Next generation wireless systems and networks phần 6 pot

244 ALL-IP WIRELESS NETWORKING Application Layer (WAE) Session Layer (WSP) Transaction Layer (WTP) Security Layer (WTLS) Transport Layer (WDP) Other Services and Applications GSM Bearers IS-136 CDMA PHS CDPD PDC-P iDEN FLEX Figure 5.3 WAP architecture and reference model [508]. no result message, reliable with no result message, and reliable with one reliable result message. The WSP and WTP layers correspond to Hypertext Transfer Protocol (HTTP) in the TCP/IP protocol suite. WTLS – Wireless Transport Layer Security provides many of the same security features found in the Transport Layer Security (TLS) part of TCP/IP. It checks data integrity, provides encryption and performs client and server authentication. WDP – The Wireless Datagram Protocol works in conjunction with the network carrier layer. The WDP makes it easy to adapt the WAP to a variety of bearers because all that needs to change is the information maintained at this level. Network Carriers – Also called bearers, these can be any of the existing technologies that wireless providers use, as long as information is provided at the WDP level to interface WAP with the bearer [509]. Some of the services now offered by the WAP include an External Functionality Interface (EFI) for access to external devices (like digital cameras and GPS units), a User Agent Profile (UAProf) to convey to an application server the preferences of a device’s user and that device’s inherent capabili- ties. A special set of rules supports WAP is “Push,” which allows data to be sent (“pushed”) to mobile devices for the enhancement of real-time applications. A Persistent Storage Interface standardizes the services that mobile devices use to organize and access data, and the Multimedia Messaging Service (MMS) makes the delivery of a variety of types of content to mobile devices possible. Pic- tograms – tiny images that can convey a message in a small space – have been integrated into WAP services [511]. The WAP is very similar to the combination of HTML and HTTP except that it is optimized for low-bandwidth, low-memory, and low-display capability environments, such as PDA (Personal Digital Assistant), wireless phones, and pagers [510]. 5.6 IP on Mobile Ad Hoc Networks A Mobile Ad Hoc Network (MANET) [518] consists of autonomous mobile users and their communi- cations devices (PDAs, for example), which all act as wireless network nodes. When users activate their devices, the network self-organizes and the nodes find one another automatically. Once the network ALL-IP WIRELESS NETWORKING 245 topology is discovered, the nodes collaborate to establish a stream of communication. In that stream, each node can act as a source, relay point, or destination. The communication flow starts with the source node and, in the case of out-of-range nodes, may hop across a number of intermediary nodes before reaching the destination node. These multiple hops use less power, cause less interference and utilize available frequencies better than direct links, and may enable more traffic to be carried on the MANET. In addition, there is no single point of failure on a MANET, as there could be on a WLAN (access points) or cellular network (base stations). If a MANET node joins or leaves the network, the MANET can reconfigure itself appropriately [520]. IP-based technologies can be advantageously applied to MANETs. The protocols employed by such MANETs are standards-based and enjoy routing flexibility, efficiency, and robustness. Their interoperability with the Internet is greatly enhanced, and many QoS questions are taken care of by IP standardization [524]. When the MANET nodes utilize IP, they are assigned unique IP addresses. It is not necessary for all nodes to be in range of all the others – two nodes that are communicating and in the range of each other at one point in time might find themselves still communicating (via intermediary nodes), but out of range (due to their mobility) at a later time. One concern regarding MANETs is whether the nodes should keep track of routes to all possible destinations on the network, or only keep track of destinations that are of immediate use. There are trade-offs to consider with either approach. Keeping track of all possible routes means that initial latency is minimized, but additional control traffic needs to be constantly exchanged, lowering network efficiency and raising battery use. If routes are only discovered as needed, initial communication delays will be high, but power consumption and control traffic are kept low [523]. Some of the challenges faced by the developers of MANET technology and protocols stem directly from Internet connectivity. How many of the nodes in an ad hoc network should be allowed to directly connect to the Internet? Mobile IP protocol assigns a mobile node a care-of address along