Heterogeneous Network: a fast track in TIM Brasil

Heterogeneous networks (HetNet) are an innovative, interesting and natural path of expanding mobile network capacity and quality in order to foster data services. The adoption of HetNet requires new challenges, like a stronger integration between fixed and mobile networks, a deep renewal of radio planning process and a completely new set of systems and tools in order to manage the increased level of complexity. 

 

1 - As innovation can support the growth

The overtaking of data traffic on voice traffic is a global trend that is putting under stress the mobile operators infrastructure and challenging the traditional voice-centric business model. In the last few years the average monthly data consumption per subscriber is moving from some MB to more than 1 GB.
Furthermore, due to higher smartphone penetration, another side effect is the huge growth of signaling traffic that can severely affect the quality of the service.
In order to fulfill the data capacity needs, the operators can act in 3 ways:

  • Improve macro-layer adding in each site more network resources (carriers and codes, channel elements, power);
  • Densify macro-layer adding more macro-sites;
  • Add a micro-layer, creating a heterogeneous network by introducing, beside the macro-sites, a layer of low power nodes (small and femto cells, WiFi Hot Spots) cooperating strictly with the macro-layer to fulfil the capacity demand.

Having a good macro-layer is undoubtedly fundamental either for coverage or for capacity purposes, but the sites grid densification throughout the traditional macro-sites could have a strong impact on network cost. The use of smallcell is a smart way to improve quality and capacity in a faster and cheaper way. Also WiFi technology plays an important role complementing the HetNet solution catalog: it has been existing for years side by side with the mobile network, but just recently the maturity stage of some functionalities and capabilities, like seamless authentication (EAP SIM) and traffic steering (ANDSF) has helped to make 3GPP and WLAN standards more cooperative and coordinated. Some year ago the connection of a smartphone to a public WiFi hot-spot was very boring for the customer, involving external passwords, credit cards, and so on; nowadays the seamless authentication makes the connection very quick and transparent for the customer. Furthermore WiFi radio technology continues to evolve towards higher throughput (50 Mbs up to 1Gbs), exceeding that of 3G/HSPA+ and in many cases comparable to 4G. Considering that roughly 70% of data consumption is indoor and that WiFi has a cost per transferred byte very low, this technology is for sure a very good complementary way to data provide data connectivity together with standard mobile cellular system.
From the mobile access side, RAN vendors have launched new portfolio of products for 3G/4G equipment, with low power, small dimensions and weight, low energy consumption that can cooperate with the traditional macro-layer in order to expand capacity and cover signal holes.
The introduction of HetNet has to be carrier-out gradually and with strong attention to prevent, control and manage interference issue, that could jeopardize the expected capacity increase or, even worse, degrade the overall quality of service. Higher drop calls rate due increased interference level or due missed hand-over between micro and macro-layer, reduced reliability due to lack of emergency power (batteries back-up) and increased of complexity for operation and maintenance need to be considered very carefully.
TIM Brasil has embraced the HetNet architecture in order to overcome both data capacity and indoor coverage issues, particularly where the lack of spectrum at low frequency bands is affecting the data service level (Rio de Janeiro, São Paulo, Brasilia etc.).

 

2 - TIM Brasil Mobile Broadband Plan

At the end of 2012 TIM Brasil made the strategic choice to develop 4G network (at 2.500 MHz, the frequency licensed up to now for 4G by local authority agency) throughout Ran Sharing agreement with OI. This choice has given to TIM the opportunity to free-up economical resources to be reinvested for raising to state-of-the-art of its 3G mobile broadband network.
This plan, called MBB, has the reference architecture illustrated in the Figure 1.
MBB Plan addresses all the network components: Radio Access network, Metro Backhaul Network, Evolved Packet Core (including Policy and Bandwidth Management), Caching and Peering.

