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Chapter 12 WIRELESS LANs NETWORK DEPLOYMENT IN PRACTICE ANAND R. PRASAD, ALBERT EIKELENBOOM, HENRI MOELARD, AD KAMERMAN AND NEELI PRASAD Wireless Communications and Networking Division, Lucent Technologies, Nieuwegein, The Netherlands Abstract: Wireless LANs most commonly use the Industrial, Scientific, and Medical (ISM) frequency band, of 2.45 GHz. Although there have been a variety of proprietary solutions, the IEEE approved a standard, 802.11, that organizes this technology. Planning the network, which fulfills the requirements of the user in such systems, is a major issue. In this chapter we will discuss some critical issues faced during wireless LAN deployments from a practical point of view. 236 Chapter 12 1. INTRODUCTION Proliferation of computers and wireless communication together has brought us to an era of wireless networking. Continual growth of wireless networks is driven by, to name a few, ease to install, flexibility and mobility. These benefits offer gains in efficiency, accuracy and lower business costs. The growth in the market brought forward several proprietary standards for Wireless Local Area Networks (WLANs), this chaos was resolved by harmonizing effort of IEEE with an international standard on WLANs: IEEE 802.11 [1]. Wireless LANs in a Nutshell Wireless LANs mostly operate using either radio technology or infrared techniques. Each approach has it own attribute, which satisfies different connectivity requirements. Majority of these devices are capable of transmitting information up to several 100 meters in an open environment. In figure 1 a concept of WLAN interfacing with a wired network is given. The components of WLANs consist of a wireless network interface card, often known as station, STA, and a wireless bridge referred to as access point, AP. The AP interface the wireless network with the wired network (e.g. Ethernet LAN) [1], [2], [3]. Wireless LAN Deployment in Practice 237 The most widely used WLANs use radio waves at the frequency band of 2.4 GHz known as ISM (industrial, scientific and medical) band. The release of the ISM band meant the availability of unlicensed spectrum and prompted significant interest in the design of WLANs. An advantage of radio waves is that they can provide connectivity for non line of sight situations also. A disadvantage of radio waves is the electromagnetic propagation, which might cause interference with equipment working at the same frequency. Because radio waves propagate through the walls security might also be a problem. WLANs based on radio waves usually use spread spectrum technology [2], [4], [5]. Spread spectrum spreads the signal power over a wide band of frequencies, which makes the data much less susceptible to electrical noise than conventional radio modulation techniques. Spread spectrum modulators use one of the two methods to spread the signal over a wider area: frequency hopping spread spectrum, FHSS, or direct sequence spread spectrum, DSSS. FHSS works very much as the name implies. It takes the data signal and modulates it with a carrier signal that hops from frequency to frequency as a function of time over a wide band of frequencies. On the other hand direct sequence combines a data signal at a sending STA with a higher data rate bit sequence, thus spreading the signal in the whole frequency band. Infrared LANs working at 820 nm wavelength provide an alternative to radio wave based WLANs. Although infrared has its benefits it is not suitable for mobile applications due to its line of sight requirement. There are two kinds of infrared LANs, diffused and point to point. The first WLAN products appeared in the market around 1990, although the concept of WLANs was known for some years. The worldwide release of the ISM band at 2.4 GHz meant the availability of unlicensed spectrum and prompted significant interest in the design of WLANs. The next generation of these WLAN products is implemented on PCMCIA cards (also called PC card) that are used in laptop computers and portable devices[2], [3], [6]. The major technical issues for WLAN systems are size, power consumption, bit rate, aggregate throughput, coverage range and interference robustness. Considered Wireless LAN In this chapter we consider WLANs based on DSSS technology as given by IEEE 802.11. The IEEE 802.11 WLAN based on DSSS is initially aimed for the 2.4 GHz band designated for ISM applications as provided by the regulatory bodies world wide [1], [2], [3]. The DSSS system provides a WLAN with 1 Mbit/s, 2 Mbit/s, 5.5 Mbit/s and 11 Mbit/s data payload communication capability. According to the FCC regulations, the DSSS system shall provide a processing gain of at least 10 238 Chapter 12 dB. This shall be accomplished by chipping the baseband signal at 11 MHz with a 11-chip pseudo random, PN, code (Barker sequence). The DSSS system uses baseband modulations of differential binary phase shift keying (DBPSK) and differential quadrature phase shift keying (DQPSK) to provide the 1 and 2 Mbps data rates, respectively. Complementary code keying (CCK) is used to