Dissertations / Theses on the topic 'Time division duplex TDD'

Thesis (M.S.)--Wichita State University, Electrical and Computer Engineering.
"May 2006." Title from PDF title page (viewed on October 19, 2006). Thesis adviser: Hyuck M. Kwon. Includes bibliographic references (leaves 40-42).

The master thesis deals with G.fast and G.mgfast transmission technologies, including their parameters. The work deals with the principle of vector DMT modulation and the possibility of time duplex TDD and full-duplex FDX in two-way communication used in these technologies. The following is a description of the line using the KHM model, which is suitable for simulations in the transmission band using G.fast and G.mgfast technologies. Subsequently, the disturbing effects of crosstalk at the near end of NEXT and the far end of FEXT and their elimination with these technologies are discussing. Part of the work explains supporting calculations to determine the SNR and bit allocation to calculate the baud rate. The work describes the methods of compensation of crosstalk FEXT and NEXT, which affect the resulting baud rate. The work also includes an application for simulation of transmission speed as a function of distance for G.fast and G.mgfast technologies, allowing changing input parameters and adjusting the transmission bandwidth based on G.9700 and G.9701 standards. Also, in work, an application is created to display the compensation of the influence of the transmitted signal crosstalk FEXT and NEXT, which allow the import of measured crosstalk between individual participants. The issue of influencing crosstalk for accurate measurements in the laboratory is also discussing. An application in the MATLAB environment is creating to display the measured characteristics.

This thesis describes the work done in evaluating the capacity of a multi-service third generation (3G) wireless communication system based on the Universal Mobile Telecommunication System (UNITS). More specifically, the study presented in these pages examines the Time Division Duplex (TDD) paradigm supported by the 3G Partnership Project (3GPP).
The goal is to establish the probability that a new connection attempt be successful as a function of the instantaneous load on the network. The sought capacity is evaluated with the help of an analytical model and a simulation tool. Both tools used a so-called system-level approach. The model and the simulator were developed based on 3GPP's standard and available data from link-level simulations.
Some of the significant results presented are: (1) A maximum of around 7 to 9 orthogonal codes can be used per timeslot. (2) A UMTS TDD CDMA system should be used in pico- and micro-cellular environments in order to support efficient data transmissions. (3) The multicode interference is often wrongfully neglected in capacity studies. (4) Capacity is downlink interference-limited, even with a modest MUD efficiency.

In recent years, cellular systems based on orthogonal frequency division multiple access – time division duplex (OFDMA-TDD) have gained considerable popularity. Two of the major reasons for this are, on the one hand, that OFDMA enables the receiver to effectively cope with multipath propagation while keeping the complexity low. On the other hand, TDD offers efficient support for cell-specific uplink (UL)/downlink (DL) asymmetry demands by allowing each cell to independently set its UL/DL switching point (SP). However, cell-independent SP gives rise to crossed slots. In particular, crossed slots arise when neighbouring cells use the same slot in opposing link directions, resulting in base station (BS)-to-BS interference and mobile station (MS)-to-MS interference. BS-to-BS interference, in particular, can be quite detrimental due to the exposed location of BSs, which leads to high probability of line-of-sight (LOS) conditions. The aim of this thesis is to address the BS-to-BS interference problem in OFDMA-TDDcellular networks. A simulation-based approach is used to demonstrate the severity of BS-to-BS interference and a signal-to-interference-plus-noise ratio (SINR) equation for OFDMA is formulated to aid system performance analysis. The detrimental effects of crossed slot interference in OFDMA-TDD cellular networks are highlighted by comparing methods specifically targeting the crossed slots interference problem. In particular, the interference avoidance method fixed slot allocation (FSA) is compared against state of the art interference mitigation approaches, viz: random time slot opposing (RTSO) and zone division (ZD). The comparison is done based on Monte Carlo simulations and the main comparison metric is spectral efficiency calculated using the SINR equation formulated in this thesis. The simulation results demonstrate that when LOS conditions among BSs are present, both RTSO and ZD perform worse than FSA for all considered performance metrics. It is concluded from the results that current interference mitigation techniques do not offer an effective solution to the BS-to-BS interference problem. Hence, new interference avoidance methods, which unlike FSA, do not sacrifice the advantages of TDD are open research issues addressed in this thesis. The major contribution of this thesis is a novel cooperative resource balancing technique that offers a solution to the crossed slot problem. The novel concept, termed asymmetry balancing, is targeted towards next-generation cellular systems, envisaged to have ad hoc and multi-hop capabilities. Asymmetry balancing completely avoids crossed slots by keeping the TDD SPs synchronised among BSs. At the same time, the advantages of TDD are retained, which is enabled by introducing cooperation among the entities in the network. If a cell faces resource shortage in one link direction, while having free resources in the opposite link direction, the free resources can be used to support the overloaded link direction. In particular, traffic can be offloaded to near-by mobile stations at neighbouring cells that have available resources. To model the gains attained with asymmetry balancing, a mathematical framework is developed which is verified by Monte Carlo simulations. In addition, asymmetry balancing is compared against both ZD and FSA based on simulations and the results demonstrate the superior performance of asymmetry balancing. It can be concluded that the novel interference avoidance approach is a very promising candidate to.

