4G - 4th Generation Mobile Communication Networks
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Apart from the differences mentioned above, 4G also aims to:
Evolution Path to 4G (Source: 10)
The architecture of the 4G network will more or less resemble the 3G architecture but there are some significant evolutionary changes. Circuit-switching capabilities are redundant in 4G and are thus removed. The MSC used previously to service legacy 2G voice traffic is discarded and all voice traffic is treated as packet data at the BS. Backward compatibility is maintained by segmenting voice data into packets and routing them through the IP backbone using VOIP (Voice Over IP) technology. A VOIP Gateway is used to connect to PSTN or ISDN.
Another major advancement that 4G makes is the integration of Wireless LANs into the total mobile network. The situation will be similar to what is happening today with wired LANs - the line between a wired WAN and a wired LAN has blurred with the use of same technologies in both (eg. ATM). Similarly, new air interface standards are being developed for high-speed wireless LANs in conjunction with those for the cellular 4G network, which will allow wireless LANs to be interconnected to the 4G IP backbone simply via routers with wireless access built-in.
A related concept is Ad Hoc Networking. This concept refers to the formation of wireless LANs on an ad hoc basis. In other words, a group of wireless devices will be able to create or join a wireless network without any central infrastructure or administration. All interfaces are air interfaces in this scheme and there is no need for a CM (Control Module) connected to any wired infrastructure. 4G will support ad hoc networking via a more evolved version of a currently existing standard called BlueTooth. Ad hoc networking is particularly important step because it allows for the development of a wide range of different devices which will be able to autonomously communicate with each other within a short-range even when they don't have complete cellular access capabilities.
The requirements of a 4G core network are:
The IP core network will be based on IPv6 (IP Version 6) instead of IPv4. This is more conducive to a large number of devices with IP addresses and also supports mobility far better than its predecessor. The IP core will most likely be implemented using ATM (Asynchronous Transfer Mode) - an evolutionary step from the Frame Relay based 3G core.
The Core network may be viewed as consisting of 3 layers - the Transport Network, the Service Middleware and the Applications. The Transport Network is the actual network interconnection and will be configured by routers, as with any IP network.
The Service Middleware is at the hardware and software level (hence the name, middleware). This will be implemented in Servers running specialised software. On one side, this will provide application support with such functions as billing, media conversion, location registration, billing and so on. Known as the Service Support Layer this also provides an API (Application Programming Interface) through protocols such as JAIN and Parlay which are in the process of being standardised. On the other side, the Service Middleware will perform network and transport management with functions like RRM (Radio Resource Management), MM (Mobility Management), C/SM (Call and Session Management), etc.
The Core Network is inherently network-seamless since it is based on IP, the most universal Network layer protocol. Also, nodes can be configured to allow connectivity with other types of networks. The Service Middleware provides the content-seamless and terminal-seamless service. Location Management keeps track of the whereabouts of any mobile device and its movement characteristics. Thus, media conversion can take place when necessary according to the user's current situation and preferences. For example, the video resolution may be automatically reduced when user changes from a large-screen terminal (stationary location) to a smaller screen (on the move). Another example is the conversion from real-time video to audio when the user has to drive a vehicle.
Layered view of the IP-based Core Network in 4G (Source: 2)
In 2G and 3G systems Location Management is done for individual MTs. Each device registers its current location with the Core Network whenever it crosses the border of a location registration area. This leads to a wasteful signaling load because there are several occasions when the location of each MT in a group is not independent (eg. a train full of people with mobile devices).
4G will allow for Concatenated Location Registration. If the movement characteristics of a group of MTs are more or less similar their location registrations are concatenated, provided there is a common entity to concatenate with. Using the train example, assuming that the train itself performs location registration, a MT boarding the train only has to report to the Core Network that it is concatenated to the train. For the duration of the trip the Core network can perform location management based on the train's registration information. Considering the number of MT devices that can be on the train at one time, the signaling load is considerably less than if each device performed separate location registration every time the train crosses a cell edge. This will also help in cutting out any jitter or latency that may occur at cell boundaries in the hand-over process delivering a more seamless service.
