multi-RAT Systems Research Articles

LaSR: A Supple Multi-Connectivity Scheduler for Multi-RAT OFDMA Systems

Network densification over space and spectrum is expected to be key to enabling the requirements of next generation mobile systems. The pitfall is that radio resource allocation becomes substantially more complex. In this paper, we propose LaSR, a practical multi-connectivity scheduler for OFDMA-based multi-RAT systems. LaSR makes optimal discrete control actions by solving a sequence of simple optimization problems that do not require prior information of traffic patterns. In marked contrast to previous work, the flexibility of our approach allows us to construct scheduling policies that achieve a good balance between system cost and utility satisfaction, while jointly operate across heterogeneous RATs, accommodate real-system requirements, and guarantee system stability. Examples of system requirements considered in this paper include (but are not limited to): constraints on how scheduling data can be encoded onto signaling protocols (e.g., LTE's DCI), delays when turning on/off radio units, or on/off cycles when using unlicensed spectrum. We evaluate our scheduler via a thorough simulation campaign in a variety of scenarios with e.g., mobile users, RATs using unlicensed spectrum (using a duty cycle access mechanism), imperfect queue state information, and constrained signaling protocol.

Super-MAC Design for Tightly Coupled Multi-RAT Networks

Modern wireless systems are evolving toward a heterogeneous environment where multiple radio access technologies (RATs) coexist. Most of the RATs in current use operate independently of each other, however, there is an increasing demand for coordination among different RATs in order to support exponentially growing wireless traffic. Our goal in this paper is to design a super-MAC that integrates multiple RATs in a tightly coupled manner. To this end, we propose an architecture for super-MAC, and develop an algorithm that splits IP traffic into multiple RATs and controls each RAT to exploit multi-RAT diversity. We prove the asymptotic optimality of the super-MAC algorithm by introducing a novel reference system that enables the analysis of the multi-RAT system where there is a mixture of slotted (such as cellular) and unslotted (such as WiFi) RATs. Through extensive simulations we show that the super-MAC algorithm can enhance the quality of service including throughput, energy efficiency, and fairness.

Towards Harmonious Coexistence in the Unlicensed Spectrum: Rational Cooperation of Operators.

5G New Radio (NR) operating in the unlicensed spectrum is accelerating the Fourth Industrial Revolution by supporting Internet of Things (IoT) networks or Industrial IoT deployments. Specifically, LTE-Advanced (LTE-A) is looking to achieve spectrum integration through coexistence with multi-radio access technology (RAT) systems in the same unlicensed bands with both licensed-assisted and stand-alone access. The listen-before-talk (LBT) mechanism is mainly considered to enable an LTE operator to protect other incumbent unlicensed systems. In this article, we investigate the behaviors of multiple LTE operators along with the deployment of WiFi networks in the unlicensed spectrum from both short- and long-term points of view. In countries without mandatory LBT requirements, we show that an LTE operator is susceptible to collusion with another LTE operator, thus exploiting scarce spectrum resources by deceiving other wireless networks into thinking that channels are always busy; hence, mandatory usage of LTE with LBT is highly recommended at national level to achieve harmonious coexistence in the unlicensed spectrum. We discuss several possible coexistence scenarios to resolve the operator’s dilemmaas well as to improve unlicensed spectrum efficiency among multi-RAT systems, which is viable in the near future.

On the packet allocation of multi-band aggregation wireless networks

The use of heterogeneous networks with multiple radio access technologies (RATs) is a system concept that both academia and industry are studying. In such system, integrated use of available multiple RATs is essential to achieve beyond additive throughput and connectivity gains using multi-dimensional diversity. This paper considers an aggregation module called opportunistic multi-MAC aggregation (OMMA). It resides between the IP layer and the air interface protocol stacks, common to all RATs in the device. We present a theoretical framework for such system while considering a special case of multi-RAT systems, i.e., a multi-band wireless LAN (WLAN) system. An optimal packet distribution approach is derived which minimizes the average packet latency (the sum of queueing delay and serving delay) over multiple bands. It supports multiple user terminals with different QoS classes simultaneously. We further propose a packet scheduling algorithm, OMMA Leaky Bucket, which minimizes the packet end-to-end delay, i.e., the sum of average packet latency and average packet reordering delay. We also describe the system architecture of the proposed OMMA system, which is applicable for the general case of the multi-RAT devices. It includes functional description, discovery and association processes, and dynamic RAT update management. We finally present simulation results for a multi-band WLAN system. It shows the performance gains of the proposed OMMA Leaky Bucket scheme in comparison to other existing packet scheduling mechanisms.

