Zugl.: Zürich, Techn. Hochsch., Diss., 2009

Over the last few years‚ the number of subscribers of wireless services has increased at an explosive rate. This ever growing demand for wireless communications services is constantly increasing the need for better coverage‚ improved capacity and higher quality service. Smart antennas system is an effective technology for the performance improvement of wireless communications. Switching-beam smart antennas use a number of fixed beams at an antenna site. The system provides a beam that offers the best signal enhancement and interference reduction. Using the approach of dynamic switching-beam antenna system‚ an intelligent sector beam synthesis of adjustable sector width can be established. By doing so‚ traffic load balancing can be achieved, and therefore, system capacity is increased. In this thesis, a beam-pattern synthesis algorithm proposed by M.H. Er is applied to shape array patterns with an adjustable mainlobe width and average sidelobe level reduction. Using an established database of weighting for circular arrays, the proposed smart antennas can adjust suitable sectors for the high dense subscribers not uniformly distributed. Simulation results demonstrate the proposed technique can dramatically improve the performance of traditional switching-beam antennas.

Zugl.: Aachen, Techn. Hochsch., Diss., 2005.

Techn. University, Diss., 2002--Berlin.

Abstract The performance of conventional receivers for wireless communications may severely deteriorate in the presence of unaccounted interference. The effectiveness of methods for mitigating these effects greatly depends on the knowledge that is available about the interference and signal-of-interest (SOI), therefore making the design of robust receivers a great challenge. This thesis focuses on receiver structures for channel coded systems that exploit different levels of knowledge about the SOI and interference in an iterative fashion. This achieves both robustness and overall performance improvement compared to non-iterative receivers. Code division multiple access (CDMA) and spatial division multiple access (SDMA) systems are considered. The overlay of a turbo coded direct-sequence spread-spectrum (DS-SS) system and strong digitally modulated tone interference is studied. An iterative receiver, which is capable of blind cancellation of both wideband and narrowband interference is proposed based on the adaptive self-reconfigurable -filter scheme. Asymptotic performance analysis of the iterative receiver shows that significant iteration gains are possible if the signal-to-interference-plus-noise-ratio (SINR) is relatively large and the processing gain (PG) of the SOI is relatively small. Robust diversity detection in turbo-coded DS-SS system with statistically modeled interference is studied. A non-parametric type-based iterative receiver that estimates the probability density function (PDF) of interference-plus-noise is proposed. Its performance is shown to be rather robust to the number of interferers and their distances from the victim receiver and very similar to the performance of a clairvoyant receiver. Amazingly, this is achievable with no prior knowledge about the interference parameters. Furthermore, iteration gain is shown to significantly reduce the length of the pilot sequence needed for the PDF estimation. A family of iterative minimum-mean-squared-error (MMSE) and maximum-likelihood (ML) receivers for convolutionally and space-time coded SDMA systems is proposed. Joint iterative multiuser-detection (MUD), equalization and interference suppression are proposed to jointly combat co-channel interference (CCI), inter-symbol-interference (ISI) and unknown CCI (UCCI) in broadband single-carrier systems. It is shown that both in convolutional and space-time coded systems the ISI and CCI interference can be completely eliminated if UCCI is absent. This is achievable with a number of receive antennas equal to the number of users of interest and not to the total number of transmit antennas. In case UCCI is present, the effectiveness of CCI and ISI cancellation and UCCI suppression depends on the effective degrees of freedom of the receiver. Receiver robustness can be significantly preserved by using hybrid MMSE/ML detection for the signals of interest, or by using estimation of the PDF of the UCCI-plus-noise. A low complexity hybrid MMSE/ML iterative receiver for SDMA is proposed. It is shown that its performance is not significantly degraded compared to the optimal ML receiver. Its sensitivity to spatial correlation and a timing offset is assessed by using field measurement data. It was shown that the hybrid MMSE/ML receiver is robust against spatial correlation. The sensitivity to the timing offset is significantly reduced if the receiver performs UCCI suppression.

