5G Mobile Communication Technology

There are 6 challenges not adequately addressed by 4G technology: higher capacity, higher data rate, lower end-to-end latency, massive device connectivity, reduced capital and operations cost, and consistent quality of experience (QoE).

Evolution of Wireless Technology (Gupta and Jha, 2015)

Generation	Access Technology	Data Rate	Frequency Band	Bandwidth	FEC	Switching	Applications
3G	WCDMA / UMTS	384 kbps	800 /850 / 900 / 1800 / 1900 / 210 MHz	5 Mhz	Turbo Codes	Circuit/Packet	Voice, data, video calling
3G	CDMA2000	384 kbps	800 /850 / 900 / 1800 / 1900 / 210 MHz	1.25 MHz	Turbo Codes	Circuit/Packet	Voice, data, video calling
3.5G	HSUPA/HSDPA	5-30 Mbps		5 MHz		Packet
3.5G	EVDO	5-30 Mbps		1.25MHz		Packet
3.75G	LTE (OFDMA / SC-FDMA)	100-200 Mbps	1.8 GHz, 2.6 GHz	1.4 MHz - 20 MHz	Concatenated codes	Packet	Online gaming, HDTV
3.75G	WiMax (SOFDMA), Fixed WiMAX	100-200 Mbps	3.5 GHz and 5.8 GHz initially	3.5 MHz and 7 MHz in 3.5 GHz band; 10 MHz in 5.8 GHz band
4G	LTE-A (OFDMA / SC-FDMA)	DL 3 Gbps, UL 1.5 Gbps	1.8 GHz, 2.6 GHz	1.4 Mhz - 20 MHz	Turbo codes	Packet	Online gaming, HDTV
4G	WiMax (SOFDMA), Mobile WiMAX	100-200 MBps	2.3 GHz, 2.5 GHz, 3.5 GHz initially	3.5 MHz, 5 MHz, 7 MHz, 10 MHz and 8.75 MHz initially
5G	BDMA, FBMC multiple access	10-50 Gbps expected	1.8, 2.6 GHz and expected 30-300 GHz	60 GHz	LDPC	Packet	Ultra high def. video, virtual reality apps

Beyond 2020, mobile networks need to support a 1000-fold increase in traffic relative to that of 2010, and a 10- to 100-fold increase in data rates even at high mobility and in crowded areas. This means higher capacity is required in the radio access network (RAN), backbone, backhaul and fronthaul. A combination of more spectrum, higher spectrum efficiency, network densification and offloading are necessary to address the challenges in RAN.

Network densification involves dense deployment of many small cells. High carrier frequencies are well suited for small cells. The high attenuation becomes an enabler to provide effective separation and mitigate interference between densely deployed small cells. An efficient improvement of capacity at critical locations is achieved by independently addressing coverage and capacity. This is done through an architecture where contol (C) and user data (U) planes are split among different cells. The benefit of this is that U-plane resources can be scaled independent of C-plane resources. This allows more U-plane capacity to be provided in critical areas without the need to also provide co-located C-plane functionalities. In this architecture, macrocephaly provide coverage (C+U) and small cells provide localized capacity (U).

One way to reduce the cost of 5G deployment is by minimising the number of functionalities at the base station. This can be achieved by implementing layer 1 / layer 2 functionalities in the base station and moving higher-layer functionalities to the network cloud that serves many base stations.

Quality of Experience (QoE) is a subjective user perception of how well an application or service is working. QoE is very application- and user-specific and cannot be generalised. For example, the QoE of a video application is different from that of a social media application. Low QoE leads to user dissatisfaction whereas too high QoE unnecessarily drains resources on both the user and operator. A challenge for 5G is to support applications and services with an optimal and consistent level of QoE everywhere, anytime. Despite the diversity of QoE requirements, providing low latency and high bandwidth generally improves QoE.

Traffic optimization techniques can be used to meet increasing QoE expectations. Installing caches and computing resources at the edge of the network allows an operator to place content and services close to the end user, thus, enabling very low latency and high QoE for delay-critical interactive services, like video editing.

