Combined EFM PHY using Single Carrier Modulation

Transcription

1 Combined EFM PHY using Single Carrier Modulation Combining SHDSL & QAM VDSL in an EFM PHY 802.3ah EFM Copper June 2003, Ottawa 1 Page 1

2 Supporters 2 Page 2

3 The Vision! SCM technology used over copper by IEEE 1000BaseT, considered for 10GBaseT! Autonegotiation is the best way to achieve simplicity for the end user and provider! Single EFM Copper PHY enables all the above! Single EFM Copper PHY means new entrants get a chance to catch up, no market hogs! The cost of a combined EFM PHY is slightly more than a QAM VDSL PHY today, which is ½ to 1/3 of DMT VDSL PHY 3 Page 3

4 EFM Copper Objectives! Long reach objective 2700m SHDSL adopted by 802.3ah in January! Short reach objective 750m VDSL is the technology Line code: we need to decide now between QAM and DMT 4 Page 4

5 EFM PHY structure MAC MII MII clock Gamma if. Alpha/beta if. MAC-PHY Rate Matching PMI Aggregation (optional) CRC, Scrambler TPS-TC: 64/65B encap. PMA PMD PCS 5 Page 5 Green blocks: common to both objectives PMA & PMD: QAM VDSL and SHDSL have much in common

6 Introduction the two SCM technologies! Target: Single PHY for Long and Short reach objectives! G.SHDSL PAM (Pulse Amplitude Modulation); base band (Standardized) Symmetrical rates 192kBit/s 2.3Mbps (Capability) Aggregated bit rates of up to 11.4 Mbps! QAM VDSL QAM (Quadrature Amplitude Modulation)~ Modulated PAM; pass band Symmetrical and Asymmetrical transmission technology Duplex aggregated bit rates of more than 100 Mbps 6 Page 6

7 Combining the SCM technologies! G.SHDSL and QAM VDSL in a single chipset Highest re-use of functional blocks! Means smaller die size (cost) Realized at almost no cost overhead and minimal additional space for VDSL! Means little additional complexity and die size increase over QAM VDSL die size VDSL Functions and Calculation Power fulfills most Requirements of SHDSL Optimal for EFM applications and for businesses broadband access Follows same Autonegotiation concept of 10BaseT and 100BaseT One PHY handles all EFM Copper needs 7 Page 7

8 Structure of a common SHDSL / VDSL- QAM Transceiver PMA PMD PMD TPS-TC VDSL-QAM digital functions VDSL-QAM Analog functions Hybrid Transformer SHDSL SHDSL 8 Page 8

9 Common Functions in VDSL QAM and SHDSL Transmit Path The transmit path (digital) Framer PAM Scrambler Channel Precoder Echo Cancellation Data in Scrambler QAM RS-FEC Interleaver Framer TC PAM/ QAM Encoder Echo canceller To Analog Chip Digital Power Control Notch Filter QAM Modulator TX Filter The transmit path (analog) Caption: Digital Data D/A Converter Post Filter Analog Power Control Line Driver To Hybrid Similar Functions VDSL only Functions Same Hardware - different Functions 9 Page 9

10 Common Functions in VDSL QAM and SHDSL Receive Path The receive path (analog) From Hybrid AGC Channel Equalizer Pre Filter A/D Converter Digital Data The receive path (digital) Echo Cancellation Channel Precoder From Analog Chip QAM Demodulator RX Filter DGC Linear Equalizer Slicer AGC Control Timing Control Coefficient Adaptation Decision Feedback Equalizer Data out De- Scrambler RS Decoder De- Interleaver Deframer QAM Decoder QAM Caption: Similar Functions Deframer De- Scrambler Viterbi Decoder PAM VDSL only Functions Same Hardware - different Functions 10 Page 10

11 Function Blocks of VDSL that can be used by SHDSL 11 Page 11! Scrambler / Descrambler and Framer / Deframer! QAM Encoder and TC PAM Encoder (w/o Tomlinson)! Decision Feedback Equalizer, LEQ, Slicer DFEq used as SHDSL Tomlinson Encoder at show time! Tx Filter / Rx Filter! Power control / AGC / DGC! DA converter / AD Converter Same Hardware requirements for high Bandwidth of VDSL and high resolution of SHDSL selected by Noise Shaping / Decimation parameters! Line Driver 135 Ohm nominal Impedance (SHDSL and VDSL QAM) 14.5 dbm Transmit Power (SHDSL and VDSL QAM) Crest-factor: SHDSL= 2.9 ; VDSL= 3.5! G.hs: SHDSL and VDSL are members of the 4 khz Carrier set signaling family

12 Blocks that can be used for different functions for SHDSL and for VDSL! RAM: SHDSL needs in total 75% of the amount of RAM as QAM VDSL for signal processing When FEC and interleaver comes into a standard, SHDSL will use the unused 25% for interleaving! (De-)Interleaver for VDSL: SHDSL will use the RAM for Viterbi and Echo cancellation All these blocks consist of 85% of RAM 12 Page 12

13 Coverage of SHDSL Development in Standardization A combined QAM VDSL and SHDSL PHY provides sufficient signal processing resources to perform the new SHDSL features currently discussed in standardization bodies Higher Data Rates up to 5.7 Mbps Wide PSD of 713 khz Higher constellations of 32, 64 and 128 levels (4, 5, 6 Bits per Symbol) Operation with underlying POTS (SHDSL over POTS) Forward error correction and Interleaving Bonding of high numbers of loops 13 Page 13

14 Comparison of VDSL-DMT vs. SHDSL 14 Page 14 SHDSL Amplitude Modulation Symbol frequency 64 khz 770 khz (1426 khz) Bit processing DFE Not available Trellis Viterbi for PAM with 5dB coding gain Digital Echo cancellation Synchronization on Symbols (3 or 4 bits) Crest factor 2.9 g.hs tones: 4 KHz DMT VDSL Discrete multi tone Symbol frequency 4 khz 250 or 125 µs Block processing Not available (I)FFT Not available Not available Pilot tone Crest factor 5.6 g.hs tones: KHz Summary: DMT VDSL provides many functions that cannot be used for SHDSL and vice versa. A combined chip carries a lot of overhead and is far from being optimized.

15 Summary! SCM all the way through! Follows the IEEE view of combined PHYs and Autonegotiation! QAM and SHDSL PHYs have many blocks that can be shared or re-used! QAM vendors have proven expertise and field experience in SCM - both QAM and SHDSL technologies! VDSL QAM and SHDSL are easy to implement! Development cycle for a combined SHDSL & QAM VDSL will be shorter! Size and cost of chip-set will be lower than a DMT VDSL and SHDSL PHY 15 Page 15