5G RLC MAC transmission optimization

2013

2010

Hybrid automatic retransmission request (HARQ) is widely adopted in wireless communication systems to improve the link level and system level throughput. Adaptively selecting retransmission based on the received packet can further improve the system performance by reducing the retransmission overhead. To this end, this paper first introduces the concept of instantaneous packet information (IPI). Then, a new metric is proposed to evaluate the quality of received packets based on IPI. The most important feature of the IPI metric is its in-sensitivity to channel fading. Therefore, it can be used in practice, where channel varies significantly. Furthermore, this paper introduces an IPI-metric based HARQ (IPI-HARQ) featuring an on-demand adaptive retransmission. In IPI-HARQ, a receiver is able to evaluate the quality of a received packet and estimate the desired amount of retransmission when the packet has decoding errors. The retransmission adaption in IPI-HARQ includes two aspects: how many symbols and which part of the packet should be retransmitted. The difference between the current IPI and an target IPI is used to estimate how many bits to be retransmitted. The set of bits that can most efficiently increase IPI is selected to be retransmitted and identified by an indicator vector accompanying the NACK feedback. Clustering is used in IPI-HARQ to limit the feedback overhead. The benefit of IPI-HARQ scheme lies in the fine estimation of required retransmission amount and selection of bits with respect to the quality of current received packet. Simulation results show that the proposed IPI-HARQ scheme clearly outperforms conventional HARQ scheme in terms of throughput.

2013 IEEE 77th Vehicular Technology Conference (VTC Spring), 2013

This paper discusses retransmission approaches to improve the throughput performance of Hybrid-ARQ (HARQ) schemes in a point-to-point single user 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) uplink system. One goal of communication systems is to achieve a reliable transmission with a throughput performance as close as possible to channel capacity. For that, reducing the channel utilization will improve the throughput performance. Instead of sending two retransmission packets for two HARQ processes of one users, a previously published HARQ scheme uses the XOR combining of these packets to get only one retransmission packet with the same size. Similar to this idea, a new varied scheme performs XOR combining of parts of one conventional full retransmission to generate a smaller retransmission packet. Both approaches will reduce the channel utilization. They will be compared with a HARQ system in LTE uplink using a full size retransmission and a half size retransmission. The main focus of this work is the throughput performance evaluation of these schemes in an LTE link-level simulator.

Cooperative retransmission schemes can significantly improve transmission reliability and performance over high loss and time-varying links. However, analytically comparing performance between retransmission strategies is challenging and generally requires simplistic assumptions. This paper presents a general model for the performance of distributed, slot-based contention algorithms for opportunistic decode and forward retransmission algorithms. The model is independent of specific modulation or coding schemes and may be adapted to suit state-based transmission probability models. The model is validated through QualNet simulations.

Sensors, 2019

5G and beyond networks are being designed to support the future digital society, where numerous sensors, machinery, vehicles and humans will be connected in the so-called Internet of Things (IoT). The support of time-critical verticals such as Industry 4.0 will be especially challenging, due to the demanding communication requirements of manufacturing applications such as motion control, control-to-control applications and factory automation, which will require the exchange of critical sensing and control information among the factory nodes. To this aim, important changes have been introduced in 5G for Ultra-Reliable and Low-Latency Communications (URLLC). One of these changes is the introduction of grant-free scheduling for uplink transmissions. The objective is to reduce latency by eliminating the need for User Equipments (UEs-sensors, devices or machinery) to request resources and wait until the network grants them. Grant-free scheduling can reserve radio resources for dedicated UEs or for groups of UEs. The latter option is particularly relevant to support applications with aperiodic or sporadic traffic and deterministic low latency requirements. In this case, when a UE has information to transmit, it must contend for the usage of radio resources. This can lead to potential packet collisions between UEs. 5G introduces the possibility of transmitting K replicas of the same packet to combat such collisions. Previous studies have shown that grant-free scheduling with K replicas and shared resources increases the packet delivery. However, relying upon the transmission of K replicas to achieve a target reliability level can result in additional delays, and it is yet unknown whether grant-free scheduling with K replicas and shared resources can guarantee very high reliability levels with very low latency. This is the objective of this study, that identifies the reliability and latency levels that can be achieved by 5G grant-free scheduling with K replicas and shared resources in the presence of aperiodic traffic, and as a function of the number of UEs, reserved radio resources and replicas K. The study demonstrates that current Fifth Generation New Radio (5G NR) grant-free scheduling has limitations to sustain stringent reliability and latency levels for aperiodic traffic.

We analyze the throughput and delay performance of the radio link control/media access control (RLC/MAC) protocol layers in General Packet Radio Service (GPRS) networks. Several time-slotted uplink radio frequency channels are shared by the mobiles on a request reservation based multiple access scheme. Using the theory of Markov chains, we derive expressions for the uplink throughput and delay performance of the GPRS-MAC protocol. Further, we evaluate the performance of the RLC (Acknowledged mode) layer using block level retransmission (as defined in the current GPRS) and compare it with that of using slot level retransmission (which is in the proposal stage). We show that slot level retransmission at the RLC layer performs better than block level retransmission, particularly when the channel error rate is high. I. INTRODUCTION General Packet Radio Service (GPRS) is a packet mode wireless system that has been standardized to operate on GSM infrastructure, by introducing new packet s...

