Downlink and Uplink Cell Association with Traditional Macrocells and Millimeter Wave Small Cells

Millimeter wave (mmWave) links will offer high capacity but are poor at penetrating into or diffracting around solid objects. Thus, we consider a hybrid cellular network with traditional sub 6 GHz macrocells coexisting with denser mmWave small cells, where a mobile user can connect to either opportunistically. We develop a general analytical model to characterize and derive the uplink and downlink cell association in view of the SINR and rate coverage probabilities in such a mixed deployment. We offer extensive validation of these analytical results (which rely on several simplifying assumptions) with simulation results. Using the analytical results, different decoupled uplink and downlink cell association strategies are investigated and their superiority is shown compared to the traditional coupled approach. Finally, small cell biasing in mmWave is studied, and we show that unprecedented biasing values are desirable due to the wide bandwidth.Comment: 30 pages, 9 figures. Submitted to IEEE Transactions on Wireless Communication

Downlink and Uplink User Association in Dense Next-Generation Wireless Networks

5G, the next-generation cellular network, must serve an aggregate data rate of 1000 times that of current 4G networks while reducing data latency by a factor of ten. To meet these requirements, 5G networks will be far denser than existing networks, and small cells (femtocells and picocells) will augment network capacity. However, dense networks raise questions regarding interference, user association, and handoff between base stations. Where recent papers have demonstrated that interference from small cells will not be prohibitive under multi-slope path loss models, this thesis describes how the use of different path loss models affects the design of such dense, multi-tier networks. This thesis concludes that the gains realized by downlink biasing and uplink/downlink decoupling are strongly dependent on the path loss model assumed and the density differential between base station tiers. Furthermore, this thesis argues that the gains from uplink/downlink decoupling are reduced by a factor of 50% when optimal biasing for the downlink is used.Electrical and Computer Engineerin

Study of decoupled uplink and downlink access in 5G heterogeneus systems

El projecte analitzarà les funcionalitats i problemàtiques de l'Internet tàctil.Uplink and downlink decoupling (DUDe) is a disruptive technique that has been proposed recently to reduce the uplink and downlink imbalance problem, which occurs in HetNets due to the strong transmit power disparities between macro and small cells. In this thesis, previous research done on DUDe, in particular the association probability derivation, is used to calculate how the capacity is affected when the association is made to any SCell in the scenario. This specific situation is highly realistic since one or several small cells might be unavailable due to overload reasons. Therefore, one of the main objectives of this thesis is to evaluate and compare the potential capacity gains of decoupling to any other small cell in the scenario with respect to the macro cell, association that follows classical downlink received power policies. Decoupling uplink from the macro cell can improve as well the uplink outage, metric also evaluated and compared in this study. Moreover, there is a strong trend in research to empower multi-connectivity solutions, where one user has more than one uplink connection. We refer to this case as a dual connectivity scenario, and the uplink is further studied by allowing decoupled associations in dual connectivity scenarios. Dual connectivity in the uplink is highly controversial, since the user has limited power to share between two different access points. Therefore, a part from comparing the decoupled association performance with the downlink received power policies, this study compares the performance of multi-connectivity against having one single serving cell. In this case, a comparison is done with respect to the best uplink serving cell. Results show that decoupling the access increases the capacity even if there are some SCells unreachable and presents great performance on DC scenario.El uplink and downlink decoupling (DUDe) es una novedosa técnica propuesta recientemente para reduir el problema del uplink and downlink imbalance. El uplink and downlink imbalance ocurre cuando las potencias de las antenas de una heterogeneus network (HetNet) son muy dispares. En este proyecto, teniendo en cuenta la investigación realitzada hasta la fecha sobre el DUDe (especialmente sobre la probabilidad de asociación), se calcula la capacidad asociándose a cualquier SCell. Esta situación es muy importante ya que puede ser que algunes celdas sean inalcanzables por el usuario debido a que puedn estar sobrecargadas. Por este motivo, uno de los principales objetivos del proyecto es aavaluar la mejora de capacidad al relaizar el DUDe con cualquier SCell y mantenir la asociaciín con la MCell tal y como se ha hecho hasta ahora. Esta técnica se llama downlink receive power (DRP). El DUDe también mejora la outage probability, indicador que también se evalua en el estudio. En los estudios mas recientes también se trabaja con dual connectivity para mejorar las prestacions de la conexión. Aunque dividir la transmisión en el enlace de subida puede disminuir la capacidad debido a la baja potencia del usuario, se compara la capacidad de desacoplar el acceso en dual connectivity con el escenario de single best association. Los resultados muestran que el DUDe aumenta la capacidad aun teniendo algunes SCells inalcanzables. También se ha demostrado que el DUDe funciona perfectamente con la dual connectivity.L’Uplink and downlink decoupling és una innovadora tècnica que ha sigut proposada recentment per reduir el problema de l’uplink and downlink imbalance. L’uplink and downlink imbalance es dona a les heterogeneus networks (HetNets) degut a la disparitat de potències entre les diferents antenes. Durant aquest projecte, tenint en compte la recent recerca sobre DUDe (sobretot sobre la probabilitat d’associació), s’utilitza per calcular la capacitat a qualsevol SCell. Aquesta situació és molt important d’analitzar ja que pot ser possible que algunes no estiguin accessibles per sobrecàrrega. Per aquest motiu, un dels principals objectius del projecte és avaluar la millora de capacitat entre realitzar el DUDe a qualsevol SCell i mantenir l’associació amb la MCell com s’havia fet fins ara, el que es coneix com downlink receive power (DRP). El DUDe també comporta moltes millores a la outage probability, indicador que també s’avalua a l’estudi. En els estudis més recents també treballen amb dual connectivity per millorar les prestacions. Tot i que dividir la transmissió a l’enllaç de pujada pot comportar perdre capacitat degut a la baixa potència de l’usuari, es compara la capacitat amb el DUDe en un escenari de dual connectivity amb el cas de single best association. Els resultats mostren que el fet de desacoblar l’accés augmenta la capacitat de la connexió tot i tenir algunes SCells inabastables. També s’ha demostrat que el DUDe funciona perfectament amb la dual connectivity

