Next-generation Wireless Systems Research Articles

Beamforming Tradeoffs for Initial UE Discovery in Millimeter-Wave MIMO Systems

Millimeter-wave MIMO systems have gained increasing traction towards the goal of meeting the high data-rate requirements in next-generation wireless systems. The focus of this work is on low-complexity beamforming approaches for initial UE discovery in such systems. Towards this goal, we first note the structure of the optimal beamformer with per-antenna gain and phase control and the structure of good beamformers with per-antenna phase-only control. Learning these beamforming structures in mmW systems is fraught with considerable complexities such as the need for a non-broadcast system design, the sensitivity of the beamformer approximants to small path length changes, etc. To overcome these issues, we establish a physical interpretation between these beamformer structures and the angles of departure/arrival of the dominant path(s). This physical interpretation provides a theoretical underpinning to the emerging interest on directional beamforming approaches that are less sensitive to small path length changes. While classical approaches for direction learning such as MUSIC have been well-understood, they suffer from many practical difficulties in a mmW context such as a non-broadcast system design and high computational complexity. A simpler broadcast solution for mmW systems is the adaptation of directional codebooks for beamforming at the two ends. We establish fundamental limits for the best beam broadening codebooks and propose a construction motivated by a virtual subarray architecture that is within a couple of dB of the best tradeoff curve at all useful beam broadening factors. We finally provide the received SNR loss-UE discovery latency tradeoff with the proposed constructions. Our results show that users with a reasonable link margin can be quickly discovered by the proposed design with a smooth roll-off in performance as the link margin deteriorates.

Addressing next-generation wireless challenges with commercial software-defined radio platforms

We review commercially available software- defined radio platforms and classify them with respect to their ability to enable rapid prototyping of next-generation wireless systems. In particular, we first discuss the research challenges imposed by the latest software-defined radio enabling technologies including both analog and digital processing hardware. Then we present the state-of-the-art commercial software-defined radio platforms, describe their software and hardware capabilities, and classify them based on their ability to enable rapid prototyping and advance experimental research in wireless networking. Finally, we present three experimental testbed scenarios (wireless terrestrial, aerial, and underwater) and argue that the development of a system design abstraction could significantly improve the efficiency of the prototyping and testbed implementation process.

Joint Antenna Selection and Energy-Efficient Beamforming Design

Wireless networks face the challenge of increasing energy consumption while satisfying the unprecedented demand for higher data rates. Energy-efficient transmission has been regarded as a key technology for the next-generation wireless system. Meanwhile, to reduce the cost, in practice, a base station usually has less radio chains than the antennas, which makes antenna selection an appealing transmission strategy. This letter addresses the problem of joint optimization of energy-efficient beamforming and antenna selection for downlink multiuser systems. The nonconvexity arising from both the nonlinear fractional programming and the $\ell _{0}$ -(quasi)norm presents the main difficulty in solving the joint optimization problem. Nevertheless, we develop an effective algorithm to address this problem. Numerical results are given to validate the effectiveness and the performance of the developed algorithm.

Iterative Channel Estimation Using Virtual Pilot Signals for MIMO-OFDM Systems

The number of transmit and receive antennas in multi-input multi-output (MIMO) systems is increasing rapidly to enhance the throughput and reliability of next-generation wireless systems. Benefits of large size MIMO systems, however, can be realized only when the quality of estimated channels is ensured at the transmitter and receiver side alike. In this paper, we introduce a new decision-directed channel estimation technique dealing with pilot shortage in the MIMO-OFDM systems. The proposed channel estimator uses soft symbol decisions obtained by iterative detection and decoding (IDD) scheme to enhance the quality of channel estimate. Using the soft information from the decoders, the proposed channel estimator selects reliable data tones, subtracts interstream interferences, and performs re-estimation of the channels. We analyze the optimal data tone selection criterion, which accounts for the reliability of symbol decisions and correlation of channels between the data tones and pilot tones. From numerical simulations, we show that the proposed channel estimator achieves considerable improvement in system performance over the conventional channel estimators in realistic MIMO-OFDM scenarios.

