ity and 100 Mbps for high mobility [4]. In order to support wider transmission bandwidths IEEE 802.16m and 3GPP LTE-Advanced systems introduced the carrier aggregation concept, where two or more Component Carriers (CC) belonging to a single frequency band or different frequency bands can be aggregated [2,21]. The support of system bandwidths up to 100 MHz will 'Region 1: Europe, the Middle East and Africa (EMEA); Region 2: North and South America (Americas); Region 3: Asia-Pacific (APAC) (see http://www.itu.int/ITU-R/). Mobile WiMAX. DOI: 10.1016/B978-0-12-374964-2.10011-6 Copyright © 2011 Elsevier Inc. CHAPTER 11 Multi-Carrier Operation allow an increase in both the peak data rate and the system capacity. In the scenarios of interest, the peak data rate increases almost linearly proportional to increasing bandwidth. Hence, for example, to obtain the required peak data rate of 1 Gbps in the downlink with 30 bps/Hz peak spectral efficiency (assuming 8-layer MIMO transmission), a bandwidth of only 40 MHz is sufficient. It is noted that in addition to an increase in the peak data rate, the bandwidth extension results in higher data rates for all mobile terminals in a cell, due to increased average and cell- edge throughputs. Using the carrier aggregation scheme, it would be possible to simultaneously schedule a user on multiple component carriers for downlink or uplink data transmission, resulting in some challenges in resource scheduling and load balancing across the network. In a non-adjacent inter-band aggregation scenario, where the aggregated carriers belong to different frequency bands, the fading characteristics might be different between component carriers; consequently, the coverage may vary from one carrier to another. With different locations in the cell, some users can only be scheduled on certain carriers, while other users be scheduled on all aggregated carriers; this has a negative impact on the fairness of allocation among users. The original proportional fair algorithms can be used as a trade- off b