International Journal on Communications Antenna and Propagation (I.Re.C.A.P.), Vol. 2, N. 1 ISSN 2039 - 5086 February 2012 Manuscript received and revised January 2012, accepted February 2012 Copyright © 2012 Praise Worthy Prize S.r.l. - All rights reserved 1 Adaptive Subband Allocation in FH-OFDMA with Channel Aware Frequency Hopping Algorithm Ardalan Alizadeh, Seyed Mohammad-Sajad Sadough Abstract – This paper presents a new subband allocation scheme for multiuser OFDMA systems. Adaptive OFDMA systems have focused on adapting the allocation of subcarriers and power to the instantaneous channel conditions of all users. Using frequency hopping pattern in OFDMA system allow users to minimize intercell and intracell interference, and perform frequency diversity. In contrast to conventional FH-OFDMA, which uses a channel state independent hopping sequence, the transmitter in the channel aware scheme hops to the available frequency subband which has the largest transmission gain. Simulation results demonstrate that in power constraints assumption, using our proposed channel aware frequency hopping (CAFH) along with OFDMA scheme outperforms multiuser OFDMA system with fixed subband assignment. Copyright © 2012 Praise Worthy Prize S.r.l. - All rights reserved. Keywords: OFDMA, Channel Aware Frequency Hopping Algorithm, FH-OFDMA Nomenclature (·) T Transpose operation F IFFT matrix r Number of rounds N Total number of subcarriers C i Set of subcarriers assigned to the i-th user N i Number of subcarriers assigned to the i-th user n(t) AWGN noise L Number of subbands T Duration of one OFDM symbol I. Introduction Orthogonal frequency division multiplexing (OFDM) has been presented as a new technology for next generation wireless communication systems. In OFDM systems, high-rate information can be divided into a number of parallel lower-rate streams with the advantage of avoiding the requirements of complex equalization [1]. These systems also provide the multiple access schemes termed as orthogonal frequency division multiple access (OFDMA). In OFDMA, a fraction of available subcarriers is assigned to each user based on the demand for bandwidth. Three advantages of OFDMA include (1) the flexibility in subcarriers' allocation; (2) the absence of multiuser interference due to subcarriers' orthogonality; (3) the simplicity of the receiver design [1]. To improve the system throughput and spectral efficiency, frequency hopping (FH) technique is generally used in OFDMA cellular systems. As mentioned in [2], it is desirable for FH patterns to satisfy the following conditions: (i) minimize intracell interference; (ii) average intercell interference; (iii) avoid ambiguity while identifying users; (iv) exploit frequency diversity by forcing hops to span a large bandwidth. The first aspect is relatively easy to achieve by using orthogonal hopping patterns within a cell. To average intercell interferences, hopping patterns are constructed in a way that two users in different cells interfere with each other only during a small fraction of all hops. The third condition requires base stations to have the capability of distinguishing different user efficiency according to their unique FH signatures. Finally, the last requirement not only ensures the security of the transmission, but also mitigates the effect of fading by exploiting frequency diversity [2]. On the other hand, frequency hopping pattern scheme has achieved considerable attention in both military and commercial communication systems. There has been much research on designing FH-OFDMA systems. For instance in [3], concepts of fast frequency hopping along with OFDM are provided. Orthogonal Latin squares (LSs) are presented as FH patterns in TCM/BICM coded OFDMA in [4]. In LS-aided FH-OFDMA systems, there is wide variability in performance of users within different cells. Therefore, it is not a useful scheme when the fairness consideration is important. Therefore, although users of each cell experiences significant performance improvement, the cell may not occupy all of the available bandwidth to receive full frequency diversity. Other aspects on preventing hostile jamming and pilot-assisted channel estimation in FH-OFDMA are provided in [5], [6].