Problem Description

Primary receiver

Secondary receiver

eNodeB

Aim: Reception of MIMO signals by a secondary receiver

• Parameterize design of secondary receiver with transmission optimized for primary receiver

• Detect unknown precoder

CLSMre

layin

g

(also: act as relay node)

Precoder Matrix Detection

• Goal: Design of receivers for MIMO-OFDM without PMI information at secondary user

• Approaches+ Hypothesis testing Framework

• Simple ML detection• Cluster variance

─ Blind equalization

Precoder Detection – Simple ML detector

Overview• Compute log likelihood ratios, for each precoder

Notation:• - detected transmit symbols, assuming is correct precoder• - estimated channel matrix

• Choose the precoder with highest log likelihood ratio

• Equivalent to ML detector Optimal detection when ’s are equiprobable

Precoder Detection – Cluster variance

Overview• Compute following objective function for each precoder

Notation:• - detected transmit symbols, assuming is correct precoder• - Pseudoinverse• - MMSE equalized received symbols

• Choose the precoder that minimizes • Similarity with minimum distance decision rule

BLER vs. SNR – Simple ML vs Cluster variance

Carrier frequency = 2110 MHz1000 subframes, 12 RBs scheduled, MMSE channel estimator, SSD receiver

Precoder Detection

Summary• Simple ML within 2dB of BLER performance vs. known PMI case

• Simple ML typically outperforms cluster variance, in 2x2 MIMO

• Performance gap reduced in 4x4 MIMO• Additional diversity as each codeword is sent on 2 antennas

• Computational requirement less than SSD receiver (linear in M, # precoders, constellation size)

Ongoing Work•Comparing MATLAB LTE System Toolbox with TU Vienna LTE-A simulator

MATLAB LTE System Toolbox + Compliant with 3GPP Release 8, 9, 10+ Modular structure, well documented+ End-to-end link level simulations, decode over-the-air LTE signals* + Downlink and Uplink channels modelled+ User Feedback block implemented─ No inbuilt schedulers for MU-MIMO, no inbuilt Multi-cell scenario1

─ No SSD receiver• Baseband, user mobility modelled only through Doppler shift, etc. TU Vienna (LTE-A) Simulator2

+ Built in MU-MIMO & Multi-cell scenarios+ User Feedback implemented+ End-to-end link level simulations+ Inbuilt schedulers, SSD receiver─ Poor documentation, no working Uplink? Standard Compliance, accuracy/completeness of existent blocks?

* Not real-time 1 Can be coded using the blocks 2 Based on documentation

Future Work

• Consider more elaborate simulations• Simulate both Primary and secondary user simultaneously

Test the relaying scenario proposed Vary channel conditions and relative position of receivers

• Interference from neighboring cells

• Impact of scheduling multiple users

• Design improved precoder detectors• utilize information from previous subframes