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A distributed energy efficient beamforming algorithm was studied for multicell multiuser downlink communication system.Firstly,the energy efficient optimization problem was first considered as the maximization of the ratio between the system sum rate and the system power consumption.The fractional programming optimization target was then transformed into a subtractive form via using the fractional programming theorem.Secondly,the problem was decomposed into some subproblems that can be solved respectively by introducing the concept of the interference temperature in cognitive radio networks.Finally,an effective distributed energy efficient beamforming algorithm was proposed by exploiting the Lagrangian duality theorem and optimization theorem.Compared to the classical energy efficient optimization algorithm,the proposed algorithm can achieve an obvious energy efficiency performance gain.

A distributed energy efficient beamforming algorithm was studied for multicell multiuser downlink communication system.Firstly,the energy efficient optimization problem was first considered as the maximization of the ratio between the system sum rate and the system power consumption.The fractional programming optimization target was then transformed into a subtractive form via using the fractional programming theorem.Secondly,the problem was decomposed into some subproblems that can be solved respectively by introducing the concept of the interference temperature in cognitive radio networks.Finally,an effective distributed energy efficient beamforming algorithm was proposed by exploiting the Lagrangian duality theorem and optimization theorem.Compared to the classical energy efficient optimization algorithm,the proposed algorithm can achieve an obvious energy efficiency performance gain.

An algorithm is proposed for energy-efficient resource allocation scheme in massive MIMO OFDMA downlink mobile communication system.A mathematical formulation of optimization issue is provided with the objective of maximizing system energy efficiency lower bound under the minimum data rate requirement of user,meanwhile the BS uses a zero-forcing(ZF) precoding.And then for optimizing energy efficiency function,the bandwidth allocation,power allocation and the number of antenna arrays at the BS are adjusted synchronously.First,an iterative algorithm derived from optimality condition for bandwidth assignment is proposed.Second,the properties of fractional programming and convex optimization are used to maximize the energy efficiency.Specifically,both the number of antenna arrays at the BS and the transmit data rate at the user are adjusted.Simulation results show that the proposed schemes not only have less iteration number but also have good perform for system energy efficiency and throughput.

An algorithm is proposed for energy-efficient resource allocation scheme in massive MIMO OFDMA downlink mobile communication system.A mathematical formulation of optimization issue is provided with the objective of maximizing system energy efficiency lower bound under the minimum data rate requirement of user,meanwhile the BS uses a zero-forcing(ZF) precoding.And then for optimizing energy efficiency function,the bandwidth allocation,power allocation and the number of antenna arrays at the BS are adjusted synchronously.First,an iterative algorithm derived from optimality condition for bandwidth assignment is proposed.Second,the properties of fractional programming and convex optimization are used to maximize the energy efficiency.Specifically,both the number of antenna arrays at the BS and the transmit data rate at the user are adjusted.Simulation results show that the proposed schemes not only have less iteration number but also have good perform for system energy efficiency and throughput.

The outage probability and average BER (bit error ratio) of two-way relay system with network coding using relay selection were analyzed over Nakagami channels. The cooperative relay selection criterion of minimizing the worse user's BER was proposed based on three time slots network coding. The closed-form expressions of outage probability and average BER were derived through theoretical analysis from the point of two-way communication; meanwhile, the analytical expressions of outage probability and average BER of two-way relay system using network coding without cooperative relay selection were also obtained rigorously. By the analysis of two-way relay system without cooperative relay selection, it was found that the performance gains of the proposed scheme would increase gradually with the Naka-gami channel fading parameters decreasing. Simulation results verified the correctness of theoretical analysis and illus-trated that the performance of the proposed scheme can be improved significantly relative to the network coding without cooperative relay selection.

The outage probability and average BER (bit error ratio) of two-way relay system with network coding using relay selection were analyzed over Nakagami channels. The cooperative relay selection criterion of minimizing the worse user's BER was proposed based on three time slots network coding. The closed-form expressions of outage probability and average BER were derived through theoretical analysis from the point of two-way communication; meanwhile, the analytical expressions of outage probability and average BER of two-way relay system using network coding without cooperative relay selection were also obtained rigorously. By the analysis of two-way relay system without cooperative relay selection, it was found that the performance gains of the proposed scheme would increase gradually with the Naka-gami channel fading parameters decreasing. Simulation results verified the correctness of theoretical analysis and illus-trated that the performance of the proposed scheme can be improved significantly relative to the network coding without cooperative relay selection.

