In this paper, a clustering algorithm is proposed that dynamically determines the locations of fog nodes in 5G wireless networks, which are upgraded from small cells, in order to maximize throughput assuming the number of fog nodes and small cells are given as a priori information. The proposed algorithm dynamically clusters the small cells around the fog nodes. The approach is based on a soft clustering model where one small cell can be connected to many fog nodes. The numerical results demonstrate that the proposed clustering algorithm significantly enhances the throughput and lowers the latency with respect to the distance-based K- means hard clustering algorithm or Voronoi tessellation model.

This paper proposes a new medium access control (MAC) protocol for Internet of Things (IoT) applications incorporating pure ALOHA with power domain non-orthogonal multiple access (NOMA) in which the number of transmitters are not known as a priori information and estimated with multihypothesis testing. The proposed protocol referred to as ALOHA-NOMA is not only scalable, energy efficient and matched to the low complexity requirements of IoT devices, but it also significantly increases the throughput. Specifically, throughput is increased to 1.27 with ALOHA-NOMA when 5 users can be separated via a SIC (Successive Interference Cancellation) receiver in comparison to the classical result of 0.18 in pure ALOHA. The results further show that there is a greater than linear increase in throughput as the number of active IoT devices increases.

Massive deployment of autonomous vehicles, un- manned aerial vehicles, and robots, brings in a new technology challenge to establish ultra-low end-to-end latency mobile networking to enable holistic computing mechanisms. With the aid of open-loop wireless communication and proactive network association in vehicle-centric heterogeneous network architecture, anticipatory mobility management relying on inference and learning from big vehicular data plays a key role to facilitate such a new technological paradigm. Anticipatory mobility management aims to predict APs to be connected in the next time instant and in a real-time manner, such that ultra-low latency downlink open-loop communication can be realized with proactive network association. In this paper, we successfully respond this technology challenge using big data analytics with location-based learning and inference tech- niques, to achieve satisfactory performance of predicting APs. Real vehicular movement data have been used to verify that the proposed prediction methods are effective for the purpose of anticipatory mobility management and thus ultra-low latency mobile networking.

This paper proposes an uncoordinated random medium access protocol for Internet of Thing (IoT) networks incorporating conventional slotted Aloha (SA) with power domain non-orthogonal multiple access (PD-NOMA) and multiple-input multiple-output beamforming (MIMO BF). The number of active IoT devices, which is not known a priori, is detected at the IoT gateway via multiple hypothesis testing. The proposed protocol referred to as BF-SA-NOMA is not only scalable and compatible with the power-limited IoT devices, but it also uses beamforming to significantly improve the throughput to 1.31 compared with 0.36 in conventional slotted Aloha when 6 active IoT devices can be successfully separated using 2×2 MIMO and a SIC (Successive Interference Cancellation) receiver with 3 optimum power levels. The simulation results further show that the proposed protocol achieves higher throughput than Aloha-NOMA with a lower average channel access delay.

Millimeter wave (mmWave) is a key technology to support high data rate demands for 5G applications. Highly directional transmissions are crucial at these frequencies to compensate for high isotropic pathloss. This reliance on directional beamforming, however, makes the cell discovery (cell search) challenging since both base station (gNB) and user equipment (UE) jointly perform a search over angular space to locate potential beams to initiate communication. In the cell discovery phase, sequential beam sweeping is performed through the angular coverage region in order to transmit synchronization signals. The sweeping pattern can either be a linear rotation or a hopping pattern that makes use of additional information. This paper proposes beam sweeping pattern prediction, based on the dynamic distribution of user traffic, using a form of recurrent neural networks (RNNs) called Gated Recurrent Unit (GRU). The spatial distribution of users is inferred from data in call detail records (CDRs) of the cellular network. Results show that the users spatial distribution and their approximate location (direction) can be accurately predicted based on CDRs data using GRU, which is then used to calculate the sweeping pattern in the angular domain during cell search.

The Internet of things (IoT), which is the network of physical devices embedded with sensors, actuators, and connectivity, is being accelerated into the mainstream by the emergence of 5G wireless networking and the support of Machine-to-Machine (M2M) communications. Due to the simplicity of IoT devices and their sporadic traffic in such application, a simple medium access control (MAC) protocol is needed to connect M2M devices to the Internet through a hub (IoT gateway). This paper compares two MAC protocols namely: the newly introduced slotted Aloha-NOMA protocol and the well-known carrier sensing multiple access with collision avoidance (CSMA/CA) protocol. The comparison is based on two metrics, the throughput and the average delay. Simulation results show that the throughput of slotted Aloha-NOMA is higher than CSMA/CA at low probability of transmission at the cost of increased average delay caused by novel power level selection mechanism.

The synergistic combination of Diversity and Network Coding (DC-NC) was previously introduced to provide very low end-to-end latency in recovering from a link failure and improve the throughput for a wide variety of network architectures. This paper is directed towards further improving DC-NC to be able to tolerate multiple, simultaneous link failures with less computational complexity. In this way, reliability will be maximized and the recovery time from multiple link or node failures is reduced in 5G fronthaul wireless networks. This is accomplished by modifying Triangular Network Coding (TNC) to create enhanced DC-NC (eDC-NC) that is applied to 5G wireless Fog computing-based Radio Access Networks (Fog-RAN). Our results show that using eDC-NC coding in Fog-RAN fronthaul network will provide ultra-reliability and enable near-instantaneous fault recovery while retaining the throughput improvement feature of DC-NC. In addition, the scalability of eDC-NC coding is demonstrated. Furthermore, it is shown that the redundancy percentage for complete protection is always less than 50% for the practical cases that were evaluated.

