Jouko Leinonen

MIMO MC-CDMA communications for future cellular systems

We propose an efficient multiple-input multiple-output concept based on space-time turbo coded modulation and layered spatial multiplexing architectures for cellular multicarrier code-division multiple access systems. We design appropriate receiver algorithms, and compare their performance to competing schemes in a single-cell system. We then evaluate the performance of the scheme in a seven-cell system with universal frequency reuse. The proposed MIMO scheme improves throughput significantly compared to the corresponding single-antenna communications even in the presence of spatial correlation

Performance analysis of downlink OFDMA resource allocation with limited feedback

Opportunistic resource allocation in orthogonal frequency division multiple access (OFDMA) with limited feedback improves the performance of wireless networks and it has been considered in several studies. However, the performances of reduced feedback schemes have not been characterized analytically. In this paper, the analysis of the resource allocation in downlink OFDMA with limited feedback is presented. OFDMA system with a practical resource fair round robin allocation and erroneous feedback channel is considered. The performances of the resource allocation based on three feedback methods are analyzed and compared. A resource-wise signal-to-noise ratio (SNR) quantization based feedback method is considered and two feedback strategies are based on the best-M method, where the M best resource blocks are informed to the transmitter. Analytical bit error probability (BEP) expressions are derived for binary phase-shift keying (BPSK) modulation for each feedback strategy. Furthermore, an asymptotic BEP performance for large SNR values is derived for the best-M feedback schemes. The outage capacity results are derived for the considered feedback schemes to illustrate performance with slow link adaptation. Numerical results based on the analysis are compared to those obtained by computer simulations to validate the correctness of the proposed analysis.

Performance Analysis of Downlink OFDMA Frequency Scheduling with Limited Feedback

Opportunistic user allocation based on limited feedback information has been shown to offer significant enhancement for wireless multiple access communications. In this paper, theoretical analysis of user allocation in downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is presented. The performances of resource allocation based on two feedback methods are analyzed and compared. We consider feedback based on the resource-wise SNR quantization and the ordered best-M feedback strategy, where the M best resources are informed to the transmitter. Exact bit error probability (BEP) expressions and analytical outage capacity calculus are presented for the both feedback strategies. Results indicate that significant allocation gain can be achieved with very limited feedback in wideband OFDMA systems. To achieve this allocation gain, we combine multiple resource selection and feedback strategies.

A Cooperative Moving Relay Node System Deployment in a High Speed Train

In this paper we present system level simulation results for a cooperative moving relay node (MRN) system deployed on a high speed train (HST). Recently interest has grown in using MRNs to provide enhanced cellular coverage to users in public transport, particularly HSTs, of which the modern construction materials and techniques cause high vehicle penetration loss (VPL) when signals propagate into the train. MRNs utilising antenna arrays on the exterior and interior of the train are a promising solution to overcoming this VPL in order to provide onboard users with improved service. We show that a cooperative system of 8 MRNs onboard a HST is able to provide significant improvements to achievable throughput of onboard users when compared to direct transmission, as well as indirectly improving the throughput of other users located in cells the HST is passing through.

Outage capacity analysis of downlink ODFMA resource allocation with limited feedback

Theoretical outage capacity analysis for resource allocation in a downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is presented. OFDMA system with practical resource fair round robin scheduler and erroneous feedback channel is considered. Two feedback methods are analyzed and compared. In the set best-M feedback method, the feedback word indicates the group of the M best resource units. The other feedback method is based on the resource-wise signal-to-noise ratio (SNR) quantization. Results indicate that the set best-M feedback scheme is attractive due to the low feedback overhead and significant allocation gain when few resource units are used and M les 3. The allocation based on the resource-wise one bit feedback outperforms the set best-M schemes especially with erroneous feedback at the cost of the larger feedback overhead.

