109 research outputs found

    Low-complexity smart antenna methods for third-generation W-CDMA systems

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    A novel downlink beamforming scheme for FDD/SDMA systems

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    When beamforming is employed in the uplink without feedback channel, the beam pattern for the downlink can be generated using the weight used for uplink beamforming. However, this scheme may result in significantly performance degradation in the frequency division duplex (FDD) because of carrier frequency offset between the uplink and downlink. In this paper we propose a novel downlink beamforming algorithm based on least square method with some constraint points which have same gain in the up/downlink beam pattern. From the constraint points, we generate downlink weight and also propose how to choose the constraint points in order to satisfy the desired signal-to-interference power ratio. Simulation results show that the proposed method can sufficiently reduce the interference from other space division multiple access (SDMA) signals, providing interference-free spatial channel

    ASILUM: A platform to evaluate advanced combinations of smart antennas and multi-user detection for UMTS FDD and TDD

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    The purpose of this paper is to present and explain some results of ASILUM, a project included into IST (Information Society Technologies), a research programme of European Community. This project aims to contribute to the technical innovation and policies of the European Community by validating new transceivers concepts to increase the capacity of UMTS (FDD and TDD modes) through new and efficient interference mitigation schemes. These schemes are jointly using smart antennas and multiuser detection. They have been validated through link and system level simulations

    A study of UMTS terrestrial radio access performance

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    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

    Resource Allocation for Multiple-Input and Multiple-Output Interference Networks

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    To meet the exponentially increasing traffic data driven by the rapidly growing mobile subscriptions, both industry and academia are exploring the potential of a new genera- tion (5G) of wireless technologies. An important 5G goal is to achieve high data rate. Small cells with spectrum sharing and multiple-input multiple-output (MIMO) techniques are one of the most promising 5G technologies, since it enables to increase the aggregate data rate by improving the spectral efficiency, nodes density and transmission bandwidth, respectively. However, the increased interference in the densified networks will in return limit the achievable rate performance if not properly managed. The considered setup can be modeled as MIMO interference networks, which can be classified into the K-user MIMO interference channel (IC) and the K-cell MIMO interfering broadcast channel/multiple access channel (MIMO-IBC/IMAC) according to the number of mobile stations (MSs) simultaneously served by each base station (BS). The thesis considers two physical layer (PHY) resource allocation problems that deal with the interference for both models: 1) Pareto boundary computation for the achiev- able rate region in a K-user single-stream MIMO IC and 2) grouping-based interference alignment (GIA) with optimized IA-Cell assignment in a MIMO-IMAC under limited feedback. In each problem, the thesis seeks to provide a deeper understanding of the system and novel mathematical results, along with supporting numerical examples. Some of the main contributions can be summarized as follows. It is an open problem to compute the Pareto boundary of the achievable rate region for a K-user single-stream MIMO IC. The K-user single-stream MIMO IC models multiple transmitter-receiver pairs which operate over the same spectrum simultaneously. Each transmitter and each receiver is equipped with multiple antennas, and a single desired data stream is communicated in each transmitter-receiver link. The individual achievable rates of the K users form a K-dimensional achievable rate region. To find efficient operating points in the achievable rate region, the Pareto boundary computation problem, which can be formulated as a multi-objective optimization problem, needs to be solved. The thesis transforms the multi-objective optimization problem to two single-objective optimization problems–single constraint rate maximization problem and alternating rate profile optimization problem, based on the formulations of the Δ-constraint optimization and the weighted Chebyshev optimization, respectively. The thesis proposes two alternating optimization algorithms to solve both single-objective optimization problems. The convergence of both algorithms is guaranteed. Also, a heuristic initialization scheme is provided for each algorithm to achieve a high-quality solution. By varying the weights in each single-objective optimization problem, numerical results show that both algorithms provide an inner bound very close to the Pareto boundary. Furthermore, the thesis also computes some key points exactly on the Pareto boundary in closed-form. A framework for interference alignment (IA) under limited feedback is proposed for a MIMO-IMAC. The MIMO-IMAC well matches the uplink scenario in cellular system, where multiple cells share their spectrum and operate simultaneously. In each cell, a BS receives the desired signals from multiple MSs within its own cell and each BS and each MS is equipped with multi-antenna. By allowing the inter-cell coordination, the thesis develops a distributed IA framework under limited feedback from three aspects: the GIA, the IA-Cell assignment and dynamic feedback bit allocation (DBA), respec- tively. Firstly, the thesis provides a complete study along with some new improvements of the GIA, which enables to compute the exact IA precoders in closed-form, based on local channel state information at the receiver (CSIR). Secondly, the concept of IA-Cell assignment is introduced and its effect on the achievable rate and degrees of freedom (DoF) performance is analyzed. Two distributed matching approaches and one centralized assignment approach are proposed to find a good IA-Cell assignment in three scenrios with different backhaul overhead. Thirdly, under limited feedback, the thesis derives an upper bound of the residual interference to noise ratio (RINR), formulates and solves a corresponding DBA problem. Finally, numerical results show that the proposed GIA with optimized IA-Cell assignment and the DBA greatly outperforms the traditional GIA algorithm

