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MIMO Channel Synchronization for Channel Capacity Enhancement

초록/요약

Multiple antenna systems, such as Multiple Input Multiple Output (MIMO), are an essential part of latest standards of wireless communications such as IEEE 802.11n (Wi-Fi), 3GPP Long Term Evolution and its advanced versions (LTE and LTE-A), WiMAX, HSPA+ and future technologies. In these days, MIMO is deployed in many of the modern wireless routers to improve the throughput of a wireless local area network (WLAN). The future of MIMO is to be deployed in mobile cellular standards such as IEEE 802.16 which is known as WiMAX ,third Generation Partnership Long Term Evolution (3GPP LTE) (3GPP and in mobile communication devices with MIMO capabilities. The MIMO technology is important in achieving high data rates for the demands of standards broadband and multimedia services. In this paper we have proposed a twostep channel capacity enhancement scheme where the channel capacities of a multiple antenna System can be enhanced by some amount without using extra transmit power or spectral bandwidth. Multiple antenna techniques can be either diversity techniques or spatial multiplexing techniques. In this scheme, our objective is to investigate the characteristics of spatial multiplexing techniques to improve the transmission speed. By exploiting the channel state information (CSI) and channel matrix symmetry at both the transmitter and receiver; we can enhance the capacity of the channel. In this scheme, we will exploit the spatial correlations between transmitter and receiver ends to enhance the overall capacity of the MIMO channel in two steps. The first step is by decomposing and factoring the channel matrix into independent orthogonal AWGN(Additive White Gaussian Noise) sub channels to minimize correlation among the transmitted streams and this will facilitate the channel capacity to be the algebraic sum of the independent orthogonal sub channels. The problem here is it will be very difficult to practically implement it as it needs full knowledge of the channel matrix at the side of transmitting component. This means CSI is required to be known at the transmitting end. Since the channel matrix is merely estimated at the receiving side and sending this information to the transmitting side would need additional resources. By estimating the channel state, H, at the side of receiving end and feeding it to side of transmitting end at the expense of some additional resource, we can enhance the capacity and reliability of the channel. This is especially good approach for slowly fading channels. The second step is by configuring transmit and receive antennas in such a way that the resulting channel matrix would be symmetrical and well-conditioned channel where the matrix whose elements in opposite pairings about the iii matrix’s diagonal elements are equal. This arrangement results in enhanced channel capacity and reliability as the decomposed channel matrix will tend have full rank. Finally, the performance of our scheme is evaluated in Matlab simulation environments using Monte Carlo simulation mechanisms for different scenarios. The simulation results show that a significant improvement in performance of channel capacity enhancement can be brought about at the expense some additional resources and system complexity.

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목차

TABLE OF CONTENTS
Master Dissertation......................................................................................i
ACKNOWLEDGEMENTS ........................................................................i
ABSTRACT.................................................................................................ii
1. Introduction...........................................................................................1
2. Background and related works ...........................................................3
2.1 Multiple Input Multiple Output channels......................................................3
2.2 Related works ...................................................................................................7
3. Channel Estimation ..............................................................................9
3.1 Least Square (LS)...........................................................................................10
3.2 Minimum Mean Squared Error(MMSE) ....................................................12
3.3 Kalman filter...................................................................................................13
4. Channel State Information ................................................................16
4.1 Channel State Information at the Receiver Side.........................................16
4.2 Channel State Information at the Transmitter Side ....................................17
4.2.1 Using Channel Reciprocity ..........................................................................18
4.2.2 CSI Feedback................................................................................................19
5. Channel Capacity Enhancement.......................................................20
5.1 Problem Formulation.....................................................................................21
5.2 Channel Capacity Without CSI ....................................................................22
5.3 Channel Capacity Enhancement With CSI .................................................24
5.3.1 Parallel channels...........................................................................................25
v
5.3.2 Channel Symmetry and Synchronization ..................................................27
5.3.3 Condition number ........................................................................................29
6. Performance Evaluation ....................................................................30
7. Conclusion and Future Work............................................................36
REFERENCES..........................................................................................37

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