36,262 research outputs found
Uplink Linear Receivers for Multi-cell Multiuser MIMO with Pilot Contamination: Large System Analysis
Base stations with a large number of transmit antennas have the potential to
serve a large number of users at high rates. However, the receiver processing
in the uplink relies on channel estimates which are known to suffer from pilot
interference. In this work, making use of the similarity of the uplink received
signal in CDMA with that of a multi-cell multi-antenna system, we perform a
large system analysis when the receiver employs an MMSE filter with a pilot
contaminated estimate. We assume a Rayleigh fading channel with different
received powers from users. We find the asymptotic Signal to Interference plus
Noise Ratio (SINR) as the number of antennas and number of users per base
station grow large while maintaining a fixed ratio. Through the SINR expression
we explore the scenario where the number of users being served are comparable
to the number of antennas at the base station. The SINR explicitly captures the
effect of pilot contamination and is found to be the same as that employing a
matched filter with a pilot contaminated estimate. We also find the exact
expression for the interference suppression obtained using an MMSE filter which
is an important factor when there are significant number of users in the system
as compared to the number of antennas. In a typical set up, in terms of the
five percentile SINR, the MMSE filter is shown to provide significant gains
over matched filtering and is within 5 dB of MMSE filter with perfect channel
estimate. Simulation results for achievable rates are close to large system
limits for even a 10-antenna base station with 3 or more users per cell.Comment: Accepted for publication in IEEE Transactions on Wireless
Communication
Cellular Systems with Many Antennas: Large System Analysis under Pilot Contamination
Base stations with a large number of transmit antennas have the potential to
serve a large number of users simultaneously at higher rates. They also promise
a lower power consumption due to coherent combining at the receiver. However,
the receiver processing in the uplink relies on the channel estimates which are
known to suffer from pilot interference. In this work, we perform an uplink
large system analysis of multi-cell multi-antenna system when the receiver
employs a matched filtering with a pilot contaminated estimate. We find the
asymptotic Signal to Interference plus Noise Ratio (SINR) as the number of
antennas and number of users per base station grow large while maintaining a
fixed ratio. To do this, we make use of the similarity of the uplink received
signal in a multi-antenna system to the representation of the received signal
in CDMA systems. The asymptotic SINR expression explicitly captures the effect
of pilot contamination and that of interference averaging. This also explains
the SINR performance of receiver processing schemes at different regimes such
as instances when the number of antennas are comparable to number of users as
well as when antennas exceed greatly the number of users. Finally, we also
propose that the adaptive MMSE symbol detection scheme, which does not require
the explicit channel knowledge, can be employed for cellular systems with large
number of antennas.Comment: 5 pages, 4 figure
Phase properties of a new nonlinear coherent state
We study phase properties of a displacement operator type nonlinear coherent
state. In particular we evaluate the Pegg-Barnett phase distribution and
compare it with phase distributions associated with the Husimi Q function and
the Wigner function. We also study number- phase squeezing of this state.Comment: 8 eps figures. to appear in J.Opt
Probabilistic computing with future deep sub-micrometer devices: a modelling approach
An approach is described that investigates the potential of probabilistic "neural" architectures for computation with deep sub-micrometer (DSM) MOSFETs. Initially, noisy MOSFET models are based upon those for a 0.35 /spl mu/m MOS technology with an exaggerated 1/f characteristic. We explore the manifestation of the 1/f characteristic at the output of a 2-quadrant multiplier when the key n-channel MOSFETs are replaced by "noisy" MOSFETs. The stochastic behavior of this noisy multiplier has been mapped on to a software (Matlab) model of a continuous restricted Boltzmann machine (CRBM) - an analogue-input stochastic computing structure. Simulation of this DSM CRBM implementation shows little degradation from that of a "perfect" CRBM. This paper thus introduces a methodology for a form of "technology-downstreaming" and highlights the potential of probabilistic architectures for DSM computation
New nonlinear coherent states and some of their nonclassical properties
We construct a displacement operator type nonlinear coherent state and
examine some of its properties. In particular it is shown that this nonlinear
coherent state exhibits nonclassical properties like squeezing and
sub-Poissonian behaviour.Comment: 3 eps figures. to appear in J.Opt
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