The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’06) CHALLENGES IN PACKET SCHEDULING IN 4G WIRELESS NETWORKS Harri Paloheimo Nokia Research Center harri.paloheimo@nokia.com Jukka Manner, Johanna Nieminen, Antti Yl¨ a-J¨ a¨ aski Helsinki University of Technology jmanner,jmantti3,anttiyj@cc.hut.fi ABSTRACT Network information theory states that novel methods, such as, cooperative communication and relaying can increase the overall network transport capacity. These methods are not uti- lized in current networking technologies. The 3G RAN will not scale up to meet the requirements set for telecommunica- tion in the next decade. We need a novel Fourth Generation (4G) RAN design. This paper analyses challenges in wireless packet scheduling algorithms for 4G systems and proposes en- ergy efficient scheduling and queue management solutions for the 4G wireless environment. Focus in our work is kept on a relay networking scenarios, which comprise of operator man- aged RAN including relays together with user controlled mo- bile routers. I. I NTRODUCTION The user demand for higher data rates for wireless connec- tions is expected to rise in the foreseeable future. Moreover, flexibility in networking solutions allowing more freedom to users will be required. It is expected that the 3G technologies will not scale to the required extent. Significant improvements and changes will be needed on the layers 1 and 2 of the ISO OSI model. The goal of this paper is to investigate the role of scheduling in different 4G network scenarios and identify the most important factors that should be taken into account in the algorithm design. The 4G concept can be introduced in various ways. A high- level perspective can be chosen based on the generation of com- munication technology, or the technology itself. The Fourth Generation can be seen as an evolution of 3G or part of “Be- yond 3G” (B3G) development [1, 2], as parallel to other legacy and potential future access technologies [1], as a comprehen- sive access solution that enables the use of current and future technologies and solutions [3, 4], or as a uniform congrega- tion of high-speed seamless access technologies and intelligent agents [5]. Prediction of the future 4G solution is hard. The reason for this is simply the limited knowledge of the future environment in which 4G is presumably implemented. More- over, assumptions are often coupled to prevailing or preceding technologies [6]. What can be said about the deployment of 4G is that it will differ from the preceding generations. Distinctive fact is that 4G will be implemented among various competing access technologies. Despite the progress made in wireless net- working standardization, our working assumption is that wire- less access technologies will continue to diversify and overlap. In this paper, we discuss the challenges in designing a scheduling algorithm for hybrid 4G networks, that include single- and multi-hop networking. Based on the study, we present a combined energy efficient queue management and scheduling algorithm for minimizing delay and energy con- sumption. This is an important goal as many components of a future 4G system will be running on battery power, and, thus, we need to consider the effects of scheduling and battery con- sumption in a holistic way. II. FOURTH GENERATION WIRELESS NETWORKS In this paper the emphasis is put on the hybrid architectures [7], i.e., networks that include both single hop and multi-hop networking. In our case the hybrid architecture comprises of both infrastructure and ad hoc parts. A. 4G Hybrid Relaying Scenarios Even though hybrid architectures are still research items they have been considered to have potential for next-generation wireless networks [8]. Relaying, on the other hand, has been in- cluded in a Third-Generation Partnership Project (3GPP) draft standard. Our work differs from the existing work as it adds relaying on the operator infrastructure and it is based on a spe- cific 4G requirement set. Figure 1 illustrates the hybrid exten- sions to 4G scenarios presented in our earlier work [9]. The de- scribed networking approaches utilizing relays are as follows. 1. Access point (AP) coverage is extended with Relay Sta- tion (RS) structure. Connections between AP and Relay Stations (RS) are point-to-point. Direct connection be- tween MTs is also possible (A-B) 2. Multi-hop relay network can benefit from cooperative strategies (C-D-E) or assists in ad-hoc network traffic op- timization (F-G-H). 3. An isolated ad-hoc network is connected (I-J-K) to the 4G RAN via Mobile Gateways (MGW). The functions of the Access Router (AR) are to aggregate traffic towards the backbone network and route traffic between subnetworks. The Access Point (AP) is analogous to a base sta- tion providing radio coverage, and possesses advanced capabil- ities, such as, support for various radio technologies. The Re- lay Station (RS) is a cost-wise simplified AP with similar tasks but equipped only with wireless connections. The Relay Sta- tion is analogous to a radio coverage extender in 2G or WLAN. However, the relay function is designed to route traffic on lay- ers 2 or 3 in addition to simple reception and amplification of the RF signal. On the physical layer this requirement means the use of more advanced forwarding methods such as decode- and-forward or estimate-and-forward. RS can be designed to be either fixed, movable or mobile. The Mobile Terminal (MT) 1-4244-0330-8/06/$20.00 c 2006 IEEE