Global Mobile Broadband Internet Access to high speed internet anytime, anywhere

A Term Paper Report

Rupesh Gupta 2006EE50413

INDEX Topic

Page No.

1. Introduction

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2. Evolution of Broadband

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3. 4G: Main Features

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4. Access Scheme for 4G

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5. OFDMA Advantages

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6. 4G All IP Core Architecture

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7. Seamless Global Connections of Networks

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8. In-flight Internet

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9. Conclusion

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10. References

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Global Mobile Broadband Internet Introduction Mobile Web refers to using a mobile phone device incorporating a web browser to access the World Wide Web. The first access to the mobile web was commercially offered in Finland in 1996 and since then the distinction between the mobile web and native mobile applications has increasingly blurred. Owing to the persistent improvement in mobile internet experience, the total number of mobile web users grew past the number of desktop based web users for the first time in 2008. There has been an increasing demand not just of low data rate web applications like email but also high data rate applications like video streaming, video calling and interactive gaming on mobile devices. In short, today there is a ubiquitous demand for pervasive high speed mobile internet access ‘onthe-move’. Mobile internet still suffers from interoperability problems. Interoperability issues stem from the lack of a unifying global standard and platform fragmentation of mobile devices. 4G, with its all IP based core network architecture appears promising in this regard with the standard providing methods for full convergence of services which would ultimately lead to seamless global mobility. In this report the evolution of mobile broadband internet is briefly described followed by a discussion on 4G technology. The suitable access schemes for 4G and the 4G architecture are discussed primarily in the context of broadband internet. The concept of mobile broadband internet with seamless global mobility along with some state-of-the-art solutions is presented next. A short discussion on novel in-flight internet access technologies is also included towards the end.

Evolution of Broadband 2G digital networks with enhancements like GPRS and EDGE started supporting low data rate internet applications like e-mail, limited web browsing and smaller file downloads. The download speeds ranged 25 to 100 kbps. To meet the growing demands in network capacity, rates required for high speed data transfer and multimedia applications, 3G standards started evolving.

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Fig 1. Evolution of technologies 3G came up with initial data speeds in the range 100 to 300 kbps. It gave the operators flexibility to adapt their mix of voice and data offerings over time without any hardware changes. Since then there has been a constant effort to achieve the maximum download capacity of 3G. 3G enhancements like High Speed Packet Access (HSPA) Evolution (sometimes also referred to as ‘Beyond 3G (B3G)‘ technologies) allowed for data rates greater than 1 Mbps making the mobile internet ‘broadband’, supporting high data rate applications like video streaming, voice over IP, video calling and interactive gaming. HSPA evolution introduced a flat network architecture [1] with a main motive to lower the network latency by having less network elements in the path of the user traffic. System latency is important for many IP-based applications such as fast email synchronization and real time gaming. As shown in Fig 2. I-HSPA specification addressed the network latency by collapsing RNC functionality into NodeB and bypassing SGSN in the data path.

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Fig 2. HSPA evolution architecture In spite of the high data rates and low network latency offered by B3G, it did not provide any method for interoperability across various existing wireless standards. Various heterogeneous wireless access networks typically differ in terms of coverage, data rate, latency and loss rate. Therefore, each of them is practically designed to support different set of specific services and devices.

4G: Main Features 4G differs from the earlier standards in various aspects. The major differences are tabulated in Table 1. From this table it can be easily noticed that 4G will offer very high data rates, support a single standard and the core network will be IP based.

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Table 1. Comparison of 4G with earlier standards

The main features of 4G [2] in the context of mobile broadband are illustrated in Fig 3 and briefly described below. 

High Performance: 4G will feature extremely high quality video comparable to HDTV. Wireless downloads at speeds reaching 100 Mbps, i.e. 50 times of 3G, are possible with 4G.

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Interoperability and Easy Roaming: Multiple standards of 3G make it difficult to roam and interoperate across various networks. 4G provides a global standard that will allow global mobility. This will lead to Service Personalization i.e. various types of terminals providing common services.

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Fully Converged Services: The user would be able to access the network from different platforms like cell phones, laptops and PDAs.

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Scalability: It refers to the ability to handle ever increasing number of users and services. The 4G core network will be an all IP based layer which is easily scalable and hence ideally suited to meet this challenge.