However efficiently the frequency spectrum is utilised the maximum achievable channel capacity over a given bandwidth B is limited by the Nyquist Bandwidth formula, given by:
The value of C for 3G systems is less than the minimum value of 20 Mbps for 4G communications. Hence, it is inevitable that higher frequency bands will have higher frequency bands will have to be used in order to use a wider bandwidth in order to achieve the high data rates. This is not a simple task however, because the frequency band has an effect on the cell-sizes that 4G can accommodate.
4G will provide varied service quality according to distance from dense urban areas. Data rates in rural areas are expected to be lower than those enjoyed in dense urban areas. In the most likely case 4G coverage will extend to metropolitan areas and 3G systems will be utilised beyond them. The reason is partly economical, but cell-sizes also play a role in this.
The 4G cell radius will, in general, most likely be smaller because the propagation loss is increased by operating at higher frequencies and at higher transmission bit rates the received signal level threshold must be higher than at lower bit rates, in order to compensate for the greater affect of noise at higher bit rates (i.e to receive the signal at an adequate SNR).
The Equations that govern cell size:
Greater bit rates as well as higher frequency bands both result in smaller cell size. A cell-size decrease by half will result in 4 times the number of BSs being required to cover the same area. This is a very important consideration because laying down infrastructure incurs the greatest cost to the network providers. Another consequence of this is that cell sojourn time (average time spent within a cell) is reduced and hand-over frequency is increased.
Due to the increased hand-over frequency the load on RNC signal processing equipment is also increased greatly. This is detrimental to system performance and seamless service. At such high data rates the hand-over process must be as quick and efficient as possible.
A change in the RAN (Radio Access Network) architecture can provide a solution to thia. Instead of forming a 'Star' structure with BSs the RNC forms a 'Ring' known as a Cluster. The RNC also acts as a BS. It becomes the 'Cluster Head'. Diversity Hand-over is carried out in a distributed manner within the cluster. The uplink signal received by multiple BSs is passed onto one of the BSs which acts as a 'Temporal Agent'. The dynamically assigned Temporal Agent performs the signal processing previously handled singularly by RNC. The processed signal is sent to the Cluster Head to be sent to the forwarded to the Core Network. On the downlink the Cluster Head multicasts received packets to the BSs in the Cluster. Each BS monitors the required transmitting power and the Downlink quality for the MT connected to it in order to decide autonomously whether or not to transmit to the MT. In this way unnecessary or high-power transmissions are avoided in this way.
To the Core Network a Cluster appears as one 'virtual BS'. The Core Network only has to deal with the hand-over details when a MT moves from one Cluster to another. In this situation the hand-over destination cluster is decided upon co-operatively by the MT and the RRM unit in the Service Middleware layer. Re-routing to the hand-over destination is conducted by the MM unit in the Service Middleware layer.
Clustered Diversity hand-over scheme in 4G (Source: 3)
Among the diverse range of wireless devices that 4G will support there will be many that are not capable of cellular access because of impracticality due to antenna size, power consumption, etc. Instead these devices will have short-range communications capabilities allowing Ad Hoc networking with other devices. Thus, they can access the 4G backbone through other cellular capable devices. When any device connects to the backbone it is assigned an IP address and the device effectively becomes a MH (Mobile Host) that is part of a MN (Movable Network). If the MH and the gateway MT move away from each other there must be support services to allow the MH to be disconnected from the MN while staying connected to the backbone by being handed over to another access point or MT.
Mobile devices based on IP need some form of mobility control so that data can continue to be routed to them correctly. However, the IP address is based on the Network ID and this may change as the user roams.
Mobile IP is the mechanism that provides mobility control. It works on the principle of discovering, registering and tunneling to a temporary 'Care-of Address' (CoA) while the devices is on the move, away from where it first connected to the IP backbone. A MT on the move arranges for nodes within the Core Network known as Mobile Agents (MAs) and Home Agents (HAs) to redirect packets addressed to its original address, to its CoA. While the first packet has been redirected from the HA to the MA to the MT, the source is notified of the MA's address, and subsequent packets are sent straight to the MA bypassing the HA, thereby creating a 'tunnel'.
Tunneling reduces the number of hops that data must undergo and also reduces the amount of control signaling required for mobility control. The value of this is especially appreciable when tunneling is applied to Ad Hoc networks.
