Showing papers by "Matti Latva-aho published in 2006"

Data transmission parameter optimization in mimo communications system

Abstract: A solution for optimizing beamforming configurations and transmit power allocation configurations in a telecommunication system comprising a base station and a plurality of user entities is provided. The base station and the user entities are capable of multiple-input multiple-output (MIMO) communications, i.e. capable of communicating through spatial subchannels. The base station calculates iteratively optimal beamforming configurations for the base station and for each user entity and transmit power allocation configurations for each spatial subchannel used in MIMO communications. The base station carries out the calculation on the basis of channel state information received from the user entities by utilizing the information on correlation of different spatial subchannels, i.e. interference between the subchannels, in order to update beamforming configurations and transmit power allocation configurations.

Nonblind and Semiblind Space-Frequency Multiuser Detection for Multirate MC-CDMA Systems

Abstract: Multicarrier code-division multiple access (MC-CDMA) is a promising candidate for the air interface of future wireless communication systems. After the development of a unified signal model that applies to the different multirate MC-CDMA schemes studied in this paper, a novel space-frequency multiuser detection scheme for multirate uplink MC-CDMA systems with multiple receive antennas is proposed. In particular, a space-frequency minimum mean-squared error (MMSE)-based hybrid serial/parallel interference cancellation receiver (SF-MMSE/HIC) is developed which produces the SF-MMSE combiner as a byproduct. The signal processing of this new detector is jointly carried out in space and frequency domains which leads to the advantage of combating the interference resulting from different sources simultaneously. Based on subspace estimation, a semiblind implementation of the receiver is introduced for slow fading channels. Furthermore, the impact of subcarrier interleaving is investigated for variable spreading factor (VSF) MC-CDMA systems. Based on the characteristic function (CF) of a complex Gaussian random vector (CGRV), a method for analyzing the bit error probability (BEP) performance is presented. Several representative simulation examples of the detector are provided to demonstrate the performance of the proposed receiver. In a fully loaded system, the proposed receiver can offer performance close to the single-user bound. Moreover, the results indicate that multicode and VSF MC-CDMA schemes give very similar performance

Co-existence measurements between UMTS and UWB systems

Abstract: The paper presents results of a co-existence measurement study between multiple ultra wideband (UWB) transmitters and a Universal Mobile Telecommunications System (UMTS) mobile phone. Two environments were explored: an anechoic chamber with one operating UMTS link and a true operational UMTS network. A large number of FCC compatible UWB transmitters were used to generate interference for an active UMTS connection. In an anechoic chamber, only the voice service was studied between a radio communication analyser (used as a base station) and a mobile terminal. In the true commercial UMTS network case, both the voice and data services were investigated in a shelter having a low UMTS signal level. The results clearly show that UMTS and high pulse repetition rate UWB devices can co-exist at link level when a moderate number of simultaneously active UWB devices operate in close proximity of the UMTS 'victim' receiver. The results also show that the activity factor of the UWB transmitter disproportionately impacts the effective interference. When using low activity factors, even with high pulse repetition rates and very large numbers of UWB devices, it is difficult to detect UMTS link performance degradation. As the activity factors grow beyond 5%, the impact of the UWB interference becomes visible. However, this study covers only one active UMTS link in both environments but does not report on the UWB impact on the UMTS radio access network.

Weighted Sum MSE Minimization for MIMO Broadcast Channel

Abstract: A MIMO broadcast channel with linear transceiver schemes is considered in this paper. The base station (BS) is equipped with a scheduler, using a simple opportunistic beamforming strategy, which associates an intended user for each of the transmitted data streams. For the case when the channel of the scheduled users is available at the BS we propose an iterative algorithm for joint design of the transmit and the receive beam-formers according to mean square error minimization criterion. The proposed method can handle multiple antennas at the BS and at the mobile user with single and/or multiple data streams per scheduled user. The optimization problems encountered in the beamformer design (e.g., covariance rank constraint) are not convex in general. Therefore, the problem of finding the global optimum is intrinsically non-tractable. However, by exploiting the uplink-downlink SINR duality, we decompose the original optimization problem as a series of simpler optimization problems which can be efficiently solved by using standard convex optimization tools. There is no guarantee that the global optimum has been found due to the nonconvexity of the problem, but, the simulations show that the algorithms converge fast to a solution, which can be a local optimum, but is still efficient.