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A Flexible 5G Wide Area Solution for TDD with Asymmetric Link Operation
Abstract
A flexible multi-service 5G wide area (WA) solution for time division duplex (TDD) operation is outlined in this article. In particular, the associated frame design is in focus. Given the fundamental tradeoffs between capacity, coverage, latency, and reliability, a flexible solution that allows optimization on a per-link basis is proposed. The solution encompasses the possibility to schedule users with different transmission time intervals to best match their service requirements and radio conditions. Due to the large downlink/uplink transmission power imbalance for each link, asymmetric link operation is proposed, where users operate with different minimum transmission times for the two link directions. This is achieved by using a highly flexible asynchronous hybrid automatic repeat request (HARQ) scheme, as well as a novel solution with in-resource control channel signaling for the scheduling grants. Performance results for the proposed 5G WA TDD solution show clear benefits over current LTE, for example, reduced latency and more scalable control overhead to better support users with different QoS requirements.
... In addition, conventional LTE BSs require synchronization of uplink and downlink switching points, otherwise, the disparity in transmit power between the BS and the mobile user equipment (MUE) may lead to irreconcilable cross-link interference. However, this is not the case for pico BSs in HetNets, as their transmit power is very close to that of the MUE, which allows pico BSs to independently adjust their uplink and downlink switching points to better adapt to the services they carry [12], [13]. These new features provide strong grips on scheduling the network at a finer granularity but also bring challenges that more complex factors inevitably have to be taken into account when designing scheduling policies. ...
... interference suffered by MUE u/BS b when receives data from BS b/UE u on subchannel c during subslot τt r c,t b,u , r c,t u,b perceived downlink/uplink rate between BS b and MUE u on subchannel c during time slot t R DL u , R UL u minimum downlink/uplink rate requirement of MUE u cross-link interference [12]. On the contrary, each PBS is allowed to determine its switching point independently, because it has a similar transmit power to the user, making it not prone to severe cross-link interference. ...
... To explicitly formulate the instantaneous interference I c,τt b,u , we let N TDD t,b to be the subslot after which BS b switches to downlink in time slot t, and I x y to be an indicator that takes the value of 1 when x ≤ y and 0 otherwise, while I x y does the opposite. Hence, I c,τt b,u can be calculated using (12). ...
With the proliferation of mobile terminals and the continuous upgrading of services, 4G LTE networks are showing signs of weakness. To enhance the capacity of wireless networks, millimeter waves are introduced to drive the evolution of networks towards multi-band 5G heterogeneous networks. The distinct propagation characteristics of mmWaves and microwaves, as well as the vastly different hardware configurations of heterogeneous base stations, make traditional access strategies no longer effective. Therefore, to narrowing the gap between theory and practice, we investigate the access strategy in multi-band 5G heterogeneous networks, taking into account the characteristics of mobile users, asynchronous switching between uplink and downlink of pico base stations, asymmetric service requirements, and user communication continuity. We formulate the problem as integer nonlinear programming and prove its intractability. Thereby, we decouple it into three subproblems: user association, switch point selection, and subchannel allocation, and design an algorithm based on optimal matching and spectral clustering to solve it efficiently. The simulation results show that the proposed algorithm outperforms the comparison methods in terms of overall data rate, effective data rate, and number of satisfied users.
... Asymmetric Link Operation: The TTI size may in many cases be different for a user's uplink and downlink transmission. From a coverage perspective, especially a macro cell-edge user may be required to transmit with larger TTI sizes to maintain its uplink coverage, while still being schedulable with a small TTI size in the downlink due to the higher available transmit power at the base station [14]. ...
... Figure 1 shows an example for a downlink HARQ process, where the timing elements such as the processing times, the TTI duration, the ACK/NACK duration and the network architecture delay influence on the downlink HARQ RTT. In this particular example, the UE is scheduled with a small TTI size in the downlink, while the uplink ACK/NACK transmission time is much longer to fulfill the users' coverage requirements, that is, assuming the UE is coverage challenged [6,14]. On the contrary, a user in better coverage conditions could be configured to transmit the ACK/NACK in the uplink over a shorter time, leading to a reduced HARQ RTT. ...
... For the sake of simplicity, the processing time at both the eNB and the UE is assumed to equal 0.1 ms. 1 A minimum TTI duration of 0.125 ms is set. The feedback transmission time varies from 0.0625 ms for UEs with very good coverage up to 1 ms for extreme coverage-challenged UEs [14]. It is shown in Table 1 that the HARQ RTT can be as short as 0.5 ms by transmitting with a short TTI size of 0.125 ms. ...
