What is Multiple Input Multiple Output?

17 November 2011 |


Multiple Input Multiple Output (MIMO) technology leverages multiple transmit and receive antennas at both the radio base station and the device, in order to increase data rates and capacity on a network.

 

In essence, the technology helps to increase efficiency of existing spectrum, providing additional capacity without acquiring more bandwidth. According to a study from GSMA, it is now an established feature of both HSPA and LTE technology.

How does MIMO help increase capacity in a network?

By using the antennas at both transmitter and receiver, MIMO can create multiple uncorrelated radio links, known as ‘streams’, between both devices. By creating more streams between transmitter and receiver, more information is able to be transferred at a higher data rate.

According to GSMA, MIMO is most effective at creating uncorrelated streams when a device has good coverage, but no line of sight (LoS) to the base station. This, it says, is generally the case in urban environments, which is typically where higher capacity is required.

MIMO is said to provide at least a 20% increase in the overall capacity of a network. In particular, it can successfully deliver higher peak data rates in each iteration of +HSPA – from 28Mbps in release 7 to 168Mbps in release 10, and even beyond.

How and where can operators deploy MIMO?

According to GSMA, one of the main challenges in deploying MIMO is enabling it to coexist in legacy HSPA terminals, namely pre-release 7. This challenge dates back to 2007 when early HSPA terminals with advanced receivers were first deployed.

An HSPA terminal can be categorised by the performance level of its receivers, but the specified performance requirements are based on a number of assumptions, which can cause the deployment of MIMO to become inherently complex. Some infrastructure vendors, however, have developed a mix of standards-based (3GPP) and proprietary network-based algorithms, which can be implemented in the base station and do not pose any requirements or dependencies to standard end-user devices.

Implementing MIMO is also becoming a more affordable option for operators than earlier implementations may have first suggested. Firstly most telecoms operators have the relevant antenna configurations and RF feeders to support MIMO, while handheld devices and tablets are increasingly using dual-antenna systems.

How successful has MIMO proved in increasing capacity in networks?

GSMA indicates that since 2009, several operators have conducted lab and field trials of MIMO technology, before commercially deploying the technology in several networks. Vodafone Group, France Telecom and M1 Singapore are just some of the operators that have conducted MIMO trials.

Standard 2x2 MIMO HSPA terminals are already in commercial use, while commercial trials and commercial applications worldwide are said to have proved that MIMO offers significant performance and capacity gains, without compromising legacy HSDPA services.

The latest baseline performance tests conducted in several live networks run by top-tier operators are said to indicate that more than 25% average cell throughput gain is achieved by an HSPA MIMO solution compared to the single transmission mode. This was also achieved without affecting the performance of the non-MIMO legacy HSDPA users operating in the same cell.

How will operators utilise MIMO within networks in the future?

GSMA says MIMO can fit with a wide range of network HSPA deployment strategies and is necessary for all the next 3GPP evolution paths, from HSPA (release 9 onwards) to LTE.

For operators looking to remain competitive in mobile broadband, deploying MIMO could prove a cost effective step in improving performance and capacity on their networks without making significant investment.