Adaptive Multicell 3D Beamforming in Multi-Antenna Cellular Networks

We consider a cellular network with multi-antenna base stations (BSs) and single-antenna users, multicell cooperation, imperfect channel state information, and directional antennas each with a vertically adjustable beam. We investigate the impact of the elevation angle of the BS antenna pattern, denoted as tilt, on the performance of the considered network when employing either a conventional single-cell transmission or a fully cooperative multicell transmission. Using the results of this investigation, we propose a novel hybrid multicell cooperation technique in which the intercell interference is controlled via either cooperative beamforming in the horizontal plane or coordinated beamfroming in the vertical plane of the wireless channel, denoted as adaptive multicell 3D beamforming. The main idea is to divide the coverage area into two disjoint vertical regions and adapt the multicell cooperation strategy at the BSs when serving each region. A fair scheduler is used to share the time-slots between the vertical regions. It is shown that the proposed technique can achieve performance comparable to that of a fully cooperative transmission but with a significantly lower complexity and signaling requirements. To make the performance analysis computationally efficient, analytical expressions for the user ergodic rates under different beamforming strategies are also derived.Comment: Accepted for publication in IEEE Transaction on Vehicular Technolog

Coordinated user scheduling in the multi-cell MIMO downlink

We propose a novel, coordinated user scheduling (CUS) algorithm for inter-cell interference (ICI) mitigation in the downlink of a multi-cell multi-user MIMO system. In the proposed algorithm, ICI mitigation is performed through the exchange of necessary channel state information (CSI) among the base stations, and the revision of the scheduling decisions and beamformer designs at each base station. Furthermore, ICI mitigation is performed only for the cell-edge users so that the amount of inter-base station signaling overhead is minimized. Our simulation results demonstrate that the proposed coordination scheduling algorithm significantly improves the cell-edge users' throughput compared to conventional systems with only a negligible amount of CSI sharing among the base stations and a relatively small throughput loss for the cell-interior users

An Efficient Signaling for Multi-mode Transmission in Multi-user MIMO

In this paper the downlink of a multi-user MIMO (MUMIMO) system with multi-mode transmission is considered. We propose a low-complexity algorithm for selecting users and the corresponding number of data streams to each user, denoted as user transmission mode (UTM). The selection is only based on the average received signal-to-noise ratio (SNR) from the base station (BS) for each user. This reduces the overall amount of feedback for scheduling, as opposed to techniques that assume perfect instantaneous channel state information (CSI) from all users. Analytical average throughput approximations are derived for each user at different UTMs. Simulation results demonstrate that the proposed algorithm provides performance close to dirty paper coding (DPC) with considerably reduced feedback

Protective effects of hydrogen sulfide on chronic kidney disease by reducing oxidative stress, inflammation and apoptosis

The current study aimed to examine the renoprotective effects of long-term treatment with sodium hydrosulfide (NaHS), a prominent hydrogen sulfide donor, in 5/6 nephrectomy animal model. Twenty-four rats were randomly divided into 3 groups including sham-operated group (Sham), 5/6-nephrectomized group (5/6 Nx), and NaHStreated group (5/6Nx+NaHS). NaHS (30 micromol/l) was added twice daily into the drinking water and renal failure was induced by 5/6 nephrectomy. Twelve weeks after surgical procedure, blood pressure, creatinine clearance (CCr), urine concentration of neutrophil gelatinase associated lipocalin (NGAL) and tissue concentration of malondialdehyde (MDA), superoxide dismutase (SOD), as well as renal morphological changes, apoptosis (cleaved caspase-3) and inflammation (p-NF-κB) were measured. Five-sixth nephrectomy induced severe renal damage as indicated by renal dysfunction, hypertension and significant histopathological injury which were associated with increased NGAL and MDA levels, oxidant/antioxidant imbalance, decreased SOD activity and CCr and also overexpression of p-NF-κB and cleaved caspase-3 proteins. Instead, NaHS treatment attenuated renal dysfunction through reduction of NGAL concentration, hypertension, CCr, oxidant/antioxidant imbalance, inflammation and apoptosis. These findings suggest that long term NaHS treatment can be useful in preventing the progression of CKD by improving oxidant/antioxidant balance and reducing inflammation and apoptosis in the kidney

