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User Scheduling for Heterogeneous Multiuser MIMO Systems: A Subspace Viewpoint  [PDF]
Xinping Yi,Edward Au
Mathematics , 2011,
Abstract: In downlink multiuser multiple-input multiple-output (MU-MIMO) systems, users are practically heterogeneous in nature. However, most of the existing user scheduling algorithms are designed with an implicit assumption that the users are homogeneous. In this paper, we revisit the problem by exploring the characteristics of heterogeneous users from a subspace point of view. With an objective of minimizing interference non-orthogonality among users, three new angular-based user scheduling criteria that can be applied in various user scheduling algorithms are proposed. While the first criterion is heuristically determined by identifying the incapability of largest principal angle to characterize the subspace correlation and hence the interference non-orthogonality between users, the second and third ones are derived by using, respectively, the sum rate capacity bounds with block diagonalization and the change in capacity by adding a new user into an existing user subset. Aiming at capturing fairness among heterogeneous users while maintaining multiuser diversity gain, two new hybrid user scheduling algorithms are also proposed whose computational complexities are only linearly proportional to the number of users. We show by simulations that the effectiveness of our proposed user scheduling criteria and algorithms with respect to those commonly used in homogeneous environment.
Energy-Efficient Design of MIMO Heterogeneous Networks with Wireless Backhaul  [PDF]
Howard H. Yang,Giovanni Geraci,Tony Q. S. Quek
Mathematics , 2015,
Abstract: As future networks aim to meet the ever-increasing requirements of high data rate applications, dense and heterogeneous networks (HetNets) will be deployed to provide better coverage and throughput. Besides the important implications for energy consumption, the trend towards densification calls for more and more wireless links to forward a massive backhaul traffic into the core network. It is critically important to take into account the presence of a wireless backhaul for the energy-efficient design of HetNets. In this paper, we provide a general framework to analyze the energy efficiency of a two-tier MIMO heterogeneous network with wireless backhaul in the presence of both uplink and downlink transmissions. We find that under spatial multiplexing the energy efficiency of a HetNet is sensitive to the network load, and it should be taken into account when controlling the number of users served by each base station. We show that a two-tier HetNet with wireless backhaul can be significantly more energy efficient than a one-tier cellular network. However, this requires the bandwidth division between radio access links and wireless backhaul to be optimally designed according to the load conditions.
Optimized Training and Feedback for MIMO Downlink Channels  [PDF]
Mari Kobayashi,Nihar Jindal,Giuseppe Caire
Mathematics , 2009,
Abstract: We consider a MIMO fading broadcast channel where channel state information is acquired at user terminals via downlink training and channel feedback is used to provide transmitter channel state information (CSIT) to the base station. The feedback channel (the corresponding uplink) is modeled as an AWGN channel, orthogonal across users. The total bandwidth consumed is the sum of the bandwidth/resources used for downlink training, channel feedback, and data transmission. Assuming that the channel follows a block fading model and that zeroforcing beamforming is used, we optimize the net achievable rate for unquantized (analog) and quantized (digital) channel feedback. The optimal number of downlink training pilots is seen to be essentially the same for both feedback techniques, but digital feedback is shown to provide a larger net rate than analog feedback.
Research on Downlink Precoding for Interference Cancellation in Massive MIMO Heterogeneous UDN  [PDF]
Hua He He, Jing Jiang, Rong Jin
Journal of Applied Mathematics and Physics (JAMP) , 2018, DOI: 10.4236/jamp.2018.61026
Abstract: In order to solve the data surge brought by largescale increasing of mobile de-vices, Massive MIMO ultra dense networking can greatly improve the system spectral efficiency and energy efficiency. It plays an important role in coping with the exponential growth of the business, but also brought big problems and challenges. For heterogeneous ultra dense networks, both macro and femto users are facing with both the cross-layer interference and co-layer in-terference. The precoding technology studied in this paper resolves the cross-layer interference and co-layer interference for macro users and femto users, and lays a theoretical foundation for the deployment of heterogeneous and ultra dense networks.
A Hybrid Genetic Scheduling Algorithm to Heterogeneous Distributed System  [PDF]
Yan Kang, Defu Zhang
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.37111
Abstract: In parallel and distributed computing, development of an efficient static task scheduling algorithm for directed acyclic graph (DAG) applications is an important problem. The static task scheduling problem is NP-complete in its general form. The complexity of the problem increases when task scheduling is to be done in a heterogeneous environment, consisting of processors with varying processing capabilities and network links with varying bandwidths. List scheduling algorithms are generally preferred since they generate good quality schedules with less complexity. But these list algorithms leave a lot of room for improvement, especially when these algorithms are used in specialized heterogeneous environments This paper presents an hybrid genetic task scheduling algorithm for the tasks run on the network of heterogeneous systems and represented by Directed Acyclic Graphs (DAGs). First, the algorithm assigns a coupling factor to each task to present the tasks should be scheduled onto the same processor by avoiding the large communication time. Second, the algorithm generate some high quality initial solution by scheduling the tasks which are strongly coupled with each other onto the same processor, and improve the quality of the solution by using coupling initial solutions, random solution, near optimal solutions obtained by the list scheduling algorithm in the crossover and mutation operator. The performance of the algorithm is illustrated by comparing with the existing effectively scheduling algorithms.