The spectral efficiency of the downlink of multi-user multiple-input and single-output (MU-MISO) was ana-lyzed in the time-division duplex (TDD) communication systems with large-scale antennas. Assuming that the number of users was fixed and the antenna number (M) of base station (BS) increases without limit, the conclusions through theo-retical derivations and analyses were drawn that, when the transmit power of the BS reduces to 1/M of that of BS with single antenna, the system spectral efficiency tends to a constant value with the increase of M if the BS acquires the per-fect channel state information (CSI). The adverse effects of the inter-user interferences and the fast fading could also be eliminated through simple pre-processings. Although the multicell system is affected by the pilot contamination, which is the reason why the inter-cell interferences cannot be eliminated, the reduced transmit power makes the system changed from interference-limited to noise-limited. The limit expression of the system spectral efficiency using zero-forcing (ZF) normalized precoding is equal to that using maximum ratio transmission (MRT) normalized precoding. Finally, the lower bound of the spectral efficiency of multi-user downlink applying space time block code was presented and the correctness of the above conclusions was confirmed by the simulation analyses.

The spectral efficiency of the downlink of multi-user multiple-input and single-output (MU-MISO) was ana-lyzed in the time-division duplex (TDD) communication systems with large-scale antennas. Assuming that the number of users was fixed and the antenna number (M) of base station (BS) increases without limit, the conclusions through theo-retical derivations and analyses were drawn that, when the transmit power of the BS reduces to 1/M of that of BS with single antenna, the system spectral efficiency tends to a constant value with the increase of M if the BS acquires the per-fect channel state information (CSI). The adverse effects of the inter-user interferences and the fast fading could also be eliminated through simple pre-processings. Although the multicell system is affected by the pilot contamination, which is the reason why the inter-cell interferences cannot be eliminated, the reduced transmit power makes the system changed from interference-limited to noise-limited. The limit expression of the system spectral efficiency using zero-forcing (ZF) normalized precoding is equal to that using maximum ratio transmission (MRT) normalized precoding. Finally, the lower bound of the spectral efficiency of multi-user downlink applying space time block code was presented and the correctness of the above conclusions was confirmed by the simulation analyses.

Two pilot contamination reduction methods in very large MIMO cellular network were proposed by dividing all cells into two types of one-dimensional very large MIMO network.The same pilot sequences were used in cells in the same category while orthogonal pilot sequences were used between these two categorie.Then the pilot power control method can be used to achieve the purpose of alleviating pilot contamination.By coordinating among base stations,the nearly optimal length of pilot sequences and assignment of pilot transmission could be found through minimizing the sum of channel estimation mean square error of all base stations.Thus,much better performance of channel estimation could be obtained,greatly enhancing the sum rate in downlink in all cells.

Two pilot contamination reduction methods in very large MIMO cellular network were proposed by dividing all cells into two types of one-dimensional very large MIMO network.The same pilot sequences were used in cells in the same category while orthogonal pilot sequences were used between these two categorie.Then the pilot power control method can be used to achieve the purpose of alleviating pilot contamination.By coordinating among base stations,the nearly optimal length of pilot sequences and assignment of pilot transmission could be found through minimizing the sum of channel estimation mean square error of all base stations.Thus,much better performance of channel estimation could be obtained,greatly enhancing the sum rate in downlink in all cells.

Multi-cell multi-user downlink beamforming schemes considering transceiver impairments were developed,with the objective of minimizing the maximum mean square error (MSE) and the sum of MSE of all users.The optimiza-tion problem was transformed into a second-order cone programming(SOCP) standard form,and a hierarchical iterative algorithm was developed to solve the original problem.Compared with the traditional beamforming methods developed for ideal transceivers,numerical results show that our proposed optimization algorithms greatly reduce the impact of im-pairments and improve the system performance.

Multi-cell multi-user downlink beamforming schemes considering transceiver impairments were developed,with the objective of minimizing the maximum mean square error (MSE) and the sum of MSE of all users.The optimiza-tion problem was transformed into a second-order cone programming(SOCP) standard form,and a hierarchical iterative algorithm was developed to solve the original problem.Compared with the traditional beamforming methods developed for ideal transceivers,numerical results show that our proposed optimization algorithms greatly reduce the impact of im-pairments and improve the system performance.

The recent IEEE 802.11ac adopted a novel multi-user access technique,which was the downlink multi-user MIMO (MU-MIMO) transmission.This was very different from the former IEEE 802.11 standard's protocols.The MU-MIMO transmission technique in IEEE 802.11ac draft was studied and proposed some optimal designs.Finally,the performance of the IEEE 802.11ac MU-MIMO transmission schemes and gives the simulations.The simulation results show that the proposal transmission schemes can achieve gains of BER and throughput in theory and simulations.

The recent IEEE 802.11ac adopted a novel multi-user access technique,which was the downlink multi-user MIMO (MU-MIMO) transmission.This was very different from the former IEEE 802.11 standard's protocols.The MU-MIMO transmission technique in IEEE 802.11ac draft was studied and proposed some optimal designs.Finally,the performance of the IEEE 802.11ac MU-MIMO transmission schemes and gives the simulations.The simulation results show that the proposal transmission schemes can achieve gains of BER and throughput in theory and simulations.

