Introduction to Wireless Networks

Ubiquitous Connectivity

Nowadays, we have come to expect ubiquitous connectivity.

Wireless networks make this possible. They are based on common proinciples, tradeoffs, and have common constraints.

Types of Wireless Networks

Network: group of devices connected to one another

Wireless network: typically uses radio communication as medium

There are lots of technologies for lots of applications, so there are many ways to classify different wireless networks

Performance Fundamentals of Wireless Networks

Every wireless technology has its own set of constraints, but they all have a maximum channel capacity, determined by the same underlying principles

• $C=BW\times {\text{log}}_2(1+\frac{S}{N})$
  • $C$: channel capacity (bits per second)
  • $BW$: available bandwidth (hertz)
  • $S$ signal (watts)
  • $N$ noise (watts)

Bandwidth

Radio communication uses a shared medium: radio waves!

So, sender + reciever need to agree on specific requency range over which communation will occur

Who determines the requency range and its allocation?

• In the US- the TCC

What matters for performance? he size of the asigned frequency range (channel bit rate directly proportional to this)

Note: not all frequency ranges ofer the same performance

• Low frequency: travel father and larger areas- require larger antennas
• High frequency: transfer more ata but not as far

Signal Power

This is the second fundamental limiting power

Signal power: compares level of desired signal to level of background noise and interference

• Larger amount of background noise- stronger signal needs to be

Remember: shared medium- get unwanted interference

2 effects

• Near-far problem: when strong signal crowds out weaker signal such that receiver can’t detect it
• Cell-breathing: condition where coverage area expands and shrinks based on cumulative noise and interference levels

Modulation

Algorithm by which signal is encoded can also have a significant effect

Modulation: digital (1s and 0s)-to-analog (radio waves) conversion

Example

• Receiver/sender can process 1,000 pulses/symbols per second (1,000 baud)
• Each symbol represents a different bit-sequence, (e.g. in 2-bit. alphabet)
• Bit rate of channel is 1,000 x 2 bits per symbol (2,000 bits per second)

Higher order moduilation alphabet comes at cost of reduced robustness to noise and interference

Measuring Real-World Wireless Performance

In summary

All radio-powered communication is:

• Done over radio waves (shared medium)
• Regulated to use specific:
  • Bandwidth frequency ranges
  • Transmit power rates
• Subject to:
  • Continuously changing background noise/intererence
  • Constraints of chosen wireless tech and device

The performance of any wireless network is affected by just a few factors:

• Distance between receiver + sender
• Background noise in current location
• Interference from users in same network
• Interference from users in other, nearby networks
• Processing power + chosen modulation scheme

Basically, to get maximum throughjput

• Place receiver and sender as close as posible
• Give all the power they want
• Select best modulation mehtod