with a HA, effectively adding a new IP address to the mobile node. Decisions about which nodes in a MANET can function as Internet gateways and what to do when one of them leaves the network are still being deliberated. MANET routing becomes complicated when packets are routed across the MANET’s boundary, and routing protocols for MANETs are still evolving [521]. One of the problems associated with MANETs stems from the lack of any centralized authority in an ad hoc network and the need for all the nodes to collaborate in order to perform infrastructural tasks like routing and forwarding: nodes need to cooperate in a “disinterested” manner to keep the network up and running. The fear is that, in the absence of an authority figure, some nodes may begin to function in a self-interested way, refusing to expend its resources for the good of the network. This may occur because of a particular device’s internal set of battery conservation rules, or because a device may be programmed to “hoard” available bandwidth rather than relay packets for other nodes, for instance. Worse, a device may fail to abide by the network’s back-off protocol or contention resolution rules. Current protocol proposals require that all nodes cooperate to correct route failures when a node leaves the network. This, in turn, requires that nodes transmit route failure messages to a sender “disinterestedly.” If they fail to do so, the sender will erroneously interpret the lack of acknowledgements as a congestion situation and take inappropriate action. Research is under way to modify ad hoc network protocols to account for these possibilities [522]. Research is also under way to ensure the security of MANETs and put intrusion detection systems in place, especially for MANETs that arise when first responders (police, fire, and health officials) arrive on the scene of a public safety incident. The first responders’ PDAs and laptops could quickly establish a network to work together, and researchers are developing secure routing protocols that do not rely on preexisting trust associations between nodes or the availability of an online service to establish trust associations. Intrusion detection is of obvious importance in such situations, first to maintain the privacy of affected individuals and second to prevent malicious nodes from entering and disrupting the network [519]. 246 ALL-IP WIRELESS NETWORKING Because of their dynamic topology and variable link capacity, MANETs require special attention to QoS issues. The current model in existence relies on “best effort” routing and queuing mechanisms, but better methods are under research. This will become increasingly important as services such as streaming video are implemented in MANET devices [517]. 5.7 All-IP Routing Protocols Many of the fundamental characteristics of wired routing protocols can be found in all-IP routing protocols as well: they use routing tables and metrics to determine optimal paths for packets to travel, strive for simplicity and low overhead costs, endeavor to be robust and stable, and have some built-in flexibility for reacting to network changes and problems. However, wireless routing protocols must also take into consideration certain concerns that are specific to a wireless environment: they must be even more adaptable to changes in the network topology (moving nodes can find that their shortest paths to other moving nodes change dramatically), strive even harder to maximize throughput and minimize delay, and keep the power consumption level of the network as low as possible (since mobile nodes are typically run off battery power) [525]. Two well-known wired routing protocols are the Routing Information Protocol (RIP) and the Open Shortest Path First protocol (OSPF). Each has corresponding wireless counterparts: Ad hoc On-demand Distance Vector (AODV) routing can be thought of as RIP for wireless networks, and both Dynamic Source Routing (DSR) and the Zone Routing Protocol (ZRP) are roughly analogous to the OSPF. All of the ideas that have been proposed for wireless routing protocols can be found within AODV, DSR, and ZRP (when taken as a whole). The Distance-Vector family of protocols (which includes the Destination-Sequenced Distance Vector Routing protocol) is proactive. AODV and DSR are reactive protocols, whereas ZRP takes a hybrid approach. AODV can handle both unicast and multicast routing. As its name implies, it was designed for use in ad hoc mobile networks and is an on-demand protocol that only constructs routes from source to destination at the request of a transmitting node. This is done using route request queries and route reply responses. When a transmitting node does not already have a route to a particular destination, it broadcasts a route request (RREQ) across the network. When nodes receive this request they update their information about the