Radio over Fibre (RoF) Distributed Antenna Systems can be deployed in combination with pre-4G and 4G technologies, proposed by the IEEE 802.16 and 3GPP LTE standards, in order to support the increased demand for capacity and coverage for various outdoor, inbuilding and underground scenarios. However, the Physical and Medium Access Control (MAC) protocols have not been designed to account for the additional propagation delay that the optical distribution network inserts. This thesis presents a detailed theoretical analysis of protocol effects in Time Division Duplex (TOO) IEEE 802.16 and 3GPP LTE RoF networks, supported by mathematical analyses. The round trip delays and the timing boundaries of the wireless technologies under investigation might be affected when the optical propagation delay is not taken into account. The analysis indicates that the default durations of the TransmitIReceive Transition Gap (TTG) and the Guard Period, which allow for the downlink-uplink timing synchronisation between the Base Station (BS)Evolved Node B (eNB) and the users, can accommodate fibre lengths up to 14.4 km, 27 km and 69.7 km for legacy IEEE 802.16, IEEE 802.16m and 3GPP TD-LTE systems, respectively. Also, the initial Ranging (IR) slot and the Physical Random Access Channel duration, used for the estimation of the user's distance from the BS/eNE, can accommodate fibre lengths up to 13.2 km, 93 km and 69 Ian for legacy IEEE 802.16, IEEE 802.16m and 3GPP TD-LTE systems, respectively. Furthennore, the OFDM symbol's CP duration has to be chosen based on the maximum difference in fibre lengths between the Remote Antenna Units that needs to be supported in the RoF network. The maximum fibre length differences allowed by the default CP in legacy IEEE 802.16, IEEE 802.l6m and 3GPP TD-LTE systems are equal to 2.2 km, 2.2 km and 1.15 km, respectively. However, it is shown that the system perfonnance deteriorates when these parameters are adapted in order to accommodate longer optical propagation delays and greater fibre length differences. The required protocol and parameter changes for the alleviation of the limitation imposed on the maximum fibre link length are presented. The proposed solutions concern the IR procedure and the MAC management Medium Access Protocol (MAP) messages' timing relevance. The optical propagation delay is compensated and the downlink-uplink timing synchronization between the as and the users is maintained. Thus, the wireless propagation delay estimation (ranging) is successfully carried out, even when the optical propagation delay is greater than what the IR slot and/or the TTG duration can accommodate, and the system's performance is improved, without the need of increased overhead.

