Copyright 2010 ACM 978-1-4503-0062-9/10/06/ ...$10.00. Simple decentralised market-oriented management of OFDMA Femto-cells Virgilio Rodriguez Institute for Theoretical Information Technology RWTH Aachen Aachen, Germany rodriguez@ti.rwth-aachen.de Rudolf Mathar Institute for Theoretical Information Technology RWTH Aachen Aachen, Germany mathar@ti.rwth-aachen.de ABSTRACT A femto access point (FAP) is a low-cost, low-power device in- tended to be installed by a home owner, to turn the home into a tiny wireless communication cell, that operates underneath a standard cell, in licensed spectrum bands. Femto-cells can improve user experience in indoor locations, and increase overall system capac- ity with modest monetary investment. But the unplanned dynamic nature of these cells, significantly complicate resource allocation and interference control. We propose a relatively simple, decen- tralised market-oriented scheme for sub-channel and power allo- cation when femto-cell users co-exist with those of an OFDMA macro-cell. Our scheme utilises the Dutch auction (price progres- sively falls until a participant buys the object). Special “confirma- tion messages” are used to control interference, achieve channel reuse across Femto-cells, and mitigate the “hidden terminal” prob- lem. Secure software inside each terminal may record transactions for eventual payment collection, or the auction can be interpreted as a prioritised decentralised allocation algorithm, without real money exchange. Categories and Subject Descriptors C.2.3 [Computer Systems Organization]: Computer-Communication Networks—Network Operations, Network management General Terms Algorithms, Economics, Management Keywords OFDMA, femto-cells, resource allocation, power, interference, sub- channel, scheduling, auction, game theory, microeconomics, pric- ing, LTE, WiMAX 1. INTRODUCTION Decreasing the separation between transmitters and receivers can increase overall system capacity by increasing link quality, and resource reuse. This can be accomplished in a cellular network Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. IWCMC’10 June 28 - July 2, 2010, Caen, France through the deployment of additional infra-structure, such as dis- tributed antenna arrays, relay nodes, or additional base stations (to reduce cell size). However, infra-structure is expensive, and may face many practical and regulatory hurdles, in particular, in con- nection to antenna placement. As an alternative, a femto access point (FAP) is an inexpensive, low-power device suitable for “do-it-yourself” installation. A FAP is intended to service a very small area covering, for example, a home. The area serviced by a FAP is called a “femto-cell” (FC). Unlike Wi-FI wireless routers, a FAP operates in licensed spectrum and is directly connected to a standard BS through a dedicated link, such as DSL, fibre or a separate radio channel [2]. Femto-cells can provide many of the benefits of traditional infra- structure, at a fraction of the cost; and this cost is at least par- tially absorbed by the end-user. However, the unplanned and dy- namic nature of Femto-cells (they can be installed anywhere, and switched on/off at any time) creates some important challenges. These include: (i) interference mitigation and management, includ- ing macro to femto, femto to femto, and femto/handset interfer- ence; (ii) handouts (femto to macro), hand-ins (macro to femto), and handovers (femto to femto), as well as (iii) network architec- ture, scalability, and planning and (iv) Integration with the core network[3]. Because of the above, resource management scheme for Femto-cells must be relatively simple, and suitable for at least partially decentralised implementation. Femto-cells operating under orthogonal frequency-division mul- tiple access (OFDMA) are of special interest, because OFDMA is the technology of fourth-generation (4G) cellular networks. OFDMA resource management is notoriously difficult, even for a single cell without Femto-cells. It involves allocating sub-channels to users on the basis of channel-state information (CSI). CSI varies per user, per sub-carrier, and per time interval. Furthermore, a to- tal amount of down-link power must be allocated among the var- ious sub-carriers. Finally, adaptive modulation and coding may be needed to increase the system efficiency. The presence of Femto- cells increases the difficulty of the problem, because, among other reasons, it introduces sub-channel sharing among some Femto-cells, but only if they do not interfere one another[6]. In [10] we propose a relatively simple, decentralised market- oriented scheme for sub-channel and power allocation for the down- link of an OFDMA macro-cell. Our scheme utilises auctions to al- locate sub-carriers, and pricing to allocate power. Secure software inside each terminal may record transactions for eventual payment collection as “service fees”, or the scheme can be interpreted as a prioritised decentralised low-complexity algorithm, without real money exchange. Below we extend [10] to cover Femto-cells. For interference control, and channel reuse across Femto-cells, we utilise special “confirmation messages”. 1106