Forces Driving Wireless Technology Evolution

To understand the wireless technology trends, and to see why noninfrastructure-based mo-bile ad hoc networks are poised to play an important role in the evolution of future wire-less networks, it helps to review the evolution path of different technology generations.

Table 1.1 summarizes the technologies, architectures, and applications for each of these generations.

One can argue that the commercial history of wireless started with the first generation or 1G in 1980s, which supported analog cell phones using FDMA and was relatively un-sophisticated. Because different regions of the world pursued different mobile phone stan-dards, 1G phones typically could only be used within one country. E Examples of 1G sys-tems include NMT, TACS in Europe, and AMPS in North America.

The cellular industry began deployment of second-generation networks, 2G, a decade or so ago. 2G digitizes the mobile system and adds fax, data, and messaging capabilities on top of the traditional voice service. This evolution was triggered by the high demand for low-speed data access required to enable popular mobile data services like email, SMS, and so on. Again, different standards were deployed in different regions of the world; for example, Europe and Asia use GSM, whereas North America uses a mix of TDMA, CDMA, and GSM as 2G technologies. Recently, 2G has been extended to 2.5G to provide better support for transmitting low-speed data up to 384 kbps.

Currently, efforts are under way to transition the wireless industry from 2G networks to third-generation (3G) networks that would follow a common global standard based on CDMA and provide worldwide roaming capabilities. 3G networks offer increased band-width of 128 Kbps when mobile device is moving at higher speeds, for example, a car, up to 384 Kbps for mobility at pedestrian speed, and 2 Mbps in stationary applications, mak-ing it possible to deliver live video clips. There are still different flavors of the air inter-faces though: Europe and Asia are promoting W-CDMA and EDGE, whereas North America works on cdma2000, each developed by different standard bodies—3GPP for Europe and Asia and 3GPP2 for North America.

1.2. REVIEW OF WIRELESS NETWORK EVOLUTION 7

Table 1.1. Wireless Technology Generations

Generation 1G 2G 2.5G 3G 4/5G

Time Frame 1980s 1990s Late1990s 2000s 2010s

(2010 full deployment)

Signal Type Analog Digital Digital Digital Digital

Access

Multiple access FDMA/FDD TDMA/FDD EDGE, GPRS CDMA, W-CDMA, MC-CDMA, OFDM

CDMA/FDD TD-SCDMA

Frequency 824–894 MHz 1800–2400 MHZ Higher-frequency

spectrum 890–960 MHz (varies country bands 2–8 GHz

1850–1990 to country)

MHz (PCS)

Bandwidth 5–20 Mhz ⱖ100 MHz

Antenna Optimized antenna, Smarter antenna,

multiband adapter Multiband and wide-band support

FEC Convolutional rate, Concatenated

1/2, 1/3 coding scheme Network Architecture

Media type Voice Mostly voice Mostly Voice Voice Converged voice/

Low-speed Higher-speed High-speed data data/multimedia data services data (10–384 (144 kbps–2 over IP; Ultra-high-via modem kbps) Mbps) speed data (2–100

(10–70 kbps) Mbps)

Network type Cellular Cellular Cellular WWAN Integrated WWAN, Cell based WMAN, WLAN

(Wi-Fi, Bluetooth) and WPAN (Bluetooth) Structure Infrastructure Infrastructure Infrastructure Infrastructure- Hybrid of

based based based based network infrastucture-based and ad hoc network Switching Circuit Circuit Circuit Circuit switched Packet switched

switched switched switched and packet switched

IP support N/A N/A N/A Use several air All IP based (IP6.0) link protocols,

including IP5.0

New Applications Emails, Ubiquitous

maps/directions, computing with News, shopping, location intelligence

Despite the high expectations for 3G networks, 3G is facing difficulties getting de-ployed and meeting its promised performance and throughput due to architecture and ca-pability limitations. On the other hand, recent technology advancements enable new ser-vices and thus impose new requirements on system capabilities that were not taken into consideration in the original 3G system design. Let us take a closer look at some of these.

1.2.3.1. The need to integrate various types of wireless networks. Today’s wireless communication systems are primarily designed to provide cost-efficient wide-area coverage for users with moderate bandwidth demands, and 3G is based on primarily a wide-area concept. Many other types of wireless networks have since been designed and are gaining popularity, including wireless LAN and PAN networks, but these are being de-signed as logically separate networks. The various wireless networks need to be integrated in order to provide seamless wireless services. Emerging technology trends indicate that future-generation communication systems will consist of a high-speed wired backbone and wireless local area networks attached to the periphery of the network. Wireless LANs and PANs will extend the coverage of broadband services and provide ubiquitous network access to mobile users [172].