provide 5.5 and 11 Mbps. Regulatory Bodies Requirements The regulatory bodies in each country govern the ISM band. Table 1 lists the available frequency bands and the restrictions to devices which use this band for communications [3], [7]. In the USA, the radiated emissions should also conform to the ANSI uncontrolled radiation emission standards (IEEE Std C95.1-1991). Deployment in General Scarcity of spectrum is the biggest issue in wireless communication [10]. The challenge is to serve the largest number of users with a specified system quality. For this purpose network deployment and study thereof plays a very important role. In this chapter we will deal with critical issues such as (1) Coverage, (2) Cell planning, (3) Interference, (4) Power management, (5) Data rate and (6) Security especially for IEEE 802.11 WLAN based on DSSS in 2.4 GHz ISM band. Chapter Organization We will start this chapter with an explanation on WLAN system design, section 2. In section 3 a study on multiple access scheme (Carrier Sense Multiple Access with Collision Avoidance, CSMA/CA) is given together with results on throughput. A study on RF propagation and coverage is presented in section 4 while interference and coexistence issues are given in Wireless LAN Deployment in Practice 239 section 5. Power management and cell planning are given in section 6 and 7 respectively. 2. SYSTEM DESIGN In this section we will discuss various aspects of WLAN system design. As systems design can vary, we will concentrate on the system design of Lucent Technologies IEEE 802.11 compliant WLAN system: WaveLAN [2], [3], [6]. Distribution of functions A WLAN network card and a set of software modules cooperate to offer a 802.11 LAN connection for a PC. At the highest software interface, the equivalent services are offered as for a traditional Ethernet (802.3) LAN. At the air interface, the 802.11 RF/baseband modulation and protocols are used. Figure 2 gives a schematic overview of the major functional elements of the hard- and software and describes how the various functions are distributed over these elements. A typical WLAN card (in our case Lucent Technologies WaveLAN) is used in laptop computers — the antenna side protrudes from the laptop cabinet. The transceiver front-end is mounted in a plastic cover and this slightly thicker part of the card contains the internal antenna. 240 Chapter 12 Network cards are available for a number of standard hardware interfaces like PCMCIA, (Figure 3), PCI and ISA. Roaming WLANs provide roaming within the coverage boundaries of a set of APs, which are interconnected via a (wired) distribution system. The APs send beacon messages at regular intervals (100 ms). STAs can keep track of the conditions at which the beacons are received per individual AP. The running average of these receive conditions is determined by a communications quality (CQ) indicator (Figure 4). The different zones within the full range CQ scale refer to various states of activities at which a STA tracks or tries to find an AP. When a STA’s CQ with respect to its associated AP decreases, this STA starts searching more actively. After the STA has found a second AP that gives a sufficiently good CQ, the STA arrives in a handover state and will re-associate to this second AP. The APs deploy an Inter Access Point Protocol to inform each other about STA handovers. The APs can use channel frequencies from a set of frequencies defined for 802.11 DSSS. TEAMFLY Team-Fly ® Wireless LAN Deployment in Practice 241 Power management For battery powered PC devices the power consumption of a LAN card is a critical factor. The 802.11 standard defines power management protocols that can be used by STAs. Power management schemes result in a lower consumption of (battery) power compared to traditional operation where a STA is always monitoring the medium during idle periods. To achieve savings in power consumption, a LAN card in a STA must have a special low power state of operation called DOZE state. In this state the LAN card will not monitor the medium and will be unable to receive a frame. This state differs from the OFF state in the sense that the card must be able to make a transition from DOZE state to fully operational receive (AWAKE) state in a very short time (250 µ s). A transition from OFF to AWAKE state will take much more time. Power Management allows a STA to spend most of its idle time in DOZE state, while still maintaining connection to the rest of the network to receive unsolicited messages. For the latter requirement, the other STAs or the AP must temporarily buffer the messages that are destined to a STA operating in a power management scheme, and such a STA must “wakeup” on regular intervals to check if there are messages buffered for it. Automatic Rate Fallback The different modulation techniques used for the different data rates of WLAN can be characterized by more robust communication at the lower rate. This translates into different reliable communication ranges for the 242 Chapter 12 different rates, 1 Mbit/s giving the largest range. STAs moving around in such a large cell