A transmit MIMO scheme with frequency domain pre-equalization for wireless frequency selective channels

In this paper, we introduce a transmit multiple-input multiple-output (MIMO) scheme with frequency domain pre-equalization for a multipath or frequency selective channel. In this scheme, MIMO processing in the frequency domain is performed at the transmitter or base station so that the receiver or mobile station only requires limited processing. This scheme provides high data rates and also inherits from the frequency domain equalization the property of relatively low complexity in severe multipath environments. The MIMO transmit processing is derived by minimizing the minimum mean square errors (MMSE), and expressions for the signal-to-interference-plus-noise ratio and error probability based on the Gaussian approximation of the interference term are provided. Some important associated issues, such as channel errors and computational complexity, are also investigated. Numerical simulations are also provided and these demonstrate the improved performance of our proposed scheme compared to other transmit MIMO schemes. In particular, they show that the proposed system can attain multipath or frequency diversity of the channel.     

Compact dual-frequency PIFA designs using LC resonators

We report our investigation into single-feed dual-frequency planar inverted F antenna (PIFA) designs which make use of LC resonators (or “RF traps”). We introduce three basic methods for incorporating the LC resonator into the PIFA, including a variant of the meandering PIFA. Experimental results are provided and these show that dual-frequency operation at 900 (cellular systems) and 1800 MHz (personal communication systems) can be achieved for all three designs     

Compact integrated diversity antenna for wireless communications

We introduce a compact integrated antenna that has two feed ports with more than 20 dB isolation between them. The significance of the design is that it can be utilized in compact wireless communication handsets to provide diversity signals or act as a duplexer allowing the receive and transmit signals to be well isolated. The antenna design is based on merging two patch antennas together in combination with capacitive loading so that a compact design can be obtained. Justification for the design is provided by considering the mutual coupling using the reaction principle and finite-dimensional time-domain (FDTD) simulations. Experimental results are also presented for a design that operates in the 2100-2200 MHz band for possible application in forthcoming third-generation wireless systems. Results include radiation patterns, S-parameters, and signal correlations between ports so that the diversity performance and isolation characteristics of the antenna can be demonstrated. These show that in typical wireless environments envelope cross correlations of less than 0.1 between the ports are obtained     

Recent developments in hot plate welding of thermoplastics

This paper considers the hot plate welding process applied to three injection molded thermoplastic materials: polypropylene, high impact polystyrene, and poly(phenylene oxide). Weld quality was assessed by tensile testing. The process was found to be suitable for all three materials, although tolerance to variations in process parameters varied. The parameters in the heating phase, i.e., hot plate temperature and time, were the most important for achieving good welds, whereas parameter variations in the consolidation phase were relatively unimportant.     

A pre-BLAST-DFE technique for the downlink of frequency-selective fading MIMO channels

In this paper, we propose a pre-Bell Laboratories layered space-time (BLAST)-decision-feedback equalization technique for the downlink of frequency-selective fading multiple-input multiple-output (MIMO) channels to combat multiple-access interference (MAI) and intersymbol interference (ISI). In our technique, we perform MIMO pre-equalization and prelayered space-time processing at the transmitter or base station, with a simplified receiver at the mobile station that requires only limited signal processing. An important application is in the downlink, so that a simplified mobile station can be constructed. An expression for the signal-to-noise ratio (SNR) and error probability based on the Gaussian approximation of the output noise term is derived. Performance is investigated by analysis and simulation results. In particular, it is demonstrated that the diversity order of this technique is higher than that of the MIMO orthogonal frequency-division multiplexing (OFDM) with vertical (V)-BLAST and MIMO OFDM with linear transmit preprocessing. It is also noticed that this technique performs better at high SNR values.     

