Uplink Capacity Research Articles

Massive MIMO for Communications With Drone Swarms

We illustrate the potential of Massive MIMO for communication with unmanned aerial vehicles (UAVs). We consider a scenario, where multiple single-antenna UAVs simultaneously communicate with a ground station (GS) equipped with a large number of antennas. Specifically, we discuss the achievable uplink (UAV to GS) capacity performance in the case of line-of-sight conditions. We develop a realistic geometric model, which incorporates an arbitrary orientation, of the GS and UAV antenna elements to characterize the polarization mismatch loss, which occurs due to the movement and orientation of the UAVs. A closed-form expression for a lower bound on the ergodic rate for a maximum-ratio combining receiver with estimated channel state information is derived. The optimal antenna spacing that maximizes the ergodic rate achieved by an UAV is also determined for uniform linear and rectangular arrays. It is shown that when the UAVs are spherically uniformly distributed around the GS, the ergodic rate per UAV is maximized for an antenna spacing equal to an integer multiple of one-half wavelength.

Joint Pilot Design and Uplink Power Allocation in Multi-Cell Massive MIMO Systems

This paper considers pilot design to mitigate pilot contamination and provide good service for everyone in multi-cell massive multiple-input-multiple-output systems. Instead of modeling the pilot design as a combinatorial assignment problem, as in prior works, we express the pilot signals using a pilot basis and treat the associated power coefficients as continuous optimization variables. We compute a lower bound on the uplink capacity for Rayleigh fading channels with maximum ratio detection that applies with arbitrary pilot signals. We further formulate the max-min fairness problem under power budget constraints, with the pilot signals and data powers as optimization variables. Because this optimization problem is non-deterministic polynomial-time hard due to signomial constraints, we then propose an algorithm to obtain a local optimum with polynomial complexity. Our framework serves as a benchmark for pilot design in scenarios with either ideal or non-ideal hardware. Numerical results manifest that the proposed optimization algorithms are close to the optimal solution obtained by exhaustive search for different pilot assignments and the new pilot structure and optimization bring large gains over the state-of-the-art suboptimal pilot design.

Joint Pilot Design and Uplink Power Allocation in Multi-Cell Massive MIMO Systems

This paper considers pilot design to mitigate pilot contamination and provide good service for everyone in multi-cell Massive multiple input multiple output (MIMO) systems. Instead of modeling the pilot design as a combinatorial assignment problem, as in prior works, we express the pilot signals using a pilot basis and treat the associated power coefficients as continuous optimization variables. We compute a lower bound on the uplink capacity for Rayleigh fading channels with maximum ratio detection that applies with arbitrary pilot signals. We further formulate the max-min fairness problem under power budget constraints, with the pilot signals and data powers as optimization variables. Because this optimization problem is non-deterministic polynomial-time hard due to signomial constraints, we then propose an algorithm to obtain a local optimum with polynomial complexity. Our framework serves as a benchmark for pilot design in scenarios with either ideal or non-ideal hardware. Numerical results manifest that the proposed optimization algorithms are close to the optimal solution obtained by exhaustive search for different pilot assignments and the new pilot structure and optimization bring large gains over the state-of-the-art suboptimal pilot design.

Uplink Capacity of Two-Hop Relay TDD-CDMA Cellular Networks with Time-Slot Scheduling

In code division multiple access network, the interference has more effect on the capacity than the other cellular networks. To increase the uplink capacity of traditional time division duplex-code division multiple access (TDD-CDMA) cellular networks, the method of two-hop relay is adopted. In this paper, we first present a two-hop relay TDD-CDMA cellular system model, and then design two kinds of time slot scheduling schemes and power control models. Based on the system model, the total interference power to target cell can be analyzed, and then the closed form expressions of the uplink capacity are obtained by mathematical calculating. Finally the impact of different system parameters on networks’ capacity is discussed.