Researchers found that most wireless users are indoor 80% of their time. For indoor users to communicate with the outdoor base station, the signals have to travel through walls, causing very high penetration loss, which corresponds to reduced spectral efficiency, data rate and energy efficiency. 5G overcomes this problem with a cellular network architecture design that is able to distinguish between indoor and outdoor set up.

This design involves the use of MIMO technology, where geographically dispersed array of antennas are deployed. Current MIMO systems use either two or four antennas. A Massive MIMO system is an evolving technology that takes advantage of large array antenna elements in terms of huge capacity gains. Its main objective is to extract all the benefits of MIMO on a larger scale. Massive MIMO is capable of improving the radiated energy efficiency by 100 times while increasing the capacity in the order of ten or more.

Constructing a Massive MIMO network involves two steps:

1. The outdoor base stations are fitted with large antenna arrays and some are dispersed around the cell and linked to the base station through optical fiber cables, using MIMO technology. The outdoor mobile users are fitted with a certain number of antenna units from which a large virtual antenna arrays can be constructed. Together with antenna arrays of the base station, these form a massive virtual MIMO links.
2. A building is installed with large antenna arrays from the outside to communicate with outdoor base stations (must be in line of sight). The wireless access points inside the building are connected with the large antenna arrays through cable for communicating with indoor users. This significantly improves energy efficiency, cell average throughput, data rate and spectral efficiency but at the expense of increased infrastructure cost.

With this architecture, indoor users connect with indoor wireless access points while large antenna arrays remained installed outside the buildings. Indoor communications make use of technologies like Wi-Fi, small cell, ultra wideband etc.

5G Cellular Network Architecture (Gupta and Jha, 2015)

An integral part of 5G technology is the mobile small cell concept, which consists of mobile relay and small cells. It caters to high mobility users (e.g., users in cars and trains). A mobile small cell covers an area within a vehicle so that users can communicate while massive MIMO unit outside vehicles communicate with the outdoor base station.

The 5G network architecture consists of two logical layers, namely radio network and network cloud. The network function virtualization (NFV) cloud consists of a user plane entity (UPE) and a control plane entity (CPE), which perform higher layer functionalities related to the user control planes, respectively. Network functionality as a service (XaaS) is provided as needed (e.g., resource pooling). XaaS is the connection between the radio network and network cloud.

The 5G protocol stack is shown below.

The physical and MAC layers define the wireless technology and are based on Open Wireless Architecture (OWA).

The network layer is IP. Mobile IP is used to cater for user mobility. A mobile terminal acts as a foreign agent (FA) and maintains a care-of address (CoA) for the current wireless network. A mobile node can attach to more than one mobile or wireless networks at the same time and it maintains different IP addresses for each radio interface. The fixed IP address is implemented in the mobile device by the device manufacturer.

The 5G mobile device maintains virtual multi wireless network environment. Therefore, the network layer is separated into two sub layers, namely the lower network layer (for each interface) and upper network layer (for the mobile terminal). The middleware between the upper and lower network layers maintains address translation from the upper network address (IPv6) to different lower network IP address (IPv4 or IPv6) and vice versa.

TCP assumes lost segments are due to network congestion, but in a wireless network, losses might be due to higher bit error rate. Therefore, TCP has to be modified and adapted for wireless networks so that it retransmits the lost segments over the wireless link only. 5G allows mobile terminals to download and install a suitable transport layer from the base stations — this is called the Open Transport Protocols (OTP).

At the application layer, the aim of mobile terminals is to provide intelligent QoS management over various networks. With previous technologies, users manually select the wireless interface to access an Internet service without being able to use QoS history to select the best wireless connection for the service. 5G makes it possible for service quality testing and storage of measurement information to be stored on the mobile terminal. QoS parameters (e.g., delay, jitter, reliability) are stored in a database on the mobile terminal and are used to provide the best wireless connection for a required QoS and personal cost constraints.