Current mobile communications systems have a rather simple and single-mode HARQ functionality that is applied for all services. In this article we argue for having a set of user-centric HARQ enhancements that are configurable in coherence with its service requirements, as a means to more efficiently optimize the end-to-end performance. A set of HARQ enhancements are therefore proposed that can be enabled and configured per user as needed. The presented enhancements include more flexible HARQ timing configurations, early feedback estimation for latency-critical communication, options for adaptive redundancy matching with enriched feedback, more efficient handling of large transport block sizes, and optimizations particularly suited for communication with low cost and low energy-consuming devices.
... Although there are advantages of TDD over FDD, there are also disadvantages. The first disadvantage is the limited coverage due to the relatively small portion of time resources for UL transmission [12]. By assigning the majority of time resources to the DL, only a small portion of time resources can be allocated to the UL resulting in a smaller coverage (see Fig. 1). ...
... In fact, for many of the 4G systems utilizing FDD, the UL is often underutilized while the DL is under heavy use. In 5G, most of the new carriers are TDD carriers and therefore to address such issues [12]. Of course, the fundamental problem of coverage limitation of TDD is still not addressed. ...
In this paper, an advanced duplex scheme called cross-division duplex (XDD) is proposed to enhance uplink (UL) coverage in time division duplex (TDD) carriers by utilizing self-interference cancellation (SIC) capability at a base station. With XDD, it is possible to combine TDD’s ability to efficiently handle asymmetric UL and downlink (DL) traffic with frequency division duplex’s coverage advantage. To do so, XDD simultaneously operates UL and DL on the same TDD carrier but on different frequency resources. Such operation leads to severe interference on the received UL signal at the base station which requires two levels of SIC implementation; antenna and digital SIC. More than 50 dB of interference is removed through the antenna SIC using electromagnetic barriers between the transmitting and receiving antennas. The remaining interference is removed by the digital SIC based on estimating the non-linear channel of the circuit at the receiver baseband. It is verified by simulation and analysis that with the proposed XDD, the UL coverage can be improved by up to 2.37 times that of TDD. To check the feasibility of XDD, a Proof-of-Concept was developed where it was observed that the benefits of XDD can indeed be realized using the proposed SIC techniques.
... As the early 5G commercial enrollments are foreseen over the 3.5 GHz unpaired spectrum, due to its wide spectrum availability [3], time-division duplexing (TDD) technology is vital for the success of the 5G. With dynamic TDD, base-stations (BSs) independently utilize either a downlink (DL) or uplink (UL) transmission opportunity at a time in order to meet their capacity and latency demands, respectively [4]. ...
... (1) URLLC latency and reliability performance is highly challenged in dynamic TDD deployments, due to the nonconcurrent downlink and uplink transmission opportunities, and the additional cross-link interference (CLI), (2) thus, the real-time optimization of the radio pattern structure becomes vital towards a decent URLLC outage performance, (3) accordingly, machine learning techniques can be efficiently utilized to offer a proactive pattern estimation learning gain, (4) in this regard, reinforcement Q-learning has been adopted due to its online (real-time) learning capabilities, and simple implementation complexity under the adopted system model, and (5) proposed solution demonstrates a flexible and dynamic radio pattern selection strategy to autonomously trade-off the CLI intensity with the URLLC outage performance; however, the achievable gain is shown to be loaddependent. As a future extension of this study, various learning approaches such as the state-action-reward-state-action (SARSA) shall be considered in order to learn and further optimize the selection of TDD radio patterns. ...
The fifth generation (5G) radio access technology is designed to support highly delaysensitive applications, i.e., ultra-reliable and low-latency communications (URLLC). For dynamic time division duplex (TDD) systems, the real-time optimization of the radio pattern selection becomes of a vital significance in achieving decent URLLC outage latency. In this study, a dual reinforcement machine learning (RML) approach is developed for online pattern optimization in 5G new radio TDD deployments. The proposed solution seeks to minimizing the maximum URLLC tail latency, i.e., min-max problem, by introducing nested RML instances. The directional and real-time traffic statistics are monitored and given to the primary RML layer to estimate the sufficient number of downlink (DL) and uplink (UL) symbols across the upcoming radio pattern. The secondary RML sub-networks determine the DL and UL symbol structure which best minimizes the URLLC outage latency. The proposed solution is evaluated by extensive and highly-detailed system level simulations, where our results demonstrate a considerable URLLC outage latency improvement with the proposed scheme, compared to the state-of-the-art dynamic-TDD proposals.