1.2.3.2. The need to integrate wireless platforms with fixed network back-bone infrastructures. The consumer of telecommunication services of tomorrow will expect to receive the same services in a wireless fashion as he receives from a fixed net-work. A wireless system should, therefore, be transparent to the user and thus highly inte-grated with the fixed network backbone like Internet and PSTN networks.

1.2.3.3. The need to support high-speed multimedia services. Growth in In-ternet information services and the emergence of new multimedia applications including music, video streaming, or videoconferencing make multimedia services highly attractive to wireless users. In 3G systems, the maximum data speed supported is 2 Mbit/s, band-width that is not sufficient to meet the needs of these high-performance applications [143]. Very high-speed data transmission speed has to be supported in order to enable multimedia services on mobile devices.

1.2.3.4. The need for convergence in network infrastructure. Today, wireless communications are heavily biased toward voice. With data traffic growing at almost ex-ponential speed and IP becoming prevalent, maintaining two separate backbone infra-structure for voice and data traffic becomes untenable. Converged IP-based digital packet networks that can support voice, data, as well as multimedia applications at the same time provide the ideal platform to lower network operating cost and enable new breeds of net-work services [15].

1.2.3.5. The need to support high mobility and device portability. High mo-bility and device portamo-bility enable wireless users to connect to networks and communi-cate with other users or devices anytime, anywhere [12]. 3G systems cannot yet fully sup-port this transparency, such as dynamically changing network addresses and device locations. Progress is needed to eliminate the shortcomings of wireless systems so that the inherent convenience of mobility will no longer cause deterioration of system functionali-ties.

Another aspect of portability relates to the need to make the mobile device more us-able, to extend the battery power, make devices smaller, and create better user interfaces that match the conventional environment.

1.2.3.6. The need to support noninfrastructure-based networks. Current wireless systems rely on preconfigured infrastructure (routers, MSCs, base stations) to deliver wireless services. This limits the service availability in established areas. However, in many situations networking services are required where infrastructure is not available or not deliverable in a short period of time, for example, in combat or emergency situa-tions. Support and integration of noninfrastructure-based networks becomes important in these situations.

1.2.3.7. The need to add location intelligence. As adoption of mobile wireless systems continues to grow, wireless users will demand services that utilize the conve-nience stemming from mobility. Among these services, location-based information ser-vices, such as getting driving or service directions, location-dependent query support, and system configuration are becoming commonplace and need to be gradually added to sys-tem capabilities.

1.2.3.8. The need to lower the cost of wireless services. Cost is one of the key nontechnical issues that need to be dealt with in 3G systems. For example, the cost is ex-ceedingly high for deployment. 3G spectrum licenses are auctioned at very high prices of more than $100 billion. Being able to lower these costs while providing better services is a key requirement for future network success. One of the ways to lower the infrastructure cost is, for example, by successfully implementing convergence of voice and multimedia into IP networks.

1.2.3.9. The need for greater standard interoperability. Multiple air interface standards in 3G are making it difficult for devices to roam and interoperate across net-works. Furthermore, global mobility and service portability cannot be fully achieved without universal network standardization. Areas needing additional standardization start from lower-layer issues such as modulation techniques, spectrum allocation, and signal-ing, and continue all the way up to protocols and enabling architectures discussed in the remainder of this chapter.

To meet these new requirements and overcome the limitations and problems of current 3G systems, new architectures and capabilities need to be incorporated into the next-gen-eration wireless systems to provide the much needed improvements.

1.2.4. 4G Wireless Architecture and Capabilities

4G is all about an integrated global network based on an open-systems approach. Integrat-ing different types of wireless networks with wireline backbone networks seamlessly and the convergence of voice, multimedia, and data traffic over a single IP-based core network will be the main focus of 4G. With the availability of ultrahigh bandwidth of up to 100 Mbps, multimedia services can be supported efficiently. Ubiquitous computing is enabled with enhanced system mobility and portability support, and location-based services and support of ad hoc networking are expected. Figure 1.1 illustrates the networks and compo-nents within the 4G network architecture.

1.2. REVIEW OF WIRELESS NETWORK EVOLUTION 9

1.2.4.1. Network Integration. 4G networks are touted as the hybrid broadband networks that integrate different network topologies and platforms. In Figure 1.1, the inte-gration of various types of networks in 4G is represented by the overlapping of different network boundaries. There are two levels of integration: the first is the integration of het-erogeneous wireless networks with varying transmission characteristics such as wireless LAN, WAN, and PAN as well as mobile ad hoc networks; the second level includes the in-tegration of wireless networks and fixed network-backbone infrastructure, the Internet and PSTN.

1.2.4.2. All-IP Networks. 4G starts with the assumption that future networks will be entirely packet-switched using protocols evolved from those in use in today’s Internet.