With the goal to optimize the multi-cell downlink beamforming based on the criterion of the worst-user rate maximization,the Lagrangian duality theory was first used to derive a virtual multi-cell uplink optimization problem that was dual to the primal multi-cell downlink beamforming optimization problem.Base on that,an iterative algorithm was developed to solve the virtual uplink problem by combining the methods of bisection search and geometric programming.Then,the primal multi-cell downlink coordinated beamforming optimization problem could be solved by converting the solution of the virtual uplink problem to the downlink.Simulation results demonstrate that,in contrast to the existing coordinated beamforming schemes,the proposed scheme achieves better performance in terms of both the worst-user rate and the rate per energy (RPE).

With the goal to optimize the multi-cell downlink beamforming based on the criterion of the worst-user rate maximization,the Lagrangian duality theory was first used to derive a virtual multi-cell uplink optimization problem that was dual to the primal multi-cell downlink beamforming optimization problem.Base on that,an iterative algorithm was developed to solve the virtual uplink problem by combining the methods of bisection search and geometric programming.Then,the primal multi-cell downlink coordinated beamforming optimization problem could be solved by converting the solution of the virtual uplink problem to the downlink.Simulation results demonstrate that,in contrast to the existing coordinated beamforming schemes,the proposed scheme achieves better performance in terms of both the worst-user rate and the rate per energy (RPE).

The performance of the zero-forcing (ZF) coordinated transmit strategy in multiple-input multiple-output (MIMO) interference channels was investigated.With the goal to derive analytical expression of its performance metric such as the sum rate and the outage probability,the asymptotic behavior of the performance metric was examined with the MIMO dimension tending to infinity.Using the random ma ix theory,an asymptotic estimate of all the eigenvalues of the effective channel matrix in the ZF coordinated transmit strategy was first proposed.Based on that,two closed-form expressions of the sum rate were derived,from which the scaling law of the sum rate with the MIMO dimension was obtained.Furthermore,using the multivariate statistics about the probability density distribution of the minimum eigenvalue of a Wishart matrix,the analytical expression of the outage probability for the coordinated transmit scheme was achieved under two special cases.Simulation results show that the proposed tical expression of the performance metric is valid not only in the large-dimension regime,but also in the normal-dimension regime.

The performance of the zero-forcing (ZF) coordinated transmit strategy in multiple-input multiple-output (MIMO) interference channels was investigated.With the goal to derive analytical expression of its performance metric such as the sum rate and the outage probability,the asymptotic behavior of the performance metric was examined with the MIMO dimension tending to infinity.Using the random ma ix theory,an asymptotic estimate of all the eigenvalues of the effective channel matrix in the ZF coordinated transmit strategy was first proposed.Based on that,two closed-form expressions of the sum rate were derived,from which the scaling law of the sum rate with the MIMO dimension was obtained.Furthermore,using the multivariate statistics about the probability density distribution of the minimum eigenvalue of a Wishart matrix,the analytical expression of the outage probability for the coordinated transmit scheme was achieved under two special cases.Simulation results show that the proposed tical expression of the performance metric is valid not only in the large-dimension regime,but also in the normal-dimension regime.

A joint network coding (NC) and superposition coding scheme was proposed to realize a cooperative transmission.The use of NC was able to improve spectral efficiency over classical decode and forward relaying strategy by relaxing the orthogonality constraint between different data streams and mitigating the resultant interference through precoding.In contrast to using the CSI based beamforming scheme which could achieve near optimal performance but involves huge computational complexity,designing the beamforming vector using the form of superposition coding was proposed,such that CSI at the transmitters were not required and the involved computation was greatly reduced.The theoretical analysis and simulation results reveal that the proposed scheme shows performances close to the near-optimal CSIT based scheme.

Coordinated downlink beamforming optimization was studied for the time division duplexed(TDD)multicell system with limited inter-BS communication.With the objective to reach the particular point on the Pareto boundary of user rates with the maximum worst-user rate,a near-optimal two-step centralized solution was first proposed.Based on that,a distributed solution was then developed,in which only limited number of positive scalars were needed to exchange between the BSs.Numerical simulation results show that the proposed distributed solution achieves a rate performance close to the centralized solution.

A joint network coding (NC) and superposition coding scheme was proposed to realize a cooperative transmission.The use of NC was able to improve spectral efficiency over classical decode and forward relaying strategy by relaxing the orthogonality constraint between different data streams and mitigating the resultant interference through precoding.In contrast to using the CSI based beamforming scheme which could achieve near optimal performance but involves huge computational complexity,designing the beamforming vector using the form of superposition coding was proposed,such that CSI at the transmitters were not required and the involved computation was greatly reduced.The theoretical analysis and simulation results reveal that the proposed scheme shows performances close to the near-optimal CSIT based scheme.

Coordinated downlink beamforming optimization was studied for the time division duplexed(TDD)multicell system with limited inter-BS communication.With the objective to reach the particular point on the Pareto boundary of user rates with the maximum worst-user rate,a near-optimal two-step centralized solution was first proposed.Based on that,a distributed solution was then developed,in which only limited number of positive scalars were needed to exchange between the BSs.Numerical simulation results show that the proposed distributed solution achieves a rate performance close to the centralized solution.