4,647 research outputs found
Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit-Receive Systems
This paper proposes an active radio frequency (RF) cancellation solution to
suppress the transmitter (TX) passband leakage signal in radio transceivers
supporting simultaneous transmission and reception. The proposed technique is
based on creating an opposite-phase baseband equivalent replica of the TX
leakage signal in the transceiver digital front-end through adaptive nonlinear
filtering of the known transmit data, to facilitate highly accurate
cancellation under a nonlinear TX power amplifier (PA). The active RF
cancellation is then accomplished by employing an auxiliary transmitter chain,
to generate the actual RF cancellation signal, and combining it with the
received signal at the receiver (RX) low noise amplifier (LNA) input. A
closed-loop parameter learning approach, based on the decorrelation principle,
is also developed to efficiently estimate the coefficients of the nonlinear
cancellation filter in the presence of a nonlinear TX PA with memory, finite
passive isolation, and a nonlinear RX LNA. The performance of the proposed
cancellation technique is evaluated through comprehensive RF measurements
adopting commercial LTE-Advanced transceiver hardware components. The results
show that the proposed technique can provide an additional suppression of up to
54 dB for the TX passband leakage signal at the RX LNA input, even at
considerably high transmit power levels and with wide transmission bandwidths.
Such novel cancellation solution can therefore substantially improve the TX-RX
isolation, hence reducing the requirements on passive isolation and RF
component linearity, as well as increasing the efficiency and flexibility of
the RF spectrum use in the emerging 5G radio networks.Comment: accepted to IEE
Hardware Impairments Aware Transceiver Design for Full-Duplex Amplify-and-Forward MIMO Relaying
In this work we study the behavior of a full-duplex (FD) and
amplify-and-forward (AF) relay with multiple antennas, where hardware
impairments of the FD relay transceiver is taken into account. Due to the
inter-dependency of the transmit relay power on each antenna and the residual
self-interference in an FD-AF relay, we observe a distortion loop that degrades
the system performance when the relay dynamic range is not high. In this
regard, we analyze the relay function in presence of the hardware inaccuracies
and an optimization problem is formulated to maximize the signal to
distortion-plus-noise ratio (SDNR), under relay and source transmit power
constraints. Due to the problem complexity, we propose a
gradient-projection-based (GP) algorithm to obtain an optimal solution.
Moreover, a nonalternating sub-optimal solution is proposed by assuming a
rank-1 relay amplification matrix, and separating the design of the relay
process into multiple stages (MuStR1). The proposed MuStR1 method is then
enhanced by introducing an alternating update over the optimization variables,
denoted as AltMuStR1 algorithm. It is observed that compared to GP, (Alt)MuStR1
algorithms significantly reduce the required computational complexity at the
expense of a slight performance degradation. Finally, the proposed methods are
evaluated under various system conditions, and compared with the methods
available in the current literature. In particular, it is observed that as the
hardware impairments increase, or for a system with a high transmit power, the
impact of applying a distortion-aware design is significant.Comment: Submitted to IEEE Transactions on Wireless Communication
Wide spread spectrum watermarking with side information and interference cancellation
Nowadays, a popular method used for additive watermarking is wide spread
spectrum. It consists in adding a spread signal into the host document. This
signal is obtained by the sum of a set of carrier vectors, which are modulated
by the bits to be embedded. To extract these embedded bits, weighted
correlations between the watermarked document and the carriers are computed.