Channel Maximization in Wireless Backhaul Based HETNETs

In this paper, we consider the optimization of wireless capacity-limited back-haul links in future heterogeneous networks (HetNets). We assume that the HetNet is formed with one macro-cell base station (MBS), which is associated with multiple small-cell base stations (SBSs). It is also assumed both the MBS and the SBSs are equipped with massive arrays, while all mobiles users (macro-cell and small-cell users) have single antenna. For the back-haul links, we propose to use a capacity-aware beam-forming scheme at the SBSs and MRC at the MBS. Using particle swarm optimization (PSO), each SBS seeks the optimal transmit weight vectors that maximize the back-haul up-link capacity and the access up-links signal-to-interference plus noise ratio (SINR). The performance evaluation in terms of the symbol error rate (SER) and the ergodic system capacity shows that the proposed capacity-aware back-haul link scheme achieves similar or better performance than traditional wireless back-haul links and requires considerably less computational complexity.

Towards estimating the untapped potential: a global malicious DDoS mean capacity estimate

ABSTRACTWhat is the malicious reflected distributed denial of service (rDDoS) mean potential of the internet? The authors have been using data from the openNTP project which measures the number of reflectors on the internet since 2014 until now, and completed a graph that roughly estimates a lower boundary for global rDDoS mean potential across four internet protocols (IPs); SSDP, NTP, SNMP and open recursive DNS. By summing these values, and adjusting for average uplink capacity from reflectors, we come to a single number: 108.49 Tb/s as an estimate of rDDoS magnitude potential across IPv4. Tracking this number over time can give us insights into global remediation and clean-up efforts and where to invest our resources in when battling of rDDoS attacks. This paper demonstrates that the upstream throughput is the main contributing, measurable limiting factor for a volumetric rDDoS attack. The largest DDoS event reported by a single target (Dyn in 2016) was 1.2 Tb/s. In contrast, our lower estimate for the global attack potential is two orders of magnitude larger than the Dyn attack.The key contribution is an extensible methodology for measuring global potential for rDDoS attacks, with surprising policy implications.

Blended Antenna Wearables for an Unconstrained Mobile Experience

We envision a world in which everyday life experiences can be augmented on-demand via the real-time cloud processing of information sourced at multiple wireless end points. While current wireless systems focus their effort on improving downlink capacity, these life-changing augmented experiences will only become a reality if the uplink capacity increases at the same or even higher rate. As a catalyzer for the capacity increase in both directions of the wireless communication link, we propose an innovative idea that brings the spectral and energy efficiency benefits of massive MIMO systems directly to the end user without compromising device size, weight, or power consumption. We propose a radio enhanced garment composed of blended textile antennas for seamless high data rate connectivity anytime, anywhere, addressing immediate and future needs. The real-world applications for such a solution are tremendous, including enhanced connectivity in crowded spaces and remote areas, as well as symmetric extremely high data rates for access to next generation real-time services (e.g., augmented reality and cognition, real-time computer vision, telepresence, 3D video sharing) from ever lighter end user devices (e.g., Google Glass).

Channel Maximization in Wireless Backhaul Based HETNETs

In this paper, we consider the optimization of wireless capacity-limited back-haul links in future heterogeneous networks (HetNets). We assume that the HetNet is formed with one macro-cell base station (MBS), which is associated with multiple small-cell base stations (SBSs). It is also assumed both the MBS and the SBSs are equipped with massive arrays, while all mobiles users (macro-cell and small-cell users) have single antenna. For the back-haul links, we propose to use a capacity-aware beam-forming scheme at the SBSs and MRC at the MBS. Using particle swarm optimization (PSO), each SBS seeks the optimal transmit weight vectors that maximize the back-haul up-link capacity and the access up-links signal-to-interference plus noise ratio (SINR). The performance evaluation in terms of the symbol error rate (SER) and the ergodic system capacity shows that the proposed capacity-aware back-haul link scheme achieves similar or better performance than traditional wireless back-haul links and requires considerably less computational complexity.

