Sparse Automotive MIMO Radar for Super-Resolution Single Snapshot DOA Estimation With Mutual Coupling

A novel sparse automotive multiple-input multiple-output (MIMO) radar configuration is proposed for low-complexity super-resolution single snapshot direction-of-arrival (DOA) estimation. The physical antenna effects are incorporated in the signal model via open-circuited embedded-element patterns (EEPs) and coupling matrices. The transmit (TX) and receive (RX) array are each divided into two uniform sparse sub-arrays with different inter-element spacings to generate two MIMO sets. Since the corresponding virtual arrays (VAs) of both MIMO sets are uniform, the well-known spatial smoothing (SS) algorithm is applied to suppress the temporal correlation among sources. Afterwards, the co-prime array principle between two spatially smoothed VAs is deployed to avoid DOA ambiguities. A performance comparison between the sparse and conventional MIMO radars with the same number of TX and RX channels confirms a spatial resolution enhancement. Meanwhile, the DOA estimation error due to the mutual coupling (MC) is less pronounced in the proposed sparse architecture since antennas in both TX and RX arrays are spaced larger than half wavelength apart

Exploiting Constructive Mutual Coupling in P2P MIMO by Analog-Digital Phase Alignment

In this paper, we propose a joint analog-digital (A/D) beamforming scheme for the point-to-point multiple-input-multiple-output system, where we exploit mutual coupling by optimizing the load impedances of the transmit antennas. Contrary to the common conception that mutual coupling strictly harms the system performance, we show that mutual coupling can be beneficial by exploiting the concept of constructive interference. By changing the value of each load impedance for the antenna array based on convex optimization, the mutual coupling effect can be manipulated so that the resulting interference aligns constructively to the useful signal vector. We first prove that the full elimination of mutual coupling effect is not achievable solely by tuning the values of the antenna load impedances. We then introduce the proposed A/D scheme for both PSK and QAM modulations, where performance gains with respect to conventional techniques are obtained. The implementation of the proposed schemes is also discussed, where a lookup table can be built to efficiently apply the calculated load impedances. The numerical results show that the proposed schemes can achieve an improved performance compared to systems with fixed mutual coupling, especially when the antenna spacing is small

Characteristics and Channel Capacity Studies of a Novel 6G Non-Stationary Massive MIMO Channel Model Considering Mutual Coupling

In the sixth generation (6G) wireless communicationnetworks, ultra-massive multiple-input multiple-output (MIMO)communication is one of the most promising technologies. Inultra-massive MIMO channels, the mutual coupling (MC) effectis more obvious when antenna elements are more closely spaced.In this paper, a novel 6G space-time-frequency (STF) nonstationarymassive MIMO channel model is proposed, whichjointly considers MC, antenna efficiency, and near-field steeringvectors of different antenna topologies. As the Shannon capacitytheorem is based on the wide-sense stationary (WSS) channelassumption and cannot be applied to non-stationary channels,we propose a novel non-stationary channel capacity calculationmethod that divides the non-stationary channel into WSS subchannels. Important statistical properties and channel capacities of the proposed channel model are derived and verified by ultra-massive MIMO channel measurements and data postprocessing. The results show that the simulated spatial crosscorrelationfunction (CCF) and channel capacity considering MC and antenna efficiency are closer to measured results. It also shows that antenna topologies have an impact on channel capacities. Furthermore, channel capacities using the proposednovel calculation method match the measured channel capacities in non-stationary channels

Information Theoretic Limits for Wireless Information Transfer Between Finite Spatial Regions