Feedback Reduction for MIMO Broadcast Channel with Heterogeneous Fading  [PDF]
Jin-Hao Li,Hsuan-Jung Su
Mathematics , 2011,
Abstract: This paper considers feedback load reduction for multiuser multiple input multiple output (MIMO) broadcast channel where the users' channel distributions are not homogeneous. A cluster-based feedback scheme is proposed such that the range of possible signal-to-noise ratio (SNR) of the users are divided into several clusters according to the order statistics of the users' SNRs. Each cluster has a corresponding threshold, and the users compare their measured instantaneous SNRs with the thresholds to determine whether and how many bits they should use to feed back their instantaneous SNRs. If a user's instantaneous SNR is lower than a certain threshold, the user does not feed back. Feedback load reduction is thus achieved. For a given number of clusters, the sum rate loss using the cluster-based feedback scheme is investigated. Then the minimum number of clusters given a maximum tolerable sum rate loss is derived. Through simulations, it is shown that, when the number of users is large, full multiuser diversity can be achieved by the proposed feedback scheme, which is more efficient than the conventional schemes.
Adaptive Pilot Clustering in Heterogeneous Massive MIMO Networks  [PDF]
Rami Mochaourab,Emil Bj?rnson,Mats Bengtsson
Mathematics , 2015,
Abstract: We consider the uplink of a cellular massive MIMO network. Acquiring channel state information at the base stations (BSs) requires uplink pilot signaling. Since the number of orthogonal pilot sequences is limited by the channel coherence, pilot reuse across cells is necessary to achieve high spectral efficiency. However, finding efficient pilot reuse patterns is non-trivial especially in practical asymmetric BS deployments. We approach this problem using coalitional game theory. Each BS has a few unique pilots and can form coalitions with other BSs to gain access to more pilots. The BSs in a coalition thus benefit from serving more users in their cells, at the expense of higher pilot contamination and interference. Given that a cell's average spectral efficiency depends on the overall pilot reuse pattern, the suitable coalitional game model is in partition form. We develop a low-complexity distributed coalition formation based on individual stability. By incorporating a searching budget constraint for each BS, we are able to control the algorithm's complexity and ensure its convergence to a solution of the game called individually stable coalition structure. Simulation results reveal fast algorithmic convergence and substantial performance gains over the baseline schemes with no pilot reuse, full pilot reuse, or random pilot reuse pattern.
Interference Alignment for Partially Connected MIMO Cellular Networks  [PDF]
Liangzhong Ruan,Vincent K. N. Lau
Mathematics , 2012, DOI: 10.1109/TSP.2012.2192432
Abstract: In this paper, we propose an iterative interference alignment (IA) algorithm for MIMO cellular networks with partial connectivity, which is induced by heterogeneous path losses and spatial correlation. Such systems impose several key technical challenges in the IA algorithm design, namely the overlapping between the direct and interfering links due to the MIMO cellular topology as well as how to exploit the partial connectivity. We shall address these challenges and propose a three stage IA algorithm. As illustration, we analyze the achievable degree of freedom (DoF) of the proposed algorithm for a symmetric partially connected MIMO cellular network. We show that there is significant DoF gain compared with conventional IA algorithms due to partial connectivity. The derived DoF bound is also backward compatible with that achieved on fully connected K-pair MIMO interference channels.
MIMO Hardware Simulator: Algorithm Design for Heterogeneous Environments  [PDF]
Bachir Habib, Gheorghe Zaharia, Ghais El Zein
Circuits and Systems (CS) , 2013, DOI: 10.4236/cs.2013.42029

A wireless communication system can be tested either in actual conditions or by a hardware simulator reproducing actual conditions. With a hardware simulator it is possible to freely simulate a desired type of a radio channel and making it possible to test “on table” mobile radio equipment. This paper presents an architecture for the digital block of a hardware simulator of MIMO propagation channels. This simulator can be used for LTE and WLAN IEEE 802.11ac applications, in indoor and outdoor environments. However, in this paper, specific architecture of the digital block of the simulator is presented to characterize a scenario indoor to outdoor using TGn channel models. The switching between each environment in the scenario must be made in a continuous manner. Therefore, an algorithm is designed to pass from a considered impulse response in the environment to another in other environment. The architecture of the digital block of the hardware simulator is presented and implemented on a Xilinx Virtex-IV FPGA. Moreover, the impulse responses are transferred into the simulator. The accuracy, the occupation on the FPGA and the latency of the architecture are analyzed.

An Efficient Searching and an Optimized Cache Coherence handling Scheme on DSR Routing Protocol for MANETS  [PDF]
Rajneesh Kumar Gujral,Anil Kapil
International Journal of Computer Science Issues , 2011,
Abstract: Mobile ad hoc networks (MANETS) are self-created and self organized by a collection of mobile nodes, interconnected by multi-hop wireless paths in a strictly peer to peer fashion. DSR (Dynamic Source Routing) is an on-demand routing protocol for wireless ad hoc networks that floods route requests when the route is needed. Route caches in intermediate mobile node on DSR are used to reduce flooding of route requests. But with the increase in network size, node mobility and local cache of every mobile node cached route quickly become stale or inefficient. In this paper, for efficient searching, we have proposed a generic searching algorithm on associative cache memory organization to faster searching single/multiple paths for destination if exist in intermediate mobile node cache with a complexity O(n) (Where n is number of bits required to represent the searched field).The other major problem of DSR is that the route maintenance mechanism does not locally repair a broken link and Stale cache information could also result in inconsistencies during the route discovery /reconstruction phase. So to deal this, we have proposed an optimized cache coherence handling scheme for on -demand routing protocol (DSR).
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