In this series:

This blog post discusses massive MIMO applications beyond the conventional Long Term Evolution (LTE) fourth generation (4G) evolution path. Increasing network capacity by a factor of thousand over the next ten years can be achieved by massive network densification through the use of small cells.

This vision is shared by Qualcomm in their “1000x mobile data challenge”. Their proposed solution consists of the following improvements


  1. Increasing the efficiency of existing infrastructure
  2. Employing more resources in the form of small cells and spectrum, as well as
  3. AdoptingFinding new ways to acquire, deploy, operate, and manage these resources

To take heterogeneous networks (hetnets), which include small cells, to the next level, Qualcomm suggests that network densification should begin with existing spectrum and the use of techniques like “range expansion” optimizations – all of which is possible today with HSPA+ and in the future with LTE Advanced. Deploying low-cost and ad-hoc small cells while leveraging existing premises and backhauls will require that the new small cells be plug-and-play and have self-organizing (SON) capabilities. They also must be deployable both indoors and outdoors. They can even be installed by end-users, but are always managed by the operators and coordinate with the macro base stations (BSs) and other small cells [1].

On the other hand, the vision from Alcatel-Lucent centers around the smart use of excess antennas [2]. In this vision, time-division duplexing (TDD) is to be the key enabler for the new hetnet architecture. They propose an architecture based on a co-channel deployment of macro BSs with very large antenna arrays and a secondary tier of small cells (SCs) with a few antennas. Both tiers employ a synchronized TDD protocol. The resulting channel reciprocity enables not only the estimation of large-dimensional channels at the BSs but also an implicit coordination between tiers without the need to exchange user data or channel state information (CSI) over the backhaul.

In particular, for the uplink (UL), the BSs and SCs can locally estimate the dominant interference sub-space. This knowledge can be leveraged for downlink (DL) precoding to reduce intra- and inter-tier interference (making smart use of excess antennas). The authors in [2] demonstrate a precoding technique based on received interference covariance estimation that can achieve very attractive rates. For example, with 100 antennas at each BS and four antennas at each SC, the authors observed an aggregate area throughput of 7.63 Gb/s/km2 (DL) and 8.93 Gb/s/km2 (UL) on a 20-MHz band shared by about 100 mobile devices.

On the educational side of things, Nutaq’s research program includes universities like Laval, Sherbrooke, and INRS Telecom, who are conducting research on massive MIMO and cognitive radio design and prototyping using the PicoSDR software-defined radio development platform [3]. Nutaq also supports a small cell program for both 2G and 4G markets [4]. Nutaq recently demonstrated a 2×2 LTE base station prototype consisting of a PicoSDR communicating with LTE USB dongles from a third-party trusted provider [4]. This hardware and software forms a baseline for next-generation network design and prototyping and goes hand-in-hand with the visions from Qualcomm and Alcatel-Lucent.


[1] Qualcomm, The 1000x Data Challenge,

[2]  J. Hoydis, K. Hosseini, S. ten Brink, and M. Debbah, Making Smart Use of Excess Antennas: Massive MIMO, Small Cells, and TDD, Bell Labs Technical Journal, vol. 18, no. 2, pp. 5-21, Sep. 2013.

[3] Nutaq inc, “PicoSDR with QAM64 MIMO OFDM reference design,”

[4]  Nutaq inc, “GSM/EDGE SuperFemto,”