Effects of Monensin on Metabolism and Production in Dairy Saanen Goats in Periparturient Period

This trial evaluated the effects of dietary supplementation with monensin sodium on dry matter intake, metabolic parameters and milk yield and milk composition of dairy Saanen goats in the periparturient period. Twelve Saanen pregnant dairy goats were assigned to a treatment and a control group. Saanen goats were fed monensin as its 10% sodium salt in the amount of 33 mg/kg of total dry matter intake during 30 d before parturition till d 42 in milk. Blood samples were collected from each goat at d 30, 15 and 7 before expected kidding time and also in d 1, 7, 13, 19, 21, 28, 35 and 42 postpartum. The serum concentrations of β-Hydroxybutyrate (BHBA), non-esterifed fatty acid (NEFA), calcium, magnesium, inorganic phosphorus, cholesterol, triglyceride, urea, total protein, albumin and glucose and aspartate aminotransferase (AST) activity were determined. The BHBA concentration significantly decreased in goats, which received monensin in comparison to controls in the postpartum period (p = 0.049). The concentration of sodium (Na) was significantly influenced by monensin treatment in the postpartum period (p = 0.048). In addition, the difference in dry matter intake was highly significant between the two groups during the pre-partum period. Controls had more dry matter intake (DMI) than treatment goats (p = 0.0001). Mean 3.5% fat corrected milk production was not influenced by monensin treatment. However, milk fat percentage was significantly decreased in monensin treated goats (p = 0.0017)

Base Station Coordination in Multicell MIMO Networks

The use of multi-antenna technology, also referred to as multiple-input multipleoutput (MIMO), has been shown to improve both the achievable data rates and the link reliability in single-cell wireless systems without a need for extra power or bandwidth. The promised gains of MIMO techniques are, however, severely degraded in a multicell environment due to the presence of intercell interference,especially for users at the cell edge. One efficient technique to combat intercell interference is via exploiting coordination among multiple base stations, which is known as multicell processing or simply base station coordination. This thesis investigates the design and the performance of practically implementablebase station coordination schemes. The main contribution of this thesis is to formally study different types of coordination, to develop analytical tools for their performance evaluation, and to propose simple algorithms for their implementation. First, we focus on the most complex form of coordination, namely the networkMIMO. In this scheme all coordinating base stations share the data and the channel state information of all users, and act as a single distributed multi-antennatransmitter to serve them. We develop an analytical framework to facilitate the ergodic rate analysis of such a system under linear precoding. We also proposea simple scheduling algorithm, which only requires the knowledge of long-term channel statistics.In the next stage, we consider a simpler form of coordination in which the data of each user is served only by one base station. The scheduling and beamformingdesign, however, can be shared among the coordinating base stations.For this scheme, we propose a low-complexity joint user scheduling and beamforming strategy selection which requires a limited level of inter-base station informationexchange, while providing significant performance improvement over non-coordinated systems.Finally, we investigate the effect of the antenna elevation tuning parameter, referred to as antenna tilt, on the performance of multicell multiple-input singleoutput(MISO) systems. We propose a framework in which multiple base stations jointly adjust their tilt angles based on the location of the scheduled users to maximize their sum throughput. We also provide an analytical expression forthe sum throughput, enabling the decentralized implementation of the proposed scheme at each base station

