The emergence of next-generation network (NGN) technologies and high bandwidth devices has led to an exponential increase in data traffic and this trend calls for an urgent transformation of operators’ backhaul networks. As telecom companies extend their 3G network roll-out to Tier 2 and Tier 3 cities and broadband wireless access (BWA) spectrum winners start deploying long term evolution-time division duplex (LTE-TDD) access infrastructure, there will be an increasing demand for backhaul connections and capacity. Bandwidth-hungry applications such as mobile TV and multimedia content streaming would require a sharp increase in capacity for cell sites and operators will need to optimise their existing transport networks.

Currently, Indian telecom companies mostly use legacy time division multiplexing (TDM)-based microwave backhaul systems (suited for voice services) between their base stations and aggregation points. Microwave backhaul is now used at 60-80 per cent of mobile cell sites in India. However, this architecture may not be the best solution for catering to the backhaul requirements of a data-oriented 3G/BWA market. In this situation, optic fibre links are preferred over microwave solutions. But limited fibre connectivity in India and the high cost of fibre network deployment (especially in dense urban or remote rural areas) pose major challenges in scaling up of existing networks to meet the requirements of NGN technologies. As a result, most analysts are of the view that microwave backhaul dependency in the country will increase in the short to medium term.

Like their global counterparts, operators in India are looking for an IP transition to support NGN mobile technologies and are transforming their networks. Femtocells and high speed packet access points are also being considered to reduce backhaul congestion in markets, where xDSL is widely deployed. The existing microwave backhaul infrastructure needs significant upgradation to cater to data traffic growth; and manage the increasing subscriber base, variations in the type of traffic transported across the network and the demand for quality of service.

Operator initiatives

There is a general consensus that the 5 MHz of licensed 3G spectrum allocated to operators in India is inadequate and far less as compared to global standards. The operators are bound to face a capacity crunch once 3G services gain traction and 4G services are rolled out. Therefore, service providers are taking several steps to avoid congestion on networks.

In line with global trends, they are looking to shift their backhaul networks to packet technology. However, given that voice still is a major source of revenue for Indian operators, all-IP would take time to dominate the backhaul network. Currently, operators are looking for a solution which takes care of both the TDM and IP traffic. They are focusing on hybrid backhaul solutions, where voice and real-time traffic are separated from high speed downlink packet access and mobile broadband services. The former is mostly transmitted over TDM lines, while the latter is offloaded to a new packet switched backhaul network.

Idea Cellular has been witnessing a surge in data demand since 3G service launch and has taken several steps to tackle backhaul challenges. It has moved its TDM microwave link to IP. To enhance its backhaul capacity, the operator has installed fibre-based backhaul at several sites. Currently, 12-15 per cent of its sites in cities where 3G services have been launched are fibre based. Idea intends to increase this to around 20 per cent in 2012, and extend its fibre network to smaller towns. It plans to move to an all-IP domain in the next two years, at least in the top 50-60 towns. 3G repeaters are also being considered for improving the company’s in-building coverage.

Reliance Communications (RCOM) owns and operates an extensive NGN-IP- enabled connectivity infrastructure, comprising over 277,000 km of optic fibre cable systems. RCOM has a fibre-based backhaul, which supports high bandwidth and provides one of the lowest latencies in the industry. All its 3G sites are connected through IP backhaul to provide maximum download speeds.

Bharti Airtel has transport platforms in its network infrastructure. The operator also has 120,000 km of fibre. The operator was initially planning to migrate to a carrier Ethernet solution to manage 3G data traffic. But it ruled out this option as it required the upgradation of the operator’s existing installed base of over 20,000 multi-service provisioning platforms. Instead it selected an all-native packet transport solution, which handles TDM and packet traffic, and delivers business and cellular services over a common infrastructure. The company is also evaluating the use of mini base stations for 3G and LTE-TDD rollouts.

Tata Teleservices Limited (TTSL) has been expanding its network for both coverage and capacity in the mobility and enterprise business segments. Since this requires backhaul for both TDM and IP traffic, TTSL has deployed Japan-based NEC’s iPASOLINK platform to upgrade its backhaul mobile transport network. The platform is designed to support the transition from hybrid TDM and Ethernet backhaul to full IP transport.

State-owned Bharat Sanchar Nigam Limited (BSNL) has one of the largest backhaul networks in the country with a 50,430 route km microwave network and over 600,000 km of optic fibre. This low-cost backhaul fibre network provides BSNL an edge over its competitors, particularly in rural areas. The company is aware of the inherent TDM limitations with respect to NGN technologies and has been transforming its networks to packet based. The company, in its tenders for current and future mobile network expansion, is focusing on procuring equipment that can manage voice, data and video traffic across a single core  and backhaul infrastructure.

Emerging trends

Indian operators are also considering the Wi-Fi option to offload data. In early 2011, Aircel launched 50,000 Wi-Fi hotspots across the country, and partnered with O-Zone Networks and Tikona Digital Networks to offer public Wi-Fi services to its subscribers. The operator has also initiated the installation of macrocells for 3G rollout and intends to move to femtocells for in-building coverage. It would use picocells for meeting the requirements of the enterprise segment. Bharti Airtel has also tied up with O-Zone for setting up a Wi-Fi network. Idea is also planning to use femtocells and Wi-Fi to offload a large part of its data traffic.

Other emerging technologies in the backhaul space include the use of femtocells, picocells and E-Band communication. Femtocells are low-power, small indoor access points designed to provide dedicated mobile network coverage within a small area. They provide backhaul connectivity through the customer’s internet connection (usually xDSL or cable modems). E-Band (71-76 GHz and 81-86 GHz) is a worldwide band allocated for multi-Gbps point-to-point communication. The two allocated bands, each with a 5 GHz bandwidth, are much wider than most cellular and microwave bands, making them suitable for high-data-rate wireless communications through relatively simple radio architecture. Further, these bands have all-weather availability and offer fibre-like benefits.

The growing focus on green telecom puts pressure on operators to improve the efficiency of their radio access network and backhaul designs. This requires equipment vendors to balance computational power at the base station with that at the local exchanges and mobile switching centres.

The government’s role

Operators have largely focused on densely populated urban markets for rolling out data-intensive mobile broadband applications. This has left the rural areas underserved with poor 2G services and limited presence of 3G and high speed services.  Though urban market saturation and regulations have brought in a shift in operators’ attention towards the rural market, there is still a long way to go. The government has an important role to play in addressing the growing backhaul requirements. The National Optical Fibre Network project, which is under implementation, aims to provide backhaul connectivity to village panchayats by extending the existing optic fibre network.

Further, the Department of Telecommunications is considering the proposal of its Wireless Planning and Coordination (WPC) wing to provide additional spectrum channels to broadband players for backhaul. As per the existing norms, broadband players are allocated two channels of spectrum. Each microwave channel has 28 MHz of spectrum and is capable of transmitting data at a speed of 50 Mbps. However, with 4G technology expected to offer speeds of up to 150 Mbps, operators would need three to four microwave links. Hence, the WPC has proposed that four channels of airwaves be allotted to BWA players. While the additional spectrum channels would allow BWA players to offer high speed data services more efficiently, the government also stands to gain as operators will pay a higher revenue share.

Recently, BSNL announced its plans to auction spare bandwidth at the backhaul infrastructure and access levels. This will help new private players, which do not have strong fibre and wireless transport networks to address the capacity crunch, in ensuring backhaul connectivity.

Going forward