LTE Network Design and Deployment Strategy

The report entitled Evolution to LTE released in October 2010 by the Global mobile Suppliers Association (GSA) confirms that 156 operators in 64 countries are currently investing in LTE. This figure comprises 113 firm commitments by operators to deploy commercial LTE systems in 46 countries, and a further 43 “pre-commitment” trials or pilots in an additional 18 countries.

The pace of LTE development has quickened, and people have high expectations. However, it is a new technology and the whole industry needs time to optimize networks and develop mature terminals. Compared with 2G/3G, LTE has different architecture, key technologies, network design, and planning.

Continuous Networking vs. Discontinuous Networking

The coverage of some wireless data services—including WiFi—may be discontinuous. However, 2G/3G mobile networks are designed for continuous coverage. LTE mobile broadband technology is now widely seen as the evolution path for 2G/3G mobile networks such as GSM/GPRS/EDGE, WCDMA/HSPA and CDMA/HRPD. Although WCDMA and CDMA networks are fundamentally continuous, HSPA or HRPD can be designed for either continuous or discontinuous coverage.

Most LTE networks are designed according to the continuous principle. Continuous networking improves user experience at cell edges, reduces inter-RAT handover requirements, and facilitates evolution from 2G/3G to LTE. In LTE continuous networking, consideration needs to be given to continuous coverage of RSRP, RSRQ, best service cells, and traffic channels in both the uplink and downlink (PUSCH and PDSCH). LTE discontinuous coverage is usually applied in special scenarios such as discrete hotspots. Discontinuous coverage takes advantage of high-order modulation and coding under good radio conditions to improve cell throughput and user experience at cell centers.

Frequency and Bandwidth

LTE has many spectrum options. Frequency bands available for LTE include 2.6GHz, 1.8GHz, AWS (1.7GHz in the uplink and 2.1GHz in the downlink), 700MHz, DD (800MHz), and 2.1GHz. Such a wide range of frequency bands makes it possible to deploy LTE in different countries. However, different frequency bands bring about challenges for LTE equipment production, networking, and LTE-based international roaming.

LTE also supports flexible carrier bandwidths—from 1.4MHz up to 20MHz (1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, and 20MHz). In most cases, LTE FDD supports a symmetric bandwidth in the uplink and downlink. For scenarios with bandwidth and interference restrictions, asymmetric bandwidths between the uplink and downlink may be supported.

Intra-Frequency Networking vs. Inter-Frequency Networking

The quality of an LTE network is primarily affected by inter-cell intra-frequency interference. Serious interference of this type may be caused by intra-frequency networking, and the simplest way to alleviate it is to use inter-frequency networking. However, inter-frequency networking may decrease spectrum efficiency. So Inter-Cell Interference Coordination (ICIC) is introduced.

ICIC can be implemented in several ways. Depending on the period of resource coordination, ICIC is classified into static ICIC, semi-static ICIC, and dynamic ICIC. It can also be classified into fractional frequency reuse, soft frequency reuse, and full frequency reuse according to the type of resource coordination. No matter which ICIC solution is used, frequency allocation for cell edge users needs to be carefully considered. The cell edge can have a frequency reuse factor of 3 while the cell center has a frequency reuse factor of 1.

Antenna and MIMO

Multiple Input Multiple Output (MIMO) technologies have been introduced into LTE. Antenna selection should take into account not only frequency bands and Half Power Beam Width (HPBW) but also the number and polarization of antenna elements.

Two antennas per sector is the basic configuration for initial LTE networking. For scenarios in which coverage or capacity is sensitive, four antennas per sector can be adopted. ZTE’s LTE base stations support two antennas or four antennas per sector.  

Co-Site vs. New Site

Co-siting 2G, 3G, and LTE base stations means that equipment racks, transport, power supply, and air-conditioning can be shared. ZTE’s Uni-RAN solution integrates 2G, 3G, and LTE into a multimode unified platform and supports co-site design, implementation, operation, and maintenance.

While new sites are built to meet different frequency bands and networking requirements, co-siting is used as much as possible. New sites are complementary. Emerging LTE operators who have no legacy mobile networks may deploy new sites for greenfield networks.

Cell Capacity

LTE cell capacity involves peak throughput and spectral efficiency. Peak throughput is only achieved under ideal conditions, while spectral efficiency is based on real network conditions. Cell peak throughputs for different bandwidths comply with 3GPP specifications. Cell spectral efficiency varies in different radio environments and traffic models and can be measured through network tests or be estimated using system simulation.

Radio Network Planning

Planning for LTE networks is similar to that of 2G/3G networks, though detailed contents and parameters are different. Procedures for LTE network dimensioning and planning are illustrated respectively in Figure 3 and Figure 4.

LTE network dimensioning involves input of frequency and bandwidth, coverage and QoS requirement, target services at cell edge, number of subscribers, traffic profile per subscriber, and indoor penetration. Maximum Allowed Path Loss (MAPL), cell range, number of sites and sectors, and eNodeB configuration are included as output.

Compared with network dimensioning, digital map is additional input necessary for detailed network planning. Additional output for detailed network planning includes uplink and downlink coverage simulation result, uplink and downlink achievable bit rate map, antenna azimuth and tilt, cell ID and neighbor cell parameters.

ZTE has developed its own tools such as ZXPOS CNP-FL, ZXPOS CNT-FL, ZXPOS CNA-FL, and ZXPOS NEXMAX-FL for LTE network design, planning, and optimization. Other LTE network planning tools such as Atoll by Forsk have also been released. Versions of these tools are continually updated.

Network Deployment Strategy

LTE offers mobile data service with QoS guarantee. It can cover densely-populated urban areas, suburban areas, or rural areas. A nationwide LTE network can be deployed in four steps:

■    Cover densely-populated urban areas in capital and metropolitan cities;

■    Cover densely-populated urban areas in ordinary cities;

■    Cover suburban or rural areas in capital and metropolitan cities;

■    Cover other areas.

ZTE has much experience in deploying 2G, 3G, and 4G networks worldwide. As of December 2010, ZTE has concluded 12 LTE commercial contracts and built 65 LTE trials all over the world. With full confidence in the ability to design, plan, and deploy LTE networks, ZTE is ready to join hands with global operators in building cutting-edge LTE networks.