Yesterday's papers and social media feeds were flooded with news about Airtel's retaliation to Reliance Jio's ambitious initiative with special packs being launched and aggressive pricing of their 4G data plans. For a moment, let’s stay away from terms like 2G, 3G, 4G, Jio, VoLTE and ask a simple question; Will all this hype and free bytes improve the service quality when some fundamental issues on the ground remain unsolved? My simple answer is - NO.
I have a friend who stays in Heritage City, one of the best localities in Gurgaon. He has a wonderfully located ground floor flat surrounded by colourful flower pots. There are two bedrooms, one large drawing cum dining room and a small balcony with glass cover. There is one small problem, though. Whenever he gets a call on his cellphone, he picks up the phone and walks up to an obscure corner of his house where there is some signal for his cellphone to work. With very poor signal strength, he experiences frequent call drops and his cell phone will work only at that little spot near the right-hand side of the balcony. Nowhere else there is enough signal for the phone. First came the 3G services. That did not mean any relief to him. He thought that with 4G services, his problem probably will be over. So like everyone else he bought a 4G compatible phone. But the situation has deteriorated if not improved. And now Reliance Jio is promising the moon for free. This time, he thought the problem will certainly be over. But his regular visits to the obscure corner of the balcony still continues.
Cellular network in urban India is like a robust network with very poor end connections. It’s like taking an auto (Tuk- Tuk) to reach metro station, then travelling in the metro to your destination and then searching for another auto (Tuk Tuk) to reach home. It’s like a highway with poor connections. When two cellphones talk, one wireless link is at the calling number end and another wireless link at the called number end. And a robust fibre optic backbone connecting both ends.
All the problems that we face these days are due to poor wireless connectivity at these two ends. No amount of software enhancement, protocol, tariff plans are going to help because this first/last mile problem is a hard physical limitation.
When wireless is used for communication, the information that we want to transmit is first converted to electrical signals and then somehow encrypted into a high-frequency carrier and then radiated into the open space. This method is called modulation and there are two ways of doing this. If a signal modulates the amplitude of the radio frequency source, the process is called AM or Amplitude Modulation. If a signal modulates the frequency of the radio frequency source, the process is called FM or Frequency modulation. Frequency modulation produces better quality signal compared to amplitude modulation but uses larger frequency band. This is because external noise and electromagnetic induction easily affects the amplitude of a signal but cannot (generally) mimic and influence the frequency of a signal. In modern communication systems, all analogue signals are first converted to digital and then used for frequency modulation. Often the digitised signal is encoded in some form or other before used for modulation and transmission.
When such a modulated signal is demodulated after being received, the original encoded digital signal comes out. This signal after any decoding if required is converted back to analogue to get the voice signal.
In a wireless cellular system wireless signal is available everywhere within the geographic transmitting range of the transmitter. When a cell phone handset is switched on, it starts radiating wireless signal (in the range 900Mhz -2100Mhz) and the most suitable cell tower (typically whose signal is strongest near the phone) picks up the signal from the phone. Communication is established and the tower takes note of the IMEI (International Mobile Equipment Identity) number and the SIM (Subscriber identity module) details of the phone. From the SIM number, the cellular system looks up the mobile number and the subscriber name. With that done, the cellular system knows which subscriber with which phone is connected to which cell tower.
When the subscriber with his cell phone starts moving away from the connected tower, the signal from the cell tower he is connected to gets weaker and weaker. As he moves farther, he gets in the range of other cell towers. At some time, he may be within the working range of one or a few more towers. As the subscriber keeps moving farther and farther away, the signal weakens steadily and he runs the risk of getting disconnected from his original tower and loses connectivity from the system. Before this can happen, a system called BSC (Base Station Controller) identifies the “best” incoming tower (depending upon traffic, signal strength,the volume of data, etc.). Once that is done, BSC disconnects the subscriber from his original tower and connects him to the new identified tower. This process is called “handover”. After a successful handover, BSC informs another system called MSC (Mobile Switching Center) the new cell tower number that the subscriber is now connected to. Thus even when the subscriber is moving, the cellular system keeps tracking which cell phone tower he is connected to and the system keeps on handing over the subscriber from one tower to the next.
Thus if I call my friend’s number from my residence in Gurgaon, the tower to which I am connected takes my call and hands over it to the MSC (Mobile Switching Center). The mobile switching centre takes my friend's number and looks up the IMEI and SIM card details of my friends number and finds out which tower my friend is connected to at this point of time. Let’s say my friend is not at home and is driving around Connaught Place in Delhi. As he drives the MSC knows the tower number say CX755AT-327 (an arbitrary number) that his phone has been last handed over to. The call is diverted to that particular tower (by MSC) and his handset rings. Let’s say he picks up the phone and while talking he is still driving. As he is moving away from the tower he is currently connected to, his connectivity is handed over from tower to tower seamlessly.
