There are five methods of multiple antennas have been defined for the LTE downlink to improve the performance:
- Receive diversity at the mobile
- Transmit diversity using SFBC at the eNB (evolved Node B)
- MIMO spatial multiplexing at the eNB, for one or two users
- Cyclic Delay Diversity (CDD) at the eNB, used in conjunction with spatial multiplexing
- Beam steering (user specific)
The first two Multi-antenna Techniques LTE methods are relatively conventional diversity. The third and fourth Multi-antenna Techniques LTE methods use frequency encoding mechanisms space to spread data across multiple antennas. The diversity of cyclic delay deliberately introduced delays between the antennas to create artificial multipath. It applies more dynamically than other LTE radio systems. The techniques are applied differently depending on the type of physical sign or physical channel.
Both SIMO and MISO are used in third generation (3G) cellular systems, and will be launched in LTE networks. Its purpose is to improve the integrity of the connection and to improve error rates, particularly when the connection undergoes poor SNR (for example, on the edge of a cell). Conventional beam steering arrangement introduces phase shifts in phase and amplitude to the total signal power of each transmit antenna. The intention is to concentrate the signal power in a particular direction.
The same Multi-antenna Techniques LTE of applying phase and amplitude offsets can be used in the receive antennas to make the most sensitive to signals from a particular direction receiver. In LTE, the amplitude and phase of individual resource blocks is adjustable and making orientation much more flexible and user-specific beam. Beam steering not increase data rates, but has a similar diversity effect in terms of increasing the strength of the signal.
The effectiveness of the orientation of the beam increases with the number of transmitting antennas, which enables the creation of a narrower beam. The possible gains with only two antennas usually not considered worthwhile Thus, beam steering by generally only considered the choice of four antennas.
User Equipment (UE) diversity reception (SIMO) is mandatory for the UE. It is usually performed using maximum ratio combining. In a mobile environment, the signal from a single antenna reception level suffer fluctuations due to the different types of discoloration. With the wider bandwidth channel LTE nature can also be a frequency dependent on the level of detectable signal. By combining the received signal from two antennas, the UE can regain a stronger signal. Receive diversity provides up to 3 dB gain at low SNR in Multi-antenna Techniques LTE.