Closed‐Loop transmit diversity (transmit beamforming) for mitigation of interference and multipath fading in wireless communication systems

The wireless communication channel suffers from many impairments such as the thermal noise often modeled as Additive White Gaussian Noise (AWGN), the path loss in power as the radio signal propagates, the shadowing due to the presence of fixed obstacles in the radio path, and the fading which combines the effects of multiple propagation paths and the rapid movement of mobile units reflectors. Deploying multiple  antennas at the transmitter has been shown to increase diversity and therefore improve signal quality with increased throughput. This paper proposes a transmit diversity scheme, where multiple transmit antennas are used at the transmitter. A feedback path is provided from the receiver to communicate the channel seen by the receiver to the transmitter (closed-loop). When closed]loop transmit diversity is applied, the symbol from each transmit antenna is multiplied with a complex number  corresponding to the inverse of the phase of the channel so as to ensure that the signals add constructively at the receiver. From this research it was found that sending the same information on multiple transmit antenna does not always provide diversity gain. However if the transmitted symbols are multiplied by a complex phase to ensure that the phases align at the receiver, there is diversity gain though the bit error rate performance seems to be slightly poorer than the maximal ratio combining case.Key words: Closed-loop, transmit diversity, transmit beamforming,  single-input single-output, multipath fading, mmaximal ratio combinin

Comprehensive OPNET based Scalability Analysis and Performance Evaluation of MANET Routing Protocols

A Mobile Ad-hoc Network (MANET) is a collection of communication and computing devices equipped with communication capabilities in which the nodes communicate with each other without any pre-existing infrastructure. Unlike the infrastructure based networks, there are no BTSs and BSCs in MANETs. The nodes involved in the MANETs, therefore, act as both routers and hosts. The nodes involved in the MANETs, therefore, act as both routers and hosts. The network topology varies dynamically and unpredictably due to mobility of the nodes. The conventional IP based routing protocols are not able to handle the unique characteristics of MANETs. Different protocols that can handle the unique characteristics such as dynamic and unpredictably varying topology have therefore been developed. These protocols have different performance and scalability behaviors in different network operation conditions. It is therefore imperative to analyze their scalability and evaluate their performances with respect to the control variables on which MANET networks are mainly optimized and characterized such as the network size, mobility and traffic type and load. In this paper, the scalability and performance behaviors of AODV, DSR and OLSR are analyzed under scalable network size, mobility speed and FTP traffic loads with respect to average end-to-end delay and throughput. OPNET Modeler 14.5 was used as a simulation tool. The results indicated that there is an overall throughput performance increment with increasing network size and FTP traffic load while the delay performance was decreasing. It was also observed that the mobility scaling has not a significant effect on the performance behavior of the protocols. OLSR performs better than the AODV and DSR in terms of delay while AODV performs better than the other two in terms of throughput in all the scenarios considered. Keywords: AODV, Delay, DSR, Throughput, FTP, MANET, OLS

Evaluating performance of WRP and AODV MANETs routing protocols under mobility

The Mobile ad hoc networks (MANET) is a wireless networks which have no central bridge, and where each node acts as a destination as well as a router. The MANETs are dynamic networks because the network topology keeps on changing because of the mobility of the nodes. There are many protocols that have been developed to aid in routing in these types of networks. Each of these protocols is designed with some certain mobility scenarios in mind. To achieve effective routing in a given scenario, the right protocol must be chosen. Choosing the right protocol involves  evaluating many interdependent performance metrics that define the effectiveness of a routing protocol, and this often poses a challenge to application designers. This research endeavored to model a simulation platform on which various protocols could be evaluated under various mobility scenarios to determine their suitability. The GloMoSim was used as the simulation platform and two MANET protocols namely wireless routing protocol (WRP) and ad hoc ondemand distance vector (AODV) evaluated. Our results demonstrated the usefulness of this modeled platform as it was able to establish that the AODV outperformed WRP in four out of the five of the measured performance metrics. The AODV is thus a better  protocol for MANETs compared to WRP. The same simulation platform could be used test other protocols.Key words: MANET, WRP, AODV, Simulation, GloMoSi

