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Optimal linear precoding in multiuser MIMO systems: A large system analysis
 in Proceedings of Globecom 2014
, 2014
"... Abstract—We consider the downlink of a singlecell multiuser MIMO system in which the base station makes use of N antennas to communicate with K singleantenna user equipments (UEs) randomly positioned in the coverage area. In particular, we focus on the problem of designing the optimal linear prec ..."
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Abstract—We consider the downlink of a singlecell multiuser MIMO system in which the base station makes use of N antennas to communicate with K singleantenna user equipments (UEs) randomly positioned in the coverage area. In particular, we focus on the problem of designing the optimal linear precoding for minimizing the total power consumption while satisfying a set of target signaltointerferenceplusnoise ratios (SINRs). To gain insights into the structure of the optimal solution and reduce the computational complexity for its evaluation, we analyze the asymptotic regime where N and K grow large with a given ratio and make use of recent results from large system analysis to compute the asymptotic solution. Then, we concentrate on the asymptotically design of heuristic linear precoding techniques. Interestingly, it turns out that the regularized zeroforcing (RZF) precoder is equivalent to the optimal one when the ratio between the SINR requirement and the average channel attenuation is the same for all UEs. If this condition does not hold true but only the same SINR constraint is imposed for all UEs, then the RZF can be modified to still achieve optimality if statistical information of the UE positions is available at the BS. Numerical results are used to evaluate the performance gap in the finite system regime and to make comparisons among the precoding techniques. I.
Interference management in 5G reverse TDD HetNets: A large system analysis
 IEEE J. SEL. AREAS COMMUN
, 2014
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1Large System Analysis of Base Station Cooperation for Power Minimization
"... IEEE Abstract—This work focuses on a largescale multicell multiuser MIMO system in which L base stations (BSs) of N antennas each communicate with K singleantenna user equipments. We consider the design of the linear precoder that minimizes the total power consumption while ensuring target user ..."
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IEEE Abstract—This work focuses on a largescale multicell multiuser MIMO system in which L base stations (BSs) of N antennas each communicate with K singleantenna user equipments. We consider the design of the linear precoder that minimizes the total power consumption while ensuring target user rates. Three configurations with different degrees of cooperation among BSs are considered: the coordinated beamforming scheme (only channel state information is shared among BSs), the coordinated multipoint MIMO processing technology or network MIMO (channel state and data cooperation), and a single cell beamforming scheme (only local channel state information is used for beamforming while channel state cooperation is needed for power allocation). The analysis is conducted assuming that N and K grow large with a non trivial ratio K/N and imperfect channel state information (modeled by the generic GaussMarkov formulation form) is available at the BSs. Tools of random matrix theory are used to compute, in explicit form, deterministic approximations for: (i) the parameters of the optimal precoder; (ii) the powers needed to ensure target rates; and (iii) the total transmit power. These results are instrumental to get further insight into the structure of the optimal precoders and also to reduce the implementation complexity in largescale networks. Numerical results are used to validate the asymptotic analysis in the finite system regime and to make comparisons among the different configurations. I.
Deterministic Equivalent for MaxMin SINR over Random User Locations
"... AbstractThe maxmin signaltointerferenceplusnoise ratio (SINR) problem is considered in a coordinated network wherein L base stations (BSs) each equipped with N antennas serve in total K singleantenna users that are uniformly distributed in the network. We conduct the analysis in the asymptot ..."
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AbstractThe maxmin signaltointerferenceplusnoise ratio (SINR) problem is considered in a coordinated network wherein L base stations (BSs) each equipped with N antennas serve in total K singleantenna users that are uniformly distributed in the network. We conduct the analysis in the asymptotic regime in which N and K grow large to compute a deterministic approximation for the maxmin SINR. The results are independent from fastfading and users' locations and thus allow one to determine the optimal maxmin SINR given basic system parameters such as cell radius, K, N and pathloss exponent. The provided framework can be utilized for analyzing the problem without the need to run system level simulations and for finding the optimal N , K, resource allocation and BS placement. Numerical results are used to validate the analytical results in a finite system regime and to evaluate the effects of system parameters on the system performance.
Large System Analysis of Base Station Cooperation for Power Minimization
"... AbstractThis work focuses on a largescale multicell multiuser MIMO system in which L base stations (BSs) of N antennas each communicate with K singleantenna user equipments. We consider the design of the linear precoder that minimizes the total power consumption while ensuring target user rates ..."
