Broadening Broadband, Are We Ready?

Introduction

Recently our honorable Prime Minister Shri Narendra Modi has announced the “Digital India” program, which is very ambitious and aims at enhancing the efficiency of “service delivery” to all citizens. Hence, the government’s focus on enhancing Broadband connectivity is natural, as “Digital India” and “Ubiquitous Broadband” goes hand in hand. The current understanding is that the urban areas need little support, and will be able to sustain on its own. It is the rural areas, where the focus should be. The UPA government’s NOFN program aspiring to connect more than 6 lakh villages through optical fiber cable is targeted towards achieving this objective. However, the progress is slow and needs significant ramping up. But, is it true that only the rural areas needs all the support and Urban areas needs none? This note investigates this aspect, and attempts to analyses the possible opportunities, constraints, and refinements required if any, so as to prevent “weak links” becoming bottlenecks in future.

Optimal Network Architecture is the Key

Broadband can be delivered through either wireless OR wireline technologies. In order to enable adequate speeds at an optimal cost, generally a mixed approach is used. Wireless is used to connect the last-mile, and wireline serves to carry aggregated data traffic to the switching centers (located at the central hubs). This is the model, the telecom operators ideally should follow, since even in areas where the population density is moderate, the cost of digging cables to connect all the access points is exorbitantly high. Also, the model enables one to access broadband on the go, which is not possible in case one is tied to a fixed line. Though one might argue that the connectivity of fixed lines can be further extended via WiFi technology, but, it only works for very short distances. WiFi being an unlicensed technology, it is forced via regulation to transmit at much lower power to prevent it interfering with other parallel nearby WiFi networks operating in the same block of unlicensed spectrum. 

On the other hand wireless technologies like 3G, 4G operate in the licensed spectrum. These technologies can therefore transmit at much higher power levels, and therefore best suited for macro deployment to cover larger geographies, as at these power levels, wireless signals travel much larger distances compared to WiFi. Larger coverage lowers the total number of cell sites required, and therefore the need of additional backhaul links to carry traffic to switching centers, thereby saving costs.

Lack of Urban OFC will Underutilize Spectrum

Mixed approach (combination of wireless and wireline) needs lots of licensed spectrum, as the wireless technologies’ capability to drive throughput (bits/Hz) over the air is finite, but the demand for data is increasing exponentially. Hence, if spectrum is constrained, then only way of increasing overall capacity is by adding more sites, thereby increasing the intensity of “spectrum reuse”.  In urban areas finding sites for hosting equipment is quite a challenge. Also, it proportionately increases the need of backhauling traffic from these aggregation points. The current backhaul is mostly done through microwave spectrum, due to lack of urban OFC networks (as of date only 20% of the urban BTS sites are connected through OFC networks). This is potentially a problem, as the microwave link’s capability to carry traffic is disproportionately out of place with the exponential growth of data traffic.  The need for capacity is further aggravated, as to increase reliability, these links typically have to be connected with each other to form a ring, and thereby doubling capacity requirements compared to that of simple “point to point” links. These rings are used to transmit BTS’s traffic in both direction, so that in case one of the links fails, the other can be used to restore communication.

The intensity of the problem can be understood from the following calculation. In India, operators have been assigned spectrum in three bands. One each at lower, medium and higher frequency. It is understood that at some point all these bands will be used to carry data traffic. Throughput of a typically 2x5 MHz block of 3G/LTE spectrum is 7/10 Mbps/sector and of 20 MHz TDD LTE spectrum is 20 Mbps/sector (these are very conservative estimates). Typically a BTS has three sectors, and therefore total data traffic emanating out of the BTS sites will be around 120 Mbps/operator (25 Mbps for 2100 MHz, 30 Mbps for 1800 MHz, and 65 Mbps for 2300 MHz including overheads, assuming one block each of 2x5 MHz in 2100 MHz and 1800 MHz each and one block of 20 MHz in 2300 MHz). Now if we assume that 10 such sites are connected in a ring (in alignment with the current 2G architecture), the total traffic carrying capability of the ring should be 2.4 Gbps (2x120x10 = 2.4 Gbps). This is beyond the carrying capacities of the current Microwave backhaul technologies. Even the newer technology “Gigabit microwave links” might not be of much help, as its bit rate is throttled at 1 Gbps and the distance they can carry signals reliably is typically 500 meters. It is understood that in steady state situation an operator will have 50% of its BTS sites on rooftops, and rest will be on small cells. Rooftop BTSs will aggregate traffic emanating out of these small cell sites, and therefore will need much larger traffic carrying capacity. Hence, for an operator to be able to fully use the capacity of already assigned spectrum, at least these 50% of the BTS sites (which are on rooftops) must be connected through OFC.

Even the WiFi approach (being planned in many state) will not help, as these will require many more sites (compared to conventional 3G/4G) and therefore many more OFC termination points.

OFC density requirement is more in Urban than Rural

We all know that intensity of spectrum usage will be much higher in the urban areas compared to rural areas. Urban Indian will have better smartphone with the highest affinity for data compared to rural, where both the population density and purchasing power are currently lower. Hence, the number of BTS sites will also be proportionately higher in urban areas compared to rural. The international experience also points in this direction (Korea/Japan/US they all have adequate OFC networks to connect their urban BTSs). But, the focus of the government is currently only to support deployment of OFC in rural areas and urban areas are being ignored. As the intensity of traffic increases in future, the urban data networks might get congested, and operators might not be able to compensate by laying OFC networks on their own due to high cost of laying and inability to get “right of way”. Then the current controversy on “call drops” might escalate to “data blocks”. Hence, lack of OFC networks for connecting BTS sites might become the weakest link in the India’s Broadband aspirations.

 (The views are of my own and does not necessarily reflect that of my employer)