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4G Wireless Systems
The approaching 4G (fourth generation) mobile communication systems are projected to solve still-remaining problems of 3G (third generation) systems and to provide a wide variety of new services, from high-quality voice to high-definition video to high-data-rate wireless channels. The term 4G is used broadly to include several types of broadband wireless access communication systems, not only cellular telephone systems. One of the terms used to describe 4G is MAGICâ€Mobile multimedia, anytime anywhere, Global mobility support, integrated wireless solution, and customized personal service. As a promise for the future, 4G systems, that is, cellular broadband wireless access systems have been attracting much interest in the mobile communication arena. The 4G systems not only will support the next generation of mobile service, but also will support the fixed wireless networks. This paper presents an overall vision of the 4G features, framework, and integration of mobile communication. The features of 4G systems might be summarized with one wordâ€integration. The 4G systems are about seamlessly integrating terminals, networks, and applications to satisfy increasing user demands. The continuous expansion of mobile communication and wireless networks shows evidence of exceptional growth in the areas of mobile subscriber, wireless network access, mobile services, and applications.
Consumers demand more from their technology. Whether it be a television, cellular phone, or refrigerator, the latest technology purchase must have new features. With the advent of the Internet, the most-wanted feature is better, faster access to information. Cellular subscribers pay extra on top of their basic bills for such features as instant messaging, stock quotes, and even Internet access right on their phones. But that is far from the limit of features; manufacturers entice customers to buy new phones with photo and even video capability. It is no longer a quantum leap to envision a time when access to all necessary information the power of a personal computer , sits in the palm of oneâ„¢s hand. To support such a powerful system, we need pervasive, high-speed wireless connectivity.
A number of technologies currently exist to provide users with high-speed digital wireless connectivity; Bluetooth and 802.11 are examples. These two standards provide very high speed network connections over short distances, typically in the tens of meters. Meanwhile, cellular providers seek to increase speed on their long-range wireless networks. The goal is the same: long-range, high-speed wireless, which for the purposes of this report will be called 4G, for fourth-generation wireless system. Such a system does not yet exist, nor will it exist in todayâ„¢s market without standardization. Fourth-generation wireless needs to be standardized throughout the world due to its enticing advantages to both users and providers.
Advantages of 4G:-
In a fourth-generation wireless system, cellular providers have the opportunity to offer data access to a wide variety of devices. The cellular network would become a data network on which cellular phones could operate-as well as any other data device. Sending data over the cell phone network is a lucrative business. In the information age, access to data is the killer app that drives the market. The most telling example is growth of the Internet over the last 10 years. Wireless networks provide a unique twist to this product: mobility. This concept is already beginning a revolution in wireless networking, with instant access to the Internet from anywhere.
Problems with the Current System
One may then wonder why ubiquitous, high-speed wireless is not already available. After all, wireless providers are already moving in the direction of expanding the bandwidth of their cellular networks. Almost all of the major cell phone networks already provide data services beyond that offered in standard cell phones.
Unfortunately, the current cellular network does not have the available bandwidth necessary to handle data services well. Not only is data transfer slow - at the speed of analog modems - but the bandwidth that is available is not allocated efficiently for data. Data transfer tends to come in bursts rather than in the constant stream of voice data. Cellular providers are continuing to upgrade their networks in order to meet this higher demand by switching to different protocols that allow for faster access speeds and more efficient transfers. These are collectively referred to as third generation, or 3G, services. However, the way in which the companies are developing their networks is problematic â€ all are currently proceeding in different directions with their technology improvements. Figure 1 illustrates the different technologies that are currently in use, and which technologies the providers plan to use.
Although most technologies are similar, they are not all using the same protocol. In addition, 3G systems still have inherent flaws. They are not well-designed for data; they are improvements on a protocol that was originally designed for voice. Thus, they are inefficient with their use of the available spectrum bandwidth. A data-centered protocol is needed. If one were to create two identical marketplaces in which cellular providers used 3G and 4G respectively, the improvements in 4G would be easy to see. Speaking on the topic of 3G, one of the worlds leading authorities on mobile communications, William C.Y. Lee, states that 3G would be a patched up system that could be inefficient, and it would be best if the industry would leapfrog over 3G wireless technologies, and prepare for 4G (Christian). 4G protocols use spectrum up to 3 times as efficiently as 3G systems, have better ways of handling dynamic load changes (such as additional cellular users entering a particular cell), and create more bandwidth than 3G systems. Most importantly, fourth-generation systems will draw more users by using standard network protocols, which will be discussed later, to connect to the Internet. This will allow simple and transparent connectivity.
Barriers to Progress:-
Why are cellular providers not moving to 4G instead of 3G? A market place like the cellular industry can be modeled as a game, as in Table 2.