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Fig 3. Features of 4G

Access Scheme for 4G The most suitable access scheme for 4G has been the topic of debate for quite some time now. For internet data with a bursty nature and rapidly varying resource requirements, efficient and fast allocation of shared resources is necessary. There are several studies which have evaluated MCCDMA against OFDMA as the access scheme for 4G. Some important findings are presented here. It is apparent from the conclusions drawn from these studies that OFDMA wins over MC-CDMA as the access scheme for 4G. MC-CDMA is sensitive to distortion of orthogonality among users, leading to Multiple Access Interference (MAI) problem. On the other hand OFDMA can completely prevent intracell interference. OFDMA performs much better than CDMA/WCDMA in terms of resistance to frequency selective fading, lower equipment cost, simple equalization and interference cancellation [3]. To enhance the performance of OFDMA, Radio Resource Management (RRM) is used [4]. RRM performs the function of assigning subcarriers in OFDMA. The working of RRM is illustrated in Fig 4. In a fully-synchronized system, it is possible to assign the subcarriers per Base Station (BS) in such a way that no double allocation of subcarriers between the BSs occurs. This can be guaranteed up to a resource load RL = 1/mRRM, where mRRM is the total number of managed cells. Exceeding the RL, the succeeding assignment of sub-carriers is done such that the assigned sub-carriers per additional active user are randomly distributed over the remaining sub-carriers. RL for OFDM systems is defined as the ratio of the number of assigned sub-carriers to the total number of available subcarriers and correspondingly for MC-CDMA as the ratio of the number of active users to the number of maximum users.

RL 

No. of assigned subcarriers Active users  Total subcarriers Maximum users 6

Fig 4. Radio Resource Management in OFDMA systems

The simulation results of Simon Plass et. al. comparing MC-CDMA and OFDMA [4] are reproduced here for discussion. A plot of bit error rate (BER) vs. RL for an OFDMA and MC-CDMA system in a multi-cell environment was obtained as shown in Fig 5. Here d0 is the distance between the desired BS and Mobile Terminal (MT). d0 = 1 implies that the MT is at the cell edge.

Fig 5. BER vs. RL for an OFDMA and MC-CDMA system in a multi-cell environment at d0 = 1

The MT is at the cell boundary, where two interfering BSs are at the same distance as the desired BS. So, the interference is maximum. OFDMA with RRM outperforms MC-CDMA at lower loads (RL < 3/4) because the RRM can avoid any collision with the major interfering signals from the neighboring cells. MAI is a major degradation factor of MC-CDMA which is avoided to some extent in OFMA even at higher RLs. Fig 6. is a plot of BER vs. d0 for OFDMA and MC-CDMA systems at low RL. The performance for OFDMA with RRM keeps roughly constant because no sub-carriers are doubly allocated due to the 7

RRM as the RL is low. MC-CDMA performs better than OFDMA in the inner cell area (lower d0) as it exploits the whole sub-carrier diversity but suffers from intercell interference at higher values of d0.

Fig 6. BER versus d0 for an OFDMA and MC-CDMA system in a multi-cell environment at RL = 1/8

OFDMA Advantages In addition to the superiority of OFDMA over other access schemes as described in the previous section, OFDMA has the following advantages [3]: 

Physical Layer: No in-cell interference, no equalization required for multipath delay-spread. A sufficiently long cyclic prefix guarantees complete elimination of MAI and multipath interference which would be perfect to work with bandwidth efficient higher order modulation schemes such as QAM for broadband. Scalable OFDMA can be used to accommodate variable channel bandwidths. This is achieved using different FFT/IFFT sizes with the bandwidth and scaling the number of sub-channels with FFT/bandwidth.

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MAC/Link Layer: No contention based access, fast ARQ and retransmission, no overhead control messaging, large number of active users. Granular resource partition i.e. OFDMA allows fine granularity as compared to say TDMA where a whole frame must be transmitted even if the message is one tenth the size of frame.

The spectral efficiency of OFDMA can be significantly enhanced by MIMO-OFDMA which exploits spatial multiplexing of users. Reliability in transmission of high speed data over fading channels can be improved by using more antennas at the transmitter or receiver.

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4G All IP Core Architecture As stated earlier, the multiple standards of 3G make it difficult to roam and interoperate across various networks. Since 3G networks have evolved from a circuit-switched cellular network, they have their own gateways to interpret IP from the backbone network, and have their own interfaces for the communication within themselves. In short, 3G has complicated network structure with lots of protocols to cover the system structure [3]. To overcome these problems, 4G networks have a simple structure based on all-IP core network where IP packets traverse across access network and backbone without any protocol conversion. This is illustrated in Fig 7 [5].

Fig 7. All IP based 4G architecture Mobile IP provides an efficient, scalable mechanism for node mobility within the Internet. Using Mobile IP, nodes may change their point- of-attachment to the Internet without changing their IP address. This allows them to maintain transport and higher-layer connections while moving [6]. This phenomenon is known as Vertical Handoff and is depicted in Fig 8. Vertical handoff refers to a network node changing the type of connectivity it uses to access a supporting infrastructure, usually to support node mobility [7]. It can be observed from Fig 8. that even though the physical layer may change according to the availability of internet access networks, the layers above the Media Independent Handover Function remain unaffected. For example, a suitably equipped laptop may use both a high speed wireless LAN and a cellular technology for internet access as per availability at a particular location without getting disconnected. This will ensure seamless mobility across heterogeneous networks and render ‘Global Mobile Broadband Internet‘ viable. 9

Fig 7. Vertical Handoff

Seamless Global Connection of Networks Mobile broadband internet would truly become global when a single terminal would automatically connect to a local high-speed wireless access system when user is in office, home, airport etc. where wireless access networks are available (like Wireless LAN, Broadband Wireless Access, Wireless Local Loop, HomeRF or Wireless ATM). When user moves to a mobile zone the same terminal would seamlessly and automatically switch to a wireless mobile network (like GPRS, W- CDMA, cdma2000, TD-SCDMA, etc) [8]. This necessitates an interoperation of a multitude of layered wireless and wired networks as shown in Fig 8.