 

Figure 1 - TIM Brasil MBB Framework

 

2.1 - TIM Brasil Mobile Access and Core Network

2.1.1 - Mobile Access Network

For mobile radio access side, TIM Brasil is adopting, inside the MBB framework (Figura 1), all the most advanced technologies and forefront capabilities, like 3G/HSPA-DC (42 Mbps) and LTE, with addressed footprint of more than 100 cities (forecast EoY14), of which 45 served with LTE, and covering roughly 40% of Brazilian urban pop. and more than 50% of TIM total data traffic.
From the LTE perspective, the network roll-out has been carried-out with RAN sharing strategy, reaching a total of 45 covered cities, of divided into TIM and  OI, with a total of around 3.700 nodes deployed (eNodeB, cumulative TIM and OI, May 2014).

 

Figure 2 - Radio Access Evolution

 

In the case of 3G, the most challenging issues are undoubtedly the dimensioning of capacity expansions in terms of network resources (carriers and codes, channel elements, power), according to data traffic growth and providing the right service quality levels (accessibility, throughput and latency) and the improvement of indoor service coverage.

The improvement of macro sites is performed with the increase of carriers, channel elements and power, paying at the same time strong attention to preserve a healthy interference environment, measured by CQI indicator.
The increase of the number of carriers should be in line with the cell throughput assumption at cell level in BH and with the foreseen number of simultaneous active connections (SAC).
The increase of the number of channel elements (CE) should be in line with the HS services accessibility threshold (99,5%), considering that CE utilization greater than 75% at cell level will degrade the accessibility value below the expected target.
The increase of power levels have also been carefully planned, monitoring the power share allocated to HS services at cell level vs. throughput per simultaneous active connection.
Finally, while the resources expansion have as main purpose to provide the required capacity to cope with data traffic demand, at the same time they can generate an increase of interference level of the system, that has to be accurately followed-up monitoring CQI indicator distribution at cell level. A good interference environment is crucial to the data connections be established with higher modulation code schemes (16 QAM and 64 QAM), thus reaching better performances in terms of throughput per active connection.
Even with the expansion of system resources in the existing macro sites, this wouldn’t we enough to provide the required capacity, therefore the operator strategy should move to increase the density of the macro layer, adding new BTS and small cells.  At the same time new macro and micro site would be necessary also for improving indoor service coverage.
The challenge the operator has to cope with the increase of density of the macro layer is changing the operation model of sites construction, in order to harmonize requirements like: construction speed, quantity of sites, location precision, technical feasibility and economic sustainability. This change of operational model has to be performed leveraging on product and process innovation.
TIM Brasil has built along the last year a complete sites solution catalog for site densification and indoor coverage, as shown in figure 5, based on 3 solutions family:

  • Biosite: a new standard of a macro site, with low TCO
  • Small Cells: Micro, Femto, CelFi, WiFi, Repeaters
  • Shared DAS: for shopping centers, stadiums, airports etc.
 

Figure 3 - Site solutions catalog

 

The Biosite (Figure 4 and 5) is a macro site, patented by TIM Brasil, with the objective to be: low TCO (cost to serve), fast to install (time to serve) and with minimum visual impact (zero impact).
The Small Cells are micro sites outdoor, adopted by TIM as pioneer in Brazil, and with the objective to be: low TCO, fast to install, with minimum visual impact (zero impact), and with very limited management impact (zero touch commissioning, replacing model as maintenance routine).
The Femto Cells are micro sites indoor, adopted by TIM as pioneer in Brazil, and with the objective to be: low TCO, fast to install and with very limited management impact (zero touch commissioning, replacing model as maintenance routine). This kind of solution is utilized only for corporate and business customers.
All the sites solutions included in the catalog could be applied and deployed in a variety of combination, giving to TIM Brasil more flexibility in addressing capacity and coverage gaps, increasing at the same time efficiency and effectiveness.  In the Figure 6 an example of joined deployment of different sites solution in Curitiba city.

 

Figure 4 - Biosite: outside and inside views

 

Figure 5 - Examples of Biosite installation in Rio de Janeiro

 

Figure 6 - Increase the site density in Curitiba with innovative solutions

 

2.1.2 - Mobile Core Network

For mobile core network side, TIM Brasil is adopting a strategy based on 3 guidelines:

  1. Unified Packet Core
  2. Common Policy Engine
  3. Enhanced Bandwidth Management

The Packet Core common architecture is conceptually shown in Figure 7, where the same core is used for quadruple access (2G, 3G, LTE and WiFi).  

