Zijian Bai

Combining Mimo with Network Coding: A Viable Means to Provide Multiplexing and Diversity in Wireless Relay Networks

In this paper, a two-step communication protocol combined with virtual MIMO (Multiple Input Multiple Output) and network coding technique is proposed. The protocol is therefore termed MINEC (MIMO Network Coding). A three nodes network with multi-antennas on relay node is taken as an illustrative example of MINEC. Theoretical and simulative analyses of the MINEC performance under the assumption of a binary symmetric relay channel model are carried out. It is found that MINEC performs equivalent to a 2x2 V- BLAST MIMO and a two 2x1 Alamouti MISO in transmitting phase and forwarding phase, respectively. Theoretical and simulative analyses prove that MINEC protocol facilitates more reliable transmission and higher throughput.

On the Equivalence of MMSE and IRC Receiver in MU-MIMO Systems

In order to combat the residual interference in multiuser multiple-input and multiple-output systems (MU-MIMO), a number of low-complexity interference aware type of receivers have been considered. In this letter, single layer Minimum Mean Square Error (MMSE) and Interference Rejection Combiner (IRC) are applied in MU-MIMO transmission. Based on some very simple but extremely useful matrix manipulations, their equivalence is proven analytically and demonstrated via Monte Carlo simulations.

Closed loop transmission with precoding selection in LTE/LTE-Advanced system

Closed-loop transmission combined with MIMO (multiple-input multiple-output) and OFDM (orthogonal frequency division multiplexing) technologies have drawn most attentions during development of the 4G systems (fourth generation of mobile communication systems). In LTE (Long Term Evolution) and LTE-Advanced systems, which are proposed by 3GPP (Third Generation Partnership Project) to be the most competitive candidate for the 4G systems, the codebook based precoding scheme is deployed for realizing the closed-loop transmission concept. This scheme introduces the precoding matrix selection at the receiver and precoding operation at the transmitter and achieves a good tradeoff between the system complexity and the performance gain given by the closed-loop transmission. In this manuscript, the authors give a brief overview of the LTE/LTE-Advanced system downlink transmission. Furthermore, different precoding matrix selection criteria are discussed at the aim of optimal receiver design. Following the analytical and numerical results, the authors conclude that the minimum post mean squared error based criterion is the optimal candidate for precoding matrix selection at the receiver in LTE compliant systems.

On the physical layer performance with rank indicator selection in LTE/LTE-Advanced system

The 3GPP (Third Generation Partnership Project) LTE (Long Term Evolution) and LTE-Advanced activities work toward the evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA), and the solution of IMT-Advanced (International Mobile Telecommunications) and systems beyond. The combination of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple-input multiple-output) has been introduced into LTE and LTE-Advanced systems for achieving high system capacity. Furthermore, the closed-loop concept with codebook based precoding MIMO and transmission layers selection, termed as RI (rank indicator) selection have also been included to provide robust transmission in mobile wireless communication scenarios and increase the cell coverage. This manuscript focuses on the RI selection study and implementation in LTE and LTE-Advanced systems and illustrates the downlink performance evaluation and comparison with different RI selection schemes. According to the analytical and numerical results from an LTE and LTE-Advanced compliant simulator, the mutual information based scheme is chosen as the best candidate for RI selection.

On MIMO with successive interference cancellation applied to UTRA LTE

The long term evolution of UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access, abbreviated as UTRA LTE, makes use of OFDM (orthogonal frequency division multiplexing) combined with MIMO (multiple-input multiple-output), termed MIMO-OFDM. The potential maximization of transmitted data rates has been considered a most beneficial feature of MIMO schemes. This maximization shall be strived for by spatial multiplexing. In particular, high data rates in the downlink have been considered desirable. Also, in view of an efficient implementation, the downlink requires a thorough assessment. Therefore, the authors will discuss the deployment of spatial multiplexing in the UTRA LTE downlink and will show that the performance of successive interference cancellation (SIC) based data detection techniques for MIMO-OFDM is beneficial.

MIMO Schemes in UTRA LTE, A Comparison

The long term evolution of UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access, abbreviated as UTRA LTE, will be based on OFDM (orthogonal frequency division multiplexing). Furthermore, MIMO (multiple-input multiple-output) techniques have been considered as a means for the improvement of wireless connectivity. In wireless systems, high data rates in the downlink are desirable: Furthermore, with respect to an efficient implementation, the downlink requires a thorough assessment. In particular, the Alamouti and the V-BLAST (Vertical Bell Labs Layered Space Time) schemes are seen as interesting concepts. In this communication, the authors will compare these two MIMO schemes w.r.t. the achievable performance in the UTRA LTE downlink using up to two transmit and two receive antennas. Furthermore, the authors will discuss the deployment of spatial multiplexing in the UTRA LTE downlink and will show that the performance of successive interference cancellation (SIC) based data detection techniques for MIMO-OFDM is beneficial.

