Reza Holakouei

Power allocation strategies for distributed precoded multicell based systems

Multicell cooperation is a promising solution for cellular wireless systems to mitigate intercell interference, improve system fairness, and increase capacity. In this article, we propose power allocation techniques for the downlink of distributed, precoded, multicell cellular-based systems. The precoder is designed in two phases: first the intercell interference is removed by applying a set of distributed precoding vectors; then the system is further optimized through power allocation. Three centralized power allocation algorithms with per-BS power constraint and different complexity trade-offs are proposed: one optimal in terms of minimization of the instantaneous average bit error rate (BER), and two suboptimal. In this latter approach, the powers are computed in two phases. First, the powers are derived under total power constraint (TPC) and two criterions are considered, namely, minimization of the instantaneous average BER and minimization of the sum of inverse of signal-to-noise ratio. Then, the final powers are computed to satisfy the individual per-BS power constraint. The performance of the proposed schemes is evaluated, considering typical pedestrian scenarios based on LTE specifications. The numerical results show that the proposed suboptimal schemes achieve a performance very close to the optimal but with lower computational complexity. Moreover, the performance of the proposed per-BS precoding schemes is close to the one obtained considering TPC over a supercell.

Multiuser precoding techniques for a distributed broadband wireless system

In this paper we propose and asses multiuser linear precoding techniques for the downlink of distributed MIMO OFDM systems. We consider a distributed broadband wireless system where the base stations are transparently linked by optical fiber to a central unit. We further assume that both the distributed base stations and the user terminals are equipped with an antenna array. This architecture provides a high speed backhaul channel allowing an efficient joint multiuser multicell processing. The precoder is designed in two phases: first the intercell interference is removed by applying a block diagonalization algorithm. Then the system is further optimized by using a new power allocation algorithm, based on minimization of the sum of inverse signal-to-noise ratio (SNR−1) on each user terminal over the available subcarriers. The motivation to minimize the sum of SNR−1 instead of bit error rate is the fact that the first criterion achieves a closed-form solution, which is more interesting from practical point of view. The aim is to propose a practical distributed precoding technique to remove the intercell interference and improve the user’s fairness at the cell-edges. The performance of the proposed scheme is evaluated and compared with an iterative precoding scheme designed to minimize the bit error rate, extended to the proposed multiuser distributed scenario, considering typical pedestrian scenarios based on LTE specifications.

Precoded multiuser distributed MIMO OFDM systems

In this paper, we consider a multiuser distributed MIMO system, under multipath fading channels, with orthogonal frequency division multiplexing (OFDM) technology. The aim is to extend and evaluate, co-located precoding schemes that have been recently proposed, in a distributed scenario. Assuming knowledge of CSI prior to transmission, we can remove the interference among users by employing precoding schemes for the downlink. We assessed closed form and iterative schemes based on block diagonalization (BD) to improve the performance of the distributed antenna system. The results show that the iterative scheme outperforms the closed one. The simulation results show that the studied schemes can be efficient for distributed MIMO OFDM based systems.

A novel distributed power allocation scheme for coordinated multicell systems

Coordination between base stations (BSs) is a promising solution for cellular wireless systems to mitigate intercell interference, improving system fairness, and increasing capacity in the years to come. The aim of this manuscript is to propose a new distributed power allocation scheme for the downlink of distributed precoded multicell MISO-OFDM systems. By treating the multicell system as a superposition of single cell systems we define the average virtual bit error rate (BER) of one single-cell system, allowing us to compute the power allocation in a distributed manner at each BS. The precoders are designed in two phases: first the precoder vectors are computed in a distributed manner at each BS considering two criteria, distributed zero-forcing and virtual signal-to-interference noise ratio; then the system is optimized through distributed power allocation with per-BS power constraint. The proposed power allocation scheme minimizes the average virtual BER over all user terminals and the available subcarriers. Both the precoder vectors and the power allocation are computed by assuming that the BSs have only knowledge of local channel state information. The performance of the proposed scheme is compared against other power allocation schemes that have recently been proposed for precoded multicell systems based on LTE specifications. The results also show that although our power allocation scheme is based on the minimization of the virtual uncoded BER, it also has significant gains in coded systems.

Power allocation strategies for SVD multicell MIMO-OFDM based systems

The aim of this paper is to propose and evaluate power allocation techniques for SVD precoded multicell multiuser MIMO-OFDM based systems. We consider a highspeed backhaul network where the base stations are transparently linked by optical fiber to a central unit. This architecture allows an efficient joint multicell multiuser processing. The considered precoder is designed in two phases: first the intercell interference is removed by applying a SVD based algorithm. Then the system is further optimized by proposing three power allocation algorithms with per-BS power constraint and different complexity tradeoffs: one optimal to minimize the average BER and two suboptimal. The performance of the proposed schemes is evaluated, considering typical pedestrian scenarios based on LTE specifications. Numerical results show that the proposed suboptimal power allocation schemes achieve a performance very close to the optimal.

