06-01-2012, 01:59 PM
The objectives of the 4G wireless communication standard:
• A spectrally efficient system (in bits/s/Hz and bits/s/Hz/site)
• High network capacity: more simultaneous users per cell.
• A nominal data rate of 100 Mbit/s while the client physically moves at high speeds relative to the station, and 1 Gbit/s while client and station are in relatively fixed positions as defined by the ITU-R
• A data rate of at least 100 Mbit/s between any two points in the world
• Smooth handoff across heterogeneous networks
• Seamless connectivity and global roaming across multiple networks.
• High quality of service for next generation multimedia support (real time audio, high speed data, HDTV video content, mobile TV, etc)
• Interoperability with existing wireless standards and an all IP, packet switched network.
In short, the 4G system should dynamically share and utilize network resources to meet the minimal requirements of all the 4G enabled users.
4G features
The infrastructure and the terminals of 4G will have almost all the standards from 2G to 4G implemented. Although legacy systems are in place to adopt existing users, the infrastructure for 4G will be only packet-based (all-IP). Some proposals suggest having an open Internet platform. Technologies for 4G include: Flash-OFDM, the 802.16e mobile version of WiMax (also known as WiBro in South Korea), and HC-SDMA.. 3GPP Long Term Evolution may reach the market 1–2 years after Mobile WiMax is released. An even higher speed version of WiMax is the IEEE 802.16m specification. LTE Advanced will be the later evolution of the 3GPP LTE standard
Access Schemes
As the wireless standards evolved, the access techniques used also exhibited increase in efficiency, capacity and scalability. The first generation wireless standards used plain TDMA and FDMA. In the wireless channels, TDMA proved to be less efficient in handling the high data rate channels as it requires large guard periods to alleviate the multipath impact. Similarly, FDMA consumed more bandwidth for guard to avoid inter carrier interference. So in second generation systems, one set of standard used the combination of FDMA and TDMA and the other set introduced a new access scheme called CDMA. Usage of CDMA increased the system capacity and also placed a soft limit on it rather than the hard limit. Data rate is also increased as this access scheme is efficient enough to handle the multipath channel. This enabled the third generation systems to use CDMA as the access scheme IS-2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA. The only issue with CDMA is that it suffers from poor spectrum flexibility and scalability.
Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved FDMA and Multi-carrier code division multiple access (MC-CDMA) are gaining more importance for the next generation systems. WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is being considered for the downlink. By contrast, IFDMA is being considered for the uplink since OFDMA contributes more to the PAPR related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus avoids amplifier issues. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved.
The other important advantage of the above mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently requires high complexity equalization at the receiver.
• A spectrally efficient system (in bits/s/Hz and bits/s/Hz/site)
• High network capacity: more simultaneous users per cell.
• A nominal data rate of 100 Mbit/s while the client physically moves at high speeds relative to the station, and 1 Gbit/s while client and station are in relatively fixed positions as defined by the ITU-R
• A data rate of at least 100 Mbit/s between any two points in the world
• Smooth handoff across heterogeneous networks
• Seamless connectivity and global roaming across multiple networks.
• High quality of service for next generation multimedia support (real time audio, high speed data, HDTV video content, mobile TV, etc)
• Interoperability with existing wireless standards and an all IP, packet switched network.
In short, the 4G system should dynamically share and utilize network resources to meet the minimal requirements of all the 4G enabled users.
4G features
The infrastructure and the terminals of 4G will have almost all the standards from 2G to 4G implemented. Although legacy systems are in place to adopt existing users, the infrastructure for 4G will be only packet-based (all-IP). Some proposals suggest having an open Internet platform. Technologies for 4G include: Flash-OFDM, the 802.16e mobile version of WiMax (also known as WiBro in South Korea), and HC-SDMA.. 3GPP Long Term Evolution may reach the market 1–2 years after Mobile WiMax is released. An even higher speed version of WiMax is the IEEE 802.16m specification. LTE Advanced will be the later evolution of the 3GPP LTE standard
Access Schemes
As the wireless standards evolved, the access techniques used also exhibited increase in efficiency, capacity and scalability. The first generation wireless standards used plain TDMA and FDMA. In the wireless channels, TDMA proved to be less efficient in handling the high data rate channels as it requires large guard periods to alleviate the multipath impact. Similarly, FDMA consumed more bandwidth for guard to avoid inter carrier interference. So in second generation systems, one set of standard used the combination of FDMA and TDMA and the other set introduced a new access scheme called CDMA. Usage of CDMA increased the system capacity and also placed a soft limit on it rather than the hard limit. Data rate is also increased as this access scheme is efficient enough to handle the multipath channel. This enabled the third generation systems to use CDMA as the access scheme IS-2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA. The only issue with CDMA is that it suffers from poor spectrum flexibility and scalability.
Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved FDMA and Multi-carrier code division multiple access (MC-CDMA) are gaining more importance for the next generation systems. WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is being considered for the downlink. By contrast, IFDMA is being considered for the uplink since OFDMA contributes more to the PAPR related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus avoids amplifier issues. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved.
The other important advantage of the above mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently requires high complexity equalization at the receiver.