Une nouvelle génération des réseaux mobiles, connue sous le nom de 5G NR, est en cours de standardisation à travers des améliorations apportées à son prédécesseur 4G/4G+. 5G NR va introduire un nouveau niveau de flexibilité, scalabilité et efficacité afin de satisfaire plusieurs classes de services. Le mode de duplexage TDD est le plus favorable pour 5G NR grâce aux avantages qu’il représente par rapport au mode FDD en termes de capacité, flexibilité et convenance de déploiement avec les autres technologies attendues dans le cadre de la 5G comme FD-MIMO. Une variante du TDD, connue sous le nom du dynamique TDD (D-TDD), attire de plus en plus l’attention. D-TDD est désigné pour l’adaptation des configurations des sous-trames DL et UL en se basant sur une estimation instantanée du trafic. Cependant, l’utilisation de ce mode nécessite l’implémentation des mécanismes capable de réduire deux types d’interférence additionnelles : l’interférence générée par les stations de bases qui impacte le signal UL des utilisateurs et l’interférence générée par les mobiles en UL qui interfère avec le signal DL des stations de base. La première partie de cette thèse est consacrée à l’analyse des performances du mode D-TDD en termes de ISR et de la probabilité de couvertures dans 2 types de déploiement : macro-cells et small-cells. Ensuite, nous proposons deux techniques de mitigation des interférences dont la première est destinée aux macro-cells et basée sur le 3D beamforming tandis que la 2ème est le cell clustering et appliquée au small-cells. Dans la 2ème partie de cette thèse, nous étudions la problématique du dimensionnement de l’OFDMA qui sera une technologie de base pour la 5G NR. Etant donné que le dimensionnement des ressources radio est une tâche primordiale dans l’ingénierie radio, nous proposons un modèle analytique qui permet la réalisation de cette tâche en considérant un scheduling proportional fair. Nous distinguons entre 2 types d’utilisateurs : utilisateurs indoor qui sont modélisés par un PPP spatial et utilisateurs outdoor qui sont modélisés selon un processus de Cox conduit par un PLP. Plusieurs résultats analytiques et numériques sont exposés afin de justifier l’exactitude et la précision de ce modèle
A new generation of cellular networks, known as 5G new radio (NR), has been standardized through improvements in the current 4G/4G+ concepts and features in order to bring a new level of flexibility, scalability and efficiency. Time division duplex (TDD) is expected to be one of the key features of 5G NR since it offers more advantages than frequency division duplex (FDD) mode in terms of capacity, flexibility and implementation adequacy with other features, such as full dimension multiple input multiple output antenna (FD-MIMO) technology. A variant operational mode of TDD, known as D-TDD, is in the scope. It is designed to deal with uplink (UL) and downlink (DL) traffic asymmetry since it is based on instantaneous traffic estimation and offers more flexibility in resource assignment. However, the use of D-TDD requires new interference mitigation schemes capable to handle two additional types of interference called cross link interference (CLI) and stands for DL to UL and UL to DL interference. The first part of this thesis is devoted to tackle the problem of interference modeling in D-TDD based macro-cell and small-cell deployments. We provide a complete analytical approach to derive relevant metrics, such as interference-to-signal-ratio (ISR) and the coverage probability formulas, considering adequate geometry models for each type of deployment. Then, we propose an interference mitigation scheme based on 3D beamforming for macro-cells and a cell-clustering scheme for small-cells. Additionally, we investigate another problematic which is Orthogonal Frequency Division Multiplex (OFDM) radio resource dimensioning. Since 5G NR takes in consideration a wide array of emerging use cases and also the possibility of having future requirements, the third Generation Partnership Project (3GPP) comes up with a variant of OFDM known as scalable OFDM and having different sub carriers' spacing. This feature appears to be an ideal choice for 5G NR since it offers a high spectral efficiency, robustness to selective fading channels, convenience with diverse spectrum bands and compatibility with other features. Therefore, dimensioning OFDM is a major task to accomplish in the context of NR. To this purpose, we provide an analytical model to dimension OFDM based systems with a proportional fair resources' allocation policy. We model indoor users by a spatial PPP and outdoor users according to a Cox process driven by PLP. Different analytical and numerical results are provided to justify the accuracy of this model

In-band full duplex is a new duplexing scheme that allows radio nodes to transmit and receive, utilizing the same frequency and time resources. The implementation of in-band full duplex was not feasible in practice, due to the effect of self-interference. But then, advances in signal processing made it possible to reduce this effect. However, the system level performance of in-band full duplex has not been investigated thoroughly.Through computer simulations, we investigate the performance of in-band full duplex, for indoor 5G small cell wireless networks. We examine the performance of in-band full duplex in comparison to dynamic and static time division duplexing. Additionally, we analyze the performance of the duplexing schemes with two interference mitigation techniques, namely beamforming and interference cancellation.Our results indicate that for highly utilized wireless networks, in-band full duplex should be combined with beamforming and interference cancellation, in order to achieve a performance gain over traditional duplexing schemes. Only then, in-band full duplex is considered advantageous, at any network utilization, and any downlink to uplink traffic demand proportion. Our results also suggest that in order to achieve a performance gain with in-band full duplex in both links, the transmit power of the access points should be comparable to the transmit power of the mobile stations.
Inomband hel duplex är en ny typ av duplexmetod som tillåter radionoder att sända och ta emot i samma frekvensoch tidsresurs. Att implementera inomband hel duplex har fram tills nu inte ansetts praktiskt genomförbart till följd av självstörningar. Framsteg inom signalbehandling har dock gjort det möjligt att begränsa denna självstörningseffekt. Emellertid har systemprestanda av inomband hel duplex inte undersökts tillräckligt noga i tidigare verk.Inomband hel duplex och dess prestanda för trådlösa 5G småcellsnätverk inomhus har studerats med hjälp av datasimuleringar och jämförts med dynamisk och statisk tidsdelning. Utöver detta har prestanda för de olika duplexmetoderna med avseende på två tekniker för störningsundertryckning, lobformning och störningseliminering, också undersökts.Våra resultat indikerar att för trådlösa nätverk med högt radioresursutnyttjande bör inomband hel duplex kombineras med lobformning och störningseliminering för att uppnå en prestandavinst jämfört med traditionella duplexmetoder. Bara då kan inomband hel duplex anses vara fördelaktig oberoende av radioresursutnyttjande och andelen upp- och nedlänkstrafik.Resultaten tyder också på att sändareffekten för radioaccesspunkterna bör vara jamförbar med den för mobilenheterna för att en prestandavinst med inomband hel duplex ska kunna uppnås.
Wireless networks, In-band full duplex, Static-time division duplexing, Dynamic-time division duplexing, Interference mitigation techniques, small cell, 5G, mmWave bands, Beamforming, Interference cancellation.