... Various URLLC use cases require one-way radio latency of one or several milliseconds with an outage probability below 10 −5 [2]. As most of the 5G URLLC deployments are envisioned over the 3.5 GHz band, the time division duplexing (TDD) becomes a vital candidate transmission mode due to its frame adaptation, in order to dynamically match the sporadic URLLC capacity in both downlink (DL) and uplink (UL) directions [3]. ...
... With the 5G new radio (NR), the agile frame structure with variable transmission time interval (TTI) duration is introduced [3,4]. Thus, 5G-NR TDD offers more adaptation flexibility with much faster link-direction update periodicity, that is slot-dependent instead of being frame-based, i.e., ≤ 1 ms. ...
The fifth generation (5G) mobile technology features the ultra-reliable and low-latency communications (URLLC) as a major service class. URLLC applications demand a tight radio latency with extreme link reliability. In 5G dynamic time division duplexing (TDD) systems, URLLC requirements become further challenging to achieve due to the severe and fast-varying cross link interference (CLI) and the switching time of the radio frame configurations (RFCs). In this work, we propose a quasi-dynamic inter-cell frame coordination algorithm using hybrid frame design and a cyclic-offset-based RFC code-book. The proposed solution adaptively updates the RFCs in time such that both the average CLI and the user-centric radio latency are minimized. Compared to state-of-the-art dynamic TDD studies, the proposed scheme shows a significant improvement in the URLLC outage latency, i.e., 92% reduction gain, while boosting the cell-edge capacity by 189% and with a greatly reduced coordination overhead space, limited to B-bit.
... To enhance the system performance at the cell edge, a solution termed as "virtual cells" [15], allows users with overlapping coverage to utilize sub-frames from neighbor eNBs facilitating customized TDD frames that match best application specific UL/DL demands. The notion of efficient user multiplexing with highly diverse service requirements via a flexible TDD frame structure is elaborated in [16] focusing on different transmission time intervals considering also the radio conditions. ...
... In this context, is defined as a binary variable, which is 1 only if the link is enclosed in Ω i sub-graph. Finally, (16) shows that the summation of all should be equal to 1. ...
... By doing this, no inter-operator (i.e., inter-frequency) CLI occur, and also intra-carrier co-channel CLI is avoided. The disadvantage of applying such static DL-heavy TDD radio frames configurations is reduced UL coverage due to the sparse availability of only one time slot out of every five slots for UL transmission [9], [10]. ...
This article presents sub-band full duplex (SBFD) as a duplexing scheme to improve the uplink (UL) throughput in 5G–Advanced networks, as an alternative to traditional time-division duplexing (TDD). SBFD provides opportunities to transmit and receive simultaneously on non-overlapping frequency resources. To accomplish this, SBFD time slots include both UL and downlink (DL) transmission. This leads to UL transmission being more expanded in the time domain rather than the frequency domain, which allows to increase in the amount of UL transmission opportunity, as compared to TDD where the majority of time slots are used for DL. Concurrent UL and DL transmission create different types of interference, which makes cancellation approaches essential for appropriate performance. The SBFD interference types, including self-interference as the main challenge of SBFD deployment, are outlined and corresponding analytical models are proposed to provide a realistic evaluation of SBFD performance. System-level simulations with different load conditions in a high-power urban macro environment are used to evaluate the SBFD performance in comparison with TDD as the baseline. The results indicate a four times increase in the UL throughput for cell-edge users as well as 32% and 6% increase in average UL throughput, at low and medium loads, respectively. Furthermore, simulation results determine that at least 149 dB of self-interference mitigation is required for acceptable performance in SBFD. Results also show that SBFD benefits are limited by inter-site gNB-to-gNB interference.
... The indoor factory automation (InF) [4,5] use cases are emerging where the 5G-NR cellular communications are envisioned to replace the Ethernet-based interconnections. The early 5G commercial roll-outs are expected over the unpaired spectrum due to the available large free bandwidth [6,7]. Therefore, the time division duplexing (TDD) is vital for the 5G success. ...
