High power laser pulses can be a threat to sensors, including the human eye. Traditionally this threat has been alleviated by colour filters that blocks radiation in chosen wavelength ranges. Colour filters’ main drawback is that they block radiation regardless of it being useful or damaging, information is removed for wavelengths at which the filter protect. Protecting the entire wavelength range of a sensor would block or strongly attenuate the radiation needed for the operation of the sensor. Sol-gel glasses highly doped with Pt-Acetylide chromophores have previously shown high optical quality in combination with efficient optical power limiting through reverse saturable absorption1. These filters will transmit visible light unless the light fluence is above a certain threshold. A key design consideration of laser protection filters is linear absorption in relation to threshold level. By increasing chromophore concentration the threshold is lowered at the expense of higher linear absorption. This means that the user’s view is degraded through the filter. Adding small amounts of gold nanoparticles to the glasses resulted in an increase in optical power limiting performance. The optimal concentration of gold nanoparticles corresponded to a mean particle distance of several micrometers. The work in this licentiate thesis is about the characterization and explanation of this effect. The glasses investigated in this work were MTEOS Sol-Gel glasses doped with either only gold nanoparticles of varying shape and concentration, 50mM of PE2-CH2OH codoped with gold nanoparticles or 50mM of PE3-CH2OH codoped with gold nanoparticles. The glasses only doped with gold nanoparticles showed high optical power limiting performance at 532nm laser wavelength, but no optical power limiting at the fluences tested at 600nm. The PE2-CH2OH glasses codoped with gold nanoparticles showed an enhancement of optical power limiting at 600nm for the low gold nanoparticle concentration glasses. The enhancement was weakened or not present for higher concentrations. A similar enhancement above noise level for the PE3-CH2OH glasses was not found. A population model is used to give a qualitative explanation of the findings. The improvement in optical power limiting performance for the PE2-CH2OH glasses is explained by the gold nanoparticles helping to more quickly populate the highly absorbing triplet state during the rising edge of the laser pulse by enhancing two-photon absorption. The lack of any marked enhancement for the PE3-CH2OH glasses is explained by the PE3-CH2OH chromophore already being of sufficiently high performance to quickly populate the highly absorbing triplet state during the rising edge of the laser pulse. Further work is necessary to validate this model against other chromophores and improving its quantitative predictive power.

In 5G systems, two radio air interfaces, evolved LTE and New Radio (NR), will coexist. By using millimeter waves, NR will provide high throughputs, but the higher frequencies will also lead to increased losses and a worse coverage. Multi-connectivity is therefore envisioned as a way to tackle these effects by connecting to multiple base stations simultaneously, allowing users to benefit from both air interfaces’ advantages. In this thesis, we investigate how multi-connectivity can be used efficiently in ultra-dense networks, a new paradigm in which the number of access nodes exceeds the number of users within the network. A framework for secondary cell association is presented and an energy efficiency’s condition is proposed. Upper and lower bounds of the network’s energy efficiency are analytically expressed. Algorithms for secondary cell selection are designed and evaluated through simulations. Multi-connectivity showed an improvement of up to 50% in reliability and and an increase of up to 20% in energy efficiency.

<p>Three of the most important factors with regards to wireless multi-hop networks, namely reachability, energy consumption and network stability are considered in our transmitter macrodiversity supported broadcasting routing algorithms. Broadcasting applications are not only used to send routing table, queries, programming logic, any specific request etc. to all the nodes from access point but are also capable of playing a vital role in wireless TV distributions and visual sensor networks. All the algorithms are simulated in the MATLAB environment in which the nodes are random and are battery driven on a multi-hop randomized topology. Four new single frequency network (SFN) based algorithms (SFN-A, SFN-B, SFN-C and SFN-D) are formed in order to work over multi-hopping and where three of the algorithms SFN-A, SFN-B and SFN-D bear more or less the same amount of reachability. These three algorithms are able to reach more than 90% of reachability in only Tx power -8dBm whereas non-SFN requires -4dBm and SFN-C requires -2dBm and, in addition can achieve a maximum of 29 percentage points more reachability than the non-SFN algorithm. However, the best algorithm SFN-D consumes a maximum of 58.76% less energy than the SFN-A and a maximum of 14.28% less energy than the SFN-B. The SFN-D algorithm achieves a maximum 3.43 dB diversity gain together with the maximum 37.33% energy consumption gain in comparison to the non-SFN algorithm.</p>

