Soft Computing j (2004) 1 – 15 DOI 10.1007/s00500-003-0354-3 FOCUS A. Oikonomou Á P. Demestichas Á K. Tsagkaris G. Koundourakis Á M. Theologou Management of the power control operation in HIPERLAN/2 networks Published online: jjj Ó Springer-Verlag 2003 Abstract BRAN/WLAN systems, e.g., HIPERLAN/2, circuit-switched voice services. The migration of second IEEE 802.11a, etc., are seen as a promising solution for generation (2G) towards the 2.5G era [1] and the covering residential, business, transport, tourism, etc., development of third generation (3G) mobile wireless environments, and generally areas of high demand, systems aim to enable networks to provide users with characterized as ‘‘hot spots’’. This paper presents man- instantaneous bit rates of up to 2 Mbit/s, significantly agement functionality for augmenting the potential improving packet-data transmission and mobile multi- exploitation of one of these systems, HIPERLAN/2, by media applications. This will be materialized through making feasible their (loose or tight) integration in a the gradual introduction of the Universal Mobile Tele- composite radio (CR) context. The approach will be the communications System (UMTS) [2, 3, 4]. following. The first point will be to revisit the main In addition, even higher data rates can be obtained features of a HIPERLAN/2 system. Next, the architec- for local area networks using novel short-range wire- ture of a general Service and Network Management less technologies. Bandwidth demanding, real-time and System (SNMS), which has been developed for assisting interactive multimedia services, such as high-quality vi- wireless systems in their operation in a CR context, will deo distribution, client-server multimedia applications, be briefly presented. The next main point will be the and data-bank access, are typical applications for this presentation of the functionality of the SNMS compo- technology. Therefore, new wireless networks with nent that is tailored to the managed HIPERLAN/2 broadband capabilities are being sought to provide high- technology and specifically to the configuration of the speed integrated services (data, voice, and video) with Power Control (PC) functionality. An algorithm for cost-effective support for Quality of Service (QoS). This configuring the PC operation, based on a greedy algo- leads to the introduction of systems collectively called rithm and a neural network, will be presented. A rele- Broadband Radio Access Networks (BRANs) and/or vant resource management problem, which should be Wireless Local Area Networks (WLANs). efficiently solved for exploiting HIPERLAN/2 networks, A particular class of such systems, operating at the will be addressed. Numerical results will be presented. 5 GHz band, promises to offer high data rates at ade- quate capacity volumes, for short-range communica- Keywords HIPERLAN/2 Á IEEE 802.11a Á tions with limited mobility. Therefore, they are seen as a IEEE 802.11h Á Power control promising solution for covering residential (home), corporate (business, office, etc.), transport (e.g., airport, train, etc.), and other environments, which are often 1 Introduction characterized as hot-spot areas. The class includes the IEEE 802.11a and 802.11h systems, the High Perfor- Present day wireless telecommunications networks, mance Radio LAN Type 2 (HIPERLAN/2) [5–11], which are primarily narrowband, are mostly used for specified by the European Telecommunications Stan- dards Institute (ETSI), and Japan’s High Speed Wireless Access Network (HiSWAN). The spectrum allocation in A. Oikonomou(&) the three systems is presented in Fig. 1 National Technical University of Athens, Moreover, a recent trend, often called ‘‘wireless be- Electrical and Computer Engineering Department, yond 3G’’, assumes that cellular, BRAN/WLAN and Telecommunications Laboratory, 9 Heroon Polytechneiou Street, DVB (Digital Video Broadcast) systems can be co- Zographou 15773, Athens, Greece operating systems in a composite radio (CR) infra- E-mail: [email protected] structure [12–14]. According to the CR concept, a 50000354 Dispatch: 12.1.2004 Journal : Soft Computing No. of pages: 15 Journal number Manuscript number B Author’s disk received 4 Used 4 Corrupted Mismatch Keyed 2 Fig. 1 Current spectrum allocation at the 5 GHz band network provider (NP) can rely on diverse radio tech- will pose various requirements. The presented manage- nologies for efficiently covering service area regions. ment functionality aims at the fast adaptation of the This may mean that the NP either possesses licenses for system to the new requirements. deploying and operating diverse radio systems (tight The control actions in a HIPERLAN/2 network are integration between the radio technologies), or cooper- mainly Link Adaptation, Dynamic Frequency Selection ates with other NPs that own alternate radio networks (DFS), and Power Control (PC). The quality of the (loose integration between the radio technologies). Effi- radio link, which is dependent on the radio environment, cient coverage means offering as high as possible (re- changes over time and in accordance