Publications 2007

Academic theses (2)

T. Nihtilä, “Advanced receivers and antenna diversity in WCDMA HSDPA“, Licenciate thesis, University of Jyväskylä, Finland, 2007.

This work studies the system level performance of a basic and an advanced signal reception algorithm in combination with antenna diversity techniques of Wideband Code Division Multiple Access (WCDMA) user entities in a High Speed Data Access (HSDPA) network. 

N. Kolehmainen, “Laskevan siirtotien kanavanlaadun mittaus E-UTRAN soluverkoissa”, M.Sc. thesis, University of Jyväskylä, 2007.

Journal articles (2)

K. Aho, J. Kurjenniemi, V. Haikola, C. Callender and T. Ristaniemi, “Multimedia Broadcast Multicast Service Performance and its Enhancements in WCDMA Networks“, Wireless Personal Communications, ISSN 0929-6212, 2007.

Multimedia Broadcast Multicast Service (MBMS) in Wideband Code Division Multiple Access (WCDMA) networks is used to transmit information from one source to vast amount of recipients. The MBMS technique eases the load of the network and therefore allows network to serve more subscribers.

The very aim of this study is to evaluate the performance of Release 6 MBMS and its performance enhancements in WCDMA networks.

Special attention will be focused on macro and receive diversity which are considered in addition to time diversity provided by long interleaving as enhancements on MBMS performance. 3GPP Release 6 specifications for MBMS introduce two macro diversity schemes: soft and selective combining. 

T. Nihtilä, J. Kurjenniemi, M. Lampinen and T. Ristaniemi, “Performance of Receiver Diversity and LMMSE Chip Equalization Performance in WCDMA HSDPA Network“, Wireless Personal Communications, vol. 43, no. 2, October 2007, pp 261-280.

More advanced receiver structures than the conventional single antenna Rake can be used to improve the signal-to-noise (SNR) ratios, which is especially beneficial in order to utilize the high bit rates provided by the HSDPA concept in Wideband Code Division Multiple Access (WCDMA) network.

In WCDMA system, orthogonal Walsh–Hadamard sequences are used as channelization codes. In frequency-selective fading channels the orthogonality of channelization codes disappears and intra-cell multiple access interference (MAI) arises.

In order to mitigate the effect of MAI, chip-level equalization has shown to be a simple and effective solution. The effectiveness of chip equalization, however, degrades at the cell borders where the inter-cell interference dominates rather than MAI. Dual antenna reception is a straight-forward solution to mitigate that performance drop.

In this paper, we present an analysis of the expected gains of advanced receivers over conventional single antenna Rake receiver in realistic situations by using a dynamic WCDMA system-level tool. Considered advanced receivers include single and dual antenna Linear Minimum Mean Squared Error (LMMSE) chip-level equalizers and dual antenna Rake receiver.

The network performance with advanced receivers is studied also from a more practical point of view by assuming that the penetration of advanced HSDPA terminal receivers is gradually increased in the network.

Conference articles (8)

K. Aho, J. Kurjenniemi, V. Haikola and T. Ristaniemi, “System Level Performance of Multimedia Broadcast Multicast Service (MBMS) with Macro Diversity“, Proc. of the IEEE Wireless Communications and Networking Conference, Hong Kong, March 11-15, 2007.

The aim of this paper is to evaluate the system level performance of multimedia broadcast multicast service (MBMS) in WCDMA networks. To enhance coverage and data rates of MBMS users, two macro diversity concepts were introduced in 3GPP release 6: soft and selective combining.

Prior work on the evaluation of MBMS with macro diversity schemes has been restricted to link level studies or to very limited scenarios in system level studies.

This paper examines the concepts in more detail with dynamic system level tool in which e.g. mobility of users and interactions of the radio resource management functionalities are explicitly taken into account.