IEEE/ACM Transactions on Networking

Emerging 5G systems will need to efficiently support both enhanced mobile broadband traffic (eMBB) and ultra-lowlatency communications (URLLC) traffic. In these systems, time is divided into slots which are further subdivided into minislots. From a scheduling perspective, eMBB resource allocations occur at slot boundaries, whereas to reduce latency URLLC traffic is pre-emptively overlapped at the minislot timescale, resulting in selective superposition/puncturing of eMBB allocations. This approach enables minimal URLLC latency at a potential rate loss to eMBB traffic. We study joint eMBB and URLLC schedulers for such systems, with the dual objectives of maximizing utility for eMBB traffic while immediately satisfying URLLC demands. For a linear rate loss model (loss to eMBB is linear in the amount of URLLC superposition/puncturing), we derive an optimal joint scheduler. Somewhat counter-intuitively, our results show that our dual objectives can be met by an iterative gradient scheduler for eMBB traffic that anticipates the expected loss from URLLC traffic, along with an URLLC demand scheduler that is oblivious to eMBB channel states, utility functions and allocation decisions of the eMBB scheduler. Next we consider a more general class of (convex/threshold) loss models and study optimal online joint eMBB/URLLC schedulers within the broad class of channel state dependent but minislot-homogeneous policies. A key observation is that unlike the linear rate loss model, for the convex and threshold rate loss models, optimal eMBB and URLLC scheduling decisions do not de-couple and joint optimization is necessary to satisfy the dual objectives. We validate the characteristics and benefits of our schedulers via simulation. Index Terms-wireless scheduling, URLLC traffic, 5G systems 2 The sharing granularity among various eMBB users is at the level of Resource Blocks (RB), which are small time-frequency rectangles within a slot. In LTE today, these are (1 msec × 180 KHz), and could be smaller for 5G systems. 3 In 3GPP, the formal term for a 'slot' is eMBB TTI, and a 'minislot' is a URLLC TTI, where TTI expands to Transmit Time Interval.

IEEE Transactions on Vehicular Technology, 2004

In this paper, we analyze the performance of various layers of the general packet radio service (GPRS) protocol stack, including radio link control/medium-access control (RLC/MAC) layer and logical link-control (LLC) layer on the uplink. In the GPRS MAC protocol, several time-slotted uplink radio-frequency channels are shared by the mobiles on a request-reservation-based multiple-access scheme. Using the theory of Markov chains, we derive expressions for the average throughput and delay performance of the GPRS MAC protocol. We evaluate the performance of the RLC layer (in acknowledged mode) using block-level retransmission (BLR), as defined in the current GPRS standard, and compare it with that of using slot-level retransmission (SLR). We show that SLR at the RLC layer performs significantly better than the BLR, particularly when the channel-error rates are moderate to high. We further investigate the choice of parameters (e.g., number of retransmission attempts) for the automatic repeat request schemes at the RLC and LLC layers. Our results show that it is more beneficial to do error recovery by allowing more retransmission attempts at the RLC layer than at the LLC layer. We also evaluate the performance of transmission-control protocol with BLR and SLR at the RLC layer.

2018

In this paper, we use a New Radio (NR) simulator, based on ns-3, to assess the impact of 5G NR numerologies on the end-to-end (E2E) latencies in a realistic and complex scenario, including TCP and UDP flows. As expected, we found that TCP goodput increases with the numerology, since a larger numerology allows reducing the round-trip-time. However, although counter-intuitive, simulation results exhibit that the E2E latency of uplink (UL) UDP flows may not be reduced with the numerology. In fact, it depends on two key factors and their relationship: the processing delays (fixed or numerologydependent) and the inter-packet arrival time, which depends on the UDP flow rate and the packet size. We demonstrate how, in some cases, the latency is worsened by an increasing signaling exchange that grows with the numerology. In particular, this is due to a handshake mechanism in UL (scheduling request and UL grant) that is performed each time a data packet encounters empty RLC buffers. For some combination of flow rate, packet size, and processing delays that are not numerologydependent, increasing the numerology may not reduce the E2E delay. Therefore, we conclude that the selection of the numerology in an NR system should be carefully made by taking into account the traffic patterns and the processing delays.

Proceedings of the International Conference on Signal Processing and Multimedia Applications, 2008

Mobile telecommunication new services are based on data networks specially Internet. These services include http, telnet, ftp, Simple Mail Transfer Protocol (SMTP), etc. Besides we recognize a mobile network as a multiuser network. Transmission Control Protocol/Internet Protocol (TCP/IP) which is sensitive to link congestion in wireline data links is also used in wireless networks. In order to improve the system performance, the TCP layer uses flow control and congestion control. Besides, Radio Link Control (RLC) has been introduced to compensate the deficiency of TCP layer in wireless environment. MAC and RLC have important roles in quality of service improvement of UMTS. In this paper we verify TCP over Automatic Repeat reQuest (ARQ) error control mechanism and finally quality of service improvement results from it in the fading channels.