Fig 8. Interoperation of layered wireless and wired networks 10

‘Gobi’ by Qualcomm [9] is the first embedded mobile wireless solution for notebook PC providing global connectivity. It allows the end user to connect to any public carrier cellular network of his/ her choice. This means that the user can have mobile internet access wherever he/she can make a mobile phone call.

In-flight Internet It is surprising that in-spite of an increasing demand by air travellers very few airlines today provide internet connectivity while on the move. In-flight internet in particular is a challenging task as the operator has to ensure low-power transmissions inside aircraft so that the mobiles do not interfere with the aircraft systems. Also, satellite based internet was considered as the only option for in-flight internet until recently when a company came up with novel Air-to-Ground Networks. In-flight internet was launched in 2004 using geostationary (GEO) satellite system. Here the aircraft was equipped with pico-cell systems. The pico-cell is a small low-powered transceiver inside the aircraft that interacts with the satellite and links to passengers' handsets. The main problems with satellite based internet were, bulky transceiver, large propagation delay, anticipated scarcity of satellite resources in the near future and low download speeds allowing a maximum rate of 100 kbps [10]. In-flight internet was revolutionized when Aircell launched air-to-ground networks in 2008 in US. This service named Gogo works as depicted in Fig 9.

Fig 9. Air-to-ground network

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As shown in Fig 9, a mobile broadband network of ground towers tilted skywards covers the entire sky. Equipment onboard the airplane continuously selects the strongest connection from the towers below turning the airplane into a Wi-Fi hotspot [11]. The users can access internet with their wi-fi enabled devices at broadband speeds.

Conclusion 4G has the potential to make Global Mobile Broadband Internet viable. It will interconnect the entire world seamlessly by ensuring ubiquitous mobile access and full convergence of services. The choice of access scheme for 4G is extremely important for efficient and fast allocation of shared resources. OFDMA with radio resource management is a clear winner when compared to the other strong contender MC-CDMA which is sensitive to multiple access interference in a multi-cell environment. Other main advantages of OFDMA include granular resource partitioning, no overhead control messaging and support for large number of active users. 4G provides an elegant all IP based simple architecture to support seamless vertical handoff. The media independent handover function ensures that the IP address and hence the upper layers of a node remain unaffected even though it may change its point- of-attachment to the Internet at the lower layer. Novel ideas like the air-to-ground networks are elegant schemes offering in-flight broadband internet services to users without relying upon the satellite networks. The final success of Global Mobile Broadband Internet will depend upon the interoperation of a multitude of layered wireless and wired networks. In such a scenario, it would be challenging to ensure highest data-rate to the user, best sharing of network resources and optimal management of service quality.

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References [1] “HSPA evolution brings mobile broadband to consumer mass markets”. Nokia and Nokia Siemens Networks, 2008 [2] Afaq H. Khan, Mohammed A. Qadeer, Juned A. Ansari, Sariya Waheed, "4G as a Next Generation Wireless Network," icfcc, pp.334-338, 2009 International Conference on Future Computer and Communication, 2009 [3] Imran Hussain, Sadia Hussain, Imtiaz Khokhar, Raja Iqbal, "OFDMA as the Technology for the Next Generation Mobile Wireless Internet," icwmc, pp.14, Third International Conference on Wireless and Mobile Communications (ICWMC'07), 2007 [4] S.Plass, S.Kaisar, “MC-CDMA versus OFDMA in Cellular Environments “, EUSIPCO 2005, Turkey, Sept. 06 [5] http://blog.taragana.com/index.php/archive/4g-guide [6] G. Lampropoulos et al., “Media Independent Handover for Seamless Service Provision in Heterogeneous Networks”, IEEE Communications Magazine, pp. 64-71, Jan. 2008. [7] http://en.wikipedia.org/wiki/Vertical_handoff [8] Hussain, S., Hamid, Z., and Khattak, “Mobility management challenges and issues in 4G heterogeneous networks”. Proceedings of the First international Conference on integrated internet Ad Hoc and Sensor Networks (Nice, France, 2006) [9] http://www.qctconnect.com/products/gobi.html [10] http://news.cnet.com/In-flight-Internet-Grounded-for-life---page-2/2100-7351_3-62277362.html?tag=mncol [11] http://www.gogoinflight.com/gogo/cms/work.do

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