MIMO Testing Challenges

Over at Betavine Witherwire there's an interesting post on the challenges of consistently testing multi-antenna devices which will shortly appear on the market. The author of the post mentions that even without MIMO, 3G network capacity could increase by 50% if all devices are equipped with multiple receive antennas and sophisticated noise cancellation algorithms. Obviously that also translates in higher throughput per device. Consequently, network operators are likely to be very interested in these developments and accurate testing of the performance enhancements is a must.

While many tests with mobile devices today are performed with the air interface simulated over a cable, that won't work that easily anymore for MIMO and receive diversity as the antennas in the device are effectively bypassed. It's the antennas and their location and shape inside the device, however, that will make the big difference. More details in the post linked to above.

So I wonder if it's possible to model the impact of the antennas by simulating their characteristics in addition to the signal path with a simulator box that sits on the cable between a real base station and the mobile device)!?

A formidable challenge and I look forward to what the guys in 3GPP RAN4 come up with.

One thought on “MIMO Testing Challenges”

  1. Hi Martin,

    To answer your question. Modeling the antenna should be a relatively easy task once you have measured it correctly.

    The easiest would be to model the antenna of the base station. They are typically located in a relatively undisturbed environment.

    More complicated is the modeling of the mobile antenna, most of us hold the mobile close to our heads with out hands… and our heads, hands and how we hold the mobile is all different.

    How to model this is not easy and we did discuss this in RAN4 a long time ago.. I remember that Telia made quite a lot of work on that back then. They also had a memorable contribution on replacement antennas with LED that were sold in Japan. We all know that LEDs are non-linear elements and this causes harmonics. One of the harmonics from the GSM band ended up in the air traffic control radar systems….

    Anyway to put in this sort of static model of one or more antennas should be one of the easiest tasks for any fading simulator. They simulate very complex dynamic scenarios, in real time.

    For me the whole area of testing is mostly a receiver testing issue (and maybe antenna pattern)

    I must also say that I tend to disagree with the statement that multiple receive antennas are more worth then multiple transmit antennas. From a system point of view it can not be the case. It is all about the correlation of the two antennas. From a design point of view it is probably easier to make single transmit systems.
    Here the problem most likely lies in the fact that when we do not have a connection to the network, then the network is to blame…. not the mobile. So where is then the motivation for a mobile manufacturer to implement receive diversity? It will have a cost in power consumption and manufacturing.. Are we ready to pay for that?
    (The Japanese 2G system PDC mandated receive diversity also for the mobiles)

    Now all of this has not really covered MIMO testing. For me MIMO testing is when we have multiple transmitters and multiple receivers. The key issue here is how do you model the channel? The number of combinations are just endless.


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