Introducing In-Band Full Duplex for Broadband Powerline...
Transcript of Introducing In-Band Full Duplex for Broadband Powerline...
Gautham Prasad and Lutz Lampe
Introducing In-Band Full Duplexing for Broadband Power Line
Communication
Gautham Prasad and Lutz Lampe
Or can we?
Introducing In-Band Full Duplexing for Broadband Power Line
Communication
Introduction
• Simultaneous bidirectional communication over the same line and in the same band potentially doubles transmission efficiency
• Other (more important?) benefits include:– Alternate PHY solution to the hidden node problem
– Full duplex relaying in multi-hop networks to improve throughput efficiency
– Continuous cognitivity
– Relaxed scheduling constraints
In-Band Full Duplex (IBFD)
• Hindrance: Interference of the large “self-transmitted” signal (echo/SI) with the received signal-of-interest (SOI)
To/From PLC
TX
RX
TXS
SOI
SOI Echo/SI
Echo Cancellation (EC)
• Very old – Analog telephone: transformer based isolation
– DSL/Ethernet/Wireless• Hybrid/Circulator: Elementary isolation in analog domain
• Analog Cancellation: analog circuitry to cancel non-linear components and achieve additional cancellation
• Digital cancellation: digital filters implemented in time or frequency domain or a combination of both
– Low-rate narrowband PLC: line hybrid and digital cancellation [IEC 62488-1:2012, Tripodi, Ferraro, Pighi, Raheli, “Echo cancellation in a power line modem in the presence of abrupt channel variations”, IEEE ISPLC 2014]
Factors for Consideration of IBFD for BB-PLC
• Cancellation gains:– Transmit PSD = -55dBm/Hz, noise PSD (NPSD) > -130dBm/Hz
– Max gain required for BB-PLC applications < 75 dB
• Non-linear effects: – BB-PLC Analog Front Ends restrict non-linear SI components at 75 to
80 dB below max SI power
• Increase in Quantization Noise (QN): – SQNRdB = 6.02ENOB + 4.77 - PAPRdB
– About 60 dB SQNR for a 12-bit ADC
– QN < -55 - 60 = -115 dBm/Hz
use hybrid and a digital cancellation circuit
Proposed IBFD Solution
• Use hybrid and a digital cancellation circuit
TX
FIR EC Filter
Hybrid
RX
To/From PLC
1
2
3
Active hybrid circuit, e.g. [Wenzel, “Low FrequencyCirculator/Isolator Uses No Ferrit or Magnet”, RF Design, 1991.]
Low Frequency Hybrid • Ideally, Z1=ZTX, Z2=ZPLC, Z3=ZRX
for maximum isolation• At Port 1:
ZS is typically small,AFE constraints=> Set Z1≅ ZS
• At Port 2:ZPLC is unknown and varying=> Set e.g. Z2=100W
• At Port 3:ZRX typically large=> Set Z3=ZRX
Hybrid Isolation – Preliminary Simulation Results
- Maximum isolation at ZPLC = 100 + j0 W
where isolation = Vs/VRX
Digital Cancellation
• The received signal contains
• This is used to train the adaptive filter weights using an LMS algorithm and the resulting estimated signal is subtracted fromy(n) y(n)
Digital Cancellation
• Weight update and signal cancellation can be performed in time or frequency or a combination of time and frequency domain
AFEs &AFEs &
LMS Adaptation to LPTV Changes
• Traditional LMS algorithm performs poorly under fast channel changes
• Channel changes in PLC are often Linearly Periodic Time Varying (LPTV)
• We modify the existing LMS algorithm to adapt to LPTV changes by re-using previously updated filter weights for the same channel condition
Our LPTV-LMS Algorithm• LPTV changes are periodic to one AC half cycle (HC)• Detect the cyclic channel change (CCC) positions
during the first/fresh HC• In every following HC, re-use the last updated
weights of every CCC from the previous HC• Detect non-CCC (N-CCC) by monitoring the resulting
MSE levels• Reset weights with an LS estimate and jump back to
the fresh HC when a N-CCC is detected
CC
CN
-CC
C
Some Preliminary Results*• The EC filter, which replicates the echo, is trained using the received signal y(n)
• Notice that the strength of the SOI component decreases with increase in PLC channel attenuation => less overall ‘noise’ for echo estimation, resulting in better echo estimate and higher EC gain (ECG)
*Note: use with caution
20 25 30 35 40 4540
42
44
46
48
50
52
54
56
58
60
PLC channel + hybrid attenuation (dB)
Inte
rfere
nce c
ancela
tion
gain
(dB
)
PSD
, dB
m/H
zTXS
Noise
SOI
SI
Ch
ann
el attenu
ation
When canceled-SI PSD is in -
DRG < 1
1 < DRG < 2
DRG = 2
Hybrid isolation
ECG
Canceled-SI
Data Rate Gain (DRG) – Some Estimations*
*Note: max. const. 1024 QAM, SNR-to-rate translation using results for CC rate ¾ from [Tsugi and Itami, “A study on adaptive modulation of OFDM under impulsive rate”, ISPLC 2008]
Noise PSD = -105dBm/Hz Noise PSD = -115 dBm/Hz
Ch. Att
ECG SNR BHD SCINR BFD DRG SNR BHD SCINR BFD DRG
14 46 36 10 22 6 1.2 46 10 22 6 1.2
20 52 30 8 21 6 1.5 40 10 21 6 1.2
26 56 24 6 20 6 2.0 34 10 20 6 1.2
34 58 16 4 15 4 2.0 26 6 15 4 1.3
Conclusions
• Interesting possibilities with IBFD for BB-PLC
• Suggest the use of a low frequency active hybrid to provide impedance balance and initial isolation
• In tandem with a digital echo cancellation• Need to work out some details on the
hybrid, EC, and the gains achievable