On the Number of RF Chains and Phase Shifters, and Scheduling Design with Hybrid Analog-Digital Beamforming

This paper considers hybrid beamforming (HB) for downlink multiuser massive multiple input multiple output (MIMO) systems with frequency selective channels. For this system, first we determine the required number of radio frequency (RF) chains and phase shifters (PSs) such that the proposed HB achieves the same performance as that of the digital beamforming (DB) which utilizes $N$ (number of transmitter antennas) RF chains. We show that the performance of the DB can be achieved with our HB just by utilizing $r_t$ RF chains and $2r_t(N-r_t + 1)$ PSs, where $r_t \leq N$ is the rank of the combined digital precoder matrices of all sub-carriers. Second, we provide a simple and novel approach to reduce the number of PSs with only a negligible performance degradation. Numerical results reveal that only $20-40$ PSs per RF chain are sufficient for practically relevant parameter settings. Finally, for the scenario where the deployed number of RF chains $(N_a)$ is less than $r_t$, we propose a simple user scheduling algorithm to select the best set of users in each sub-carrier. Simulation results validate theoretical expressions, and demonstrate the superiority of the proposed HB design over the existing HB designs in both flat fading and frequency selective channels.Comment: IEEE Transactions on Wireless Communications (Minor Revision

Low-jitter symbol timing recovery for M-ary QAM and PAM signals

This thesis focuses on low-jitter symbol timing recovery schemes applicable to M-ary QAM and PAM signals. Franks and Bubrowski introduced highpass prefiltering and symmetric bandpass post-filtering for jitter-free operation of a symbol timing recovery scheme using a squarer for binary signaling. We show that the same conditions are also applied to M-ary PAM or QAM signals. In this work, we have investigated the effects of imperfections in both prefiltering and post-filtering on the jitter performance using analysis, simulation and experiments. It is shown that, although a zero-jitter cannot be achieved due to the imperfections, a good selection of pre-filtering can significantly reduce the timing jitter of the recovered clock signal. Jitter performance of the squarer with and without prefiltering for M-ary PAM signals is presented. We also demonstrated that a perfect prefiltering of the received baseband signal essentially produces an equivalent double-sided band, suppressed-carrier (DSB-SC) passband signal centered at the Nyquist frequency (i.e., $1\over2$ of the symbol clock frequency). (Abstract shortened by UMI.

Blind user identification in a chip-synchronous CDMA system

User identification provides valuable information about the active users in a Code Division Multiple Access (CDMA) system that could be used in numerous applications. Most importantly, it can produce a reliable estimate of multiple access interference, whose cancellation is the main objective of multiuser detection schemes. Several schemes have been introduced for user identification in a synchronous CDMA system. The main distinguishing factor between different user identification schemes is the amount of information about each user required to be available in advance at the receiver. The existing schemes require prior knowledge of users' spreading codes or some other forms of assistance. However, the proposed method does not need the prior knowledge of the spreading codes nor relies on any assistance. Thus, using the scheme proposed in the thesis, one will be able to perform complete blind identification for a group of users. This identification involves determination of the spreading codes of active users and estimation of their relative timings. In this thesis, a scheme for blind identification of users in a chip-synchronous Direct Sequence CDMA (DS-CDMA) system is presented. The proposed approach is based on the subspace decomposition and searches for a solution that minimizes a defined cost function. The search is performed over both signal space and time domain. By completing the identification of the users, other important parameters such as user timings and power can be evaluated. Blind identification of users for an asynchronous CDMA system lends itself to several applications such as CDMA up-links, ad-hoc networking, signal interception and non-intrusive tests

MIMO Evolution Beyond 5G Through Reconfigurable Intelligent Surfaces and Fluid Antenna Systems

With massive deployment, multiple-input-multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas

A MUSIC-Based Algorithm for Blind User Identification in Multiuser DS-CDMA

A blind scheme based on multiple-signal classification (MUSIC) algorithm for user identification in a synchronous multiuser code-division multiple-access (CDMA) system is suggested. The scheme is blind in the sense that it does not require prior knowledge of the spreading codes. Spreading codes and users' power are acquired by the scheme. Eigenvalue decomposition (EVD) is performed on the received signal, and then all the valid possible signature sequences are projected onto the subspaces. However, as a result of this process, some false solutions are also produced and the ambiguity seems unresolvable. Our approach is to apply a transformation derived from the results of the subspace decomposition on the received signal and then to inspect their statistics. It is shown that the second-order statistics of the transformed signal provides a reliable means for removing the false solutions

Adipose derived stem cells for treatment of mandibular bone defects: An autologous study in dogs

Background: The aim of this research was to evaluate the effect of adipose derived stem cells on bone repair in through and through mandibular bone defects of canine. Materials and Methods: In this prospective comparative study, adipose-derived stem cells were isolated from subcutaneous fat of lateral thoracic area of 4 dogs. The isolated cells were cultured and expanded through 3 passages. The undifferentiated stem cells were seeded in Collatamp and transferred into mandibular bone through-and-through defects. Similar defects on control group were filled with cell-free Collatamp. After 6 weeks, biopsies were taken and histomorphometric analysis was performed. The percentage of new bone formation was measured in each case. The data were subject to statistical analysis using the Wilcoxon test. Differences at P≤0.05 were considered significant. Results: H and E staining of decalcified samples revealed more bone formation in the group, which stem cells were seeded. Cell-free collatamp group revealed an average bone regeneration of %41±13.21, while adipose derived stem cell-seeded collatamp group showed %49±8.24. Conclusion: The use of stem cell seeded collatamp scaffold in mandibular defects caused more bone regeneration

Survival rate of breast cancer based on geographical variation in Iran: A national study

BACKGROUND: Breast cancer is the most common cancer among women worldwide. Based on the latest Iranian national cancer department report, the total number of women registered with breast cancer was 6976 cases during 2007. Five year survival is one of the indicators used for evaluation of the quality for care to different types of malignancies including breast cancer. OBJECTIVES: The aim of this study was to estimate survival rate of breast cancer in 6147 Iranian patients at a national level in different geographic regions. MATERIALS AND METHODS: 6147 cases of breast cancer, which had telephone number and were diagnosed between 2001-2006, were called to obtain information about their life status. Survival estimates were calculated using the Kaplan-Meier method, and the survival probability was calculated for the overall cohort and in different categories of gender, age and pathologic type of tumor. Hazard ratios (HR) according to demographic and risk variables were calculated by Cox's proportional hazard model. RESULTS: The overall 5-year survival rate was 71.0%. The mean survival time was different between men and women, which was statistically significant. The number of men involved with breast cancer was 172 (2.8%) of all cases. The 5-year survival rate for patients in age group 41-50 years was significantly higher than other age groups (P = 0.001). The likelihood of death was higher in patients with 61 years old or more years rather than those below forty years old (HR = 1.31; 95% CI: 1.12-1.55). CONCLUSIONS: The findings of this study might help Iranian health managers: 1) to be more conscious about geographical and regional determinants which will affect overall survival rate. 2) To carry preventive activities such as public education particularly in Iranian men. 3) To think about screening and early detection of breast cancer

MIMO evolution beyond 5G through reconfigurable intelligent surfaces and fluid antenna systems

Abstract With massive deployment, multiple-input–multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas