Wireless Network Design: Optimization Models and Solution ...

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9 Routing in Mobile Ad Hoc Networks 203 ergy constraints), the requirements of LANs and WLANs are the same: high data rates, full connectivity, broadcast capability, etc. We present in the following the two main link layer technologies for ad hoc networks: the IEEE 802.11 standard for WLANs and the Bluetooth specifications for WPANs. As detailed in the previous section, a “single-hop” ad hoc network implies that all the stations must be within the same transmission area to be able to communicate. The range of the network can be extended by adding network layer protocols, including routing mechanisms. Solutions leading to multi-hop ad hoc networks are described in the next section. 9.3.1 Ad Hoc Mode in Wi-Fi Proposed in 1997, the IEEE 802.11 standard [2] (commercially called Wi-Fi, the acronym of Wireless Fidelity) defines the two first layers of the OSI model for a wireless local area network: the physical layer and the link layer. While three different physical layers are proposed, the link layer is unified. Indeed, to transmit data between nodes, it can use either: infrared (IF) pulse position modulation, direct sequence spread spectrum (DSSS), or frequency-hopping spread spectrum (FHSS). Frequencies are in the Industrial, Scientific and Medical (ISM) band, ranging from 2.4000 GHz to 2.4835 GHz. This standard allows data rates equal to 1 or 2 Mbit/s. Since then, it has been extended by several task groups, which are designated by letters. In 1999, the extensions IEEE 802.11a and IEEE 802.11b were proposed in order to improve data rates: up to 54 Mbit/s in the 5 GHz band for the former and up to 5.5 or 11 Mbit/s in the 2.4 GHz band for the latter (with backward compatibility). In 2003, the IEEE 802.11g extended the IEEE 802.11b to support 54 Mbit/s in the 2.4 GHz band, by applying the same OFDM based transmission scheme as IEEE 802.11a. Nowadays, there exist around thirty amendments, offering higher throughput, security services, handover capabilities, etc. [1]. Two operational modes are specified in the standard: • Infrastructure-based mode. In this mode, all the communications between nodes have to go via a specific node: the Access Point (AP). The network area is then determined by the transmission range of the AP. The set of nodes around the AP is called Basic Service Set (BSS). To extend the network, it is possible to merge several BSSs. For this, the AP can be connected to another AP, generally with a wired network such as Ethernet. • Ad hoc mode. No AP is required in this mode, the network being totally distributed. Nodes can communicate if they are within their respective transmission range. They constitute an Independent Basic Service Set (IBSS). Moreover, the Medium Access Control (MAC) layer of the IEEE 802.11 standard defines a contention-free service, called the Distributed Coordination Function (DCF) based on a multiple access method. As an optional access method, the standard defines the Point Coordination Function (PCF), implemented on top of the
204 Khaldoun Al Agha and Steven Martin DCF and based on a polling scheme. Since there is no central authority to act as a point coordinator in ad hoc networks, the PCF cannot be readily applied in such environments. In the DCF mode, a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is used. Hence, to transmit a packet, a node has to first listen to the channel. If it is idle, then the node can send its packet. Otherwise, that is to say if the node senses energy above a specific threshold on the medium, the transmission is deferred for a random interval, reducing the probability of collisions on the channel. More precisely, when the current transmission ends, the node wanting access waits a Distributed Inter-Frame Spacing (DIFS) before choosing a random back-off value. This value is then decremented only when the channel is idle. As soon as the value reaches zero, the node sends its packet. Despite this mechanism, collisions may occur. Contrary to the CSMA/CD used in the IEEE 802.3 standard, collision detection is not feasible in the IEEE 802.11 standard, due to the use of half duplex antennas. This hinders the node from sending and receiving simultaneously. Collisions are then detected indirectly; to confirm the correct reception of information, acknowledgment (ACK) packets are sent from the receiver to the sender. In order to send the ACK just after the received packet, another inter-frame spacing is defined: the Short Inter-Frame Spacing (SIFS). This one being shorter than the DIFS, ACKs are sent as a priority, preceding any other packet transmission. Another problem occurs in wireless networks: the hidden node problem. Indeed, consider Figure 9.2 where node C wants to transmit a packet to node B, which is already receiving a packet from node A. As C and A are not within the transmission range of each other, when node C applies the CSMA protocol and listens to the channel, it cannot detect the transmission between A and B. This creates a collision, scrambling data. Fig. 9.2 Hidden node (1) and exposed node (2) problems To solve this problem, the physical carrier sensing mechanism CSMA can optionally be supplemented by an additional mechanism, a virtual carrier-sensing mechanism based on the exchange of Request To Send (RTS) and Clear To Send (CTS) packets between the sender and the intended receiver. The IEEE 802.11 RTS/CTS exchange is defined as follows. Before sending packets, the source sends to the intended receiver a short packet, named RTS. If the RTS packet is well transmitted, the receiver replies (after a SIFS) by another short packet, named CTS. Then, the
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International Series in Operations
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Editors Jeff Kennington Eli Olinick
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vi Preface assistance. The work of
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viii Contents 3.4.1 Experiments to
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x Contents 8.3.2 The Solution Proce
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xii Contents References . . . . . .
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List of Contributors Khaldoun Al Ag
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List of Contributors xvii Nitin Sal
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Chapter 1 Introduction to Optimizat
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1 Introduction to Optimization in W
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1 Introduction to Optimization in W
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Part I Background
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10 Dinesh Rajan The goal of this ch
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12 Dinesh Rajan The source encoder
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14 Dinesh Rajan ping (FH) CDMA, and
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16 Dinesh Rajan of SNR is given in
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18 Dinesh Rajan 2.3 Information The
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20 Dinesh Rajan Perror ≤ e −nE
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22 Dinesh Rajan For instance, for t
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24 Dinesh Rajan 2.4.1 Block Codes I
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26 Dinesh Rajan B(z) = 1 � (1 + z
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28 Dinesh Rajan layers. Two of the
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30 Dinesh Rajan nel can support a p
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32 Dinesh Rajan 2.5.2 Physical laye
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34 Dinesh Rajan matched filter for
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36 Dinesh Rajan codes) leads to bet
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38 Dinesh Rajan a length N Inverse
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40 Dinesh Rajan the transmission of
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42 Dinesh Rajan setting, a node may
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44 Dinesh Rajan weighting of the si
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46 Dinesh Rajan 29. Oestges, C., Cl
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48 K. V. S. Hari terrain of operati
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50 K. V. S. Hari fading is calculat
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52 K. V. S. Hari terms have been pr
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54 K. V. S. Hari Fig. 3.1 Normalize
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56 K. V. S. Hari Table 3.3 Impulse
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58 K. V. S. Hari where m antennas a
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60 K. V. S. Hari 3.5.2.4 Dominant R
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62 K. V. S. Hari March, 1984-13 Sep
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64 K. V. S. Hari 47. Van Rees, J.:
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66 J. Cole Smith and Sibel B. Sonuc
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Part II Optimization Problems for N
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102 Eli Olinick carrying capacity.
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104 Eli Olinick 93 85 160 16 38 21
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106 Eli Olinick Amaldi et al. [7] p
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108 Eli Olinick levels (possibly le
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110 Eli Olinick gmℓ ∑ ∑ m∈M
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112 Eli Olinick Using bk to denote
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114 Eli Olinick 5.3.5 Additional De
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116 Eli Olinick capacity, provide n
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118 Eli Olinick ficult optimization
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120 Eli Olinick and-bound so that t
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122 Eli Olinick solution times. Cai
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124 Eli Olinick 27. Glover, F.: Tab
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Chapter 6 Optimization Based WLAN M
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6 Optimization Based WLAN Modeling
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Chapter 7 Spectrum Auctions Karla H
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7 Spectrum Auctions 149 full value.
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7 Spectrum Auctions 151 also decide
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Chapter 12 Simulation-Based Methods
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12 Simulation-Based Methods for Net
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296 Hang Jin and Li Guo formance in
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298 Hang Jin and Li Guo (ISI) as lo
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300 Hang Jin and Li Guo ARQ (HARQ)
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302 Hang Jin and Li Guo 13.3 Radio
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304 Hang Jin and Li Guo Table 13.2
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306 Hang Jin and Li Guo is transmit
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308 Hang Jin and Li Guo uplink powe
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310 Hang Jin and Li Guo The link ad
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314 Hang Jin and Li Guo 13.4.4.3 Ex
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316 Hang Jin and Li Guo Fig. 13.9 P
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318 Hang Jin and Li Guo 1. Guarante
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Chapter 14 Cross Layer Scheduling i
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14 Cross Layer Scheduling in Wirele
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Chapter 15 Major Trends in Cellular
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15 Major Trends in Cellular Network
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