Introduction (chapter objectives) Power spectral density Matched filters Recall former Chapter that random signals are used to convey information. Noise is also described in terms of statistics. Thus, knowledge of random signals and noise is fundamental to an understanding of communication systems

3.9 Time-Division Multiplexing Definition. Time-division multiplexing (TDM) is the time interleaving of samples from several sources so that the information from these sources can be transmitted serially over a single communication channel

Communication Defined The transmission of information and understanding through the use of common symbols from one person to another Common symbols may be

Packet Multiple Access SHARED UPLIN TERMINAL APPL TERMINALL TRANS NET LLC DLC MAC

Routing Must choose routes for various origin destination pairs o/d pairs) or for various sessions Datagram routing: route chosen on a packet by packet basis Using datagram routing is an easy way to split paths Virtual circuit routing: route chosen a session by session basis Static routing: route chosen in a prearranged way based on O/D pairs Eytan Modiano

Used for analyzing network performance In packet networks, events are random Random packet arrivals Random packet lengths While at the physical layer we were concerned with bit-error-rate, at the network layer we care about delays How long does a packet spend waiting in buffers?

Modulation Representing digital signals as analog waveforms Baseband signals Signals whose frequency components are concentrated around zero Passband signals Signals whose frequency components are centered at some frequency fc away from zero Baseband signals can be converted to passband signals through modulation Multiplication by a sinusoid with frequency fc Eytan Modiano

Channel Coding When transmitting over a noisy channel, some of the bits are received with errors Example: Binary Symmetric Channel (BSc) Pe= probability oferror Q: How can these errors be removed? A: Coding: the addition of redundant bits that help us determine what was sent with greater accuracy

Source coding Source Encode Channel Alphabet alphabet Source symbols Letters of alphabet, ASClI symbols, English

Sampling Given a continuous time waveform, can we represent it using discrete samples? How often should we sample? Can we reproduce the original waveform?