MIGRATION TO 4G

Due to success of the second generation (2G) mobile system, the third generation (3G) system was developed. 3G systems were designed to provide higher data rate services. A range of wireless systems including GPRS, IMT - 2000, Bluetooth, WLAN and Hyper-LAN have been developed, each with their own merits and short comings. No single system exists for integration of all these technologies; thus a 4G system that integrates existing and newly developed wireless systems is a more feasible option. 4G technology is still in the research & development stage and international standards do not exist. 3G technology has proper standards and many big companies have invested huge sums to acquire the needed spectrum space. The predicament is whether or not companies should bypass 3G and adopt 4G straight away. It is being argued that 3G and 4G technologies are not mutually exclusive but are complementary to each other (Sharma, 2002). Those countries that have made huge investments in 3G require a evolutionary path for migration to 4G, but developing countries which have not made investments for 3G need not follow the 3G-migration route, as they can easily by-pass 3G technology and adopt directly 4G networks. 4G networks are being designed to accommodate WLANs and PANs based on Bluetooth technologies. 3G has bandwidth limitations. 4G core networks are all IP networks which have been extended to radio access nodes, so the disadvantages of circuit switching are totally absent. These networks will be incorporating advanced IPv6; even the signaling will be done through IP. The setting up cost will be lower as they can be built on top of existing network and won't require operators to completely retool. Hence, 4G technology will be suitable to esp. those countries which have not yet adopted 3G.

Figure 1 gives an understanding of driving forces behind the adoption of 4G and impeding forces that forces the corporate house to use it commercially in future in adopting 4G Wireless networks.

 
Figure 1: Driving and impeding forces for adoption of 4G wireless network

Roadmap for Achieving 4G

Recently there have been major advances in wireless access technologies for planning roadmap to 4G. Among the new schemes of technology being proposed for 4G, 802.16e and 802.20 standards are OFDMA, Single Carrier FDMA, and MC-CDMA. The new technologies, while offering the efficiencies of the older technologies such as CDMA, also offer advantages in scalability. Current working assumptions for physical layer multiple access schemes is OFDMA for downlink and Single Carrier FDMA (SC-FDMA) for uplink.

One way to increase system capacity is to implement a Multiple-Input Multiple-Output (MIMO) antenna scheme. A wireless system with single antennas obeys Shannon's classical limit for capacity, which can be expressed as C = log₂(1+SNR). Ideal capacity therefore increases as the log of the signal-to-noise ratio. MIMO systems, on the other hand, are modeled to increase capacity linearly with respect to the number of transmit and receive pairs that are used.