Magnus Lundevall

Evolving 3G mobile systems: broadband and broadcast services in WCDMA

The third-generation WCDMA standard has been enhanced to offer significantly increased performance for packet data and broadcast services through the introduction of high-speed downlink packet access (HSDPA), enhanced uplink, and multimedia broadcast multicast services (MBMS). This article provides an overview of the key technologies used, the reasons behind their selection, and their integration into WCDMA. Performance results are also included to exemplify the performance possible in an evolved WCDMA network.

Delivery of Broadcast Services in 3G Networks

TV is regarded as a key service for mobile devices. In the past, Mobile TV was often associated with broadcast transmission. However, unicast technology is sufficient in many cases, especially since mobile users prefer to access content on-demand, rather than following a fixed schedule. In this paper we will focus on 3G mobile networks, which have been primarily optimized for unicast services. Based on a traffic model we will discuss the capacity limits of 3G networks for unicast distribution of Mobile TV. From the results it can be concluded that the capacity is sufficient for many scenarios. In order to address scenarios in which broadcast is a more appropriate technology, 3GPP has defined a broadcast extension, called Multimedia Broadcast Multicast Service (MBMS). MBMS introduces shared radio broadcast bearers and has thus the capabilities of a real broadcasting technology. We will give a short overview about MBMS including a discussion on MBMS capacity. Since MBMS is primarily a new transport technology, additional application and service layer technologies are required, like electronic service guide and service protection. These mechanisms are standardized by the Open Mobile Alliance (OMA) and are favorably combined with MBMS or 3G unicast distribution in order to create complete end-to-end solutions. In order to optimize a system for delivery of broadcast services over 3G networks, the advantages of broadcast and unicast should be combined. We argue that hybrid unicast-broadcast delivery offers the best system resource usage and also the best user experience, and is thus favorable not only for broadcast delivery in 3G networks, but actually also for non-cellular broadcast systems like DVB-H or DMB

The 3G Long-Term Evolution - Radio Interface Concepts and Performance Evaluation

3GPP is in the process of defining the long-term evolution (LTE) for 3G radio access, sometimes referred to as super-3G, in order to maintain the future competitiveness of 3G technology. The main targets for this evolution concern increased data rates, improved spectrum efficiency, improved coverage, and reduced latency. Taken together these result in significantly improved service provisioning and reduced operator costs in a variety of traffic scenarios. This paper gives an overview of the basic radio interface principles for the 3G long-term evolution concept, including OFDM and advanced antenna solution, and presents performance results indicating to what extent the requirements/targets can be met. It is seen that the targets on three-fold user throughput and spectrum efficiency compared to basic WCDMA can be fulfilled with the current working assumptions. More advanced WCDMA systems, employing e.g. advanced antenna solutions may however achieve similar performance gains. Enhancements for reduced latency and IP optimized architectures and protocols are further applicable to both LTE and WCDMA

Downtilted Base Station Antennas - A Simulation Model Proposal and Impact on HSPA and LTE Performance

This paper proposes a low-complexity model for vertical antenna radiation patterns, e.g. for inclusion in system- level simulations. They can be seen as extensions to the horizontal radiation pattern model used in 3GPP simulation scenarios. The model is verified against and compared to predicted and measured data from real networks. The impact on system-level performance is also investigated. It is seen that using the proposed model, simulated geometry distributions and soft handover statistics closely matching those of real networks may be achieved. The analysis also concludes that many real networks have better cell isolation than what is modeled by the 3GPP antenna model. As a consequence, the horizontal radiation pattern model significantly under-estimates the system level performance in such networks. Furthermore, the proposed model is used to assess the LTE and HSPA system-level performance for realistic scenarios.

Streaming applications over HSDPA in mixed service scenarios

High-speed downlink packet access (HSDPA) is included in release 5 of the WCDMA specifications to increase downlink capacity and bitrates. This paper considers performance aspects of streaming applications over HSDPA in a mixed streaming and best-effort service scenario. Different scheduling algorithms are evaluated with the aim of providing sufficient quality-of-service for streaming. The simulation results show that reasonable streaming performance can be achieved without service differentiation if a somewhat fair scheduler is used, and that a streaming-aware scheduler further can protect streaming quality-of-service in high load conditions.

Using dedicated in-building systems to improve HSDPA indoor coverage and capacity

In WCDMA systems, in particular with the introduction of high-speed multimedia services, the demand for good indoor coverage will become important. Overlaying macro cells can provide a sufficient level of general indoor coverage for most of the cases. However, in order to be able to provide WCDMA indoor coverage and capacity within traffic hot spots, such as airports, shopping malls and large office buildings, the deployment of dedicated in-building systems may be required. In this paper, the gain of deploying dedicated in-building systems in terms of HSDPA indoor coverage and capacity is studied; first, with a simple analytical reasoning and after that, with advanced system simulations. The results show that the HSDPA performance can be improved considerably within the indoor hotspot area by deploying a dedicated in-building system. The results also demonstrate how a dedicated in-building system can off-load the overlaying macro cell, and as a result of that, improve the grade of service considerably for the co-existing non-HSDPA users.

The LTE radio interface - key characteristics and performance

Mobile broadband usage is taking off, demanding improved services and increased capacity of mobile networks. To meet these requirements, 3GPP has defined LTE (the 3GPP Long Term Evolution). This paper presents some key characteristics of the LTE radio interface, including physical layer and radio resource management functions, and evaluates their impact on system performance. As compared to a reference system with more basic characteristics, represented by mobile WiMax, results point to a combined gain in spectrum efficiency of 60% in downlink and 100% in uplink. Cell-edge bitrate gains are about 100% in both downlink and uplink. A closer analysis of the individual system characteristics indicates that these performance differences are due to rather uniform contributions from a set of distinctive features.

Performance of link admission control in a WCDMA system with HS-DSCH and mixed services

Link admission control is one of the fundamental radio resource management functions in radio networks, determining which users should have access to the radio channels. The introduction of the shared high-speed channel, HS-DSCH, in release 5 of WCDMA poses new requirements on such an algorithm. Different kinds of users on dedicated as well as the shared high-speed channel must be handled so that radio resources are allocated properly among different kinds of services, and so that overload situations are avoided. A simple threshold algorithm is evaluated here in a mixed services scenario where speech users are allocated to dedicated channels and data users to the HS-DSCH. The threshold applies to the total power used by the non-HS channels in each cell. By selecting the threshold appropriately, resources can be shared efficiently between the two types of services while avoiding overload situations.

Multi-User OFDM System Performance Subject to Control Channel Reliability in a Multi-Cell Environment

Dynamic mechanisms such as adaptive modulation and coding or scheduling have been shown to significantly improve the performance of cellular systems. This gain comes at the cost of additional signaling overhead that needs to be delivered from the transmitter to the receiver. In this paper, we explore a resource- constraint control channel that delivers resource assignments in a multi-cell environment with a frequency reuse of 1. We show that despite the presence of co-channel interference signaling data can reliably be delivered. We also present means to increase the channels reliability by dynamic power control.

A novel approach to WCDMA radio network dimensioning

A novel dimensioning approach for WCDMA radio networks is suggested. It is derived to handle real-time services on dedicated channels, but can easily be augmented to include best-effort traffic on the high-speed downlink shared channel. The method facilitates calculation of transmit power distributions based on detailed link gain statistics, enabling fast, yet accurate, estimation of, e.g., network design and cost. It is shown that good agreement with detailed dynamic simulations can be achieved.