A Practical Cooperative Multicell MIMO-OFDMA Network Based on Rank Coordination

An important challenge of wireless networks is to boost the cell edge performance and enable multi-stream transmissions to cell edge users. Interference mitigation techniques relying on multiple antennas and coordination among cells are nowadays heavily studied in the literature. Typical strategies in OFDMA networks include coordinated scheduling, beamforming and power control. In this paper, we propose a novel and practical type of coordination for OFDMA downlink networks relying on multiple antennas at the transmitter and the receiver. The transmission ranks, i.e.\ the number of transmitted streams, and the user scheduling in all cells are jointly optimized in order to maximize a network utility function accounting for fairness among users. A distributed coordinated scheduler motivated by an interference pricing mechanism and relying on a master-slave architecture is introduced. The proposed scheme is operated based on the user report of a recommended rank for the interfering cells accounting for the receiver interference suppression capability. It incurs a very low feedback and backhaul overhead and enables efficient link adaptation. It is moreover robust to channel measurement errors and applicable to both open-loop and closed-loop MIMO operations. A 20% cell edge performance gain over uncoordinated LTE-A system is shown through system level simulations.Comment: IEEE Transactions or Wireless Communications, Accepted for Publicatio

Packet scheduling in the presence of channel estimation error in multi-user OFDM wireless systems

In this paper, we investigate the effect of channel estimation error on the performance of channel aware techniques in a packet-based multi-user OFDM wireless system. To this end, we consider the use of two channel estimation schemes; one is a simple linear and the other is an optimum Wiener-type channel estimator. We examine the effect of channel impulse response (CIR) estimation error on coherent reception and the effect of signal-to-interference and noise ratio (SINR) estimation error on channel aware transmission techniques (e.g., packet scheduling). It is shown that the performance of coherent reception is relatively less susceptible to the CIR estimation error, but the performance of channel aware schemes can be very sensitive to the SINR estimation error. To alleviate this problem, we propose a robust scheduling scheme which can work without significant performance degradation even in the presence of large channel estimation error. Finally, we verify the performance of the proposed scheduling scheme by computer simulation.Ministry of Information & Communications, Kore

Effect of channel estimation error on packet-based multi-user OFDM systems

In this paper, we consider the performance of a packetbased multi-user orthogonal frequency division multiplexing (OFDM) wireless system in the presence of channel estimation error. To investigate the effect of incorrect channel information on the system performance, we consider the use of two channel estimation schemes; one is a simple linear and the other is an optimum Wiener-type channel estimator. We analyze the effect of channel impulse response (CIR) estimation error on coherent reception and the effect of instantaneous signal to interference and noise ratio (SINR) estimation error on channel aware techniques associated with packet scheduling. It is shown that the performance of coherent reception is relatively less susceptible to the CIR error, but the performance of channel aware schemes can be very sensitive to the SINR estimation error, mainly due to incorrect scheduling. To alleviate this scheduling problem, we propose an improved scheduling method which can be employed even with the use of a simple channel estimator. Finally, we verify the performance of the proposed scheduling scheme by computer simulation