353 research outputs found
Wireless Cellular Networks
When aiming for achieving high spectral efficiency in wireless cellular networks, cochannel interference (CCI) becomes the dominant performancelimiting factor. This article provides a survey of CCI mitigation techniques, where both active and passive approaches are discussed in the context of both open- and closed-loop designs.More explicitly, we considered both the family of flexible frequency-reuse (FFR)-aided and dynamic channel allocation (DCA)-aided interference avoidance techniques as well as smart antenna-aided interference mitigation techniques, which may be classified as active approach
Multiuser Millimeter Wave Beamforming Strategies with Quantized and Statistical CSIT
To alleviate the high cost of hardware in mmWave systems, hybrid
analog/digital precoding is typically employed. In the conventional two-stage
feedback scheme, the analog beamformer is determined by beam search and
feedback to maximize the desired signal power of each user. The digital
precoder is designed based on quantization and feedback of effective channel to
mitigate multiuser interference. Alternatively, we propose a one-stage feedback
scheme which effectively reduces the complexity of the signalling and feedback
procedure. Specifically, the second-order channel statistics are leveraged to
design digital precoder for interference mitigation while all feedback overhead
is reserved for precise analog beamforming. Under a fixed total feedback
constraint, we investigate the conditions under which the one-stage feedback
scheme outperforms the conventional two-stage counterpart. Moreover, a rate
splitting (RS) transmission strategy is introduced to further tackle the
multiuser interference and enhance the rate performance. Consider (1) RS
precoded by the one-stage feedback scheme and (2) conventional transmission
strategy precoded by the two-stage scheme with the same first-stage feedback as
(1) and also certain amount of extra second-stage feedback. We show that (1)
can achieve a sum rate comparable to that of (2). Hence, RS enables remarkable
saving in the second-stage training and feedback overhead.Comment: submitted to TW
Study the Effect of Co-Channel Interference in STC MIMO-OFDM System and Mitigation of CCI using Beamforming Technique
In this modern age of high speed wireless data communication, Multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) schemes have recently drawn wide interests due to their capability of high data rate transmission over multipath fading channels. This thesis work introduces the study of multi- user and multi-antenna MIMO-OFDM systems. In this work, the performances of two main classes of MIMO-OFM system i.e. multi-user and multi-antenna MIMO-ODM techniques have been studied. The transmitted data is sent using BPSK, QPSK modulation techniques. The performance of the system in Rayleigh and AWGN channel is studied. Space time coding technique also used in transmitting side of the multi-antenna MIMO system.Study and analysis of the effect of co-channel interference over wireless communication system is considered the main objective of this project work .Beamforming technique is one of the best techniques to mitigate co-channel interference. There are several beamforming techniques like LMS, RLS style beamforming techniques. LMS style adaptive beamforming technique is applied to the system. The performance of the LMS style beamforming technique for mitigation of co-channel interference has been analyzed for different modulation techniques.The performance comparison between the adaptive beamforming and null steering beamforming techniques is carried out for the space time coded MIMO-OFDM system. From the performance analysis, it is observed that to mitigate the co-channel interference in ST coded MIMO-OFDM system, adaptive beamforming technique outperforms the method based on the null steering beamforming
Design and Prototyping of Hybrid Analogue Digital Multiuser MIMO Beamforming for Non-Orthogonal Signals
To enable user diversity and multiplexing gains, a fully digital precoding
multiple input multiple output (MIMO) architecture is typically applied.
However, a large number of radio frequency (RF) chains make the system
unrealistic to low-cost communications. Therefore, a practical three-stage
hybrid analogue-digital precoding architecture, occupying fewer RF chains, is
proposed aiming for a non-orthogonal IoT signal in low-cost multiuser MIMO
systems. The non-orthogonal waveform can flexibly save spectral resources for
massive devices connections or improve data rate without consuming extra
spectral resources. The hybrid precoding is divided into three stages including
analogue-domain, digital-domain and waveform-domain. A codebook based beam
selection simplifies the analogue-domain beamforming via phase-only tuning.
Digital-domain precoding can fine-tune the codebook shaped beam and resolve
multiuser interference in terms of both signal amplitude and phase. In the end,
the waveform-domain precoding manages the self-created inter carrier
interference (ICI) of the non-orthogonal signal. This work designs over-the-air
signal transmission experiments for fully digital and hybrid precoding systems
on software defined radio (SDR) devices. Results reveal that waveform precoding
accuracy can be enhanced by hybrid precoding. Compared to a transmitter with
the same RF chain resources, hybrid precoding significantly outperforms fully
digital precoding by up to 15.6 dB error vector magnitude (EVM) gain. A fully
digital system with the same number of antennas clearly requires more RF chains
and therefore is low power-, space- and cost- efficient. Therefore, the
proposed three-stage hybrid precoding is a quite suitable solution to
non-orthogonal IoT applications
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