On Optimal Policies for Network-Coded Cooperation: Theory and Implementation

Network-coded cooperative communication (NC-CC) has been proposed and evaluated as a powerful technology that can provide a better quality of service in the next-generation wireless systems, e.g., D2D communications. Previous contributions have focused on performance evaluation of NC-CC scenarios rather than searching for optimal policies that can minimize the total cost of reliable packet transmission. We break from this trend by initially analyzing the optimal design of NC-CC for a wireless network with one source, two receivers, and half-duplex erasure channels. The problem is modeled as a special case of Markov decision process (MDP), which is called stochastic shortest path (SSP), and is solved for any field size, arbitrary number of packets, and arbitrary erasure probabilities of the channels. The proposed MDP solution results in an optimal transmission policy per time slot, and we use it to design near-optimal heuristics for packet transmission in a network of one source and N ≥ 2 receivers. We also present numerical results that illustrate the performance of the proposed heuristics under a variety of scenarios. To complete our analysis, our heuristics are implemented in Aalborg University's Raspberry Pi testbed and compared with random linear network coding (RLNC) broadcast in terms of completion time, total number of required transmissions, and percentage of delivered generations. Our measurements show that enabling cooperation only among pairs of devices can decrease the completion time by up to 4.75 times, while delivering 100% of the 10000 generations transmitted, as compared to RLNC broadcast delivering only 88% of them in our tests.

IJARCCE - Computer and Communication Engineering

In the context of WLAN (Wireless Local Area Network) and WPAN (Wireless Personal Area Network) systems for High Data Rate (HDR) wireless communications, the unlicensed frequency band available in the millimeter wave region has become more and more attractive. Currently focus is on use of OFDM system to cater for increased data rate of wireless medium with good performance. Diversity techniques play an important role in achieving higher performance level for limited power wireless systems. Wavelet analysis has some strong advantages over Fourier analysis, as it allows a time-frequency domain operation, allowing optimal resolution and flexibility. Wavelets have been satisfactorily used in almost all the fields of wireless communication systems including OFDM which is a strong candidate for next generation of wireless system. This paper proposes a DWT-OFDM Diversity to achieve better performance in terms of SNR and bit error rate (BER) for TSV model based channel at 60 GHz. The performances of different discrete wavelets for channels defined by IEEE 802.15.4a are analyzed. The results indicate better BER performance in case of lower order wavelet.

Demonstration of a Symmetric 40 Gbit/s TWDM-PON Over 40 km Passive Reach Using 10 G Burst-Mode DML and EDC for Upstream Transmission [Invited

To meet the 2015 timeline, a hybrid time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been selected as the pragmatic path toward the second stage of the next-generation PON (NG-PON2). High-end business users and mobile front-haul/back-haul for next-generation wireless systems that highly rely on symmetrical data rate services are believed to be the main deployment drivers for NG-PON2. In this paper, for the first time to the best of our knowledge, we demonstrate a symmetric 40  Gbit/s TWDM-PON system that fully complies with the up-to-date full service access network/International Telecommunication Union NG-PON2 migration path. There are two distinguishing features from previously reported systems. One is that four symmetric 10  Gbit/s wavelength pairs are supported at the final NG-PON2 wavelength plan [i.e., (C−/L+) band] over 40 km passive reach, and the other is that a burst-mode tunable directly modulated laser and burst-mode electronic dispersion compensation are demonstrated for 10 G upstream transmission instead of tunable external modulated lasers. The selection of the final NG-PON2 wavelength plan is first briefly reviewed. Then the key enabling technologies for our demonstrated TWDM-PON are analyzed and their technological choices, availability, and performances are further investigated. After illustrating the demonstrated system architecture and configuration, measurements and analysis are presented to prove the system feasibility and technical availability. In this demonstration, N1 and N2 optical distribution network (ODN) classes can be totally supported without amplifiers, whereas preamplification is needed to achieve E1 and E2 ODN classes. Both downstream and upstream optical parameters are summarized.