will be capable of higher speed operation in the inner regions of the cell. To ensure usage of the highest practicable data rate at each moment, WLANs include an automatic rate fallback (ARF) algorithm. This algorithm causes a fallback to the lower rate when a STA wanders to the outer regions and an upgrade to the higher rate when it moves back into the inner region. Figure 5 shows the four cell regions associated with the four data rates. The ARF functions come into play when the ARF boundary is crossed in either direction. Besides resulting in a bigger range, the lower rates will also be more robust against other interfering conditions like high path loss, high background noise, and extreme multipath effects. The ARF scheme will do a (temporary) fallback when such conditions appear and an upgrade when they disappear. Security WLANs compliant to IEEE 802.11 combats the security problem with open system and shared key authentication and RC4 based encryption [1], [2], [3], [6], [9]. Open system authentication is essentially a null authentication in which any STA is authenticated by the AP. Shared key authentication supports authentication of STAs as either a member of those who know a shared secret key or a member of those who do not. IEEE 802.11 shared key authentication accomplishes this without the need to transmit the secret key in the clear; requiring the use of the wired equivalent Wireless LAN Deployment in Practice 243 privacy, WEP, mechanism. Closed system authentication, a proprietary scheme, is implemented in WaveLAN, which provides further security. WLAN is envisaged to be used in corporate and public environments and the existing level of security will not be enough for these environments. In general a corporate environment has an Ethernet based LAN with OS related authentication procedure (Microsoft, Apple, Unix etc.). We will refer to such corporate environment as enterprise environment. Enterprises have closed network environment where reasonable security can be achieved by using network name and shared key authentication. “Reasonable” because shared key and network name based authentication is not a very secure process. Another major concern in Enterprises is the rate of change in personnel, both short and long term. Distributing keys to them and making sure they can not misuse a key once they have left the company is a major managerial problem. Besides enterprises there are academic and other institutions where either OS based authentication is used or in certain cases Kerberos is used. Kerberos is Unix based; it includes authentication, access control and session encryption. The authentication is decoupled from access control so that resource owners can decide who has access to their resources. In this sense, Kerberos meets the managerial needs given above. For such institutions, the WLAN system must be compatible to Kerberos with the wireless part giving the same level of security as Kerberos. The public or dial in environment users make use of untrusted communications facilities to access systems of their employer or an internet service provider, ISP. Therefore both authentication and session security are needed. This environment is dominated by Microsoft platforms. Operators and service providers frequently use RADIUS (remote authentication dial in user service). RADIUS services are used especially when people are mobile and require access to their corporate network or when people want to access a ISP from home. WLAN working in such environment will require compatibility to RADIUS and extra security for the wireless part. 3. MEDIUM ACCESS The 802.11 CSMA/CA protocol is designed to reduce the collision probability between multiple STAs accessing the medium [1], [2], [3], [7], [11]. The highest probability of a collision would occur just after the medium becomes free, following a busy medium. This is because multiple STAs would have been waiting for the medium to become available again. Therefore, a random backoff arrangement is used to resolve medium contention conflicts, Figure 6. A very short duration carrier detect turn- 244 Chapter 12 around time is fundamental for this random wait characteristic. The 802.11 standard DSSS uses a slotted random wait behavior based on 20 µ s time slots, which cover the carrier detect turn-around time. In addition, the 802.11 MAC defines an option for medium reservation via RTS/CTS (request-to-send/clear-to-send) polling interaction and point coordination (for time-bounded services). Throughput Throughput can be measured based on the amount of transferred net data and the required transfer time. A typical method of measuring throughput is by copying a file between a wireless STA and server connected to the wired infrastructure. The effective net throughput depends on the bit rate at which the wireless STA communicates to its AP, but there are a lot of overhead like data frame preamble, MAC (medium access control layer) header, ACK (acknowledgement) frame, transmission protocol overhead (per packet and by request/response packets), processing delay in local/remote computer, forwarding around the AP (Figure 7). The measurement results are given in Figure 8. To consider throughput measurement with multiple STAs divided over more than one AP we have to look to other aspects like adjacent channel interference (section 5) and medium reuse effects. 