The evaluation of combining set size and data rates with different thresholds and delays in the combining procedures are especially emphasized. Considering point-to-multipoint (p-t-m) mode of MBMS, the studies indicated clear performance improvements to be gained with macro diversity. In addition, the impact of delays in combining set update procedures was observed to be rather small.

K. Aho, J. Kurjenniemi, V. Haikola and T. Ristaniemi, “Performance enhancement of Multimedia Broadcast Multicast Service (MBMS) with Receive Diversity“, Proc. of the International Conference on Networking, Sainte-Luce, Martinique, April 22-28, 2007.

The aim of this paper is to evaluate the effect of receive diversity on multimedia broadcast multicast service (MBMS) performance in wideband code division multiple access (WCDMA) networks.

In addition to time diversity provided by long interleaving and receive diversity provided by multiple receive antennas, 3GPP release 6 specifications for MBMS introduce two macro diversity schemes: soft and selective combining.

Diversity techniques are introduced in order to improve the MBMS performance. Improvements help especially the cell edge MBMS users who suffer most from the fading channel conditions. As receive diversity is one of the most efficient diversity techniques this paper examines the system level performance of MBMS point-to-multipoint (p-t-m) mode with receive diversity together with and without macro diversity schemes.

These concepts are studied with dynamic system level tool in which e.g. mobility of users and interactions of the radio resource management functionalities are explicitly taken into account. Our studies indicate that the receive diversity brings significant gains to the MBMS performance. Receive diversity together with macro diversity schemes improves the performance even more.

T. Nihtilä, J. Kurjenniemi and E. Virtej, “System Level Analysis of Interference Aware LMMSE Chip Equalization in HSDPA Network“, Proc. of the IEEE Symposium on Computers and Communications, Aveiro, Portugal, July 1-4, 2007.

In this paper we present a system level performance analysis of ideally interference aware linear minimum mean squared error (LMMSE) chip-level equalizer capable of both intra-cell and inter-cell interference suppression with high-speed downlink packet access (HSDPA).

The evaluation is performed with and without receive diversity, having the intra-cell interference suppressing LMMSE equalizer as a reference.

The study is performed with fully dynamic system simulator which includes the modeling of LMMSE equalizer, HSDPA functionality, UE mobility and the most fundamental radio resource management algorithms. The used system scenario is HSDPA network with proportional fair scheduler.

J. Kurjenniemi and C. Callender, “System Level Analysis of Dynamic Receiver Reconfiguration for MBMS on S-CCPCH“, Proc. of the IEEE Symposium on Personal, Indoor and Mobile Radio Communications, Athens, Greece, September 3-7, 2007.

In this paper, we present results of a simulation study intended to investigate the feasibility of dynamic receiver reconfiguration in case of multimedia broadcast multicast service (MBMS). Based on current radio channel conditions one receiver branch of a UE which has 2Rx rake receiver can be switched off dynamically for power saving purposes.

The study performed consisted of dynamic system level simulations of MBMS point-to-multipoint (p-t-m) transmission. This scenario can be considered a favorable one for dynamic receiver reconfiguration as there are no scheduling or power control feedback issues, and other users of the system should not be heavily impacted by dynamic reconfiguration of a particular UE.

However, there is still the possibility that the MBMS service coverage area could be impacted by individual user switching decisions, and the intention of this study is to examine MBMS coverage when a population of UEs implement dynamic receiver reconfiguration.

Based on the findings of this study it seems that 2Rx rake receiver can operate with a single antenna significant amount of time without sacrificing desired coverage and thus provide clear power saving opportunities.

T. Nihtilä, J. Kurjenniemi and M. Lampinen, “Effect of ideal inter-cell interference cancellation to HSDPA system performance“, Proc. of the IEEE Symposium on Personal, Indoor and Mobile Radio Communications, Athens, Greece, September 3-7, 2007.

High speed downlink packet access (HSDPA) concept in wideband code division multiple access (WCDMA) system provides spectrally efficient packet access connection by means of dynamic link adaptation, low spreading factor and higher order modulation.