transmitting node, create backwards pointers to it in their route tables, and, if they are not the destination node and have not already established a route to the destination, rebroadcast the RREQ. If a node is the destination or has already established a route to the destination, it sends a route reply (RREP) back to the transmitting source node – via any intermediary node that had forwarded the RREQ. As the RREP returns to the source, the intermediary nodes create forward pointers to the destination node. When the source node receives the RREP it can begin to transmit data to the destination node. Such routes are maintained as long as they are “active,” that is, as long as data packets are using the route within a set timeout period. If the route times out or a link in the route breaks, the sending node can reinitiate route discovery. Breaks in routes are reported to the source node in route error (RERR) messages when intermediary nodes perceive them [526]. AODV is the on-demand counterpart to table-based Dynamic State Routing DSDV wireless routing [526]. DSR is also an on-demand routing protocol, but, unlike the AODV, it does not use hop-by-hop routing. Instead, it employs packet headers that carry an ordered list of the nodes that constitute the route from source to destination. With DSR, intermediary nodes do not need to maintain route information about the various routes that they are a part of (although they do store the routes that they themselves have established when acting as a transmitting source). To discover a needed route, a transmitting source node broadcasts a ROUTE REQUEST packet to neighboring nodes. Only nodes that have not yet seen this ROUTE REQUEST forward it, and when they do so, they update the header with their own address (in the proper sequence). When either the destination node or a node which has already established a route to the destination receives the packet, it responds with a ROUTE REPLY ALL-IP WIRELESS NETWORKING 247 with the sequence of nodes in the route taken from the ROUTE REQUEST header. If a route breaks and the source node learns that its messages are not reaching their destination, route discovery is reinitiated. DSR does not make use of periodic transmissions of routing information and therefore nodes consume less power than in other protocols. However, the large headers employed by DSR make it most efficient in networks of small diameter [525]. ZRP combines the advantages of the proactive (table-driven) protocols like OSPF and the reactive (on-demand) protocols like DSR and AODV into a hybrid routing protocol for ad hoc wireless networks. Purely proactive routing works best for networks with a high call rate, and purely reactive routing works best for networks with high node mobility. The hybrid ZRP is designed to work well in a network with both of these characteristics; that is, in a network with mobile nodes that frequently transmit data [528]. ZRP divides a network’s map into zones, roughly centered on individual nodes or small clusters of nodes. These zones may overlap. The zone radius is an important property for the performance of ZRP. If a zone radius of one hop is used, routing is purely reactive and broadcasting degenerates into flood searching. If the radius approaches infinity, routing is reactive. The selection of radius is a trade-off between the routing efficiency of proactive routing and the increasing traffic for maintaining the view of the zone [529]. The design of ZRP assumes that the largest part of the traffic is directed to nearby nodes in an ad hoc network. Therefore, ZRP reduces the proactive scope to a zone centered on each node. In a limited zone, the proactive maintenance of routing information is easier. Further, the amount of routing information that is never used is minimized. Still, nodes farther away can be reached with reactive routing. Since all nodes proactively store local routing information, RREQs can be more efficiently performed without querying all the network nodes. ZRP refers to the locally proactive routing component as the Intrazone Routing Protocol (IARP). The globally reactive routing component is named the Interzone Routing Protocol (IERP) [529]. These are not specific, rigidly defined protocols because ZRP provides only a framework within which any of a number of well- defined protocols can be implemented, depending on the circumstances. In order to learn about its direct neighbors, a node may use the MAC protocols directly. Alternatively, it may require a Neighbor Discovery Protocol (NDP). Such a NDP typically relies on the transmission of “hello” beacons by each node. If a node receives a response to such a message, it may note that it has a direct point-to-point connection with this neighbor. The NDP is free to select nodes on various criteria, such as signal strength or frequency/delay of beacons. Once the local routing information has been collected, the node periodically broadcasts discovery messages in order to keep its map of neighbors up to date. Communication between the different zones is controlled by the IERP and provides routing capabilities among peripheral nodes (nodes on the periphery of a zone) only. If a node encounters a packet with a destination outside its own zone, that is, it does not have a valid route for this packet, it forwards it to its peripheral nodes, which maintain routing information for the neighboring zones, so that they can make a decision of where to forward the packet. Through the use of a bordercast algorithm rather than flooding all peripheral nodes, these queries become more efficient [527]. Instead of broadcasting packets, ZRP uses a concept called bordercasting, which utilizes the topology information provided by IARP to direct query request to the border of the zone. The bordercast packet delivery service is provided by the Bordercast Resolution Protocol (BRP). BRP uses a map of an extended routing zone to construct bordercast trees for the query packets. Figure 5.4 shows the relationships between the various protocols of ZRP. Route maintenance is especially important in ad hoc networks, where links are broken and estab- lished as nodes with limited radio coverage move. In purely reactive routing protocols, when routes containing broken links fail, a new route discovery or route repair must be performed. Until the new route is available, packets are dropped or delayed. In ZRP, the knowledge of the local topology can be used for route maintenance. Link failures and suboptimal route segments within one zone can be bypassed. Incoming packets can be directed around the broken link through an active multihop 248 ALL-IP WIRELESS NETWORKING ZRP IARP IERP BRP Network Layer MAC Layer: NDP Packet flow Interprocess communication Figure 5.4 The components of ZRP [529]. path. Similarly, the topology can be used to shorten routes; for example, when two nodes have moved within each other’s radio coverage. For source-routed packets, a relaying node can determine the clos- est route to the destination that is also a neighbor. Sometimes, a multihop segment can be replaced by a single hop. If next-hop forwarding is used, the nodes can make locally optimal decisions by selecting a shorter path [529]. 6 Architecture of B3G Wireless Systems The first cellular phone systems (the first wireless networks) were introduced in the late 1970s. They were modeled after wired phone systems and used transmitted analog data across a mobile network. They were called first generation (1G) wireless systems when the next generation of cellular networks was deployed in the 1990s. These “second generation” (2G) networks transmitted digital voice data on mobile networks. Their accompanying wireless e-mail and Internet applications are often referred to as 2.5G technologies. The third generation (3G) of wireless technology is currently in use. It is designed for high-speed multimedia applications with data rates from 128 kbps to approximately 10 Mbps, and upgrades to around 100 Mbps in WLANs. Research and development efforts are now focused on the next generation of wireless technology – referred to as 4G or B3G (for beyond 3G). These systems may deliver 1 Gbps transmission rates, with bandwidth up to 100 MHz. The year 2010 is often set as a rough target date for implementing B3G systems (but some applications will probably be deployed in 2006–2007). B3G technology will make it possible to watch movies and television on a (moving) cell phone. For this to happen, more of new technology must be put in place, involving upgrades of ad hoc mobile networking, satellite systems, spectrum allocation, and higher wireless data speeds. The proposed IEEE 802.20 standards will coordinate B3G design efforts. One important aspect of the standardization process will be to provide for ubiquitous access to the wide variety of wireless networks already in place (802.11 and HiperLAN/2 WLANs, 802.15 and Bluetooth Personal Area Networks (PAN)s, 802.16 MANs (Metropolitan Area Networks), and existing 3G networks) [531], which each have their own range, data rate, and mobility limits. Many useful and interesting services and applications can be developed, assuming that ubiquitous and high-speed B3G wireless access is available (“always connected, everywhere” access). One of the main forces behind B3G development is the demand for higher data throughputs in a variety of scenarios. The planners of B3G include terminal and infrastructure equipment manufacturers, academics, operators, service providers, regulatory bodies, and governmental agencies. It should not be surprising to learn that finding a universal definition of B3G/4G is a very elusive task, even after several years of activity and numerous attempts in the literature. B3G designers are aiming for the following technical targets: (1) data rates of 100 Mbps in wide coverage, and 1 Gbps in a local area; (2) all-IP networking; (3) ubiquitous, mobile, seamless communications; (4) shorter latency; (5) connection delays of less than 500 ms; (6) transmission delays of less than 50 ms; (7) costs per bit significantly lower, perhaps 1/10th to 1/100th lower than that Next Generation Wireless Systems and Networks Hsiao-Hwa Chen and Mohsen Guizani  2006 John Wiley & Sons, Ltd 250 ARCHITECTURE OF B3G WIRELESS SYSTEMS Table 6.1 The goals of B3G planners Data rates 100 Mbps in wide coverage, 1 Gbps in a local area Networking All-IP Communications Ubiquitous, mobile, seamless Latency Shorter than that of 3G Connection delays Less than 500 ms Transmission delays Less than 50 ms Costs per bit 1/10 to 1/100 lower than that of 3G Infrastructure cost Lower, perhaps 1/10 lower than that of 3G of 3G; and (8) lower infrastructure cost, perhaps 1/10 lower than that of 3G. The same is shown in Table 6.1. It is envisioned that this type of technology will enable enhanced e-commerce, add to work productivity, and make available ways to improve personal free time. B3G technology may one day be found in vehicles, public places, health care, education, and in the entertainment industry. “Personal managers” may keep a user informed about personal finances, health, security, and local news and weather. “Home managers” may help manage comfort, security, and maintenance. B3G will likely facilitate mobile shopping, tourism, and mobile gaming scenarios [532]. 6.1 Spectrum Allocation and Wireless Transmission Issues B3G technology requires high bandwidth in order to provide multimedia services at a lower cost than is presently the case. In the United States, B3G systems will likely migrate to the 5.2–5.9 GHz range (assuming regulatory approval). It must be stressed, however, that there are serious spectrum allocation issues associated with B3G technology, simply because today unallocated spectrum either does not exist in some countries or is in short supply. Long-term planning is necessary to make spectrum available for B3G applications [530]. In addition, worldwide standardization of spectrum allocation for B3G systems would be desirable for maintaining connections when moving anyplace in the world – the “always connected, anywhere” philosophy. In the United States, there is a bright spot in the spectrum allocation arena. The FCC has noted that there are large portions of allotted spectrum that are unused, and this is true both spatially and temporally. In other words, there are portions of assigned spectrum that are used only in certain geographical areas and there are some portions of assigned spectrum that are used only for brief periods of time. Studies have shown that even a straightforward reuse of such “wasted” spectrum can provide an order of magnitude improvement in available capacity. Thus, the issue is not that spectrum is scarce – the issue is that we do not currently have the technology to effectively manage access to it in a manner that would satisfy the concerns of the current licensed spectrum users. The Defense Advanced Research Projects Agency (DARPA) is developing a new generation of spectrum access technology that is not only ostensibly oriented toward military applications, but also applicable to advanced spectrum management for communication services. The DARPA program is pursuing an approach wherein static allotment of spectrum is complemented by the opportunistic use of unused spectrum on an “instant-by-instant” basis in a manner that limits interference to primary users. This approach is called opportunistic spectrum access spectrum management and the basic parts of this approach are as follows: (1) sense the spectrum in which you want to transmit; (2) look for spectrum holes in time and frequency; and (3) transmit so that you do not interfere with licencees. ARCHITECTURE OF B3G WIRELESS SYSTEMS 251 There are a number of research challenges to this adaptive spectrum management, including (1) wideband sensing; (2) opportunity identification; (3) network aspects of spectrum coordination when using adaptive spectrum management; (4) the need for a new regulatory policy framework; (5) traceability so that sources can be identified in the event that interference does occur; and (6) verification and accreditation. The National Science Foundation (NSF) has a research program entitled Programmable Wireless Networking (NeTS-ProWiN). This research program addresses issues that result from the fact that wireless systems today are characterized by wasteful static spectrum allocations, fixed radio functions, and limited network and systems coordination. This has led to a proliferation of standards that provide similar functions – wireless LAN standards (e.g., Wi-Fi/802.11, Bluetooth) and cellular standards (e.g., 3G, 4G, CDMA, and GSM) – which in turn has encouraged hybrid architectures and services and has discouraged innovation and growth. Emerging programmable wireless systems can overcome these constraints as well as address urgent issues such as the increasing interference in unlicensed frequency bands and low overall spectrum utilization. The NSF research is based on the concept of programmable radios. Programmable radio systems offer the opportunity to use dynamic spectrum management techniques to help lower interference, adapt to time-varying local situations, provide greater QoS, deploy networks and create services rapidly, enhance interoperability, and in general enable innovative and open network architectures through flexible and dynamic connectivity [533]. Some of the proposed technologies for wireless transmissions in a B3G environment are detailed in the subsequent text. Each has its own implications for spectrum allocation concerns. 6.1.1 Modulation Access Techniques: OFDM and Beyond Multi-carrier modulation has been identified as a key technology for B3G, and Orthogonal Frequency Division Multiplexing (OFDM) is the main technique under proposal. It is already present in IEEE 802.11a WLANs. OFDM was originally proposed for single users but extensions to multiusers, for example OFDMA, 1 support multiple access. Usually OFDM is combined with other access tech- niques, typically CDMA and TDMA, to allow more flexibility in multiuser scenarios. Multi-carrier Code Division Multiple Access (MC-CDMA) is another access technique with great potential. OFDM and CDMA are robust against multipath fading, which is a primary requirement for high data rate wireless access techniques. With overlapping orthogonal carriers, OFDM results in a spectrally effi- cient technique. Each carrier conveys lower data rate bits of a high-rate information stream; hence it can cope better with the intersymbol interference (ISI) problem encountered in multipath channels. The delay-spread tolerance and good utilization of the spectrum has put OFDM techniques in a rather dominant position among future communication technologies. OFDM, on the other hand, has strict time and frequency synchronization requirements and is prone to the peak-to-average power ratio (PAPR) problem. 6.1.2 Nonconventional Access Architectures Wide coverage and local coverage are the two most distinctive B3G access components. It is expected that the requirement for higher data throughput and support for a great number of users will result in a shift to higher and less-congested frequency bands, for example the 5-GHz band, and wider bandwidths (20–100 MHz). In cellular access, this would mean that the link budget would be seriously degraded and unreasonable high power would have to be used to compensate for the higher attenuation occurring in this frequency band. This could easily exceed the regulation for power emission from base stations, and also it could dramatically reduce (the already challenged) battery life in terminals. 1 OFDMA is short for orthogonal frequency division multiple access, which provides multiple access scheme for a multiuser communication system. On the other hand, OFDM is only a multiplexing scheme for a single user. MoretreatmentsonOFDMaregiveninSection7.5. 252 ARCHITECTURE OF B3G WIRELESS SYSTEMS Therefore, nonconventional access architectures for wide-area access are being considered to cope with this problem. Multi-hop cellular, and particularly two-hop, approaches appear to be an effective solution to the problem of achieving wide coverage and high data throughput. By using relaying (repeating) stations, the equivalent distance between base station and mobile station can be reduced. Efficient use of radio resources can also be attained since some resources can be reused in different hops. In principle, the relay stations can be fixed (called infrastructure-based relaying)ormobile(ad hoc relaying). In the distributed radio access approach, a base station has under its control a number of remote access sites, each with its own antenna(s) and covering a small area. The small-sized cells covering a large cell reduce the distance between the mobile terminal and its most suitable/closest access point. The base station is connected to the remote radio access sites by using optical fiber or radio links. Distributed radio access is a cost-effective approach to scalable networks. In local- area access, several architectures can be used in addition to the single-hop cellular access approach. Several ad hoc access concepts have shown their potential for short-range communications, including multi-hop, peer-to-peer, and cooperative communications. Collaboration among users (or nodes) aims to benefit either a single user or several (or all) collaborating users. Through cooperation (at intra- and/or interlayer level), the data throughput can be increased and signal quality can be enhanced. Moreover, power efficiency can be boosted, which equates to an increased battery life in terminals. 