Cloud Radio Access Networks (Cloud RAN) is an emerging architectural paradigm that attempts to exploit operational efficiencies through centralization of baseband functions, pooling efficiencies for RAN baseband processing, and air-interface performance gains by fast-time-scale multi-cell coordination. In this paper, we aim to derive insights underlying key technologies and tradeoffs that drive Cloud RAN. We highlight principles that explain the impact of Cloud RAN architectures and functional splits on multi-cell coordination gains. We show that the ability to extract pooling gains can differ significantly between RAN functions, depending on whether they are per-user or per-cell functions. We propose a method for elastic scaling of RAN functions that takes into account both real-time and non-real-time needs. We conclude with a proposal for a methodology for operators to evaluate the overall tradeoffs they will face in deciding whether to adopt Cloud RAN.

Multi-Cell coordination or Coordinated Multi-Point (CoMP) schemes are seen as the next evolution of LTE-Advanced to yield a further improvement in overall system performance. In this paper, we study in detail the performance of one such CoMP scheme, namely Multi-cell coordinated scheduling (MuCCS). In our previous work, we have shown that the performance of MuCCS using a distributed "liquid cooperation cluster," where each cell coordinates with its nearest neighbors, out-performs a centralized scheme where the coordination is done over a small set of non-overlapping cells (either three cell or nine cells). In this work, we answer the question of whether there are any additional gains to be obtained by a centralized implementation, if the cooperation cluster is allowed to be arbitrarily large. We also quantify the additional performance gain obtained from allowing intermediate transmit power values besides just the binary on/off power values. Finally, we evaluate the performance of MuCCS when the eNodeBs are connected by a non-ideal backhaul, and devise a distributed MuCCS scheme that retains its advantage over a centralized coordination scheme even in the presence of a non-ideal backhaul. Overall, our results validate that additional high-complexity extensions of coordinated scheduling does not yield large gains over the distributed MuCCS scheme with "liquid cooperation clusters" and on/off power values. In this paper, we use the geometric mean of UE throughputs as the performance metric, and we motivate the rationale behind use of this as a single metric for performance comparison.

Requirements and use cases for the 5G era are demanding in key dimensions such as throughput, latency, scalability and automation. From these, an end-to-end architectural vision has been developed in a holistic way and including novel architectural concepts including 5G access domain and 5G era horizontal layers in conjunction with cloud, software defined and cognitive networks transformation. End-to-end architecture for the 5G era is decomposed in a systematic manner, key attributes and characteristics of the associated architectural domains are described.

We compare the algorithms for centralized and decentralized multi-cell joint optimization of coordinated scheduling with muting. For conventional non-overlapping clusters of cooperating cells, we show that for the same latency of communication, an appropriate decentralized algorithm can equivalently achieve the same jointly optimal solution achieved by a centralized approach. In this decentralized algorithm, cells do not exchange CSIs of all users with other cells, but instead exchange per-cell benefit metrics. In non-overlapping clusters, border cells in a cluster do not coordinate with strong interferers outside the cluster. We introduce a new cluster design called Liquid Cluster which allows a cell to flexibly cooperate with all its relevant interferers. The decentralized algorithm easily extends to Liquid Clusters, performing better than conventional non-overlapping 9-cell clusters.

Dynamic Point selection (DPS) is a key Downlink (DL) Coordinated Multipoint (CoMP) technique that switches the serving data Transmission Point (TP) of a User Equipment (UE) dynamically among the UE's cooperating set of TPs without requiring a cell handover. It provides performance improvement due to TP selection-diversity gains and dynamic UE load balancing benefit. In this paper, we propose two simple DPS schemes that take into account the UE's current channel conditions and the cell loading conditions to make the UE's TP switching decisions. We show that these schemes improve the system performance under different practical and realistic settings, such as, cell handover margin, TP switching periods, bursty traffic conditions, and cooperation cell cluster sizes.

As 3G wireless systems evolve towards 4G, various wireless network technology organizations looking at network architectures for 4G are considering a redesign of the network away from the traditional centralized, hierarchical design towards a more distributed operation of network functions. In this paper, we present some mechanisms for distributed operation of paging in 4G systems. Our focus is on highlighting the tradeoffs that drive the design choice of whether to centralize or distribute the paging operation. One such tradeoff arises from considerations of service reliability and availability. We present a distributed redundancy scheme for improving the reliability and availability for distributed paging. We analyze the fraction of time that mobiles remain reachable through paging (i.e. the paging service availability) in idle mode in the presence of base station and backhaul failures.

