Cell-free Massive MIMO and Radio Stripes

I have recorded a popular science video that explains how a cell-free network architecture can provide major performance improvements over 5G cellular networks, and why radio stripes is a promising way to implement it:

If you want more technical details, I recommend our recent survey paper “Ubiquitous Cell-Free Massive MIMO Communications“. One of the authors, Dr. Hien Quoc Ngo at Queen’s University Belfast, has created a blog about Cell-free Massive MIMO. In particular, it contains a list of papers on the topic and links to the programming code of some of them.

9 thoughts on “Cell-free Massive MIMO and Radio Stripes”

  1. Hi Emil,

    Thanks for sharing.
    Any comments on where the PAs sit for these antennas? What type of processing can be done in these black boxes?


    1. The PAs are placed next to each antenna. I’m imagining an output power per antenna of around 0.1 W, similar to a mobile phone.

      As much processing as possible should be done in the black boxes, so that the complexity of the tasks that must be done centrally becomes independent of the number of antennas – this gives a kind of scalability for systems with massive number of distributed antennas. In the uplink, it could, for example, be MR or LMMSE processing using the locally available CSI. The softly decoded data signals are then accumulated along the stripe so that the central processing unit only gets an accumulated version that is used for final hard decoding.

    1. This will of course be taken into account in the design. Suppose the stripe is using a design similar to an Ethernet cable with a power over Ethernet protocol. Then we could use at least 100 W per stripe, which would be enough for 100 antennas (0.1 W transmit power per antenna and the rest for antenna processing).

      1. Prof. Emil

        Thank you so much for the reply.
        I noticed that the antennna should be located along some straight line, as shown in your paper, so is it because the blended antenna’s performance will be degraded and disabled, including gain and directivity diagram?

        1. The paper only contains illustrations and are not conclusive when it comes to deployment strategies. One of the good properties with radio stripes is that they can be bended and deployed in many different ways. If the antennas are roughly omni-directional, there is no need to think about directivity when deploying the stripe. If the antenna elements have clear directivity, one probably needs to have antennas that point in different directions or small arrays with beamforming capability to ensure coverage in all directions.

  2. Hi Emil,

    I’m interested in the 5g vs cell free massive MIMO SINR diagram at 20:00 mins. In 5g SINR color diagram you have given different cones with less yellow color (good SINR part). Each cone represent a beam (I mean ssb indicated beam) in 5g? (Question 1). If so good SINR part is less, so you mean even though we do hybrid beamforming for a UE, within the beam there will be cell center, middle and edge kind of SINR variations? (Question 2). My basic question is in 5g the hybrid beamforming done for a cell center vs cell middle vs cell edge UE varies? I mean SINR seen by the UE will varies? Please let me know.

    1. Question 1: No, each cone in the cellular case represents a cell and the data rate that a user can get at different places in the cell.

      Question 2: Since the base stations are well separated in a cellular network, there are large variations in signal strength between different parts of the cell (center, middle, edge). It can very by 1 million times! Beamforming improves the signal quality for all UEs but it does not reduce the signal strength variations.

      PS. I’m not sure why you are asking about _hybrid_ beamforming. It is digital beamforming that the system should preferably use.

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