Henning Wiemann

The LTE link-layer design

The LTE radio interface for 3GPP Release 8 was specified recently. This article describes the LTE link-layer protocols, which abstract the physical layer and adapt its characteristics to match the requirements of higher layer protocols. The LTE link-layer protocols are optimized for low delay and low overhead and are simpler than their counterparts in UTRAN. The state of- the-art LTE protocol design is the result of a careful crosslayer approach where the protocols interact with each other efficiently. This article provides a thorough overview of this protocol stack, including the sub-layers and corresponding interactions in between them, in a manner that is more intuitive than in the respective 3GPP specifications.

Internet Access Performance in LTE TDD

The Time Division Duplex (TDD) uplink-downlink configuration of the 3GPP Long Term Evolution (LTE) determines how the ten subframes in a radio frame are divided between the downlink and the uplink. The specified configurations cover a wide range of allocations from a downlink-heavy resource distribution ratio (9:1) to an uplink-heavy ratio (2:3). In this paper, we compare the performance of Internet access using the TCP protocol in different downlink-heavy asymmetries. We find that the performance depends on many factors such as the transferred file size, the control channel errors and the downlink/uplink traffic mix. When the file size is small, TDD can not fully utilize its potentially higher downlink capacity because of longer uplink access delays as well as shortage of uplink resources in the chosen configurations. With an increased file size, this effect fades away and TDD provides higher download bit rates than FDD. The realized increase in bit rate is however not as high as the calculated increase in available downlink resources.

ARQ Concept for the UMTS Long-Term Evolution

Work is ongoing in 3GPP to significantly extend the performance of UMTS in the work item long term evolution (LTE). LTE contains a new system architecture with fewer infrastructure nodes and it has been decided to terminate the ARQ functionality in the evolved node B. This paper describes the requirements that exists for an LTE ARQ concept and outlines a solution that fulfills these requirements in the new LTE architecture. The solution builds on two layered ARQ feedback mechanisms that provide sufficient reliability with a low resource cost for the feedback The paper contains thorough stepwise argumentation how we arrived at the proposed ARQ concept.

A generic link layer in a beyond 3G multi-radio access architecture

A major aspect of beyond 3G networks is the efficient integration of multiple radio access technologies in a common network. One advantage of this multi-radio access integration will be an increased radio resource efficiency, e.g., due to a larger trunking gain and reduced radio cost per link. One realization of the multi-radio access integration is based on a generic link layer, which provides generic data processing for a multitude of radio access technologies. The generic link layer enables fast and lossless access selection. The functional architecture of the generic link layer is discussed, including the separation of radio dependent and radio independent functions. Furthermore, the relationship of the generic link layer to (multi-) radio resource management functions and radio specific transmission functions is presented and an example of access selection is described. Finally, we present how the generic link layer is included into a beyond 3G network architecture.

Integration of multi-radio access in a beyond 3G network

A major aspect of Beyond 3G networks is the efficient integration of multiple radio access technologies in a common network. One advantage of this multi-radio access integration is the increase in radio resource efficiency, e.g. due to a larger trunking gain and reduced radio cost per link. This paper analyses and compares the different ways of how multi-radio access integration can be achieved. In particular, it investigates three multi-radio integration alternatives, two of them solving the problem at the network level and the third one on the link level. The comparison of the different approaches reveals that link level integration allows access path switching on a shorter time scale than network level integration. Another difference is where they allow the multi-radio resource management functions to take place, on network side or on user terminal side. In general, it is concluded that all schemes have certain advantages and disadvantages depending on the considered scenario. It is also highlighted, that these different integration schemes can be combined, i.e. some radio access technologies can be integrated on link level, while others can be integrated on network level.

Control Signaling Robustness in LTE

In LTE, the control signaling required for scheduling and HARQ on the MAC layer is partly protected by cyclic redundancy checks (CRC) but no ARQ, or other error recovery mechanisms, are used. Therefore, errors occur with a certain probability and may or may not be detected. Errors in HARQ feedback and scheduling grants could cause underutilization of resources, longer delays, redundant retransmissions, collisions, and HARQ failures. In this study, the frequency of these effects, and the influence of control channel quality, data channel block error rate (BLER), and ACK/NACK detection thresholds are investigated. It is shown that the effects are acceptable small when the control channel performance is within the 3GPP target requirements. Keywords-LTE, 3GPP, control, signaling, HARQ, error

Support of Multicast Services in 3GPP

ABSTRACT In line with the growing interest in efficient data distribution services to large mobile user groups, 3GPP is standardizing the introduction of support for multicast services into GSM and WCDMA networks. The mobile infrastructure needs to be enhanced in the wireless and in the wireline parts to support new signaling and payload transport procedures. Also mobility, charging and radio resource handling aspects have to be considered. Starting from group distribution services and their requirements, this paper motivates and describes the solutions defined and discussed within 3GPP, namely the introduction of new nodes, new bearers and new procedures to efficiently support multicast services.

Performance of shared and dedicated resources in WCDMA

For data transmission WCDMA offers dedicated transport channels (DCH) and common transport channels, i.e. random access channels (RACH) and forward access channels (FACH). Both types of transport channels have different characteristics in terms of transmission performance and radio resource usage. In this paper these characteristics are described and a simulation model for the performance evaluation is presented. The effect of some parameters influencing the performance and efficiency of the different transport channel types is discussed, e.g. channel configuration, traffic load and traffic characteristics. It is demonstrated that common transport channels provide better performance than dedicated channels for a low traffic load of bursty traffic. For low data volumes they are also more resource efficient. However for an increasing traffic load dedicated channels provide a better service quality and radio resource utilisation.

An Outlook on the Unlicensed Operation Aspects of NR

The standardization of 5G New Radio (NR) has started and addresses a wide range of use-cases. The 5G application demands include among others, very high data rates, support for huge number of low-power devices and mission critical communication. NR design supports operation in both traditional licensed frequency spectrum bands as well as unlicensed frequencies. In this paper, we present some of the design aspects and architectural details of NR to support spectrum sharing in the unlicensed spectrum. Moreover, we present system level simulation results showing the NR spectrum sharing capabilities while complying with the regulatory requirements.