Unfortunately, even without any attack, the obtained set of bits can be
corrupted due to the interference with the host signal (host interference) and
also due to the interference with the others carriers (inter-symbols
interference (ISI) due to the non-orthogonality of the carriers). Some recent
watermarking algorithms deal with host interference using side informed
methods, but inter-symbols interference problem is still open. In this paper,
we deal with interference cancellation methods, and we propose to consider ISI
as side information and to integrate it into the host signal. This leads to a
great improvement of extraction performance in term of signal-to-noise ratio
and/or watermark robustness.Comment: 12 pages, 8 figure
Hardware Impairments Aware Transceiver Design for Bidirectional Full-Duplex MIMO OFDM Systems
In this paper we address the linear precoding and decoding design problem for
a bidirectional orthogonal frequencydivision multiplexing (OFDM) communication
system, between two multiple-input multiple-output (MIMO) full-duplex (FD)
nodes. The effects of hardware distortion as well as the channel state
information error are taken into account. In the first step, we transform the
available time-domain characterization of the hardware distortions for FD MIMO
transceivers to the frequency domain, via a linear Fourier transformation. As a
result, the explicit impact of hardware inaccuracies on the residual
selfinterference (RSI) and inter-carrier leakage (ICL) is formulated in
relation to the intended transmit/received signals. Afterwards, linear
precoding and decoding designs are proposed to enhance the system performance
following the minimum-mean-squarederror (MMSE) and sum rate maximization
strategies, assuming the availability of perfect or erroneous CSI. The proposed
designs are based on the application of alternating optimization over the
system parameters, leading to a necessary convergence. Numerical results
indicate that the application of a distortionaware design is essential for a
system with a high hardware distortion, or for a system with a low thermal
noise variance.Comment: Submitted to IEEE for publicatio
Secrecy Energy Efficiency of MIMOME Wiretap Channels with Full-Duplex Jamming
Full-duplex (FD) jamming transceivers are recently shown to enhance the
information security of wireless communication systems by simultaneously
transmitting artificial noise (AN) while receiving information. In this work,
we investigate if FD jamming can also improve the systems secrecy energy
efficiency (SEE) in terms of securely communicated bits-per- Joule, when
considering the additional power used for jamming and self-interference (SI)
cancellation. Moreover, the degrading effect of the residual SI is also taken
into account. In this regard, we formulate a set of SEE maximization problems
for a FD multiple-input-multiple-output multiple-antenna eavesdropper (MIMOME)
wiretap channel, considering both cases where exact or statistical channel
state information (CSI) is available. Due to the intractable problem structure,
we propose iterative solutions in each case with a proven convergence to a
stationary point. Numerical simulations indicate only a marginal SEE gain,
through the utilization of FD jamming, for a wide range of system conditions.
However, when SI can efficiently be mitigated, the observed gain is
considerable for scenarios with a small distance between the FD node and the
eavesdropper, a high Signal-to-noise ratio (SNR), or for a bidirectional FD
communication setup.Comment: IEEE Transactions on Communication
Digitally-Enhanced Software-Defined Radio Receiver Robust to Out-of-Band Interference
A software-defined radio (SDR) receiver with improved robustness to out-of-band interference (OBI) is presented. Two main challenges are identified for an OBI-robust SDR receiver: out-of-band nonlinearity and harmonic mixing. Voltage gain at RF is avoided, and instead realized at baseband in combination with low-pass filtering to mitigate blockers and improve out-of-band IIP3. Two alternative “iterative” harmonic-rejection (HR) techniques are presented to achieve high HR robust to mismatch: a) an analog two-stage polyphase HR concept, which enhances the HR to more than 60 dB; b) a digital adaptive interference cancelling (AIC) technique, which can suppress one dominating harmonic by at least 80 dB. An accurate multiphase clock generator is presented for a mismatch-robust HR. A proof-of-concept receiver is implemented in 65 nm CMOS. Measurements show 34 dB gain, 4 dB NF, and 3.5 dBm in-band IIP3 while the out-of-band IIP3 is + 16 dBm without fine tuning. The measured RF bandwidth is up to 6 GHz and the 8-phase LO works up to 0.9 GHz (master clock up to 7.2 GHz). At 0.8 GHz LO, the analog two-stage polyphase HR achieves a second to sixth order HR > dB over 40 chips, while the digital AIC technique achieves HR > 80 dB for the dominating harmonic. The total power consumption is 50 mA from a 1.2 V supply
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