6.1.3 Multiantenna Techniques Multiantenna techniques 2 are regarded as among the most important enabling technologies for B3G technology. In principle, no technique other than the use of multiple antennas will easily permit a high spectral efficiency. By exploiting these techniques, data throughput can be increased, link quality improved, cell coverage extended, and network capacity enlarged. Three approaches can be used, namely, diversity, beam-forming (smart antennas), and spatial multiplexing. Diversity techniques require widely separated antenna elements (several wavelengths at least). Actual separation depends on the type of channel. Directional channels (narrow angular spread) require large separation and vice versa. Diversity techniques exploit the fact that the associated channels fade independently, while diversity domains can be space, time, frequency, and polarization. Diversity gain will improve the average signal-to-noise ratio. In beam-forming, signals are coherently combined (either in reception or transmission) so as to enhance the array response in preferred directions. Nulls can also be spatially controlled. Beam-forming allows the establishment of directional links. In beam-forming, it is assumed that the channel or direction of arrival is known to the transmitter/receiver. Unlike with diversity, by using beam-forming, the variability of the signal (e.g., fading statistics) is not affected. The array gain is proportional to the number of elements of the array. Spatial multiplexing offers a linear increase in capacity by exploiting the parallel transmission of different information from different antennas. This is essential for attaining the high spectral efficiencies required by B3G. For the receiver to separate and decode the parallel streams, it is assumed that the signal propagates in a rich scattering channel and the number of reception antennas is at least equal to number of transmission antennas. The term MIMO refers in principle to any technique exploiting multiple antennas at the receiver and transmitter. 6.1.4 Adaptive Modulation and Coding Adaptive Modulation and Coding (AMC) is a form of link adaptation that is used in response to the changing characteristics of a radio channel. AMC jointly selects the most appropriate modulation and coding scheme according to channel conditions. The better the radio conditions, the higher the mod- ulation rate and code rate combination, and vice versa. Clearly, AMC is more effective in packet 2 Section 8 has more discussions on multiantenna techniques, also called multiple-input-multiple-output (MIMO) systems. ARCHITECTURE OF B3G WIRELESS SYSTEMS 253 networks – the networks envisioned for B3G. Conventional wireless services have mostly been designed for constant rate applications, such as voice transmission. To combat channel fading, com- munication systems have usually been designed to maximize time diversity with a combination of interleaving and coding for better bit error rate performance. B3G wireless systems must target packet data, and thus are usually designed to maximize throughput for a given battery energy budget while allowing a certain delay. 6.1.5 Software Defined Radio Since different wireless interfaces will be used in B3G, Software Defined Radio (SDR) appears to be a cost-effective solution to implement several access approaches in one terminal. SDR uses a flexible architecture that allows the wireless interface to be reconfigured. This allows multistandard wireless interface operation with a common hardware platform, opening the door for forward compatibility. Furthermore, SDR is an enabler for cooperative networks. SDR allows dynamic modifications of the radio frequency, baseband processing, and even the MAC layer of the terminal (which can utilize a particular wireless interface by reconfiguring the system). The degree of flexibility brought by real- time reconfigurability opens up a new world of possibilities for users, operators, services providers, and terminal manufacturers. Users can establish connection to any network, allowing simple local and global roaming. Users can also benefit from the low-cost terminals that this technology can entails. Hardware and software updates can easily and wirelessly be carried out by users or operators. Manufacturers can also take advantage of SDR as large volumes of terminals with identical hardware (and fewer components) are produced. Even upgrades or changes in the terminals can be easily effected. In addition, service providers can exploit this flexibility to match their operation and services to user demands better [532]. The shift in B3G toward IP-based, high-speed multimedia wireless traffic demands a high spectral efficiency. A natural corollary to this is a need for