System level evaluation of TDD based LTE-Advanced MIMO-OFDMA systems

This paper presents system level downlink performance evaluation results for the TDD based LTE-Advanced networks utilizing some of the most recent technologies for mobile systems. The main enhanced technology components used in the systems include multi-user (MU)-MIMO, intra-site coordinated multipoint (CoMP) transmission and space-time-frequency proportional fair scheduling. Performance comparison between single-user (SU)-MIMO, MU-MIMO and MU-MIMO with intra-site CoMP OFDMA systems is presented. System level results show that MU-MIMO and MU-MIMO with intra-site CoMP systems exceed the downlink cell average and cell edge user throughput requirements of the IMT-Advanced systems set by ITU-R in urban micro ITU environment. Furthermore, it is shown that MU-MIMO system with intra-site CoMP outperforms uncoordinated MU-MIMO system in terms of throughput. Hence, intra-site CoMP can be considered as a key technique to further improve the throughput performance of LTE-Advanced.

Energy efficient transmission techniques for LTE

The goal of the European ICT Project EARTH is to enhance energy efficiency of current LTE cellular networks by 50 percent, enabling operators to provide more extensive coverage, namely to less densely populated areas, while ensuring high levels of efficiency, hence, reducing the carbon footprint. In order to achieve this objective, different strategies, at different levels, are being addressed. Energy efficient transmission techniques for LTE, proposed within the framework of EARTH, are addressed and discussed, with an emphasis on beamforming and MIMO. It is concluded that the strategic objective of EARTH is achievable. Combined MIMO mode selection, resource allocation, scheduling and precoding strategies will allow an energy consumption reduction of more than 50 percent in macro-cells. A reduction in MIMO power consumption of 91.7 percent (factor of 12) can be achieved in pico-cells.

Space-Frequency Scheduling in TDD Based LTE-Advanced MIMO-OFDMA Systems

Space-frequency resource allocation and multiuser beamforming are crucial techniques to obtain high spectral efficiency requirements of IMT-A technologies. In this paper, we consider system level evaluation results of downlink TDD based LTE-A MIMO-OFDMA networks in ITU-R specific IMT-A evaluation environments. Efficient multiuser MIMO beamforming with and without intra-site coordinated multipoint (CoMP) and proportional fair space-frequency scheduling algorithms are particularly investigated. The system level results indicate that MU-MIMO and CoMP are needed in urban micro (UMi) environment to achieve the ITU-R specific spectral efficiency requirements. In ITU specific indoor scenario, MU-MIMO system is able to provide very high spectral efficiency because intercell interference is not limiting performance so strongly. The considered MU-MIMO CoMP seems to work also in rural macro environment with high mobility users and outdated CSI.

Modulation classification in adaptive OFDM systems

One possible solution to improve the utilization of the capacity of time-varying radio channels is to make the transceivers adaptive. Application of adaptive modulation in orthogonal frequency division multiplexing (OFDM) systems is of particular interest. The objective of this paper is to investigate the receiver algorithms capable of blindly recognizing the modulation format of the received signal in adaptive OFDM systems of the HiperLAN/2 type. The performance of the studied algorithms is considered by computer simulations in OFDM system with adaptive modulation and channel estimation. The maximum likelihood (ML) and the generalized likelihood ratio test (GLRT) classifiers require only few symbols to provide acceptable performance when good channel estimation and relatively high SNR values are available. The novel classifier requires high SNR and more symbols to achieve acceptable performance, but its computational complexity is still lower than that of the ML and the GLRT classifiers.

Performance evaluation of vehicular LTE mobile relay nodes

European Telecommunication Standards Institute (ETSI) is standardizing the 3GPP Long Term Evolution Advanced (LTE-A) relay nodes (RNs) which are intended to be used for providing enhanced cell edge coverage and capacity. We present simulation results on the prospected LTE-A mobile relay node (MRN) applications. The future vehicles can communicate with their environment by exchanging information with surrounding sensor networks and objects. This is related to the concept of Internet of Things (IoT), in which even the smallest objects are equipped with sensors and connectivity capabilities, in order to report information on, e.g., temperature and air pressure. We consider a scenario where in-car connectivity is provided by a short range wireless link such as Wi-Fi or Bluetooth, which can be utilized by the passengers, various sensors, or the vehicle itself. We study the achievable system performance improvement when MRNs are utilized in comparison with the case, in which the users are independently connected to the LTE network. Through simulations, we show that the wireless links via MRNs can give significant advantage when compared to the direct connections from personal handsets to LTE base stations (eNBs).