1,589 research outputs found
Self-Defense, Defense of Others, and the State
With the wide spread of wireless technology, the time for 4G has arrived, and 5G will appear not so far in the future. However, no matter whether it is 4G or 5G, low latency is a mandatory requirement for baseband processing at base stations for modern cellular standards. In particular, in a future 5G wireless system, with massive MIMO and ultra-dense cells, the demand for low round trip latency between the mobile device and the base station requires a baseband processing delay of 1 ms. This is 10 percentage of todayâs LTE-A round trip latency, while at the same time massive MIMO requires large-scale matrix computations. This is especially true for channel estimation and MIMO detection at the base station. Therefore, it is essential to ensure low latency for the user data traffic. In this masterâs thesis, LTE/LTE-A uplink physical layer processing is examined, especially the process of channel estimation and MIMO detection. In order to analyze this processing we compare two conventional algorithmsâ performance and complexity for channel estimation and MIMO detection. The key aspect which affects the algorithmsâ speed is identified as the need for âmassive complex matrix inversionâ. A parallel coding scheme is proposed to implement a matrix inversion kernel algorithm on a single instruction multiple data stream (SIMD) vector processor. The major contribution of this thesis is implementation and evaluation of a parallel massive complex matrix inversion algorithm. Two aspects have been addressed: the selection of the algorithm to perform this matrix computation and the implementation of a highly parallel version of this algorithm.Med den breda spridningen av trĂ„dlös teknik, har tiden för 4G kommit, och 5G kommer inom en överskĂ„dlig framtid. Men oavsett om det gĂ€ller 4G eller 5G, lĂ„g latens Ă€r ett obligatoriskt krav för basbandsbehandling vid basstationer för moderna mobila standarder. I synnerhet i ett framtida trĂ„dlöst 5G-system, med massiva MIMO och ultratĂ€ta celler, behövs en basbandsbehandling fördröjning pĂ„ 1 ms för att klara efterfrĂ„gan pĂ„ en lĂ„g rundresa latens mellan den mobila enheten och basstationen. Detta Ă€r 10 procent av dagens LTE-E rundresa latens, medan massiva MIMO samtidigt krĂ€ver storskaliga matrisberĂ€kningar. Detta Ă€r sĂ€rskilt viktigt för kanaluppskattning och MIMO-detektion vid basstationen. DĂ€rför Ă€r det viktigt att se till att det Ă€r lĂ„g latens för anvĂ€ndardatatrafik. I detta examensarbete, skall LTE/LTE-A upplĂ€nk fysiska lagret bearbetning undersökas, och dĂ„ sĂ€rskilt processen för kanaluppskattning och MIMO-detektion. För att analysera denna processing jĂ€mför vi tvĂ„ konventionella algoritmers prestationer och komplexitet för kanaluppskattning och MIMO-detektion. Den viktigaste aspekten som pĂ„verkar algoritmernas hastighet identifieras som behovet av "massiva komplex matrisinversion". Ett parallellt kodningsschema föreslĂ„s för att implementera en "matrisinversion kernel-algoritmen" pĂ„ singelinstruktion multidataström (SIMD) vektorprocessor. Det största bidraget med denna avhandling Ă€r genomförande och utvĂ€rdering av en parallell massiva komplex matrisinversion kernel-algoritmen. TvĂ„ aspekter har tagits upp: valet av algoritm för att utföra denna matrisberĂ€kning och implementationen av en högst parallell version av denna algoritm
Large-Scale MIMO Detection for 3GPP LTE: Algorithms and FPGA Implementations
Large-scale (or massive) multiple-input multiple-output (MIMO) is expected to
be one of the key technologies in next-generation multi-user cellular systems,
based on the upcoming 3GPP LTE Release 12 standard, for example. In this work,
we propose - to the best of our knowledge - the first VLSI design enabling
high-throughput data detection in single-carrier frequency-division multiple
access (SC-FDMA)-based large-scale MIMO systems. We propose a new approximate
matrix inversion algorithm relying on a Neumann series expansion, which
substantially reduces the complexity of linear data detection. We analyze the
associated error, and we compare its performance and complexity to those of an
exact linear detector. We present corresponding VLSI architectures, which
perform exact and approximate soft-output detection for large-scale MIMO
systems with various antenna/user configurations. Reference implementation
results for a Xilinx Virtex-7 XC7VX980T FPGA show that our designs are able to
achieve more than 600 Mb/s for a 128 antenna, 8 user 3GPP LTE-based large-scale
MIMO system. We finally provide a performance/complexity trade-off comparison
using the presented FPGA designs, which reveals that the detector circuit of
choice is determined by the ratio between BS antennas and users, as well as the
desired error-rate performance.Comment: To appear in the IEEE Journal of Selected Topics in Signal Processin
Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks
Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this paper, we describe the
sources of the inefficiencies in such networks. First we present results of the
studies on how much Carbon footprint such networks generate. We also discuss
how much more mobile traffic is expected to increase so that this Carbon
footprint will even increase tremendously more. We then discuss specific
sources of inefficiency and potential sources of improvement at the physical
layer as well as at higher layers of the communication protocol hierarchy. In
particular, considering that most of the energy inefficiency in cellular
wireless networks is at the base stations, we discuss multi-tier networks and
point to the potential of exploiting mobility patterns in order to use base
station energy judiciously. We then investigate potential methods to reduce
this inefficiency and quantify their individual contributions. By a
consideration of the combination of all potential gains, we conclude that an
improvement in energy consumption in cellular wireless networks by two orders
of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843
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