Global allocations in the upper mid-band spectrum (4-24 GHz) necessitate a comprehensive exploration of the propagation behavior to meet the promise of coverage and capacity. This paper presents an extensive Urban Microcell (UMi) outdoor propagation measurement campaign at 6.75 GHz and 16.95 GHz conducted in Downtown Brooklyn, USA, using a 1 GHz bandwidth sliding correlation channel sounder over 40-880 m propagation distance, encompassing seven Line of Sight (LOS) and 13 Non-Line of Sight (NLOS) locations. Analysis of the path loss (PL) reveals lower directional and omnidirectional PL exponents compared to mmWave and sub-THz frequencies in the UMi environment, using the close-in (CI) free space PL (FSPL) model with a 1 m reference distance. Additionally, a decreasing trend in root mean square (RMS) delay spread (DS) and angular spread (AS) with increasing frequency was observed. The measured NLOS RMS DS and RMS AS mean values (as computed by 3GPP methods) are found to be consistently lower compared to 3GPP model predictions. Point-data tables with corresponding site-specific environmental information for all measured statistics at each TX-RX location are provided to support the models and results. The spatio-temporal statistics presented here offer valuable insights for the design of nextgeneration wireless systems and networks.

The letter presents an improved algorithm for computation of general integer-order Hankel transforms, which is back-projection based. The original algorithm breaks the Hankel transform into an inverse fast Fourier transform and a discrete summation involving trigonometric terms (which is more computationally intensive). In this work, by varying the number of terms of the discrete summation with the transform order, the number of trigonometric computations and multiplications can be reduced drastically, which leads to overall computational complexity improvement. To be precise, the time complexity constant is reduced so much that our algorithm is faster than the state-of-the-art, while being O(N2). The algorithm has been simulated in MATLAB and a performance improvement of 6.04x in the discrete summation step (average case) over the original algorithm has been obtained. Finally, computational error of our proposed algorithm has been obtained, which is better than the baseline algorithm, and is comparable to the state-ofthe-art.

This paper proposes and analyzes novel deep learning methods for downlink (DL) single-user multiple-input multiple-output (MIMO) and multi-user MIMO (MU-MIMO) systems operating in time division duplex mode. A motivating application is the 6G upper midbands (7-24 GHz), where the base station (BS) antenna arrays are large, user equipment array sizes are moderate, and theoretically optimal approaches are practically infeasible for several reasons. To deal with uplink (UL) pilot overhead and low signal power issues, we introduce the channel-adaptive pilot, as part of the novel analog channel state information feedback mechanism. Deep neural network (DNN)-generated pilots are used to linearly transform the UL channel matrix into lower-dimensional latent vectors. Meanwhile, the BS employs a second DNN that processes the received UL pilots to directly generate near-optimal DL precoders. The training is end-to-end which exploits synergies between the two DNNs. For MU-MIMO precoding, we propose a DNN structure inspired by theoretically optimum linear precoding. The proposed methods are evaluated against genie-aided upper bounds and conventional approaches, using realistic upper midband datasets. Numerical results demonstrate the potential of our approach to achieve significantly increased sum-rate, particularly at moderate to high signal-to-noise ratio and when UL pilot overhead is constrained.

Intelligent reflecting surfaces (IRS) have the potential to provide coverage extension and capacity improvement in many scenarios, particularly at millimeter wave (mmWave) and terahertz (THz) frequencies, by making the wireless channels controllable to mitigate blockages in propagation environments. In this paper, we present key propagation-related characteristics and optimal phase shift solutions of IRSs for different incident and reflection angles. Raytracing-based simulations of IRSs were performed at 28 GHz in both indoor and outdoor scenarios, and the results show that IRS can greatly extend coverage and improve capacity at low cost.

In this paper, we investigate the interference generated by the High Altitude Platform Station (HAPS) deployments to the Terrestrial Networks (TNs) and quantify interference impact on the TN performance for the co-channel and adjacent channel deployment scenarios. For each case, both the unsynchronized Time-Division Duplexing (TDD) and synchronized TDD scenarios are considered. For the co-channel case, we observe that the synchronized TDD scenario requires a smaller inter-system distance than the unsynchronized case with respect to either the 5th percentile loss in spectral efficiency (SE) or the 95th percentile of the interference-to-noise ratio (I/N). For the adjacent channel case, we conclude that the resulting I/N is always below the minimum threshold of -6dB for both unsynchronized and synchronized scenarios. In addition to considering the full buffer traffic model, we also present results for a bursty traffic model under varying traffic loads.

The capability to achieve high-precision positioning accuracy has been considered as one of the most critical requirements for vehicle-to-everything (V2X) services in the fifth-generation (5G) cellular networks. The non-line-of-sight (NLOS) connectivity, coverage, reliability requirements, the minimum number of available anchors, and bandwidth limitations are among the main challenges to achieve high accuracy in V2X services. This work provides an overview of the potential solutions to provide the new radio (NR) V2X users (UEs) with high positioning accuracy in the future 3GPP releases. In particular, we propose a novel selective positioning solution to dynamically switch between different positioning technologies to improve the overall positioning accuracy in NR V2X services, taking into account the locations of V2X UEs and the accuracy of the collected measurements. Furthermore, we use high-fidelity system-level simulations to evaluate the performance gains of fusing the positioning measurements from different technologies in NR V2X services. Our numerical results show that the proposed hybridized schemes achieve a positioning error ≤ 3 m with ≈ 76% availability compared to ≈ 55% availability when traditional positioning methods are used. The numerical results also reveal a potential gain of ≈ 56% after leveraging the road-side units (RSUs) to improve the tail of the UE's positioning error distribution, i.e., worst-case scenarios, in NR V2X services.

High Altitude Platform Station (HAPS) has the potential to provide global wireless connectivity and data services such as high-speed wireless backhaul, industrial Internet of things (IoT), and public safety for large areas not served by terrestrial networks. A unified HAPS design is desired to support various use cases and a wide range of requirements. In this paper, we present two architecture designs of the HAPS system: i) repeater based HAPS, and ii) base station based HAPS, which are both viable technical solutions. The energy efficiency is analyzed and compared between the two architectures using consumption factor theory. The system performance of these two architectures is evaluated through Monte Carlo simulations and is characterized in metrics of spectral efficiency using LTE band 1 for both single-cell and multi-cell cases. Both designs can provide good downlink spectral efficiency and coverage, while the uplink coverage is significantly limited by UE transmit power and antenna gain. Using directional antennas at the UEs can improve the system performance for both downlink and uplink.

Technology advances have enabled unmanned aerial vehicles (UAV) to stay afloat in the stratosphere for several months as base station platforms with the communication payload powered by solar energy. These UAV-based High Altitude Platform Stations (HAPS) can provide i) connectivity for remote areas not served by terrestrial networks, ii) global coverage for IoT devices, and iii) services for public safety and transportation industries. At a typical altitude of 20 Km, an HAPS can cover a large service area with a higher throughput and a lower latency compared to satellite links.In this paper, we present a reference design of a New Radio (NR) HAPS communication system comprised of both service and feeder links that can serve multiple cells within a large coverage area. The use of an adaptive antenna array with beam steering enables the system to continuously serve users from the same cell while the aircraft conducts a repetitive flight pattern above the fixed service area. Achievable capacity and coverage of the service link design at a sub-6 GHz carrier frequency are first estimated in a link budget analysis and then evaluated through Monte Carlo simulations. We observe that good spectral efficiency and coverage can be expected for outdoor line-of-sight users in the downlink, while the uplink performance is limited by the transmit power and antenna gain of the user terminal. We also demonstrate that 5G NR in the mmWave band can be used for the feeder link and can satisfy the throughput and availability requirement.

Multihop self-backhauling is a key enabling technology for millimeter wave cellular deployments. We consider the multihop link scheduling problem with the objective of minimizing the end-to-end delay experienced by a typical packet. This is a complex problem, and so we model the system as a network of queues and formulate it as a Markov decision process over a continuous action space. This allows us to leverage the deep deterministic policy gradient algorithm from reinforcement learning to learn the delay minimizing scheduling policy under two scenarios: 1) an ideal setup where a centralized scheduler performs all per slot scheduling decisions and has full instantaneous knowledge of network state and 2) a centralized scheduler, but where network state feedback and scheduling decisions are limited to once per frame, which is many slots. For the second scenario, we model the scheduler with a recurrent neural network to capture the evolution of the network state over the frame. Detailed system-level simulations show that for the more realistic second scenario, the delay experienced by the 5thpercentile packets under backpressure based scheduling and max-min scheduling can be up to 230% and 260%, respectively more than that under the proposed scheduler.