Ericsson Brasil / The International Telecommunications Union (ITU) established through the International Mobile Telecommunications (IMT)-Advanced a set of requirements for high performance of 4th Generation (4G) communication systems and, with the aim of meeting such requirements, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is considering a set of enhancements, referred to as LTE-Advanced. In the LTE-Advanced context, Coordinated Multi-Point (CoMP) communication appears as a promising technology to boost system throughput and to allow for an efficient Radio Resource Allocation (RRA). CoMP systems promise very high performance in terms of spectral efficiency and coverage benefits when perfect Channel State Information (CSI) is available at the transmitter. However, perfect CSI is difficult to obtain in CoMP systems due to an increased number of channel parameters to be estimated at the receiver and to be fed back to the transmitter. So, the performance of such systems is compromised when the CSI is not perfectly known during CoMP processing, which is an important problem to be addressed. Space Division Multiple Access (SDMA) grouping algorithms are usually employed in order to find a suitable set of users for spatial multiplexing. The largest SDMA group is not always the best group in a given data transmission such that higher gains might be achieved by dynamically adjusting the SDMA group size. Besides, algorithms that balance the Signal to Interference-plus-Noise Ratio (SINR) among different links might ensure a certain level of link quality and so provide a more reliable communication for the scheduled users. This master thesis provides system-level analyses for RRA algorithms that exploit coordination in the downlink of CoMP systems to implement adaptive resource reuse and so improve system throughput. Herein, RRA strategies which consider dynamic SDMA grouping, joint precoding and power allocation for SINR balancing are studied in CoMP systems assuming imperfect CSI in order to obtain a better approximation with regard to the real-world implementations. It is shown through system-level analyses that quite high throughput gains are achieved through intelligent RRA. In conclusion, the results show that Sequential Removal Algorithms (SRAs) and SINR balancing provide system spectral efficiency gains. However, a critical degradation on the performance of these RRA strategies due to imperfect CSI is also shown. / A UniÃo Internacional para TelecomunicaÃÃes (ITU) estabeleceu atravÃs da iniciativa para o Sistema AvanÃado Internacional de TelecomunicaÃÃes MÃveis (IMT-Advanced), um conjunto de requisitos de alto desempenho para os sistemas de comunicaÃÃo de quarta geraÃÃo (4G) e, com o objetivo de atender tais requisitos, a EvoluÃÃo de Longo Prazo (LTE) do Projeto de Parceria para a Terceira GeraÃÃo (3GPP) està considerando um conjunto de melhorias, referidas como LTE-AvanÃado. No contexto do LTE-AvanÃado, a comunicaÃÃo multi-ponto coordenada (CoMP) aparece como uma tecnologia promissora para aumentar a vazÃo do sistema e permitir uma AlocaÃÃo de Recursos de RÃdio (RRA) eficiente. Os sistemas CoMP prometem alto desempenho em termos de eficiÃncia espectral e benefÃcios de cobertura quando a InformaÃÃo do Estado do Canal (CSI) perfeita està disponÃvel no transmissor. No entanto, CSI perfeita à difÃcil de se obter em sistemas CoMP devido a um alto nÃmero de parÃmetros de canal a serem estimados no receptor e enviados para o transmissor. Assim, o desempenho de tais sistemas à comprometido quando a CSI nÃo à perfeitamente conhecida durante o processamento CoMP tal que esse à um problema importante a ser abordado. Algoritmos de agrupamento para MÃltiplo Acesso por DivisÃo no EspaÃo (SDMA) geralmente sÃo utilizados a fim de encontrar um conjunto adequado de usuÃrios para multiplexaÃÃo espacial. O maior grupo SDMA nem sempre à o melhor grupo em uma transmissÃo de dados tal que maiores ganhos podem ser obtidos ajustando dinamicamente o tamanho do grupo SDMA. AlÃm disso, os algoritmos que balanceiam a RazÃo Sinal-InterferÃncia mais RuÃdo (SINR) entre diferentes canais podem garantir um certo nÃvel de qualidade de canal e assim proporcionar uma comunicaÃÃo mais confiÃvel para os usuÃrios agrupados. Esta dissertaÃÃo de mestrado fornece anÃlises em nÃvel sistÃmico para algoritmos de RRA que exploram a coordenaÃÃo no enlace direto de sistemas CoMP para implementar reuso adaptativo de recursos e assim melhorar o desempenho do sistema. SÃo estudadas aqui estratÃgias de RRA em sistemas CoMP que consideram agrupamento SDMA dinÃmico, precodificaÃÃo e alocaÃÃo de potÃncia conjuntas para balanceamento de SINR, sendo assumida CSI imperfeita a fim de conseguir maior aproximaÃÃo com relaÃÃo Ãs implementaÃÃs em cenÃrios reais. à mostrado atravÃs de anÃlises em nÃvel sistÃmico que ganhos de vazÃo bastante altos sÃo alcanÃados atravÃs de RRA inteligente. Em conclusÃo, os resultados mostram que Algoritmos de RemoÃÃo Sequencial (SRAs) e de balanceamento de SINR proporcionam ganhos de eficiÃncia espectral do sistema. No entanto, à tambÃm mostrada uma degradaÃÃo crÃtica no desempenho dessas estratÃgias de RRA devido à CSI imperfeita.

