Introducing In-Band Full Duplexing for Broadband Power Line Communication. Gautham Prasad and Lutz Lampe

Transcription

1 Introducing In-Band Full Duplexing for Broadband Power Line Communication Gautham Prasad and Lutz Lampe

2 Introducing In-Band Full Duplexing for Broadband Power Line Communication Gautham Prasad and Lutz Lampe Or can we?

3 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

4 In-Band Full Duplex (IBFD) Hindrance: Interference of the large selftransmitted signal (echo/si) with the received signal-ofinterest (SOI) TX RX TXS To/From PLC SOI SOI Echo/SI

5 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 :2012, Tripodi, Ferraro, Pighi, Raheli, Echo cancellation in a power line modem in the presence of abrupt channel variations, IEEE ISPLC 2014]

6 Factors for Consideration of IBFD for Cancellation gains: BB-PLC 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): SQNR db = 6.02ENOB PAPR db About 60 db SQNR for a 12-bit ADC QN < = -115 dbm/hz use hybrid and a digital cancellation circuit

7 Proposed IBFD Solution Use hybrid and a digital cancellation circuit TX FIR EC Filter 1 Hybrid To/From PLC 2 3 RX Active hybrid circuit, e.g. [Wenzel, Low Frequency Circulator/Isolator Uses No Ferrit or Magnet, RF Design, 1991.]

8 Low Frequency Hybrid Ideally, Z 1 =Z TX, Z 2 =Z PLC, Z 3 =Z RX for maximum isolation At Port 1: Z S is typically small, AFE constraints => Set Z 1 Z S At Port 2: Z PLC is unknown and varying => Set e.g. Z 2 =100W At Port 3: Z RX typically large => Set Z 3 =Z RX

9 Hybrid Isolation Preliminary Simulation Results - Maximum isolation at Z PLC = j0 W where isolation = V s /V RX

10 Digital Cancellation The received signal contains This is used to train the adaptive filter weights using an LMS algorithm and the resulting estimated signal ŷ(n) is subtracted from y(n)

11 Digital Cancellation Weight update and signal cancellation can be performed in time or frequency or a combination of time and frequency domain AFEs & AFEs &

12 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

13 N-CCC CCC 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

14 Some Preliminary Results* The EC filter, which replicates the echo, is trained using the received signal y(n) 60 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) Interference cancelation gain (db) *Note: use with caution PLC channel + hybrid attenuation (db)

15 PSD, dbm/hz TXS SI SOI Hybrid isolation Channel attenuation When canceled-si PSD is in - DRG < 1 1 < DRG < 2 DRG = 2 ECG Canceled-SI Noise

16 Data Rate Gain (DRG) Some Estimations* Ch. Att Noise PSD = -105dBm/Hz Noise PSD = -115 dbm/hz ECG SNR BHD SCINR BFD DRG SNR BHD SCINR BFD DRG *Note: max. const 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]

17 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