The mm-wave spectra at 71-76 GHz (70 GHz) and 81-86 GHz (80 GHz) have the potential to endow fifth-generation new radio (5G-NR) with mobile connectivity at gigabit rates. However, a pressing issue is the presence of incumbent systems in these bands, which are primarily point-to-point fixed stations (FSs). In this paper, we first identify the key properties of incumbents by parsing databases of existing stations in major cities to devise several modeling guidelines and characterize their deployment geometry and antenna specifications. Second, we develop a detailed uplink interference framework to compute the aggregate interference from outdoor 5G-NR users into FSs. We then present several case studies in densely populated areas, using actual incumbent databases and building layouts. Our simulation results demonstrate promising 5G coexistence at 70 and 80 GHz as the majority of FSs experience interference well below the noise floor, thanks to the propagation losses in these bands and the deployment geometry of the incumbent and 5G systems. For the few FSs that may incur higher interference, we propose several passive interference mitigation techniques such as angular-based exclusion zones and spatial power control. The simulation results show that the techniques can effectively protect FSs, without tangible degradation of the 5G coverage.

Ultra-Reliable and Low Latency Communications (URLLC) is an important emerging area for the fifth generation (5G) cellular network. The requirements for URLLC are as stringent as 1-10-5reliability for a 32-byte packet with user plane latency of 1 ms. To achieve these requirements, grant-free transmission with repetitions of data packet has been recently proposed for uplink transmissions. However, the resource overhead and collisions among URLLC user equipments (UEs) become limiting factors to achieving optimal system performance. In this work, a hybrid resource allocation scheme is proposed to optimally allocate dedicated resource units and/or a shared resource pool to a group of UEs. Numerical results based on theoretical analysis show that the target requirements of URLLC can be achieved with up to 70% reduction in resource utilization compared to the conservative transmission scheme.

There is an expected explosion in the number of users which will be connected to future wireless networks with the continued expansion of the Internet of Things. New technologies are needed in order to keep up with this connectivity demand. Non-orthogonal multiple access (NOMA) is one technology which seeks to improve spectral efficiency and allow for more connected users. NOMA seeks to overload resources in order to allow more users to access the same time and frequency resource blocks. There have been various proposals on how to realize NOMA in the network, including power domain non-orthogonal multiple access (PD-NOMA), interleave division multiple access(IDMA), and sparse code multiple access (SCMA). This paper investigates these three proposals and simulates them in the uplink setting in order to analyze their performance and compare them. Advantages and disadvantages for each technique are discussed with an emphasis on practical considerations.

The Internet of Things (IoT) is expected to reach a massive scale in the next few years and LTE has introduced a feature in Rel-13 called eMTC to support wide-area connectivity for IoT devices. One important trend for IoT is the integration of voice capability into the devices. However, low-cost, low-complexity IoT User Equipment (UE) typically supports only half-duplex communication and low data rates. In this paper, we compare the performance and coverage of low-complexity eMTC UE with legacy non-eMTC UE for delay-sensitive Voice over LTE (VoLTE) service. It is shown that eMTC UE can provide similar coverage to non-eMTC UE using the same delay and block error rate requirements. If the delay budget or quality of service can be relaxed for eMTC, then eMTC can provide slightly better VoLTE coverage. This allows service operators to support voice capability for IoT devices using existing infrastructure footprint.

In 3GPP Rel-13, a narrowband wide-area cellular system, named Narrowband Internet of Things (NB-IoT), has been introduced to provide low-cost, low-power connectivity for the Internet of Things. This system, based on Long Term Evolution (LTE) technology, can be deployed in three operation modes - in-band within LTE carrier, in the guard-band of LTE carrier, and stand-alone. Guard-band deployment allows the operator to support NB-IoT without requiring new spectrum and with minimal impact to LTE. This paper provides an overview and presents a study of NB-IoT deployment in LTE guard band. An analysis of coexistence of NB-IoT with LTE is presented and demonstrates that while there is mutual interference between NB-IoT and LTE on the uplink, the impact on either system is small. A performance analysis of NB-IoT is also presented. The link budget analysis demonstrates how the coverage target can be achieved for the uplink and downlink data channels. Illustrative uplink and downlink link-level simulation results are provided. The analysis in the paper shows that guard-band operation of NB-IoT is feasible and can provide support for massive number of low-throughput IoT devices.

A promising way of realizing the fifth generation (5G) wireless systems is to operate 5G deployments at higher frequency bands, specifically in the millimeter-wave (mmW) spectrum (30-300 GHz). Access to such spectrum bands will enable future 5G wireless systems to meet the 5G requirements of peak rate greater than 10 Gb/s, and cell edge rate of up to 1 Gb/s. However, the emerging 5G systems will need to coexist with a number of incumbent systems in these bands. This paper provides an extensive study of the co-channel coexistence of 5G in two critical mmW bands, 27.5-28.35 GHz (28 GHz) and 71-76 GHz (70 GHz) bands, where fixed satellite service (FSS) and fixed service (FS), such as wireless backhaul, are the predominant incumbent users. In the 28-GHz study, we show that interference from 5G into the FSS space stations can be kept below the FSS interference protection criterion. We also characterize the minimum separation distance between the FSS earth stations (ESs) and 5G in order to protect the 5G system from interference due to the ESs transmissions. In the 70-GHz study, we show that the 5G-to-FS interference could be a potential issue in certain scenarios, but we introduce techniques to significantly suppress this interference, while maintaining acceptable performance of the 5G systems. For each study, we suggest appropriate deployment strategies for a 5G system based on our results.

Millimeter wave (mmWave) communications have recently attracted large research interest, since the huge available bandwidth can potentially lead to the rates of multiple gigabit per second per user. Though mmWave can be readily used in stationary scenarios, such as indoor hotspots or backhaul, it is challenging to use mmWave in mobile networks, where the transmitting/receiving nodes may be moving, channels may have a complicated structure, and the coordination among multiple nodes is difficult. To fully exploit the high potential rates of mmWave in mobile networks, lots of technical problems must be addressed. This paper presents a comprehensive survey of mmWave communications for future mobile networks (5G and beyond). We first summarize the recent channel measurement campaigns and modeling results. Then, we discuss in detail recent progresses in multiple input multiple output transceiver design for mmWave communications. After that, we provide an overview of the solution for multiple access and backhauling, followed by the analysis of coverage and connectivity. Finally, the progresses in the standardization and deployment of mmWave for mobile networks are discussed.

For the potential of providing rates of multiple Giga-bps in a single channel, millimeter wave (mmWave) communications have recently attracted substantial research interest. While mmWave technology is already being used in stationary scenarios such as indoor hotspots or backhaul, it is challenging to use mmWave frequencies in mobile networks, where transmitting/receiving nodes may be moving, channels may have a complicated structure, and the coordination among multiple nodes is difficult. To fully exploit the high potential rates of mmWave in mobile networks, many significant technical challenges must be tackled. The main objective of this IEEE JSAC Special Issue on “Millimeter wave communications for future mobile networks” is to collect the most recent technical advances in mmWave for future mobile networks. The response from the community to the call has been overwhelming. We received 96 submissions with a call period short than 4 months. Many of the submissions are from the most well known research groups in the field. After a strict review process, we decided to accept 38 papers, which will be published in two issues. The papers were selected based on the technical relevance and merits. Unfortunately, due to space limitations, a number of interesting papers were not selected, despite the merits that they had. We sincerely hope those papers can find other publishing venues.

Initial deployments of millimeter wave (mm-wave) cellular networks are likely to be enabled with self-backhauling. In this paper, we propose a random spatial model to analyze uplink (UL) and downlink (DL) signal to interference plus noise ratio distribution and mean rates corresponding to different access-backhaul and UL-DL resource allocation schemes in a self-backhauled mm-wave cellular network with Poisson point process (PPP) deployment of users and base stations (BSs). In particular, we focus on heuristic implementations of static and dynamic time division duplexing (TDD) for access links with synchronized or unsynchronized access-backhaul (SAB or UAB) time splits. We propose PPP approximations to characterize the distribution of the new types of interference encountered with dynamic TDD and UAB. These schemes offer better resource utilization than static TDD and SAB, however, potentially higher interference makes their choice non-trivial and the offered gains sensitive to different network parameters, including UL/DL traffic asymmetry, user load per BS or number of slave BSs per master BS. One can harness notable gains from UAB and/or dynamic TDD only if backhaul links are designed to have much larger throughput than the access links.

