Anique Akhtar

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Directional MAC Protocol for IEEE 802.11ad WLANs (PDF Draft)

  • Abstract:
    Millimeter-wave (mmWave) communications is a promising technology that enables high rate (Giga-bit) multimedia applications. We consider the directional multigigabit (DMG) transmission problem in IEEE 802.11ad wireless local area network (WLAN). Traditional directional MAC uses Network Allocation Vector (NAV) to decrease collisions drastically by making nodes which have their NAV set, defer their communication. Directional MAC protocols usually implement either directional RTS/CTS (DRTS/DCTS), multi-directional sequential (Circular) RTS/CTS (CRTS/CCTS) or multi-directional concurrent RTS/CTS control packets. IEEE 802.11ad MAC implements an A-BFT phase where each node beamforms (BF) with the Access Point (AP). In this thesis, we propose a Directional MAC protocol for Basic STAs (DMBS) that uses DRTS/DCTS as well as CRTS/CCTS control packets along with two NAVs (NAV1 and NAV2) to fully leverage spatial reusability and tackle deafness and hidden terminal problem without using any complicated hardware. DMBS makes each node keep a beamforming table (BF table) to store location information of other nodes. We implement an Intelligent Listening during A-BFT (ILA) mechanism where STAs gather beamforming information by listening to the channel during A-BFT phase and update their BF table. This considerably reduces the overall network beamforming associated overhead. Furthermore, if a node already have BF information of the destination node, it uses DRTS/DCTS packet to communicate otherwise CRTS/CCTS packet is used to gather location information. This assures that the control overhead is minimal and the protocol doesn't have to use any complicated technique or hardware or rely on upper layers for location tracking. NAV1 keeps a list of all the nodes that are busy and is set every time a RTS/CTS packet is received. A node would not initiate communication with a node that is in NAV1 subsequently reducing deafness. With the help of RTS/CTS control packets received, the nodes determine whether they can cause interference to an ongoing communication. NAV2 is only set if a node can cause interference to an ongoing communication. If NAV2 is set, then the node defers its multi-directional communication but still communicates directionally. This increases spatial reusability all the while keeping interference minimal which increases the overall network throughput. We perform extensive simulations by comparing DMBS with other commonly used protocols and by comparing different features of DMBS in different scenarios. Simulations demonstrate that the DMBS improves the network throughput considerably, especially at higher network size.

  • Novelties:

    • A full Directional MAC for Basic STAs (DMBS) protocol that works without any aditional hardware.

    • Combines the usage of both DRTS/DCTS and CRTS/CCTS control packets. CRTS/CCTS packet is used when the location information of the other node is not available or is outdated where as DRTS/DCTS is used when the location is already known.

    • Intelligent Listening during A-BFT (ILA) mechanism is proposed in which the stations gather beamforming/location information of their neighboring nodes.

    • DMBS employs two NAVs: NAV1 and NAV2. NAV1 is used to keep a list of all the busy nodes in order to resolve the deafness problem. NAV2 is used to determine the interfering links in order to resolve hidden terminal problem while exploiting spatial reusability.

    • DMBS does not require any additional hardware for tracking the location of neighboring nodes nor any complex receiver for determining the direction of incoming packets.

  • Simulations:

    • The simulations are performed in an event-based simulator created in MATLAB, called MMWAVEMAC.

    • We provide the source code for MMWAVEMAC on this page and also explain the working of the simulator.

MMWAVEMAC:

  • An event based MAC protocol simulator for directional communication in MATLAB.

  • MMWAVEMAC is used to compare DMBS with five previously proposed protocols. The codes for all of these protocols are provided below.

  • Simulation Code:

    • Directional MAC protocol for Basic STAs (DMBS).

    • Basic DMAC (BDMAC).

    • Circular RTS and CTS MAC (CRCM).

    • CRCM Without Deferring on control packets (CRCM-W/0-D).

    • Circular and Directional control packets Hybrid MAC (CDHM).

    • CDHM Without Deferring on control packets (CDHM-W/0-D).

  • The code is fully commented and is easy to understand. If there are still any questions, you can reach us at aakhtar13@ku.edu.tr

  • Conclusion:
    In this work, we propose a Directional MAC for Basic STA (DMBS) protocol that uses DRTS/DCTS as well as CRTS/CCTS control packets along with two NAVs (NAV1 and NAV2) to fully leverage spatial reusability and tackle deafness, hidden terminal and location problem without using any complicated hardware. We implement an Intelligent Listening during A-BFT (ILA) mechanism where STAs gather beamforming information by listening to the channel during A-BFT phase and update their BF table. We make use of CRTS/CCTS packets to collect location information and use DRTS/DCTS packets for communication. Furthermore, nodes detect using received control packets whether they can cause interference to an ongoing communication. If they can cause interference, they defer only their circular communication. Simulation results show that DMBS out performs other protocols in almost all scenarios with both mobile and stationary nodes even when we have single destination or multiple destinations. The improvement is higher when each node has multiple destinations which is due to DMBS features that minimizes overhead and tracks the location of other nodes. Simulation results show that NAV1 helps with deafness problem whereas NAV2 mechanism helps eliminate the hidden terminal problem. ILA mechanism and updating BF table on the reception of each control packet helps with location tracking and decreases the beamforming associated overhead of the system. This in turns helps protocol leverage spatial diversity.