The fifth generation (5G) new radio supports a diversity of network deployments. The industrial factory (InF) wireless automation use cases are emerging and drawing an increasing attention of the 5G new radio standardization groups. Therefore, in this paper, we propose a service-aware time division duplexing (TDD) frame selection framework for multi-traffic deployments. We evaluate the performance of the InF network deployments with the state-of-the-art 3GPP modeling assumptions. In particular, we consider the dynamic TDD mode along with optimized uplink power control settings. Multi-traffic coexistence scenarios are also incorporated such that quality of service (QoS) aware dynamic user scheduling and TDD link selection are introduced. Extensive system level simulations are performed in order to evaluate the performance of the proposed solutions, where the proposed QoS-aware scheme shows 68% URLLC outage latency reduction compared to the QoS-unaware solutions. Finally, the paper offers insightful conclusions and design recommendations on the TDD radio frame selection, uplink power control settings and the best QoS-coexistence practices, in order to achieve a decent URLLC outage latency performance in the state-of-the-art InF deployments.
... Furthermore, the global regulatory bodies have envisioned early 5G deployments over the 3.5 GHz spectrum due to its abundant available unpaired bands. Accordingly, dynamic time division duplexing (TDD) has become of a great significance [3]. With dynamic TDD, base-stations (BSs) independently and dynamically in time select their respective link directions based on individual objective functions, leading to an improved transmission adaptation to the sporadic traffic arrivals. ...
Dynamic time division duplexing (TDD) is envisioned as a vital transmission technology of the 5G new radio, due to its reciprocal propagation characteristics. However, the potential cross-link interference (CLI) imposes a fundamental limitation against the feasibility of the ultra-reliable and low latency communications (URLLC) in dynamic-TDD systems. In this work, we propose a near-optimal and complexity-efficient CLI suppression scheme using orthogonal spatial projection, while the signaling overhead is limited to B-bit, over the back-haul links. Compared to the state-of-the-art dynamic-TDD studies, proposed solution offers a significant improvement of the URLLC outage latency, e.g., -199% reduction, while boosting the achievable capacity per the URLLC packet by +156%.
... Accordingly, the link direction switching periodicity can be slot-based, i.e., ≤ 1 ms, instead of being RFCbased. Thus, 5G-NR TDD systems significantly improve the spectrum utilization and the ergodic capacity for services with fast-varying and asymmetric DL and uplink UL traffic [5]. However, the coexistence of different link directions over same frequency resources in adjacent cells results in potential cross link interference (CLI), i.e., user-to-user (UE-UE), and basestation to base-station (BS-BS) interference [6]. ...
The fifth generation (5G) of the wireless communication networks supports wide diversity of service classes, leading to a highly dynamic uplink (UL) and downlink (DL) traffic asymmetry. Thus, dynamic time division duplexing (TDD) technology has become of a significant importance, due to its radio frame flexibility. However, fully dynamic TDD systems suffer from potentially severe inter-cell cross link interference (CLI). In this paper, we propose a novel inter-cell radio frame coordination (RFC) scheme based on sliding codebook for fully dynamic TDD 5G networks. Proposed coordination scheme simultaneously addresses two optimization objectives of minimizing the average CLI while reliably maximizing the achievable DL/UL capacity, by virtually extending the RFC degrees of freedom through a sliding phase-offset RFC codebook design. Compared to the state-of-the-art TDD studies, the proposed scheme shows significantly improved ergodic capacity, i.e., at least 40% gain under both the TCP and UDP protocols, and with much less signaling overhead, limited to B-bit. The paper offers valuable insights about how to most efficiently pre-mitigate potential CLI in Macro TDD systems.
... Such an approach, named virtual cells, facilitates customized TDD frames that best matches application specific UL/DL demands. A similar concept concentrating on a flexible TDD frame structure that allows an efficient multiplexing of users with highly diverse service requirements is elaborated in [25]. The proposed solution schedules users with different transmission time intervals to best match their service requirements considering the radio conditions, allowing an optimization on a per-link basis. ...
This paper introduces the concept of network slicing in the emerging Time Division Duplex (TDD) 5G networks, considering asymmetric traffic conditions. The proposed approach relies on a flexible—soft spectrum—slicing considering the entire spectrum band by allocating service oriented network slices that can independently adjust the Uplink/Downlink (UL/DL) ratio based on forecasted traffic and user mobility information. Two novel resource re-configuration mechanisms are introduced: i) a joint slice resource allocation and TDD frame selection and ii) a slice allocation with independent distributed UL/DL ratio adjustment. An analytical model formulating the slice resource allocation scheme as a weighted optimization problem is presented whereas an exhaustive simulation campaign is carried out to validate our proposals against state-of-the art approaches.