In conventional applications of time division duplex (TDD) in cellular systems, the time resource split between uplink (UL) and downlink (DL) is fixed across all base stations (BSs) in the network. This leads to under utilization of BS resources when there is a mismatch between the expected and experienced UL/DL traffic in a given cell. A dynamic split that varies in each cell is desirable, but is challenging due to the high interference experienced by UL receivers in one cell from DL transmissions in adjacent cells. This paper analyzes the performance of UL users in dynamic TDD enabled next generation cellular networks using a stochastic geometry framework. The analysis highlights the trade-off between spectral efficiency and resource utilization for dynamic TDD. With appropriate interference mitigation, dynamic TDD offers a significant gain in data rates as compared to static TDD, which is higher when the BSs are lightly loaded and/or the fraction of UL users is low.

In 3GPP, a narrowband system based on Long Term Evolution (LTE) has been introduced to support the Internet of Things. This system, named Narrowband Internet of Things (NB-IoT), provides low-cost devices, high coverage (20 dB improvement over LTE/GPRS), long device battery life (more than 10 years), and massive capacity. Latency is relaxed although a delay budget of 10 seconds is the target for exception reports. NB-IoT can be deployed in three different operation modes - (1) stand-alone as a dedicated carrier, (2) in-band within the occupied bandwidth of a wideband LTE carrier, and (3) within the guard-band of an existing LTE carrier. In this paper, we undertake a deployment study of NB-IoT using existing LTE infrastructure. We consider the case when only a fraction of the existing LTE cell sites support NB-IoT (so called partial deployment of NB-IoT). In this case, NB-IoT devices cannot attach to the best cell if that cell does not support NB-IoT. As a result, the path loss can be very high. In addition, they also suffer from high interference from non-NB-IoT cells. We examine potential techniques to compensate for the high path-loss and high interference and provide analysis to indicate when partial deployment of NB-IoT is feasible. We also examine interference issues in asynchronous deployments and study performance.

For the development of new 5G systems to operate in bands up to 100 GHz, there is a need for accurate radio propagation models at these bands that currently are not addressed by existing channel models developed for bands below 6 GHz. This document presents a preliminary overview of 5G channel models for bands up to 100 GHz. These have been derived based on extensive measurement and ray tracing results across a multitude of frequencies from 6 GHz to 100 GHz, and this document describes an initial 3D channel model which includes: 1) typical deployment scenarios for urban microcells (UMi) and urban macrocells (UMa), and 2) a baseline model for incorporating path loss, shadow fading, line of sight probability, penetration and blockage models for the typical scenarios. Various processing methodologies such as clustering and antenna decoupling algorithms are also presented.

In-band full-duplex communication has been proposed as a technique in 5G to increase spectral efficiency. Traditionally full duplex wireless communication has been considered very challenging due to large self-interference that is generated. However in recent years researchers have begun to challenge this assumption with breakthroughs in self- interference cancellation (SIC). Most work on full duplex up to this point has been focused on point to point communication links and relatively little work has looked into the system level challenges. One of the largest unanswered questions about full duplex is whether it is a viable technology for access in future cellular networks. The main concern with deploying full duplex is how the additional interference will affect the system performance. In this paper, SIC will be modeled and link level simulations will be presented showing that full duplex only slightly degrades the uplink frame error rate performance of a full duplex capable eNB. These results will then be used to determine an appropriate link to system mapping for full duplex. From there multiple cellular system deployment scenarios will be investigated and the feasibility of full duplex will be explored. It will be shown that for Indoor Hotspot (InH) deployment scenario 20 percent sum throughput gain can be achieved with full duplex capability. For the outdoor scenari-os full duplex can grant up to 20 percent gains and 3 percent gains for the Urban Micro (UMi) and Urban Macro (UMa) deployment scenarios respectively depending upon the amount of sectorization used. Based on these initial results and some of the assumptions used it will be concluded that full duplex is challenging for outdoor access and may only be viable for indoor scenarios and other use cases (e.g. backhaul, unlicensed spectrum).

This paper presents and compares two candidate large-scale propagation path loss models, the alpha-beta-gamma (ABG) model and the close-in (CI) free space reference distance model, for the design of fifth generation (5G) wireless communication systems in urban micro- and macro-cellular scenarios. Comparisons are made using the data obtained from 20 propagation measurement campaigns or ray- tracing studies from 2 GHz to 73.5 GHz over distances ranging from 5 m to 1429 m. The results show that the one-parameter CI model has a very similar goodness of fit (i.e., the shadow fading standard deviation) in both line-of-sight and non-line-of-sight environments, while offering substantial simplicity and more stable behavior across frequencies and distances, as compared to the three-parameter ABG model. Additionally, the CI model needs only one very subtle and simple modification to the existing 3GPP floating-intercept path loss model (replacing a constant with a close-in free space reference value) in order to provide greater simulation accuracy, more simplicity, better repeatability across experiments, and higher stability across a vast range of frequencies.

In 3GPP, a narrowband system based on Long Term Evolution (LTE) is being introduced to support the Internet of Things. This system, named Narrowband Internet of Things (NB-IoT), can be deployed in three different operation modes - (1) stand-alone as a dedicated carrier, (2) in-band within the occupied bandwidth of a wideband LTE carrier, and (3) within the guard-band of an existing LTE carrier. In stand-alone operation mode, NB-IoT can occupy one GSM channel (200 kHz) while for in-band and guard-band operation modes, it will use one physical resource block of LTE (180 kHz). The design targets of NB-IoT include low-cost devices, high coverage (20-dB improvement over GPRS), long device battery life (more than 10 years), and massive capacity. Latency is relaxed although a delay budget of 10 seconds is the target for exception reports. The specifications for NB-IoT are expected to be finalized in 2016. In this paper, we describe the targets for NB-IoT and present a preliminary system design. In addition, coverage, capacity, latency, and battery life analysis are also presented.

Large antenna arrays will be needed in future millimeter wave (mmWave) cellular networks, enabling a large number of different possible antenna architectures and multiple-input multiple-output (MIMO) techniques. It is still unclear which MIMO technique is most desirable as a function of different network parameters. This paper, therefore, compares the coverage and rate performance of hybrid beamforming enabled multiuser (MU) MIMO and single-user spatial multiplexing (SM) with single-user analog beamforming (SU-BF). A stochastic geometry model for coverage and rate analysis is proposed for MU-MIMO mmWave cellular networks, taking into account important mmWave-specific hardware constraints for hybrid analog/digital precoders and combiners, and a blockage-dependent channel model which is sparse in angular domain. The analytical results highlight the coverage, rate, and power consumption tradeoffs in multiuser mmWave networks. With perfect channel state information at the transmitter and round robin scheduling, MU-MIMO is usually a better choice than SM or SU-BF in mmWave cellular networks. This observation, however, neglects any overhead due to channel acquisition or computational complexity. Incorporating the impact of such overheads, our results can be re-interpreted so as to quantify the minimum allowable efficiency of MU-MIMO to provide higher rates than SM or SU-BF.

The use of high-frequency millimeter wave (mmWave) bands for 5G communication systems has received much attention over the last few years. Analog-to-digital converters (ADCs) contribute significantly to the implementation cost and power consumption of wireless receivers. The use of large antenna arrays in mmWave communications causes these costs to rise even further. Using low precision quantizers in ADCs can reduce these costs significantly. In this paper, we propose a novel receiver design using low precision quantizers drawing ideas from the parallel ADC design literature. Utilizing structural similarities between multi-antenna receivers and parallel ADCs, we show that the signal-to-noise ratio and achievable rate, respectively, scale linearly and logarithmically with the number of antennas. We also extend the idea to the scenario where multiple streams can be transmitted simultaneously. Our simulations of the receiver show promising bit error rate performance under different scenarios and also show how error control coding can be incorporated to improve performance. All our designs depend only on symbol rate sampling, which eliminates costly oversampling of high bandwidth signals.

The Internet of Things will bring about billions of connected devices. In the cellular space, machine type communications using LTE is under consideration by many operators. LTE, however, was designed to provide broadband high-speed data service with very low latency. Machine type communications, on the other hand, have a different set of requirements, namely low-rate, low-overhead, low-power-consumption, and low-cost. To address these requirements and also to minimize impact from machine traffic to human traffic, 3GPP has been working on numerous LTE features such as power saving, overload control, signaling reduction, complexity reduction, and coverage enhancement. This paper will provide an overview of LTE enhancements for machine type communications. The paper will also present LTE capacity analysis for machine traffic as well as the battery life of the devices.