This paper incorporates fog networking into heterogeneous cellular networks that are composed of a high power node (HPN) and many low power nodes (LPNs). The locations of the fog nodes that are upgraded from LPNs are specified by modifying the unsupervised soft-clustering machine learning algorithm with the ultimate aim of reducing latency. The clusters are constructed accordingly so that the leader of each cluster becomes a fog node. The proposed approach significantly reduces the latency with respect to the simple, but practical, Voronoi tessellation model, however the improvement is bounded and saturates. Hence, closed-loop error control systems will be challenged in meeting the demanding latency requirement of 5G systems, so that open-loop communication may be required to meet the 1ms latency requirement of 5G networks.

This paper is directed towards improving both throughput and reliability of 5G wireless Cloud Radio Access Networks (C-RANs) by the synergistic combination of Diversity Coding and Network Coding (DC-NC). In this paper, we directly apply the concept of DC-NC coding to two network scenarios: first, remote radio heads in a CRAN connected to the baseband unit in two hierarchical tiers with optical and wireless fronthaul links, second, most remote radio heads are connected directly to the baseband unit via wireless links. Our results show that the combination of Diversity and Network Coding increases the throughput of fronthaul networks for downlink broadcasting or multicasting applications, while enabling reliable networking with near-instant latency in fault recovery by using forward error control across spatially diverse paths. Moreover, the number of redundant links inherent in Diversity Coding can be decreased using the proposed scheme.

Energy efficiency is essential for Wireless Body Area Network (WBAN) applications because of the battery-operated nodes. Other requirements such as throughput, delay, quality of service, and security levels also need to be considered in optimizing the network design. In this paper, we study the case in which the nodes access the medium probabilistically and we formulate an energy efficiency optimization problem under the rate and access probability constraints for IEEE 802.15.6 Impulse Radio Ultra- wideband (IR-UWB) WBANs. The proposed algorithm, dubbed Energy Efficiency Optimization of Channel Access Probabilities (EECAP), determines the optimal access probability and payload frame size for each node. The simulation results show that our algorithm rapidly converges to the optimal solution. We also provide detailed insights on the relationship between the optimal access probabilities and other network parameters such as the link distance, the number of nodes, and the minimum rate constraints.

Advances in sensor networks enable pervasive health monitoring and patient-specific treatments that take into account the patients medical history, current state, genetic background, and personal habits. However, sensors are often battery power limited and vastly differ in their application related requirements. In this paper, we address both of these problems. Specifically, we study IEEE 802.15.6 ultra-wideband (UWB) wireless body area networks (WBANs) that use impulse radio (IR). We formulate the joint optimization of the payload size and number of pulses per symbol to optimize the energy efficiency under the minimum rate constraint. The proposed algorithm, cross-layer optimization for energy efficiency (CLOEE), enables us to carry out a cross-layer resource allocation that addresses the rate and reliability trade-off in the physical (PHY) layer as well as the packet size optimization and transmission efficiency for the medium access control (MAC) layer. Simulation results demonstrate that CLOEE can provide an order of magnitude improvement in energy efficiency or extend the range by a factor of two compared to static strategies.

This paper describes how user-specific QoS requirements may improve spectral utilization in heterogeneous networks. Throughput improvements of FTP (File Transfer Protocol) applications benefiting from the rate adaptation and MAC scheduling algorithms for video applications that incorporate user-specific QoS to improve system capacity are demonstrated. These improvements are achieved while user satisfaction for video applications, as measured by the Mean Opinion Score (MOS), is maintained at an acceptable level. OPNET system simulations were performed for a set of FTP users and video users that were assigned specific QoS target levels in LTE systems. Simulation results show that significant system capacity improvements and acceptable MOS levels can be achieved for FTP users and video users, respectively, if such user-specific QoS requirements are considered in heterogeneous networks.

This paper presents the proof-of-concept investigation for a miniaturized vectorcardiogram [VCG] system for ambulatory on-body applications that continuously monitors the electrical activity of the heart in three dimensions. We investigate the minimum distance between a pair of leads in the X, Y and Z axes such that the signals are distinguishable from the noise. The target dimensions for our VCG are 3×3×2 cm and, based on our preliminary results, it is possible to achieve these dimensions. The next step in our research is to build the miniaturized VCG system that includes processing, learning and communication capabilities.

This paper describes how user-specific QoS requirements are a critical innovation that may be used to improve spectral utilization in wireless systems. Rate adaptation and MAC scheduling algorithms that process user-specific QoS to improve system capacity are proposed and evaluated. Through dynamically adapting the AMR codec mode or video data rate and the MAC scheduling algorithm to the user-specific QoS requirements, system capacity, as measured by the number of supportable users, is maximized, while user satisfaction, as measured by the Mean Opinion Score (MOS), is maintained at an acceptable level. OPNET system simulations were performed for a set of VoIP users and video users that were assigned specific QoS target levels. Simulation results show that significant system capacity improvement and acceptable MOS level can be achieved if such user-specific QoS requirements are considered in the rate adaptation and MAC scheduling algorithms.

