Heterogeneous Networks For 5G

Heterogeneous Network (HetNet) - 

Enabling Seamless Movement between Wi-Fi, DAS, Small Cells and Mobile Networks

- Small Cells

The concurrent operation of macro-, micro-, pico- and femto-cells is termed as heterogeneous Networks (HetNets). Heterogeneous network is used in wireless networks using different access technologies. HetNet indicates the use of multiple types of access nodes in a wireless network. A Wide Area Network can use some combination of macrocells, microcells, picocells, and femtocells in order to offer wireless coverage in an environment with a wide variety of wireless coverage zones, ranging from an open outdoor environment to office buildings, homes, and underground areas. 

Mobile experts define a HetNet as a network with complex interoperation between macrocell, small cell, and in some cases Wi-Fi network elements used together to provide a mosaic of coverage, with handoff capability between network elements.

Next generation 5G wireless networks will run applications requiring high demand for data rates. One of the solution to solve the data rate requirement is to allow densification of network by deploying small cells. Such densification results in higher spectral efficiency and can also reduce the power consumption of mobile due to its communication with nearby pico-cell. This solution significantly improves network coverage. However, this solution requires innovation in hardware miniaturization and cost reduction in the design of small cell base-station. Such small cell base-stations can be deployed as low powered femtocells typically used in enterprise/residential deployments or higher powered pico cells for improving outdoor coverage of macro cells. 

- New Carrier Types

There has been recent push from both the academia and industry (3GPP) to enhance the operation of small cells by splitting control and data plane. The main idea here is that control plane provides connectivity and mobility, whereas user plane provides the data transport. This results in the fact that user equipment (UE) is connected to multiple base-stations, namely, macro and small cell. Such a definition of new carrier type in 3GPP (Rel 8-10), results in improved spectral efficiency as data transport is handled by small cell. There is also significant gain in energy efficiency of network infrastructure as small cells can be switched off in case of lightly loaded scenarios.

- LTE and Wi-Fi Coexistence

5G wireless network design will see lot of convergence happening between LTE and Wi-Fi networks. There has already been push from the industry to operate LTE in unlicensed bands. Such an approach will allow easier offloading of traffic from LTE to unlicensed bands. However, such offloading poses quality of service (QoS) issues for end users due to unmanaged and over-crowded nature of Today’s Wi-Fi deployments. 

LTE and Wi-Fi coexistence technologies share a common premise - using an LTE air interface in the 5-GHz unlicensed band. Cellular service providers have exclusive rights to operate networks in spectrum they purchased. Wi-Fi is deployed in the 2.4- or 5-GHz (U-NII-1 and U-NII-3) unlicensed bands available to anyone and everyone as long as users follow the laws that govern the spectrum. While sharing the spectrum is an opportunity, it also presents many challenges. Thus, multiple proposals are being considered for standardization. 

- Device To Device Communications

Direct Device-to-Device (D2D) communication, which refers to direct communication between devices (i.e. users) without data traffic going through any infrastructure node, has been widely foreseen to be an important cornerstone to improve system performance and support new services beyond 2020 in the 5G system. 

D2D communications is an approach where terminals close by discover themselves automatically and interact with each other without the base-station. Such an approach is highly efficient from power control standpoint and can also reduce interference in unlicensed frequency bands. In general, the benefits resulting from D2D operation include, among others, highly increased spectral efficiency, improved typical user data rate and capacity per area, extended coverage, reduced latency, and enhanced cost and power efficiency. 

These benefits are resulting from the proximity of the users employing D2D communication (proximity gain), an increased spatial reuse of time and frequency resources (reuse gain) and from using a single link in the D2D mode rather than using both an uplink and a downlink resource when communicating via the base station in the cellular mode (hop gain).

Conventional cellular architecture does not allow for user equipments (UEs) to communicate directly. However, when the devices are close by, this can be very inefficient and D2D can be especially useful in machine-type-communication (MTC) scenarios where there are large number of devices operating closely with each other. D2D when combined with the fact that it can be coordinated with base-stations can bring significant advantages to the existing cellular architecture in terms of both energy efficiency and spectral efficiency. D2D is currently an active topic of discussion within 3GPP.

- Network Selection in Wireless Heterogeneous Network

Heterogeneous network is a network connecting mobile station with different kinds of wireless network. It will provide an efficient network connection for mobile users. When considering various wireless access technologies, it's difficult to search out reliable criteria to pick out the most effective offered wireless heterogeneous network. 

One of the main challenges in wireless heterogeneous networks which is the issue of selecting the best networks. Although the QoS parameters such as bandwidth, latency, throughput, interference...etc. are major factors that influence the selection criteria, but the user preference factors are also significant, as they are representing the user satisfaction and experience. The combination of the QoS parameters and the user preference factors can comprehensively increase the evaluation criteria for the user to select the best network that serves his/her needs. 

[More to come ...]