Deployment of LTE in unlicensed bands is being considered in Rel-13 of LTE. This feature is called Licensed-Assisted Access (LAA) using LTE. Unlicensed band is attractive due to the large amount of available spectrum. However, in shared spectrum the coexistence between LAA and WiFi systems becomes a primary challenge. This paper presents an analytical framework to investigate the downlink coexistence performance between two systems with a simple listen-before-talk (LBT) mechanism enforced on LAA. Using this framework, theoretical models based on Markov chains are established for both systems and downlink throughput can be calculated. Numerical results from the models show that the simple listen-before-talk scheme is very effective in LAA and LAA coexistence scenario (i.e. two LAA systems sharing the same spectrum). In LAA and WiFi coexistence scenario, it can improve WiFi performance substantially.

Device-to-device (D2D) communication is a new feature being introduced to LTE in 3GPP Release 12. This feature will provide proximity services including support for public safety applications. For D2D communication within the network coverage area, network assistance is very beneficial for interference management purpose to ensure reliable communication. In this case, a simple algorithm can be used wherein the network manages the number and selection of simultaneous D2D transmissions within its cell. This will help manage interference from D2D transmission in case of time-frequency reuse to ensure that minimum performance requirement can be satisfied. In this paper, we outline a method for determining the maximum number of simultaneous D2D transmitters in a given cell. In addition, a method for selecting D2D pairs for simultaneous transmission is also provided. It is shown that, with network assistance, the percentage of reliable D2D communication links can be improved significantly.

This paper evaluates the theoretic performance of single-user multi-stream beamforming for heterogeneous LTE-A urban deployments (i.e. Macro and Pico cells). The work investigates the impact of six different Base Station (BS) antenna configurations on system level capacity. Our standard configuration assume 8 BS and 8 User Equipment (UE) antenna elements. To enhance capacity the BS antenna number was increased to 12 and 16. A 3D laser-scanned database for the city of Bristol (UK) was used as input to the 3D channel propagation model along with measured 3D complex voltage and polarimetric antenna patterns for the individual BS and UE antenna elements. More than 50,000 ray-traced Pico and Macro cellular links per BS configuration were investigated to ensure statistical relevance. Our analysis quantifies the capacity of an 8×8 Single-User Multiple-Input-Multiple-Output (SU-MIMO) solution in realistic urban heterogeneous environments. Results address the system level benefits of increasing the number of BS antenna elements as well as the sensitivity of capacity to vertical and horizontal spatial element configurations.

Millimeter wave (mmWave) cellular systems will require high-gain directional antennas and dense base station (BS) deployments to overcome a high near-field path loss and poor diffraction. As a desirable side effect, high-gain antennas offer interference isolation, providing an opportunity to incorporate self-backhauling, i.e., BSs backhauling among themselves in a mesh architecture without significant loss in the throughput, to enable the requisite large BS densities. The use of directional antennas and resource sharing between access and backhaul links leads to coverage and rate trends that significantly differ from conventional UHF cellular systems. In this paper, we propose a general and tractable mmWave cellular model capturing these key trends and characterize the associated rate distribution. The developed model and analysis are validated using actual building locations from dense urban settings and empirically derived path loss models. The analysis shows that, in sharp contrast to the interference-limited nature of UHF cellular networks, the spectral efficiency of mmWave networks (besides the total rate) also increases with the BS density, particularly at the cell edge. Increasing the system bandwidth does not significantly influence the cell edge rate, although it boosts the median and peak rates. With self-backhauling, different combinations of the wired backhaul fraction (i.e., the fraction of BSs with a wired connection) and the BS density are shown to guarantee the same median rate (QoS).

Fifth-generation wireless systems are expected to employ multiple-antenna communication at millimeter wave (mmWave) frequencies using small cells within heterogeneous cellular networks. The high path loss of mmWave and the physical obstructions make communication challenging. To compensate for the severe path loss, mmWave systems may employ a beam alignment algorithm that facilitates highly directional transmission by aligning the beam direction of multiple antenna arrays. This paper discusses a mmWave system employing dual-polarized antennas. First, we propose a practical soft-decision beam alignment (soft-alignment) algorithm that exploits orthogonal polarizations. By sounding the orthogonal polarizations in parallel, the equality criterion of the Welch bound for training sequences is relaxed. Second, the analog beamforming system is adapted to the directional characteristics of the mmWave link, assuming a high Ricean K-factor and poor scattering environment. A soft-alignment algorithm enables the mmWave system to align a large number of narrow beams to the channel subspace in an attempt to effectively scan the mmWave channel. Third, we propose a method to efficiently adapt the number of channel sounding observations to the specific channel environment based on an approximate probability of beam misalignment. Simulation results show that the proposed soft-alignment algorithm with adaptive sounding time effectively scans the channel subspace of a mobile user by exploiting polarization diversity.

A 2D antenna array introduces a new level of control and additional degrees of freedom in multiple-input-multiple-output (MIMO) systems particularly for the so-called “massive MIMO” systems. To accurately assess the performance gains of these large arrays, existing azimuth-only channel models have been extended to handle 3D channels by modeling both the elevation and azimuth dimensions. In this paper, we study the channel correlation matrix of a generic ray-based 3D channel model, and our analysis and simulation results demonstrate that the 3D correlation matrix can be well approximated by a Kronecker production of azimuth and elevation correlations. This finding lays the theoretical support for the usage of a product codebook for reduced complexity feedback from the receiver to the transmitter. We also present the design of a product codebook based on Grassmannian line packing.

The case study in this paper compares various options for deploying picocells in a three-carrier LTE macrocell network in a suburban North American city. Beginning with a single carrier macrocell network on a 5 MHz FDD carrier in LTE band 25 (2 GHz), a 20 MHz TDD carrier in band 41 (2.6 GHz) is added to significantly increase capacity. An additional 5 MHz FDD carrier in band 26 (875 MHz) enhances coverage. The picocell deployment options include placing picocells in band 25, in band 41, or on a dedicated band 41 20 MHz TDD carrier. In addition, picocells may be split between the FDD carrier and the dedicated TDD carrier to simulate a phased rollout as spectrum becomes available. Since the band 41 carrier has a larger bandwidth, network capacity is higher when picocells are placed on this carrier (compared to band 25) even though the number of picocells required to maintain a constant network outage is similar. Dedicated band picocell deployment requires fewer picocells and has higher capacity due to reduced interference.

The Internet of Things will bring billions of devices that are inter-connected using cellular networks. LTE cellular systems are being deployed worldwide and will remain in place for the foreseeable future. However, LTE was designed for high data-rate broadband services. Even with M2M features being added in LTE Rel-12, it is not optimized for low data-rate and wide area M2M services such as smart meters, remote sensors, and consumer devices. In this paper, we present a design of a new narrowband M2M system built from existing LTE functionalities for Low Power Wide Area (LPWA) systems. Salient features of this new system include low-cost devices, high coverage, long device battery life, and high capacity. It can be deployed using minimum of one GSM channel and can also share spectrum with existing broadband LTE systems. Cost analysis shows significant reduction compared to LTE UEs. In addition, coverage analysis and capacity results are presented. Finally, coexistence with GSM is analyzed.

Millimeterwave band is a promising candidate for 5th generation wireless access technology to deliver peak and cell-edge data rates of the order of 10 Gbps and 100 Mbps, respectively, and to meet the future capacity demands. The main advantages of the millimeterwave band are availability of large blocks of contiguous bandwidth and the opportunity of using large antenna arrays composed of very small antenna elements to provide large antenna gains. The line-of-sight operation requirement in this band, due to its unique propagation characteristics, makes it necessary to build the network with enough redundancy of access points and the users may have to frequently handoff from one access point to another whenever its radio link is disrupted by obstacles. In this paper we investigate the handoff rate in such an access network. Based on analysis of various deployment scenarios, we observe that, typical average handoff interval is several seconds, although for certain types of user actions the average handoff interval can be as low as 0.75 sec.

