NEW DELHI: State-run Bharat Sanchar Nigam Ltd ( BSNL ) is investing around Rs 7,000 crore to install 21,000 new mobile towers to arrest service quality issues. The company, however, said it has the lowest number of call drops when compared with private sector rivals.BSNL is working on a three-fold strategy that includes network expansion in all circles including the Northeast where call drop ratio is a little higher, conducting drive tests and network optimisation as well as infrastructure sharing with private players to further ease network congestion and, hence, services. BSNL is in talks with Vodafone India and Bharti Airtel to formally ink intra-circle roaming ( ICR ) deals.“We are in the process of investing Rs 7,000 crore in radio networks, and adding 21,000 new mobile towers across all licensed service areas, which itself is a huge capital expenditure to improve services,” BSNL chairman Anupam Shrivastava told ET.The telco had a mobile consumer market share of 9% of India's total base of 1,034.25 million subscriptions as of April this year, as per telecom regulator Trai.The current base transceiver station (BTS) expansion is part of BSNL's ‘Phase 7+’ initiative to put additional 21,000 towers, after an addition of 25,000 sites under the phase 7 programme, concluded recently, to take the total to 50,000.“Our comprehensive BTS expansion plan that will include locations affected by Left wing extremism, covering Northeast, would take the total count to 50,000 mobile towers by the end of 2016-17,” the top executive added.To mitigate service issues, the telco has renewed its focus on the Northeast with its network expansion programme to fill coverage gaps in the region’s bumpy terrain.BSNL is also working on a parallel strategy of network sharing with private service providers through intra-circle roaming (ICR) pacts and spectrum sharing.According to the telco’s top executive, this helps BSNL to devise network spending strategy on a specific location to improve coverage while the other partner telcos would take care of the rest, thus minimising overall spend for the two operators.The company recently entered into ICR arrangements with Aircel 2G , and Reliance Jio Infocomm , which is yet to make a commercial foray in 4G services.