WiMAX Downlink OFDMA Burst Placement for Optimized Receiver Duty-Cycling

Abstract

Mobile wireless broadband access networks are now becoming a reality, thanks to the emerging IEEE 802.16e standard. This kind of network offers different challenges when compared to the fixed ones, as power consumption becomes a major concern. In this standard, a strict organization of the downlink bursts is not guaranteed in the OFDMA frame and this may lead to extra power consumption for the receiver, decreasing the device's lifetime. In the present paper, we introduce an optimization algorithm capable of reducing the activity of each receiver in the system for decoding its addressed bursts, thanks to a better time-frequency organization of the bursts. We first work on fitting bursts within the smallest frame, and show that the minimal number of OFDM symbols is enough in 70 to 80% of the cases, while one extra is needed otherwise. Using a binary tree implementation of an exhaustive burst placement search, we also show that we can gain 20 to 30% in duty-cycling of the receivers by selecting the best configuration, hence gaining the corresponding energy. This holds for receivers decoding either their bursts only or all the bursts from the beginning of the frame up to their own bursts before sleeping, depending on the scenario. The full search is sustainable for up to 8 user bursts per frame.

OFDMA Downlink Burst Allocation Mechanism for IEEE 802.16e Networks

“…As the DL-MAP is broadcasted to all SSs, minimizing its size will also reduce the awake period of every SS. Some algorithms [6] specifically deal with this goal, as we will see in Section 2.3.…”

“…In [6], authors seek to optimize the receiver awake cycle by reducing the average duration and delay of the bursts within a given frame. Although this is an important goal for a resource allocator as stated in Section 2.2, the algorithm uses a full search approach, making it impractical for more than eight users.…”

OCSA: An algorithm for burst mapping in IEEE 802.16e mobile WiMAX networks

“…Claude Desset and his colleges [5] showed that only 8 users at a maximum can be supported with a binary-tree full search algorithm for burst mapping in a rectangular shape. However, this work does not consider the variations of possible mapping pairs for each particular burst.…”

“…In this example, we try all possible widths (from 2 to 12) resulting in 2×19, 3×13, 4×10, 5×8, 6×7, 7×6, 8×5, 9×5, 10×4, 11×4, 12×4. These mappings will result in the over allocation of 1,2,3,3,5,5,3,8,3,7, and 11, respectively. The constraints of the maximum allowable width and height still apply.…”

Scheduling in IEEE 802.16e mobile WiMAX networks: key issues and a survey

“…This violates our goal of minimizing burst overhead. The binary-tree full search can support only 8 subscribers [13] and so it is not of any practical use.…”