Wireless data traffic is projected to skyrocket 10 000 fold within the next 20 years. To tackle this incredible increase in wireless data traffic, a first approach is to further improve spectrally efficient systems such as 4G LTE in bands below 6 GHz by using more advanced spectral efficiency techniques. However, the required substantial increase in system complexity along with fundamental limits on hardware implementation and channel conditions may limit the viability of this approach. Furthermore, the end result would be an extremely spectrally efficient system with little room for future improvement to meet the ever-growing wireless data usage. The second approach is to move up in frequency, into an unused nontraditional spectrum where enormous bandwidths are available, such as at millimeter wave (mmWave). The mmWave option enables the use of simple air interfaces since large bandwidths can be exploited (e.g., 2 GHz) to achieve high data rates rather than relying on highly complex techniques originally aimed at achieving a high spectral efficiency with smaller bandwidths. In addition, mmWave systems will easily evolve to even higher system capacities, because there will be plenty of margin to improve the spectral efficiency as data demands further increase. In this paper, a case is made for using mmWave for a fifth generation (5G) wireless system for ultradense networks by presenting an overview of enhanced local area (eLA) technology at mmWave with emphasis on 5G requirements, spectrum considerations, propagation and channel modeling, air-interface and multiantenna design, and network architecture solutions.

This paper addresses two fundamental and interrelated issues in device-to-device (D2D) enhanced cellular networks. The first issue is how D2D users should access spectrum, and we consider two choices: overlay (orthogonal spectrum between D2D and cellular UEs) and underlay (non-orthogonal). The second issue is how D2D users should choose between communicating directly or via the base station, a choice that depends on distance between the potential D2D transmitter and receiver. We propose a tractable hybrid network model where the positions of mobiles are modeled by random spatial Poisson point process, with which we present a general analytical approach that allows a unified performance evaluation for these questions. Then, we derive analytical rate expressions and apply them to optimize the two D2D spectrum sharing scenarios under a weighted proportional fair utility function. We find that as the proportion of potential D2D mobiles increases, the optimal spectrum partition in the overlay is almost invariant (when D2D mode selection threshold is large) while the optimal spectrum access factor in the underlay decreases. Further, from a coverage perspective, we reveal a tradeoff between the spectrum access factor and the D2D mode selection threshold in the underlay: as more D2D links are allowed (due to a more relaxed mode selection threshold), the network should actually make less spectrum available to them to limit their interference.

Multicast device-to-device (D2D) transmission is important for applications like local file transfer in commercial networks and is also a required feature in public safety networks. In this paper we propose a tractable baseline multicast D2D model, and use it to analyze important multicast metrics like the coverage probability, mean number of covered receivers and throughput. In addition, we examine how the multicast performance would be affected by certain factors like dynamics (due to e.g., mobility) and network assistance. Take the mean number of covered receivers as an example. We find that simple repetitive transmissions help but the gain quickly diminishes as the number of repetitions increases. Meanwhile, dynamics and network assistance (i.e., allowing the network to relay the multicast signals) can help cover more receivers. We also explore how to optimize multicasting, e.g. by choosing the optimal multicast rate and the optimal number of retransmission times.

The stadium environment represents one of the tougher environments for cellular systems given the extreme density of users and the potential for a large amount of uplink traffic. This paper presents the design and evaluation of 2D antenna arrays employed with azimuth and elevation sectorization in the stadium environment to improve the 3GPP LTE mobile network performance. A typical stadium model is introduced and different deployment options for a 2D antenna array with multiple sector beams are considered. It is found that only 2 to 4 antenna sites are sufficient to provide effective stadium coverage with up to 44 parallel spatially multiplexed sectors by using the antenna arrays consisting of 10×16 (elevation × azimuth) cross-polarized antenna element pairs. For more efficient performance the beams of each antenna array should be oriented towards the nearest stadium stands under the antenna suspension point. Using the results of system-level simulations it is estimated that the spectral efficiency of the stadium deployment can be up to 1.5-1.8 bit/s/Hz/sec resulting in the overall throughput of up to 1.5 Gbit/s which should be sufficient to provide the connectivity for tens of thousands people attending the stadium events.

Heterogeneous networks (HetNets) and carrier aggregation (CA) are two distinct features of next-generation cellular networks. Small cells in HetNets are vital for data off-loading and can significantly improve area and cell edge spectral efficiency compared to using just macrocells. CA further increases the transmission bandwidth and thus network capacity by aggregating multiple component carriers on the physical layer. In this paper, we propose a tractable multi-band multi-tier model to study multi-flow CA in HetNets, where base station positions in each tier follow an independent Poisson point process. Our model incorporates an appropriate notion of load which allows the study of the impact of biasing on HetNet performance. For a typical HetNet consisting of two tiers, macro cells and small cells, and two bands, 800MHz band and 2.4GHz band, we observe that the gain (in terms of UE ergodic rate) is about 35% to 40% if the small cells adopt optimal biasing factor compared to the case without biasing. Our model also incorporates the impact of band deployment. For the typical HetNet described, our study suggests that deploying the 800MHz band and 2.4GHz band in both the macro and small cells helps the HetNet best exploit the CA feature.

Availability of large untapped spectrum resources in the millimeter wave (Mmwave) band is suitable for providing a gigabit experience with true local feel using high capacity small cells. Unlike traditional cellular systems, millimeter wave transmissions do not benefit from diffraction and dispersion making it difficult for them to propagate around obstacles thus resulting in higher shadowing loss. They also have less favorable link budgets due to lower power amplifier (PA) output powers and greater pathloss at these higher frequencies. Also, current costs of the Mmwave circuits are higher, but the costs will become much lower when the technology becomes mainstream. One advantage of millimeter wave, however, is that the smaller wavelengths allow for the fabrication of antenna arrays having a much higher number of antenna elements in a much smaller area than is typical at microwave bands. In this article, we outline a framework for Beyond-4G (B-4G) local area network in the millimeter wave band for both access and backhaul including air-interface, antenna-arrays and IC technology. It is shown that Mmwave B-4G small cell technology can provide peak and cell edge rates greater than 10 Gbps and 100 Mbps respectively with latency less than 1msec for local area network.

A suburban North American city is used as the basis for comparing the relative effectiveness of deploying picocells or macrocells to meet burgeoning 4G traffic demand. The study starts with an existing macro deployment and employs detailed models to examine 3X and 5X traffic growth relative to the capacity of the current macro network. 3D building models are used to generate accurate pathloss planes modeling both outdoor and indoor propagation. Spatial traffic distributions are derived from 3G network data and constrained such that 70% of the users reside indoors. A Monte Carlo simulation utilizes user densities consistent with 3X and 5X traffic growth to determine how many picocells or macrocells are required to meet a 1 Mbps cell edge capacity for both outdoor and indoor users.

Machine type communications (MTC) is defined as data communication among devices without the need for human interaction. With the decommissioning of legacy cellular systems, migration of MTC devices to LTE is under investigation by many operators. It is desirable that the cost of LTE MTC devices is similar to that of existing GSM devices. Several cost reduction techniques have been studied. This paper summarizes cost reduction techniques for MTC devices and examines system impacts from such devices being introduced in LTE. Performance is evaluated for the Advanced Metering Infrastructure used in smart grid. It is seen that LTE offers significant capacity for smart metering even with low-cost devices. For a system with 10 MHz bandwidth, approximately 2% of the system resource is required to support AMI in an urban deployment scenario.

In this paper, LTE Rel-10 eICIC, an advanced interference mitigation technique using semi-static coordination and DL CoMP techniques relying on dynamic scheduling are jointly applied in a heterogeneous network comprising of macro and low power nodes. It is shown that these algorithms, when applied jointly and if supported with appropriately designed feedback schemes, can provide complementary benefits and can significantly improve both system capacity and user experience in the network. Using covariance matrix feedback, we observe that the joint application of CoMP and eICIC can provide more than 20% system throughput improvement and more than 40% cell-edge throughput improvement that exceed the gains of either CoMP or eICIC applied individually.

Large online service providers (OSPs) often build private backbone networks to interconnect data centers in multiple locations. These data centers house numerous applications that produce multiple classes of traffic with diverse performance objectives. Applications in the same class may also have differences in relative importance to the OSP's core business. By controlling both the hosts and the routers, an OSP can perform both application rate-control and network routing. However, centralized management of both rates and routes does not scale due to excessive message-passing between the hosts, routers, and management systems. Similarly, fully-distributed approaches do not scale and converge slowly. To overcome these issues, we investigate two semi-centralized designs that lie at practical points along the spectrum between fully-distributed and fully-centralized solutions. We achieve scalability by distributing computation across multiple tiers of an optimization machinery. Our first design uses two tiers, representing the backbone and classes, to compute class-level link bandwidths and application sending rates. Our second design has an additional tier representing individual data centers. Using optimization, we show that both designs provably maximize the aggregate utility over all traffic classes. Simulations on realistic backbones show that the 3-tier design is more scalable, but converges slower than the 2-tier design.