    Técnicas de equalização e pré-codificação para sistemas MC-CDMA

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    Mestrado em Engenharia EletrĂłnica e TelecomunicaçÔesO nĂșmero de dispositivos com ligaçÔes e aplicaçÔes sem fios estĂĄ a aumentar exponencialmente, causando problemas de interferĂȘncia e diminuindo a capacidade do sistema. Isto desencadeou uma procura por uma eficiĂȘncia espectral superior e, consequentemente, tornou-se necessĂĄrio desenvolver novas arquitecturas celulares que suportem estas novas exigĂȘncias. Coordenação ou cooperação multicelular Ă© uma arquitectura promissora para sistemas celulares sem fios. Esta ajuda a mitigar a interferĂȘncia entre cĂ©lulas, melhorando a equidade e a capacidade do sistema. É, portanto, uma arquitectura jĂĄ em estudo ao abrigo da tecnologia LTE-Advanced sob o conceito de coordenação multiponto (CoMP). Nesta dissertação, considerĂĄmos um sistema coordenado MC-CDMA com prĂ©-codificação e equalização iterativas. Uma das tĂ©cnicas mais eficientes de prĂ©-codificação Ă© o alinhamento de interferĂȘncias (IA). Este Ă© um conceito relativamente novo que permite aumentar a capacidade do sistema em canais de elevada interferĂȘncia. Sabe-se que, para os sistemas MC-CDMA, os equalizadores lineares convencionais nĂŁo sĂŁo os mais eficientes, devido Ă  interferĂȘncia residual entre portadoras (ICI). No entanto, a equalização iterativa no domĂ­nio da frequĂȘncia (FDE) foi identificada como sendo uma das tĂ©cnicas mais eficientes para lidar com ICI e explorar a diversidade oferecida pelos sistemas MIMO MC-CDMA. Esta tĂ©cnica Ă© baseada no conceito Iterative Block Decision Feedback Equalization (IB-DFE). Nesta dissertação, Ă© proposto um sistema MC-CDMA que une a prĂ©-codificação iterativa do alinhamento de interferĂȘncias no transmissor ao equalizador baseado no IB-DFE, com cancelamento sucessivo de interferĂȘncias (SIC) no receptor. Este Ă© construĂ­do por dois blocos: um filtro linear, que mitiga a interferĂȘncia inter-utilizador, seguido por um bloco iterativo no domĂ­nio da frequĂȘncia, que separa eficientemente os fluxos de dados espaciais na presença de interferĂȘncia residual inter-utilizador alinhada. Este esquema permite atingir o nĂșmero mĂĄximo de graus de liberdade e permite simultaneamente um ganho Ăłptimo de diversidade espacial. O desempenho deste esquema estĂĄ perto do filtro adaptado- Matched Filter Bound (MFB).The number of devices with wireless connections and applications is increasing exponentially, causing interference problems and reducing the system’s capacity gain. This initiated a search for a higher spectral efficiency and therefore it became necessary to develop new cellular architectures that support these new requirements. Multicell cooperation or coordination is a promising architecture for cellular wireless systems to mitigate intercell interference, improving system fairness and increasing capacity, and thus is already under study in LTE-Advanced under the coordinated multipoint (CoMP) concept. In this thesis, efficient iterative precoding and equalization is considered for coordinated MC-CDMA based systems. One of the most efficient precoding techniques is interference alignment (IA), which is a relatively new concept that allows high capacity gains in interfering channels. It is well known that for MC-CDMA systems standard linear equalizers are not the most efficient due to residual inter carrier interference (ICI). However, iterative frequency-domain equalization (FDE) has been identified as one of the most efficient technique to deal with ICI and exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems, namely the one based on Iterative Block Decision Feedback Equalization (IB-DFE) concept. In this thesis, it is proposed a MC-CDMA system that joins iterative IA precoding at the transmitter with IB-DFE successive interference cancellation (SIC) based receiver structure. The receiver is implemented in two steps: a linear filter, which mitigates the inter-user aligned interference, followed by an iterative frequency-domain receiver, which efficiently separates the spatial streams in the presence of residual inter-user aligned interference. This scheme provides the maximum degrees of freedom (DoF) and allows almost the optimum space-diversity gain. The scheme performance is close to the matched filter bound (MFB)