Mitigation of Uplink ICI and IBI in OFDMA Two-Tier Networks

For two-tier networks using orthogonal frequency-division multiple access (OFDMA) over frequency-selective channels, macrocell-user (MU) signals generally arrive at small-cell base stations (SBSs) with different delays and can hardly be synchronized in time, causing intercarrier interference (ICI) and interblock interference (IBI) in OFDM demodulation. The effects on small-cell uplink capacity by ICI and IBI and their mitigation have not been well addressed in the literature. In this paper, the ICI and IBI of OFDMA two-tier networks with fractional power control (FPC) in multipath fading channels are formulated, and closed-form expressions of their covariance matrices at the SBS with random MU locations are derived. Simulation results verify the validity of the theoretical analysis. It is shown that small-cell uplink capacity is substantially degraded in the presence of ICI and IBI. A precoding method for small cells for mitigating the effects of ICI and IBI on uplink capacity is proposed. In the method, the received signals over small-cell subcarriers at the SBS are decorrelated jointly by small-cell user (SU) precoders and an equalizer at the SBS. Closed-form design procedures for precoding of different subcarrier sizes to maximize uplink capacity under different information feedback are developed. Simulation results demonstrate that the proposed method for using all the subcarriers for precoding has a large capacity gain over that of no small-cell precoding. Moreover, the method can perform very well, even if MU locations are the only information fed back from the macrocell.

An unequal error protection scheme for reliable peer-to-peer scalable video streaming

This paper proposes an unequal error protection (UEP) scheme for transporting scalable video packets over packet-lossy peer-to-peer networks. In our scheme, given an estimated system uplink capacity, a receiver-driven joint source-channel coding (JSCC) mechanism is proposed by which each child-peer minimizes the received visual distortion by subscribing to appropriate numbers of source and channel coding packets. Because the bandwidth for inter-peer transmissions may fluctuate largely due to peer dynamics, in our method, a peer estimates the available system uplink capacity based on consensus propagation to avoid the fluctuating allocations of JSCC. To efficiently utilize the uplink bandwidth of peers, parent-peers utilize sender-driven contribution-guided peer selection to reject the low-contribution subscriptions requested from candidate child-peers. Simulation results demonstrate that our method significantly improves the visual quality, compared to other state-of-the-art schemes.

Rate-distortion-optimized multi-view streaming in wireless environment using network coding

Multi-view video streaming is an emerging video paradigm that enables new interactive services, such as 3D video, free viewpoint television, and immersive teleconferencing. Because of the high bandwidth cost they come with, multi-view streaming applications can greatly benefit from the use of network coding, in particular in transmission scenarios such as wireless network, where the channels have limited capacity and are affected by losses. In this paper, we address the topic of cooperative streaming of multi-view video content, wherein users who recently acquired the content can contribute parts of it to their neighbors by providing linear combinations of the video packets. We propose a novel method for selection and network encoding of the transmitted frames based on the users’ preferences for the different views and the rate-distortion properties of the stream. Using network coding enables the users to retrieve the content in a faster and more reliable manner and without the need for coordination among the senders. Our experimental results prove that our preference-based approach provides a high-quality decoding even when the uplink capacity of each node is only a small fraction of the rate of the stream.

Uplink Downlink Rate Balancing in Cooperating Cellular Networks

Broadcast MIMO techniques can significantly increase the throughput in the downlink of cellular networks, at the price of channel state information (CSI) feedback from the mobiles, sent over the uplink. Thus, these techniques create a mechanism that can tradeoff some uplink capacity for increased downlink capacity. In this paper, we quantify this tradeoff and study the exchange ratio between the feedback rate (over the uplink) and the downlink rate. We study both finite and infinite networks and show that for high enough (but finite) SNR, the uplink rate can be exchanged for increased downlink rate with a favorable exchange ratio. This exchange ratio is an increasing function of the channel coherence time, and a decreasing function of the number of measured base stations. We also show that in finite networks, devoting a constant fraction of the uplink to CSI feedback can increase the downlink multiplexing gain continuously from 0 to 1, as a function of the fraction size. On the other hand, in infinite networks (with infinite connectivity) our lower bound is only able to show doubly logarithmic scaling of the rate with SNR. The presented results prove that the adaptation of the feedback rate can control the balance between the uplink and downlink rates. This capability is very important in modern cellular networks, where the operators need to respond to continuously changing user demands.

Uplink Capacity of a Cellular WCDMA System with Two High Altitude Platform Stations

In this paper, the uplink capacity of a cellular code division multiple access system is improved by using two high altitude platform stations (HAPSs). By considering a practical shadowing model, uplink capacity is numerically analyzed, and it is shown that the capacity can significantly be improved when two HAPSs are used, as compared to that of a single HAPS system.