4. PROPAGATION AND COVERAGE The success of any communication system depends on the influence of the propagation medium. Propagation in a medium is affected by atmosphere and terrain [8]. The degree of influence depends primarily on the frequency of the wave. Before proceeding we must understand the propagation [...]... communications and wireless networks His current interests lie in Voice over IP for wireless networks Kumar is the author of a dozen publications, and holds sixteen patents Chapter 9 Practical Deployment of Frequency Hopping in GSM Networks for capacity enhancement DR ANWAR BAJWA founded Camber Systemics Limited (CSL) in April 1997 and is the managing director of the company CSL is a wireless technology... Kamerman, H Moelard and A Eikelenboom, "Indoor Wireless LANs Deployment", under review VTC 2000 Spring, Tokyo, Japan, 15-18 May 2000 [11] K.C Chen, "Medium Access Control of Wireless LANs for Mobile Computing," IEEE Network, September/October 1994, pp 50-63 CONTRIBUTORS PART I Chapter 1 OVERVIEW AND ISSUES IN DEPLOYMENTS Science, Engineering and Art of Cellular Network Deployment SALEH FARUQUE received... at the AP 7 CELL PLANNING AND DEPLOYMENT There are two basic requirements for a WLAN network deployment: throughput and coverage On one hand a network can be deployed with the primary requirement being coverage Such network will have low aggregate throughput and larger cells Such network deployment will require lesser Wireless LAN Deployment in Practice 253 APs and thus will be cheaper On the other hand... AD KAMERMAN (1954) is a member of technical staff assigned to a product development team in the Wireless Communication and Networking Division of Lucent Technologies in The Netherlands He works on wireless LANs, designing their system performance as it relates to the radio-frequency environment, signal processing, and network throughput Mr Kamerman received a B.S and M.S in electrical engineering from... transmission system and digital cellular CDMA networks Since 1995, he has been a part of the Network Planning and Engineering department at GTE Laboratories near Boston He is actively involved in wireless system design analysis and research and his work has been incorporated in GRANET - a cellular radio planning tool for network optimization which helps GTE Wireless and other GTE business units optimally... chairman of the International Conference on Personal Wireless Communications, to be held in December 2000 in India He was also the lead editor of the book "Wireless Multimedia Network Technologies", published by Kluwer Academic Publishers in 1999 KAVEH PAHLAVAN, is a Professor of ECE, a Professor of CS, and Director of the Center for Wireless Information Network Studies, Worcester Polytechnic Institute,... Network (PSTN) 4, 154, 167 Public Lands Mobile Network (PLMN) 198 Q Quality of Service (QoS) 80, 131135, 146, 173-178, 185-186,200, 203 R RADIUS .243 Receiver intermodulation 104 , 106 , 117 Reconfigurable Transceivers .153, 166, 168-169 reliability point 25 resource allocation 134, 138, 142-145 reuse factor 60, 68, 135-136, 142 reverse link capacity 44, 93-94 T third-order intercept 102 -104 ,... result for WLAN working at 11 Mbps in presence of commercial microwave ovens with AP and STA 3 m apart and microwave oven and STA at 1 m is given as figure 13 Team- Fly Wireless LAN Deployment in Practice 251 Coexistence Coexistence is a major issue for wireless communication systems working in ISM band In this section coexistence study with FHSS IEEE 802.11 and Bluetooth are presented FHSS FHSS 802.11 WLAN... L Monteban, "WaveLAN-II: A High-Performance Wireless LAN for the Unlicensed Band", Bell Labs Technical Journal, vol 2, no 3, 1997, pp 118–133 [4] A Kamerman, “Spread Spectrum Schemes for Microwave-Frequency WLANs”, Microwave Journal, vol 40, no 2, February 1997, pp 80-90 [5] K Pahlavan and A.H Levesque, Wireless Information Networks, Wiley, 1995, ISBN 0471 -106 7-0 [6] http://www.wavelan.com/ [7] R van... journals PART IV Chapter 10 DEPLOYMENT OF WIRELESS DATA NETWORKS General Packet Radio Service (GPRS) HAKAN INANOGLU received his Ph.D in Electrical Engineering from Technical University of Istanbul in Istanbul, Turkey in 1998 He started to work for Military Electronic Company of Turkey (ASELSAN) as a RF Design Engineer from 1987 to 1991 From 1992 to 1996 he acted as a Senior Wireless System Engineer . INTRODUCTION Proliferation of computers and wireless communication together has brought us to an era of wireless networking. Continual growth of wireless networks is driven by, to name a few, ease. as station, STA, and a wireless bridge referred to as access point, AP. The AP interface the wireless network with the wired network (e.g. Ethernet LAN) [1], [2], [3]. Wireless LAN Deployment. frequencies defined for 802.11 DSSS. TEAMFLY Team- Fly ® Wireless LAN Deployment in Practice