Mutual Authentication in Wimax Security using Diffie Hellman

Network security is becoming an area of concern with the expansion of wireless technology. Many businesses have lost a lot of money as a result of compromised network security. The Worldwide Interoperability for Microwave Access (WiMAX) is one example of 3G technology which is getting popular. Most business establishemnst use WiMAX to network their communication equipments. The popularity of WiMAX and its security vulnarability are the key motivation for this study. Presently, PKM versions of authentication are used to secure WiMAX networks. The PKM authentication methods expose the WiMAX network to third party risks like Man in the Middle attacks, eavesdropping and jamming attacks.  WiMAX is thus vulnerable to network attacks that compromise the radio links between the communicating Subscriber Station (SS) and the serving Base Station (BS). The PKMv1 process involves a one sided authentication. The BS authenticates the SS but the SS has no capacity to authenticate a BS. As a result, a rogue BS can successfully enter the network of a SS without prevention. The rogue BS can then tap all the unencrypted management messages. This constitutes a major security flaw. The Man-In- The-Middle (MITM) attack exploits this weakness in the network by eavesdropping, interception and fabrication of the management messages, resulting in a breach in the reliability of the entire network. In this research, a modification of the Diffie-Hellman (DH) key exchange protocol is used to mitigate the man-in-the middle attack in WiMAX by modeling using the Dev C++ programming language. The DH protocol uses a unique algorithm whose solution must be obtained by both the SS and the BS for communication to be allowed. Both the BS and the SS are given an opportunity to authenticate one another before any communication can proceed. Keywords: Diffie Hellman; Mutual Authentication; Security; WiMAX

Optimization of Base Station Location in 3G Networks using Mads and Fuzzy C-means

Distribution of Base Transceiver Stations (BTS) with an aim of maintaining high Quality of Service and coverage is important to mobile operators. Rapid expansion of telecommunication industry results in stiff competition among service providers which in turn leads to greater focus on quality of services delivered. Increase in number of mobile phone usage has also led to unprecedented network expansion. Coupled to these challenges is rapid change in telecommunication technology from 2G to 4G in a short space of time. A combination of MADS and FUZZY C- MEANS is used to aid in planning Base Station Transceivers (BTS) location efficiently in order to curb capital and maintenance costs. Keywords: BTS placement, MADS, Fuzzy C-Mean

First In First Out (FIFO) And Priority Packet Scheduling Based On Type Of Service (TOS)

Mobile Ad Hoc Networks (MANETs) require prudent resource allocations especially in scheduling mechanisms that manage buffering of packets during waiting time. Various scheduling algorithms may be implemented to govern packet transmission and control packet loss hence managing the Quality of Service (QoS). Such mechanisms include first-in-first-out (FIFO), priority queuing (PQ), and weighted-fair queuing (WFQ). In this research paper, a comparison is made between FIFO and PQ mechanisms in a mixed traffic scenario (HTTP, FTP and VoIP applications). PQ is implemented on the basis of packet Type of Service (ToS), with VoIP data packets being given the upper hand. OPNET simulator is utilized in this paper. The study has been carried out on some issues like: Traffic dropped Traffic Received and packet end to end delay and the simulation results shows that WFQ technique has a better-quality than the other techniques. Keywords: MANETS, QoS, PQ, FIFO, Queuing, ToS, OPNE

Application of adaptive neuro-fuzzy inference system technique in design of rectangular microstrip patch antennas

The recent explosion in information technology and wireless communications has created many opportunities for enhancing the performance of existing signal transmission and processing systems and has provided a strong motivation for developing novel devices and systems. An indispensable element of any wireless communication system is the antenna. microstrip patch antenna (MPA) is well suited for wireless communication due to its light weight, low volume and low profile planar configuration which can be easily conformed to the host surface. In this paper, an adaptive neuro‐fuzzy inference systems (ANFIS) technique is used in design of MPA. This artificial Intelligence (AI) technique is used in determining the parameters used in the design of a rectangular microstrip patch antenna. The ANFIS has the advantages of expert knowledge of fuzzy inference system (FIS) and the learning capability of artificial neural network (ANN). By determining the patch dimensions and the feed point of a rectangular microstrip antenna, this paper shows that ANFIS produces good results that are in agreement with Antenna Magus simulation results.Key words: Artificial intelligence (AI), microstrip patch antennas (MPAs), adaptive neuro‐fuzzy inference system (ANFIS

Leucocyte counts and lymphocyte subsets in relation to pregnancy and HIV infection in Malawian women.

