Physical layer concepts Distorsion Effect of attenuation distortion

Physical layer concepts

Distorsion

Effect of attenuation, distortion, and noise on transmitted signal.

Point-to-point communication Layer 7 Layer 6 Mikrofon Högtalare Source coding 0110 Error management Layer 2 Layer 1 Digitalizating compression NACK 0110010 Source decoding 0110 . Error control 0100010 Flow control Modulation Demodulation 0110010 Bit error

Digital modulation methods Binary signal ASK = Amplitude Shift Keying (AM) FSK = Frequency Shift Keying (FM) PSK = Phase Shift Keying (PSK)

8 QAM example: Below you find eight symbols used for a so called 8 QAM modem (QAM=Quadrature Amplitude Modulation). The symbols in the first row represent the messages 000, 001, 011 and 010 respectively (from left to right). The second row representents 100, 101, 111 and 110.

Example 2 cont.

Bit rate vs baud rate Bit rate in bit/s: Where M is the number of symbols and fs is the symbol rate in baud or symbols/s.

Bit and baud rate comparison Units Bits /symbol Baud rate Bit Rate Bit 1 N N 4 -PSK, 4 -QAM Dibit 2 N 2 N 8 -PSK, 8 -QAM Tribit 3 N 3 N 16 -QAM Quadbit 4 N 4 N 32 -QAM Pentabit 5 N 5 N 64 -QAM Hexabit 6 N 6 N 128 -QAM Septabit 7 N 7 N 256 -QAM Octabit 8 N 8 N Modulation ASK, FSK, 2 -PSK

Sine wave example Complex representation 5 Volt л/2 radians =I 90º

Figure 5. 14 The 4 -QAM and 8 -QAM constellations Q (Quadrature phase) I (Inphase)

Figure 5. 11 The 4 -PSK characteristics

Figure 5. 12 The 8 -PSK characteristics

Figure 5. 16 16 -QAM constellations

Figure 5. 20 The V. 32 constellation and bandwidth

Spectrum of ASK, PSK and QAM signal

Figure 9. 3 ADSL modem

Figure 9. 4 DSLAM

Other DSL Technologies • SDSL (Symmetric DSL) divides frequencies evenly • HDSL (High-rate DSL) provides DS 1 bit rate in both directions · Short distances · Four wires • VDSL (Very high bit rate DSL) provides up to 52 Mbps · Very short distance · Requires Optical Network Unit (ONU) as a relay