A device (lets call it Device A) joining a MN would use the MN's gateway to the backbone (eg. a MT with cellular access - lets call it B) as its MA. However, B, along with its MN, is itself moving, has an original HA and traversing MAs within the Core Network. Only the very first packet must endure a number of hops - from the HA of A to the HA of B to the MA of B to B to A. Subsequent packets however, are routed straight to the MA of B, then to B (as with any traffic to B) and finally on to A. As long as A stays part of the MN the HAs can be completely bypassed even though it is moving along with the MN.
One of the major evolutionary steps on the path to 4G is the integration of Wireless LANs so that they can access the IP backbone of a 4G network.
A Wireless LAN is an extension to wired LAN where it uses electromagnetic airwaves for communication whereas wired LAN does uses cables. Wireless LAN types include Infrared (IR) Technology, Spread Spectrum Technology, Frequency hopping, Direct sequence and Narrowband Technology.
There are several advantages of using WLANs. They enable data to be transmitted over air, thus reducing cabling. WLANs offer productivity, convenience, and cost advantages over traditional wired networks such as increased installation speed, increased simplicity and flexibility, reduced cost-of-ownership and scalability. Also they combine data connectivity with user mobility, increasing flexibility as well as allowing ad-hoc and roaming access within a limited range.
Since the 4G core network is basically an IP-based network connecting a Wireless LAN to the 4G backbone is similar in principle to connecting wired LAN in a wired Internet. This is done through a router with a radio transmitter capable of cellular access.
Wireless LAN data rates are presently far lower than the expected data rates for 4G. Thus, Wireless LAN technology will also need research to handle increased data rates.
HIPER LAN 2 is one such broadband wireless technology. It operates in the 5 GHz frequency band and is intended to provide untethered connectivity for mobile devices in corporate, public, and home environments. It uses a new type of radio technology called Orthogonal Frequency Division Multiplexing (OFDM).
HyperLAN will provide mobility and high-speed transmission with a raw over-the-air data rate of 54 Mbps at the physical layer as well as sustained throughput. For applications such as voice and video, the transmission speeds are somewhat lower at 20 Mbps.
The fact that 4G networks will support Ad Hoc Networking has been made quite clear but how it will do this has not yet been elaborated upon. BlueTooth is most likely to be the standard that will be a part of the 4G standards allowing for this functionality.
BlueTooth is a Radio Frequency standard that provides a low-cost, low-power solution with industry-wide support. It provides agreement at the physical level with specifications at both link layer and application layer. It enables wireless links between mobile computers, mobile phones, portable handheld devices, and connectivity to the Internet. The developers of BlueTooth aim to bypass the problems that come with both infrared and cable synchronising systems.
The main features of BlueTooth include the fact that it is wireless, its inexpensive, you don't have to think about it because it works behind the scenes, and it communicates in an unlicensed frequency of 2.45 GHz radio spectrum, which was set aside by international agreement for the use of Industrial, Scientific and Medical devices (ISM) ensuring communication compatibility worldwide.
These characteristics of BlueTooth make it the ideal standard to use for the support Ad Hoc networking in 4G. Although present data rates for BlueTooth are not high enough to be 4G-capable, research into this technology is expected to improve on the present performance.
Devices in a piconet share a common communication data channel. It has a total capacity of 1 Mbps, with headers and handshaking data consuming 20% of this capacity. A piconet has a master and up to seven slaves. The master transmits in even time slots, slaves in odd time slots. A data channel hops randomly 1,600 times/sec between the 79 (or 23) RF channels. Each channel is divided into time slots 625Ás long. Packets can be up to five time slots wide. Data in a packet can be up to 2,745 bits in length.
The five layers are Application Program Interface libraries, Logical Link Control & Data, Adaptation Protocol, Physical link control, Data processing & transmission management and Transmission/reception. These layers distribute functional responsibility, the bottom layers handle the lowest level details and progressively higher layers handle ever more general concerns.
In an increasingly mobile phone-dependent society, we need to carefully consider what sort of social implications there can be as a result of the availability of such high level services practically anywhere, anytime.