Recently, there has been considerable interest in new tiered network cellular architectures, which would likely use many more cell sites than found today. Two major challenges will be i) providing backhaul to all of these cells and ii) finding efficient techniques to leverage higher frequency bands for mobile access and backhaul. This paper proposes the use of outdoor millimeter wave communications for backhaul networking between cells and mobile access within a cell. To overcome the outdoor impairments found in millimeter wave propagation, this paper studies beamforming using large arrays. However, such systems will require narrow beams, increasing sensitivity to movement caused by pole sway and other environmental concerns. To overcome this, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a corresponding performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. The results show significant performance improvement with reduced search time.

Carrier aggregation (CA) and small cells are two distinct features of next-generation cellular networks. Cellular networks with different types of small cells are often referred to as HetNets. In this paper, we introduce a load-aware model for CA-enabled multi-band HetNets. Under this model, the impact of biasing can be more appropriately characterized; for example, it is observed that with large enough biasing, the spectral efficiency of small cells may increase while its counterpart in a fully-loaded model always decreases. Further, our analysis reveals that the peak data rate does not depend on the base station density and transmit powers; this strongly motivates other approaches e.g. CA to increase the peak data rate. Last but not least, different band deployment configurations are studied and compared. We find that with large enough small cell density, spatial reuse with small cells outperforms adding more spectrum for increasing user rate. More generally, universal cochannel deployment typically yields the largest rate; and thus a capacity loss exists in orthogonal deployment. This performance gap can be reduced by appropriately tuning the HetNet coverage distribution (e.g. by optimizing biasing factors).

Two emerging trends of Internet applications, video traffic becoming dominant and usage-based pricing becoming prevalent, are at odds with each other. Given this conflict, is there a way for users to stay within their monthly data plans (data quotas) without suffering a noticeable degradation in video quality? In this work, we develop an online video adaptation system, called Quota Aware Video Adaptation (QAVA), that manages this tradeoff by leveraging the compressibility of videos and by predicting consumer usage behavior throughout a billing cycle. We propose the QAVA architecture and develop its main modules, including Stream Selection, User Profiling, and Video Profiling. Online algorithms are designed through dynamic programming and evaluated using real video request traces. Empirical results suggest that QAVA can provide an effective solution to the dilemma of usage-based pricing of heavy video traffic.

It has been recognized that a primary method of further enhancing the downlink spectral efficiency of LTE Release-10 is to introduce support for coordinated multi-point (CoMP) transmission. This paper investigates the performance improvements due to downlink CoMP within the framework of LTE (specifically LTE Release-11). A realistic estimate of achievable CoMP throughput performance is provided with respect to variations in deployment scenario, amount of feedback information and at different traffic loads. It is observed that the performance gains due to CoMP are limited to cell edge UE (user equipment) throughput improvements of up to 30%. Further, we show that dynamic cell selection can realize most of the CoMP gains with less feedback than joint transmission and it is more robust under practical conditions.

Machine type communications (MTC) is defined as data communication among devices without the need for human interaction. Examples of MTC services include security, tracking, payment, smart grid, and remote monitoring. With the widespread introduction of LTE and decommissioning of legacy systems, migration of MTC devices to LTE is under investigation by many cellular operators. This paper examines LTE uplink coverage and capacity for machine type communications. It is seen that LTE provides similar coverage to other cellular systems but significantly higher capacity for MTC services. Capacity, however, may be significantly reduced for devices with lower maximum transmit power devices or QPSK-only modulation. MTC on LTE is also shown to be robust to interference and can be deployed in unlicensed band with only a moderate reduction in capacity.

Interference management techniques are critical to the performance of heterogeneous cellular networks, which will have dense and overlapping coverage areas, and experience high levels of interference. Fractional frequency reuse (FFR) is an attractive interference management technique due to its low complexity and overhead, and significant coverage improvement for low-percentile (cell-edge) users. Instead of relying on system simulations based on deterministic access point locations, this paper instead proposes an analytical model for evaluating Strict FFR and Soft Frequency Reuse (SFR) deployments based on the spatial Poisson point process. Our results both capture the non-uniformity of heterogeneous deployments and produce tractable expressions which can be used for system design with Strict FFR and SFR. We observe that the use of Strict FFR bands reserved for the users of each tier with the lowest average \sinr provides the highest gains in terms of coverage and rate, while the use of SFR allows for more efficient use of shared spectrum between the tiers, while still mitigating much of the interference. Additionally, in the context of multi-tier networks with closed access in some tiers, the proposed framework shows the impact of cross-tier interference on closed access FFR, and informs the selection of key FFR parameters in open access.

We investigate the following fundamental question—how fast can information be collected from a wireless sensor network organized as tree? To address this, we explore and evaluate a number of different techniques using realistic simulation models under the many-to-one communication paradigm known as convergecast. We first consider time scheduling on a single frequency channel with the aim of minimizing the number of time slots required (schedule length) to complete a convergecast. Next, we combine scheduling with transmission power control to mitigate the effects of interference, and show that while power control helps in reducing the schedule length under a single frequency, scheduling transmissions using multiple frequencies is more efficient. We give lower bounds on the schedule length when interference is completely eliminated, and propose algorithms that achieve these bounds. We also evaluate the performance of various channel assignment methods and find empirically that for moderate size networks of about 100 nodes, the use of multifrequency scheduling can suffice to eliminate most of the interference. Then, the data collection rate no longer remains limited by interference but by the topology of the routing tree. To this end, we construct degree-constrained spanning trees and capacitated minimal spanning trees, and show significant improvement in scheduling performance over different deployment densities. Lastly, we evaluate the impact of different interference and channel models on the schedule length.

Server side measurements from several Wi-Fi hot-spots deployed in a nationwide network over different types of venues from small coffee shops to large enterprises are used to highlight differences in traffic volumes and patterns. We develop a common modeling framework for the number of simultaneously present customers. Our approach has many novel elements: (a) We combine statistical clustering with Poisson regression from Generalized Linear Models to fit a non-stationary Poisson process to the arrival counts and demonstrate its remarkable accuracy; (b) We model the heavy tailed distribution of connection durations through fitting a Phase Type distribution to its logarithm so that not only the tail but also the overall distribution is well matched; (c) We obtain the distribution of the number of simultaneously present customers from an Mt/G/∞ queuing model using a novel regenerative argument that is transparent and avoids the customarily made assumption of the queue starting empty at an infinite past; (d) Most importantly, we validate our models by comparison of their predictions and confidence intervals against test data that is not used in fitting the models.

In LTE Rel-8, mobile stations are equipped with only one transmit antenna while the base stations can employ multiple receive antennas. As a result, multi-user MIMO can be used in the uplink to enhance system capacity. This paper describes multi-user MIMO in the uplink for LTE and presents system-level simulation results under indoor hotspot, micro-cell, and macro-cell deployment scenarios. Two user pairing strategies, random and orthogonal pairing, are compared. Our results show that random pairing performs as well as orthogonal pairing under realistic implementation constraints. With four receive antennas at the base station, uplink MU-MIMO can increase cell capacity by approximately 30% in indoor hotspot, and 10% in micro-cell and macro-cell deployment. Corresponding improvements in user throughput are also observed, including a gain of between 9-28% in cell edge user throughput.

We investigate the tradeoff between two mutually conflicting performance objectives-throughput and delay-for fast, periodic data collection in tree-based sensor networks arbitrarily deployed in 2-D. Two primary factors that affect the data collection rate (throughput) and timeliness (delay) are: 1) efficiency of the link scheduling protocol, and 2) structure of the routing tree in terms of its node degrees and radius. In this paper, we utilize multiple frequency channels and design an efficient link scheduling protocol that gives a constant factor approximation on the optimal throughput in delivering aggregated data from all the nodes to the sink. To minimize the maximum delay subject to a given throughput bound, we also design an (α, β)-bicriteria approximation algorithm to construct a Bounded-Degree Minimum-Radius Spanning Tree, with the radius of the tree at most β times the minimum possible radius for a given degree bound Δ*, and the degree of any node at most Δ*+ α , where α and β are positive constants. Lastly, we evaluate the efficiency of our algorithms on different types of spanning trees and show that multichannel scheduling, combined with optimal routing topologies, can achieve the best of both worlds in terms of maximizing the aggregated data collection rate and minimizing the maximum packet delay.