An all-IP-based 4G wireless network has intrinsic advantages over its predecessors. IP is compatible with, and independent of, the actual radio access technology. This means that the core 4G network can be designed and can evolve independently from access networks.

Using an IP-based core network also means the immediate tapping of the rich protocol

HA DFA

FA MH

FA CH

Cellular

Built 150BC

Satellite Network

GW/AP

4GW Architecture

WLAN

WPAN

MANET

HA DFA

FA MH

FA CH

Cellular Network Cellular Network

Internet Backbone PSTN

GW

router

Figure 1.1. 4G wireless network architecture.

suites and services already available, for example, voice and data convergence, can be supported by using a readily available VoIP set of protocols such as MEGACOP, MGCP, SIP, H.323, and SCTP. Finally, the converged all-IP wireless core networks will be packet based and support packetized voice and multimedia on top of data. This evolution is ex-pected to greatly simplify the networks and reduce cost for maintaining separate networks for different traffic types.

1.2.4.3. Lower Cost and Higher Efficiency. 4G IP-based systems are expected to be cheaper and more efficient. First, equipment costs are four to ten times lower than equivalent circuit-switched equipment for 2G and 3G wireless infrastructures. An open converged IP wireless environment further reduces costs for network buildout and mainte-nance. There will be no need to purchase extra spectrum, as 2G/3G spectrum can be reused in 4G and much of the spectrum needed by WLAN and WPAN is public and does not require a license.

1.2.4.4. Ultrahigh Speed and Multimedia Applications. 4G systems aim to provide ultrahigh transmission speeds of up to 100 Mbps, 50 times faster than those in 3G networks. This leap in transmission speed will enable high-bandwidth wireless services, allowing users to watch TV, listen to music, browse the Internet, access business pro-grams, perform real-time video streaming, and other multimedia-oriented applications, such as E-Commerce, as if they were sitting at home or in the office.

1.2.4.5. Ubiquitous Computing. A major goal toward the 4G Wireless evolution is the provision of pervasive computing environments that can seamlessly and ubiquitous-ly support users in accomplishing their tasks, in accessing information or communicating with other users at any time, anywhere, and from any device. In this environment [172], computers get pushed further into the background; computing power and network connec-tivity are embedded in virtually every device to bring computation to us, no matter where we are or under what circumstances we work. These devices will personalize themselves in our presence to find the information or software needed.

1.2.4.6. Support of Ad Hoc Networking. Noninfrastructure-based mobile ad hoc networks (MANETs) are expected to become an important part of the 4G architecture. An ad hoc mobile network is a transient network formed dynamically by a collection of arbi-trarily located wireless mobile nodes without the use of existing network infrastructure or centralized administration. Mobile ad hoc networks are gaining momentum because they help realize network services for mobile users in areas with no preexisting communica-tions infrastructure [8]. Ad hoc Networking enables independent wireless nodes, each limited in transmission and processing power, to be “chained” together to provide wider networking coverage and processing capabilities. The nodes can also be connected to a fixed-backbone network through a dedicated gateway device, enabling IP networking ser-vices in areas where Internet serser-vices are not available due to lack of preinstalled infra-structure. All these advantages make ad hoc networking an attractive option in the future wireless networks arena.

1.2.4.7. Location Intelligence. To support ubiquitous computing requirements, 4G terminals need to be more intelligent in terms of user’s locations and service needs, including recognizing and being adaptive to user’s changing geographical positions, as

1.2. REVIEW OF WIRELESS NETWORK EVOLUTION 11

well as offering location-based services [94]. Anytime, anywhere requires the intelligent use of location information and the embedding of this information in various applica-tions.

Outdoor wireless applications can use the Global Positioning System (GPS) to obtain location information. GPS is a satellite-based system that can provide easy and relatively accurate positioning information almost anywhere on earth. Many GPS implementations are available, including integrating a GPS receiver into a mobile phone (GPS/DGPS), or adding fixed GPS receivers at regular intervals to obtain data to complement readings on a phone (A-GPS), or by using help from fixed base stations (E-OTD). These implementa-tions provide different fix times and accuracies ranging from 50 m to 125 m. For indoor applications, since GPS signals cannot be received well inside buildings, alternative tech-nologies like infrared, ultrasound, or radio have to be used.

Possible location-based services include finding nearest service providers, e.g., restau-rants and cinemas; searching for special offers within an area; warning of traffic or weath-er situations; sending advweath-ertisements to a specific area; searching for othweath-er collocated users; active badge systems, and so on.

Location information can also be used to help enhance other 4G network services; for example, by using location information to aid and optimize routing in mobile ad hoc net-works. Geocasting is another new application that involves broadcasting messages to re-ceivers within a user-defined geographical area.