 

Figure 7 - TIM Unified Packet Core evolution

 

Figure 8 - Effect of transparent caching measured in the TIM Network

 

Figure 9 - Evolution of performance in Natal before and after MBB project (TIM drive test results)

 

PCC (Policy Control and Charging) engine and Bandwidth Management modules represent key elements for applying and enforcing policies and rules (PCC) and bandwidth optimization.  The latter is a suite of appliances for video optimization, Web acceleration, Web Supporting Tool (toolbar for on-line quota control with upselling options, one time redirection, captive portal, parental control, personal firewall, antivirus).
One of the key function, essential to improve customer experience, is Transparent Caching that stores near to EPC the most accessed contents, delivering faster download speed and reduced latency time, as shown in the Figure 10 with reference to Recife and Natal cities. Transparent caching was implemented in all TIM Brasil network in September 2013.
In the Figure 9 and 10 it is shown the effect on performance of the new MBB architecture in the city of Natal (source: drive test made by TIM) and the 39 cities completed in 2013 as seen from Speedtest database (the application used by customers to measure network performance).

 

Figure 10 - Evolution of performance in 39 cities of 2013 MBB project (OOKLA Speedtest DB)

 

3 - The evolution of TIM Brasil Fixed Access Network

The high capacity backhaul is probably the most important issue for mobile operator, because requires huge investments. TIM launched the FTTS (Fiber to the Site) project with a mixed fiber-microwave architecture that optimise capex and roll-out speed (the metropolitan fiber rings collect directly the sites or indirectly via a one-hope microwave). In the first year of deployment, about 3.500 sites were connected with a high capacity backhaul.
With the strong growth in mobile data, the profile of the backhaul network within the broader end-to-end mobile network has grown substantially. As carriers are evolving to HetNet concept, and considering that HetNet means more access elements, in opposite to the traditional approach of macro cells, the backhaul become the main issue to be solved, considering the challenge over cost and capacity.
Facing this challenge, TIM starts in 2010 the project FTTS (Fiber to the Site) with an aggressive deployment of fiber rings in the main cities. This project is divided in three phases:

  • Metropolitan backbone (Metro ring) – fiber ring connecting the Hub sites (sites that concentrate several other sites, connected through microwave radio). This phase allowed the reduction of microwave radio chain increasing the average capacity of city backhaul.
  • FTTS access rings – Increasing the penetration of fiber in the backhaul and preparing the city to MBB project (over 85% of the sites with more than 40 Mbps backhaul capacity).
  • Power Node approach – Deployment of small POP’s, in a street cabinet approach, to support multiservice network, supporting corporate customers connection, VDSL UBB or GPON residential customers connection, WiFi Access Point and Small/Metro Cells connections.

For the Small Cell backhaul, TIM is considering the following options:

  1. Direct Fiber to the FTTS access ring: High bandwith (> 1Gbs), high cost. 
  2. Microwave: High bandwith (up to 1Gbs), complexity (LoS), medium cost.
  3. VDSL access to Power Node: medium bandwith (70-80 Mbs), low cost, fast installation.
  4. Fiber access to Power Node: High bandwith (> 1Gbs), medium cost.

With these solutions, the cost of a good Small Cell backhaul varies from US$ 8.000 for outdoor antennas to US$ 250 for indoor antennas, solving one of the most critical problem in HetNet deployment.

 

Figure 11 - FTTS Network Topology

 

Figure 12 - Power Node based on FTTS access network

 

Figure 13 - Small cell connected to a MSAN (Power Node) for backhaul in Rio de Janeiro

 