with traffic in quired) Quality of Service (QoS) levels, at adequate surrounding radio cells. To cope with variations, a Link capacity volumes, in a cost-effective manner. Adaptation scheme is applied. In addition, the DFS A typical CR scenario will include 2.5G/3G mobile operation allows several operators to share the available networks, BRAN/WLAN and DVB systems. In this spectrum and avoids the use of interfered frequencies. context, BRAN/WLAN systems should properly man- Frequency selection is based on interference measure- age their resources, so as to have capacity available, ments performed by the access point and associated which can be used for cooperating with other networks mobile terminals. The functionality of this paper is in the of the infrastructure. The cooperation is materialized direction of managing the PC operation, in order to through the agreement of absorbing traffic from other ensure that the traffic handled by the network is served networks of the CR infrastructure, in order to assist in a most efficient way, reducing, nevertheless, the gen- them to the handling of new service area conditions (e.g., erated interference as much as possible. hot-spot situations, traffic demand alterations, etc.), or The reference system for this paper will be service management requests. Achieving this operation, HIPERLAN/2, however, our practices are applicable to however, requires upgraded service and network man- the IEEE 802.11a, IEEE 802.11h and HiSWAN systems agement systems (SNMSs). This paper will present that have similar specifications. Our approach in this (essential parts of ) such an SNMS. It will be assumed paper is the following. Section 2 revisits the basic fea- that a BRAN/WLAN network, operated by an arbitrary tures of the HIPERLAN/2 system. Section 3 briefly NP, is covering a given area. The proposed management presents a management system that enables HIPER- functionality extends the exploitation possibilities (and LAN/2 networks to act as parts of a CR environment. therefore, the chances of success) of the BRAN/WLAN Section 4 presents the management functionality that network, by enabling its (loose) integration in an overall will configure the PC operation [15, 16]. It will be based CR infrastructure, which comprises also other NPs that on a greedy algorithm (Sect. 4.4) and a neural network operate various types of networks. (Sect. 4.5). Sections 5 and 6 include sample numerical It should be noted that BRAN/WLAN systems pos- results and concluding remarks. sess a ‘‘self-sufficient’’ mode of operating, in the sense, that they are adequately dynamic (autonomous) for adapting to the environment conditions. This is mainly 2 HIPERLAN/2 Overview motivated by the fact that these systems will operate in a license-exempt spectrum band. Therefore, under these This section revisits the basic features of the HIPER- conditions, the introduction of management function- LAN/2 system [5–11]. ality can be essential. The reason is the provision of Figure 2a depicts the reference architecture of statistical guarantees regarding performance and QoS, HIPERLAN/2 networks. Each Access Point (AP) con- towards the CR infrastructure. The CR infrastructure trols a cell. It offers wireless connectivity to the mobile 3 Fig. 2 a Reference architecture of HIPERLAN/2 networks. b Figure 2b presents, in a high level manner, the func- Functionality (protocol stacks) of an AP. c Structure of the medium tionality (protocol stacks) of an AP. The convergence access control (MAC) frame layer realizes the mapping between the core network protocols and the lower layers of the HIPERLAN/2 terminals (MTs) of the cell, and is, therefore, the inter- system. The physical layer uses Orthogonal Frequency face between the radio and the fixed network. Typically, Division Multiplexing (OFDM). The carrier spacing is a HIPERLAN/2 system will comprise a fixed network 20 MHz, which means that in Europe there can be 19 segment that enables the interworking with core net- carriers available (most likely, 12 will be for outdoor/ works, as well as the communication between APs. indoor use, and 7 only for indoor use). Each carrier is 4 split into 52 sub-carriers (48 are used for data and 4 are physical layer mode that can be selected, and conse- pilots). Table 1 lists the seven physical layer modes quently, the throughput that can be achieved. The provided regarding the sub-carrier modulation and appropriate physical layer mode is selected through the code-rate schemes, and the resulting bit-rates. The link adaptation operation. The transmitter power con- modulation schemes supported are binary phase shift trol operation is a means for improving the CIR levels. keying (BPSK), quaternary PSK (QPSK), 16-quadrature Section 4 presents management functionality for man- amplitude modulation (16-QAM), and 64-QAM. The aging (properly configuring) the power control proce- code-rates are 1/2, 3/4, and 9/16. dure, and therefore improving the CIR. The medium access control (MAC) is based on a time division duplex (TDD) and time division multiple access (TDMA) scheme, controlled by the AP.