This paper describes the design and implementation of a Miniature Anchored Robotic Videoscope for Expedited Laparoscopy (MARVEL) and Camera Module (CM) that features wireless communications and control. The CM decreases the surgical-tool bottleneck experienced by surgeons in state-of-the art Laparoscopic Endoscopic Single-Site (LESS) procedures for minimally invasive abdominal surgery. The system includes: (1) a near-zero latency video wireless communications link, (2) a pan/tilt camera platform, actuated by two motors that provides surgeons a full hemisphere field of view inside the abdominal cavity, (3) a small wireless camera, (4) a wireless illumination control system, and (5) a wireless human-machine interface (HMI) to control the CM. An in-vivo experiment on a porcine subject was carried out to test the performance of the system. The robotic design is a Research Platform for a broad range of experiments in a range of domains for faculty and students in the Colleges of Engineering and Medicine and at Tampa General Hospital. This research is the first step in developing semi-autonomous wirelessly controlled and networked laparoscopic devices to enable a paradigm shift in minimally invasive surgery and other domains such as Wireless Body Area Networks.

Cooperative Networking is a new technology which exploits the massive deployment of nodes in wireless sensor networks. Cooperative Networking synergistically integrates Networking with cluster-based Cooperative Communications to improve reliability and enhance network performance. In this paper, we consider the effect of link-level feedback and retransmissions on the performance of wireless sensor networks using Cooperative Networking, and we present scenarios where link-level retransmission offers a significant improvement in network throughput. Generally, Cooperative Networking with link-level retransmission provides higher throughput when the network node density is low (i.e., sparse networks) or in environments with adverse conditions such as high probability of transmission loss and low connectivity among the nodes.

Fast downlink scheduling algorithms play a central role in determining the overall performance of high-speed cellular data systems, characterized by high throughput and fair resource allocation among multiple users. We propose a flexible channel-dependent downlink scheduling scheme, named the (weighted) alpha-rule, based on the system utility maximization that arises from the Internet economy of long-term bandwidth sharing among elastic-service users. We show that the utility as a function of per-user mean throughput naturally derives the alpha-rule scheme and a whole set of channel-dependent instantaneous scheduling schemes following different fairness criteria. We evaluate the alpha-rule in a multiuser CDMA high data rate (HDR) system with space-time block coding (STBC) or Bell Labs layered space-time (BLAST) multiple-input multiple-output (MIMO) channel. Our evaluation shows that it works efficiently by enabling flexible tradeoff between aggregate throughput, per-user throughput, and per-user resource allocation through a single control parameter. In other words the Alpha-rule effectively fills the performance gap between existing scheduling schemes, such as max-C/I and proportional fairness (PF), and provides an important control knob at the media-access-control (MAC) layer to balance between multiuser diversity gain and location-specific per-user performance.

Non-cooperative behaviors in communication networks can significantly adversely affect the entire network. The WWAN/WLAN two-hop-relay system (Wei, H.-Y. and Gitlin, R.D., 2004) integrates two types of wireless technologies to improve wireless access throughput and coverage. Relay nodes in the two-hop-relay system can be wireless relay routers deployed by wireless service providers, or dual-mode users who voluntarily relay traffic for other users. However, it is likely that all dual-mode terminals are selfish and are not willing to relay for other users without an incentive. We propose a proper scheduling algorithm as an incentive mechanism for the hybrid wireless relay network. We use the basic concepts of game theory, especially the Nash equilibrium concept, to design our scheduling algorithms. Several scheduling algorithms, including the maximum rate C/I scheduler, the proportional fair scheduler, and the round robin scheduler, are examined to understand performance while operating under the assumption that all users are selfish. Under the C/I scheduler or the proportional fair scheduler, Nash equilibriums exist at the operating points where no user relays for other users - an undesirable situation. Under the round robin scheduler, selfish users are indifferent on relaying voluntarily or not relaying. Therefore, we are inspired to design a novel incentive scheduling algorithm to encourage relay. By applying the proposed incentive scheduler at the base station, all selfish users relay cooperatively at the Nash equilibrium.

Handoff and cell site selection schemes in multi-cell cellular systems are traditionally developed for mobile stations (MS) of dedicated (circuit-switched) channels to/from base stations (BS). The schemes usually only consider physical-layer signal quality in decision making. In high-speed packet access systems, where a downlink channel is being shared by multiple users within each cell, those schemes are subject to local congestion and asymmetric packet call blocking across multiple cells. A way to reduce the hot-spots and alleviate asymmetry loading in such systems is the target of our study. To do so, we formulate the handoff and cell site selection procedures into a problem of iterative optimal channel assignment in multiple cells, and approximately solve the issue by incorporating a distributed load-awareness scheme into the procedures in order to keep the complexity low but practicality high. Extensive experiments show the effectiveness of our scheme and its advantages over the legacy schemes in load balancing and congestion reduction. With our scheme, a multi-cell wireless system in support of high-speed packet data access can accommodate more satisfied users and be more robust to asymmetric load dynamics across the whole system.