cooperation across subnetworks and the use of multi-hop relaying. Regulatory reforms could free up bandwidth currently used for analog broad- casting – high-frequency bands – for B3G systems [534]. The more efficient modulation schemes discussed above cannot be retrofitted into 3G architecture, which is one of the reasons B3G research is being conducted before 3G systems are fully implemented (another reason is that 3G performance may not be sufficient for future high-performance applications like full-motion video and wireless teleconferencing). Spectrum regulation bodies must get involved in guiding the researchers by indi- cating which frequency bands might be used for B3G. Along with regulatory reforms, a number of spectrum allocation decisions, spectrum standardization decisions, spectrum availability decisions, technology innovations, component development, signal processing, and switching enhancements, plus intervendor cooperation have to take place before the vision of B3G will materialize. Standard- ization of wireless networks in terms of modulation techniques, switching schemes, and roaming is an absolute necessity for B3G technology. However, B3G is not an independent replacement archi- tecture for existing systems. Network architects must base their vision of B3G architecture on hybrid network concepts that integrate wireless WANs, wireless LANs (IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.15, and IEEE 802.16), Bluetooth technology, and fiber-based backbones with broadband wireless (B3G) networks. Moreover, B3G planning must allow for a smooth transition from the current state of existing networks to their coexistence with B3G systems [535]. 6.2 Integration of WMAN/WLAN/WPAN and Mobile Cellular As mentioned above, B3G systems will need to assimilate and integrate existing technologies, rather than supplant them. It is envisioned that present mobile cellular systems will be “blended into” B3G [...]... and every active user is assigned a particular time slot in the Next Generation Wireless Systems and Networks Hsiao-Hwa Chen and Mohsen Guizani  20 06 John Wiley & Sons, Ltd 268 MULTIPLE ACCESS TECHNOLOGIES FOR B3G WIRELESS frame for its transmission A specific user will transmit only at a time slot assigned to it, and should refrain from transmission until the same slot appears in the next frame, and. .. communications can also be found in [551– 561 , 707, 764 – 766 , 769 –771] 7.1 What does B3G Wireless Need? Beyond 3G (B3G) wireless systems should deliver higher data transmission rates and more diverse services than current 2- to 3G systems can The all-IP wireless architecture has emerged as the most preferred platform for B3G wireless communications Therefore, the design of a future wireless air interface has to... [549] 6. 8 Other Challenging Issues Several other technologies can be thought of as essential for B3G systems and require more research • Ultra-wideband (UWB) techniques3 for short-range communications • Optical wireless techniques for short-range communications 3 More discussions on UWB technologies are given in Section 7 .6 ARCHITECTURE OF B3G WIRELESS SYSTEMS 265 • Techniques for seamless vertical and. .. managing a reconfigurable network [541]  262 ARCHITECTURE OF B3G WIRELESS SYSTEMS Reconfigurability and spectrum issues are changing the way wireless networks are planned Planners are mindful of QoS constraints and the need to reduce infrastructure costs in the B3G era Traditionally, mobile operators have designed and deployed the radio access networks to cover the traffic demand of the planned services in a... dynamic networks taking into account multistandard radio network elements must be performed and the requisite recommendations for network planning must be deduced Automatic network planning is another use-case for reconfigurable, multistandard network elements, for example, the autonomous selection of carrier frequencies [548]  264 ARCHITECTURE OF B3G WIRELESS SYSTEMS 6. 7 Satellite Systems in B3G Wireless. .. 10–100 m 1 mW HiperLAN2 Up to 54 Mbps 868 MHz, 915 MHz, or 2.4 GHz 5 GHz 30–150 m IrDA Up to 4 Mbps HomeRF 1 Mbps (v1.0) 10 Mbps (v2.0) 32–134 Mbps up to 75 Mbps up to 15 Mbps Infrared (850 nm) 2.4 GHz ∼10 m (line of sight) ∼50 m 200 mW or 1W Distance based 10 66 GHz . lower than that Next Generation Wireless Systems and Networks Hsiao-Hwa Chen and Mohsen Guizani  20 06 John Wiley & Sons, Ltd 250 ARCHITECTURE OF B3G WIRELESS SYSTEMS Table 6. 1 The goals of. variety of wireless networks already in place (802.11 and HiperLAN/2 WLANs, 802.15 and Bluetooth Personal Area Networks (PAN)s, 802. 16 MANs (Metropolitan Area Networks) , and existing 3G networks) [531],. integrate wireless WANs, wireless LANs (IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.15, and IEEE 802. 16) , Bluetooth technology, and fiber-based backbones with broadband wireless (B3G) networks.