397 research outputs found
Limiting Performance of Conventional and Widely Linear DFT-precoded-OFDM Receivers in Wideband Frequency Selective Channels
This paper describes the limiting behavior of linear and decision feedback
equalizers (DFEs) in single/multiple antenna systems employing
real/complex-valued modulation alphabets. The wideband frequency selective
channel is modeled using a Rayleigh fading channel model with infinite number
of time domain channel taps. Using this model, we show that the considered
equalizers offer a fixed post signal-to-noise-ratio (post-SNR) at the equalizer
output that is close to the matched filter bound (MFB). General expressions for
the post-SNR are obtained for zero-forcing (ZF) based conventional receivers as
well as for the case of receivers employing widely linear (WL) processing.
Simulation is used to study the bit error rate (BER) performance of both MMSE
and ZF based receivers. Results show that the considered receivers
advantageously exploit the rich frequency selective channel to mitigate both
fading and inter-symbol-interference (ISI) while offering a performance
comparable to the MFB
Layered Steered Space–Time-Spreading-Aided Generalized MC DS-CDMA
Abstract—We present a novel trifunctional multiple-input– multiple-output (MIMO) scheme that intrinsically amalgamates space–time spreading (STS) to achieve a diversity gain and a Vertical Bell Labs layered space–time (V-BLAST) scheme to attain a multiplexing gain in the context of generalized multicarrier direct-sequence code-division multiple access (MC DS-CDMA), as well as beamforming. Furthermore, the proposed system employs both time- and frequency-domain spreading to increase the number of users, which is also combined with a user-grouping technique to reduce the effects of multiuser interference
Parallel Interference Cancellation Based Turbo Space-Time Equalization in the SDMA Uplink
A novel Parallel Interference Cancellation (PIC) based turbo Space Time Equalizer (STE) structure designed for multiple antenna assisted uplink receivers is introduced. The proposed receiver structure allows the employment of non-linear type of detectors such as the Bayesian Decision Feedback (DF) assisted turbo STE or the Maximum Aposteriori (MAP) STE, while operating at a moderate computational cost. Receivers based on the proposed structure outperform the linear turbo detector benchmarker based on the Minimum Mean-Squared Error (MMSE) criterion, even if the latter aims for jointly detecting all transmitters’ signals. Additionally the PIC based receiver is capable of equalizing non-linear binary pre-coded channels. The performance difference between the presented algorithms is discussed using Extrinsic Information Transferfunction (EXIT) charts. Index Terms—PIC, EXIT chart, precoding, Bayesian, STE
Two–Way Relaying Communications with OFDM and BICM/BICM-ID
Relay-aided communication methods have gained strong interests in academic community
and been applied in various wireless communication scenarios. Among different techniques
in relay-aided communication system, two-way relaying communication (TWRC) achieves
the highest spectral efficiency due to its bi-directional transmission capability. Nevertheless,
different from the conventional point-to-point communication system, TWRC suffers from
detection quality degradation caused by the multiple-access interference (MAI). In addition,
because of the propagation characteristics of wireless channels, fading and multipath
dispersion also contribute strongly to detection errors. Therefore, this thesis is mainly concerned
with designing transmission and detection schemes to provide good detection quality
of TWRC while taking into account the negative impacts of fading, multipath dispersion
and multiple-access interference.
First, a TWRC system operating over multipath fading channels is considered and orthogonal
frequency-division multiplexing (OFDM) is adopted to handle the inter-symbol
interference (ISI) caused by the multipath dispersion. In particular, adaptive physical-layer
network coding (PNC) is employed to address the MAI issue. By analyzing the detection
error probability, various adaptive PNC schemes are discussed for using with OFDM and
the scheme achieving the best trade-off among performance, overhead and complexity is
suggested.
In the second part of the thesis, the design of distributed precoding in TWRC using
OFDM under multipath fading channels is studied. The objective is to design a distributed
precoding scheme which can alleviate MAI and achieve multipath diversity to combat fading.
Specifically, three types of errors are introduced when analyzing the error probability in the
multiple access (MA) phase. Through analysis and simulation, the scheme that performs
precoding in both time and frequency domains is demonstrated to achieve the maximum
diversity gains under all types of errors.
Finally, the last part of the thesis examines a communication system incorporating forward
error correction (FEC) codes. Specifically, bit-interleaved code modulation (BICM)
without and with iterative decoding (BICM-ID) are investigated in a TWRC system. Distributed
linear constellation precoding (DLCP) is applied to handle MAI and the design
of DLCP in a TWRC system using BICM/BICM-ID is discussed. Taking into account the
multiple access channel from the terminal nodes to the relay node, decoding based on the
quaternary code representation is introduced. Several error probability bounds are derived
to aid in the design of DLCP. Based on these bounds, optimal parameters of DLCP are
obtained through analysis and computer search. It is also found that, by combining XORbased
network coding with successful iterative decoding, the MAI is eliminated and thus
DLCP is not required in a BICM-ID system
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