There are three basic paths the game can take: Nobody makes the conversion to 4G All end up upgrading to 2.5G and 3G services. The upgrades are incremental, and donâ„¢t require a complete reworking of the system, so they are fairly cheap â€ the equipment required is already developed and in mass production in other places in the world. Everyone makes the conversion to 4G The equipment and technology needed for 4G will be cheap, because of all of the cellular manufacturers investing in it. Cellular providers will market additional services to its customers. Some of the players make the conversion to 4G Because not all of the players have chosen 4G, the equipment will be more expensive than the second scenario. Even though converters will be able to sell more services to their customers, it will not be enough to cover the higher costs of converting to 4G.
Therefore, if a player chooses the 4G strategy, but nobody else follows suit, that player will be at a significant disadvantage. No cellular provider has incentive to move to 4G unless all providers move to 4G. An outside agent â€ the national government â€ must standardize on 4G as the wireless standard
for the communication. Of course, legitimate concerns can be posed to the idea of implementing 4G nationwide. A common concern is the similarity of this proposal to the forced introduction of HDTV in the US, which has (thus far)
failed miserably. There are two key differences, however, between 4G and HDTV. The first is the nature of the service providers. There are many small television broadcasters in rural areas whose cost of conversion would be as much as 15years of revenue. The cellular industry, however, does not have this problem. The players are multi-billion dollar companies, who already have enough capital; continual network upgrades are part of their business plan. Our proposal is simply choosing a direction for their growth.
An often overlooked area of financial liability for cellular providers is in the area of information security. Providers could lose money through fraudulent use of the cellular system or unauthorized disclosure of user information over the airwaves. Both of these cases could be caused by an insecure wireless system.
Most modern cellular phones are based on one of two transmission technologies: time-division multiple access (TDMA) or code-division multiple access (CDMA) (Prizeman 2000, 40).These two technologies are collectively referred to as second-generation, or 2G. Both systems make eavesdropping more difficult by digitally encoding the voice data and compressing it, then splitting up the resulting data into chunks upon transmission.
TDMA, or Time Division Multiple Access, is a technique for dividing the time domain up into sub channels for use by multiple devices. Each device gets a single time slot in a procession of devices on the network, as seen in Figure 3. During that particular time slot, one device is allowed to utilize the entire bandwidth of the spectrum, and every other device is in the quiescent state.
The time is divided into frames in which each device on the network gets one timeslot. There are n timeslots in each frame, one each for n devices on the network. In practice,every device gets a timeslot in every frame. This makes the frame setup simpler and more efficient because there is no time wasted on setting up the order of transmission. This has the negative side effect of wasting bandwidth and capacity on devices that have nothing to send (Leon-Garcia and Widjaja 2000).
One optimization that makes TDMA much more efficient is the addition of a registration period at the beginning of the frame. During this period, each device indicates how much data it has to send. Through this registration period, devices with nothing to send waste no time by having a timeslot allocated to them, and devices with lots of pending data can have extra time with which to send it. This is called ETDMA (Extended TDMA) and can increase the efficiency of TDMA to ten times the capacity of the original analog cellular phone network.
The benefit of using TDMA with this optimization for network access comes when data is bur sty. That means, at an arbitrary time, it is not possible to predict the rate or amount of pending data from a particular host. This type of data is seen often in voice transmission, where the rate of speech, the volume of speech, and the amount of background noise are constantly varying. Thus, for this type of data, very little capacity is wasted by excessive allocation.
CDMA, or Code Division Multiple Access, allows every device in a cell to transmit over the entire bandwidth at all times. Each mobile device has a unique and orthogonal code that is used to encode and recover the signal (Leon-Garcia and Widjaja 2000). The mobile phone digitizes the voice data as it is received, and encodes the data with the unique code for that phone. This is accomplished by taking each bit of the signal and multiplying it by all bits in the unique code for the phone. Thus, one data bit is transformed into a sequence of bits of the same length as the code for the mobile phone. This makes it possible to combine with other signals on the same frequency range and still recover the original signal from an arbitrary mobile phone as long as the code for that phone is known. Once encoded, the data is modulated for transmission over the bandwidth allocated for that transmission. A block diagram of the process is shown in Figure 4.
The process for receiving a signal is shown in Figure 5. Once the signal is demodulated, acorrelator and integrator pair recovers the signal based on the unique code from the cellular
phone. The correlator recovers the original encoded signal for the device, and the integrator transforms the recovered signal into the actual data stream.
CDMA has been patented in the United States by Qualcomm, making it more expensive to implement due to royalty fees. This has been a factor for cellular phone providers when choosing which system to implement.
