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Opportunistic Two-Stage Feedback and Scheduling for MIMO Downlink Systems
Moonsik Min,Dongsik Kim,Hyun-Myung Kim,Gi-Hong Im IEEE 2013 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.61 No.1
<P>We propose an opportunistic two-stage feedback and scheduling algorithm that is based upon zero-forcing beamforming with semi-orthogonal user selection (ZFBF-SUS) to reduce its feedback load. In an SUS algorithm, a base station schedules semi-orthogonal users using the feedback of all users' channel information. However, such feedback overhead significantly increases with the number of users. To reduce the feedback load of ZFBF-SUS systems, the proposed two-stage feedback scheme opportunistically and separately exploits the signal-to-interference-plus-noise ratio and orthogonality in each stage such that only a fraction of users feed back their channel information. Based on this opportunistic feedback scheme, we decouple the entire process of the SUS into two sub-processes. The proposed two-stage feedback and scheduling scheme effectively exclude the inappropriate users for ZFBF transmission in both feedback and scheduling periods, and thus save the scarce resources consumed for the feedback process. We derive an analytical expression for the average number of feedback bits of the proposed system and optimize it in an averaged sense. Further, the sum-rate of the proposed system is theoretically investigated. Both analytical and simulation results show that the proposed algorithm achieves the performance of conventional ZFBF-SUS systems with a significantly reduced number of feedback bits.</P>
On the Performance Analysis of MISO Broadcast Channels with Spatial Heterogeneity
Moonsik Min,Hyun-Myung Kim,Gi-Hong Im IEEE 2013 IEEE COMMUNICATIONS LETTERS Vol.17 No.4
<P>We consider the sum-rate performance of multiple-input/single-output broadcast channels in which each user has a different average signal-to-noise ratio (SNR) corresponding to their distance from the base station. Although there are already studies investigating the sum-rate growth under this channel assumption, their proofs are limited to the cases where the pathloss exponent is equal to one or two. However, the path-loss exponent is greater than two in realistic wireless environments. Therefore, by deriving the cumulative distribution function of the channel gain, which differs from the previous results, we can provide an asymptotic sum-rate and a general proof for the sum-rate growth regardless of the value of the pathloss exponent.</P>
On Achievable Multiplexing Gain of BD in MIMO Broadcast Channels With Limited Feedback
Moonsik Min,Yo-Seb Jeon,Gi-Hong Im IEEE 2016 IEEE Transactions on Wireless Communications Vol.15 No.2
<P>To maintain a specific degree of multiplexing gain with limited feedback in multiple-input/multiple-output broadcast channels, the number of feedback bits has been increased linearly with the signal-to-noise ratio (SNR) measured in decibel, and conditions for the slope of this increase have been derived in previous studies. However, previous studies mostly focused on the chordal distance (ChD) for channel quantization, although it is not an optimally designed distance measure. Thus, the possibility exists that the same degree of multiplexing gain can be obtained by using fewer feedback bits than the existing method requires. In this paper, we propose an optimal distance measure that can maximize the multiplexing gain achieved by limited-feedback-based block diagonalization over broadcast channels. Then, we provide a sufficient condition for the number of feedback bits to achieve a specific degree of multiplexing gain with the proposed method. The sufficient number of feedback bits is given by a linear function of the SNR (decibel) as in previous studies, but the slope of the linear increase can be much less than that obtained in previous studies. As a consequence, the proposed method achieves higher multiplexing gain and corresponding throughput than the existing methods with the same number of feedback bits.</P>