High-speed cellular data systems demand fast downlink scheduling algorithms and multiple-input multiple-output (MIMO) techniques. The associated multiuser diversity and antenna diversity play a central role in achieving high system throughput and fair resource allocation among multiple users. For such systems we evaluate the cross-layer interactions between channel-dependent scheduling schemes and MIMO techniques, such as space-time block coding (STBC) or Bell Laboratories Layered Space-Time (BLAST), and propose a new scheduling algorithm named the alpha-rule. The evaluation shows that the STBC/MIMO provides a reliable channel but at a certain cost of spectral efficiency. Comparatively BLAST/MIMO provides larger capacity and enables higher scheduling throughput. Thus BLAST/MIMO may be a more suitable technique for high-rate packet data transmission at the physical layer. At the medium access control (MAC)-layer, the alpha-rule is shown to be more flexible or efficient to exploit the diversity gains than the exiting max-C/I or proportionally fair (PF) scheduling schemes. It enables online tradeoff between aggregate throughput, per-user throughput, and per-user resource allocation.

We investigate a wireless system of multiple cells, each having a downlink shared channel in support of high-speed packet data services. In practice, such a system consists of hierarchically organized entities including a central server, Base Stations (BSs), and Mobile Stations (MSs). Our goal is to improve global resource utilization and reduce regional congestion given asymmetric arrivals and departures of mobile users. For this purpose, we propose a scalable cross-layer framework to coordinate packet-level scheduling, call-level cell-site selection and handoff, and system-level loading balancing based on load, throughput, and channel measurements at different layers. In this framework, an opportunistic scheduling algorithm---the weighted Alpha-Rule---exploits multiuser diversity gain in each cell independently, trading aggregate (mean) downlink throughput for fairness and minimum rate guarantees among MSs. Each MS adapts to its channel dynamics and the load fluctuations in neighboring cells, in accordance with MSs' mobility and their arrivals or departures, by initiating load-aware handoff and cell-site selection. The central server adjusts the scheduling parameters of each cell to coordinate cells' coverage, or cell breathing, by prompting distributed MS handoffs. Across the whole system, BSs and MSs constantly monitor their load, throughput, or channel quality in order to facilitate the overall system coordination.Our specific contributions in such a framework are highlighted by the minimum-rate guaranteed Weighted Alpha-Rule scheduling, the load-aware MS handoff/cell-site selection, and the Media Access Control (MAC)-layer cell breathing. Our evaluations show that the proposed framework can improve the global resource utilization and load balancing, which translates into a smaller blocking rate of MS arrivals without extra resources, while the aggregate throughput remains roughly the same or improved around the hot-spots. Our tests also show that the coordinated system is robust to dynamic load fluctuations and is scalable to both system size and MS population.

The integration of 3rd generation (3G) cellular networks and the IEEE 802.11 wireless local area networks has drawn considerable attention from the research and commercial communities. Emerging dual-mode mobile terminals could provide flexibility and system performance enhancement by providing seamless roaming between 3G WWANs and 802.11 WLANs. In this paper, we proposed a novel integrated WWAN/WLAN two-hop-relay architecture that both enhances the system capacity of 3G cellular systems and extends the system coverage area of 802.11 terminals. The proposed two-hop-relay architecture utilizes temporal channel quality variation to achieve increased system capacity. Typically, the system throughput is increased by 200-400% in a HDR system.

Abstract We consider dynamic channel management (DCM), more specifically power control and channel allocation, in multi‐carrier multi‐antenna wireless cellular systems. A quasi‐static channel model is assumed such that the channels remain approximately time‐invariant within each packet. On a packet‐by‐packet basis, the mobile station (MS) receivers feed back the DCM parameters to the corresponding base station (BS) transmitters in order to minimize the transmission power and strive to satisfy every individual user's data‐rate request. While optimum, centralized DCM for all active cells typically requires solution of a non‐convex optimization problem (which is subject to local minima) and requires intense channel feedback to a central controller. We instead consider sub‐optimal distributed DCM, where each individual cell locally optimizes its own performance based on the local channel information. In particular, we compare three distributed DCM schemes, namely the two‐dimensional DCM, which jointly adjusts both spatial and frequency sub‐channels of each BS–MS link, the one‐dimensional DCM, which adjusts only the frequency sub‐channels and the scalar DCM, which adjusts each BS–MS link by one scalar power coefficient. These DCM schemes are investigated in multi‐cell environments with realistic parameters; and it is seen that due to the multiple antennas, the maximum supportable rate (i.e. the rate supported by practically finite transmission power) is significantly increased, for example by a factor of two for users using four antennas and close to cell boundary. Copyright © 2004 John Wiley & Sons, Ltd.

The candidate access router (CAR) discovery protocol is designed for use in wireless IP networks to dynamically collect information about neighboring access routers and their capabilities. This capability enables mobile nodes to dynamically execute low-latency hand-offs and to intelligently select a target access router. This paper presents possible approaches for CAR discovery, a security analysis of those approaches, and our novel security CAR discovery mechanisms.

This paper introduces a fast handoff mechanism, NeighborCasting, for use in wireless IP networks that utilize neighboring foreign agent (FA) information. NeighborCasting is based on the policy of utilizing, or perhaps even wasting, wired bandwidth between foreign agents, while minimizing RF (radio frequency) bandwidth exchanges, so that handoff latency is minimized. We demonstrate that the handoff latency is substantially reduced, while the typical overhead is minimally increased. Handoff latency is minimized by initiating data forwarding to the possible new foreign agent candidates (i.e., the neighbor foreign agents) at the time that the mobile node initiates the link-layer handoff procedure. NeighborCasting builds upon the Mobile IP handoff procedure by adding a small number of additional message types. The handoff mechanism is a unified procedure for inter-domain, intra-domain and inter-technology (e.g., LAN to WAN or TDMA to CDMA) handoffs and provides flexible choices to the network, while maintaining transparency to the mobile node. The neighbor FA discovery process is a distributed and dynamic mechanism, and the fast handoff schemes are scalable and reliable.

