Throughput of cellular uplink with dynamic user activity and cooperative base-stations (original) (raw)
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Uplink capacity of a variable density cellular system with multicell processing
IEEE Transactions on Communications, 2009
In this work we investigate the information theoretic capacity of the uplink of a cellular system. Assuming centralised processing for all base stations, we consider a power-law path loss model along with variable cell size (variable density of Base Stations) and we formulate an average path-loss approximation. Considering a realistic Rician flat fading environment, the analytical result for the per-cell capacity is derived for a large number of users distributed over each cell. We extend this general approach to model the uplink of sectorized cellular system. To this end, we assume that the user terminals are served by perfectly directional receiver antennas, dividing the cell coverage area into perfectly non-interfering sectors. We show how the capacity is increased (due to degrees of freedom gain) in comparison to the single receiving antenna system and we investigate the asymptotic behaviour when the number of sectors grows large. We further extend the analysis to find the capacity when the multiple antennas used for each Base Station are omnidirectional and uncorrelated (power gain on top of degrees of freedom gain). We validate the numerical solutions with Monte Carlo simulations for random fading realizations and we interpret the results for the real-world systems.
The Multicell Processing Capacity of the Cellular MIMO Uplink Channel under Correlated Fading
2009 IEEE International Conference on Communications, 2009
In the information-theoretic literature, it has been widely shown that multicell processing is able to provide high capacity gains in the context of cellular systems and that the per-cell sum-rate capacity of multicell processing systems grows linearly with the number of Base Station (BS) receive antennas. However, the majority of results in this area has been produced assuming that the fading coefficients of the MIMO subchannels are totally uncorrelated. In this direction, this paper investigates the ergodic per-cell sum-rate capacity of the MIMO Cellular Multiple-Access Channel under correlated fading and multicell processing. More specifically, the current channel model considers Rayleigh fading, uniformly distributed User Terminals (UTs) over a planar cellular system and power-law path loss. Furthermore, both BSs and Uts are equipped with correlated multiple antennas, which are modelled according to the Kronecker model. The per-cell sum-rate capacity closed form is derived using a Free Probability approach and numerical results are produced by varying the cell density of the system, as well as the level of correlation.
Uplink capacity of MIMO cellular systems with multicell processing
ISWCS'08 - Proceedings of the 2008 IEEE International Symposium on Wireless Communication Systems, 2008
Multiple antennas are known to increase the link throughput by providing a multiplexing gain which scales with the number of antennas. Especially in cellular systems, multiple antennas can be exploited to achieve higher rates without the need for additional Base Station (BS) sites. In this direction, this paper investigates the multi-antenna capacity scaling in a cellular system which employs multicell processing (hyperreceiver). The model under investigation is a MIMO Gaussian Cellular Multiple-Access Channel (GCMAC) over a planar cellular array in the presence of power-law path loss and flat fading. Furthermore, the considered cellular model overcomes the assumption of user collocation utilized by previous models by incorporating uniformly distributed User Terminals (UTs). The asymptotic eigenvalue distribution (a.e.d.) of the covariance channel matrix is calculated based on free-probabilistic arguments. In this context, we evaluate the effect of multiple BS/UT antennas on the optimal sum-rate capacity by considering a variable-density cellular system. Finally, the analytical results are interpreted in the context of a typical real-world macrocellular scenario.
A Statistical Model of Uplink Inter-Cell Interference with Slow and Fast Power Control Mechanisms
IEEE Transactions on Communications, 2013
Uplink power control is in essence an interference mitigation technique that aims at minimizing the inter-cell interference (ICI) in cellular networks by reducing the transmit power levels of the mobile users while maintaining their target received signal quality levels at base stations. Power control mechanisms directly impact the interference dynamics and, thus, affect the overall achievable capacity and consumed power in cellular networks. Due to the stochastic nature of wireless channels and mobile users' locations, it is important to derive theoretical models for ICI that can capture the impact of design alternatives related to power control mechanisms. To this end, we derive and verify a novel statistical model for uplink ICI in Generalized-K composite fading environments as a function of various slow and fast power control mechanisms. The derived expressions are then utilized to quantify numerically key network performance metrics that include average resource fairness, average reduction in power consumption, and ergodic capacity. The accuracy of the derived expressions is validated via Monte-Carlo simulations. Results are generated for multiple network scenarios, and insights are extracted to assess various power control mechanisms as a function of system parameters.
On the statistics of uplink inter-cell interference with greedy resource allocation
2011 8th International Symposium on Wireless Communication Systems, 2011
In this paper, we introduce a new methodology to model the uplink inter-cell interference (ICI) in wireless cellular networks. The model takes into account both the effect of channel statistics (i.e., path loss, shadowing, fading) and the resource allocation scheme in the interfering cells. Firstly, we derive a semi-analytical expression for the distribution of the locations of the allocated user in a given cell considering greedy resource allocation with maximum signal-to-noise ratio (SNR) criterion. Based on this, we derive the distribution of the uplink ICI from one neighboring cell. Next, we compute the moment generating function (MGF) of the cumulative ICI observed from all neighboring cells and discuss some examples. Finally, we utilize the derived expressions to evaluate the outage probability in the network. In order to validate the accuracy of the developed semi-analytical expressions, we present comparison results with Monte Carlo simulations. The major benefit of the proposed mechanism is that it helps in estimating the distribution of ICI without the knowledge of instantaneous resource allocations in the neighbor cells. The proposed methodology applies to any shadowing and fading distributions. Moreover, it can be used to evaluate important network performance metrics numerically without the need for time-consuming Monte Carlo simulations.