Fronthaul Compression for Cloud Radio Access Networks: Signal processing advances inspired by network information theory

Cloud radio access networks (C-RANs) provide a novel architecture for next-generation wireless cellular systems whereby the baseband processing is migrated from the base stations (BSs) to a control unit (CU) in the ?cloud.? The BSs, which operate as radio units (RUs), are connected via fronthaul links to the managing CU. The fronthaul links carry information about the baseband signals?in the uplink from the RUs to the CU and vice versa in the downlink?in the form of quantized in-phase and quadrature (IQ) samples. Due to the large bit rate produced by the quantized IQ signals, compression prior to transmission on the fronthaul links is deemed to be of critical importance and is receiving considerable attention. This article provides a survey of the work in this area with emphasis on advanced signal processing solutions based on network information theoretic concepts. Analysis and numerical results illustrate the considerable performance gains to be expected for standard cellular models.

Spectrum efficiency sub-carrier and energy efficiency power allocation for downlink multi-user CoMP in multi-cell system

Coordinated multi-point transmission/reception (CoMP) was proposed currently as an effective technology to improve cell-edge throughput in next-generation wireless systems. Most of the existing work discussed clustering methods mostly to maximize the edge user throughput while neglecting the problem of energy efficiency, such as those algorithm clustering base stations (BSs) of better channel condition and BSs of worse channel condition together. In addition, BSs usually increase the transmit power to achieve higher throughput without any considering of interference caused to other users, that may result in energy waste. The authors focus on the throughput maximizing problem while fully considering energy saving problem in CoMP systems. A coefficient is defined to describe the fitness of clusters. Then a sub-carrier allocation algorithm with clustering method is put forward for CoMP downlink, which can save the transmit power of BS and increase the throughput. Furthermore a power allocation scheme is proposed based on non-cooperation game; in which the transmit power is decreased by BSs generally to reach the Nash equation (NE). Simulation shows that the proposed sub-carrier allocation scheme and power allocation algorithm are better than the existing ones on users’ throughput while consumes much less energy.

Practical and Simple Wireless Channel Models for Use in Multipolarized Antenna Systems

The next-generation wireless systems are expected to support data rates of more than 100 Mbps in outdoor environments. In order to support such large payloads, a polarized antenna may be employed as one of the candidate technologies. Recently, the third generation partnership standards bodies (3GPP/3GPP2) have defined a cross-polarized channel model in SCM-E for MIMO systems; however, this model is quite complex since it considers a great many channel-related parameters. Furthermore, the SCM-E channel model combines the channel coefficients of all the polarization links into one complex output, making it impossible to exploit the MIMO spatial multiplexing or diversity gains in the case of employing polarized antenna at transmitter and receiver side. In this paper, we present practical and simple 2D and 3D multipolarized multipath channel models, which take into account both the cross-polarization discrimination (XPD) and the Rician factor. After verifying the proposed channel models, the BER and PER performances and throughput using the EGC and MRC combining techniques are evaluated in multipolarized antenna systems.

Propagation Channel Models for Next-Generation Wireless Communications Systems

As new systems and applications are introduced for next-generation wireless systems, the propagation channels in which they operate need to be characterized. This paper discusses propagation channels for four types of next-generation systems: (i) distributed Multiple-Input Multiple-Output (MIMO) and Cooperative MultiPoint (CoMP) systems, which require the characterization of correlation between channels from a mobile station to different base stations or access points; (ii) device-to-device communications, where propagation channels are characterized by strong mobility at both link ends (e.g., in vehicle-to-vehicle communications), and/or significant impact of moving shadowing objects; (iii) full-dimensional MIMO, where antenna arrays extend in both the horizontal and vertical dimension, so that azimuthal and elevation dispersion characteristics of the channel become relevant, and (iv) millimeter wave Wireless Local Area Network (WLAN) and cellular communication systems, where the high carrier frequency leads to a change (compared to microwave communications) concerning which propagation processes are dominant. For each of these areas, we give an overview of measurements and models for key channel properties. A discussion of open issues and possible future research avenues is also provided.

