IEEE S 80216 m08457 Advanced downlink MIMO design

IEEE S 80216 m-08/457 Advanced downlink MIMO design Document Number: IEEE S 80216 m-08/457 Date Submitted: 2008 -5 -11 Source: Hongwei YANG, Xiaolong ZHU, Keying WU, Song YANG, Liyu CAI Alcatel Shanghai Bell Co. , Ltd Voice: E-mail: +86 -21 -58541240 Ext. 7796 Hongwei. Yang@alcatel-sbell. com. cn *<http: //standards. ieee. org/faqs/affiliation. FAQ. html> Venue: IEEE 802. 16 m-08/016 r 1 Call for Contributions on Project 802. 16 m System Description Document (SDD) Target topic: Downlink MIMO schemes Base Contribution: IEEE C 80216 m-08/457 Purpose: To be discussed and adopted by TGm for use in the IEEE 802. 16 m SDD. Notice: This document does not represent the agreed views of the IEEE 802. 16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802. 16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: <http: //standards. ieee. org/guides/bylaws/sect 6 -7. html#6> and <http: //standards. ieee. org/guides/opman/sect 6. html#6. 3>. Further information is located at <http: //standards. ieee. org/board/pat-material. html> and <http: //standards. ieee. org/board/pat >.

Introduction • IEEE 802. 16 m requires higher performances of peak data rate, sector throughput, cell edge user throughput, mobility, and coverage • To achieve these targets, advanced MIMO techniques shall be an important building block • To adapt to services and environments, multiple MIMO modes shall coexist with a uniform architecture

Overview of MIMO modes • Single-User MIMO (SU-MIMO) – Each user is served by a single BS – Mainly target for optimizing the single-user-achievable peak data rate • Multi-User MIMO (MU-MIMO) – Multiple users are served by one BS sharing the same radio resource – Most suitable for heavily loaded systems in cell center, where maximization of overall system throughput is the primary concern • Multi-BS MIMO – Multiple users are served by multiple BSs sharing the same radio resources – With BS coordination, the cell-edge user throughput and cell coverage are improved significantly due to efficient interference reduction

Application scenario of MIMO modes

SU-MIMO • 2 -Tx – Rate-1 • Space-Time Block Coding: STBC – Applied at low mobility • Space-Frequency Block Coding: SFBC – Applied in environments with low delay spread • Recommend the switched STBC and SFBC – Both defined as Matrix A, but with different mapping pattern – Mode adaptation according to mobility and delay spread – Rate-2 • V-BLAST code as Matrix B – Sensitive to channel condition • Full diversity full rate code as Matrix C – Long decoding delay – High decoding complexity • Recommend a linearly dispersed SM code – High robustness with low complexity

SU-MIMO (Continued) • 4 -Tx – Rate-1 • Cyclic Delay Diversity: CDD – Increases the frequency selectivity of channel by artificial multiple paths – Suitable for control signaling which should be received by all types of terminals – Performance is highly dependent on the delay setting • Recommend an antenna permuted CDD to alleviate the impact of delay setting – Antenna permuted CDD can be combined with STBC and SFBC

SU-MIMO (Continued) • 4 -Tx – Rate-2 • Scheme 1: Antenna permuted CDD can be combined with SM • Scheme 2: Recommend layered SM – Multiplex two Alamouti-coded matrixes. Each Alamouti-coded matrix is referred to as a layer – Different layers employ different power levels, which are designed with the aid of very limited long-term feedback – Advantages: • both diversity and multiplexing gains • Low detection complexity, to the same order as Alamouti Interleaver Phase rotation (e. g. , 0 degree) Power level

SU-MIMO (Continued) • 4 -Tx – Rate-4 • Recommend layered SM scheme

MU-MIMO • MU precoding – Based on fixed beamforming – Based on adaptive beamforming • BS designs the precoding matrixes based on channel information to multiple users • Recommend the multi-user eigen-mode transmission (MET) algorithm – – BS performs simultaneous transmissions on the eigen-modes of different users The eigen-modes to different users are weighted such that they are mutually orthogonal The number of orthogonal beams is no more than the number of transmit antennas Co-channel interference (CCI) is effectively controlled, thereby increasing the overall throughput even for single-antenna users • MU scheduling – To maximize the overall throughput by selecting users for transmission – With imperfect CSI or precoding information used, increasing the user number may reduce throughput when BS fails to control the CCI – Recommend a feedback-aided scheduling technique • • • Adjust the user number based on CSIT error covariance or CCI measurement at the user side Users capable of estimating the covariance of CSIT error feedback the covariance so that BS can refine the scheduling results Otherwise, users measure the inter-user CCI power and check if it is too high. They then feed back their decisions to the BS, which collects feedbacks from all users and adjusts the user number accordingly

MU-MIMO (Continued) • MU channel measurement – To provide BS with channel information for precoding and scheduling – Recommend a hierarchical sounding/feedback mechanism to reduce the overhead for MU channel measurement • Long-term statistical channel information of all users is used for MU scheduling – E. g. , mean channel matrix, channel quality information • Instantaneous channel information of selected users is used for MU precoding

Multi-BS MIMO • With BS coordination, some of the cellular mobile network limitations such as inter-cell interference (ICI) can be reduced significantly by multi-BS MIMO • Key features – Each MS can receive its signals from multiple BSs over the same radio resource – Each BS can transmit multiple MSs’ signals over the same radio resource • Multi-BS transmit solutions – Different solutions shall give different tradeoffs between performance and implementation cost • Optimal performance with high complexity: Network MIMO • Suboptimal performance with low complexity: Collaborative MIMO • Downlink pilot design – Both flexibility and efficiency should be considered to support different MIMO modes – Recommend a flexible pilot pattern design with configurable pilot reuse factor • Inter-BS exchange of channel information and control signaling – Backhaul and a certain inter-BS coordination functional entity to be involved in the BS

Text Proposal [Refer to the base contribution IEEE C 80216 m-08/457 ]