Competitive access in multi-RAT systems with regulated interference constraints

Deployment of multiple radio access technologies (RATs) at the same cell site enables the system to flexibly support different types of devices and services. Such multi-RAT systems call for an efficient utilization of the system resources as well as simplified management. In this paper, we take a user-centric approach and let each individual user equipment decide its own access strategy in a multi-RAT system with regulated interference constraints. The formulated problem is a generalized Nash equilibrium (GNE) problem. We show that there always exists a GNE but its uniqueness is not guaranteed. A closed form solution is provided to characterize a special class of the GNEs. We then propose a primal-dual algorithm with detailed convergence analysis for computing a GNE. The proposed algorithm may have practical implications in the design of multi-RAT systems.

The Omitted Dimension: Exploiting Multiuser Diversity in Multi-Radio Access Technology Data Cellular Communication Systems

Performance of cellular communication systems is typically enhanced by leveraging the three dimensions of system transmission bandwidth, area frequency reuse, i.e. system access point (AP) density, and spectral efficiency of employed radio air interface, referred to as the radio access technology (RAT). In particular, refined RATs are continuously introduced to compensate for limited spectrum availability and restrictions on system AP densification in cellular communication systems. While the performance of cellular communication systems is maximized by employing a single RAT providing maximal spectral efficiency, varying capabilities of user equipment compels the co-deployment of multiple RATs in cellular communication systems and entails fragmenting system radiofrequency resources between co-deployed RATs. Nevertheless, the inefficient structuring of multi-RAT systems as independently operated collocated single-RAT subsystems results in unbalanced system loading, suboptimal spectrum utilization, and the omission of multiuser diversity as a performance enhancement dimension in multi-RAT systems. The omitted dimension of multiuser diversity is exploited in this paper, through multiple means and techniques, to further enhance the performance of multi-RAT data cellular communication systems. Unifying the architectural structure of multi-RAT systems is proposed to eliminate the redundant duplication of radio access network functions and elements, reduce system deployment costs and operational complexity, improve system scalability, and enable the joint execution of non-radio transmission functions for all co-deployed RATs. By fully exploiting system multiuser diversity, the joint allocation of system radiofrequency resources under autonomous spectrum assignment is shown to substantially enhance the performance of all employed RATs, in addition to the overall performance of multi-RAT systems, without extending any of the three typical performance enhancement dimensions of cellular communication systems.

On the Utilization of Multi-Mode User Equipment in Multi-Radio Access Technology Cellular Communication Systems

Multi-radio access technology (RAT) cellular communication systems limit connected users to utilizing a single RAT even when employing multi-mode user equipment (UE) capable of utilizing multi-RATs. Single-mode access, combined with static spectrum partitioning between co-deployed RATs and independent resource allocation for employed RATs, results in suboptimal spectrum utilization in multi-RAT systems. This paper models user access in multi-RAT systems and proposes enabling multi-mode UE to simultaneously utilize multiple RATs, using multi-RAT carrier aggregation, to improve the performance and spectrum utilization of multi-RAT systems. Several realizations of multi-mode access with varying implementation requirements are presented and discussed. Detailed system-level simulations, for a system co-deploying High Speed Packet Access (HSPA) and Long-Term Evolution (LTE), are performed to investigate the gains and limitations of different user access configurations in multi-RAT systems.

A Robust Multi-RAT VANET/LTE for Mixed Control & Entertainment Traffic

Intelligent Transportation Systems (ITS) have been receiving significant interest from various stakeholders worldwide. ITS promise major enhancements to the efficiency, safety, convenience and sustainability of transportation systems. To satisfy the diverse vehicular application requirements, this paper proposes an integration of IEEE 802.11-based VANET and LTE cellular network using mobile vehicular gateways. IEEE 802.11 g is used for V2V communications and LTE for V2I communications. A burst communication technique is applied to prevent packet losses in the critical uplink ITS traffic. A performance simulation-based study is conducted to validate the feasibility of the proposed system in an urban vehicular environment. The system performance is evaluated in terms of data loss, data rate, delay and jitter. The results indicate that the proposed Multi-RAT system offers acceptable performance that meets the requirements of the different vehicular applications.

Dynamic Spectrum Management in Multi-Radio Access Technology (RAT) Cellular Systems

Fixed Spectrum Allocation (FSA) results in suboptimal spectrum utilization, unbalanced system loading and the inability to adapt to system traffic variations when employed in multi-Radio Access Technology (RAT) systems. This paper proposes the use of flexible spectrum management techniques in multi-RAT systems. A Dynamic Spectrum Management (DSM) framework that addresses the shortcomings of FSA, while ensuring the reliable operation of all co-deployed RATs, is presented. Simulations for a system co-deploying HSPA and LTE show that the proposed framework outperforms FSA schemes and is capable of adapting to system traffic variations.