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This article explains how to design a DAS (distributed antenna system) to achieve MIMO-like performance without the added expense of a full MIMO implementation.  

The need for high-performance cellular infrastructure has many organizations considering more advanced deployment methodologies for wireless networks, including Multiple-Input Multiple-Output (MIMO). This option uses multiple antennas at both the transmitter and receiver ends of a DAS architecture to improve communication performance. Here are some of the key reasons why organizations are considering a MIMO implementation for their cellular and mobile networks: 

Increased Capacity and Throughput 

MIMO technology allows for multiple data streams to be transmitted simultaneously, significantly increasing the data capacity and throughput of a wireless network. This is particularly important in high-density areas like stadiums, airports, and large corporate buildings with high data traffic.  

Enhanced Signal Quality 

MIMO systems improve signal quality and reliability by exploiting spatial diversity. Multiple antennas help in mitigating issues like multipath fading, where signal strength can be severely affected due to obstructions or reflections.  

Better User Experience 

With improved signal strength and reliability, users experience fewer dropped calls and higher data speeds, leading to a generally more reliable and satisfying wireless experience.  

Efficient Spectrum Utilization 

As the demand for wireless bandwidth continues to grow, efficient use of the available spectrum is crucial. MIMO allows more data to be transmitted without needing additional spectrum. 

Future-Ready Infrastructure 

As wireless technology evolves, particularly with the rollout of 5G, MIMO is becoming a standard feature. Integrating MIMO into DAS ensures that the infrastructure is compatible with current and future wireless standards, avoiding obsolescence.  

Support for Multiple Operators and Technologies 

MIMO-enabled DAS can support multiple wireless operators and a wide range of technologies (like 4G and 5G). This makes it a versatile solution for organizations that need to cater to diverse wireless needs. 

Reduced Interference 

MIMO systems are adept at managing interference, which is crucial in environments where there is a high density of wireless signals.  

Cost-Effectiveness 

While integrating MIMO into DAS requires an initial investment, the long-term benefits of higher capacity and better service quality can lead to cost savings. It also reduces the need for additional infrastructure to handle increased data traffic.  

Given these advantages, why isn’t every DAS installation capable of MIMO?

Part of the answer may be that the organization simply does not require higher levels of performance but, primarily, the significant issue is the cost of traditional MIMO. Because this setup requires multiple antennas to both transmit and receive, the added expense often has stakeholders weighing the tradeoffs.  

A sensible solution that’s getting a lot of attention right now is interleaved MIMO, where the DAS is designed with alternating transmitters and receivers to provide MIMO-level performance for key coverage areas. This is possible without the additional cost of multiple antennas at each access point.  

With interleaved MIMO, the access points are separated by distance and the branch signals from each access point are interleaved—or mixed alternatively—across the coverage area. This significantly improves radio coverage and minimizes power imbalances among the RAUs (Remote Antenna Units)—resulting in lower fading, higher capacity, and significantly improved data rates.  

Unlike traditional MIMO, which requires antennas for each data stream, interleaved MIMO requires less cabling and antennas, so the cost to implement it is significantly lower. The result is MIMO equivalent performance that will meet the needs of many organizations for whom a traditional MIMO deployment would not be cost-effective. 

Configuring Interleaved MIMO 

Implementing Interleaved MIMO Successfully  

While the design and spacing requirements for an interleaved MIMO network are building-specific, there are two important factors to consider:  

• The signal-to-interference-plus-noise ratio (SINR) needs to be greater than 20 dB to ensure the channel can support a higher data rate. Any design that meets the typical targeted key performance indicators (KPIs) should support this requirement.
• In a 2×2 MIMO configuration, the two paths should be within 12 dB of each other, so the two streams are balanced. 

Interleaved MIMO offers several advantages over traditional MIMO—even without considering cost. These include:  

Improved Signal Robustness 

Interleaving in MIMO spreads the data across multiple antennas and time intervals, reducing signal fading and interference. This is particularly beneficial in environments with high signal reflection or obstruction and leads to more reliable communication.  

Enhanced Error Correction 

By distributing data across multiple paths, interleaved MIMO facilitates better error correction. If one path experiences interference or loss, the data can still be reconstructed accurately using the information received from other paths, thus improving the overall error correction capability. 

Increased Spectral Efficiency 

Interleaved MIMO can achieve higher spectral efficiency than traditional MIMO. This is because the interleaving process allows for more effective utilization of the available spectrum, leading to increased data throughput without the need for additional bandwidth.  

Better Handling of Multipath Propagation 

In wireless communication, signals often reach the receiver through various paths. Interleaved MIMO is more adept at handling these multipath effects, turning what is typically a drawback in wireless systems into an advantage for enhancing signal diversity and strength.  

Enhanced Capacity in High-Interference Environments  

Interleaved MIMO is particularly effective in environments with high levels of interference. By spreading the signal across multiple antennas and time slots, it reduces the likelihood that interference will significantly impact the entire signal, thus maintaining higher data transmission capacity even in challenging conditions. These advantages make interleaved MIMO a desirable choice for advanced wireless communication systems, especially in scenarios where reliability and efficient use of bandwidth are critical. 

Interleaved MIMO with Zinwave Active DAS  

Wilson Electronics offers interleaved MIMO with our Zinwave Active DAS. Specifically designed for large facilities and complexes of more than 250k sq. ft., Zinwave Active DAS is ideal for locations where reliable communication and advanced connectivity are critical for safety, security, and digital transformation. It delivers the highest quality signal and a superior mobile experience to hospitals, airports, government buildings, college campuses, and other public venues.  

With our Zinwave DAS, all signal sources are aggregated to a single point-of-interface that connects to a primary hub, which transports an optical signal via fiber to secondary hubs and remote radio units—optimizing frequencies from 150 MHz to 5GHZ.  

Designed for energy efficiency, scalability and easier installation, Zinwave Active DAS requires less space than competitive solutions and allows for reuse of your existing fiber network. Real-time remote monitoring capability is built-in for troubleshooting and maintenance. Implementing interleaved MIMO requires design, planning, and some additional equipment. For only about 10% more than a SISO solution, you can have an interleaved MIMO solution that will provide significantly better performance.