<p>Unlicensed Mobile Access (UMA) provides transparent access to 2G and 3G networks for Mobile Stations over the unlicensed radio interface. Unlicensed radio tehnologies such as Bluetooth or WLAN technology connects the Mobile Station to the fixed IP network of the home or office and delivers high bandwith to the Mobile Station.</p><p>The purpose of this report is to examine if subscribers can feel as secure using UMA as they do when using any of the alternetive mobile technologies that UMA supports. The security evaluation is performed by first investigating the current security level of GSM, GPRS and UMTS and then compares them to the security mechanisms of UMA.</p><p>This evaluation noticed two distinct flaws in UMA that could compromise security. The conclusion is that these flaws do not have a major inpact and UMA does provide a general higher level of security than the 2G and 3G counterparts.</p>

<p>The GSM network technology has been developed and improved during several years which have led to an increased complexity. The complexity results in more network parameters and together with different scenarios and situations they form a complex set of configurations. The definition of the network parameters is generally a manual process using static values during test execution. This practice can be costly, difficult and laborious and as the network complexity continues to increase, this problem will continue to grow.This thesis presents an implementation of an automated performance optimization algorithm that utilizes genetic algorithms for optimizing the network parameters. The implementation has been used for proving that the concept of automated optimization is working and most of the work has been carried out in order to use it in practice. The implementation has been applied to the Link Quality Control algorithm and the Improved ACK/NACK feature, which is an apart of GSM EDGE Evolution.</p> / <p>GSM-nätsteknologin har utvecklats och förbättrats under lång tid, vilket har lett till en ökad komplexitet. Denna ökade komplexitet har resulterat i fler nätverksparameterar, tillstånd och standarder. Tillsammans utgör de en komplex uppsättning av olika konfigurationer. Dessa nätverksparameterar har hittills huvudsakligen bestämts med hjälp av en manuell optimeringsprocess. Detta tillvägagångssätt är både dyrt, svårt och tidskrävande och allt eftersom komplexiteten av GSM-näten ökar kommer problemet att bli större.Detta examensarbete presenterar en implementering av en algoritm för automatiserad optimering av prestanda som huvudsakligen använder sig av genetiska algoritmer för att optimera värdet av nätverksparametrarna. Implementeringen har använts för att påvisa att konceptet med en automatiserad optimering fungerar och det mesta av arbetet har utförts för att kunna använda detta i praktiken. Implementeringen har tillämpats på Link Quality Control-algoritmen och Improved ACK/NACK-funktionaliteten, vilket är en del av GSM EDGE Evolution.</p>

<p>New high quality mobile telecommunication services are offered everyday and the demand for higher data rates is continuously increasing. To maximize the uplink throughput in HSPA when transmission is propagated through a dispersive channel causing self-interference, equalizers are used. One interesting solution, where the equalizer and decoder exchange information in an iterative way, for improving the equalizer performance is Turbo equalization.</p><p>In this thesis a literature survey has been performed on Turbo equalization methods and a chosen method has been implemented for the uplink HSPA standard to evaluate the performance in heavily dispersive channels. The selected algorithm has been adapted for multiple receiving antennas, oversampled processing and HARQ retransmissions. The results derived from the computer based link simulations show that the implemented algorithm provide a gain of approximately 0.5 dB when performing up to 7 Turbo equalization iterations. Gains up to 1 dB have been obtained by disabling power control, not using retransmission combining and utilizing a single receiver antenna. The algorithm has also been evaluated considering alternative dispersive channels, Log-MAP decoding, different code rates, number of Turbo equalization iterations and number of Turbo decoding iterations.</p><p>The simulation results do not motivate a real implementation of the chosen algorithm considering the increased computational complexity and small gain achieved in a full featured receiver system. Further studies are needed before concluding the HSPA uplink Turbo equalization approach.</p>

<p>The wide spread use of IEEE Wireless LAN 802.11 in battery operated mobile devices introduced the need of power consumption optimization while meeting Quality-of-Service (QoS) requirements of applications connected through the wireless network. The IEEE 802.11 standard specifies a baseline power saving mechanism, hereafter referred to as standard Power Save Mode (PSM), and the IEEE 802.11e standard specifies the Automatic Power Save Delivery (APSD) enhancement which provides support for real-time applications with QoS requirements. The latest amendment to the WLAN 802.11 standard is the IEEE 802.11n standard which enables the use of much higher data rates by including enhancements in the Physical and MAC Layer. In this thesis, different 802.11n MAC power saving and QoS optimization possibilities are analyzed comparing against existing power saving mechanisms.</p><p>Initially, the performance of the existing power saving mechanisms PSM and Unscheduled-APSD (UAPSD) are evaluated using the 802.11n process model in the OPNET simulator and the impact of frame aggregation feature introduced in the MAC layer of 802.11n was analyzed on these power saving mechanisms. From the performance analysis it can be concluded that the frame aggregation will be efficient under congested network conditions. When the network congestion level increases, the signaling load in UAPSD saturates the channel capacity and hence results in poor performance compared to PSM. Since PSM cannot guarantee the minimum QoS requirements for delay sensitive applications, a better mechanism for performance enhancement of UAPSD under dynamic network conditions is proposed.</p><p>The functionality and performance of the proposed algorithm is evaluated under different network conditions and using different contention settings. From the performance results it can be concluded that, by using the proposed algorithm the congestion level in the network is reduced dynamically thereby providing a better power saving and QoS by utilizing the frame aggregation feature efficiently.</p>