The objective of the Mobile and Wireless Communications Enablers for Twenty-twenty Information Society (METIS) is to develop the overall 5G radio access network design and to provide the technical enablers needed for an efficient integration and use of the various 5G technologies and components currently developed. METIS envisions the following scenarios to help address the challenges and provide the right enabling technology components for 5G:

1. Amazingly fast. This targets the end-user experience of instantaneous connectivity, where all apps have a flash behaviour — one click and the response is perceived as instantaneous. An example of this scenario is the virtual reality office, where gigabytes of data are exchanged to enable interactive work among people in remote locations in such a way that it feels like everyone is in the same physical location. To support this scenario, data rates of at least 1 Gbps and 5Gbps in 95% and 20% of office locations, respectively, are required, and during 90% of the busy period.
2. Great Service in a crowd. This caters to end-user needs for connectivity in very crowded places, such as stadiums, shopping malls and public events. Currently, users in large crowds often suffer from service denials due to network overload. Users should be provided with at least reasonably good service in this condition. Addressing this shortcoming is a significant challenge. To cater to this scenario, the traffic volume per subscriber of 9 Gbytes/hour during busy period and a user data rate between 0.3 and 20 Mbps are required.
3. Best experience follows you. This aims to provide the same good user experience for end users on the move as for end users at home or in the office. Users on the move should have the impression that the network infrastructure follows them. High data rate coverage is offered at every location of the service area, including in remote rural areas. The technical challenge is to provide robust and reliable connectivity solutions and the ability to efficiently manage mobility with lower batter consumption of end-user terminals and at low cost.
4. Super real-time and reliable connections. Today's communication systems are designed for human users. Future systems will include M2M communications with real-time constraints, e.g., traffic safety and critical control for industrial applications. These applications will require much higher reliability and lower latency than today's systems. The expected payload sizes are about 1500 bytes and messages should be transferred with 99.999% reliability with a delay around 8 ms at the application layer. The key challenge is reducing end-to-end latency while providing high accessibility and reliability of the communication services.
5. Ubiquitous things communicating. This addresses the communication needs of ubiquitous machine-type devices, ranging from low-complexity devices (e.g., sensors) to advanced devices (e.g., medical devices). The requirements vary widely in terms of payload size, transmission frequency, cost, energy consumption, latency etc, which cannot be met by today's cellular network. The requirements are to provide connectivity for 300,000 devices within a cell, enable long battery life (order of a decade) and low cost device implementation. The challenge is to integrate the communication of ubiquitous things in mobile networks and to manage the overhead created by the number of devices. The expected experienced data rate is 300 Mbps downlink and 60 Mbps uplink in 95% of locations and time, and 10 Mbps between devices.

METIS uses horizontal topics (HTs), which integrates a subset of the technology components to provide the most promising solution, to build the overall system concept. the HTs are:

• D2D communication refers to direct communications between devices without user-plane traffic going through any network infrastructure. Usually, the network controls the radio resource usage of the direct links to minimise interference. The goals are to increase coverage, offload backhaul, provide fallback connectivity and increase spectrum utilisation and capacity per area.
• Massive machine communication (MMC) provides up- and down-scalable connectivity solutions for tens of billions of network devices. The characteristics and requirements for machine-centric communications vary widely from human-centric communications.
• Moving networks (MNs) enhance and extend coverage for potentially large populations that are part of jointly moving communication devices. A MN node or a group of MN nodes can form a moving network that communicates with its environment, i.e., other fixed/mobile nodes inside/outside the moving entity.
• Ultra dense networks (UDNs) address the high traffic demands via infrastructure densification. The aims are to increase capacity, increase energy efficiency of radio links and enable better spectrum exploitation. UDNs are orders of magnitude denser that today's network.
• Ultra reliable communication (URC) enables high degrees of availability. The aim is to provide scalable and cost-effective solutions for networks supporting services with extreme availability and reliability requirements.
• Architecture (Arch) provides a consistent architectural framework integrating differnet centralised and decentralised approaches.

Source

• A. Gupta and R.K. Jha, "A Survey of 5G Network: Architecture and Emerging Technologies", IEEE Access, Volume 3, 2015
• A. Osseiran et al, "Scenarios for 5G Mobile and Wireless Communications: The Vision of the METIS Project", IEEE Communications magazine, Vol. 52, Issue 5, 2014