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This work presents the comparison made through simulations of discreet events, accomplished with the software ARENA, the techniques of Time Division Duplex (TDD) and Frequency Division Duplex (FDD). Techniques present in the pattern IEEE 802.16 and used by WiMAX in the bi-directional channels of uplink and downlink. The simulation model considered in the line of arrival of the services the concept FIFO (First-In, First-Out) and the simulations were accomplished considering five applications (Streaming, Download, Web, E-mail and Small-Transaction) for downlink and uplink. The number of channels in the Base Station varied from 4 to 60, with a throughput of 600 kbps. The regarded efficiency parameter was the minimum number of channels necessary in each one of the standard channels. The simulations were accomplished in three sceneries., In the first scenery it was considered the same profile of traffic for downlink and uplink, in the second scenery a traffic of downlink 2, 5, 10 and 15 times larger than the one of uplink. And, in the third scenery it was considered different proportions of traffics varying from 2 to 5 times more, 5 to 10 times more and from 10 to 15 times more. The analyses were done considering as efficiency parameter the converge of the waiting time of the users. ,It was verified that in asymmetric data traffic, the TDD technique was more efficient and there were spectrum idleness in the FDD technique.
Este trabalho apresenta a compara??o efetuada por meio de simula??es de eventos discretos, realizadas com o software ARENA, das t?cnicas de Duplexa??o por Divis?o no Tempo (TDD) e Duplexa??o por Divis?o da Freq??ncia (FDD), t?cnicas presentes no padr?o IEEE 802.16 e utilizadas pelo WiMAX nos canais bidirecionais de uplink e downlink. O modelo de simula??o considerou na fila de chegada dos servi?os o conceito FIFO (First-In, First-Out) e as simula??es foram realizadas considerando cinco aplica??es (Streaming, Download, Web, E-mail e Small-Transaction) para downlink e uplink. O n?mero de canais na Base Station variou de 4 a 60, com um throughput de 600 kbps. O par?metro de efici?ncia considerado foi o n?mero m?nimo de canais necess?rio em cada um dos canais padr?es. As simula??es foram realizadas em tr?s cen?rios, sendo que, no primeiro cen?rio se considerou o mesmo perfil de tr?fego para downlink e uplink, no segundo cen?rio com tr?fego de downlink 2, 5, 10 e 15 vezes maior que o de uplink. E, no terceiro cen?rio com propor??es variadas de tr?fegos variando de 2 a 5 vezes mais, 5 a 10 vezes mais e de 10 a 15 vezes mais. Realizadas as simula??es foram feitas as an?lises dos desempenhos, tomando como par?metro de efici?ncia a taxa de chegada e o tempo de espera do usu?rio perante aplica??es t?picas utilizadas na tecnologia de banda licenciada WiMAX, que segue este padr?o. A an?lise efetuada permitiu identificar, dada estas condi??es de tr?fego, qual das t?cnicas seria a mais indicada. Constatou-se ainda que em tr?fego de dados assim?tricos a t?cnica TDD se apresentou mais eficiente e, observou-se existir ociosidade de espectro na t?cnica FDD.

