Andreas Mäder

An analytic approximation of the uplink capacity in a UMTS network with heterogeneous traffic

The fast computation of blocking probabilities and the resulting capacity is one of the crucial tasks in the planning process of UMTS networks. The admission control in WCDMA networks is based on the momentary interference which includes both own-cell and other-cell interference. Since both interference terms are stochastic values we speak of soft blocking. The number of users in the system is not sufficient for deciding whether to accept a new call or not. Instead, it is blocked with a certain probability depending on the number of users in the system, the activity of the users, and the other-cell interference. In this paper we present a time-efficient algorithm to compute blocking probabilities in a WCDMA network operating with several services. Assuming Bernoulli activity and modelling the other-cell interference as a lognormal random variable the blocking probabilities are computed using an approximation based on the Kaufman-Roberts recursion.

An Analytical Model for Best-Effort Traffic Over the UMTS Enhanced Uplink

The next step in the evolution of UMTS is the Enhanced Uplink or high speed uplink packet access (HSUPA), which is designed for the efficient transport of packet switched data. One of the major novelties is the relocation of the scheduling control from the RNC to the NodeB which enables a faster reaction to cell load and radio condition variations. Our contribution is an analytic modelling approach for the performance evaluation of the UMTS uplink in a single cell with best-effort users over the enhanced uplink and QoS-users over dedicated channels. The model considers two different scheduling disciplines for the enhanced uplink: Parallel scheduling and one-by-one scheduling. The model also considers the effect of power control errors and other-cell interference fluctuations as well as multiple dedicated channel service classes.

An analytic model for deriving the node-B transmit power in heterogeneous UMTS networks

UMTS operates with WCDMA over the air interface. Most studies dealing with the capacity of CDMA networks consider the uplink (reverse link) and evaluate the coverage or capacity of a cell or network. This focus on the uplink originates in the fact that the IS-95 network was a single voice network, such that the network performance was limited by the uplink. Furthermore, fast power control was then implemented on the uplink only. The introduction of 3G networks leaves the pure voice networks behind and instead provides a variety of different services which produce asymmetric traffic, with the bulk on the downlink (forward link). This traffic asymmetry shifts the capacity limit from the uplink to the downlink. The 3gpp standard prescribes the use of fast power control for the downlink as well. We propose a model to calculate the first and second moment of the node-B transmit power which allows us to approximate its distribution and to determine the probability that the system becomes unstable when a certain transmit power is exceeded.

A novel performance model for the HSDPA with adaptive resource allocation

We propose a novel performance model for the HSDPA in presence of circuit-switched dedicated channels. The model consists of two parts: An HSDPA bandwidth model which considers the SIR distribution according to the multi-path model and the number of available channelization codes, and an analytical capacity model which integrates HSDPA and dedicated channels under assumption of adaptive resource allocation for the HSDPA. Additionally, the model considers the impact of location dependent bandwidths on the spatial user distribution. The accuracy of the model is demonstrated for an example scenario.

Performance evaluation and parameterization of the IEEE 802.16 contention-based CDMA bandwidth request mechanism for the OFDMA physical layer

The IEEE 802.16 standard specifies two contention-based mechanisms for the OFDMA physical layer to transmit bandwidth requests from subscriber station to base station: the standard mechanism is based on Slotted Aloha with a truncated binary exponential backoff; the alternative one is based on CDMA. This paper describes the CDMA-based contention mechanism and presents an analytic model to compute its performance in terms of delay and consumed resources. The tunable parameters for the CDMA-based random access procedure are the number of ranging subchannels, the number of codes per ranging subchannels, and the detection threshold. An optimal configuration is derived for a given load in terms of the request arrival rate.

Impact of HSDPA Radio Resource Allocation Schemes on the System Performance of UMTS Networks

In UMTS networks, HSDPA users share radio resources like transmit power and OSVF codes with QoS-users, which use dedicated channels as primary transport method. Several options for the resource allocation for HSDPA exist, which center around the question whether resources should be exclusively reserved for HSDPA, or whether the resources for the HSDPA should be adapted to the requirements of the QoS users. We investigate the impact of three radio resource allocation schemes on the HSDPA and on the dedicated channel performance by means of a time-dynamic simulation. The numerical results show the trade-offs between dedicated channel and HSDPA performance and the sensitivity of the system against power and code reservation parameters.

On the performance of mobile IP in wireless LAN environments

Wireless Local Area Networks (WLANs) based on the IEEE 802.11 standard have become more and more popular in the last few years. In such networks, a handover has to be performed when moving from one cell to another. When considering small-scale scenarios like an office building, these handovers can be performed on the ISO/OSI layer two solely. However, the size of one subnet is rather restricted. Therefore, the handover has to be lifted to the network layer as well. The performance of this network layer handover will be shown in this paper.

A flow-level simulation framework for hsdpa-enabled umts networks

The High Speed Downlink Packet Access is designed for the efficient transport of best-effort traffic in UMTS networks. HSDPA uses fast scheduling with adaptive modulation and coding for the rapid adaptation of the instantaneous channel bandwidth to the channel quality. A simulator for such a system has to model these mechanism properly, which is classically done with help of link-level simulations. Additionally, traffic-dynamics on flow-level and radio resource management have a significant influence on the system performance, but a statistical sound evaluation requires long simulation runs, which prohibits an exact simulation on a small time-scale. Our contribution is a novel flow-level simulation framework, which captures on the one hand the impact of the physical layer, and enables on the other hand the efficient simulation of large scenarios over a long time. The framework uses analytical methods to calculate user bandwidths for different scheduling types and propagation environments as well as the required transmit powers and code resources for arbitrary radio resource management schemes.

Analytic modeling of the UMTS enhanced uplink in multi-cell environments with volume-based best-effort traffic

The UMTS enhanced uplink enables the efficient transport of packet-switched Internet traffic. With bit rates comparable to DSL links, it is expected that best-effort services like file-sharing become increasingly popular in UMTS networks. These services are often volume-based, which means that the sojourn time of a connection depends on the transmitted data volume. In this work, we propose an analytic model for the interference and capacity in the enhanced Uplink, which considers the impact of volume-based traffic on system capacity, other-cell interference and co-existing time-based QoS users. The analytic model is validated with a flow-level event-discrete simulation.

Interference estimation for the HSDPA service in heterogeneous UMTS networks

For the planning and deployment of the 3.5G enhancement of UMTS, the High Speed Downlink Packet Access, mobile telecommunication providers need to estimate the signal-to-interference-ratio of the HSDPA users. Although the received signal power is easy to calculate due the channel adaptive principle of HSDPA, the received interference includes the signal powers of the power controlled dedicated channel users and is therefore more challenging. Our contribution is a semi-analytical method to calculate the spatial distribution of the received interference. The method considers the interference generated in the own cell and in the surrounding cells including the load dependent interference coming from the dedicated channel users.