Joint blind channel shortening and compensation of transmitter I/Q imbalances and CFOs for uplink SC-IFDMA systems

This paper deals with receiver design for the uplink of a single-carrier interleaved frequency-division multiple-access (SC-IFDMA) system, which is a promising candidate for non-adaptive transmission in next-generation wireless systems. In particular, channel shortening is required in asynchronous SC-IFDMA systems operating over highly-dispersive channels, since the length of the cyclic prefix (CP) is insufficient to compensate for the combined effects of timing offsets and channel dispersion; other major sources of performance degradation are the in-phase/quadrature-phase (I/Q) imbalance introduced at each transmitter, and the carrier frequency offsets (CFOs) between the transmitters and the receiver. The proposed multistage receiver is designed to jointly counteract all these impairments: specifically, the minimum mean-output energy (MMOE) criterion is adopted to synthesize a time-domain equalizer, which performs blind multiuser channel shortening of all the user channels (including the corresponding time offsets), without requiring a priori knowledge of the channel impulse responses to be shortened, or compensation of the CFOs and transmitter I/Q imbalances. Moreover, after channel shortening and (total or partial) CP removal, the MMOE criterion is also employed to compensate for the CFOs and mitigate I/Q impairments. Monte Carlo computer simulations are carried out to assess the effectiveness of the proposed receiver.

Downlink Scheduling and Resource Allocation for Cognitive Radio MIMO Networks

Cognitive radio is regarded as the ideal candidate for enhancing the efficiency of spectrum usage for next-generation wireless systems. In fact, this emerging technology allows unlicensed cognitive users to transmit over frequency bands that are initially owned by license holders through the use of dynamic spectrum sharing. In this paper, we propose a novel algorithm that efficiently solves the problem of spectrum sharing and user scheduling in a cognitive downlink multi-input-multi-output system (MIMO). We study the scenario where primary receivers do not allow any interference from a multiantenna cognitive base station, which serves cognitive users. Using graph theory, we model, formulate, and develop an algorithm that finds near-optimal spectrum sharing with the objective of approaching the maximum achievable secondary sum rate. Since the formulated graph-coloring problem is shown to be NP-hard, we design a low-complexity greedy algorithm. Following, we add the well-known proportional fairness to the proposed algorithm to ensure time-based fairness and to efficiently resolve the fairness/sum rate tradeoff. The problem is also formulated as a binary integer programming problem to find the optimal coloring solution. Computer simulations show that the proposed algorithm is able to achieve near-optimal performances with low computational complexity.

Buffer-Aware Network Coding for Wireless Networks

Network coding, which can combine various traffic flows or packets via algebraic operations, has the potential of achieving substantial throughput and power efficiency gains in wireless networks. As such, it is considered as a powerful solution to meet the stringent demands and requirements of next-generation wireless systems. However, because of the random and asynchronous packet arrivals, network coding may result in severe delay and packet loss because packets need to wait to be network-coded with each others. To overcome this and guarantee quality of service (QoS), we present a novel cross-layer approach, which we shall refer to as Buffer-Aware Network Coding, or BANC, which allows transmission of some packets without network coding to reduce the packet delay. We shall derive the average delay and power consumption of BANC by presenting a random mapping description of BANC and Markov models of buffer states. A cross-layer optimization problem that minimizes the average delay under a given power constraint is then proposed and analyzed. Its solution will not only demonstrate the fundamental performance limits of BANC in terms of the achievable delay region and delay-power tradeoff, but also obtains the delay-optimal BANC schemes. Simulation results will show that the proposed approach can strike the optimal tradeoff between power efficiency and QoS.

PERFORMANCE OF ADAPTIVE LIFE TIME BASED VERTICAL HANDOFF ALGORITHM IN HETEROGENEOUS NETWORKS

The convergence of heterogeneous wireless networks combines existing wireless networks. An effective combination of diff erent wireless networks should enable them to complement each other and pro vide high-speed data rate, wide area coverage, and quality of service (Q oS) guarantee. In Next Generation Wireless Systems (NGWS), seamless handof f between different wireless access networks plays a vital role. One of the major challenges for seamless mobility is the creation of a vertical han doff protocol. In this paper, the performance of vertical handoff is studi ed using the integration of third generation (3G) cellular and wireless loca l area networks (WLAN). The effect of application-based signal stre ngth threshold (ASST) and path loss exponent on an adaptive lifetime-base d vertical handoff (ALIVE-HO) strategy is studied in terms of number o f handoffs, aggregated throughput, and packet delay. Therefore the vertical handoff performance can be optimized in wireless and mobile networks. The present work is done for different channel conditio ns as well as different mobility schemes.