The 3GPP Long Term Evolution (LTE) systems have been designed to deliver higher peak data rates, higher capacity and lower air-interface latency compared to prior 2G and 3G systems. This high performance will make it possible to support more demanding applications beyond web browsing and voice, which will require higher data rates and QoS guarantees. Video services are becoming very popular over the Internet. With the wide deployment of LTE in the near future, the demand for high data-rate video applications over cellular wireless will grow. However, in order to make these services commercially viable, it is necessary that the LTE air-interface can deliver high quality services to a sizeable number of users simultaneously. In this paper we investigate the downlink video capacities of the LTE air-interface by dynamic system simulation using realistic video traffic models and detailed models of the LTE air-interface. We investigate how video quality and system outage criteria impact the air-interface video capacities and describe observations on video stream quality and operator revenue under certain cost assumptions.

It has been recognized that a primary method of further enhancing the spectral efficiency of LTE Release-8 is to improve support for multi-user (MU) MIMO transmission in the downlink in an efficient manner. This paper investigates the performance improvements due to the enhanced support of single-cell MU-MIMO within the framework of LTE evolution (specifically LTE Release-9 and Release-10 also known as LTE-Advanced) considering a 4Tx-2Rx system. A realistic estimate of achievable MU-MIMO full-buffer throughput performance is provided with respect to variations in the propagation environment, feedback accuracy, antenna polarizations, antenna calibration as well as receiver type. It is observed that a closely spaced uniform linear array (ULA) at the base station and interference rejection capability at the mobile is essential to maximize MU-MIMO gains. Further, channel reciprocity based spatial channel feedback in a TDD scenario can provide significantly higher MU-MIMO throughput compared to codebook based feedback.

UMTS LTE system can support flexible bandwidth configuration up to 20 MHz. Currently, system enhancements are being considered to provide substantial improvements to LTE and allow it to meet or exceed IMT-Advanced requirements. One key enhancement feature is bandwidth extension via carrier aggregation to support deployment bandwidth up to 100 MHz. This will allow peak target data rates in excess of 1 Gbps in the downlink and 500 Mbps in the uplink to be achieved. Carrier aggregation is attractive because it allows operators to deploy a system with larger bandwidth by aggregating several smaller contiguous or non-contiguous carriers while providing backward compatibility to legacy users. For instance, an 80 MHz system can be constructed using contiguous or non-contiguous 4 × 20 MHz component carriers. Legacy users can then access the system using one of the component carriers. This paper provides an overview of carrier aggregation and discusses major technical issues including aggregation structure, scenarios, implementation, control signalling design and coexistence with legacy LTE systems.

The 3GPP Long Term Evolution (LTE) Release-8 specifications are designed to deliver higher peak data rates, higher throughput and lower air-interface latency compared to 2G and 3G systems. This higher performance will make it possible to support more demanding applications beyond web-browsing and voice, requiring higher data rates and stricter QoS constraints. Video services are becoming increasingly popular over the Internet indicating that the demand for such high data-rate video applications over cellular wireless will continue to grow. However, in order to make these services commercially viable in a LTE system it is necessary for the air-interface to deliver high quality services to a significant number of users simultaneously. In this paper we investigate the video capacity of a LTE air-interface using realistic video traffic models. An LTE air-interface can support multiple-antenna transmit arrays and several multiple antenna transmission modes to increase system capacity. We investigate the benefits of using 4 transmit antennas compared to 2 transmit antennas on the video capacity of an LTE system. The results from our investigation indicate that the capacity benefits with 4 transmit antennas are much higher with video services than those observed with other traffic models such as the full-buffer traffic model. The results also show that a 10MHz TDD LTE system can service upto 48 users per sector with 256Kbps video streams in the downlink indicating that such services can be commercially viable.

Obtaining reliable channel state information (CSI) in future wireless standards is critical for the operation of downlink closed-loop techniques such as SU-MIMO, MU-MIMO, and coordinated multipoint (CoMP). However, this CSI is difficult to obtain especially when considering the potentially strong interference from neighboring sectors/base stations on the downlink reference symbols (RSs, aka pilot symbols) used to obtain the CSI. This paper describes three possible CSI RS designs for enabling such closed- loop feedback in light of the strong interference environment and discusses some tradeoffs between the designs. First, two code-division multiplexing (CDM) designs are proposed where one has nine orthogonal sequences and the other has three orthogonal sequences. Next a new CSI-RS design is described which uses mutually unbiased bases (MUB) to provide a 6 dB quasi-orthogonal gain over neighboring cells. The MUB design is shown in system-level simulation to have performance close to a design with 9 orthogonal sequences while providing a finer frequency-domain sampling than the 9-orthogonal approach.

Fast and periodic collection of aggregated data is of considerable interest for mission-critical and continuous monitoring applications in sensor networks. In the many-to-one communication paradigm known as convergecast, we consider scenarios where data packets are aggregated at each hop en route to a sink node along a tree-based routing topology and focus on maximizing the data collection rate at the sink by employing TDMA scheduling and multiple frequency channels. Our key result in the paper lies in proving that minimizing the schedule length for an arbitrary network in the presence of multiple frequencies is NP-hard, and in designing approximation algorithms with worst-case provable performance guarantees for geometric networks. In particular, we design a constant factor approximation for networks modeled as unit disk graphs (UDG) where every node has a uniform transmission range, and a O(Delta(T)log n) approximation for general disk graphs where nodes have different transmission ranges; n is the number of nodes in the network and Delta(T) is the maximum node degree on a given routing tree T. We also prove that a constant factor approximation is achievable on UDG even for unknown routing topologies so long as the maximum node degree in the tree is bounded by a constant. We also show that finding the minimum number of frequencies required to remove all the interfering links in an arbitrary network in NP-hard. We give an upper bound on the maximum number of such frequencies required and propose a polynomial time algorithm that minimizes the schedule length under this scenario. Finally, we evaluate our algorithms through simulations and show various trends in performance for different network parameters.

Long-term evolution (LTE) of the UMTS network provides improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To achieve these enhancements, a new design for the air interface including state-of-art multi-antenna technology was developed. This article describes multi-antenna schemes for UMTS LTE and provides system performance of different multi-antenna schemes under various scenarios.

WiMaX is the commercial name for the 4G OFDM based wireless broadband data transmission standard 802.16, developed by IEEE ([1] and [2]). It is currently being deployed in several countries around the world. Sub-channels (which are the basic unit of resource allocation) are formed by grouping together sub-carriers in one of two formats - PUSC or AMC. In PUSC the set of sub-carriers in a sub-channel are distributed throughout the bandwidth while in AMC the sub-carriers in a subchannel are contiguous within a portion of the bandwidth. In this paper we study two candidates that offer the potential to improve the system performance of PUSC and identify scenarios when this improvement is possible: (i) compare the performance of PUSC with two flavors of AMC; and (ii) study how the PUSC performance can be improved by a Fractional Frequency Reuse (FFR) scheme that tries to perform interference mitigation/co-ordination and improve the throughput of users at the edge of the cell.

Long-Term Evolution (LTE) will provide substantial enhancements to UMTS 3G systems including improved system capacity and coverage, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. LTE supports both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes to provide deployment flexibility in accordance with operator’s preference and spectrum allocation. This paper presents an overview of LTE TDD design and highlights key differences with FDD. Design challenges unique to TDD are presented together with adopted technical solutions. Finally, simulation results are provided to demonstrate typical TDD system performance with data applications.

The performance of the uplink physical channel of the 3GPP LTE system is considered in this paper. Assuming a single user spatial division multiple access transmission scheme, where users' signals are transmitted over different subcarriers, a low complexity channel estimation technique is proposed for the physical uplink shared channel (PUSCH). The proposed channel estimation technique is shown to have significant gains in performance compared to other well known channel estimation techniques such as the maximum-likelihood (ML) and the inverse fast Fourier transform (IFFT) channel estimation methods [5]. Simulation results for different channel models and modulation and coding schemes (MCS) using incremental redundancy (IR) based hybrid automatic repeat request (HARQ) operation are also shown. Finally, a robust detection scheme is proposed for the physical uplink control channel (PUCCH) and simulation results are summarized.

Link performance of WiMAX (802.16e) downlink and uplink using partial usage subchannelization (PUSC) is evaluated through link-level simulations. WiMAX using single transmit and two receive antennas is compared to a WiMAX system with four transmit and two receive antennas with closed-loop beamforming in the downlink and one transmit and eight receive antennas in the uplink. Two dimensional channel estimators are applied to estimate the channel frequency response using pilot symbols. Spatial channel modeling method is used to model the antenna correlations between multiple transmit and the multiple receive antennas. Link simulations demonstrate that significant link performance improvements can be achieved using closed-loop beamforming for downlink and using more receive antennas for uplink.

