Priority aware frame packing for OFDMA systems in distributed permutation mode

ABSTRACT: As of today the two candidates for 4G which has been commercially deployed are the Institute of Electrical and Electronics Engineers (IEEE) standard 802.16e (“Mobile WiMaX”) and the 3rd Generation Partnership Project (3GPP) standard Long Term Evolution (LTE-Advanced). Both standards make use of Orthogonal Frequency Division Multiple Access (OFDMA) as their downlink modulation schemes and allocations for users must be carried out using both time and frequency (sub-channels vs. symbols). In this thesis we focus on the IEEE 802.16e in Partially Used Sub-Carrier (PUSC) mode which is taking advantage of frequency diversity. For each 5 milliseconds frame, the data for different users must be placed into the DL part of the frame based on the decision of a scheduler. Once the scheduling is complete a packing algorithm will then try to fit all requests into the frame considering channel quality, selecting Modulation and Coding Scheme (MCS) and deciding on the number of bytes per slot per burst. The empirical channel model adopted in the thesis is the COST 231 extended version of the Hata model using 2360-2370 MHz band. All simulations were done using the MATLAB platform and writing dedicated functions for each task. We consider an urban microcell environment and assume that based on the traffic characteristics the admission control module has admitted 20 connections. The cell coverage area was assumed to be circular with a diameter of 4 km. The starting values of the radial distance (in meters) of the mobile stations in the cell were determined using varieties drawn from a uniform distribution in the range 100-2000 meters. Then, for the future frames, the position of each Mobile Station (MS) was re-calculated assuming a vehicular speed chosen uniformly between 0-60 km/h either towards or away from the Base Station (BS). First, the well-known Enhanced One Column Stripping with Non-Increasing Area First Mapping (eOCSA) algorithm was used for packing and then a novel packing algorithm making use of priority aware packing was proposed to extend the eOCSA in order to get a more efficient packing algorithm. In the priority-aware extended eOCSA algorithm each user was given a priority number between 1 and 6. When the number is 1 or 2, the user’s bursts are assumed to be “low-priority”, and when it is between 3 and 6, the bursts are considered to be “high-priority.” The priority-aware packing algorithm would first pack the bursts in the high-priority class and then would move on to the ones in the low-priority class. If a burst cannot be fitted into a frame, its priority number would be increased (by one unit) in an attempt to upgrade its class in the next frame. That way, the leftover bursts would be progressively given higher priority numbers in upcoming frames. If the priority number associated with a burst become larger than 6, the algorithm would drops that burst. To show the effectiveness of the newly proposed priority aware packing algorithm we compared the average percentage of unallocated burst in our proposed algorithm against that of eOCSA which was obtained using 6 seconds worth of simulation (1200 frames) for the 100 times the simulation was repeated. Keywords: SOFDMA; WiMaX; PUSC; eOCSA; Priority-Aware eOCSA. …………………………………………………………………………………………………………………………………………………………………………………………………………