... Such different applications and diverse requirements make the uplink (UL)/downlink (DL) traffic asymmetry more and more serious. 9 So time division duplex (TDD) systems play an important role in 5G networks due to its capability to support asymmetric services by adjusting the fraction of time dedicated to UL and DL transmissions as well as reduce signaling and radio frequency front-end complexity by exploiting channel reciprocity. 10,11 In addition, D2D communication and TDD system have the same characteristics that each transmitter-receiver pair has the freedom to schedule its time and frequency resources, which not only can minimize the interference between simultaneously transmitting radio entities but also support diverse services. ...
The explosive demands for mobile broadband service bring a major challenge to 5G wireless networks. Device-to-device communication, adopting side links for user-direct communication, is regarded as a main technical source for offloading large volume of mobile traffic from cellular base station. This article investigates the joint power and subcarrier allocation scheme for device-to-device communication in 5G time division duplex systems. In time division duplex system, instead of utilizing an exclusive portion of the precious cellular spectrum, device-to-device pairs reuse the subcarriers occupied by cellular users, thus producing harmful interference to cellular users in both uplink and downlink communication, and strongly limiting the spectrum efficiency of the system. To this end, we focus on the maximization of device-to-device throughput while guaranteeing both uplink and downlink channel quality of service of cellular users as well as device-to-device pairs. The problem is formulated as a mixed integer non-linear programming (MINLP) problem. To make it tractable, we separate the original MINLP problem into two sub problems: power allocation and sub-carrier reusing. The former is to develop optimal power allocation for each device-to-device pair and each cellular user, with the constraints of maximum power and quality of service. It is solved by geometric programming technique in convex optimization method. The latter is derived as a one-to-many matching problem for scheduling multiple subcarriers occupied by cellulars to device-to-device pairs. It is solved by Hungarian method. Simulation results show that the proposed scheme significantly improves system capacity of the device-to-device underlay network, with quality of service of both device-to-device users and cellular users guaranteed.
With the proliferation of mobile terminals, the continuous upgrading of services, 4G LTE networks are showing signs of weakness. To enhance the capacity of wireless networks, millimeter waves are introduced to drive the evolution of networks towards multi-band 5G heterogeneous networks. The distinct propagation characteristics of mmWaves, microwaves, as well as the vastly different hardware configurations of heterogeneous base stations, make traditional access strategies no longer effective. Therefore, to narrowing the gap between theory, practice, we investigate the access strategy in multi-band 5G heterogeneous networks, taking into account the characteristics of mobile users, asynchronous switching between uplink, downlink of pico base stations, asymmetric service requirements, user communication continuity. We formulate the problem as integer nonlinear programming, prove its intractability. Thereby, we decouple it into three subproblems: user association, switch point selection, subchannel allocation, design an algorithm based on optimal matching, spectral clustering to solve it efficiently. The simulation results show that the proposed algorithm outperforms the comparison methods in terms of overall data rate, effective data rate, number of satisfied users.
METIS is the EU flagship 5G project with the objective of laying the foundation for 5G systems and building consensus prior to standardization. The METIS overall approach toward 5G builds on the evolution of existing technologies complemented by new radio concepts that are designed to meet the new and challenging requirements of use cases today??s radio access networks cannot support. The integration of these new radio concepts, such as massive MIMO, ultra dense networks, moving networks, and device-to-device, ultra reliable, and massive machine communications, will allow 5G to support the expected increase in mobile data volume while broadening the range of application domains that mobile communications can support beyond 2020. In this article, we describe the scenarios identified for the purpose of driving the 5G research direction. Furthermore, we give initial directions for the technology components (e.g., link level components, multinode/multiantenna, multi-RAT, and multi-layer networks and spectrum handling) that will allow the fulfillment of the requirements of the identified 5G scenarios.
From the editors of the highly successful LTE for UMTS: Evolution to LTE-Advanced, this new book examines the main technical enhancements brought by LTE-Advanced, thoroughly covering 3GPP Release 10 specifications and the main items in Release 11. Using illustrations, graphs and real-life scenarios, the authors systematically lead readers through this cutting-edge topic to provide an outlook on existing technologies as well as possible future developments. The book is structured to follow the main technical areas that will be enhanced by the LTE-Advanced specifications. The main topics covered include: Carrier Aggregation; Multiantenna MIMO Transmission, Heterogeneous Networks; Coordinated Multipoint Transmission (CoMP); Relay nodes; 3GPP milestones and IMT-Advanced process in ITU-R; and LTE-Advanced Performance Evaluation. Key features: Leading author and editor team bring their expertise to the next generation of LTE technology. Includes tables, figures and plots illustrating the concepts or simulation results, to aid understanding of the topic, and enabling readers to be ahead of the technological advances.
