occasional sustained, multi-year transmission in some regions of China.Author summary: Dengue is the most prevalent and rapidly spreading mosquito-borne viral disease globally. Because of the multiple introductions, dengue outbreaks occurred in epidemic seasons in Southern China, supported by suitable weather conditions. Surveillance data from 2013 to 2016 in China showed that Guangdong, Yunnan and Fujian provinces were the high-risk areas, with dengue outbreaks occurring almost every year. However, knowledge has been lacking of the epidemiological characteristics and the evolution pattern of dengue virus in these high-risk areas. This study shows a variety of epidemiological characteristics and sources of imported cases among the high-risk areas in China, with likely origins primarily from countries in Southeast Asia. Seven genotypes of the DENV 1-3 variety co-circulated with DENV1-I, the main genotype, and DENV 2-Cosmopolitan, the secondary. Genetic relationships among viral strains suggest that the indigenous viruses in the high-risk areas arose from imported viruses and sometimes persisted between years into the next epidemic season, especially in Guangdong Province. Population movement has played a vital role in dengue epidemics in China. This information may be useful in dengue control, especially during epidemic seasons and in the development of an early warning system within the region, in collaboration with bordering countries.
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