Multi-antenna Techniques LTE to improve the downlink performance
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.
Multi-Antenna Techniques in LTE to Improve Downlink Performance
In LTE, multi-antenna techniques are employed to enhance the downlink performance, improve spectral efficiency, and ensure better coverage and reliability. These techniques make use of multiple antennas at the transmitter (eNodeB) and receiver (UE) to exploit spatial diversity, multiplexing, and interference management. Below are the key multi-antenna techniques used in LTE for downlink performance enhancement:
- Spatial Multiplexing: Spatial multiplexing allows multiple data streams to be transmitted simultaneously over the same frequency channel by using different spatial paths. This increases the data throughput without requiring additional bandwidth. The eNodeB transmits separate streams to different antennas, and the UE, with multiple receiving antennas, decodes them simultaneously, improving downlink throughput and capacity.
- Transmit Diversity: Transmit diversity uses multiple antennas at the eNodeB to send the same signal over different spatial channels. This ensures that even if some signals experience fading or interference, others will still be received reliably by the UE. It enhances the reliability of the downlink by reducing the impact of signal degradation due to fading and interference.
- Beamforming: Beamforming is a technique where multiple antennas at the eNodeB focus their signal towards a specific direction, improving the signal strength received by the UE. It enhances the downlink performance by increasing the signal-to-noise ratio (SNR) at the receiver, thereby improving coverage and data rates, especially at the cell edge. Beamforming can be done in both open-loop and closed-loop modes.
- Closed-Loop MIMO: In closed-loop MIMO, the UE provides feedback to the eNodeB regarding the channel conditions. Based on this feedback, the eNodeB adjusts its transmission strategy, such as beamforming and spatial multiplexing, to optimize the downlink transmission. This adaptive approach ensures that the downlink performance is maximized based on real-time channel conditions.
- Coordinated Multi-Point (CoMP): CoMP is a technique where multiple eNodeBs coordinate their transmission to a single UE. By transmitting the same signal from multiple eNodeBs, CoMP reduces interference and increases the signal strength for the UE, particularly at the cell edge. This improves coverage and user experience, especially in areas where signal quality is poor due to distance or obstacles.
By using these multi-antenna techniques, LTE is able to significantly improve downlink performance, increase data throughput, reduce interference, and enhance coverage, ensuring a better user experience and more efficient use of available resources.