IEEE Transactions on Wireless Communications, 2009
In the context of cellular systems, it has been shown that multicell processing can eliminate inter-cell interference and provide high spectral efficiencies with respect to traditional interference-limited implementations. Moreover, it has been proved that the multiplexing sum-rate capacity gain of multicell processing systems is proportional to the number of Base Station (BS) antennas. These results have been also established for cellular systems, where BSs and User Terminals (UTs) are equipped with multiple antennas. Nevertheless, a common simplifying assumption in the literature is the uncorrelated nature of the Rayleigh fading coefficients within the BS-UT MIMO links. In this direction, this paper investigates the ergodic multicell-processing sum-rate capacity of the Gaussian MIMO Cellular Multiple-Access Channel in a correlated fading environment. More specifically, the multiple antennas of both BSs and UTs are assumed to be correlated according to the Kronecker product model. Furthermore, the current system model considers Rayleigh fading, uniformly distributed UTs over a planar coverage area and power-law path loss. Based on free probabilistic arguments, the empirical eigenvalue distribution of the channel covariance matrix is derived and it is used to calculate both Optimal Joint Decoding and Minimum Mean Square Error (MMSE) Filtering capacity. In addition, numerical results are presented, where the per-cell sum-rate capacity is evaluated while varying the cell density of the system, as well as the level of fading correlation. In this context, it is shown that the capacity performance is greatly compromised by BS-side correlation, whereas UT-side correlation has a negligible effect on the system's performance. Furthermore, MMSE performance is shown to be greatly suboptimal but more resilient to fading correlation in comparison to optimal decoding.
Information theoretic capacity of the cellular uplink - average path loss approximation
2008
In this paper we investigate the information theoretic capacity of the uplink of a cellular system where all base station receivers jointly decode the received signals ("hyper-receiver"). Considering a distance depended power-law path loss and a more realistic Rician fading environment, we model a variable cell density network with geographically distributed user terminals. Multiple tiers of interference are considered and using an average path loss approximation model the analytical result for the per cell sum-rate capacity is found. We examine the various parameters that are affecting the capacity of the system. Especially the effect of the user distribution across the cells and the density of the cells in the cellular system is investigated. We validate the numerical solutions with Monte Carlo simulations for random fading realizations and we interpret the results for the real-world systems.
Cooperative multi-cell networks: impact of limited-capacity backhaul and inter-users links
2007
Cooperative technology is expected to have a great impact on the performance of cellular or, more generally, infrastructure networks. Both multicell processing (cooperation among base stations) and relaying (cooperation at the user level) are currently being investigated. In this presentation, recent results regarding the performance of multicell processing and user cooperation under the assumption of limited-capacity interbase station and inter-user links, respectively, are reviewed. The survey focuses on related results derived for non-fading uplink and downlink channels of simple cellular system models. The analytical treatment, facilitated by these simple setups, enhances the insight into the limitations imposed by limited-capacity constraints on the gains achievable by cooperative techniques.
IEEE Transactions on Wireless Communications, 2007
Cooperation between base stations and collaborative transmission between mobile terminals are two technologies currently under study as promising paradigms for next generation communications systems. In this paper, we provide a first look to the interplay between these two approaches by studying the per-cell achievable sum-rate (throughput) of different cooperative protocols under a simplified model for the uplink of a TDMA cellular system. The analysis is limited to non-regenerative (Amplify-and-Forward) cooperation schemes between terminals for their simplicity and appeal to a practical implementation. A closed form expression for the (asymptotic) achievable rate of multicell processing combined with Amplify-and-Forward collaboration at the terminals is derived for an AWGN (i.e., no fading) scenario. Moreover, the impact of fading is investigated numerically, allowing to draw some conclusions on the impact of multicell diversity (or macrodiversity) on the performance of collaborative schemes among the terminals. In particular, we show that while AF cooperation is generally advantageous for single cell processing (i.e., with no collaboration between base stations), its benefits when combined with multicell processing are limited to the regime of low to moderate transmission rates.
Low-SNR analysis of cellular systems with cooperative base stations and mobiles
2006 Fortieth Asilomar Conference on Signals, Systems and Computers, 2006
In this paper, joint (cooperative) decoding at the base stations combined with collaborative transmission at the mobile terminals is investigated as a means to improve the uplink throughput of current cellular systems over fading channels. Intra-cell orthogonal medium access control and Decodeand-Forward collaborative transmission among terminals are assumed. Moreover, the cellular system is modelled according to a simpli ed framework introduced by Wyner. The focus of this work is on low-power transmission (or equivalently on the wideband regime), where the ergodic per-cell throughput can be described by the minimum energy per bit required for reliable communication and the slope of the spectral ef ciency at low SNR. These two parameters are derived for different system con gurations and, capitalizing on the analysis, the relative merits of both cooperation among base stations and among terminals are assessed.