Omnidirectional Precoding Based Transmission in Massive MIMO Systems

Meng, Xiangxu; Gao, Xiqi; Xia, Xiang-Gen

doi:10.1109/tcomm.2015.2498159

Cited by 85 publications

(71 citation statements)

References 36 publications

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“…From this we know that the SNR distribution is given by (19). Thus, maximizing the probability of coverage is equivalent to minimizing λ LS in (20). This is done by inserting (25) into (20), differentiating with respect to ρ P , and equating the result to zero.…”

Section: Estimating the Channelmentioning

confidence: 99%

“…3) Find the optimal power distribution for this large-scale coefficient by inserting β W into (20), the expression for λ LS , and minimize this as described above.…”

Section: Estimating the Channelmentioning

confidence: 99%

“…In general, this open-loop transmission-when the APs do not have any CSI-can be a limiting factor when it comes to network coverage, as coherent beamforming cannot be utilized. Downlink broadcasting of system information in LTE is described in general terms in [18]; in [19], [20], the downlink broadcasting of system information in a conventional, cellular massive MIMO system was analyzed.Previous studies on the outage probability of wireless networks, e.g.[21]-[23], differ from the current paper in at least three aspects: First, they (sometimes implicitly) assume perfect CSI at the receiver while we consider CSI obtained from downlink pilots. Second, the terminals considered here are inactive; hence, no CSI is available at the transmitter.…”

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Techniques for System Information Broadcast in Cell-Free Massive MIMO

Karlsson

Björnson

Larsson

2019

IEEE Trans. Commun.

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We consider transmission of system information in a cell-free massive MIMO system, when the transmitting access points do not have any channel state information and the receiving terminal has to estimate the channel based on downlink pilots. We analyze the system performance in terms of outage rate and coverage probability, and use space-time block codes to increase performance.We propose a heuristic method for pilot/data power optimization that can be applied without any channel state information at the access points. We also analyze the problem of grouping the access points, which is needed when the single-antenna access points jointly transmit a space-time block code. 3 is necessary for an inactive terminal to connect to and function within the network [18], [19].Normally when analyzing a massive MIMO system, transmission starts with the terminal transmitting uplink pilots, in order for the APs to estimate the (reciprocal) channel between the APs and the terminal. However, only active terminals, who have successfully decoded the system information, knows when and how to transmit pilots. The system information is transmitted and received without any prior CSI. In general, this open-loop transmission-when the APs do not have any CSI-can be a limiting factor when it comes to network coverage, as coherent beamforming cannot be utilized. Downlink broadcasting of system information in LTE is described in general terms in [18]; in [19], [20], the downlink broadcasting of system information in a conventional, cellular massive MIMO system was analyzed.Previous studies on the outage probability of wireless networks, e.g.[21]-[23], differ from the current paper in at least three aspects: First, they (sometimes implicitly) assume perfect CSI at the receiver while we consider CSI obtained from downlink pilots. Second, the terminals considered here are inactive; hence, no CSI is available at the transmitter. Third, here, a terminal is served jointly by all the APs, implying that there is no inter-cell interference.Although coverage, coverage probability, and outage probability have been mentioned in previous work on cell-free massive MIMO [1], [2], these papers also consider active terminals while we consider inactive ones.This paper aims to quantify the coverage in a cell-free massive MIMO system in terms of outage rate and coverage probability for the transmission of system information to inactive users. We analyze the coverage when the APs as well as the terminals does not have any CSI prior to transmission. Moreover, the effects of adding spatial diversity in terms of a space-time block code are also investigated. A. NotationScalars are denoted by lower-case letters (x), vectors by lower-case, bold-faced letters (x), and matrices with upper-case, bold-faced letters (X). CN (0, X) is a circularly-symmetric, complex, Gaussian random variable with zero mean and covariance matrix X. An exponentially distributed random variable with mean λ −1 is denoted by Exp (λ). A chi-squared distributed random variable with d degrees of...

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Section: Estimating the Channelmentioning

confidence: 99%

“…3) Find the optimal power distribution for this large-scale coefficient by inserting β W into (20), the expression for λ LS , and minimize this as described above.…”

Section: Estimating the Channelmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Techniques for System Information Broadcast in Cell-Free Massive MIMO

Karlsson

Björnson

Larsson

2019

IEEE Trans. Commun.

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“…Opponents of massive mimo have said that transmission without csi is the issue that will inhibit the realization of a cellular massive mimo system [15]. Recently, several articles have tried to tackle this problem, with the use of space-time block codes [16][17][18][19][20].…”

Section: Massive Mimomentioning

confidence: 99%

Aspects of Massive MIMO

Karlsson¹

2016

Linköping Studies in Science and Technology. Licentiate Thesis

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Next generation cellular wireless technology faces tough demands: increasing the throughput and reliability without consuming more resources, be it spectrum or energy. Massive mimo (Multiple-Input Multiple-Output) has proven, both in theory and practice, that it is up for the challenge. Massive mimo can offer uniformly good service to many users using low-end hardware, simultaneously, without increasing the radiated power compared to contemporary system. In Massive mimo, the base stations are equipped with hundreds of antennas. This abundance of antennas brings many new, interesting aspects compared to single-user mimo and multi-user mimo. Some issues of older technologies are nonexistent in massive mimo, while new issues in need of solutions arise. This thesis considers two aspects, and how these aspects differ in a massive mimo context: physical layer security and transmission of system information. First, it is shown that a jammer with a large number of antennas can outperform a traditional, single-antenna jammer in degrading the legitimate link. The excess of antennas gives the jammer opportunity to find and exploit structure in signals to improve its jamming capability. Second, for transmission of system information, the vast number of antennas prove useful even when the base station does not have any channel state information, because of the increased availability of space-time coding. We show how transmission without channel state information can be done in massive mimo by using a fixed precoding matrix to reduce the pilot overhead and simultaneously apply space-time block coding to use the excess of antennas for spatial diversity.iii iv SammanfattningDet ställs hårda krav på nästa generations cellulära trådlösa system: att simultant öka datatakten på kommunikationen och dess tillförlitlighet utan att konsumera mer resurser, oavsett om det spektrum eller energi. Massiv mimo (eng: Multiple-Input Multiple-Output) har visat, både i teori och praktik, att tekniken är redo att tackla utmaningen. Massiv mimo kan betjäna många användare samtidigt, med god service, utan att öka den utstrålade effekten jämfört med nuvarande system. Massiv mimo, där basstationerna är utrustade med hundratals antenner, skiljer sig från dagens system vilket gör att många nya problem dyker upp och nya infallsvinklar på befintliga problem krävs. Denna avhandling analyserar två problem, och hur dessa förändras i ett massiv mimo sammanhang: säkerhet för fysiska lagret och överföring av systeminformation. Särskiljt visas att en störsändare med ett stort antal antenner kan överträffa en traditionell störsändare med en enda antenn. Antalet antenner ger störsändaren möjlighet att hitta strukturer i signaler och utnyttja detta för att förbättra störningens effekt. Det stora antalet antenner visar sig vara användbart även för överföring av systeminformation, där basstationen inte har någon kanalkännedom. Antennerna ger möjligheten att tillämpa spatial kodning (eng: space-time block coding). Vi visar hur överföringen utan kanalkännedom ...

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