It might be the case that many will become totally hooked to their personal mobile device and it may affect their social skills. The availability of on-demand entertainment services will play a major role in this regard.
Also, with the level of intelligence and inter-connectivity that PDAs and other personal devices are likely possess, they may end up running our lives more or less. We may become overly dependent on them to take care of all the details in our lives (eg. control home appliances automatically, seek out location-dependent information and services, etc). Alternately, they may be viewed as helping hands that free up our time and resources. The line between the two interpretations however, is quite thin.
The most important social issue that is likely to come up time and time again is that of privacy. What personal information will be required to be stored, what part of this can be divulged publicly, what level of authentication and encryption will be required to secure communications - these are all questions that have to be answered but there are no straightforward answers. Solutions will most probably be found in legislation and it is quite likely that not everyone will agree with these.
Apart from the technological challenges there are a number of economic and political challenges that will also come into play. It is not just a case of best technology prevails.
The situation in a decades time could be such that strict adherence to standards is not practiced despite years of effort for a stramlined unified standard. In fact, it may not be practical for a single unified standard to operate. Instead, quick and easy software solutions are found for continued interoperability. This is a very open situation where developments occur freely and uncontrolled. This can only be fuelled by the availability of software solutions and high user demand and support in all sectors.
Alternately, it could be the case that tight regulation is needed in light of personal integrity and security issues. Central bodies may have to place the technology developers and distributors under tight scrutiny to make sure they conform to the rules. This, and higher complexity of systems resulting from the lack of an open environment, may push prices up too.
A third scenario may also come to exist where service providers may be
able to provide a high level of service but the technology is so expensive
that it can only be afforded by a relatively small proportion.
Assuming that widely accessible and affordable systems are in place within the next decade 4G systems will have a major effect on the economy and the way business is carried out. Higher levels of efficiency will be facilitated by the superior communications systems. For example, video Telephony will eliminate or reduce the need for 'face-to-face' meetings and the information and transaction services will be avaiabilityon the move.
The main concern, apart from mental health issues relating to social implecations, is that of radiation levels. The effects of exposure to radio transmissions are still being researched. Although there is no unanimous, concrete connection between mobile devices and deterioration of health, the heavier, more condensed traffic characteristics of future generation mobile networks do pose a risk that must be studied in more detail.
Within a matter of years the demand for mobile data services will outgrow the advancements of 3G. 4G will feature very high data rates and primarily multimedia services facilitated by various architectural and operational improvements. It completes the transition from circuit switching to packet switching, a much more efficient approach.
This does however need a lot of research to address issues and challenges that stand in the way. As problems are solved and practical solutions are found it will become possible for concrete standards to be developed. Many existing standards also need to be revised so that they can be better suited for 4G. There are already a number of telcos such as NTT DoCoMo of Japan that have begun active experimentation and testing of key technologies that will be part of 4G. However, it is extremely important not to be carried away with technological development alone. In this process we do need to consider social, economic, ethical and health-related issues.
Ad Hoc Networking: Networks formed without any central administration or infrastructure.
Backbone: Foundation of 4G network. The packet-switching heart, also known as the IP Backbone Network
Cellular: Form of communication where the signal is derived from land-based terrestrial stations. Each such station is located near the middle of its own cell. Thus moving from A to B a mobile user may be travelling across a number of cells dynamically changing base stations that are relaying the data.
Mobile: Mobile is a description for devices that can be used anytime, anywhere. Sometimes used synonymously with 'wireless' but the subtle difference is important.
Wireless: Communication through electro-magnetic waves, i.e via the air interface as opposed to wires.
(1) Which of these are not part of the characteristics of 4G?
(2) What does SGSN stand for?
(3) What does MSC stand for?
(4) What is the expected maximum data rate for 4G?
(5) What application will require BlueTooth?
(6) What are some of the major architectural differences exist between 3G and 4G?
(7) Which of these is not a function of the Service Middleware in the IP Core Network?
(8) Why are cell sizes likely to be smaller in 4G?
(9) What Location Management feature does 4G support?
(10) In the clustered diversity hand-over scheme that is used in 4G, the __________ is dynamically assigned to perform signal-processing combine the multiple signals into one: