MIMO MC-CDMA WITH DIFFERENTIAL UNITARY SPACE TIME FREQUENCY MODULATION FOR HIGH MOBILITY SCENARIO

Future generation communication systems require high data rate and high mobility communication which has good performance, good resistance to errors and good spectral efficiency. The recent multicarrier scheme although it can give high data rate communication system but the performance is poor while being used in high mobility scenario. The current multicarrier scheme require channel estimation to decode the received signal, but there are some conditions when the channel state information practically can be acquired, for example where the channel condition change very fast when user in high mobility condition. To solve this problem, non-coherent transmission system without channel estimation is the answer. In this thesis the non-coherent transmission scheme that used is Differential Unitary Space Time Frequency Modulation (DUSTFM) for 2x2 MIMO and 4x4 MIMO are proposed. The proposed schemes are combined with MC-CDMA to give better performance in high mobility condition. The combined methods exploit the advantage of each scheme (MIMO, MC-CDMA, differential modulation, STFC), in order to achieve a high data rate communication system which is robust against frequency selective fading, multipath fading, and fast fading. The proposed DUSTFM scheme for 2x2 MIMO can give better performance compared to the main reference that have been proposed by Tran when BPSK is used as mapper but the performance of the proposed system while QPSK is used as mapper, is significantly decline due to the inability of the symbol detection to separate the symbols effectively. The proposed DUSTFM for 4x4 MIMO can give better performance until 8dB of gain compared to the 2x2 MIMO with DUSTFM when both of them BPSK is used as mapper. However the 4x4 MIMO with DUSTFM model only can work well when every antenna is using different frequency band, this means the spectral efficiency of the 4x4 MIMO with DUSTFM model is very bad compared to the 2x2 MIMO with DUSTFM model

Maximum likelihood detection for differential unitary space-time modulation with carrier frequency offset

Can conventional differential unitary space time modulation (DUSTM) be applied when there is an unknown carrier frequency offset (CFO)? This paper answers this question affirmatively and derives the necessary maximum likelihood (ML) detection rule. The asymptotic performance of the proposed ML rule is analyzed, leading to a code design criterion for DUSTM by using the modified diversity product. The resulting proposed decision rule is a new differential modulation scheme in both the temporal and spatial domains. Two sub-optimal multiple-symbol decision rules with improved performance are also proposed. For the efficient implementation of these, we derive a modified bound intersection detector (BID), a generalization of the previously derived optimal BID for the conventional DUSTM. The simulation results show that the proposed differential modulation scheme is more robust against CFO drifting than the existing double temporal differential modulation

Bound-intersection detection for multiple-symbol differential unitary space-time modulation

This paper considers multiple-symbol differential detection (MSD) of differential unitary space-time modulation (DUSTM) over multiple-antenna systems. We derive a novel exact maximum-likelihood (ML) detector, called the bound-intersection detector (BID), using the extended Euclidean algorithm for single-symbol detection of diagonal constellations. While the ML search complexity is exponential in the number of transmit antennas and the data rate, our algorithm, particularly in high signal-to-noise ratio, achieves significant computational savings over the naive ML algorithm and the previous detector based on lattice reduction. We also develop four BID variants for MSD. The first two are ML and use branch-and-bound, the third one is suboptimal, which first uses BID to generate a candidate subset and then exhaustively searches over the reduced space, and the last one generalizes decision-feedback differential detection. Simulation results show that the BID and its MSD variants perform nearly ML, but do so with significantly reduced complexity

Differential space-time block-coded OFDMA for frequency-selective fading channels

Combining differential Alamouti space-time block code (DASTBC) with orthogonal frequency-division multiple access (OFDMA), this paper introduces a multiuser/multirate transmission scheme, which allows full-rate and full-diversity noncoherent communications using two transmit antennas over frequency-selective fading channels. Compared with the existing differential space-time coded OFDM designs, our scheme imposes 10 restrictions on signal constellations, and thus can improve the spectral efficiency by exploiting efficient modulation techniques such as QAM, APSK etc. The main principles of our design are s follows: OFDMA eliminates multiuser interference, and converts multiuser environments to single-user ones; Space-time coding achieves performance improvement by exploiting space diversity available with multiple antennas, no matter whether channel state information is known to the receiver. System performance is evaluated both analytically and with simulations

Asymptotic Estimates for Some Dispersive Equations on the Alpha-modulation Space

The alpha-modulation space is a function space developed by Grobner in 1992. The alpha-modulation space is a generalization of the modulation space and Besov space. In this thesis we obtain asymptotic estimates for the Cauchy Problem for dispersive equation, a generalized half Klein-Gordon, and the Klein-Gordon equations. The wave equations will also be considered in this thesis too. These estimates were found by using standard tools from harmonic analysis. Then we use these estimates with a multiplication algebra property of the alpha-modulation space to prove that there are unique solutions locally in time for a nonlinear version of these partial differential equations in the function space of continuous function in time and alpha-modulation in the spatial component. These results are obtained by using the fixed point theorem