5/6/99 HDSL2 Modem Modeling and Simulation 1HDSL2 Modem Modeling andHDSL2 Modem Modeling andSimulationSimulationPatrick JacksonReza Koohrangpour5/6/99 HDSL2 Modem Modeling and Simulation 2HDSL2 OverviewHDSL2 Overviewl High-bit-rate Digital Subscriber Line - 2ndGeneration– Symmetric 1.544 Mbps– Applications• T1 replacement• Telecommuting• Internet access– Advantages Over T1• Much easier to deploy– Bridge taps OK– 12,000 feet range– Spectral compatibility• Single twisted pair5/6/99 HDSL2 Modem Modeling and Simulation 3Project OverviewProject Overviewl Ptolemy Simulation– Trade-off analysis• Highly configurable• Extensible– SDF domainl Reference Design– HDSL2– Other modemsl Ptolemy Contributions5/6/99 HDSL2 Modem Modeling and Simulation 4Startup ModeStartup Model Equalize channel– Reverse distortions– Adaptive filters in receiver– Training sequencel Communicate parameters back totransmitter– Equalizer coefficients– Convolutional encoder polynomial5/6/99 HDSL2 Modem Modeling and Simulation 5Startup Mode SimulationStartup Mode SimulationlConfigurable– Channel model– Adaptive equalizerlPasses parameters to data mode through files5/6/99 HDSL2 Modem Modeling and Simulation 6Data ModeData Model Operating Mode– Sending and receiving datal Additional Components– Transmitter• Trellis encoder• Tomlinson precoder– Receiver• Viterbi decoder5/6/99 HDSL2 Modem Modeling and Simulation 7Trellis EncoderTrellis Encoderl Trellis Encoder– Adds redundancy– Output depends on state and input (512 states)– 3 bits in - 16-PAM pulse outConvolutionalEncoderSerial toParallelX(2)Bit-to-LevelMapperX(1)X(0)5/6/99 HDSL2 Modem Modeling and Simulation 8Programmable EncoderProgrammable EncoderX1(m-1)a1a0TsTsTsa2.........a19a20b1Y0(m)Y1(m)X1(m-20)X1(m-19)X1(m)b0b2b19b20l Convolutional Encoder– Ts = delay of one symbol time– ⊕ = binary exclusive-OR– ⊗ = binary AND5/6/99 HDSL2 Modem Modeling and Simulation 9Trellis DecoderTrellis Decoderl Viterbi Algorithm– Maximum likelihood sequence detection• Calculate difference between receivedcodes and codes leading to next possiblestates• Choose minimal difference sequence– Window length• Sequence depth before decision• Trade-off: complexity,latency/gain5/6/99 HDSL2 Modem Modeling and Simulation 10Data Mode SimulationData Mode Simulation5/6/99 HDSL2 Modem Modeling and Simulation 11Simulation ParametersSimulation Parameters5/6/99 HDSL2 Modem Modeling and Simulation 12ConclusionConclusionl Contributions– Configurable/extensible simulation– Reference design– Ptolemy• Programmable Viterbi decoder• Tomlinson Precoderl Limitations and Future Work– Startup-to-data mode sequence• Mixed FSM, BDF, and SDF– Timing recovery• Mixed BDF and
View Full Document
Unlocking...