The development of lab-on-a-chip systems has moved from the demonstration of individual components to a complex assembly of components. Due to the increased complexities associated with model setup and computational time requirements, current design approaches using spatial and time-resolved multiphysics modeling, though viable for component-level characterization, become unaffordable for system-level design. To overcome these limitations, we present models for the system-level simulation of fluid flow, electric field, and analyte dispersion in microfluidic devices. Compact models are used to compute the flow (pressure driven and electroosmotic) and are based on the integral formulation of the mass, momentum, and current conservation equations. An analytical model based on the method-of-moments approach has been developed to characterize the dispersion induced by combined pressure and electrokinetic-driven flow. The methodology has been validated against detailed three-dimensional (3-D) simulations and has been used to analyze hydrostatic-pressure effects in electrophoretic separation chips. A 100-fold improvement in the computational time without significantly compromising the accuracy (error less than 10%) has been demonstrated.

In a GPRS or EDGE system, fluctuations in the wireless link rate can cause the buffer in the BSS to either overflow or underflow if the data flow into the BSS buffer from the SGSN is not controlled properly. Currently available algorithms for controlling this data flow rely on imperfect estimates of the wireless link rate and cannot ensure that the BSS buffer will never overflow or underflow. We present a new low-complexity algorithm that ensures that the BSS buffer will never overflow or underflow, without requiring any estimate of the wireless link rate. If there is no feedback delay between the SGSN and BSS, the algorithm is optimal: among all algorithms that ensure that the BSS buffer will never overflow or underflow, it requires the smallest amount of buffering in the BSS. The algorithm also has a fixed point, i.e. if the wireless link rate remains constant, the BSS buffer remains in equilibrium and no flow control updates are required.

The information-theoretic capacity of continuous-time queues was analyzed recently by Anantharam and Verdu (see ibid. vol.42, p.4-18, 1996). Along similar lines, we analyze the information-theoretic capacity of two models of discrete-time queues. The first model has single packet arrivals and departures in a time slot and independent packet service times, and is the discrete-time analog of the continuous-time model analyzed by Anantharam and Verdu. We show that in this model, the geometric service time distribution plays a role analogous to that of the exponential distribution in continuous-time queues, in that, among all queues in this model with a given mean service time, the queue with geometric service time distribution has the least capacity. The second model allows multiple arrivals in each slot, and the queue is modeled as serving an independent random number of packets in each slot. We obtain upper and lower bounds on the capacity of queues with an arbitrary service distribution within this model, and show that the bounds coincide in the case of the queue that serves a geometrically distributed number of packets in each slot. We also discuss the extremal nature of the geometric service distribution within this model.

In this paper, we consider the problems of finding corresponding points from multiple perspective projection images (the correspondence problem), and estimating the 3-D point from which these points have arisen (the triangulation problem). We pose the triangulation problem as that of finding the Bayesian maximum, a posteriori estimate of the 3-D point, given its projections in N images, assuming a Gaussian error model for the image point co-ordinates and the camera parameters. We solve this by an iterative steepest descent method. We then consider the correspondence problem as a, statistical hypothesis verification problem. Given a set of 2-D points, under the hypothesis that the points are in correspondence, the MAP estimate of the 3-D point is computed. Based on the MAP estimate, we derive a statistical test for verifying this hypothesis. To find sets of corresponding points when multiple points in each of N images are given, we propose a method that does the Bayesian triangulation and hypothesis verification on each N-tuple of points, selecting those that pass the hypothesis test. We characterize the performance of the Bayesian triangulation in terms of the average distance of the triangulated 3-D point from the true 3-D point, and of the point correspondence method in terms of its misdetection and false alarm rates.

The problems of finding corresponding points from multiple perspective projection images, and estimating the 3-D points from which these points have arisen, are addressed. The problem of finding corresponding points is formulated as a hypothesis verification problem. Given a set of 2-D points, one from each of N perspective projection images, under the hypothesis that the points are projections of the same 3-D point, the coordinates of the 3-D point are estimated. The triangulation problem-the problem of estimating the coordinates of a 3-D point, given its projections in N perspective projection images-is posed as a Bayesian estimation problem, taking into account the uncertainties in the observed image points and the camera parameters. Based on the Bayesian estimate of the triangulated point, a statistical test is derived for verifying the hypothesis that the given set of image points is in correspondence. For finding N-tuples of corresponding points from N perspective projection images, this test can be used on each N-tuple of points to verify the hypothesis that that N-tuple of points is in correspondence, selecting those N-tuples that pass the hypothesis test. Experiments are described for characterizing the distance of the 3-D point estimated by the Bayesian triangulation from the true 3-D point, and characterizing the misdetection and false alarm rates of this method of finding corresponding points.

A corner is modelled as the intersection of two lines. A corner point is that point on an input digital arc whose a posteriori probability of being a corner is the maximum among all the points on the arc. The performance of the corner detector is characterized by its false alarm rate, misdetection rate, and the corner location error all as a function of the noise variance, the included corner angle, and the arc length. Theoretical expressions for the quantities compare well with experimental results.>