By keeping security in mind while designing the new system, the creators of 2G wireless were able to produce a usable system that is still in use today. Unfortunately, 2G technology is beginning to feel its age. Consumers now demand more features, which in turn require higher data rates than 2G can handle. A new system is needed that merges voice and data into the same digital stream, conserving bandwidth to enable fast data access. By using advanced hardware and software at both ends of the transmission, 4G is the answer to this problem.
Ultra Wide Band Networks
Ultra Wideband technology, or UWB, is an advanced transmission technology that can be used in the implementation of a 4G network. The secret to UWB is that it is typically detected as noise. This highly specific kind of noise does not cause interference with current radio frequency devices, but can be decoded by another device that recognizes UWB and can reassemble it back into a
signal. Since the signal is disguised as noise, it can use any part of the frequency spectrum, which means that it can use frequencies that are currently in use by other radio frequency devices (Cravotta ).
An Ultra Wideband device works by emitting a series of short, low powered electrical pulses that are not directed at one particular frequency but rather are spread across the entire spectrum (Butcher ). As seen in Figure 6, Ultra Wideband uses a frequency of between 3.1 to 10.6 GHz.
The pulse can be called shaped noise because it is not flat, but curves across the spectrum. On the other hand, actual noise would look the same across a range of frequencies it has no shape. For this reason, regular noise that may have the same frequency as the pulse itself does not cancel out the pulse. Interference would have to spread across the spectrum uniformly to obscure the pulse.
UWB provides greater bandwidth â€ as much as 60 megabits per second, which is 6 times faster than todayâ„¢s wireless networks. It also uses significantly less power, since it transmits pulses instead of a continuous signal. UWB uses all frequencies from high to low, thereby passing through objects like the sea or layers of rock. Nevertheless, because of the weakness of the UWB signal, special antennas are needed to tune and aim the signal.
Multiple smart antennas can be employed to help find, tune, and turn up signal information. Since the antennas can both listen and talk, a smart antenna can send signals back in the same direction that they came from. This means that the antenna system cannot only hear many times louder, but can also respond more loudly and directly as well (ArrayComm 2003).
There are two types of smart antennas:
Switched Beam Antennas (as seen in Figure 7) have fixed beams of transmission, and can switch from one predefined beam to another when the user with the phone moves throughout the sector
Adaptive Array Antennas (as seen in Figure 8) represent the most advanced smart antenna approach to date using a variety of new signal processing algorithms to locate and track the user, minimize interference, and maximize intended signal reception
Although UWB and smart antenna technology may play a large role in a 4G system, advanced software will be needed to process data on both the sending and receiving side. Thissoftware should be flexible, as the future wireless world will likely be a heterogeneous mix of technologies.
4G will likely become a unification of different wireless networks, including wireless LAN technologies (e.g. IEEE 802.11), public cellular networks (2.5G, 3G), and even personal area networks. Under this umbrella, 4G needs to support a wide range of mobile devices that can roam across different types of networks (Cefriel ). These devices would have to support different networks, meaning that one device would have to have the capability of working on different networks. One solution to this multi-network functional device is a software defined radio.
Software Defined Radio
A software defined radio is one that can be configured to any radio or frequency standard through the use of software. For example, if one was a subscriber of Sprint and moved into an area where Sprint did not have service, but Cingular did, the phone would automatically switch from operating on a CDMA frequency to a TDMA frequency. In addition, if a new standard were to be created, the phone would be able to support that new standard with a simple software update. With current phones, this is impossible.
A software defined radio in the context of 4G would be able to work on different broadband networks and would be able to transfer to another network seamlessly while traveling outside of the userâ„¢s home network.
A software defined radioâ„¢s best advantage is its great flexibility to be programmed for emerging wireless standards. It can be dynamically updated with new software without any changes in hardware and infrastructure. Roaming can be an issue with different standards, but with a software defined radio, users can just download the interface upon entering new territory, or the software could just download automatically (Wang 2001). Of course, in order to be able to download software at any location, the data must be formatted to some standard. This is the job of the packet layer, which will split the data into small packets.
Implementation of Packets
Current System: IPv4
Currently, the Internet uses the Internet Protocol version 4 (IPv4) to locate devices. IPv4 uses an address in the format of xxx.xxx.xxx.xxx where each set of three digits can range from 0 to 255 (e.g 188.8.131.52). Though combinations are reserved, but this address format allows for approximately 4.2 billion unique addresses. Almost all IP addresses using IPv4 have been assigned, and given the number of new devices being connected to the Internet every day, space is running out. As people begin to connect refrigerators, cars, and phones to the Internet, a larger address space will be needed.