Analytic estimation for uplink capacity reduction due to co-channel interference in LTE networks

To achieve high system capacity, most fourth-generation (4G) cellular communication systems, including long term evolution (LTE), tend to adopt aggressive frequency reuse scheme. Although this scheme can increase system capacity, it has a major challenge of suffering severe intercell co-channel interference (CCI), which will reduce cell-edge user throughput and increase outage probability. In this paper, an analytical method is presented for estimating the uplink capacity reduction due to CCI in a cellular LTE network. This method is based on an interference analysis that accounts for random distribution of user locations, propagation shadow fading effect, and user-equipment output power limitations. The results indicate that CCI can cause up to 50 % reduction in throughput for cell-edge users. The proposed method is helpful for estimating the CCI impacts when building a 4G network.

Distributed Fronthaul Compression and Joint Signal Recovery in Cloud-RAN

The cloud radio access network (C-RAN) is a promising network architecture for future mobile communications, and one practical hurdle for its large scale implementation is the stringent requirement of high capacity and low latency fronthaul connecting the distributed remote radio heads (RRH) to the centralized baseband pools (BBUs) in the C-RAN. To improve the scalability of C-RAN networks, it is very important to take the fronthaul loading into consideration in the signal detection, and it is very desirable to reduce the fronthaul loading in C-RAN systems. In this paper, we consider uplink C-RAN systems and we propose a distributed fronthaul compression scheme at the distributed RRHs and a joint recovery algorithm at the BBUs by deploying the techniques of distributed compressive sensing (CS). Different from conventional distributed CS, the CS problem in C-RAN system needs to incorporate the underlying effect of multi-access fading for the end-to-end recovery of the transmitted signals from the users. We analyze the performance of the proposed end-to-end signal recovery algorithm and we show that the aggregate measurement matrix in C-RAN systems, which contains both the distributed fronthaul compression and multiaccess fading, can still satisfy the restricted isometry property with high probability. Based on these results, we derive tradeoff results between the uplink capacity and the fronthaul loading in C-RAN systems.

Uni-MUMAC: a unified down/up-link MU-MIMO MAC protocol for IEEE 802.11ac WLANs

Due to the dominance of the downlink traffic in Wireless Local Area Networks (WLANs), a large number of previous research efforts have been put to enhance the transmission from the Access Point (AP) to stations (STAs). The downlink Multi-User Multiple-Input Multiple-Output (MU-MIMO) technique, supported by the latest IEEE amendment-802.11ac, is considered as one of the key enhancements leading WLANs to the Gigabit era. However, as cloud uploading services, Peer-to-Peer (P2P) and telepresence applications get popular, the need for a higher uplink capacity becomes inevitable. In this paper, a unified down/up-link Medium Access Control (MAC) protocol called Uni-MUMAC is proposed to enhance the performance of IEEE 802.11ac WLANs by exploring the multi-user spatial multiplexing technique. Specifically, in the downlink, we implement an IEEE 802.11ac-compliant MU-MIMO transmission scheme to allow the AP to simultaneously send frames to a group of STAs. In the uplink, we extend the traditional one round channel access contention to two rounds, which coordinate multiple STAs to transmit frames to the AP simultaneously. 2-nd round Contention Window (CW2nd), a parameter that makes the length of the 2-nd contention round elastic according to the traffic condition, is introduced. Uni-MUMAC is evaluated through simulations in saturated and non-saturated conditions when both downlink and uplink traffic are present in the system. We also propose an analytic saturation model to validate the simulation results. By properly setting CW2nd and other parameters, Uni-MUMAC is compared to a prominent multi-user transmission scheme in the literature. The results exhibit that Uni-MUMAC not only performs well in the downlink-dominant scenario, but it is also able to balance both the downlink and uplink throughput in the emerging uplink bandwidth-hungry scenario.

Scaling Wireless Uplink Capacity with Multi-User Beamforming

Due to the fact that the wireless spectrum is limited but the wireless demand can grow unlimited, how to improve the wireless capacity becomes one of the hot topics in wireless network field. In this paper, we focus on the scenario of busy wireless environment, and present a protocol with multiple user beamforming. The protocol enables a network to scale its uplink throughput with the number of access points. Theoretical and experimental results show that our protocol have higher uplink throughput compared with 802.11. Moreover, our protocol is the first method that shows that linear scaling of uplink throughput with the number of access points is possible.