The increased demand for wireless mobile communications coupled with the finite available spectrum has motivated investigation into alternative methods of tracking users and delivering calls. We present a new scheme for delivering mobile terminated calls named reverse virtual call setup (RVC). Only a few new fixed network SS7 signaling messages are needed to implement this protocol; we specify them here. RVC can function within the existing cellular paging network or with an integrated overlaid paging network. The relative performance of RVC for both scenarios is investigated.

We propose a time-frequency-code-slicing technique that allows multiple users with different speed requirements access to a communications resource in a manner that is cost effective over a wide range of access speeds. Conventional systems require low-speed users to either pay a cost premium (e.g., high-speed burst modems for TDMA) or end up wasting some of the spectrum (e.g., universal time slots). The advantages of our proposed scheme can be demonstrated with any two combinations (or all three) of time slicing, frequency slicing, and code slicing. For instance, with a time-frequency-slicing approach, users can be assigned different portions of the spectrum (e.g., on a slot-by-slot basis), allowing them access to only the needed fraction of the shared resource. With time-code slicing, users are dynamically granted portions of the code space, during specified time periods. Finally, in frequency-code slicing, a user may be assigned a number of codes in different frequency bands. These codes can be of constant or variable chip rates.

pg 100 diversity coding, as introduced in Ayanoglu et al. (1990), is a method of protection against failures in a communication network or a storage system, which is based on introducing a digital error-correcting code across independent links. This technique makes efficient use of the extra network capacity needed for coding and has the additional advantages of being nearly instantaneous, not requiring a feedback channel, rerouting, or resynchronization. In high-speed (multi Gbps) networks, digital coding will be difficult to implement, and the purpose of the present paper is to demonstrate how diversity coding may be implemented in the analog domain using the discrete fourier transform (DFT). In particular, the authors show that the DFT is a continuous-amplitude maximum-distance separable code over the field of complex numbers when the transform kernel is a prime root of unity. This code can be used to generate self-healing or fault-tolerant communication networks for continuous- or discrete-amplitude signals, as long as continuous-amplitude parity channels are available. The authors describe electrical and optoelectronic implementations, and a signal estimation approach to combat channel noise and thereby improve the performance of the analog diversity coding system. The most important advantage of this technique is in greatly simplifying the encoders and decoders of diversity coding systems for high-speed networks, such as fiber-optic wavelength division multiplexed networks. Application of analog diversity coding to systems with analog sources, such as telemetry systems is also possible.>

For a broad class of interference-dominated wireless systems including mobile, personal communications, and wireless PBX/LAN networks, the authors show that a significant increase in system capacity can be achieved by the use of spatial diversity (multiple antennas), and optimum combining. This is explained by the following observation: for independent flat-Rayleigh fading wireless systems with N mutually interfering users, they demonstrate that with K+N antennas, N-1 interferers can be nulled out and K+1 path diversity improvement can be achieved by each of the N users. Monte Carlo evaluations show that these results also hold with frequency-selective fading when optimum equalization is used at the receiver. Thus an N-fold increase in user capacity can be achieved, allowing for modular growth and improved performance by increasing the number of antennas. The interferers can also be users in other cells, users in other radio systems, or even other types of radiating devices, and thus interference cancellation also allows radio systems to operate in high interference environments. As an example of the potential system gain, the authors show that with 2 or 3 antennas the capacity of the mobile radio system IS-54 can be doubled, and with 5 antennas a 7-fold capacity increase (frequency reuse in every cell) can be achieved.>

The use of two resource-sharing techniques for congestion control in a backbone asynchronous transfer mode (ATM) network consisting of ATM cross-connects interconnected with high-speed optical links such as 2.4-Gb/s OC-48c fibers is studied. Memory sharing allows an optimal shared use of buffer space in an ATM switch fabric. Channel (or line) sharing, on the other hand, takes advantage of spare line capacity in the system to permit temporary increases in the output rates of the congested output ports. Fundamental bounds on delay-throughput performance and buffer requirements for specific cell loss rates are presented, and two practical application scenarios, representing line protection arrangements with and without service access capabilities, are introduced.>

Th authors explore the use of a wireless network having a two-tier architecture to serve both conventional mobile subscribers and quasi-stationary (e.g., PCN (personal communications network)) subscribers. The latter are served by microcells which are embedded within macrocells that serve the mobile users. This provides a balance between maximizing the number of users per unit area (which favors small cells) and minimizing the network control associated with handoff (which favors large cells). Four approaches to sharing the spectrum between the two tiers, using per-cell capacity as the measure, are evaluated. The first two feature spread-spectrum sharing, i.e., they use TDMA (time-division multiple access) among microcell users and CDMA (code-division multiple access) among macrocell users (System I), or vice versa (System II). The other two approaches feature orthogonal sharing, i.e., they use TDMA in both tiers, with time slots (System III) or frequency channels (System IV) partitioned so there is no overlap between tiers. Analysis shows that the capacity tradeoffs are poor for Systems I and II because of the large amounts of cross-tier interference: and that System IV gives the best capacity tradeoffs.>