Since the first multiple-input multiple-output (MIMO) experiments performed at Bell Laboratories in the late 1990’s, it was clear that wireless communication systems can achieve improved performances using multiple antennas simultaneously during transmission and reception. Theoretically, the capacity of MIMO systems scales linearly with the number of antennas in favorable propagation conditions. However, the capacity is significantly reduced when the antennas are collocated. A generalized paradigm for MIMO systems, spatially distributed MIMO systems, is proposed as a solution. Spatially distributed MIMO systems transmit information from a spatial region to another with each region occupying a large number of antennas. Hence, for a given constraint on the size of the spatial regions, evaluating the information theoretic performance limits for information transfer between regions has been a central topic of research in wireless communications. This thesis addresses this problem from a theoretical point of view. Our approach is to utilize the modal decomposition of the classical wave equation to represent the spatially distributed MIMO systems. This modal analysis is particularly useful as it advocates a shift of the “large wireless networks” research agenda from seeking “universal” performance limits to seeking a multi-parameter family of performance limits, where the key parameters, space, time and frequency are interrelated. However, traditional performance bounds on spatially distributed MIMO systems fail to depict the interrelation among space, time and frequency. Several outcomes resulting from this thesis are: i) estimation of an upper bound to degrees of freedom of broadband signals observed over finite spatial and temporal windows, ii) derivation of the amount of information that can be captured by a finite spatial region over a finite bandwidth, iii) a new framework to illustrate the relationship between Shannon’s capacity and the spatial channels, iv) a tractable model to determine the information capacity between spatial regions for narrowband transmissions. Hence, our proposed approach provides a generalized theoretical framework to characterize realistic MIMO and spatially distributed MIMO systems at different frequency bands in both narrowband and broadband conditions

MIMO application for the quadrifilar helix antenna

Capacity increase of the current land mobile satellite (LMS) communication systems is highly desirable to cater for more data-centric applications such as broadcasting. Since the Multiple-input Multiple-output (MIMO) offers high spectral efficiency without additional bandwidth and transmit power, its implementation in the LMS system has been widely investigated in terms of channel characterisation, channel modelling and coding algorithms. However, the aspect of receive antenna design and its performance evaluation has not yet been considered even though it has enormous impacts on the system performance. This thesis presents a study on designing a novel dual circularly polarised receive antenna system for the LMS MIMO system that utilises the printed quadrifilar helix antenna (PQHA) and also the required performance evaluation methods. The PQHA was miniaturised using two new methods, which are the element folding and combination of element folding and meandering where more than 50% size reduction can be achieved. These miniaturised PQHAs were combined to create a variety of dual circularly polarised arrays such as the dual circularly polarised single folded PQHA (SFPQHA) horizontal array and folded meandered PQHA (FMPQHA) vertical array. For evaluating the branch power ratio of these arrays, a newly derived formulation of the mean effective gain (MEG) in a Ricean fading channel that incorporates the polarisation of the line-of-sight (LoS) component and the corresponding antenna gain has been proposed. Further evaluation of these arrays as the receive antenna in this system was carried out using measurement campaigns. Results show that both arrays provide substantial capacity increase when compared to a single link system in both LoS and NLoS channels. A more comprehensive study on the effect of antenna properties was conducted using a newly, developed channel model that integrates the array characteristics with the propagation channel. This modelling approach allows for a performance comparison between the designed SFPQHA array and other antennas to be easily implemented, which is very useful in the process of designing MIMO antennas.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Energy-Efficient System Design for Future Wireless Communications

The exponential growth of wireless data traffic has caused a significant increase in the power consumption of wireless communications systems due to the higher complexity of the transceiver structures required to establish the communication links. For this reason, in this Thesis we propose and characterize technologies for improving the energy efficiency of multiple-antenna wireless communications. This Thesis firstly focuses on energy-efficient transmission schemes and commences by introducing a scheme for alleviating the power loss experienced by the Tomlinson-Harashima precoder, by aligning the interference of a number of users with the symbols to transmit. Subsequently, a strategy for improving the performance of space shift keying transmission via symbol pre-scaling is presented. This scheme re-formulates complex optimization problems via semidefinite relaxation to yield problem formulations that can be efficiently solved. In a similar line, this Thesis designs a signal detection scheme based on compressive sensing to improve the energy efficiency of spatial modulation systems in multiple access channels. The proposed technique relies on exploiting the particular structure and sparsity that spatial modulation systems inherently possess to enhance performance. This Thesis also presents research carried out with the aim of reducing the hardware complexity and associated power consumption of large scale multiple-antenna base stations. In this context, the employment of incomplete channel state information is proposed to achieve the above-mentioned objective in correlated communication channels. The candidate’s work developed in Bell Labs is also presented, where the feasibility of simplified hardware architectures for massive antenna systems is assessed with real channel measurements. Moreover, a strategy for reducing the hardware complexity of antenna selection schemes by simplifying the design of the switching procedure is also analyzed. Overall, extensive theoretical and simulation results support the improved energy efficiency and complexity of the proposed schemes, towards green wireless communications systems