Leadless pacing using induction technology: impact of pulse shape and geometric factors on pacing efficiency

AIMS Leadless pacing can be done by transmitting energy by an alternating magnetic field from a subcutaneous transmitter unit (TU) to an endocardial receiver unit (RU). Safety and energy consumption are key issues that determine the clinical feasibility of this new technique. The aims of the study were (i) to evaluate the stimulation characteristics of the non-rectangular pacing pulses induced by the alternating magnetic field, (ii) to determine the extent and impact of RU movement caused by the beating heart, and (iii) to evaluate the influence of the relative position between TU and RU on pacing efficiency and energy consumption. METHODS AND RESULTS In the first step pacing efficiency and energy consumption for predefined positions were determined by bench testing. Subsequently, in a goat at five different ventricular sites (three in the right ventricle, two in the left ventricle) pacing thresholds using non-rectangular induction pulses were compared with conventional pulses. Relative position, defined by parallel distance, radial distance, and angulation between TU and RU, were determined in vivo by X-ray and an inclination angle measurement system. Bench testing showed that by magnetic induction for every alignment between TU and RU appropriate pulses can be produced up to a distance of 100 mm. In the animal experiment pacing thresholds were similar for non-rectangular pulses as compared with conventional pulse shapes. In all five positions with distances between 62 and 102 mm effective pacing was obtained in vivo. Variations in distance, displacement and angle caused by the beating heart did not cause loss of capture. At pacing threshold energy consumptions between 0.28 and 5.36 mJ were measured. Major determinants of energy consumption were distance and pacing threshold. CONCLUSION For any given RU position up to a distance of 100 mm reliable pacing using induction can be obtained. In anatomically crucial distances, up to 60 mm energy consumption is within a reasonable range.

Dynamic transmission mode selection in LTE/LTE-Advanced system

Recently, the LTE (Long Term Evolution) and LTE-Advanced systems, developed by the 3GPP (Third Generation Partnership Project), has been proposed as the candidate for the 4G systems (forth mobile communication systems). The combination of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple-input multiple-output) transmission technologies has been introduced into LTE systems for achieving high system performance required by 4G systems. Furthermore, the closed-loop concept with codebook based precoding MIMO and dynamic transmission mode selection, termed as RI (rank indicator) selection, have also been deployed in LTE systems to provide robust link connection and large cell coverage. In this manuscript, the authors focused on the study of dynamic transmission mode selection and its implementation in LTE systems. Different RI selection schemes were proposed in this manuscript with the corresponding downlink performance evaluation. According to the analytical and numerical results, the authors conclude that the mutual information based scheme is the best candidate for RI selection in LTE/LTE-Advanced compliant systems.

Feedback Generation for CoMP Transmission in Unsynchronized Networks with Timing Offset

Coordinated multipoint (CoMP) transmission is a promising technique in long term evolution (LTE) systems to provide coverage and broadband communication for cell edge user equipments (UEs). However, as signals from multiple transmitters may reach the UE at different times, CoMP networks might experience high time offsets, leading to significant performance loss in closed-loop transmission. In this paper we show that spacing between reference signals (RSs) imposes a phase offset on the transmit covariance matrix in presence of timing offset (TO), affecting the feedback generation. The promised advantages of closed-loop CoMP transmission vanish in presence of TO due to improper precoding matrix index (PMI) selection. Keeping the phase shift close to zero, reliable PMI selection can be guaranteed and as a result near optimum performance is achieved for closed-loop CoMP transmission in unsynchronized networks with TO present.

Analysis of CQI Prediction for MU-MIMO in LTE Systems

The aim of this paper is to get an insight of multiuser multiple-input and multiple-output (MU-MIMO) channel quality indicator (CQI) prediction for long term evolution (LTE) systems. MU-MIMO CQI predictions have been investigated for LTE Release 8 (rank one, Transmission Mode 5) and for LTE Release 9 (adaptive rank, Transmission Mode 8) at the link level. The relationship between CQI reporting and channel conditions is analytically analysed and demonstrated. The tradeoff between the performance gain and the feedback overhead w.r.t. MUMIMO CQI prediction is investigated as well. The results have shown how MU-MIMO CQI prediction is influenced by channel correlation and that significant improvements can be achieved through rank adaption and receiver choice. The results have also shown the potentially most efficient system configuration (feedback design and CQI prediction scheme) to facilitate MUMIMO transmission for practical LTE systems.