Marko Lampinen

Performance of linear multi-user MIMO precoding in LTE system

For scenarios with a large number of users to be served in one cell, high capacity gains can be achieved by transmitting independent data streams to different users sharing the same time-frequency resources. This technique is known as Multi-User MIMO (MU-MIMO). In this paper we investigate the performance of MU-MIMO operation in 3GPP LTE for different frequency granularities of the precoder at the OFDM transmitter. We also investigate the impact of channel correlation on the performance of the receiver when it is unaware of the interfererpsilas precoding vector. The performance is evaluated by means of semistatic system simulations.

Performance of receive diversity and LMMSE chip equalization in WCDMA HSDPA network

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.

WCDMA HSDPA network performance with receive diversity and LMMSE chip equalization

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 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, a 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 is a straight-forward solution to mitigate that performance drop. In this paper we consider receivers equipped with dual antenna and linear minimum mean squared error (LMMSE) chip-level equalizers and present an analysts of the expected gains over conventional single and dual antenna rake receivers in realistic situations by using a dynamic WCDMA system-level tool

Open-loop MIMO extensions for HSDPA with practical constraints

In this paper, we investigate three different open-loop multi antenna schemes and compare their performance to the traditional receive diversity in high speed downlink packet access (HSDPA) system, which is a packet enhancement to the third generation wideband code division multiple access (WCDMA) mobile communication system. The studied schemes are per antenna rate control (PARC), space time transmit diversity (SITD) and matrix modulation (MaMo) each with 2times2 antenna configuration. In this study a chip equalizer based receiver is used, because the optimal receiver is prohibitively complex for practical implementation. The link throughput results show that multiple-input multiple-output (MIMO) schemes outperform the traditional receive diversity in low delay spread channels especially, if up-to-date and error free link adaptation feedback is available. However, with practical constraints on the link adaptation feedback , geometry distribution and delay spread, the receive diversity performs almost as well as the studied MIMO schemes

HSDPA performance with parallel interference cancellation

We investigate an advanced receiver technique called multistage parallel interference cancellation applied to high speed downlink packet access (HSDPA), which is a packet enhancement to the third generation wideband code division multiple access (WCDMA) mobile communication system. The advanced receiver packet error rate and throughput performance is compared to conventional rake receiver with link level simulations in single antenna case, and the results show that considerable gain is possible by using the advanced receiver in multipath fading channels, where the rake has already reached error floor.

Effect of Ideal Inter-Cell Interference Cancellation to HSDPA System Performance

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 UEs and radio resource management algorithms are modeled.

HSDPA Mimo Performance with Turbo Equalizer

In this paper, we study the effect of receiver structures to multiple-input multiple-output (MIMO) performance in a simplified model of high speed downlink packet access (HSDPA) system, which is a packet enhancement to the third generation wideband code division multiple access (WCDMA) mobile communication system. Both 2times2 open loop MIMO and traditional receive diversity are studied. In this study a chip equalizer is used as a baseline receiver due to its simplicity and performance of idealistic turbo equalizers is compared against it. Turbo equalization is an iterative approach on joint detection and channel decoding. It can be observed that chip equalizer is efficient for the receive diversity transmission but large performance improvements are obtained by using the turbo equalizer, if MIMO transmission is used. In addition, canceling only the spatial part of the interference provides relatively good performance when compared to full space-time cancellation