Spectral Efﬁciency Enhancement Using Multiaccess Scheme in Heterogeneous Network Yonghoon Choi, Khan Sohaib, Wan Choi, Seungmo Kim † , and Youngnam Han Korea Advanced Institute of Science and Technology, Daejeon, Korea Email: {yh.choi, sohaib khan, w.choi, ynhan}@kaist.ac.kr † Samsung Electro-Mechanics, Korea Email: {seungmo0604.kim}@samsung.com Abstract—In this paper, we propose a spectral efﬁciency en- hancement algorithm through simultaneous accesses to heteroge- neous networks, where a mobile station (MS) can simultaneously access different non-interfering networks with different radio access technologies (RATs). This simultaneous access (i.e., RAT diversity) is determined in terms of the distributed optimal solution, which implies that MSs can decide whether they connect with multiple RATs or not. To derive the optimal solution, we ﬁrst show the advantages of multiaccess (MA) by an example in heterogeneous networks, and analyze the spectral efﬁciency of MA in multi-RAT system. Through our analysis and simulations, it is shown that the proposed algorithm is able to achieve the increase of spectral efﬁciency compare with vertical handoff (VHO) method, which selects only one network having the best channel quality. As a result, the proposed MA algorithm can be considered as a viable solution to get more spectral efﬁciency in heterogeneous environments. keywords – spectral efﬁciency, multiaccess, simultaneous access, multi-RAT, heterogeneous network I. I NTRODUCTION The next generation wireless communication systems will need to support multiple services ubiquitously in heteroge- neous network [1]-[2]. In those heterogeneous environments, spectrum management technology is a key issue for efﬁcient sharing of the available scarce radio resource (such as spec- trum and power) among mobile users. To increase spectral efﬁciency, many researches such as multiaccess scheme and radio resource management have been done in [3]-[4]. [5] derives the achievable spectral efﬁciency in spectrum pooling systems. Recent studies have shown that dynamic systems and technologies provide a new paradigm for spectrum assignment and management, resource allocation, and adaptive network- ing, as in [6]. In heterogeneous wireless networks, the possibility of an in- tegrated architecture that is able to improve spectral efﬁciency is introduced in [4], [7]-[9]. Basically, [7] introduces a concept of integrating universal mobile telecommunications system (UMTS) with 802.11 wireless local area network (WLAN) and suggests a possible integration architecture, which allows a mobile station (MS) to maintain data service through WLAN and voice connection through UMTS in parallel. Another inte- gration model and interworking mechanisms, which combine WLANs and general packet radio service (GPRS), are dis- cussed in [8]. Also, [8] presents some interworking scenarios and signaling ﬂows to provide low-speed data over a large cov- erage area and high-speed data service over a geographically small area. Another integration model and system architecture of ad-hoc networks and cellular system is evaluated in [9]. Especially, [4] deals with radio resource management (RRM) strategies in an integrating wireless networks, and evaluates the economic revenue of dynamic channel allocation using the utility function based on pricing. These works show some integration models and interworking architectures of heteroge- neous wireless systems, so we need to consider a multiaccess (MA) transmission for increasing the system capacity. This paper analyzes the spectral efﬁciency of MA scheme in heterogeneous networks, where MSs are allowed to access to their spectrum bands with different radio access technologies (RATs). We ﬁrst show a simple example of MA to support the advantage of spectral efﬁciency, and then propose a simultaneous MA algorithm. The proposed MA algorithm is modeled and analyzed in terms of spectral efﬁciency. Through our analysis and simulations, it is shown that the proposed algorithm is able to achieve an increase in spectral efﬁciency, as compare with vertical handoff (VHO) methods, which select only one network having the best channel quality. This paper is organized as follows: Section II provides a simpliﬁed system model for MA. In Section III, an optimal solution is derived and the MA scheme is proposed. Numerical results are presented in Section IV, followed by the conclusion in Section V. II. SYSTEM MODEL A. System Model with Multiaccess Ability As shown in Figs. 1 and 3, we consider a common heterogeneous network which has overlapped regions, and focus on the smaller RAT region, where MSs can access as many RATs as possible. The mobile users are assumed to be built on a reconﬁgurable software deﬁned radio (SDR) and to be all primary users having proper license for MA to different RATs. Thus, the mobile users have no signiﬁcant interference between the users, and they can dynamically and autonomously adjust their radio operation parameters to make use of available radio resources such as spectrum. In other words, even though the mobile users subscribed to different RAT or network operator, they can utilize diverse RATs iftheir devices could maintain connections with some RATs through 978-1-4244-2515-0/09/$25.00 ©2009 IEEE