Recommended System: IPv6
The next generation addressing system uses the Internet Protocol version 6 (IPv6) to locate devices. IPv6 has a much larger address space. Its addresses take the form x:x:x:x:x:x:x:x where each x is the hexadecimal value that makes up one eighth of the address. An example of this is:FEDC:BA98:7654:3210:FEDC:BA98:7654:3210 (The Internet Engineering Task Force Network Working Group ). Using this address format, there is room for approximately 3.40 * 1038 unique addresses. This is approximately 8.05*1028 times as large as the IPv4 address space and should have room for all wired and wireless devices, as well as room for all of the foreseeable expansion in several lifetimes. There are enough addresses for every phone to have a unique address. Thus, phone in the future can use VoIP over the Internet instead of continuing to use their existing network.Voice over IP (VoIP)
Voice over IP is the current standard for voice communication over data networks. Several standards already exist for VoIP, the primary one being International Multimedia telecommunications Consortium standard H.323. VoIP is already in use in many offices to replace PBX-based systems and by several companies that offer cheap long distance phone calls over the Internet, such as Net2Phone and Go2Call. VoIP allows for flexibility the same way that data packets do; as far as the network is concerned, VoIP packets are the same as any other packet. They can travel over any equipment that supports packet-based communication and they receive all of the error correction and other benefits that packets receive. There are many interconnects between the data Internet and the phone network, so not only can VoIP customers communicate with each other, they can also communicate with users of the old telephone system.
One other thing that VoIP allows is slow transition from direct, connection based communication to VoIP communication. Backbones can be replaced, allowing old-style lephone users to connect to their central office (CO) the same way. However, the CO will then connect to an IPv6 Internet backbone, which will then connect to the destination CO. To the end user, there will not seem to be any difference, but the communication will occur primarily over a packet-based system, yielding all of the benefits of packets, outside of the short connections between either end of the communication and their CO.
Of course, in order to keep curious users from listening in by sniffing, all data, including voice, should be encrypted while in transit.
Two encryption/decryption techniques are commonly used: asymmetric and symmetric encryption. Symmetric encryption is the more traditional form, where both sides agree on asystem of encrypting and decrypting messages â€ the reverse of the encryption algorithm is the decryption algorithm. Modern symmetric encryption algorithms are generic and use a key to vary the algorithm. Thus, two sides can settle on a specific key to use for their communications. The problem then is the key transportation problem: How do both sides get the key without a third party intercepting it? If an unauthorized user receives the key, then he too can decrypt the messages.
In reality, however, the usage of different encryption schemes depends on many factors, including network data flow design. Thus, it is important that the encryption method be able to change when other determining factors change. Al-Muhtadi, Mickunas, and Campbell of University of Illinois at Urbana-Champaign showed great foresight in admitting that existing security schemes in 2G and 3G systems are inadequate, since there is greater demand to provide a more flexible, reconfigurable, and scalable security mechanism as fast as mobile hosts are evolving into full-fledged IP-enabled devices (Al-Muhtadi, Mickunas, and Campbell 2002, 60).
Unfortunately, IPv6 can only protect data in transmission. Individual applications may contain flaws in the processing of data, thereby opening security holes. These holes may be remotely exploited, allowing the security of the entire mobile device to be compromised. Thus, any wireless device should provide a process for updating the application software as security holes are discovered and fixed.
As wireless devices become more powerful, they will begin to exhibit the same security weaknesses as any other computer. For example, wireless devices may fall victim to Trojans or become corrupt with viruses. Therefore, any new wireless handheld device should incorporate antivirus software. This software should scan all e-mail and files entering through any port (e.g. Internet, beaming, or synchronizing), prompting the user to remove suspicious software in the
process. The antivirus software should also allow secure, remote updates of
the scanning software in order to keep up with the latest viruses (NIST, U.S. Dept. of Commerce , 5-34).
Consumers demand that software and hardware be user-friendly and perform well. Indeed, itseems part of our culture that customers expect the highest quality and the greatest features from what they buy. The cellular telephone industry, which now includes a myriad of wireless devices, is no exception.
Meanwhile, competition in the industry is heating up. Providers are slashing prices while scrambling for the needed infrastructure to provide the latest features as incentives, often turning to various 3G solutions. Unfortunately, this will only serve to bewilder customers in an already confusing market.
Customers want the features delivered to them, simple and straightforward. Wireless providers want to make money in a cutthroat industry. If the U.S. government wants to help, the best way to help all parties is to enforce 4G as the next wireless standard. The software that consumers desire is already in wide use. The transmission hardware to take it wireless is ready to go. And we have the security practices to make sure it all works safely. The government need only push in the right direction; the FCC need only standardize 4G in order to make the transition economically viable for all involved.
This is a need that demands a solution. Todayâ„¢s wired society is going wireless, and it
has a problem. 4G is the answer.
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