A channel coding approach called diversity coding is introduced for self-healing and fault-tolerance in digital communication networks for nearly instantaneous recovery from link failures. To achieve this goal, the problem of link failures is treated as an erasure channel problem. Implementation details of this technique in existing and future communication networks are discussed.>

The authors introduce the design of the optical distribution channel, which serves as a local-area network and facilitates high-speed interconnection among heterogeneous machines in a way that is economically justifiable. In particular, they describe a design of an almost-all-optical local-area network that is capable of providing a gigabit per second transmission rate directly to the user. The network design is based on the 802.6 topology, a field coding technique in which the header and the data fields are encoded at different rates, and the principle of almost-all-optical switching.>

Transcoding algorithms that eliminate distortion accumulation due to tandem transcodings between memoryless, finite-state, and predictive vector quantization and pulse code modulation (PCM) are presented. The algorithms can be implemented using table lookups for memoryless and finite-state vector quantization, whereas predictive vector quantization requires online calculations. Computer simulations indicate a 6 dB improvement in the case of 16 kb/s predictive vector quantizers, 48 kb/s PCM, and four tandems for speech.>

Techniques are presented that can cancel ghosts in received analog TV (for IDTV, EDTV, and HDTV) signals. The authors utilize the fact that there are short periods of time without the analog signal (the horizontal flyback interval between the lines) to periodically cleanse a finite impulse response (FIR) or an infinite impulse response (IIR) equalizer. This line-by-line processing (cleansing) overcomes the limitations of standard equalizers to allow adequate suppression of ghosts, even with nulls in the spectrum.>

The authors address the selection of a single packet size for broadband integrated packet networks (e.g., B-ISDN) that carry many traffic types, each with different performance requirements. To meet the requirements of different types of traffic in an integrated network (for example, synchronous stream traffic and delay sensitive bursty traffic, or two different types of synchronous traffic), the probability distribution of the end-to-end network delay must be determined. New insights and procedures for estimating such statistics for store-and-forward integrated packet networks that have a single packet size are presented. In particular, the authors address two problems: determining the required build-out delay to achieve a given packet loss probability for real-time stream traffic (e.g., voice), and determining a packet size that results in the required delay characteristics for delay sensitive traffic (e.g., data for parallel processing applications). The central limit theorem is used to approximate the probability distribution function for the end-to-end packet delay in a network of M/D/1 nodes.>

Techniques that can cancel ghosts in received analog TV (for improved-definition TV, extended-definition TV, and high-definition TV) signals are presented. The fact that there are short periods of time without the analog signal (the horizontal flyback interval between the lines) is utilized to periodically cleanse a finite impulse response (FIR) or an infinite impulse response (IIR) equalizer. This line-by-line processing (cleansing) overcomes the limitation of standard equalizers to allow for 40-50 dB of suppression of ghosts, even with nulls in the spectrum, as long as the ghost delay is less than the period of time without the analog signal. Furthermore, by using time inversion in combination with line-by-line processing, the stability problem of the conventional IIR equalizer can be eliminated. It is shown that it may be possible to implement this IIR equalizer on a single digital integrated circuit. Alternatively, an FIR equalizer can be used; although it requires multiple chips (i.e. more taps), it can acquire and adapt to the ghosted channel more rapidly than an IIR equalizer.>

An error-control-based approach, called diversity coding, that provides nearly instantaneous self-healing digital communication networks is presented. This is achieved by constructing an error-correcting code across logically independent channels and by treating link failures within the framework of an erasure channel model. Diversity coding is more efficient than previous approaches to self-healing communication networks since it is nearly instantaneous, is transparent to the end user, minimizes the required extra capacity, and does not need rerouting, resynchronization, or a feedback channel. It is applicable to both circuit-switched and packet-switched networks and to a wide variety of network topologies. Diversity coding can be extended to provide protection from short-duration environmental disruptions, such as multipath fading in radio networks and polarization dispersion in fiber-optic networks, or, in conjunction with previous error detection schemes, to provide forward error correction for random and burst errors.>

The fiber distributed data interface (FDDI) and the IEEE 802.6 distributed queueing dual bus (DQDB) are emerging standards for high-speed (45-150-Mb/s) local and metropolitan area networks. The authors describe several ways to build on these emerging standards to significantly increase the achievable throughput and lower th e end-to-end delay. Without increasing the number of transceivers or their rate, substantial throughput increases are obtained by a highly concurrent logical interconnection pattern of user modes, and the end-to-end delay is decreased by the use of more efficient media-access techniques. The most promising architecture is a multiconnected ring having only two transmitters and two receivers per node, where each node needs to handle or process only a small fraction of the network traffic. In one example, the authors describe a 24-node, distributed, packet-switched network, with only two 100-Mb/s transmitters and two 100-Mb/s receivers per node; it has a maximum throughput of 1.5 Gb/s-15 times the 100/Mb/s throughput of FDDI. Such a system has the potential to be a follow-on standard to FDDI (or IEEE 802.6) or to provide a high-performance LAN/MAN that can interwork with standard systems.>

