12 research outputs found
Filter Bank Multicarrier for Massive MIMO
This paper introduces filter bank multicarrier (FBMC) as a potential
candidate in the application of massive MIMO communication. It also points out
the advantages of FBMC over OFDM (orthogonal frequency division multiplexing)
in the application of massive MIMO. The absence of cyclic prefix in FBMC
increases the bandwidth efficiency. In addition, FBMC allows carrier
aggregation straightforwardly. Self-equalization, a property of FBMC in massive
MIMO that is introduced in this paper, has the impact of reducing (i)
complexity; (ii) sensitivity to carrier frequency offset (CFO); (iii)
peak-to-average power ratio (PAPR); (iv) system latency; and (v) increasing
bandwidth efficiency. The numerical results that corroborate these claims are
presented.Comment: 7 pages, 6 figure
Pilot Decontamination in CMT-based Massive MIMO Networks
Pilot contamination problem in massive MIMO networks operating in
time-division duplex (TDD) mode can limit their expected capacity to a great
extent. This paper addresses this problem in cosine modulated multitone (CMT)
based massive MIMO networks; taking advantage of their so-called blind
equalization property. We extend and apply the blind equalization technique
from single antenna case to multi-cellular massive MIMO systems and show that
it can remove the channel estimation errors (due to pilot contamination effect)
without any need for cooperation between different cells or transmission of
additional training information. Our numerical results advocate the efficacy of
the proposed blind technique in improving the channel estimation accuracy and
removal of the residual channel estimation errors caused by the users of the
other cells.Comment: Accepted in ISWCS 201
Frequency Spreading Equalization in Multicarrier Massive MIMO
Application of filter bank multicarrier (FBMC) as an effective method for
signaling over massive MIMO channels has been recently proposed. This paper
further expands the application of FBMC to massive MIMO by applying frequency
spreading equalization (FSE) to these channels. FSE allows us to achieve a more
accurate equalization. Hence, higher number of bits per symbol can be
transmitted and the bandwidth of each subcarrier can be widened. Widening the
bandwidth of each subcarrier leads to (i) higher bandwidth efficiency; (ii)
lower complexity; (iii) lower sensitivity to carrier frequency offset (CFO);
(iv) reduced peak-to-average power ratio (PAPR); and (iv) reduced latency. All
these appealing advantages have a direct impact on the digital as well as
analog circuitry that is needed for the system implementation. In this paper,
we develop the mathematical formulation of the minimum mean square error (MMSE)
FSE for massive MIMO systems. This analysis guides us to decide on the number
of subcarriers that will be sufficient for practical channel models.Comment: Accepted in IEEE ICC 2015 - Workshop on 5G & Beyond - Enabling
Technologies and Application
Time Reversal with Post-Equalization for OFDM without CP in Massive MIMO
This paper studies the possibility of eliminating the redundant cyclic prefix
(CP) of orthogonal frequency division multiplexing (OFDM) in massive
multiple-input multiple-output systems. The absence of CP increases the
bandwidth efficiency in expense of intersymbol interference (ISI) and
intercarrier interference (ICI). It is known that in massive MIMO, different
types of interference fade away as the number of base station (BS) antennas
tends to infinity. In this paper, we investigate if the channel distortions in
the absence of CP are averaged out in the large antenna regime. To this end, we
analytically study the performance of the conventional maximum ratio combining
(MRC) and realize that there always remains some residual interference leading
to saturation of signal to interference (SIR). This saturation of SIR is
quantified through mathematical equations. Moreover, to resolve the saturation
problem, we propose a technique based on time-reversal MRC with zero forcing
multiuser detection (TR-ZF). Thus, the SIR of our proposed TR-ZF does not
saturate and is a linear function of the number of BS antennas. We also show
that TR-ZF only needs one OFDM demodulator per user irrespective of the number
of BS antennas; reducing the BS signal processing complexity significantly.
Finally, we corroborate our claims as well as analytical results through
simulations.Comment: 7 pages, 3 figure
Massive MIMO with Non-Ideal Arbitrary Arrays: Hardware Scaling Laws and Circuit-Aware Design
Massive multiple-input multiple-output (MIMO) systems are cellular networks
where the base stations (BSs) are equipped with unconventionally many antennas,
deployed on co-located or distributed arrays. Huge spatial degrees-of-freedom
are achieved by coherent processing over these massive arrays, which provide
strong signal gains, resilience to imperfect channel knowledge, and low
interference. This comes at the price of more infrastructure; the hardware cost
and circuit power consumption scale linearly/affinely with the number of BS
antennas . Hence, the key to cost-efficient deployment of large arrays is
low-cost antenna branches with low circuit power, in contrast to today's
conventional expensive and power-hungry BS antenna branches. Such low-cost
transceivers are prone to hardware imperfections, but it has been conjectured
that the huge degrees-of-freedom would bring robustness to such imperfections.
We prove this claim for a generalized uplink system with multiplicative
phase-drifts, additive distortion noise, and noise amplification. Specifically,
we derive closed-form expressions for the user rates and a scaling law that
shows how fast the hardware imperfections can increase with while
maintaining high rates. The connection between this scaling law and the power
consumption of different transceiver circuits is rigorously exemplified. This
reveals that one can make the circuit power increase as , instead of
linearly, by careful circuit-aware system design.Comment: Accepted for publication in IEEE Transactions on Wireless
Communications, 16 pages, 8 figures. The results can be reproduced using the
following Matlab code: https://github.com/emilbjornson/hardware-scaling-law