LTE-advanced and 4G wireless communications [Guest Editorial

The goal of this feature topic is to give a comprehensive system-level overview of the LTE-A standard, which includes not only the description of how various new techniques work, but also the rationales and motivation behind how technical decisions were made during the Release-10 standardization process. Our hope is that this will motivate interested researchers to explore and propose newer ideas for enhancements in future LTE-A releases as well as the next-generation wireless systems.

Resource Allocation for Overlapping MBS Zones

Multicast and broadcast service (MBS) is one of the important services for next-generation wireless systems. In WiMAX, the radio resource unit (i.e., time, frequency, code, etc.) for MBS is centralized allocated by an anchor access service network gateway (Anchor ASN-GW). In MBS, a BS can dynamically join or leave an MBS Zone due to the moving of MSs. The Anchor ASN-GW must allocate nonoverlapping radio resource units to BSs for delivering different MBS contents in overlapping MBS Zones. This paper presents radio resource allocation and reallocation algorithms to minimize the number of required resource units for overlapping MBS Zones. For a given number of MBS Zones, a resource estimation model is also presented to estimate the average number of radio resource units to be reserved by the ASN-GW. Simulation results showed that the proposed algorithms can reduce the number of reallocations, and, thus, the signaling messages exchanged in the air interface and the core network are minimized. The results also showed that the proposed model can be used as a good reference for the network operator to estimate the average number of required radio resource units for a given number of MBS Zones.

Novel-integrated patch antennas with multi-band characteristics

In this study, two integrated multi-band microstrip patch antennas have been proposed for the next-generation wireless systems. The first design consists of a right isosceles triangular patch integrated with a pair of monopoles. The patch resonates at 3.5 GHz (WiMAX, worldwide interoperability for microwave access) and the monopoles at 2.45 GHz (WLAN, wireless local area network) and 1.96 GHz (PCS frequency), respectively. Furthermore, to improve the gain profile and to achieve directive radiation characteristics towards zenith, a reflector ground plane has been placed below the patch. The detailed analysis of the pattern synthesis technique has been explained. Similarly, the second proposed design consists of a semi-circular patch resonating at 3.5 GHz integrated with a slot and a monopole. The slot and monopole resonate at 5.5 GHz (WiMAX) and 2.45 GHz, respectively. Both the designs are realised on a 1.58 mm-thick FR4 substrate (dielectric constant=4.4) and have a return loss better than 10 dB with desired radiation characteristics at the specified resonant frequencies. Prototypes of the proposed designs have been fabricated and their radiation characteristics have been measured. A close agreement has been found between simulation and measurements.

Approximation Algorithms for a Link Scheduling Problem in Wireless Relay Networks with QoS Guarantee

The emerging wireless relay networks (WRNs) are expected to provide significant improvement on throughput and extension of coverage area for next-generation wireless systems. We study an optimization problem for multihop link scheduling with bandwidth and delay guarantees over WRNs. Our optimization problem is investigated under a more general interference model with a generic objective. The objective can be based on various kinds of performance indexes (e.g., throughput, fairness, and capacity), which can be determined by service providers. Through our theoretical analysis, the intractability and inapproximability of the optimization problem are shown. Due to the intractable computational complexity, we present efficient algorithms to provide a reasonable small approximation factor against any optimal solution even for a worst-case input. Furthermore, some experimental results indicate that our algorithms yield near-optimal performance in the average case.

Minimization of Handoff Failure Probability for Next-Generation Wireless Systems

During the past few years, advances in mobile communication theory have enabled the development and deployment of different wireless technologies, complementary to each other. Hence, their integration can realize a unified wireless system that has the best features of the individual networks. Next-Generation Wireless Systems (NGWS) integrate different wireless systems, each of which is optimized for some specific services and coverage area to provide ubiquitous communications to the mobile users. In this paper, we propose to enhance the handoff performance of mobile IP in wireless IP networks by reducing the false handoff probability in the NGWS handoff management protocol. Based on the information of false handoff probability, we analyze its effect on mobile speed and handoff signaling delay.