Various Technologies

Though several technologies available today play a role in achieving roadmap for 4G as it materializes; highlights few of them:

1. Orthogonal Frequency Division Multiplexing (OFDM) and OFD Multiple Access (OFDMA) transmits data by splitting radio signals that are broadcast simultaneously over different frequencies. OFDMA, used in mobile WiMax, also provides signals that are immune to interference and can support high data rates. It utilizes power more efficiently than 3G systems while using smaller amplifiers and antennas. This all translates to expected lower equipment costs for wireless carriers. In OFDM and related modulations technology, multiple coherent sub-carriers are modulated and codes are used to insure that encoded bits can be decoded even if some of the sub-carriers arrive at very low SNR. OFDM is more resistant to inter-symbol interference. OFDM could be used both as multiple access technology and modulation scheme in 4G, but has many challenges. The OFDM has many uses for 4G:
   1. Most efficient transmission technique for digital audio and video broadcasting system. Processing data at rates of 10 Mbps or higher results in a small computer inside the phone but requires higher power in the amplifier
   2. Provide robust, reliable broadband service to the most people at the greatest distance with the least amount of infrastructure,
   3. OFDM is easier to implement then CDMA by small companies, as CDMA networks need more experienced engineers.
2. Mobile WiMAX is an IEEE specification also known as 802.16e and designed to support as high as 12Mbps data-transmission speeds. It uses OFDMA and is the next-generation technology of choice for many Service provider.
3. Ultra Mobile Broadband (UMB), also known as CDMA2000 EV-DO, is an expected path to 4G for legacy CDMA network providers. It's an IP-based technology that is said to support 100Mbps through Gbps data-transmission speeds.
4. Multiple-input multiple-output (MIMO) wireless LAN technology supports two or more radio signals in a single radio channel, increasing bandwidth. MIMO does this by using multiplexing. MIMO is expected to support data rates as high as 15Mbps in 36MHz of spectrum.
5. Long Term Evolution (LTE) is a modulation technique designed for GSM/UMTS -based technology that uses OFDM and MIMO. It's being developed by the Third Generation Partnership Project (3GPP) and is said to support 45M to 144Mbps in test networks today.
6. Software Defined Radio (SDR), sometimes shortened to software radio (SR). refers to wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence. To select the desired modulation type, the proper programs must be run by microcomputers that control the transmitter and receiver (Bedell, 2005). Moreover, SDR is one form of Open Wireless Architecture (OWA). Since 4G is the collection of wireless standards, the final form of the 4G device will constitute all standards. This can be realized using SDR technology. Software-Defined Radio (SDR) is a radio communication technology that is based on software defined wireless communication protocols instead of hardwired implementations: frequency band, air interface protocol and functionality can be upgraded with software download instead of a complete hardware replacement. An SDR is capable of being re-programmed or reconfigured to operate with different waveform & protocols through dynamic loading of new waveforms and protocols. These waveforms and protocols can contain a number of different parts, including modulation techniques, security and performance characteristics defined in software as part of the waveform itself. Public safety radios, as well as commercial wireless applications, can use SDR for flexibility, and field upgradeability of their products. The ultimate goal of SDR technology is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax, wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well. It is now possible that the future commercial viability of 3G and 4G wireless networks will depend upon capacity enhancing algorithms such as smart antennas and multi-user detection, and that these are prime candidates for implementation by SDR.
7. All IP-based core networks: 4G will resemble a convergence of existing technologies rather than an entirely new standard. An all IP based 4G wireless network has many advantages as it will be compatible as well as independent of actual radio access technology. IP radio protocols can be designed a core-network that give complete flexibility in the access network type, like 802.11, WCDMA, Bluetooth, hyper LAN and new CDMA protocols. Considering the cost of the equipments for 4G, IP based wireless networks is one-fourth to one-tenth of the equipments for 2G and 3G wireless infrastructure. There will be reduction in the cost by using interoperability in equipment for service provider.
   An IP Wireless network would completely replace the old SS7 signaling system because access signal transmission consumes a large part of network bandwidth even when there is no signaling traffic. IP networks use less bandwidth expensive mechanisms to achieve reliability (Sharma, 2002).
8. Full adopted multi-layer protocol architecture: The four major factors in achieving the high degree of integration, flexibility and efficiency envisioned in 4G are seamless integration, a high performance physical layer, flexible and adaptive multiple access, and high service and application adaptation.
9. Mesh Network is a local area network (LAN) that employs one of two connection arrangements, full mesh topology or partial mesh topology. In the full mesh topology, each node (workstation or other device) is connected directly to each of the others (Govil, 2008). In the partial mesh topology, some nodes are connected to all the others, but some of the nodes are connected only to those other nodes with which they exchange the most data. But above definition mention no dependency on any time parameter -- nothing is necessarily dynamic in a mesh. However, in recent years, and in connection with wireless networks, the term "mesh" is often used as a synonym for "ad hoc" or "mobile" network. Obviously, combining the two characteristics of a mesh topology and ad hoc capabilities is a very attractive proposition.
   
   

 Figure 1: Roadmap to 4G communication system

The figure 2 shows a full mesh network with five nodes. Each node is shown as a sphere, and connections are shown as straight lines. The connections can be wired or wireless.

Figure 2: Mesh network