136 research outputs found
Loosely synchronized spreading code aided network performance of quasi-synchronous UTRA-like TDD/CDMA systems
In this paper we investigate the achievable capacity of a UTRA-like Time Division Duplex (TDD) Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes. The family of operational CDMA systems is interference limited, suffering from Inter-Symbol-Interference (ISI), since the orthogonality of the spreading sequences is destroyed by the frequency selective channel. They also suffer from Multiple-Access-Interference (MAI) owing to the non-zero cross-correlations of the spreading codes. By contrast, the family of LS codes exhibits a so-called Interference Free Window (IFW), where both the auto-correlation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both ISI and MAI in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. This contribution studies the achievable network performance in comparison to that of a UTRA-like TDD/CDMA system using Orthogonal Vari- MSO able Rate Spreading Factor (OVSF) codes
Genetically Enhanced Performance of a UTRA-like Time-Division Duplex CDMA Network
In this contribution a Dynamic Channel Allocation (DCA) algorithm is developed, which minimizes the amount of Multi-User Interference (MUI) experienced at the Base Stations (BSs) by employing Genetic Algorithms (GAs). A GA is utilized for finding a suboptimum, but highly beneficial Uplink (UL) or Downlink (DL) Timeslot (TS) allocation for improving the achievable performance of the third generation UTRA systemâs Time Division Duplex (TDD) mode. It is demonstrated that a GA-assisted UL/DL timeslot scheduling scheme may avoid the severe BS to BS inter-cell interference potentially inflicted by the UTRA TDD CDMA air interface owing to allowing all TSs to be used both in the UL and D
TĂ©cnicas de processamento com mĂșltiplas antenas para o sistema LTE
Mestrado em Engenharia ElectrĂłnica e TelecomunicaçÔesPerformance, mobilidade e partilha podem ser consideras como as trĂȘs
palavras-chave nas comunicaçÔes móveis de hoje em dia. Uma das necessidades
fundamentais do ser humano é a partilha de experiencias e informação.
Com a evolução ao nĂvel do hardware mĂłvel, a crescente popularidade de
smartphones, tablets e outros dispositivos moveis, fez com que a exigĂȘncia
em termos de capacidade e taxa de transferĂȘncia por parte das redes mĂłveis
nĂŁo parasse de crescer.
As limitaçÔes das redes 3G fizeram com que não conseguissem corresponder
a tais exigĂȘncias e como tal, a transição para uma tecnologia mais robusta e
eficiente passou a ser inevitåvel. A resposta escolhida como solução a longo
prazo é a rede designada por LTE, desenvolvida pela organização 3GPP é
assumido que serå a rede de telecomunicaçÔes predominante no futuro. As
vantagens mais sonantes sĂŁo, naturalmente, elevadas taxas de transmissĂŁo,
maior eficiĂȘncia espectral, redução da latĂȘncia e de custos de operação. As
principais tecnologias em que o LTE se baseia, sĂŁo o OFDM e sua variante
para mĂșltiplo acesso, OFDMA, usado para o downlink e o SC-FDMA para
o uplink. AlĂ©m disso, usa sistemas com mĂșltiplas antenas para impulsionar
a eficiĂȘncia espectral. Apesar de jĂĄ implementado em alguns paĂses por
diversas operadoras, constantes pesquisas continuam a ser realizadas com
o intuito de melhorar a sua performance.
Nesta dissertação Ă© proposto um esquema duplo de codificação na frequĂȘncia
e no espaço (D-SFBC) para um cenårio baseado em OFDM com 4
antenas de transmissão e duas antenas de recepção (4 à 2 D-SFBC) para
o downlink. No cenĂĄrio considerado, 4 sĂmbolos de dados sĂŁo transmitidos
utilizando unicamente 2 sub-portadoras, fazendo com que, este sistema seja
limitado pela interferĂȘncia. Para de forma eficiente descodificar os sĂmbolos
de dados transmitidos, foi desenvolvido um equalizador iterativo no domĂnio
da frequĂȘncia. Duas abordagens sĂŁo consideradas: cancelamento da interferĂȘncia
em paralelo (PIC) e sucessivo cancelamento de interferĂȘncia (SIC).
Uma vez que apenas 2 sub-portadoras sĂŁo usadas para transmitir quatro
sĂmbolos de dados em paralelo, o esquema desenvolvido duplica a taxa de
dados quando comparado com o esquema 2 Ă 2 SFBC, especificado no
standard do LTE.
Os esquemas desenvolvidos foram avaliados sob as especificaçÔes para LTE
e usando codificação de canal. Os resultados mostram que os esquemas
implementados neste trabalho utilizando um equalizador iterativo supera os
convencionais equalizadores lineares na eliminação da interferĂȘncia adicional
introduzida, em apenas 2 ou 3 iteraçÔes.Performance, mobility and sharing can be assumed as the three keywords
in the mobile communications nowadays. One of the fundamental needs of
human beings is to share experiences and information. With the evolution of
mobile hardware level, the growing popularity of smartphones, tablets and
other mobile devices, has made that the demand in terms of capacity and
throughput by mobile networks did not stop growing.
Thus, the limitations of 3G stops it of being the answer of such demand, and
a transition to a powerful technology has become unavoidable. The answer
chosen is LTE, developed by the 3GPP organization is assumed to be the
predominant telecommunications network in the future. The most relevant
advantages are high transmission rates, higher spectral efficiency, reducing
latency and operating costs. The key technologies in which LTE is based,
are OFDM and its variant schemes for multiple access, OFDMA, used for
downlink, and SC-FDMA for the uplink. It also uses multiple antennas systems
in order to improve spectral efficiency. Although already implemented
in some countries by several operators, continuous research is conducted in
order to improve their performance.
In this dissertation it is proposed a double space-frequency block coding
(D-SFBC) scheme for an OFDM based scenario with 4 transmit antennas
and 2 receive antennas (4Ă2 D-SFBC) for the downlink. In the considered
scenario, 4 data symbols are transmitted by using only 2 subcarriers and thus
the system is interference limited. To efficiently decode the transmitted data
symbols an iterative equalizer designed in frequency domain is developed.
Two approaches are considered: parallel interference cancellation (PIC) and
successive interference cancellation (SIC). Since only 2 subcarriers are used
to transmit 4 data symbols in parallel the developed scheme achieve the
double data rate when compared with the 2Ă2 SFBC, specified in the LTE
standard.
The developed schemes were evaluated under the main LTE specifications
and using channel coding. The results have show that the schemes implemented
in this work using an interactive equalizer outperforms the conventional
linear equalizers in the interference removal, just by using 2 or 3
iterations
Linear space-time modulation in multiple-antenna channels
This thesis develops linear spaceâtime modulation techniques for (multi-antenna) multi-input multi-output (MIMO) and multiple-input single-output (MISO) wireless channels. Transmission methods tailored for such channels have recently emerged in a number of current and upcoming standards, in particular in 3G and "beyond 3G" wireless systems. Here, these transmission concepts are approached primarily from a signal processing perspective.
The introduction part of the thesis describes the transmit diversity concepts included in the WCDMA and cdma2000 standards or standard discussions, as well as promising new transmission methods for MIMO and MISO channels, crucial for future high data-rate systems. A number of techniques developed herein have been adopted in the 3G standards, or are currently being proposed for such standards, with the target of improving data rates, signal quality, capacity or system flexibility.
The thesis adopts a model involving matrix-valued modulation alphabets, with different dimensions usually defined over space and time. The symbol matrix is formed as a linear combination of symbols, and the space-dimension is realized by using multiple transmit and receive antennas. Many of the transceiver concepts and modulation methods developed herein provide both spatial multiplexing gain and diversity gain. For example, full-diversity full-rate schemes are proposed where the symbol rate equals the number of transmit antennas. The modulation methods are developed for open-loop transmission. Moreover, the thesis proposes related closed-loop transmission methods, where spaceâtime modulation is combined either with automatic retransmission or multiuser scheduling.reviewe
Interference analysis of and dynamic channel assignment algorithms in TDâCDMA/TDD systems
The radio frequency spectrum for commercial wireless communications has become an expensive
commodity. Consequently, radio access techniques are required which enable the efficient
exploitation of these resources. This, however, is a difficult task due to an increasing diversity
of wireless services. Hence, in order to achieve acceptable spectrum efficiency a flexible airâ
interface is required.
It has been demonstrated that code division multiple access (CDMA) provides flexibility by
enabling efficient multi user access in a cellular environment. In addition, time division duplex
(TDD) as compared to frequency division duplex (FDD) represents an appropriate method to
cater for the asymmetric use of a duplex channel. However, the TDD technique is subject to
additional interference mechanisms in particular if neighbouring cells require different rates of
asymmetry. If TDD is combined with an interference limited multiple access technique such as
CDMA, the additional interference mechanism represents an important issue. This issue poses
the question of whether a CDMA/TDD airâinterface can be used in a cellular environment.
The problems are eased if a hybrid TDMA (time division multiple access) / CDMA interface
(TDâCDMA) is used. The reason for this is that the TDMA component adds another degree
of freedom which can be utilised to avoid interference. This, however, requires special channel
assignment techniques.
This thesis analyses cellular CDMA/TDD systems used in indoor environments. A key parameter
investigated is the interference in such systems. In the interference analysis a special
focus is placed on adjacent channel interference since the jamming entity and victim entity can
be in close proximity. The interference analysis shows that coâlocation of BSâs using adjacent
channels is not feasible for an adjacent channel protection factor that is less than 40 dB
and frame synchronisation errors of more than 10%. Furthermore, it is demonstrated that ideal
frame synchronisation does not necessarily yield the highest capacity. As a consequence, a new
technique termed âTSâopposingâ is introduced. This method is intended to enable a cellular
TDâCDMA/TDD system to apply cell independent channel asymmetry. For this purpose, a
centralised DCA is developed. It is found that this algorithm indeed enables neighbouring cells
to adopt different rates of asymmetry without a significant capacity loss.
Moreover, a decentralised DCA algorithm based on the TSâopposing principle is developed.
In this context, a novel TS assignment concept is proposed which reduces the complexity associated
with the TSâopposing technique. In addition, the TS assignment plan allows for full
spatial coverage. It is shown that the capacity of a TDâCDMA/TDD interface can be greater
than the capacity of an equivalent FDD interface. The performance of the decentralised DCA
algorithm is limited by the interference in the uplink. Therefore, additional methods which assist
in reducing the interference in the uplink are envisaged to further improve the performance
of the decentralised DCA algorithm.
The exploitation of the TSâopposing technique in two different ways demonstrates that this
method can be used to improve the performance of a TDâCDMA/TDD system significantly
Técnicas de equalização e pré-codificação para sistemas MC-CDMA
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. Ă, 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 systemâs 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)
3GPP LTE Release 9 and 10 requirement analysis to physical layer UE testing
The purpose of this thesis was to analyze the testing requirements to physical layer features which are used in LTE Release 9 and 10 timeframe. The aim of the analysis was to define test case requirements for new features from the physical layer point of view. This analysis can then be utilized to implement and design test cases using commercial eNB simulators. The analysis was carried out by studying the 3GPP specifications and by investigating the integration and system level testing requirements. Different feature specific parameters were evaluated and different testing aspects were studied in order to verify the functionalities and performance of the UE. Also, different conformance test case scenarios and field testing aspects were investigated in order to improve the test case planning in the integration and system testing phase.
The analysis showed that in Rel-9 there are two main features which have a great impact on the Rel-9 physical layer testing. These two features are the dual-layer beamforming and UE positioning which is done with OTDOA and E-CID methods. It was analyzed that the requirements for the downlink dual-layer beamforming focus on TDD side and the test plan must contain especially throughput performance testing in integration and system phase testing. OTDOA and E-CID methods, on the other hand, need test plans which are concentrating on the positioning accuracy.
In Rel-10, the analysis showed that there are plenty of new features on physical layer to ensure the transition from LTE to LTE-Advanced. The main requirements were assigned for the CA feature which has testing activities especially on the UE feedback operations. Also, different kinds of CA deployment scenarios were analyzed to evaluate more closely the initial CA testing scenarios in integration and system testing. Analysis continued with downlink multi-layer beamforming where the requirements were seen to concentrate on new CSI-RS aspects and to throughput performance testing. Uplink MIMO aspects were analyzed at the end and the studies showed that this feature may have a minor role in Rel-10 timeframe and therefore it does not have any important testing requirements which should be taken into account in test plans
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