Showing papers by "Preben Mogensen published in 2002"

A stochastic MIMO radio channel model with experimental validation

Abstract: Theoretical and experimental studies of multiple-input/multiple-output (MIMO) radio channels are presented. A simple stochastic MIMO model channel has been developed. This model uses the correlation matrices at the mobile station (MS) and base station (BS) so that results of the numerous single-input/multiple-output studies that have been published in the literature can be used as input parameters. The model is simplified to the narrowband channels. The validation of the model is based upon data collected in both picocell and microcell environments. The stochastic model has also been used to investigate the capacity of MIMO radio channels, considering two different power allocation strategies, water filling and uniform and two different antenna topologies, 4/spl times/4 and 2/spl times/4. Space diversity used at both ends of the MIMO radio link is shown to be an efficient technique in picocell environments, achieving capacities within 14 b/s/Hz and 16 b/s/Hz in 80% of the cases for a 4/spl times/4 antenna configuration implementing water filling at a SNR of 20 dB.

From antenna spacings to theoretical capacities - guidelines for simulating MIMO systems

Abstract: Capacity increases promised by multiple-input multiple-output (MIMO) systems mostly depend on the spatial correlation properties of the radio channel. The paper investigates the connection between these properties and the capacity figures. It first derives the correlation coefficient between two antenna elements as a function of their spacing, the power azimuth spectrum (PAS), the azimuth spread (AS) and the mean angle of incidence of the waves, for three different types of PAS, namely uniform, truncated Gaussian and truncated Laplacian. With the help of the established relations, correlated flat-fading MIMO channels are generated, whose capacity performance and effective degrees of freedom (EDOF) are investigated for two power allocation schemes, water-filling and uniform. The impact of channel estimation errors is also evaluated.

Experimental analysis of the joint statistical properties of azimuth spread, delay spread, and shadow fading

Abstract: Empirical results characterizing the joint statistical properties of the local azimuth spread (AS), the local delay spread (DS), and the shadow (slow) fading component are presented. Measurement data from typical urban, bad urban, and suburban (SU) environments have been analyzed. It is found that a log-normal distribution accurately fits the distribution function of all the investigated parameters. The spatial autocorrelation function of both AS, DS, and shadow fading can be modeled with an exponential decay function. However, for SU environments the spatial autocorrelation function is better characterized by a composite of two exponential decaying functions. A positive cross correlation is found between the AS and the DS, while both parameters are negatively correlated with shadow fading. All essential parameters required for the implementation of a simulation model considering the joint statistical properties of the AS, DS, and shadow fading are provided.

Performance aspects of WCDMA systems with high speed downlink packet access (HSDPA)

Abstract: In this paper, we consider the link and network layer performance aspects of a WCDMA/UTRA system with high speed downlink packet access. The study considers packet scheduling and the tradeoff among user fairness and cell throughput. We show performance numbers for different network setups and study the applicability of proportional scheduling methods. Even with conservative system and traffic settings, the best effort methods produce high user data rates and cell throughput.

The downlink orthogonality factors influence on WCDMA system performance

Abstract: The large scale statistics of the downlink orthogonality factor (OF) is addressed in this paper for typical urban macrocellular environments for terminals with standard Rake receivers. It is found that the OF improves as the user moves closer to the BS and the OF is positively correlated with the shadow fading component of the radio channel. The mean value of the OF is typically larger for users dominated by own cell interference over other cell interference. These effects result in a larger excess capacity close to the BS, compared to scenarios where the OF is assumed to be constant within the cell.

Method of performing handover by using different handover parameters for different traffic and user classes in a communication network

Abstract: The present invention relates to a method for performing handover in a communication network, wherein communication with a subscriber terminal (UE) having subscribed to said network is performed by the intermediate of at least one network entity (Node B) handling the communication of said subscriber terminal, upon a change of a communication state for said subscriber terminal within said network, which fulfills a predetermined handover trigger condition, a handover procedure is performed under control of a control entity (RNC) of the communication network, a handover procedure is defined by a handover signaling scenario (HO, HHO, SHO, SSTD) and at least one set of handover parameters per signaling scenario, the handover parameters define a respective handover trigger condition, a communication with a subscriber terminal belongs to a specific one of a plurality of traffic classes, and wherein at least one user class is defined per traffic class, the method comprising the steps of configuring a set of handover parameters and a handover signaling scenario per user class, and performing, upon detection that said handover trigger condition is fulfilled, the handover procedure for said subscriber terminal as defined by the configured handover signaling scenario and the configured set of handover parameters for the respective user class of the respective traffic class.

