3G system provides faster communication services entailing voice and internet data transfer capabilities. The aim of 3G is to provide these services anytime, anywhere throughout the globe. But, this technology is suffering from some disadvantages, out of them most important is the requirement of a single broadband network with high data rates which integrates wireless LANs, Bluetooth, cellular networks etc. This leads to the invention of highly advanced new technology, what is known as 4G technology.
4G can be considered as the fourth generation of wireless communications and it also known as "beyond 3G". They may become popular in the 2010-2015 time period and will result in another leap in wireless data rate and spectral efficiency.4G integrates wired and wireless network, wireless technologies including GSM, wireless LAN and Bluetooth as well as computers, consumer electronics, communication technology. It is a mobile multimedia at anytime, anywhere with global mobility support and integrated wireless solution.
4G is an all IP-based integrated system which is capable of providing 100 Mbps for high mobility and 1 Gbps for low mobility, with end-to-end QoS and high security, and will offer various services at any time as per user requirements, anywhere with seamless interoperability, at affordable cost. The user services include IP telephony, ultra-broadband Internet access, gaming services and High Definition Television (HDTV) streamed multimedia.
1. MIMO (multiple input multiple output)
As the name indicates it uses multiple transmitting antennas and multiple receiving antennas for spatial multiplexing. Since, it uses this multipath propagation reliability, coverage area and throughput is increased. because MIMO can transmit multiple signals across the communication channel the data rate is much increased.
2. SMART ANTENNAS
Smart or intelligent antennas are a multi-antenna concept in which a radio beam is allowed to follow the user. They are also used to provide diversity in transmission and reception.
3. ADHOC networks
Adhoc networks helps in the self organisation of network of devices which are not necessarily connected to internet. 4G will create hybrid wireless networks and data packets are sent through paths having minimal power requirements.
4. Adaptive Modulation and Coding (AMC)
Adaptive modulation and coding mechanism is used to modify the modulation and coding formats according to the instantaneous variations in channel conditions. Channel statistics helps the transmitter and receiver to optimize the system parameters such as modulation, coding, bandwidth, channel estimation filters and automatic gain control.
5. Adaptive hybrid ARQ
Since the signals are transmitted over lossy wireless channel there should be an efficient and reliable Medium Access control (MAC) to avoid the weakening of signals. For this purpose an automatic retransmission and fragmentation mechanism called Automatic Repeat Request (ARQ) is used. It will break the packets into sub packets and transmit them sequentially. This mechanism introduces time diversity into the system due to capability to recover noise and interferences.
6. Software Defined Ratio (SDR)
Software Defined Ratio can be considered as the base of 4G technology which allows some properties of a conventional radio equipment that were used to implemented in special purpose hardware, to be implemented in modifiable software operating on programmable processing technologies.