Resource allocation procedure in IEEE 802.16 (WiMAX) standard

Introduction

IEEE 802.16 is a standard for the wireless broadband access network, which provides a flexible fixed-wireless and mobile-wireless access between subscriber stations (SS) and a provider. The main advantages of IEEE 802.16 when compared to other wireless network access technologies are the longer range and a more sophisticated support for the Quality-of-Service (QoS) at the MAC level. Different application and service types can be used in 802.16 networks and the MAC layer is designed to support this convergence.

To request uplink resources, 802.16 stations may send bandwidth request by means of uplink contention. The contention resolution mechanism in the 802.16 networks differs from the one used in the IEEE 802.11 (WiFi) standard. While the WiMAX SS tries to avoid collisions by generating a random backoff timer and listening whether the medium is busy or not, the WiMAX SS just picks up randomly a transmission opportunity. Though the transmission opportunity is chosen based on the similar truncated binary exponential backoff mechanism, an SS does not detect whether another SS is transmitting at the same time or not. If the BS receives successfully the bandwidth request, then it allocates resources for the SS. Otherwise, if a collision occurs or a packet is lost, no action is taken and the SS retransmits the bandwidth request.

In IEEE 802.16 OFDMa PHY, prior to sending the bandwidth request, an SS sends a special CDMA code to request uplink resources for the bandwidth request.

Research directions

The project will concentrate on the resource allocation procedure and contention resolution mechanism details. In particular, the following aspect will be investigated:

1. The CDMA request codes correlation properties;
2. Performance comparison of different receivers for the CDMA request codes;
3. Dependence of the bit error rate and false alarm - missed detection probabilities ratio to the system 
   performance;
4. Design of the new CDMA request codes with improved correlation properties.
5. Partitioning of the CDMA codes into groups for initial ranging, bandwidth requests, and handover

Project stages

The main project development stages will include:

1. Theoretical model of the dependence of CDMA codes to the system performance;
2. Simulating the CDMA request procedure in MATLAB environment;
3. Obtaining simulation results for different codes and partitioning
4. Interface for high-level simulators to utilize the MATLAB results on CDMA code performance
5. Implementing the designed codes in NS-2 802.16 module to study the system performance.

Team members

Alexey Dudkov, University of Turku
Alexander Sayenko, Nokia Siemens Networks