<p>The new mobile standard Long Term Evolution delivers high data rates, small delay and a more efficiently utilized RF spectrum. A solution to maintain this performance in user dense areas or areas with bad reception is the deployment of so-called femtocells. Femtocells are small base stations that are deployed indoors and share the RF spectrum with the whole mobile network. The idea is that femtocells will increase mobile operators network coverage and capacity while it at the same time increase users data throughput. There are several challenges with femtocells, both technical and economical ones. The most debated issues is how femtocells should schedule users while operating in an environment where other femtocells and base stations are interfering. In this work we developed a simulation tool to simulate the scheduling interaction between femtocells and base stationsin order to show the performance of radio resource schedulers. This rapport also aims to evaluate an approach to a femtocell scheduler to solve this issue in a satisfying way. The report gives a description of the structure of the implemented simulation tool together with some reflections on how future designs of similar or more complex simulation environments could be done.</p>

<p>The demand for wireless communications is increasing every year, but the available resources are not increasing at the same rate. It is very important that the radio resources are used in an efficient way allowing the networks to support as many users as possible. The three types of networks studied in this thesis are frequency hopping GSM networks, ad hoc multi-hop networks and WCDMA networks.</p><p>One type of network with a promising future is ad hoc multi-hop networks. The users in this kind of networks communicate with each other without base stations. Instead the signal can be sent directly between two users, or relayed over one or several other users before the final destination is reached. Resources are shared by letting the users transmit in time slots. The problem studied is to minimize the number of time slots used, when the users broadcast. Two different optimization models are developed for assigning time slots to the users. A reduction of the number of time slots means a shorter delay for a user to transmit next time.</p><p>The rapid growth of the number of subscribers in cellular networks requires efficient cell planning methods. The trend of smaller cell sizes in urban areas for higher capacity raise the need for more efficient spectrum usage. Since the infrastructure of a second generation cellular system, such as GSM, already exists, and the available bandwidth of an operator is limited, frequency planning methods are of utmost importance. Because of the limited bandwidth in a GSM network, the frequencies must be reused. When planning a GSM network the frequencies can not be reused too tightly due to interference. The frequency planning problem in a GSM network is a very complex task. In this thesis an optimization model for frequency assignment in a frequency hopping GSM network is developed. The problem is to assign frequencies to the cells in the network, while keeping the interference to a minimum. Different meta heuristic methods such as tabu search and simulated annealing are used to solve the problem. The results show that the interference levels can be reduced to allow a capacity increase.</p><p>The demand for sending more information over the wireless communication systems requires more bandwidth. Voice communication was handled well by the second generation cellular systems. The third generation of mobile telecommunication systems will handle data transmissions in a greater extent. The last type of network considered in the thesis is a WCDMA cellular network. The aim is to schedule the transmission of packet data from the base station to the users. Scheduling models that maximize the utility are developed for both the downlink shared channel and the high speed downlink shared channel.</p>

<p>Cell Broadcast (CB) is a possible technical realisation of a global emergency alert system. It is a technique used for sending short text messages to all mobile stations (MSs) in a defined geographical area. An potential effect of using CB is the increase in battery consumption of the MS due to the fact that an extra channel has to be used to make the service available even when the network is otherwise congested. Another part of the service which leads to a potential problem is making CB messages available in different languages. Investigating these problems is the objective of this thesis and the studies it includes. During the first part of the thesis, we measured the battery consumption of MSs in different modes of operation in order to analyse how CB affects the amount of current drained. The tests showed that battery consumption increased only slightly when CB messages were being received at the MS. Although some of the results can be, and are, discussed, we believe that CB would have a small effect on the power consumption of an MS, particularly in a context where it would be used for emergency warning messages only. This mentioned, it would however be wishful to confirm the conclusions further through the realisation of long-term testing. The second part of the thesis deals with the investigation of the MSs’ support for CB messages with different coding schemes. Based on the investigation’s result, we have come to the conclusion that in the long term the usage of different coding schemes on the same channel is preferred. However, the usage of one, global, emergency channel is hard to realise since that requires a standardisation between all countries. In our opinion this may be achieved first in the long run and until then, the usage of separate channels seems to be necessary.</p>