Wi-Fi and WLANs Challenges and emerging technolgies

(WLANs: enhancements 11e/n/ac/ad)

Evaluation of IEEE 802.11

• IEEE 802.11–1997(legacy)
  • PHY layers
    • 1 Mbits/s over infrared frequencies
    • 1 and 2 Mbits/ over 2.4 Ghz unlicensed iSM band
    • 1 Gbit/s in 802.3z-98 (fibre optics)
    • 100 Mbit/s 8023y-98 (Ehternet)
    • 2Mbits/s 802.11-97 (Wifi)
• IEEE 802.11b
  • Improved PHY Layers
    • DSS(Direct-sequence spread spectrum)
    • 22 Mhz channel
    • Enhanced modualtion and cding
    • 5.5Mbit/s and11 Mbit/s
• IEEE 802.11g
  • one more PHY layer
    • for enhanced modulation and OFDM
  • 20 Mhz channel
  • 54 Mbits Data rates
• IEEE 80.211e
  • MAC layer improvement
    • Enhanced Distributed Channel Access (EDCA)
      • QoS(Voice over WLAN,Streaming)
      • enhances the DCF and the PCF
      • With EDCA, high-priority traffic has a higher chance of being sent than low-priority traffic
        • Vocie > Video > Best-effort > background

Othe enhancemet

IEEE 802.11
IEEE 802.11a-1999	OFDM, 54 Mbit/s, 5 GHz band
IEEE 802.11d-2001	make signaling (e.g. beacons) flexible to different countries regulations
IEEE 802.11h-2003:	Solving interference of IEEE 802.11a with satellites /radar using 5 GHz band
IEEE 802.11i-2004	Improved WPA2 security mechanism for authentication and data encrypEon
IEEE 802.11j-2004	Adaptation to 4.9-5GHz band according to Japanese spectrum regulaEons

Unified Approach (IEEE802.11-2007)

• By 2007, 10 approach, difficult to maintain ,follow and support

• IEEE802.11-2007
  • Unifield solution
  • Three frequency band(Infrared, 2.4Ghz, 5Ghz)
  • Three major PHY layers
    • Legacy: 1,2, Mbit/s
    • DSSS: 5.5 Mbit/s, and 11Mbit/s
    • OFDM: 6,9,12,18,36,48,54 Mbits/s
  • Basic(WEP) and enhanced (WPA/WPA2) scurity
  • 20 Mhz-wide channels, Up to 54Mbit/s data rates
    • Phy-Layer
      • close-to-optimal OFDM, hard to improve
    • MAC- Layer
      • low-weight signaling, hard to improve access scheme
• By that time
  • 802.aq-2006 : 10 Gbit/s (multimode filter)
  • 802.3an-2006: 10Gbits/(medium-cost cable)

Improvement on WIfi

• Appoaches

  • Extend the channel bandwidth
  • Exploit the space domain
  • Increase the channel utilization at MAC LAYER
    • BY extending the DATA frame duration
    • $Utilization=\frac{data.transmission.time}{cycle.time}$
    • There might be no content to feed such a long frame with data from a single application
      • audio frame MUST BE SHORT
      • Frame aggregation(增長術)

  #### IEEE 802.11n

  • amendment to the 802.11-2007

  • PHY LAYER

    • 20Mhz(802.11-2007) to 40Mhz channels
    • Reduced guard interval (GI) from 800ns to 400ns
      • Guard Interval : time interval between symbols
      • Better electronic allows, have evolved since 1997
    • Introudction of up to 4x4 multi-antenna transmissions (multiple-input multiple-output)(MIMO).

  • MAC Layers

    • Frame aggregation
      • Reusing the same channel access procedure to transmit multiple frames
        • PHY-layers unit aggregation(A-MSDU)
        • MAC-layers units aggregation(A-MPDU)

  • Theorectical PHY-Layer throughput

    • 54Mbit/s of 11.g (20Mhz channel) -> 58.5 Mbit/s and 65Mbit/s (Reduced GI)
    • Single Stream Data rate is up to 72.2 Mbit/s(20Mhz)
      • 40 Mhz (150Mbit/s)
      • MIMO (600Mbit/s in theory)
  • Why NO 600Mbit/s Wi-Fi
    • Declared data rate is the raw PHY-layer data rate(Single user mode, no channel access)
    • Possible errors in the channel
    • Channel access scheme(utilization is realistically around 50%)
    • IP and higher layers overheads (20-30% efficiency reduction)
    • MIMO data rate increase is far from linear
    • Channels is shared with other users
    • Interferaence

• IEEE- 802.11ac

  • amendment to the 802.11-2012
  • Features
    • 80Mhz channels + 160Mhz optional channel
    • More aggressive moudulation techniques (QAM-256,non-standard implementation of QAM-1024)
    • UP TO 8 MIMO
    • DOWN LINK (from AP to clients) multi-user MIMO(MU-MIMO)

IEEE - 802.11ad

• 60Ghz band (mmWave), 2.16Ghz channels
• up to 7Gbit/s, Typically cannot penetrate walls
• Highly-directional transmissions, large-scale antenna arrays
• Mac signaling revised from AC
• Appilcations
  • Wireless display, connectivity for UHD deplolyment, VR,AR

Chanllenges for WLAN

• Increasing data rate,
  • limited bandwidth , low distance
• High dense deployment,
  • many devices per AP, collisions
• Multi-cell ,
  • inter-cell interference
• IoT and M2M communications
• User mobility between different cells,
  • Transparent connecEvity between the cells