Data transmission method, radio network controller and base station

Abstract: The invention is related to a data transmission method in a telecommunication system. The method comprises determining (202) the number of bit rate classes, setting (204) bit rates for the bit rate classes, setting (206) a maximum transmission power target, arranging (208) resource requests into a queue, allocating (210) resources according to the requests in the queue until the maximum power target is achieved.

Directional power-based admission control for WCDMA systems using beamforming antenna array systems

Abstract: A directional power-based admission control (AC) scheme is proposed for base stations deploying beamforming antenna arrays. The proposed AC algorithm is a natural extension of the conventional power based AC scheme for cells using standard sector antennas. The directional scheme takes the load per beam/direction into account in the AC decision, so the cell load is controlled in accordance with the spatial filtering gain provided by using beamforming antenna arrays. The scheme is tested by means of Monte Carlo simulations in a multicell wideband code division multiple access (WCDMA) network, where users with different bit rates are present. The obtained results demonstrate that the directional power based AC scheme allows a higher traffic load in cells using beamforming antenna arrays without jeopardizing the stability of the network. Application of a four element antenna array is found to provide a capacity gain of a factor 2.7 for a network with many low bit rate users, while the gain is reduced to a factor 2.3 for traffic scenarios with a mixture of high and low bit rate users.

Antenna Arrays and Space Division Multiple Access

Abstract: Adaptive base station antennas also called smart antennas have recently become a hot research topic. In principle the adaptive antenna concept consists of an antenna array and a flexible beamforming network. In terms of commercial exploitation there are mainly two driving factors for introducing adaptive base station antennas, (i) range extension, (ii) capacity enhancement. The issue of range extension is briefly discussed in Section 2, but the main emphasis is put on capacity enhancement of adaptive base station antennas. As sketched in Figure 1, an adaptive antenna array typically creates a narrow beam in the direction of the desired mobile station and thereby reduces the co-channel interference level in other azimuth directions. This is called spatial filtering. There are two methods to exploit a capacity gain from spatial filtering: In the concept of Same Cell Reuse (SCR), the physical radio channels (timeslot, frequency channel) = (t,f) are

Radio resource management for WCDMA networks supporting dual antenna terminals

Abstract: The downlink performance enhancement provided by dual antenna terminals in a WCDMA network is evaluated. A UMTS network is taken as a case study and the behaviour of conventional power based radio resource management algorithms is discussed for both circuit and packet switched services. The aim is to clarify: (i) what the available capacity gain is; (ii) whether it is possible to capture this capacity gain without any higher layer overhead; and (iii) how the capacity is distributed among the users. A theoretical analysis of the dependency of the capacity gain upon the proportion of dual antenna terminals is conducted and the outcome matches the simulation results. Moreover, the impact of soft handover on the performance gain is considered. Furthermore, it is shown that the system becomes hard limited due to lack of channelisation codes, rather than excessive interference.

Power control during retransmission

Abstract: The present invention relates to a method and a device for controlling power in a network transmitted from a first station to a second station. The second station determines a power target value for a signal received from the first station and sends power control commands to the first station depending on a deviation between said power target value and a received power level. The second station detects faulty data blocks received from the first station and requests retransmission of faulty data blocks from the first station. The adjustment of the power target value to a temporary power target value during the retransmission is performed such that the temporary power target value is calculated depending on the quality of a faulty data block.

Method of transmitting data in two modes of operation, wherein one mode, the power level is indicated in the message

Abstract: The invention relates to a method and apparatus for transmitting data from a first node to a second node of a communication system, the method comprising the steps of a first mode of operation, transmitting said data via a first communication channel in which the power level of the channel at said first node is not indicated to the second node, and in a second mode of operation transmitting said data via said first communication channel and indicating the power level of the channel at said first node to said second node.

Packet Scheduling with QoS Differentiation

Abstract: This article focuses on the Quality of Service (QoS) achieved by packet scheduling. A packet scheduling algorithm, which can differentiate the QoS among user and service classes, is presented. The algorithm can be tuned from signal to interference ratio (C/I) based scheduling to Round Robin and beyond. Thus, an operator can choose between optimizing the spectral efficiency or giving a fair QoS distribution among the users within a user and traffic class. By combining the two effects, different strategies can be used for different user and service classes. Simulation results for the downlink shared channel (DSCH) are presented and implementation issues are also discussed.

