I85PREP
⌘ K
Aruba Associate study materials
Aruba Associate study resources

Aruba Associate: WLAN Fundamentals and RF Basics

Aruba Associate · Work through your exam, one topic at a time.

All guide sections

WLAN Fundamentals and RF Basics

The WLAN Fundamentals and RF Basics domain tests whether you can explain how 802.11 radios, channels, and power budgets produce a usable client connection. Questions are conceptual and numeric: identify a band or channel plan, convert dB values, interpret SNR, and choose a standard or feature for a requirement.

RF units and the link budget

  • dBm is an absolute power; dB is a relative change. +3 dB doubles power, +10 dB is ten times, and -3 dB halves it.
  • EIRP = radio transmit power (dBm) + antenna gain (dBi) - cable/connector loss (dB). Regulatory limits cap EIRP, not just the radio setting.
  • RSSI is the received signal level; noise floor is the ambient noise. SNR = RSSI - noise floor, in dB. Higher SNR supports higher modulation and coding.

Channels and spectrum

  • 2.4 GHz has three non-overlapping 20 MHz channels in North America (1, 6, 11); 5 GHz offers many more channels, including DFS channels that must vacate for radar.
  • 6 GHz adds clean spectrum but requires Wi-Fi 6E/7 hardware and has different power and indoor rules.
  • Channel width trades throughput for spectrum: 20/40/80/160 MHz. Wider channels raise throughput but consume more channels and collect more interference.
  • Co-channel interference comes from APs on the same channel; adjacent-channel interference comes from overlapping spectrum.

802.11 capabilities

  • SSID is the network name; BSSID is the radio MAC of a BSS. Association establishes the link; authentication and DHCP come later.
  • 802.11n introduced MIMO and 40 MHz in 5 GHz; 802.11ac is 5 GHz only with wider channels and downstream MU-MIMO; 802.11ax (Wi-Fi 6/6E) adds OFDMA, uplink MU-MIMO, BSS coloring, and target wake time.

Worked example

An AP radio is set to 18 dBm, feeds a 4 dBi antenna through 1 dB of cable loss. EIRP = 18 + 4 - 1 = 21 dBm. A client hears -67 dBm with a -92 dBm noise floor. SNR = -67 - (-92) = 25 dB. That is a solid data-grade link; for voice, 25 dB is typically the minimum, so the design has little margin. If the AP power is raised by 3 dB to 21 dBm radio output, EIRP becomes 24 dBm and the client may hear about -64 dBm, improving SNR to 28 dB, assuming the client transmit power and noise environment stay constant.

Traps that cost marks

  • Treating dBm and dB as interchangeable, or assuming doubling radio power doubles range.
  • Forgetting cable loss and regulatory EIRP caps in link-budget questions.
  • Choosing 80 MHz in a crowded 5 GHz deployment and then blaming coverage.
  • Assuming 2.4 GHz has more capacity because it reaches farther; it has fewer clean channels.
  • Equating RSSI with quality: a strong signal in a noisy environment can still have poor SNR.