Kimmo Hiltunen

WCDMA downlink capacity estimation

A simple estimation for the WCDMA downlink capacity is presented. A general approximation is derived from the basic CDMA theory, and is then adapted to the scenario in question with the help of results from a number of reference system simulations. Comparison with the simulations shows that the obtained approximation is valid for a variety of system scenarios and services. Furthermore, it holds also in case of multiple simultaneous services. However, unless the effect of the receiver noise is taken into account, the applicability area of the approximation seems to be limited only to quite small cells.

Comparison of Different Network Densification Alternatives from the LTE Downlink Performance Point of View

This paper presents a novel comparison of different network densification alternatives from the LTE downlink point of view. The comparison is performed for the same environment considering, among other things, an advanced three-dimensional modeling of propagation and user distribution within the traffic hotspots. The obtained results indicate that various types of heterogeneous network deployments are realistic alternatives to the traditional way of deploying new macro sites. The downside of heterogeneous deployments is that the required number of new sites becomes considerably larger, which can cause problems from the backhaul availability and power supply point of view. Hence, based on these initial results, the heterogeneous deployments seem to be the most feasible for scenarios with a limited availability of new macro sites.

CPICH power settings in irregular WCDMA macro cellular networks

In a WCDMA system, mobiles select cells based on received common pilot channel (CPICH) signal quality from the different base stations. The cell size therefore depends on radio propagation properties and transmitted CPICH power. For efficient resource utilization, it is important that the traffic is shared fairly evenly over the base stations. This is specifically challenging in irregular networks with inhomogeneous site locations and traffic distribution. This paper discusses methods for automated CPICH power planning, based on differently detailed traffic density information and predicted radio propagation. Simulations using data from a realistically planned network indicate that the tuning results in a more evenly utilized base station power. This in turn improves the overall capacity. It is furthermore fairly robust with respect to traffic density deviations from the true traffic density.

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.

Using RF Repeaters to Improve WCDMA HSDPA Coverage and Capacity Inside Buildings

The role of indoor coverage will be very important in WCDMA networks, both due to customer expectations and the introduction of high speed packet data services. General outdoor-to-indoor coverage is and will be the most common solution, but macro cells may not always be able to deliver adequate indoor coverage and capacity, suggesting the need for dedicated indoor solutions, such as RF repeaters. RF repeaters are typically deployed to extend the coverage of existing (macro) cells. They are characterized by low cost, ease of installation and low power consumption. The simulation results shown in this paper clearly indicate how the repeater deployment improves the HSDPA coverage throughout the building. The results also demonstrate how the repeater deployment off-loads the donor cell, resulting in increased cell capacity. However, this paper also discusses the trade-off between the repeater gain and the reduced uplink coverage and capacity within the donor cell, which eventually can limit the maximum achievable HSDPA performance

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.

Utilizing eNodeB sleep mode to improve the energy-efficiency of dense LTE networks

This study evaluates the performance of a scheme, where idle capacity cells are put into sleep mode to save energy. The evaluation is performed for a few different LTE network densification alternatives, and the network performance is compared from the daily energy consumption point of view. The obtained results indicate that the introduction of the sleep mode scheme results in 42-62% lower daily energy consumption, depending on the network densification alternative. Furthermore, the evaluated heterogeneous network deployments are found to be more energy-efficient than the densified macro deployment, which is a clear difference compared to scenarios without any energy saving schemes. If the sleep mode deployment is compared to a scheme, where underutilized capacity cells are completely switched off, the gain becomes equal to 26-43%. The results demonstrate also that the network energy consumption can be further reduced with the help of fast cell DTX. For example, if a fast cell DTX scheme reducing the idle state power consumption by 50% is assumed, the daily energy consumption becomes 31-37% lower than without fast cell DTX. Finally, the combination of fast cell DTX and sleep mode deployment results in 63-75% lower daily energy consumption compared to scenarios without any special energy saving schemes.

WCDMA downlink coverage: interference margin for users located at the cell coverage border

The scope of this paper is to derive a simple equation for the WCDMA downlink interference margin as a function of the relative downlink load. This interference margin can then be used as an input for a typical link budget. Due to the complexity of the WCDMA downlink, a fully analytical approach would probably result in a rather complicated and/or inaccurate approximation. Therefore, in this paper the actual equation for the interference margin is derived from the WCDMA theory, and the missing parameter values are obtained from a number of system simulations. The downside of this approach is that a fully flexible usage of the approximated interference margin requires input from a number of measurements or system simulations with different initial assumptions.

Comparison between the periodic and event-triggered intra-frequency handover measurement reporting in WCDMA

In this paper the WCDMA intra-frequency measurement reporting and handover procedure is presented, and the performance of the two main measurement reporting options, periodic and event-triggered, are compared. Furthermore, the impact of some of the parameters defined for the event-triggered mode is also studied. The comparisons are done in terms of both system quality, uplink noise rise and total base station output power, and the signaling load, i.e. the average measurement reporting and active set update rate. The system simulation results show, that the event-triggered measurement reporting scheme results in lower signaling load with the same level of system quality. Furthermore, the right choice of parameters for the event-triggered mode can improve the situation even further.

Improving the energy-efficiency of dense LTE networks by adaptive activation of cells

This study compares the performance of different LTE network densification alternatives from the daily energy consumption point of view. Furthermore, the performance of an energy saving scheme, where unnecessary capacity cells are switched off during low-traffic hours, is evaluated. The obtained results show that the densified macro network is the most energy-efficient deployment when no special energy saving schemes are assumed. Energy-efficiency of the heterogeneous deployments can be considerably improved either by targeting the low-power deployment towards the most traffic-heavy users, or with the help of fast cell DTX. The results demonstrate also that the scheme with a variable network deployment is efficient in reducing the daily energy consumption. With the help of variable network deployment the daily energy consumption becomes 23-38% lower than in case of a fixed network deployment. If both a 50% cell DTX scheme and variable network deployment are applied, the reduction in the daily energy consumption reaches 54-62%.