CityU Wireless LAN Upgrade

by S K Tsui
The majority of the wireless access points (APs) installed on campus were the outdated Aruba AP-125 model (product of year 2009) which supports legacy standards 802.11a/b/g/n but cannot support the 5th generation of Wi-Fi standard 802.11ac. In order to meet the increasing demands from user devices and to improve the Wi-Fi service performance within campus, the Computing Services Centre (CSC) started to upgrade the wireless LAN last summer by replacing the controllers and 200 x AP-325 APs to provide 802.11ac Wave 2 support in high-density areas such as Library and 4/F mall area of AC1. This summer, the CSC is going to replace 600 x AP-335 in the classrooms and Lecture Theatres and is expecting to replace the remaining 2000 legacy APs in the coming year(s). Since the new APs are fully backward compatible with the previous Wi-Fi standards, you do not need to upgrade your Wi-Fi device to work with the new APs. However, new enhancements will function only when the client devices also support the new 802.11ac standard.
Below are the major improvements in the new 802.11ac Wave 2 standard over the old standards: 
  1. Offers higher speed and better performance
    • Supports 160MHz-wide (or 80MHz+80MHz) channels in the 5 GHz band to allow higher throughput between two wireless devices and enables high-speed delivery of large files and data access.
    • Supports four spatial streams to increase the amount of signals that can be transmitted simultaneously from one device using different antennas.
    • Uses 256 Quadrature Amplitude Modulation (QAM) to achieve higher raw-data speed.

      With the above technologies, Wave 2 can provide up to 3.47 Gbps data throughput. Since 802.11ac has the headroom to support up to eight spatial streams, therefore the maximum throughput can go up to 6.93 Gbps theoretically. Below is the speed comparison of different standards:


        Frequency Band Theoretical maximum rate
      802.11ac Wave 2 5GHz 3.47 Gbps
      802.11n 2.4GHz or 5GHz 600 Mbps
      802.11g 2.4GHz 54 Mbps
  2. Uses explicit beamforming technology to improve Wi-Fi reception and reduce interference by focusing Wi-Fi signals directly to an intended client devices and vice versa.

    Beamforming improves wireless bandwidth utilisation, and can increase the performance of wireless networks at medium ranges. It also enables the support of MU-MIMO technology.

  3. Supports downlink MU-MIMO

    MU-MIMO stands for “Multi-User, Multiple-Input, Multiple-Output”. This is the multi-user version of MIMO technology that allows an AP with four antennas to simultaneously transmit data to multiple MU-MIMO capable devices (at most four devices such as smartphones, each with one antenna) to achieve more efficient use of the spectrum and greatly improve the overall wireless network capacity. The MU-MIMO boosts user capacity and ensures better experience for end users under the extremely high device-density environments.

    Unfortunately, the uplink MU-MIMO that allows multiple client devices to transmit data to the access point at the same time is not implemented in the 802.11ac Wi-Fi standard. Therefore only one client device is allowed to send data to the AP at any instant. Uplink MU-MIMO will be implemented in the next-generation Wi-Fi specification 802.11ax.

The 802.11ac standard brings many new improvements. It is designed for high speed, more stable and high density wireless network. The new technologies used can significantly improve the performance of bandwidth and latency-sensitive applications such as massive data transfer and video streaming. Users will need to use 802.11ac devices to take full advantage of the new features.

  1. Aruba Networks 802.11ac white
  2. Cisco 802.11ac Wave 2 FAQ