Protocol Framework for 5G mm Wave Backhaul Network

- SWARNASHRUTI JUPUDI

Introduction

We need a promising technology to significantly improve the network capacity and satisfy the overwhelming traffic demand from increased mobile devices, cloud computing, video streaming, IOT, etc.

We’ll need something that can provide a 1000-fold system capacity, 100-fold energy efficiency, and 10-fold lower latency as compared to the current implemented technologies.

Hence, the proposal for a 5G mm Wave backhaul network.

What’s a Wireless Backhaul?

Wireless backhaul is the wireless communication and network infrastructure responsible for transporting data from end users or nodes to the central network or infrastructure and vice versa.

It is the intermediate wireless communication infrastructure that connects smaller networks with the backbone or the primary network.

Fig 1: Typical Backhaul Deployment

Here, the data traffic transmits from UE2 to Micro1, and to Micro2, and then to Micro4, and finally comes into core network.

What’s a Wireless Backhaul?

Data is connected/transported to a Tier 1 Internet service provider or a central telecom exchange by a wireless backhaul infrastructure. It connects BS to core network

The optimum choice for wireless backhaul technology involves considerations such as network capacity, expected data speed, relative cost, electromagnetic interference and the availability of radio frequency spectrum space

Fig 2: Typical backhaul deployment

MM WAVE BACKHAUL NETWORK

- Overview

Wired backhaul is infeasible owing to the high implementation costs Current frequency bands won’t match the 5G traffic demand mm Wave has a bandwidth of 30 -300 GHz, thus occupying a wider spectral

range Advantages of mm Wave Disadvantages of mm Wave

• Larger Bandwidth• Narrow Beam Width• Highly Directional Waves• Reduced Interference• High Security• Spectrum Reuse

• Can’t penetrate through solid obstacles

• Works mostly in LOS• High Path Loss • High power required for transmission• High atmospheric attenuation

SYSTEM ARCHITECTURE FOR BACKHAULING

CentricSmall cell Base Stations (SBSs) access core network through center macrocell BS that connects gateway through fiber links DistributedAll backhaul data are relayed to a single specific SBS instead of the macrocell BS. Data is transmitted between established wired or wireless links amongst adjacent SBS, connected to the designated SBS that connects to core network through fiber links.

System overview for 5G mm-wave backhauling

Challenges and Design Goals

Overcoming Path LossBeamforming techniquesHighly steerable beams are generated to form directional links

Dynamic Link EstablishmentAdding flexibility to backhaul data transmissionEfficient routing process optimizing the data flow

Directional Beamforming

Challenges and Design Goals

Efficient Spatial Reuse• TDMA, Scheduling TDMA• Full duplexing, hybrid beamforming

and multicast beamforming• Dense small-cell scenarios using

heterogeneous infrastructure

Hybrid Beamforming and Full Duplexing

System framework for 5G mm-wave backhauling

In the frame header, routing and scheduling schemes are performed for the backhaul required flows accumulated at the S-SBS in the previous frame.STDMA scheduling in the MAC layer is followed to assign specific time slots to different hops of every flow, where multiple transmissions can be allocated in the overlapping time periods to fully exploit spatial reuse gain.Hybrid beam forming and full duplex transmission, are utilized to satisfy the transmission requirements in the 5G mm-wave backhaul system

MAC Protocol framework for 5G mm wave backhaul

The use of highly directional beam forming raises a number of new challenges in the network design. We focus only on the medium access

The design of MAC protocol for 5G mm wave backhaul network needs to take into account the following requirements and challenges: How to design the suitable MAC framework and its frame structure. How to efficiently design the beam forming training to guarantee

direction alignment between two nodes including UEs, regular base stations, and sink base stations.

How to design the signaling framework to make sure that all the control information can be transmitted.

How to provide an open MAC frame to support diverse allocation scheme among uplink, downlink and backhaul to maximize resource efficiency.

MAC PROTOCOL FRAMEWORK -Overview

Each wireless frame occupying Tm is divided into 10 sub-frames. Each sub-frame is divided into 8 slots, thus each time slot

occupies Ts. In a sub-frame unit,

The first time slot is set to be downlink time slot for beam forming training, resource allocation indicating and other system control signaling. The last time slot is set as uplink time slot for the UEs to

transmit feedback information such as the buffer state information, QoS types, Channel Quality Indicator (CQI), etc The remaining six time slots can be flexibly and dynamically

allocated to downlink, uplink and backhaul transmission according to the real-time traffic demand. We use TDD approach to design the MAC Protocol for dynamic

resource allocation. FDD uses fixed bandwidth

Multi-dimensional resource allocation for uplink, downlink and backhaul transmission In the first downlink time slot of each sub-frame,

the base station allocates spectrum resources to uplink, downlink and backhaul transmission according to the downlink traffic demand

The two-step resource allocation procedure. TDD configuration: In each sub-frame, the eight

slots can be flexibly divided to transmit on accordance to the demands.

Multi- dimensional spectrum resources: Assuming fixed beam directions, we allocate time domain and frequency domain resources to different UEs.

Uplink/Downlink/Backhaul TDD Configurations

Signaling of MAC frame structure

MAC PROTOCOL FRAMEWORK - Beam Forming Training

Beam forming training is deployed in the first time slot of sub-frame after the downlink signaling.

The base station transmits a beam training sequentially on each beam, its power recorded by each user with a fixed antenna.

Similarly, the other antenna is training during next sub-frame. Therefore, each mobile user can select the optimal beam after two sub- frames periods. In the last time slot, the UEs report their beam forming training information along with the uplink signaling.

Beam Forming Training

CONCLUSION AND FUTURE WORK

To meet the ultra-large traffic and the super-massive connection requirement of 5G wireless networks, we focus on the MAC layer technologies and especially proposed a MAC protocol framework for 5G mmWave backhaul network.

The future work includes the mmWave backhaul routing and efficient resource allocation algorithm.

REFERENCES

Yusheng Liang, Bo Li, Mao Yang*, Xiaoya Zuo, Zhongjiang Yan, Qingtian Xue “MAC Protocol Framework for 5G mmWave Backhaul Network”, IEEE 2016

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4934318/ https://www.wirelessweek.com/article/2016/03/why-wireless-backhaul-

holds-key-5g http://www.rcrwireless.com/20160313/carriers/sprint-wireless-backhaul-tag4 Small Cell Millimeter Wave Mesh Backhaul White Paper - Feb 2013 Kan Zheng, Long Zhao, Jie Mei, Mischa Dohler, Wei Xiang, and Yuexing

Peng” 10 Gb/s HetSNets with Millimeter-Wave Communications: Access and Networking – Challenges and Protocols “, IEEE 2015