    Performance analysis of multi-antenna and multi-user methods for 3G and beyond

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    Performance of cellular networks has become an issue with forecasted growing public demand for medium and high data rate services. Motivated by these expectations multi-antenna techniques such as transmit diversity (TD), channel-aware scheduling and multiple-input multiple-output (MIMO) transceivers have received a lot of enthusiasm within wireless communications community. We first focus on closed-loop (CL) TD and introduce extended mode 1 and 2 (e-mode 1 and 2) algorithms that are designed based on universal terrestrial radio access (UTRA) frequency division duplex (FDD) CL mode 1 and 2. We derive analytical performance results for e-mode 1 and 2 in terms of signal to noise ratio (SNR) gain, link capacity and bit error probability (BEP). We also consider the effect of feedback errors to the performance of closed-loop system. In the analysis of channel-aware scheduling we focus on on-off scheduling (OOS) where user's feedback consists of only a single bit. Performance results in both downlink and uplink clearly indicate that most of the achievable gain from channel-aware scheduling can be obtained with very scarce channel state information (CSI). Results also show that the design of feedback channel is of great importance because feedback errors may seriously degrade the system performance. The third topic of the thesis concentrates on MIMO techniques that can be implemented in UTRA FDD uplink without major revisions to the current air interface. We show that the UTRA FDD uplink coverage and capacity performance can be boosted by single-input multiple-output (SIMO) and MIMO transceivers. The information MIMO employing parallel multiplexing instead of transmit diversity shows its potential when extremely high user data rates are needed.Solukkoverkkojen suorituskyky on noussut tÀrkeÀÀn rooliin nopeiden datapalveluiden kasvuennusteiden myötÀ. NÀiden kasvuodotusten perusteella moniantennitekniikat kuten lÀhetysdiversiteetti, kanavan huomioon ottava lÀhetyksen aikataulutus sekÀ useaa samanaikaista datavirtaa tukevat lÀhetinvastaanotinmenetelmÀt ovat saaneet osakseen paljon kiinnostusta langattoman tietoliikenteen tutkijayhteisössÀ. Tutkimuksessa keskitytÀÀn aluksi suljettua sÀÀtöÀ kÀyttÀviin lÀhetysdiversiteettimenetelmiin, missÀ yhteydessÀ esitellÀÀn laajennetut moodien 1 ja 2 algoritmit, jotka on aiemmin kehitetty kolmannen sukupolven WCDMA jÀrjestelmÀn suljetun sÀÀdön moodien 1 ja 2 pohjalta. Laajennetuille moodien 1 ja 2 algoritmeille johdetaan analyyttisiÀ suorituskykytuloksia kÀyttÀen mittarina signaali-kohinasuhteen parannusta, linkin kapasiteettia sekÀ bittivirheiden todennÀköisyyttÀ. Myös sÀÀtövirheiden vaikutusta jÀrjestelmÀn suorituskykyyn tarkastellaan. LÀhetyksen aikataulutuksen analyysi painottuu kytkettyyn aikataulutukseen, missÀ kÀyttÀjÀn sÀÀtöinformaatio sisÀltyy yhteen bittiin. SekÀ ylÀ- ettÀ alalinkin suorituskykytulokset osoittavat selvÀsti, ettÀ suurin osa mahdollisesta parannuksesta voidaan saavuttaa hyvin karkeaan kanavatilan informaatioon perustuen. Tulokset osoittavat myös, ettÀ sÀÀtökanavan suunnittelu on tÀrkeÀÀ, koska sÀÀtövirheet voivat vakavasti heikentÀÀ jÀrjestelmÀn suorituskykyÀ. Kolmannessa aihealueessa keskitytÀÀn moniantennitekniikoihin, jotka voidaan toteuttaa WCDMA jÀrjestelmÀn ylÀlinkissÀ ilman perustavanlaatuisia muutoksia nykyiseen ilmarajapintaan. Tutkimuksessa osoitetaan, ettÀ ylÀlinkin peittoa ja kapasiteettia voidaan parantaa tutkituilla moniantennitekniikoilla olipa lÀhettimessÀ yksi tai useampia antenneja. MenetelmÀ, jossa informaatio jaetaan useisiin rinnakkaisiin datavirtoihin sen sijaan ettÀ kÀytettÀisiin vain yhtÀ datavirtaa, osoittautuu erityisen lupaavaksi kun tarvitaan hyvin nopeita tiedonsiirtoyhteyksiÀ.reviewe
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