1. Grid-of-Beams (GoB) Downlink Multi-User MIMO
Document Number: IEEE S802.16m-08/487
Date Submitted:
Source:
Stephan SAUR, Hardy HALBAUER, {Stephan.Saur, Hardy.Halbauer, Andreas.Rueegg,
Andreas RUEEGG, Frank SCHAICH
Alcatel-Lucent
Venue: Macau, China
Base Contribution: IEEE C80216m-08_487.doc
Purpose: Discuss and adopt this proposal into the 16m SDD
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2. Motivation
Several users share one DL radio resource in time and frequency in order to increase the mean cell throughput
Multi-user scheduling (user grouping) aims in minimizing the intra-cell interference
Application in systems with low frequency reuse factor requires inter-cell interference mitigation in parallel
Target: Design of DL MU-System with low complexity that maintains the capability of inter-cell interference coordination
Idea: Define a limited set of possible precoding vectors (e.g. 8 vectors) such that
vectors build up a Grid-of-Beams (GoB)
intra-cell interference is minimal for certain combinations of beams

3. Concept Description … Base Station Mobile Station #n GoB Precoding P
user signal d1
user signal dN …
Base Station
Mobile Station #n
SM Detector W
user signal dn
Channel H
feedback of desired beam index

4. Concept Description
BS assigns each data stream to one beam (precoding vector)
Closed-loop mode: MS reports required beam(s) to BS
Open-loop mode: BS derives appropriate beam(s) from UL
Certain combinations of beams share one radio resource in time and frequency without severe intra-cell interference (e.g. #2 and #6)
Several options for antenna configurations:
E.g. linear array of x-pol elements for the transmission of two independent streams to one MS with the same beam index exploiting polarization diversity #8 #7 #6 #5 #4 #3 #2 #1

5. Requirements
Closed-loop mode requires “test signal”, e.g. pilots dedicated to each beam (precoding vector) in order to determine that beam, which is received with the highest power level.
Closed-loop mode requires feedback channel. Assuming eight possible beams (precoding vectors), three uncoded bits per data stream are necessary.

6. Text Proposal to SDD
Start text proposal
MIMO modes
In 16m, three MIMO modes shall be supported:
Single-BS single-user MIMO (SU-MIMO) […]
Single-BS multi-user MIMO (MU-MIMO)
In downlink, a MU-MIMO scheme based on a limited number of possible precoding vectors building up a grid of beams with spatial separation shall be supported. This scheme aims in increasing the mean cell throughput even in cellular systems with low frequency reuse factor. Main advantage is the capability to support advanced inter-cell interference coordination techniques at the same time. The proposed scheme exhibits very low complexity and can be applied in both closed and open loop MU-MIMO. Either one or two data streams can be assigned to one user. The use of cross-polarized antennas at the base station is recommended.
[…]
Multi-BS MIMO: […]
End text proposal