4 - Why WiFi can really support mobile network

MNOs are under increasing pressure to deliver enough network capacity to satisfy the boom in data demand from smartphones and other devices. As licensed spectrum becomes more and more scarce, besides radio densification with small cells, WiFi technology appears as a very good option for supporting data traffic in semi-stationary environments.
The raw traffic handling capacity of WiFi is beyond that of a 3G/HSPA cell, and in some cases comparable to LTE. With EAP-SIM authentication the WiFi network becomes an easy and transparent opportunity for the customer.
Another important reason is cost: a carrier-grade WiFi AP costs from a third to a fifth of 3G/LTE small cell base stations and requires a very little maintenance.
Data also shows that the need for more mobile broadband capacity is localized. A few percent of mobile sites in heavy traffic areas are congested while the majority of the MNOs service area may be well served by macro cellular sites and existing spectrum. TIM Brasil, a pioneer of SIM authentication, started the process of rolling out a large-scale carrier-class WiFi network to offload 3G and to reach previously underserved communities in the cities of Rio de Janeiro and Sao Paolo. TIM Brazil’s solution offers automatic EAP-SIM authentication to smartphones and SIM-enabled tablets, working joined with mobile network in order to manage the traffic bundle of the customer.
In order to define the target areas for data offloading, TIM considered traffic density map, as shown in the figure 14 for São Paulo city.                           

 

Figure 14 - As to select a WiFi hotspot location in São Paulo city

 

The results are very interesting, mainly after the activation of automatic authentication via EAP-SIM, reaching a value between 9% up to 40% of traffic offload from the mobile network.
WiFi was also installed in Airports and Stadiums; in April 2014 during the match between Botafogo and Union Espanhola, with 44.000 people watching in the Maracanà, around 28GB of traffic were managed by TIM WiFi network.
WiFi has been acting as a fundamental support to mobile access network also in the Soccer World Cup.
In the match between Italy and England, occurred in Manaus stadium in 14th of june 2014, TIM registered an intensive use of WiFi from their customers watching the event.
In Figure 15 it is shown the traffic measured in the stadium between during the match.
All the customers made 200 GB of data traffic, 30% using WiFi, 4% using 4G and the rest on 3G and 2G network.
70% of traffic was generated by TIM post-paid customers.
In all the World Cup’s matches the WiFi offload was always between 20% and 45%, helping mobile network to provide good performance to the supporters.
We are pretty sure that at the end the term “WiFi offload” will gradually fade away, and WiFi will become soon just another radio access technology inside the operator’s infrastructure.

 

Figure 15 - Data traffic during the World Cup match Italy-England in Amazonas Arena (14/06/2014)

 

5 - Self Organizing Network

The adoption of HetNet RAN architecture has a big impact on network management.
In particular in order to manage the interworking and interoperability between macro e micro layers, it’s fundamental to adopt a solution called SON (Self Organizing Network).  SON is a suite of applications that trough different modules and acting at RNC level will automatically and dynamically configure (self-configuration), optimize (self-optimization) and protect (self-healing) the network.
The main aim of the SON suite is to perform the optimization tasks, routines and activities, usually manually carried-out by engineers, in an automated, continuous, autonomous and closed-loop way, applying pre-defined optimization policies and rules.
During 2013 TIM started a selection process for acquiring a SON suite, performing a comprehensive solution scouting, screening, testing and validation till the final selection of two suites.
The SON solution was extended to the 12 capital cities hosting the World Cup, with a footprint of 53 RNCs and more than 4.000 NodeB, equivalent to 43% of total RNC and 71% of total NodeB of MBB plan perimeter.
The initial target of SON suite introduction was the reduction of operational effort while keeping and progressively improving service quality levels, either optimizing network performance (configuration) or improving network resilience (healing), increasing service continuity and seamless perception.
For a deeper knowledge of SON functionalities and on first results in TIM Brasil it is possible to read the article “Mobile trend: Self-Organizing Networks - Notiziario Tecnico N° 2 - 2014”.

 

Figure 16 - SON concept

 

Conclusioni

The telco operators are facing a fierce competition and a tough challenge due to data traffic growth combined with the need to guarantee high service quality for leveraging service revenues stream. In this scenario an integrated approach to mobile broadband network evolution is highly recommended, covering RAN HetNet (3G/LTE, macro, small and femto cells), Unified Packet Core, Common Policy Engine, Enhanced Bandwidth Management and high capacity Backhaul.

At the same time, the operator should evolve its capabilities in:

  • Precise geo-analytical radio planning for small cells and WiFi Hotspots
  • Redefine sites construction operating model, with new products and revised process
  • Manage seamless mobility and traffic steering among layers
  • Automate Network Optimization with SON in order to manage the increased complexity

The joined  use of new technology and evolved processes will help to face the challenge.

 

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