Problem We investigated leukocyte and lymphocyte subsets in HIV-infected or HIV-uninfected, pregnant or non-pregnant Malawian women to explore whether HIV infection and pregnancy may act synergistically to impair cellular immunity. Method of study We recruited 54 pregnant and 48 non-pregnant HIV-uninfected women and 24 pregnant and 20 non-pregnant HIV-infected Malawian women. We compared peripheral blood leukocyte and lymphocyte subsets between women in the four groups. Results Parturient HIV-infected and HIV-uninfected women had more neutrophils (each P<.0001), but fewer lymphocytes (P<.0001; P=.0014) than non-pregnant women. Both groups had fewer total T cells (P<.0001; P=.002) and CD8+ T cells (P<.0001; P=.014) than non-pregnant women. HIV-uninfected parturient women had fewer CD4+ and γδ T cells, B and NK cells (each P<.0001) than non-pregnant women. Lymphocyte subset percentages were not affected by pregnancy. Conclusion Malawian women at parturition have an increased total white cell count due to neutrophilia and an HIV-unrelated pan-lymphopenia

Changes in context, typology and programme outcomes between early and recent periods of sex work among young female sex workers in Mombasa, Kenya: a cross-sectional study

INTRODUCTION: The sex work context and typology change continuously and influence HIV related risk and vulnerability for young female sex workers (YFSW). We sought to describe changes in the context and typology of sex work between the first (early) and past month (recent) of sex work among YFSW to inform HIV prevention programming for sex workers. METHODS: We used data from a cross-sectional survey (April-November 2015), administered using physical location-based sampling to 408 cis-women, aged 14-24 years, who self-identified as sex workers, in Mombasa, Kenya. We collected self-reported data on the early and recent month of sex work. The analysis focused on changes in a) sex work context and typology (defined by setting where sex workers practice sex work) where YFSW operated, b) primary typology of sex work, and c) HIV programme outcomes among YFSW who changed primary typology, within the early and recent month of sex work. We analysed the data using a) SPSS27.0 and excel; b) bivariate analysis and χ2 test; and c) bivariate logistic regression models. RESULTS: Overall, the median age of respondents was 20 years and median duration in sex work was 2 years. Higher proportion of respondents in the recent period managed their clients on their own (98.0% vs. 91.2%), had sex with >5 clients per week (39.3% vs.16.5%); were able to meet > 50% of living expenses through sex work income (46.8% vs. 18.8%); and experienced police violence in the past month (16.4% vs. 6.5%). YFSW reported multiple sex work typology in early and recent periods. Overall, 37.2% reported changing their primary typology. A higher proportion among those who used street/ bus stop typology, experienced police violence, or initiated sex work after 19 years of age in the early period reported a change. There was no difference in HIV programme outcomes among YFSW who changed typology vs. those who did not. CONCLUSIONS: The sex work context changes even in a short duration of two years. Hence, understanding these changes in the early period of sex work can allow for development of tailored strategies that are responsive to the specific needs and vulnerabilities of YFSW

HIV prevalence, testing and treatment among men who have sex with men through engagement in virtual sexual networks in Kenya: a cross-sectional bio-behavioural study

INTRODUCTION: In Kenya, men who have sex with men (MSM) are increasingly using virtual sites, including web-based apps, to meet sex partners. We examined HIV testing, HIV prevalence, awareness of HIV-positive status and linkage to antiretroviral therapy (ART), for HIV-positive MSM who solely met partners via physical sites (PMSM), compared with those who did so in virtual sites (either solely via virtual sites (VMSM), or via both virtual and physical sites (DMSM)). METHODS: We conducted a cross-sectional bio-behavioural survey of 1200 MSM, 15 years and above, in three counties in Kenya between May and July 2019, using random sampling of physical and virtual sites. We classified participants as PMSM, DMSM and VMSM, based on where they met sex partners, and compared the following between groups using chi-square tests: (i) proportion tested; (ii) HIV prevalence and (iii) HIV care continuum among MSM living with HIV. We then performed multivariable logistic regression to measure independent associations between network engagement and HIV status. RESULTS: 177 (14.7%), 768 (64.0%) and 255 (21.2%), of participants were classified as PMSM, DMSM and VMSM respectively. 68.4%, 70.4% and 78.5% of PMSM, DMSM and VMSM, respectively, reported an HIV test in the previous six months. HIV prevalence was 8.5% (PMSM), 15.4% (DMSM) and 26.7% (VMSM), p < 0.001. Among those living with HIV, 46.7% (PMSM), 41.5% (DMSM) and 29.4% (VMSM) were diagnosed and aware of their status; and 40.0%, 35.6% and 26.5% were on antiretroviral treatment. After adjustment for other predictors, MSM engaged in virtual networks remained at a two to threefold higher risk of prevalent HIV: VMSM versus PMSM (adjusted odds ratio 3.88 (95% confidence interval (CI) 1.84 to 8.17) p < 0.001); DMSM versus PMSM (2.00 (95% CI 1.03 to 3.87), p = 0.040). CONCLUSIONS: Engagement in virtual networks is associated with elevated HIV risk, irrespective of individual-level risk factors. Understanding the difference in characteristics among MSM-seeking partners in different sites will help HIV programmes to develop subpopulation-specific interventions