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AbstractThis work focuses on a largescale multicell multiuser MIMO system in which L base stations (BSs) of N antennas each communicate with K singleantenna user equipments. We consider the design of the linear precoder that minimizes the total power consumption while ensuring target user rates. Three configurations with different degrees of cooperation among BSs are considered: the coordinated beamforming scheme (only channel state information is shared among BSs), the coordinated multipoint MIMO processing technology or network MIMO (channel state and data cooperation), and a single cell beamforming scheme (only local channel state information is used for beamforming while channel state cooperation is needed for power allocation). The analysis is conducted assuming that N and K grow large with a non trivial ratio K/N and imperfect channel state information (modeled by the generic GaussMarkov formulation form) is available at the BSs. Tools of random matrix theory are used to compute, in explicit form, deterministic approximations for: (i) the parameters of the optimal precoder; (ii) the powers needed to ensure target rates; and (iii) the total transmit power. These results are instrumental to get further insight into the structure of the optimal precoders and also to reduce the implementation complexity in largescale networks. Numerical results are used to validate the asymptotic analysis in the finite system regime and to make comparisons among the different configurations.
MaxMin SINR Low Complexity Transceiver Design for Single Cell Massive MIMO
"... AbstractThis work focuses on large scale multiuser MIMO systems in which the base station (BS) outfitted with M antennas communicates with K single antenna user equipments (UEs). In particular, we aim at designing the linear precoder and receiver that maximizes the minimum signaltointerference ..."
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AbstractThis work focuses on large scale multiuser MIMO systems in which the base station (BS) outfitted with M antennas communicates with K single antenna user equipments (UEs). In particular, we aim at designing the linear precoder and receiver that maximizes the minimum signaltointerferenceplusnoise ratio (SINR) subject to a given power constraint. To gain insights into the structure of the optimal precoder and receiver as well as to reduce the computational complexity for their implementation, we analyze the asymptotic regime where M and K grow large with a given ratio and make use of random matrix theory (RMT) tools to compute accurate approximations. Although simpler, the implementation of the asymptotic precoder and receiver requires fast inversions of large matrices in every coherence period. To overcome this issue, we apply the truncated polynomial expansion (TPE) technique to the precoding and receiving vector of each UE and make use of RMT to determine the optimal weighting coefficients on a perUE basis that asymptotically solve the maxmin SINR problem. Numerical results are used to show that the proposed TPEbased precoder and receiver almost achieve the same performance as the optimal ones while requiring a lower complexity.
Interference Management in 5G Reverse TDD HetNets with Wireless Backhaul: A Large System Analysis
"... AbstractThis work analyzes a heterogeneous network (HetNet), which comprises a macro base station (BS) equipped with a large number of antennas and an overlaid dense tier of small cell access points (SCAs) using a wireless backhaul for data traffic. The static and low mobility user equipment termi ..."
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AbstractThis work analyzes a heterogeneous network (HetNet), which comprises a macro base station (BS) equipped with a large number of antennas and an overlaid dense tier of small cell access points (SCAs) using a wireless backhaul for data traffic. The static and low mobility user equipment terminals (UEs) are associated with the SCAs while those with mediumtohigh mobility are served by the macro BS. A reverse time division duplexing (TDD) protocol is used by the two tiers, which allows the BS to locally estimate both the intratier and intertier channels. This knowledge is then used at the BS either in the uplink (UL) or in the downlink (DL) to simultaneously serve the macro UEs (MUEs) and to provide the wireless backhaul to SCAs. A concatenated linear precoding technique employing either zeroforcing (ZF) or regularized ZF is used at the BS to simultaneously serve MUEs and SCAs in DL while nulling interference toward those SCAs in UL. We evaluate and characterize the performance of the system through the power consumption of UL and DL transmissions under the assumption that target rates must be satisfied and imperfect channel state information is available for MUEs. The analysis is conducted in the asymptotic regime where the number of BS antennas and the network size (MUEs and SCAs) grow large with fixed ratios. Results from large system analysis are used to provide concise formulae for the asymptotic UL and DL transmit powers and precoding vectors under the above assumptions. Numerical results are used to validate the analysis in different settings and to make comparisons with alternative network architectures.
1Power Efficient Low Complexity Precoding for Massive MIMO Systems
"... Abstract—This work aims at designing a lowcomplexity precoding technique in the downlink of a largescale multipleinput multipleoutput (MIMO) system in which the base station (BS) is equipped with M antennas to serve K singleantenna user equipments. This is motivated by the high computational co ..."
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Abstract—This work aims at designing a lowcomplexity precoding technique in the downlink of a largescale multipleinput multipleoutput (MIMO) system in which the base station (BS) is equipped with M antennas to serve K singleantenna user equipments. This is motivated by the high computational complexity required by the widely used zeroforcing or regularized zeroforcing precoding techniques, especially when K grows large. To reduce the computational burden, we adopt a precoding technique based on truncated polynomial expansion (TPE) and make use of the asymptotic analysis to compute the deterministic equivalents of its corresponding signaltointerferenceplusnoise ratios (SINRs) and transmit power. The asymptotic analysis is conducted in the regime in which M and K tend to infinity with the same pace under the assumption that imperfect channel state information is available at the BS. The results are then used to compute the TPE weights that minimize the asymptotic transmit power while meeting a set of target SINR constraints. Numerical simulations are used to validate the theoretical analysis. I.