Design and performance evaluation of RAKE finger management schemes in the soft handover region

We propose and analyze new finger assignment/management techniques that are applicable for RAKE receivers when they operate in the soft handover region. Two main criteria are considered: minimum use of additional network resources and minimum call drops. For the schemes minimizing the use of network resources, basic principles are to use the network resources only if necessary while minimum call drop schemes rely on balancing or distributing the signal strength/paths among as many base stations as possible. The analyses of these schemes require us to consider joint microscopic/macroscopic diversity techniques which have seldom been considered before and as such, we tackle the statistics of several correlated generalized selection combining output signal-to-noise ratios in order to obtain closed-form expressions for the statistics of interest. To provide a general comprehensive framework for the assessment of the proposed schemes, we investigate not only the complexity in terms of the average number of required path estimations/comparisons, the average number of combined paths, and the soft handover overhead but also the error performance of the proposed schemes over independent and identically distributed fading channels. We also examine via computer simulations the effect of path unbalance/correlation as well as outdated/imperfect channel estimations. We show through numerical exam ples that the proposed schemes which are designed for the minimum use of network resources can save a certain amount of complexity load and soft handover overhead with a very slight performance loss compared to the conventional generalized selection combining-based diversity systems. For the minimum call drop schemes, by accurately quantifying the average error rate, we show that in comparison to the conventional schemes, the proposed distributed schemes offer the better error performance when there is a considerable chance of loosing the signals from one of the active base stations

A study of UMTS terrestrial radio access performance

This thesis considers the performance evaluation of third generation radio networks, in particular UMTS Terrestrial Radio Access (UTRA). First, the performance evaluation methods are presented. The typical capacity of UTRA is estimated using those methods and a few solutions are evaluated to improve the capacity and coverage. The thesis further studies the effect of base station synchronization on the performance of UTRA time division duplex mode. The performance evaluation is based on the combination of theoretical calculations, link and system level simulations, and laboratory and field measurements. It is shown that these different evaluation methods give similar results and – when combined together – they can be used for the radio network development purposes. The simulation results indicate that the typical WCDMA, i.e. UTRA frequency division duplex mode, macro cell capacity is between 600 and 1000 kbps per sector per 5 MHz. The capacity is sensitive to the environment and to the transceiver performance. The results further show that user bit rates up to 2 Mbps can be provided locally for packet data with the basic Rake receiver, but not for full coverage circuit switched connections in macro cells. The following performance enhancement techniques are evaluated in this thesis: soft combining of packet retransmissions, base station multiuser detection and 4-branch base station receiver diversity. The link level simulations show that soft combining can provide a gain up to 2.0 dB, which can be used to increase the capacity up to 60 %. The performance of base station multiuser detection is evaluated with link and system level simulations. It is shown that the studied sub-optimal multiuser detector is able to remove 60-70 % of the intra-cell interference. That gain can be utilized to improve the uplink capacity by 50-100 % or the coverage by 1-2 dB. The performance of 4-branch antenna diversity is evaluated in the simulations and in the field measurements. The results show that the average coverage gain of 4-branch diversity with two separate cross-polarized antennas is 3 dB compared to 2-branch diversity with one cross-polarized antenna. The synchronization requirements of UTRA time division duplex base stations are studied with system simulations. The results show that synchronization is a key requirement for time division duplex operation, especially for the uplink performance. The study indicates that co-location of different operators' base stations is feasible in time division duplex operation only if the two networks are synchronized and if an identical split between uplink and downlink is used.reviewe

Performance of antenna selection schemes for massive multiple-input multiple-output systems under Non-orthogonal multiple access cooperative communication

46-50Non-orthogonal multiple access (NOMA) has emerged as a promising technology for 5G systems. The most important characteristic of NOMA is that other users' messages is available to the users with better channel conditions. In this work, a modified antenna selection scheme called Double threshold generalized selection combining (DT-GSC) to save power in receivers used for massive multiple-input multiple-output (MIMO) applications are proposed. The diversity combiner selects the paths above two threshold values set at the combiner, the input and the combiner's output. These threshold values are selected based on the practical communication scenario. The average number of combined branches and estimated path are shown mathematically. The bit error performance of DT-GSC and maximal ratio combiner (MRC) are plotted. Through numerical examples it is evident that the new combining technique performs better compared to the existing ones. This combining technique is beneficial in the massive MIMO base station and user equipment with multiple antennas or cooperative communication set up with users employing the MRC scheme. Simulation results are presented to demonstrate the performance of the proposed technique