Code Division Multiple Access (CDMA) has been used in cellular communications area, e.g., in the second generation mobile phones since early 1990’s. Wideband CDMA (WCDMA) is a newer and faster radio technology used in the third generation mobile phones. A Frequency Division Duplexing WCDMA (FDD-WCDMA) has already been employed. In the FDD mode WCDMA, the system uses different frequency bands for the Uplink and Downlink communications. In the Time Division Duplexing WCDMA (TDD-WCDMA) mode, the system uses different time slots but the Uplink and Downlink share the common frequency band. In the TDD-WCDMA, there are two options for bandwidth: 1.28MHz and 3.84MHz. Users can send their data by spreading the data parts in a slot. The Midamble part in a slot is used for channel estimation and the guard part in a slot is for multipath interference suppression. In this work, error control codings, channel estimation, multistage multiuser detection, and power control are studied for the TDD-WCDMA communications.
Thesis (M.S.)--Wichita State University, Electrical and Computer Engineering.
"May 2006."
Includes bibliographic references (leaves 40-42)

Multiple-Input Multiple-Output (MIMO) communication using multiple antennas has received significant attention in recent years, both in the academia and industry, as they offer additional spatial dimensions for high-rate and reliable communication, without expending valuable bandwidth. However, exploiting these promised benefits of MIMO systems critically depends on fast and accurate acquisition of Channel State Information (CSI) at the Receiver (CSIR) and the Transmitter (CSIT). In Time Division Duplex (TDD) MIMO systems, where the forward channel and the reverse channel are the same, it is possible to exploit this reciprocity to reduce the overhead involved in acquiring CSI, both in terms of training duration and power. Further, many popular and efficient transmission schemes such as beam forming, spatial multiplexing over dominant channel modes, etc. do not require full CSI at the transmitter. In such cases, it is possible to reduce the Reverse Channel Training (RCT) overhead by only learning the part of the channel that is required for data transmission at the transmitter. In this thesis, we propose and analyze several novel channel-dependent RCT schemes for MIMO systems and analyze their performance in terms of (a) the mean-square error in the channel estimate, (b) lower bounds on the capacity, and (c) the diversity-multiplexing gain tradeoff. We show that the proposed training schemes offer significant performance improvement relative to conventional channel-agnostic RCT schemes. The main take-home messages from this thesis are as follows: • Exploiting CSI while designing the RCT sequence improves the performance. • The training sequence should be designed so as to convey only the part of the CSI required for data transmission by the transmitter. • Power-controlled RCT, when feasible, significantly outperforms fixed power RCT.

碩士
國立清華大學
電機工程學系
104
In the multi-cell large-scale antenna TDD networks (Massive MIMO TDD networks), the channel state information (CSI) is explored by using uplink training sequences (pilots) which are transmitted by users during the training time. Due to the frequency reuse in the cellular networks and the finite length limit of pilot sequences (depending on the length of channel coherent time), the pilot sequences used in co-channel cells are unavoidable to be non-orthogonal. That is to say, the same set of pilot sequences is reused among the cells, which causes the pilot contamination problem. In this thesis, we propose a new pilot transmission scheduling scheme to completely eliminate the pilot contamination. Further, we apply least-square (LS) channel estimator to derive the estimates of both desired channels and inter-cell interference (ICI) channels, so that we do not need to know the second order statistics of channels. Besides the desired channel estimate, the ICI channel estimate also can be obtained in the this scheme. The achievable rate of downlink data transmission by Zero-Forcing (ZF) precoding is also analysed. Besides downlink data transmission, we use the estimates of interfering channels to help the base station when decoding the symbols users transmit during uplink data transmission.

碩士
國立交通大學
電信工程研究所
100
In this thesis, we consider a wireless butterfly network that consists of two source nodes, two destination nodes, and a number of intermediate nodes. The intermediate node plays an important role of a relay that cooperates with the two source nodes to transmit information to the two destination nodes. Assuming a half-duplex communication at the relays, i.e., the relays receive in t-fraction of time and transmit in (1-t) fraction of time, we determine completely a performance upper bound for any communication protocols to be applied to the wireless butterfly network with at most three relays. The performance is measured in terms of the diversity-multiplexing gain tradeoff. To be more specific, we first fix the time-division parameter t and the multiplexing gain r. We then determine the DMT performance associated with each cut-set in the network. Finally, with the above we proceed to identify the dominant cut-sets in the network and obtain the best DMT performance that can be achieved by any communication schemes at time-division parameter t and the multiplexing gain r. The true optimal DMT is then obtained after optimizing over all possible choice of t. Our result also indicates the optimal time-division t for iii the network at multiplexing gain r. Surprisingly, the time-division parameter t varies with r and is not always a constant. Finally, having the optimal cut-set DMT in mind, we compare the DMT performances of the MAC-OAF and MAC-NAF protocols against the cut-set DMT at time t=1/2. We show that these protocols are optimal in terms of DMT performance at t=1/2.