Distributed versus centralized zero-forcing precoding for multiceli OFDM systems

In this paper we propose distributed linear multiuser precoding techniques for the downlink of multicell MIMO-OFDM systems. The preceder is designed in two phases: first the intercell interference is removed by applying a set of precoding vectors based on zero-forcing criterion and computed in a distributed manner at each BS; then the system is further optimized through power allocation. Three power allocation algorithms with per-BS power constraint and different complexity tradeoffs are proposed: one optimal to minimize the average BER and two suboptimal. The performance of the proposed schemes is compared to the full centralized multicell based approaches recently proposed, and evaluated considering typical pedestrian scenarios. Numerical results show that the proposed suboptimal schemes achieve a performance very close to the optimal. Also, it is shown that for the same degrees of freedom the performance is close to the one of centralized precoding schemes but with much lower feedback load over the backhaul network.

Performance Evaluation of Distributed Precoding Schemes for Multicell OFDM Systems

In this paper we propose and evaluate distributed multiuser linear precoding techniques for the downlink of multicell MIMO OFDM systems. The precoder is designed in two phases: first the intercell interference is removed by applying a set of precoding vectors computed in a distributed manner at each BS; then the system is further optimized through power allocation. Three centralized power allocation algorithms with per-BS power constraint and different complexity tradeoffs are proposed: one optimal to minimize the average BER and two suboptimal. The performances of the proposed schemes are compared to the centralized multicell based approaches recently proposed, and evaluated considering typical pedestrian scenarios. Numerical results show that the proposed suboptimal schemes achieve a performance very close to the optimal. Also, it is shown that for the same degrees of freedom the performance is closed to the one of centralized precoding schemes but with much lower feedback load over the backhaul network.

Transmit Power Allocation for Precoded Distributed MIMO OFDM Systems

This paper deals with a new multi-user linear precoding technique for downlink of distributed MIMO OFDM systems. We consider a distributed broadband wireless system where some base stations are transparently linked by optical fiber to a central unit. We further assume that the user terminals are equipped with an antenna array and the distributed base stations equipped with either single or an antenna array. This architecture provides a high speed backhaul channel allowing an efficient joint multi-cell processing. The proposed power allocation algorithm is based on minimization of the sum of inverse signal-to-noise ratio (SNR-1) on each user terminal over the available subcarriers. The motivation to minimize the sum of SNR-1 instead of bit error rate (BER) is in the fact that the first criterion achieves a closed-form solution, which is more interesting from practical point of view. The aim is to propose a practical distributed precoding technique to remove the inter-cell interference and improve the user’s fairness at the cell-edges. The performance of the proposed scheme is evaluated, considering typical pedestrian scenarios based on LTE specifications.

Distributed Power Allocation Schemes for Precoded Multicell MISO-OFDM Systems

In this paper we propose distributed power allocation schemes for the downlink of distributed precoded multicell MISO-OFDM systems. The precoders are designed in two phases: first the precoder vectors are computed in a distributed manner at each BS considering two criteria, distributed zero-forcing and virtual signal-to-interference noise ratio; then the system is optimized through distributed power allocation with per-BS power constraint. The proposed power allocation schemes minimize the average virtual bit error rate over all user terminals and the available subcarriers. Both the precoder vectors and the power allocation are computed by assuming that the BSs have only knowledge of local channel state information. The performance of the proposed schemes are compared against other power allocation schemes that have been recently proposed for multicell systems.

Coordinated Precoding Techniques for Multi-cell MISO-OFDM Networks

The aim of this manuscript is to propose and compare several distributed linear precoding schemes for the downlink of multicell MISO-OFDM based systems. The precoder vectors are computed in a distributed manner at each BS, assuming that the BSs have only knowledge of local channel state information and considering several criteria: distributed zero-forcing (DZF), maximum ratio transmission and distributed virtual signal-to-interference noise ratio (DVSINR). Then the system is further optimized through centralized power allocation. Two centralized power allocation algorithms with per-BS power constraint and different complexity tradeoffs are proposed: namely, minimization of the instantaneous average BER and minimization of the sum of inverse of signal-to-interference noise ratio, for which a closed-form power allocation scheme is derived. The performance of the proposed schemes is compared considering typical pedestrian scenarios based on LTE specifications. The numerical results show that increasing the number of degrees of freedom or for high SNR, the proposed DZF approaches tends to the DVSINR based ones.