Optimal reception of 64 Quadrature Amplitude Modulation in High-Speed Downlink Packet Access

HSDPA on vuonna 2002 UMTS-verkkoihin lisätty ominaisuus. Sen avulla laskevalla siirtotiellä mobiililaitteiden huippunopeudeksi saadaan 14.4 megabittiä sekunnissa. Vuonna 2007 standardoitiin uusia HSDPA-ominaisuuksia, niiden mukana uusi modulaatiotyyppi 64-QAM. 64-QAM:in avulla suurin siirtonopeus saadaan nostettua 21.6:n megabittiin sekunnissa. Sekä lähettimiä että vastaanottimia on päivitettävä uuden modulaatiotyypin tukemiseksi. Vastaanottopäässä signaalin amplitudi täytyy ensin estimoida tarkasti jotta signaali voidaan vastaanottaa oikein. Signaali pitää vielä tämän jälkeen demoduloida riittävällä tarkkuudella. Samankaltaisia algoritmeja on käytetty jo vanhemmissa HSDPA-versioissa, mutta 64-QAM on huomattavasti herkempi virheille. Tässä työssä amplitudiestimointia ja demodulointia varten testattiin kolmea eri algoritmivaihtoehtoa. Algoritmien vertailuun käytettiin fyysisen kerroksen HSDPA-simulaattoria, jossa käytettiin standardin mukaisia realistisia parametreja. Lopputuloksena yksiselitteisesti parasta tapaa estimoida amplitudia ei löytynyt, mutta kaksi ehdokkaista osoitti hyviä ominaisuuksia. Parhaaksi demodulointialgoritmiksi osoittautui yksinkertaistettu versio optimaalisesta MAP-ilmaisimesta, joka hoitaa demoduloinnin yksiulotteisesti.High-speed downlink packet access (HSDPA) is a feature introduced to the universal mobile telecommunications system (UMTS) in 2002. It allows data rates of up to 14.4 Mbps in the downlink. In 2007 new features were standardized to HSDPA, including 64 Quadrature Amplitude Modulation (64-QAM). 64-QAM allows more data to be transmitted on the same bandwidth, increasing the HSDPA peak data rate to 21.6 Mbps. Transmitters and receivers must be updated with new algorithms to support this new modulation type. On the terminal side the amplitude of the signal must first be precisely estimated so that it can be demodulated correctly. Then a demodulation algorithm with good enough accuracy must be applied. Similar algorithms were already used with older HSDPA versions, but 64-QAM is much more sensitive to errors. In this thesis, three amplitude estimation and three demodulation algorithm candidates were considered. A physical layer HSDPA simulator with realistic parameters was used to compare the algorithms. There was no clear winner when selecting the best way to estimate the amplitude, but two of the algorithm candidates proved to be better than the third. The best demodulation algorithm for practical applications turned out to be a simplified MAP optimum detector that models the demodulation as a one-dimensional problem

Wireless communications in the new millennium and third generation wireless networks

At the end of the 20 century, and at the beginning of this one, wireless communications are making large advances. The new technologies are on the way to provide a high-speed, high-quality information exchange between handheld terminals, and information repositories. The so called 2,5 generation networks, using the techniques like the HSCSD1, GPRS2, EDGE3, and the 3r generation wireless systems will help the wireless world to reach those goals. In this thesis I will start from the first and second-generation wireless networks, and then look into the 2,5 generation and 3rd generation wireless communications more in detail. The latest advances in the wireless world are the main focus of this paper although a short history of wireless communications is also given. The various aspects related to 3rd generation systems will be explored in this thesis, for example the air interface discussions, its time scale, its elements like the mobile equipment, software and security, USLM4, services that will be offered, etc. In addition, the technical factors and key technologies that are likely to shape the wireless network environment of the future will be explored. This part is expected to help us to see beyond the 3rd generation