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**11 - 15**of**15**### 1Traffic-Aware Training and Scheduling for MISO Wireless Downlink Systems

"... In this paper, the problem of feedback and active user selection in MISO wireless systems such that the system’s stability region is as big as possible is examined. The focus is on a system in a Rayleigh fading environment where zero forcing precoding is used to serve all active users in every slot. ..."

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In this paper, the problem of feedback and active user selection in MISO wireless systems such that the system’s stability region is as big as possible is examined. The focus is on a system in a Rayleigh fading environment where zero forcing precoding is used to serve all active users in every slot. Acquisition of the channel states is done via uplink training in Time Division Duplexing mode by the active users. Clearly, only a subset of users can perform uplink training and the selection of this subset is a challenging and interesting problem especially in MISO systems. The stability regions of a baseline centralized scheme and two novel decentralized policies are examined analytically. In the decentralized schemes, the transmitter broadcasts periodically the queue state information and the users contend for the channel in a CSMA-based manner with parameters based on the outdated queue state information and real-time channel state information. We show that, using infrequent signaling between the base station and the users, the decentralized policies outperform the centralized policy. In addition a threshold-based user selection and training scheme for discrete-time contention is proposed. The results of this work imply that, as far as stability is concerned, the users must be involved in the active user selection and

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"... The exponentially increasing demand for wireless data services requires amassive network densification that is neither economically nor ecologicallyviable with the current cellular system architectures. A promising solution tothis problem is the concept of small-cell networks (SCNs), which is founde ..."

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The exponentially increasing demand for wireless data services requires amassive network densification that is neither economically nor ecologicallyviable with the current cellular system architectures. A promising solution tothis problem is the concept of small-cell networks (SCNs), which is founded by the idea of a very dense deployment of self-organizing, low-cost, low-power,

### 1Asymptotic Analysis of Downlink Multi-cell Systems with Partial CSIT

"... Abstract—We analyze the downlink of multiple input multiple output (MIMO) multicell systems in the presence of inter-cell interference (ICI), under different transmit channel state information (CSI) assumptions. We assume, for the first scenario, that the Base Stations (BSs) have only the statistica ..."

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Abstract—We analyze the downlink of multiple input multiple output (MIMO) multicell systems in the presence of inter-cell interference (ICI), under different transmit channel state information (CSI) assumptions. We assume, for the first scenario, that the Base Stations (BSs) have only the statistical CSI of all the channels. For the second scenario, we assume that the BSs have perfect CSI of their User Terminals(UTs) but only the statistical CSI of channels of the interfering BSs. We consider the following receiver structures at the UTs a) Optimal Decoding b) Minimum Mean Square (MMSE) receiver. We derive analytical expressions to compute the optimal number of streams each BS must use in order to maximize the total spectral efficiency of the system. We perform our analysis in the large dimensional regime (assuming the number of antennas on the BSs and UTs approaching infinity, at the same rate) using results from random matrix theory (RMT). However, the asymptotic results provide close approximation in the finite dimensional scenario. Remarkably, in the asymptotic regime, the optimization parameters depend only on the channel statistics and not on the instantaneous CSI, thus enabling a decentralized resource allocation policy in a multicell scenario. Our results show that in an interference limited regime, it is optimal for the BSs to use only a small subset of its streams to maximize the total spectral efficiency of the system. I.

### Joint Signal and Channel State Information Compression for the Backhaul of Uplink Network MIMO Systems

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