5 Pillars of 5G

5 key building blocks for 5G, as illustrated besides are elaborated herein.  Each of these blocks is discussed with highlights their role and importance for achieving 5G

Evolution of Existing RATs

5G will hardly be a specific RAT, rather it is likely that it will be a collection of RATs including the evolution of the existing ones complemented with novel revolutionary designs. As such, the first and the most economical solution to address the 1000x capacity crunch is the improvement of the existing RATs in terms of SE, EE and latency, as well as supporting flexible RAN sharing among multiple vendors. Specifically, LTE needs to evolve to support massive/3D MIMO to further exploit the spatial degree of freedom (DOF) through advanced multi‐user beamforming, to further enhance interference cancellation and interference coordination capabilities in a hyperdense small‐cell deployment scenario. WiFi also needs to evolve to better exploit the available unlicensed spectrum. IEEE 802.11ac, the latest evolution of the WiFi technology, can provide broadband wireless pipes with multi‐Gbps data rates. It uses wider bandwidth of up to 160 MHz at the less polluted 5 GHz ISM band, employing up to 256 Quadrature Amplitude Modulation (QAM). It can also support simultaneous transmissions up to four streams using multi‐user MIMO technique.

The incorporated beamforming technique has boosted the coverage by several orders of magnitude, compared to its predecessor (IEEE 802.11n). Finally, major telecom companies such as Qualcomm have recently been working on developing LTE in the unlicensed spectrum as well as integrating 3G/4G/WiFi transceivers into a single multi‐mode base station (BS) unit.

In this regard, it is envisioned that the future UE will be intelligent enough to select the best interface to connect to the RAN based on the QoS requirements of the running application.

Hyperdense Small‐Cell Deployment

Hyperdense small‐cell deployment is another promising solution to meet the 1000x capacity crunch, while bringing additional EE to the system as well. This innovative solution, also referred to as HetNet, can help to significantly enhance the area spectral efficiency (b/s/Hz/m2).

In general, there are two different ways to realise HetNet: 

(i) overlaying a cellular system with small cells of the same technology, that is, with micro‐, pico‐, or femtocells; 

(ii) overlaying with small cells of different technologies in contrast to just the cellular one (e.g. High Speed Packet Access (HSPA), LTE, WiFi, and so on). 

The former is called multi‐tier HetNet, while the latter is referred to as multi‐RAT HetNet.

Qualcomm, a leading company in addressing 1000x capacity challenge through hyperdense small‐cell deployments, has demonstrated that adding small cells can scale the capacity of the network almost in a linear fashion, as illustrated by Figure besides;

That is, the capacity doubles every time we double the number of small cells. However, reducing the cell size increases the inter‐cell interference and the required control signalling. To overcome this drawback, advanced inter‐cell interference management techniques are needed at the system level along with complementary interference cancellation techniques at the UEs. Small‐cell enhancement was the focal point of LTE R‐12, where the New Carrier Type (NCT) (also known as the Lean Carrier) was introduced to assist small cells by the host macro‐cell. This allows more efficient control plane functioning (e.g. for mobility management, synchronisation, resource allocation, etc.) through the macro‐layer while providing a high‐capacity and spectrally efficient data plane through the small cells.

Finally, reducing the cell size can also improve the EE of the network by bringing the network closer to the UEs and hence shrinking the power budget of the wireless links.

Self‐Organising Network

Self‐Organising Network (SON) capability is another key component of 5G. As the population of the small cells increases, SON gains more momentum. Almost 80% of the wireless traffic is generated indoors. To carry this huge traffic, we need hyperdense small‐cell deployments in homes – installed and maintained mainly by the users – out of the control of the operators.

These indoor small cells need to be self‐configurable and installed in a plug and play manner. Furthermore, they need to have SON capability to intelligently adapt themselves to the neighbouring small cells to minimise inter‐cell interference. For example, a small cell can do this by autonomously synchronising with the network and cleverly adjusting its radio coverage.

Machine Type Communication

Apart from people, connecting mobile machines is another fundamental aspect of 5G. Machine type communication (MTC) is an emerging application where either one or both of the end users of the communication session involve machines. MTC imposes two main challenges on the network. First, the number of devices that need to be connected is tremendously large.

Ericsson (one of the leading companies in exploring 5G) foresees that 50 billion devices need to be connected in the future networked society; the company envisages ‘anything that can benefit from being connected will be connected’. The other challenge imposed by MTC is the accelerating demand for real‐time and remote control of mobile devices (such as vehicles) through the network. This requires an extremely low latency of less than a millisecond, so called “tactile Internet” , dictating 20x latency improvement from 4G to 5G.

Redesigning Backhaul Links

Redesigning the backhaul links is the next critical issue of 5G. In parallel to improving the RAN, backhaul links also need to be reengineered to carry the tremendous amount of user traffic generated in the cells. Otherwise, the backhaul links will soon become bottlenecks, threatening the proper operation of the whole system. The problem gains more momentum as the population of small cells increases. Different communication mediums can be considered, including optical fibre, microwave and mmWave. In particular, mmWave point‐to‐point links exploiting array antennas with very sharp beams can be considered for reliable self‐backhauling without interfering with other cells or with the access links.