We address the fundamental tradeoffs among latency, reliability and throughput in a cellular network. The most important elements influencing the KPIs in a 4G network are identified, and the inter-relationships among them is discussed. We use the effective bandwidth and the effective capacity theory as analytical framework for calculating the maximum achievable rate for a given latency and reliability constraint. The analysis is conducted in a simplified LTE network, providing baseline - yet powerful - insight of the main tradeoffs. Guidelines to extend the theory to more complex systems are also presented, including a semi-analytical approach for cases with intractable channel and traffic models. We also discuss the use of system-level simulations to explore the limits of LTE networks. Based on our findings, we give some recommendations for the imminent 5G technology design phase, in which latency and reliability will be two of the principal KPIs.
The rise of machine-to-machine communications has rekindled interest in random access protocols as a support for a massive number of uncoordinatedly transmitting devices. The legacy ALOHA approach is developed under a collision model, where slots containing collided packets are considered as waste. However, if the common receiver (e.g. base station) is able to store the collision slots and use them in a transmission recovery process based on successive interference cancellation, the design space for access protocols is radically expanded. We present the paradigm of coded random access, in which the structure of the access protocol can be mapped to a structure of an erasure-correcting code defined on a graph. This opens the possibility to use coding theory and tools for designing efficient random access protocols, offering markedly better performance than ALOHA. Several instances of coded random access protocols are described, as well as a case study on how to upgrade a legacy ALOHA system using the ideas of coded random access.
5G, the mobile communication technology for beyond 2020, will provide access to information and the sharing of data anywhere and anytime for anyone and anything. This paper describes the current status of the processes moving toward 5G, or "IMT for 2020 and beyond," in ITU-R. We also provide a view of 5G opportunities, challenges, requirements and technical solutions.
The 5th generation (5G) of mobile radio access technologies is expected to become available for commercial launch around 2020. In this paper, we present our envisioned 5G system design optimized for small cell deployment taking a clean slate approach, i.e. removing most compatibility constraints with the previous generations of mobile radio access technologies. This paper mainly covers the physical layer aspects of the 5G concept design.
This article explores network densification as the key mechanism for wireless evolution over the next decade. Network densification includes densification over space (e.g, dense deployment of small cells) and frequency (utilizing larger portions of radio spectrum in diverse bands). Large-scale cost-effective spatial densification is facilitated by self-organizing networks and intercell interference management. Full benefits of network densification can be realized only if it is complemented by backhaul densification, and advanced receivers capable of interference cancellation.
As the deployment and commercial operation of 4G systems are speeding up, technologists worldwide have begun searching for next generation wireless solutions to meet the anticipated demands in the 2020 era given the explosive growth of mobile Internet. This article presents our perspective of the 5G technologies with two major themes: green and soft. By rethinking the Shannon theorem and traditional cell-centric design, network capacity can be significantly increased while network power consumption is decreased. The feasibility of the combination of green and soft is investigated through five interconnected areas of research: energy efficiency and spectral efficiency co-design, no more cells, rethinking signaling/control, invisible base stations, and full duplex radio.
To facilitate the efficient support of quality of service (QoS) in next-generation wireless networks, it is essential to model a wireless channel in terms of connection-level QoS metrics such as data rate, delay, and delay-violation probability. However, the existing wireless channel models, i.e., physical-layer channel models, do not explicitly characterize a wireless channel in terms of these QoS metrics. In this paper, we propose and develop a link-layer channel model termed effective capacity (EC). In this approach, we first model a wireless link by two EC functions, namely, the probability of nonempty buffer, and the QoS exponent of a connection. Then, we propose a simple and efficient algorithm to estimate these EC functions. The physical-layer analogs of these two link-layer EC functions are the marginal distribution (e.g., Rayleigh-Ricean distribution) and the Doppler spectrum, respectively. The key advantages of the EC link-layer modeling and estimation are: 1) ease of translation into QoS guarantees, such as delay bounds; 2) simplicity of implementation; and 3) accuracy, and hence, efficiency in admission control and resource reservation. We illustrate the advantage of our approach with a set of simulation experiments, which show that the actual QoS metric is closely approximated by the QoS metric predicted by the EC link-layer model, under a wide range of conditions.
A Flexible Frame Structure for 5G Wide Area
- K I Pedersen