Typically, MAC protocols for mobile ad hoc networks assume omnidirectional antennas, and use of directional antennas offers many advantages, such as range extension, reduced co-channel interference, increased the degree of spatial reuse, improved the throughput of networks, and reduced the transmission power. There are many wireless ad hoc MAC protocol have been proposed. However, these protocols do not provide significant improvement of network performance because they can¡¦t let nodes to support multiple simultaneous transmissions or receptions ability. In this paper, we proposed a newly designed MAC protocols, we used adaptive beam-forming system to reduce the co-channel interference problem, and our proposed MAC protocol will enable nodes with multiple simultaneous transmissions and receptions ability. The handshake mechanism of proposed MAC protocol is that used receiver initialize handshake mechanism such as MACA/BI. We changed the Ready-to-Receive (RTR) control packet, which was used to poll neighbor nodes to be a dual-used control packet, Ready-to-Receive-Transmission (RTRT). Our simulation results will show that our proposed MAC protocol do exploit the advantage of space division multiple access that significantly reduced the problem of poor networks throughput which caused by bottleneck nodes in wireless ad hoc networks.

Aims There is a high prevalence of hypertension in the African population and it is known that vascular dysfunction (including nitric oxide (NO) bio-availability markers) play an important role in the development of cardiovascular diseases. Since very little is known regarding the role of markers of NO bio-availability in Africans, the aim of this study was to compare markers of NO bio-availability (namely L-arginine, L-citrulline, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA)), ambulatory blood pressure (BP) and markers of end organ damage between African and Caucasian school teachers. Additionally, we also aimed to determine whether these markers of NO bio-availability are associated with ambulatory BP and markers of end organ damage in both ethnic groups. Methods The SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study was a cross-sectional study, including urbanised African (N=181) and Caucasian (N=209) men and women, between the ages of 25 and 65 years. Cardiovascular measurements included ambulatory blood pressure, pulse wave velocity (PWV), electrocardiographic Cornell product and carotid intima media thickness (cIMT). Anthropometric measurements included height, weight and waist circumference. Various bio-markers were analysed, including glucose, L-arginine, ADMA, SDMA, Lcitrulline, reactive oxygen species, albumin-to-creatinine ratio (ACR) and estimated creatinine clearance (eCCR). Characteristics of groups were compared with independent T-tests and Chi-square tests. Single and partial analyses were used to investigate associations between NO bioavailability markers with ambulatory BP measurements and markers of end organ damage. Analyses of covariance (ANCOVA) were used for comparison of variables between groups to determine significant differences, while adjusting for age, body mass index and antihypertensive medication. Forward stepwise multiple regression analyses were performed to determine if independent associations exist between ambulatory BP measurements or markers of end organ damage with either- L-arginine, L-citrulline, ADMA or SDMA as the main