Heterogeneous cellular netwoks under diverse coupling and association criteria

Limiting the number of simultaneous active users does not affect the coverage and average symmetric binary rate but energy efficiency improves for its lower values, since the resources of the cell are distributed among less users, at the expense of an unfairer treatment as more users are kept inactive. It has been inspected that including more picocells has no worth for average rate and fairness under average criteria mainly due to the high difference of power between both tiers but energy efficiency slightly improves as more users get inactive. Cell range expansion bias reduces coverage but fairness is maximum for its mid-range values and the energy efficiency as well as the binary rate has improved much beyond those mid-range values. Finally, slight increment in fractional power control improves coverage and joint rate and provides better user fairness treatment. Our results show that for realistic path loss models, the decoupled DL/UL association does not improve the results sufficiently to compensate for the implementation difficulties it represents.Current networks are moving towards Heterogeneous Cellular Networks (HCN) arising from the combination of small cells with existing macrocells. The aim of this thesis is to analyze various performance indicators of heterogeneous cellular networks under diverse coupling and association criteria. We considered a two-tier heterogeneous cellular network with macro and pico BSs and UEs uniformly distributed. Realistic path loss models given by 3GPP have been taken into account for both macro and pico tiers. In this work, three association criteria were used to associate users to macro or a pico tier which include the coupled and decoupled association criteria. The coupled association criteria encompass nearest BS and maximum downlink average power whereas in decoupled association criteria, users were associated in DL by maximum average receive power and in UL by minimum path loss. Cell Range Expansion (CRE) and Fractional Power Control (FPC) techniques have been considered. The results showed a remarkable lack of independence and correlation between uplink and downlink coverage has been guessed even under independent Rayleigh fading. Simulation results showed that taking into account limits on the maximum spectral efficiency and on the number of simultaneous active users within a cell strongly modify the results on joint binary rate. It has been investigated that deploying a denser infrastructure by increasing the total number of BSs, not only improves coverage and average rates but also the energy efficiency and fairness