QoS-aware dynamic resource allocation for wireless broadband access networks

Abstract The development of the advanced wireless access technologies is focusing on the enhancement of mobile user satisfaction in terms of quality of service (QoS). As the number of mobile users increases, the amount of traffic passing through base station (BS) significantly increases so that the preplanned capacity of downlink or uplink can be exceeded from time to time resulting in the degradation of users’ QoS satisfaction. A way to utilize the downlink (DL) and the uplink (UL) of an orthogonal frequency division multiple access frame efficiently is therefore needed subject to users’ bandwidth demand which changes continuously over the time. In this paper, we propose a QoS-aware dynamic resource allocation (QDRA) scheme which dynamically adjusts the DL/UL ratio to allocate bandwidth for QoS support to users based on the usage statistics. The performance of the proposed QDRA scheme was examined by applying to the WiMAX standard specifications, to show its superiority of maintaining a higher QoS support for various classes of services compared to the pre-reported adaptive method.

An Uplink Capacity Analysis of the Distributed Antenna System (DAS): From Cellular DAS to DAS with Virtual Cells

Performance of cellular networks is severely limited by intense inter-cell interference due to aggressive frequency reuse among cells. How to characterize the dependency of inter-cell interference on positions of BS antennas and users is a key question for the capacity analysis of cellular systems, which unfortunately remains elusive. In this paper, a comparative study on the uplink ergodic sum capacity of cellular systems is presented, where L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> BS antennas are either co-located at the cell center or uniformly distributed within each cell. With a large number of users, the inter-cell interference density is shown to be inversely proportional to L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> if the co-located antenna (CA) layout is adopted. With the distributed antenna (DA) layout, it scales in the order of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-α/2</sup> , where α is the path-loss factor, and is much lower than that in the CA case when L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is large. Substantial gains on the uplink sum capacity are achieved by the DA layout thanks to the reduction of inter-cell interference level. The analysis also reveals that the inter-cell interference density of each BS antenna is sensitive to its position. With the DA layout, BS antennas at cell boundary areas suffer from much higher inter-cell interference than those at the cell center, which may exacerbate the performance disparity of users in cellular systems. To tackle the cell-edge problem, a distributed antenna system (DAS) is further considered, where L BS antennas are distributed over a wide area, and each user chooses V ≪ L surrounding BS antennas as its virtual cell, i.e., its own serving BS antenna set. A uniform inter-cell interference density is shown to be achieved thanks to the adaptive formation of virtual cells. More importantly, by the use of virtual cell, the number of users served by each BS antenna decreases with an increasing L, implying that much of the signal processing and information exchange can be performed in a local and distributed way. The uplink ergodic sum capacity and the ergodic rate with orthogonal access of DASs with V=1 are further derived, and shown to be close to each other even with a large L. It is in sharp contrast to cellular systems where a significant tradeoff between performance and complexity has to be made when the number of BS antennas is large.

Cognitive Small Cell Networks: Energy Efficiency and Trade-Offs

Heterogeneous networks using a mix of macrocells and small cells are foreseen as one of the solutions to meet the ever increasing mobile traffic demand. Nevertheless, a massive deployment of small cell access points (SAPs) leads also to a considerable increase in energy consumption. Spurred by growing environmental awareness and the high price of energy, it is crucial to design energy efficient wireless systems for both macrocells and small cells. In this work, we evaluate a distributed sleep-mode strategy for cognitive SAPs and we analyze the trade-off between traffic offloading from the macrocell and the energy consumption of the small cells. Using tools from stochastic geometry, we define the user discovery performance of the SAP and derive the uplink capacity of the small cells located in the Voronoi cell of a macrocell base station, accounting for the uncertainties associated with random position, density, user activity, propagation channel, network interference generated by uncoordinated activity, and the sensing scheme. In addition, we define a fundamental limit on the interference density that allows robust detection and we elucidate the relation between energy efficiency and sensing time using large deviations theory. Through the formulation of several optimization problems, we propose a framework that yields design guidelines for energy efficient small cell networks.