independent variable. Results and conclusion The Africans and Caucasians were of similar ages. However, the Africans had higher blood pressure therefore their cardiovascular profile was unfavourable compared to that of the Caucasians. The inhibitors of NO biosynthesis, ADMA and SDMA, were significantly lower in the Africans (p=0.046; p<0.001, respectively). However, the NO bio-availability markers, L-arginine and L-citrulline, were higher in the African compared to the Caucasian participants (all p values <0.05) regarded as significant. When performing unadjusted analyses, we found significant negative associations between eCCR and L-citrulline in all four subgroups: African men (r=-0.27; p=0.013), African women (r=-0.24; p=0.021), Caucasian men (r=-0.21; p=0.044) and Caucasian women (r=-0.28; p=0.003). The association of eCCR with L-citrulline was confirmed to be independent of confounders in all groups: African men (R2=0.46; β=-0.23; p=0.006), African women (R2=0.68; β= -0.12; p=0.046), Caucasian men (R2=0.62; β= -0.24; p<0.001) and Caucasian women (R2=0.72; β= -0.13; p=0.029). This implicates that renal function may be detrimentally affected by L-citrulline concentrations. In the Caucasian men and women negative correlations between eCCR and SDMA were found before adjustments (r=-0.33; p=0.003 and r=-0.26; p=0.006, respectively). This phenomenon was confirmed in the forward stepwise multiple regression analysis in Caucasian men (R2=0.75; β= -0.27; p<0.001) and women (R2=0.73; β= -0.21; p<0.001), while no associations were found in the Africans. This result is not unexpected, since SDMA can only be eliminated by the kidneys and is therefore an important risk marker for the early detection of renal dysfunction. In Caucasian men we found that ADMA correlated with ACR (r=0.36; p=0.001), night-time SBP (r=0.34; p=0.002) and night-time DBP (r=0.25; p=0.023) with single linear regression analyses. A similar trend was shown in African men with night-time SBP (r= 0.20; p=0.089) and night-time DBP (r= 0.21; p=0.078) respectively, but this association was absent in the Caucasian and African women. After adjustments for age and body mass index, the associations with ADMA, ACR and SBP in the Caucasian men remained. However, a negative association between eCCR and ADMA also became evident in the African men (r=- 0.24; p=0.025) and remained significant in the forward stepwise multiple regression analysis (R2=0.44; β= -0.18; p=0.034). It is, however, not clear why our results were gender specific, but we could speculate that the female sex hormones may play a part in protecting the vascular endothelium. Apart from the associations described above, there were no significant independent associations between the markers of the NO cycle (such as L-arginine) and PWV, cIMT, eCCR, ACR or Cornell product. In conclusion, although Africans presented a more vulnerable cardiovascular profile, we found a consistent negative association between renal function and L-citrulline in all participants, which has only been reported previously in patients with chronic renal disease. Additionally we found a gender-specific link between renal function and ADMA in African and Caucasian men. Our results may indicate that in the general population, markers of NO bioavailability may be associated with early changes in renal function, accompanying elevated blood pressure. / Thesis (MSc (Physiology))--North-West University, Potchefstroom Campus, 2013