Impact of TCP flow control on the radio resource management of WCDMA networks

Abstract: The present paper highlights the performance of the transport control protocol over WCDMA networks. The TCP flow control adjusts the transmission rate to the network and receiver's capacity. Due to this protocol self-adaptation to the transmission conditions of the links involved in the TCP connection, the protocol performance can not be disconnected from the underlying network. In WCDMA networks, the RRM assigns the radio resources to the UE in the cell, which directly impacts the TCP throughput performance. The results show that the allocation of high bit rate dedicated channels to small file downloads (such as Web pages) produce poor channelization code efficiency compared to allocating low bit rate channels. Under certain conditions, for large file downloads (such as ftp) the code efficiency and throughput performance improve significantly due to the protocol nature to fully utilize the bottleneck capacity. This protocol performance suggests a radio resource allocation strategy for DCH channels, which increases the bit rate stepwise as the file transmission evolves starting from a low bit rate.

Performance of uplink synchronous WCDMA at network level

Abstract: The performance of uplink synchronous WCDMA systems for low dispersive environments is evaluated at network level. The capacity increase is computed for the particular case of UMTS, taking into account the impact of effects like the code shortage, the number of receiver antennas, the penetration rate, and the use of soft handover. This is done theoretically and by means of a dynamic simulator, which considers more realistic conditions. Theoretical calculations match the simulation results. According to the results generated for speech service, the main problem in uplink synchronous WCDMA systems is the code shortage. For Pedestrian A environments with the most realistic conditions uplink synchronous WCDMA provides a 9.6% capacity gain. However, a very high potential exists for situations where this code shortage can be solved, i.e. 35.8% capacity gain assuming no code restriction.

System and method for optimized utilization of code resource in communication networks

Abstract: The invention provides a method, system and network element for providing enhanced utilization of code resource in a cellular systems, preferably a terrestrial cellular CDMA systems, wherein a base station comprises an antenna system which generates several beams A spreading factor (SF) of the root channelization code sets an upper limit on the maximum bit rate. The spreading factor of the root channelization code is selected according to the set of minimum spreading factors assumed for the different beams. Packet scheduling for parallel beams is provided in such a manner that not all beams transmit on downlink, e.g. PDSCH, with high or maximum bit rates (low Spreading Factor) simultaneously. The packet scheduling in the individual beams is coordinated so that only one of the beams is transmitting with a high bit rate during the same time period. Different scheduling slots are balanced so they require nearly the same amount of code resources.

Uplink synchronous WCDMA combined with variable modulation and coding

Abstract: Previous studies show a high potential capacity gain for uplink synchronous WCDMA systems in low dispersive environments when users in the same cell are separated by orthogonal codes. However, the number of available orthogonal codes tends to limit the capacity gain of this scheme. In this paper, variable modulation and coding is introduced as a solution to improve the channelization code utilization per user equipment and thereby increase the capacity of uplink synchronous WCDMA. The radio resource management algorithms to support this scheme are presented. Theoretical and simulation results on the capacity gain of uplink synchronous WCDMA combined with variable modulation and coding are presented. A 29% capacity gain is obtained for a pedestrian micro-cell environment.

Method of transmitting data where in a first mode, the power level is not indicated in a message and an NPSK modulation scheme is used, and in a second mode, the power level is indicated in a message in an NQAM modulation scheme is used

Abstract: A method and apparatus for transmitting data from a first node to a second node of a communication system are provided. The method includes, in a first mode of operation, transmitting data via a first communication channel in which the power level of the channel at the first node is not indicated to the second node, and in a second mode of operation transmitting the data via said first communication channel and indicating the power level of the channel at the first node to the second node.

Handover in a communication network

Abstract: The present invention relates to a method for performing handover in a communication network, wherein communication with a subscriber terminal (UE) having subscribed to said network is performed by the intermediate of at least one network entity (Node B) handling the communication of said subscriber terminal, upon a change of a communication state for said subscriber terminal within said network, which fulfills a predetermined handover trigger condition, a handover procedure is performed under control of a control entity (RNC) of the communication network, a handover procedure is defined by a handover signaling scenario (HO, HHO, SHO, SSTD) and at least one set of handover parameters per signaling scenario, the handover parameters define a respective handover trigger condition, a communication with a subscriber terminal belongs to a specific one of a plurality of traffic classes, and wherein at least one user class is defined per traffic class, the method comprising the steps of configuring a set of handover parameters and a handover signaling scenario per user class, and performing, upon detection that said handover trigger condition is fulfilled, the handover procedure for said subscriber terminal as defined by the configured handover signaling scenario and the configured set of handover parameters for the respective user class of the respective traffic class