Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications

1

Jing Lin1, Tarkesh Pande2, Il Han Kim2, Anuj Batra2, Brian L. Evans3

1 Qualcomm Inc.2 Texas Instruments Inc.

3 The University of Texas at Austin

9 June /2015

2015 IEEE Int. Conf. on Communications

2

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Outline

Introduction

• Noise in PLC and previous work

Contribution

• Modulation Diversity

• Noise Estimation using sparse Bayesian techniques

Results

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Periodically varying and spectrally shaped noise

Sub-channel SNR is highly frequency-selective

and time-varying 3

Wideband impulses

Narrowband interferences

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Previous vs. Proposed Transmitter Methods

Transmitter Methods Throughput Reduction

Channel/Noise Info at Transmitter

Previous

Adaptive modulation[Nieman13] ✗ Full

Concatenated error correction coding

(PLC standards)✔ None

Proposed Time-frequency modulation diversity ✗ Partial

4

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Modulation Diversity (I)

5

s1 s2 s3 s4 s5 s6 s7 s8 s9 s10 s11 s12 s13 s14 s15

Sub-channels

SNR

b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15

X

X✔

Data rate = 1 bit / channel use

[Schober03]

Bits

Symbols

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Example: Hochwald/Sweldens Code

• Map N bits to a length-N codeword consisting of PSK symbols

– Special case: PSK repetition code– Constellation mappings are optimized for channel statistics

6

000

110

001

010011

100101

111 000

010

101

110100

011001

111 000

110

001

010011

100101

111

Optimal length-3 code in Rayleigh fading channel[Hochwald00]

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

• Allocate components of a codeword to time-frequency slots

• Require partial noise information

– Narrowband interference width– Burst duration

Tim

e-d

om

ain

nois

e

Proposed Time-Frequency Mapping(Transmitter)

7

Subcarriers

OFDM symbols

…

… …

…

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

• Combine signals received from N sub-channels

Log-likelihood ratio (LLR)

Diversity Demodulation(Receiver)

8

Diversity Demodulator

Received signal

Estimated noise power

Estimated sub-channel

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Noise Power Estimation (II)

9

TimeOffline

Semi-online

Transmission

Workload at the noise power estimator

Low

Med

High

• Offline estimation

– Utilize silent intervals between transmissions

• Semi-online estimation

– Between transmissions: Estimate start/end instances of all stationary intervals

– In transmissions: Estimate noise power spectrums

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Proposed Semi-Online Estimation

• Measure noise using cyclic prefix

• Formulate a compressed sensing problem

– (where )

– Collect multiple measurements in the same stationary interval

10

Cyclic Prefix OFDM symbol

+ -

Noise

NBI AWGN

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Hyper-prior

Prior [Zhang11]

Proposed Semi-Online Estimation (Cont.)

• Apply sparse Bayesian learning algorithm

11

Row sparsity Temporal correlation

IG - Inverse Gamma dist.; IW - Inverse Wishart dist.EM - Expectation maximization

Diversity Receiver

Slicing Error Estimation

EM Updates

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

System Parameters

Parameters Reference System TFMD System

Sampling Frequency 400kHz

FFT Size 256

CP Length 30

Data Subcarriers 23:58 (36 tones)

Convolutional Code Rate ½ K=7

Reed-Solomon Code 235/251 N/A

Interleaver Size (Bits) 4032 (packet) 36

Packet Size (Bytes) 235

Data Rate (kbps) 23.5 25ΔT symbols (TFMD) N/A 4ΔK Tones (Nd =2/Nd=3) N/A 18/12

• Noise: Model LPTV with three regions [70% 29% 1%]• Channel: Flat

13

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Results

Non-coherent Coherent

• Coherent mode gains : > 6dB

• Non-Coherent mode gains: 8dB

14

Robust Transceiver to Combat Periodic Impulsive Noise In Narrowband Power-line Communications SAC05-CSG-01: Powerline Communication Channel Characterization and Noise Mitigations

Conclusions

1. Modulation diversity as an effective method for improving performance in PLC channels

2. Developed a methodology for estimating noise variance

– Exploits the cyclic prefix

– Uses Sparse Bayesian learning techniques