Aims There is a high prevalence of hypertension in the African population and it is known that vascular dysfunction (including nitric oxide (NO) bio-availability markers) play an important role in the development of cardiovascular diseases. Since very little is known regarding the role of markers of NO bio-availability in Africans, the aim of this study was to compare markers of NO bio-availability (namely L-arginine, L-citrulline, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA)), ambulatory blood pressure (BP) and markers of end organ damage between African and Caucasian school teachers. Additionally, we also aimed to determine whether these markers of NO bio-availability are associated with ambulatory BP and markers of end organ damage in both ethnic groups. Methods The SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study was a cross-sectional study, including urbanised African (N=181) and Caucasian (N=209) men and women, between the ages of 25 and 65 years. Cardiovascular measurements included ambulatory blood pressure, pulse wave velocity (PWV), electrocardiographic Cornell product and carotid intima media thickness (cIMT). Anthropometric measurements included height, weight and waist circumference. Various bio-markers were analysed, including glucose, L-arginine, ADMA, SDMA, Lcitrulline, reactive oxygen species, albumin-to-creatinine ratio (ACR) and estimated creatinine clearance (eCCR). Characteristics of groups were compared with independent T-tests and Chi-square tests. Single and partial analyses were used to investigate associations between NO bioavailability markers with ambulatory BP measurements and markers of end organ damage. Analyses of covariance (ANCOVA) were used for comparison of variables between groups to determine significant differences, while adjusting for age, body mass index and antihypertensive medication. Forward stepwise multiple regression analyses were performed to determine if independent associations exist between ambulatory BP measurements or markers of end organ damage with either- L-arginine, L-citrulline, ADMA or SDMA as the main independent variable. Results and conclusion The Africans and Caucasians were of similar ages. However, the Africans had higher blood pressure therefore their cardiovascular profile was unfavourable compared to that of the Caucasians. The inhibitors of NO biosynthesis, ADMA and SDMA, were significantly lower in the Africans (p=0.046; p<0.001, respectively). However, the NO bio-availability markers, L-arginine and L-citrulline, were higher in the African compared to the Caucasian participants (all p values <0.05) regarded as significant. When performing unadjusted analyses, we found significant negative associations between eCCR and L-citrulline in all four subgroups: African men (r=-0.27; p=0.013), African women (r=-0.24; p=0.021), Caucasian men (r=-0.21; p=0.044) and Caucasian women (r=-0.28; p=0.003). The association of eCCR with L-citrulline was confirmed to be independent of confounders in all groups: African men (R2=0.46; β=-0.23; p=0.006), African women (R2=0.68; β= -0.12; p=0.046), Caucasian men (R2=0.62; β= -0.24; p<0.001) and Caucasian women (R2=0.72; β= -0.13; p=0.029). This implicates that renal function may be detrimentally affected by L-citrulline concentrations. In the Caucasian men and women negative correlations between eCCR and SDMA were found before adjustments (r=-0.33; p=0.003 and r=-0.26; p=0.006, respectively). This phenomenon was confirmed in the forward stepwise multiple regression analysis in Caucasian men (R2=0.75; β= -0.27; p<0.001) and women (R2=0.73; β= -0.21; p<0.001), while no associations were found in the Africans. This result is not unexpected, since SDMA can only be eliminated by the kidneys and is therefore an important risk marker for the early detection of renal dysfunction. In Caucasian men we found that ADMA correlated with ACR (r=0.36; p=0.001), night-time SBP (r=0.34; p=0.002) and night-time DBP (r=0.25; p=0.023) with single linear regression analyses. A similar trend was shown in African men with night-time SBP (r= 0.20; p=0.089) and night-time DBP (r= 0.21; p=0.078) respectively, but this association was absent in the Caucasian and African women. After adjustments for age and body mass index, the associations with ADMA, ACR and SBP in the Caucasian men remained. However, a negative association between eCCR and ADMA also became evident in the African men (r=- 0.24; p=0.025) and remained significant in the forward stepwise multiple regression analysis (R2=0.44; β= -0.18; p=0.034). It is, however, not clear why our results were gender specific, but we could speculate that the female sex hormones may play a part in protecting the vascular endothelium. Apart from the associations described above, there were no significant independent associations between the markers of the NO cycle (such as L-arginine) and PWV, cIMT, eCCR, ACR or Cornell product. In conclusion, although Africans presented a more vulnerable cardiovascular profile, we found a consistent negative association between renal function and L-citrulline in all participants, which has only been reported previously in patients with chronic renal disease. Additionally we found a gender-specific link between renal function and ADMA in African and Caucasian men. Our results may indicate that in the general population, markers of NO bioavailability may be associated with early changes in renal function, accompanying elevated blood pressure. / Thesis (MSc (Physiology))--North-West University, Potchefstroom Campus, 2013

Zugl.: Aachen, Techn. Hochsch., Diss., 2008.