With the emergence of packet-based wireless broadband systems, work has begun on long term evolution (LTE) of the UMTS Terrestrial Radio Access and Radio Access Network aimed for commercial deployment in 2010. Goals for the evolved system include support for improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To reach these goals, a new design for the air interface including control channel is envisioned. This paper provides a preliminary look at an efficient downlink control channel design to reduce the overhead required to support data transmission. Initial performance results show that close to optimal system performance can be achieved with downlink control overhead of less than 14%.

Long term evolution (LTE) of the UMTS Terrestrial Radio Access and Radio Access Network is aimed for commercial deployment in 2010. Goals for the evolved system include support for improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To reach these goals, a new design for the air interface is currently being specified in the 3GPP standards body. The Uplink (UL) for LTE is based on Single Carrier Frequency Division Multiple Access. The UL control channel carries non-data associated control signaling like CQI, ACK/NACK, Scheduling request etc. To maintain the low PA power de-rating, the single carrier property of the UL has to be maintained. As such, special consideration should be given to the UL control channel design. This paper discusses in detail the LTE UL control channel design and its performance.

As the standardization of Evolved-UTRA or LTE is ongoing in 3GPP, it is important to ensure the coexistence between two LTE systems or between LTE and legacy UMTS systems sharing the same frequency band. This paper is aimed at presenting a complete view of the status and challenges of the coexistence issue. The high-level methodology, UL power control, and ACLR modeling, etc. are discussed in detail. To ensure coexistence without tightening the RF requirements and hence increasing the cost for LTE, mitigation techniques like interference-aware resource allocation are proposed and shown to be effective by simulation results.

Comprehensive long term evolution of the Universal Mobile Telecommunications System (UMTS) specifications is currently ongoing to provide significant improvement over the current release. Important goals for the evolved system include significantly improved system capacity and coverage, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To ensure low latency, users must be able to establish a connection to the network quickly. This paper provides a preliminary design and procedure for the random access channel used to establish a connection when the mobile is not yet time-synchronized to the network in the uplink.

In this paper, the performance of WiMAX networks using multiple transmit and multiple receiver antennas are analyzed via system simulations. For downlink, two kinds of technologies are studied: i) open loop: where the base station has no knowledge of channel and uses mobile mode selection feedback to switch between single data stream STBC and multi-stream spatial multiplexing MIMO (SM-MIMO); ii) closed loop: where base station has explicit knowledge of downlink channel and transmits using adaptive beamforming. This paper compares the WiMAX downlink system performance using open loop and closed loop MIMO technologies with various frequency reuse factors and different data traffic models. The performance of WiMAX uplink is also analyzed with multiple receive antennas and using both single input multiple output (SIMO) and multi-user MIMO (MU-MIMO, a.k.a. SDMA).

With the emergence of packet-based wireless broadband systems such as 802.16e, it is evident that a comprehensive evolution of the universal mobile telecommunications system specifications is required to remain competitive. As a result, work has begun on long term evolution (LTE) of the UMTS terrestrial radio access and radio access network aimed for commercial deployment in 2010. Goals for the evolved system include support for improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To reach these goals, a new design for the air interface is envisioned. This paper provides a preliminary look at the air interface for Evolved UTRA (E-UTRA) and associated key technologies required to reach its design objectives. Initial E-UTRA system performance results show a 2 to 3x improvement over a reference Rel-6 UMTS system configuration [1, 2] for both uplink and downlink.

Multi-user scheduling and OFDM techniques are well regarded as promising candidates to provide high data- rate and reliable transmissions in future communication systems. To optimally exploit multi-user diversity and frequency selectivity, exhaustive channel information is needed for every user - an impracticality given limited feedback bandwidth. Simple and efficient feedback schemes therefore become a crucial task in designing a next generation standard. In this paper, two near-optimal feedback schemes are proposed that achieve most of the multi-user scheduling benefit with very few feedback bits. It is also shown that the feedback schemes are robust to long feedback intervals. As expected, at higher Doppler spread, the performance gap using the proposed schemes becomes larger but still provides satisfactory performance.

In this paper, the performance of WiMax network with DL SIMO, DL MIMO and UL SIMO is analyzed via system simulations. Two data traffic models are considered, namely Web browsing (HTTP) and full buffer sessions, operating in multi path fading channels such as the ITU pedestrian-B and vehicular-A channels. The control channel coverage and reliability of WiMAX using realistic overhead is also analyzed in this paper.

Evolved UTRA and UTRAN is being standardized in 3GPP standard group as a long term evolution of the 3GPP radio-access technology. The goal is to achieve 2-4 times the spectral efficiency and user throughput and much smaller latency compared to HSDPA/HSUPA. Single carrier FDMA (e.g. DFT-SOFDM) is the multiple access technique of choice for uplink transmission. Interference control is one of the key elements to achieve the target spectral efficiency and user cell- edge performance requirement, especially for uplink. In this paper, interference mitigation is implemented through slow fractional power control and interference coordination through UE alignment and FDM resource allocation. Simulation results show that these techniques significantly improve uplink sector and cell edge user throughput performance.

In this paper, the performance of a prototypical IEEE 802.16e network is analyzed via link and system simulations. The exponential effective SIR mapping (EESM) is used to map the instantaneous SINR of received signals to a service-specific packet erasure rate (PER), which is in turn used to assess the downlink and uplink network and user data throughput. A variety of data traffic models are considered, including web browsing (HTTP) and full buffer sessions, operating in flat-fading and frequency-selective multipath channels such as the ITU Pedestrian-B model. The downlink network performance of the prototypical IEEE 802.16e network is compared to a 3GPP UMTS high speed downlink packet access (HSDPA) system of similar physical dimensions. System simulation results for the prototypical IEEE 802.16e network considered show-when frequency-selective scheduling is not applied-that the IEEE 802.16e downlink has similar throughput performance as HSDPA for a 70/30 TDD DL/UL frame split but approximately 40%-50% higher spectral efficiency, although control channel overhead and uplink capacity limitation remain significant open issues for further study

Enhanced Uplink technology is being standardized in Release-6 of 3GPP W-CDMA specifications with the completion date of 2nd quarter of 2005. Advanced features being introduced include adaptive modulation and coding, Hybrid ARQ, fast rate control or scheduling by the base station, higher peak rates (5.76 Mbps) and support of 2ms TTI. These techniques reduce overall delay and increase throughput significantly compared to earlier releases of 3GPP W-CDMA (Release-99/ 4/ 5). As a result, Enhanced Uplink will significantly improve the user mobile experience and enable new services and applications. In this paper, the scheduling and resource allocation aspects of Enhanced Uplink are discussed with accompanying analysis and system simulation results. These results show that Enhanced Uplink improves sector and user throughput by approximately 50-80% compared to earlier 3GPP W-CDMA releases.

The paper compares two hybrid automatic repeat request (HARQ) schemes using incremental redundancy (IR) which have been proposed for the UMTS (W-CDMA) high speed downlink shared channel (HS-DSCH). Their relative throughput performance is reported for various channel conditions. It is shown that the two-stage rate-matching scheme has marginally worse performance compared to the alternative block interleaving scheme for certain coding rates and under some channel conditions.

An overview of the hybrid ARQ used by the 3G CDMA evolutions (1xEV-DV for cdma2000 and HSDPA for WCDMA) is provided, along with simulation data supporting several of the key design decisions. Enhancements to AMC and hybrid ARQ operation are also discussed.

In this paper, we investigate the performance of a quasi-static method used to predict link-level error performance in dynamic system simulations. Two flavors of the quasi-static approach are used to model the link characteristics: (a) static curves with fudge factors; and (b) short-term frame error curves. For the fudge factor based method, we examine the various factors (or penalties) required for the method to work properly, their limitations in capturing the various features of the high-speed packet data channel, and their effects on the overall accuracy of the technique. Here, we concentrate on three important penalties: puncturing penalty, Doppler penalty, and demapping penalty. The quasistatic method based on short-term frame error curves is used to generate frame erasures for voice and control channels associated with high-speed packet data channels. From simulation results, it is shown that both variations of the quasi-static method can provide accurate prediction of link-level performance at certain operating ranges, provided that the penalties are correctly obtained. At low frame error rates and moderate to high speeds, however, the quasi-static method often fails to accurately reflect frame error performance at the link level.