Performance analysis of maximum likelihood detection in a MIMOantenna system

We provide an analysis of the performance of maximum likelihood detection (MLD) over flat fading channels in a wireless multiple input-multiple output (MIMO) antenna system. A tight union bound with an asymptotic form on the probability of symbol error rate (SER) for MIMO MLD systems with two-dimensional signal constellations (such as QAM and PSK) is introduced. Using this analytic bound, the performance of the MIMO antenna system is demonstrated quantitatively with respect to channel estimation, constellation size, and antenna configuration     

Cytogenetic abnormalities of unfertilized oocytes generated from in-vitro fertilization and intracytoplasmic sperm injection: a double-blind study

In the present study we have assessed the cytogenetic abnormalities of unfertilized oocytes from in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) programmes during a one year period (July 1995 to July 1996) with the cytogenetic analysis being carried out in a double-blind manner. A total of 88 unfertilized ICSI and 85 unfertilized IVF oocytes were used for the study and of these 51 and 62 oocytes, in each respective group, were suitable for analysis. The haploidy, diploidy and aneuploidy rates between ICSI (62.7, 7.8 and 5.9%) and IVF (61.3, 9.7 and 14.5%) groups were similar. A significant inter-patient variation in the incidence of hypohaploidy was observed within the IVF group. Chromosomal fragmentation or breakage was observed at a similar rate in both groups of unfertilized oocytes (23.5 and 14.5% for ICSI and IVF respectively). A significantly higher proportion of ICSI oocytes contained sperm nuclei (27/51, 52.9%) than did IVF oocytes (20/62, 32.3%, P < 0.01). The distribution and state of sperm head chromatin in relation to oocyte chromosomal complement was studied in both groups. ICSI oocytes contained decondensed or swollen sperm nuclei in association with haploid oocyte chromosomes (12/27, 44.4%) or condensed sperm heads in oocytes showing no chromosomal complements (7/27, 25.9%). In IVF oocytes sperm heads were either arrested in the condensed state (5/20, 25%), metaphase stage (3/20, 15%) or had undergone premature chromosome condensation (PCC; 6/20, 30%) in association with haploid oocyte chromosomes. The incidence of PCC was similar in the two groups. A marked variation in the incidence of total chromosomal abnormality was observed between patients within both ICSI (0-75%) and IVF (0-71%) groups indicating a possible similarity in oocyte quality between the majority of male factor and tubal infertility patients. The type of sperm used in the two fertilization procedures showed an increased incidence of chromosomal breakage with ICSI-MESA (microepididymal sperm aspiration) spermatozoa (4/6, 67%) compared to the ICSI-ejaculated (6/35, 17.1%; P < 0.05), ICSI-testicular biopsy (2/10, 20%) and IVF-normospermic (9/62, 14.5%; P < 0.01) spermatozoa. Chromosomal fragmentation may be associated with the degree of difficulty experienced at sperm injection, especially with sperm retrieved from the reproductive tract. Thus chromosomal fragmentation in ICSI may need further investigation using a larger sample size in order to assess the possible causative factors.     

A capacitively loaded PIFA for compact mobile telephone handsets

A capacitively loaded planar inverted-F antenna (PIFA) is proposed and studied. It is found that the capacitive load reduces the resonance length of the PIFA from λ/4 to less than λ/S. A design with a bandwidth of 178 MHz centered at 1.8 GHz is provided to demonstrate that compact antennas for mobile telephone handsets can be constructed using this approach. The finite-difference time-domain (FDTD) method is used in the study and experimental verification is also provided     

Layered space-frequency equalization in a single-carrier MIMO system for frequency-selective channels

Frequency-domain equalization (FDE) has been shown to be an effective approach to combat frequency-selective wireless channels. In this letter, we propose a layered space-frequency equalization (LSFE) architecture for a single-carrier (SC) multiple-input multiple-output (MIMO) system, where MIMO FDE is employed at each stage or (layer) of detection. At a particular stage, a group of the best data streams in the minimum mean square error sense are detected and are canceled from the received signals. Simulation results show that our proposed LSFE structures can outperform layered space-time equalization (LSTE) structures and uncoded orthogonal frequency division multiplex (OFDM), especially at a higher delay spread. Performance is enhanced further, by incorporating the FDE with time-domain decision feedback at each stage of LSFE. We also provide performance analysis for LSFE, in comparison with OFDM.