The potential for electrical signal processing to mitigate the effect of intersymbol interference in long-haul fiber-optic systems is discussed. Intersymbol interference can severely degrade performance and consequently limit both the maximum distance and data rate of the system. Several techniques for reducing intersymbol interference in single-mode fiber systems with single-frequency lasers are presented, and those techniques which are appropriate at high data rates in direct coherent detection systems are identified. The performances of linear equalization (tapped delay lines), nonlinear cancellation (variable threshold detection), maximum-likelihood detection, coding, and multilevel signaling are analyzed. The results for a simulated binary 8-Gb/s system show that simple techniques can be used to reduce intersymbol interference substantially, thereby increasing the system margin by several decibels. A six-tap linear equalizer increases the dispersion-limited distance (due to chromatic or polarization dispersion) by 20% (or reduces the optical power penalty by as much as a factor of two) in direct detection systems, even when the distortion is nonlinear. A nonlinear cancellation technique (adjusting the decision threshold in the detector based on previously detected bits) can more than double the dispersion-limited distance and/or data rate.>

Adaptive or predictive carrier recovery systems, which are essential in high-performance quadrature-amplitude-modulated (QAM) data communications systems to correct for phase jitter and frequency offset, are considered. Analytical and experimental results are presented for two structures that implement a predictive carrier recovery system. These systems, which adapt their structure to match the spectral properties of the impairments, avoid the conflict between a wide bandwidth (to track fast jitter) and a narrow bandwidth (to minimize output noise) inherent in most carrier recovery loops. Such a system increases the likelihood that very bandwidth-efficient modems (e.g., 7 b/s/Hz for 19.2 kb/s voiceband modem applications) can provide reliable transmission in the presence of severe phase jitter and frequency offset. In particular, the predictive carrier recovery systems can track sinusoidal jitter present at more than one frequency as well as generalized time-varying phase jitter processes. Both finite-impulse-response (FIR) and infinite-impulse-response (IIR) adaptive phase tracking systems are considered. Prior limitations on adaptive IIR filters are overcome by designing a structure that is guaranteed to be stable and to possess only a global minimum as the filter coefficients converge to their desired values.>

Two related cancellation techniques based on "tentative" decisions are proposed for removing intersymbol interference, due to channel nonlinearities, for voiceband data transmission. Cancellation of intersymbol interference avoids the need for equalizing or "inverting" analog nonlinear operations as in the decision-feedback method previously proposed by Falconer. The nonlinear cancellation approach removes nonlinear interference terms without excessive noise enhancement and allows effective implementation with ROM's to generate the needed nonlinear signal variables that are to be weighted and summed. The first technique can be incorporated as an "add-on" unit to a present-day modem; the second technique requires a different receiver architecture but offers somewhat enhanced improvement. Simulation results for 9.6 kbit/s data transmission over nonlinear channel models show that both techniques can offer substantial performance improvements for 16-point QAM systems.

A digitally-implemented fractionally-spaced equalizer will generally exhibit long-term instability when the conventional tap-adjustment algorithm is used. This occurs because, in contrast to the synchronous equalizer, a fractionally-spaced equalizer will generally have many sets of tap values which result in nearly equal values of mean-squared error. Some of these tap settings are large enough to cause register overflows and consequent performance deterioration. In this paper we report how a simple modification in the tap-adjustment algorithm provides a solution to the above problem.

Echo cancellation as an effective technique for echo control on telephone circuits is burdened by the appearance of carrier frequency offsets and phase jitter in some echo paths. In this paper we present a digital phase-adaptive structure for cancellation which will automatically compensate for echo path frequency offsets as large as 0.001 of the sampling rate without any reduction in return/loss enhancement.

Adaptive mean-square-tapped-delay-line echo cancellers for voice applications are conventionally designed to stop adjustment during periods of "double-talking", i.e., when a large informationbearing signal is present along with the echo signal to be cancelled. Continuous adaption is, however, desirable in full-duplex, two-wire data transmission where the periods of double-talking are so long that the echo channel may vary. We presume that the tap weights of an echo canceller have converged during a training period free of double talking, and address the problem of subsequent echo-canceller tap adjustment via the estimated-gradient algorithm in the presence of double talking. In the estimated-gradient algorithm the tap increment should be proportional to the product of the residual echo and the tap voltage. However, when double talking occurs the residual echo can only be estimated. For an idealized double-talking model, it is demonstrated, from infinite-precision considerations, that use of the memoryless maximum-likelihood estimate of the residual echo is nearly equivalent to abrupt reduction of the step size of the adjustment algorithm when double-talking begins, and could provide an automatic mechanism for recognizing double-talking. Unfortunately, the response of a digitally implemented canceller to a sharply reduced step size can be a deterioration in performance. In fact, the use of an exceedingly small step size during periods of doubletalking may lead to a cancellation error considerably larger than that predicted by coefficient precision. It is demonstrated how averaging the estimated gradient can significantly decrease the mean-squared tap error during periods of double talking. To a first approximation, the tap-weight error can be reduced by a factor proportional to the averaging interval, with an equivalent decrease in tracking capability.

A comparison is made of several self-orthogonalizing adjustment algorithms for linear tapped delay line equalizers. These adaptive algorithms accelerate the rate of convergence of the equalizer tap weights to those which minimize the output mean-squared error of a data transmission system. Accelerated convergence of the estimated gradient algorithm is effected by premultiplying the correction term in the algorithm by a matrix which is an estimate of the inverse of the channel correlation matrix. The various algorithms differ in the manner in which this estimate is sequentially computed. Depending on the degree of complexity available, the equalizer convergence time may be reduced more than an order of magnitude from that required by the simple gradient algorithm.