Due to these the achievable data rate is vulnerable to the interference both from the serving cell and from the neighboring cells. Several linear and non-linear interference mitigation methods have been presented in literature to mitigate mainly the intra-cell interference but similar algorithms can also mitigate the inter-cell interference at the cell border area. However, the effect of inter-cell interference cancellation has not been thoroughly evaluated in system level.

In this paper we analyze the system performance of an ideal inter-cell interference cancellation in HSDPA network. The analysis considers also traditional advanced receivers, which mainly suppress or cancel intra-cell interference. Linear minimum mean square error (LMMSE) chip equalizer and receive diversity are considered.

The modeling of inter-cell interference mitigation at the UE receiver is not modeled explicitly but is based on removing a predefined portion ideally from the interference produced by selected number of strongest interfering sectors. By this way, the interference cancellation efficiency can be mapped to the actual system performance improvement.

The results are obtained from a fully dynamic system simulator, where the mobility of UE’s and radio resource management algorithms are modeled.

J. Kurjenniemi and V. Vartiainen, “Point-to-Multipoint Multimedia Broadcast Multicast Service (MBMS) Performance over HSDPA“, Proc. of the IEEE Symposium on Personal, Indoor and Mobile Radio Communications, Athens, Greece, September 3-7, 2007.

The aim of this paper is to evaluate the system level performance of point-to-multipoint (p-t-m) multimedia broadcast multicast service (MBMS) performance over high speed downlink packet access (HSDPA) scheme.

MBMS was introduced in 3GPP Release 6 to provide efficient transmission mode for multimedia delivery and Point-to-Multipoint transmission through secondary common control physical channel (S-CCPCH) or point-to-point (p-t-p) transmission using e.g. HSDPA.

As S-CCPCH lacks of power control it would seem feasible to provide p-t-m transmission over HSDPA as it supports flexible link adaptation methods. Usage of HSDPA for p-t-m MBMS delivery could be useful from link efficiency point of view as well as it would give flexibility to allocate capacity between MBMS and other services.

In this paper p-t-m MBMS over HSDPA scheme is presented and its performance is evaluated with dynamic system level simulations. P-t-m MBMS over HSDPA scheme without any link adaptation is compared to a method where number of transmissions is changed based on UE reported feedback.

Although link adaptation performance in p-t-m transmission is found to be heavily dependent on number of subscribers in the network, achieved gains ranges from 25% to 70 % in terms of saved transmission resources.

O. Fresan, T. Chen, K. Ranta-aho, T. Ristaniemi, “Dynamic Packet Bundling for VoIP Transmission Over Rel’7 HSUPA with 10ms TTI Length“, Proc. of the International Symposium on Wireless Communication Systems, 17-19 October, 2007, pp. 508 – 512.

In this paper, the system level optimization of the voice over IP transmission in the HSUPA system, configured with a 10 ms TTI length, is analyzed.

The study considers the release 7 improvements to HSUPA, in terms of the DPCCH gating concept.

A dynamic activated MAC layer bundling of two VoIP packets in a single frame is proposed and compared against the single packet per frame transmission by means of quasi-static system level simulations.

O. Fresan, T. Chen, E. Malkamaki, T. Ristaniemi, “DPCCH Gating Gain for Voice Over IP on HSUPA“, Proc. of the IEEE Wireless Communications and Networking Conference, Hong Kong, China, 11-15 March, 2007, pp. 4274 – 4278.

In this paper, the concept of DPCCH (dedicated physical control channel) gating for HSUPA (high speed uplink packet access) is analyzed.

DPCCH gating technique has been recently under consideration within WCDMA to inactivate control channels during no data transmission periods, and hence, not to misuse capacity. In order to study the concept benefit, a concrete real-time service is selected in this paper: Voice over IP (VoIP) for mobile communications.

It will be shown that VoIP would be highly beneficed by DPCCH gating inclusion in 3GPP specifications. Both analytical and simulation studies were run to confirm the gain expectations.