Scheduling and Base-Station Cooperation in MIMO Downlink Systems

Multiple input multiple output (MIMO) techniques have been shown to improvethe capacity and link reliability of wireless communication without a need to extrapower and bandwidth. In multi-user (MU) MIMO networks, a linear increaseof sum capacity in the number of transmit antennas can be achieved by usinglinear precoding combined with efficient scheduling algorithms. However, thepromising capacity gain of MU-MIMO techniques, when deployed in a multicellenvironment, is severely degraded due to other-cell interference (OCI). Thisis especially important near the cell boundaries. Furthermore, most of thesetechniques assume that perfect channel state information (CSI) is available at thetransmitter, which is very difficult to obtain.In order to increase the capacity of a cellular system, base-station (BS) cooperationcan be used to jointly transmit/receive to/from one or multiple usersin the downlink/uplink. This thesis investigates the design and performance ofspectrally-efficient MU-MIMO downlink systems with BS cooperation under morepractical scheduling algorithms with a limited feedback. Three contributions areincluded in the thesis.In Paper A the performance of a distributed antenna system (DAS) undertime-varying frequency-selective fading based on a realistic channel model is investigated.A new cellular layout is obtained by shifting the hexagonal cellularlayout in the conventional system and without a need for additional BS towers.The results show that, with the same total transmit power and bandwidth, DAScan reduce the OCI in a multi-cell environment and improve the outage capacityespecially near the cell boundary.In Paper B a low-complexity space-frequency scheduling algorithm for thedownlink of a cluster-based MU-MIMO with BS cooperation is presented. Inthe proposed algorithm, users are grouped based on the large-scale CSI fromsurrounding BSs. As the cooperation is done adaptively among BSs, there is noneed for perfect CSI from all BSs, which leads to a limited backbone overhead aswell as to reduced computational complexity.In Paper C a low-complexity algorithm for selecting users and their correspondingnumber of data streams, denoted as user transmission mode (UTM), isproposed for the downlink of a MU-MIMO system. The selection is only basedon the average received signal-to-noise ratio (SNR) from the base station (BS)for each user, which reduces the amount of feedback for scheduling. Analyticalaverage throughput approximations are derived for each user at different UTMs.Simulation results demonstrate that the proposed algorithm provides performanceclose to dirty paper coding (DPC) with considerably reduced feedback

Throughput optimization in MU-MIMO systems via exploiting bs antenna tilt

In this paper, we propose a novel framework to enhance the throughput in a single-cell multiuser multiple-input multiple-output (MU-MIMO) system via adaptive base station (BS) antenna tilting. The key idea is to partition the cell into so-called vertical regions and to apply one out of a finite number of tilt and vertical half-power beamwidth (HPBW) pairs at the BS when serving each vertical region. This strategy results in an increased average received signal-to-noise ratio (SNR) over the coverage area. A scheduler is then employed to schedule the transmission to one of the vertical regions at each time-slot with the objective to maximize a suitable utility function of users' achievable throughput. MU-MIMO zero-forcing beamforming in the horizontal plane is used at the BS to serve the users in each vertical region. Simulation results show that the proposed adaptive BS tilting scheme is a promising approach to provide a noticeable throughput gain compared to a conventional scheme employing a fixed tilt at the BS. The proposed framework also achieves a superior performance-complexity tradeoff compared to a conventional system in which the tilt can be adapted to the location of the served users at each time-slot

Throughput Optimization for MISO Interference Channels via Coordinated User-Specific Tilting

In this letter, we propose a novel framework to enhance the throughput in multiple-input single-output (MISO) mutually interfering channels via selecting the tilt angles at all base stations (BSs) in a coordinated fashion. In the proposed framework, multiple BSs adjust their tilt angles jointly to maximize the sum throughput of the scheduled users, denoted as coordinated user-specific tilting. Assuming the availability of location information of the scheduled users at all BSs, accurate analytical expression for user ergodic rate is provided, which enables a decentralized deployment of the proposed framework at each BS. Simulation results show that the proposed coordinated user-specific tilting scheme outperforms the conventional schemes employing a fixed tilt angle at each BS