The degree of complexity of a digital signal processor is closely related to the precision with which samples of an incoming analog waveform are represented. There is considerable interest in determining how coarse this representation can be without seriously degrading performance from that of an ideal processor of unquantized samples. This question is examined for a receiver of noisy, linearly distorted pulse amplitude modulation (PAM) signals. An optimum [maximum likelihood (ML)] detector, analogous to the Viterbi detector for unquantized samples, is derived for the case of a quantized sample sequence. Performance is evaluated under the assumption of high signal-to-noise ratio (SNR), and the resultant error probability is a good approximation for coarse quantization, and an upper bound for any degree of quantization. For a specified error probability, the degree of quantization suggested by this approach is conservative. Since receiver complexity is closely associated with the length of the digital representation of an input sample, an upper bound on receiver complexity is also suggested. Numerical evaluation of the error probability is quite tedious for an arbitrary channel; however, system performance may be readily evaluated for partial-response (PR) signaling. For the PR channels

A digital transversal postdetection filter for use in differential PSK demodulation is proposed, and a method for optimizing the weighting coefficients is presented. This low-pass filter is implemented using a finely spaced (relative to the symbol rate) tapped delay line whose tap weights are determined so as to minimize the overall mean-square error at the detector outputs. It is shown that even though the detector output signal is quadratic, the optimization problem can be formulated in a way similar to the well-known minimum-mean-square equalizer for linear signals. The filter design technique also accommodates nonideal detector structures, such as those employing hard limiters.

We report on the performance of band-limited staggered quadrature amplitude modulation (SQAM) in the presence of phase jitter and additive Gaussion noise. It is demonstrated that offsetting, or staggering, the in-phase and quadrature data streams by a fraction of a symbol interval improves the phase-jitter immunity of a conventional QAM data transmission system. For example, with a raised cosine pulse having unity rolloff, staggering can reduce the effective jitter variance by a factor of two. Under the constraint of no intersymbol interference, the optimum staggering epoch is shown to be half a symbol interval, and since the resulting system is equivalent to a form of vestigial sideband modulation (VSB)VSB is superior to QAM with respect to phase-jitter immunity. Using both optimum pulse design and data staggering, it is shown that the improvement over conventional QAM is proportional to the excess bandwidth. Consequently, SQAM may be warranted whenever a high-quality phase-locked loop is not used to track phase jitter. While the SQAM technique is not new, it has heretofore not been recognized as possessing the above-mentioned advantages.

A receiver structure is described, for use in pulseamplitude modulation (PAM) data communication systems, which combines null-zone detection and maximum likelihood (ML) processing to improve upon the performance of a conventional decision-feedback equalizer (DFE) while retaining a manageable level of complexity. If the output of the equalizer does not fall in the null zone, the receiver operates as a conventional DFE; however, when the equalizer output falls in the null zone, the decision on that data symbol is deferred one sampling instant and the two most likely signal levels are fed back into the equalizer, generating two competing outputs at the next sampling instant. Applying ML bit detection to this pair of outputs, and optimizing the width of the null zone, improves the effective signal-to-noise ratio of the receiver. Deferring the bit decision beyond one bit interval permits the utilization of additional received samples, and this extended receiver further increases the effective signal-to-noise ratio. The penalty paid for using a null zone, as opposed to performing ML detection on each bit, is at least a 3 dB loss of the usable (by a Viterbi algorithm (VA) receiver) energy contained in the interfering pulse samples.

A considerable amount of literature exists on the problem of selecting an efficient set ofNdigital signals with in-phase and quadrature components for use in a suppressed carrier data transmission system. However, the signal constellation which minimizes the probability of error in Gaussian noise, under an average power constraint, has not been determined when the number of signals is greater than two. In this paper an asymptotic (large signal-to-noise ratio) expression, of the minimum distance type, is derived for the error rate. Using this expression, a gradient-search procedure, which is initiated from several randomly chosenN-point arrays, converges in each case to a locally optimum constellation. The algorithm incorporates a radial contraction technique to meet the average signal power constraint. The best solutions are described for several values ofNand compared with well-known signal formats. As an example, the best locally optimum 16-point constellation shows an advantage of about 0.5 dB in signal-signal-to-noise ratio over quadrature amplitude modulation. The locally optimum constellations are the vertices of a trellis of (almost) equilateral triangles. AsN \rightarrow \infty, it is rigorously proved in the Appendix that the optimum constellations tend toward an equilateral structure, and become uniformly distributed in a circle.

Automatic equalization for digital systems often has as its immediate goal the minimization of some cost function that depends explicitly on the values of intersymbol interference, and thus implicitly on the tap settings. For ease of implementation it is often desirable to slightly modify the conventional distortion measures. A theoretical comparison of several such criteria, some of which are of the peak distortion variety and some of which are of the mean-square class, is made. With one exception, the tap settings that minimize the modified mean-square criteria yield to first-order identical values for the conventional quadratic cost function. All the analogous peak distortion criteria result in zero forcing of sample values, provided that the binary eye is open. Some comments about automatic equalization that are of a tutorial nature are also made.

An upper bound is obtained on the probability that a specified pattern of errors, caused by a combination of intersymbol interference and additive Gaussian noise, occurs in an amplitudemodulated digital data transmission system. The bound, which is a generalization of Saltzberg's upper bound for the probability of a single error, behaves as an exponential function of the signal-to-noise ratio and the overall channel impulse response. The exponent of the bound for a pair of errors is calculated for two "typical" channels and in each case is fairly close to twice the corresponding Saltzberg exponent for a single error.