A line-of-sight optimised MIMO architecture for outdoor environments

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Simulation Analysis of Wireless Channel Effect on IEEE 802.11n Physical Layer

International audienceIEEE 802.11n standard came as a rescue; the existing standards are increasingly seen as inadequate since applications become more complex and require more bandwidth. Several techniques have been put into operation to meet two basic requirements: significantly greater bit rate and radio coverage. However, studies have shown that the theoretical limit in terms of throughput is far from being reached and that the received power does not explain the performance degradation. A list of suspect parameters is analyzed in this paper to assess their effect on performance of the IEEE 802.11n physical layer taken as an application of MIMO technology in indoor context. It is shown that for values of angular spread below 27°, the data rate cannot exceed 117 Mbps and the antennas spacing can compensate the performance degradation caused by other parameters. Results are given in terms of correlation coefficient, other channel characteristics and the packet error rate

A Study of the Impact of Various Geometric Factors on the Capacity of Short Range Indoor MIMO Communications Channels

MIMO antenna array systems have been proposed as a means of increasing the spectral efficiency of wireless systems. However, their performance is likely to be sub-optimal if typical uniform antenna array structures are arbitrarily positioned; as they depend on spatial multiplexing. This is particularly true for indoor environments in which transmission ranges are short resulting in a strong correlation of the main propagation paths, especially the line-of-sight components. This makes it difficult to achieve successful spatial multiplexing which depends on a decorrelated set of signal components. Thus, the physical propagation channel and geometry of the antenna arrays, especially the inter-element spacing, can determine how effectively spatial multiplexing can be realised. This thesis investigates MIMO communications channels involving a single transmitter and receiver operating in a simple indoor environment using a ray-tracing simulation model. The results and analysis provide system designers with an understanding of the limits of MIMO system performance in the context of both the geometric properties of the arrays and the propagation conditions. These results serve to explain the often contradictory results that appear in the wider literature on MIMO systems. Guidelines for the deployment of standard array structures in an indoor environment are provided. An original solution to optimising MIMO system performance by adjusting the geometry of uniform linear arrays is described. This is done using an iterative search method based on the Metropolis algorithm in which individual array elements are repositioned. It is demonstrated through computer simulation that capacity levels, similar to those predicted by the theory for ideal Rayleigh channels, are possible to achieve with realistic modifications to uniform linear arrays

近距離MIMOシステムの通信容量に関する研究

Recently, the near field communication, abbreviated NFC, which is a form of contactless communication between devices like smartphones or tablets, is emerging quickly. Contactless communication allows a user to wave the smartphone over a NFC compatible device to send information without needing to touch the devices together or go through multiple steps setting up a connection. Fast and convenient, NFC technology is popular in parts of Europe and Asia, and is quickly spreading throughout the whole world. Over the past decade, we have witnessed the rapid evolution of Multiple-Input Multiple-Output (MIMO) systems which promise to break the frontiers of conventional architectures and deliver high throughput by employing more than one element at the transmitter (Tx) and receiver (Rx) in order to exploit the spatial domain. This is achieved by transmitting simultaneous data streams from different elements which impinge on the Rx with ideally unique spatial signatures as a result of the propagation paths‘ interactions with the surrounding environment. For exchanging massive information, for instance the videos or photos, between two devices, the future NFC systems will require higher channel capacity than current systems. Therefore, the MIMO system, which has a wider bandwidth, multi-value modulation system, and spatial multiplexing scheme, is the appropriate candidate to be employed in the high-speed NFC systems. Contrary to conventional MIMO systems, near-field MIMO communication systems transfer data in a very short range, the transmission lines are formed in parallel without multipath, and the LOS (line-of-sight) paths are the major components. The conventional MIMO works in a multipath-rich propagation environment, and is expected to achieve a high channel capacity by utilizing multipath components. The near-field MIMO, however, transfers data directly from the transmitter to the receiver, without any fading caused by multipath components. In the near-field MIMO system, a higher channel capacity results from a higher SNR and lower spatial correlation characteristics. Considering the short distance, the LOS components from each of the Tx elements arrive at the Rx array with a spherical wavefront. Therefore the beamwidth of the antenna element radiation pattern affects not only the receiving gain but also the spatial correlation characteristics. Usually, the conventional dipole antennas are used to investigate the MIMO channel capacity. However, the conventional dipoles are omni-directional in the horizontal plane. In this paper, a bi-directional element named dual-dipole element is utilized to improve the channel capacity. In the dual-dipole array, two half wave-length dipole antennas are settled parallel as only one element. By changing the internal distance between the two dipoles in one Tx element, the HPBW (half power beam width) of the element can be adjusted. Therefore, the shape of the radiation pattern can be determined by the internal distance between the two dipoles in one element. The effect of the HPBW on the channel capacity is investigated in detail. The narrower beam width of the Tx element can result for a higher SNR in the facing Rx element, however, at the meantime the power in the other sub channels will decrease. Hence, it is expected that there would be an optimum HPBW when the system could obtain the maximum channel capacity. And we find out the optimum HPBW for the near-field MIMO system with dual-dipole arrays. In addition, the improvement in the channel capacity from the conventional dipole array is considerable. Basically two factors determine the capacity of a MIMO system—the path loss and the multipath richness. The dual-dipole arrays lead to much lower path loss than the conventional dipole arrays, hence, the channel capacity improves significantly. However, the multipath richness rarely exists in the near-field MIMO. So far, all the researches on the near-field MIMO are in the free space without any obstacle. However, due to the short transfer distance of the near-field MIMO, a tiny variation of the channel will lead to a significant difference on the channel capacity. Therefore, we employ metal wire in the near-field MIMO system to increase the multipath richness and clarify the effect of obstacles in the system. The characteristics of the single metal wire are detailed investigated. And the most significant aspect is the location of the metal wire placed in the system. Generally, an object placed between two transmission antennas will decrease the channel capacity of the system. Here, we try to determine the optimal location of the object between the opposing antennas. We expect that the optimal location will alleviate the deterioration in the capacity caused by the object. However, the simulation results indicate that if the metal wire is placed in an appropriate location, a higher channel capacity can be obtained. In addition, we can set multiple metal wires in the optimum locations to achieve higher channel capacity. The different types of objects in the different types of arrays are also researched. Finally, this paper clarifies the frequency dependency of channel capacity in near-field MIMO system with metal wire. As the frequency increases, the absolute value of the channel capacity decreases. The improvement on channel capacity of using a metal wire also changes with frequency. In addition, when the frequency is very large, the effect of the metal wire is negligible. The proper location for the metal wire is found related with the corresponding wavelength of each specific frequency. Confidently, the research of the effect of the element HPBW and the objects between Tx and Rx introduced in this study can be beneficially applied in actual network preparation of future near-field MIMO wireless communications in which the improvement in the channel capacity are required