As you can see all routeings and information processing for the first mile (between the Calling handset and the connected tower) and the last mile (between the receiving handset and the connected tower) is done wirelessly. Everything else - between the caller's tower to the receiver’s tower - is processed and managed on high volume reliable media like optical fibre or microwave.
That brings us to the fundamental nature of the cellular system. In this system, an urban area is divided into geographic cells. Inside each cell, a service provider uses an allocated frequency. Typically one hexagonal cell is surrounded by six cells. These seven cells are connected geographically and must use different frequencies to avoid interference. The pattern of seven cells is repeated in such a way that adjacent cells do not use the close frequencies. Thus the same seven frequencies are reused. There is an optical fibre backbone that runs like a highway connecting all the cell towers. This is a grossly simplified description of a rather complex system.
Thus, the reliability of such a system heavily depends on two things. (1) “Identification” of which handset is (wirelessly) connected to which tower and (2) Correct and Quick “handover” of subscribers from tower to tower. And both “handover” and “Identification” depend on the availability of minimum working signal strength. Even when the signal strength is adequate, the system can degrade depending on how many subscribers are connected to a tower, how many handovers are occurring, how much of data is flowing in the channel at what speed (2G, 3G, 4G) and the type of data.
Availability of a minimum working signal strength is perhaps the most critical factor for cellular telephony. Wireless signals travel like light waves and work best when the transmitter and the receiver are in the line of sight of each other. The reason why Satellite TV system works so well is because your dish antenna is always directly looking into the satellite - hence the name - DTH (Direct To Home). Wireless signal of 900/1800/2100 Mhz frequency does not bend around physical obstructions very well. That is why physical location, the height of cell towers and the frequency used for up/down link are some of the important factors for adequate signal strength to reach each subscriber in the cell.
That is why, inside a narrow pocket formed by a few high rise buildings, the strength of the signal goes down. An extreme case is when you lose signal inside a basement parking. The problems due to this effect are more at higher frequencies. Nook and corners of an urban area which gets just adequate signal at 900 MHz, may get very poor signal strength at 1800/2100 MHz. Thus the only solution is to increase the number of towers. Data shows the number of towers required to cover an urban area at 900 MHz will double at 1800/2100 MHz – with huge infra cost for each tower. See how the signal strength at 900 MHz for 2G service (left) will reduce in large part of the area (right) when 1800/2100 MHz signal is used for 3G/4G services.
Locating the cell towers at optimum locations within the urban master plan is a huge challenge. Typically in India, we first build a city and then grapple with its drainage problems. We build roads and then think of traffic lights. In the same way, we buy 4G enabled cell phones without knowing whether 4G service will ever work in the location where you reside or work or travel. Regulatory control for registering the existing towers will not alleviate the poor signal strength problem because that will neither improve the reach nor the strength of the last and first-mile signal strength. The height of the cell tower increases the geographic reach of the signal but only to a limited degree. It is a good idea to install the Cell towers on the rooftop of tall buildings but logistic, regulatory and sharing of infrastructures between Cell phone operators continues to remain a problem.
Any cell / tower can serve only so many numbers of users. As more and more users get connected to the network, more number of cells must be created to accommodate more users. This means within the same geographic area, there have to be more cells of smaller size now. Smaller cells will result in people coming in and going out of the cell more frequently. This will result in more “handovers” and more call drops. Also if a cell is saturated then the next incoming subscriber will get dropped because there is no more bandwidth available to accommodate more subscribers.
Like main roads in urban India, cellular networks are under constant change for improvement and up-gradation - only they are not visible like ongoing road repair works. This requires constant reconfiguration of network resources. If any reconfiguration is incomplete or incorrect, this can create a situation where you enter a cell where you cannot get connected to – like a road blocked, diversion or U-turn. Improper cell frequency coordination may result in neighbouring cells with the same frequency and lead to interference to deteriorate the signal. Hardware failures like transmitter failure, supply failure, handset battery failure can also cause call drop.
More than 90% of the times it is either a wireless failure or a handover failure (which could be again due to wireless failure) that lead to dropped calls. The majority of call drops will keep happening solely due to poor wireless connectivity and the situation will not improve in the near future unless a thorough tower location/relocation planning for 3G/4G services requiring the use of 1800/2100 frequencies is carried out and implemented by TRAI. Cell phone operators are reluctant to share towers. There are approximately 5, 50,000 towers in India, and industry associations reckon another 1, 00,000 are needed. The lower radio bands need fewer towers to travel longer distances, so when telecom companies offer richer services like 3G or 4G, they have to be at higher frequencies (2,100 MHz or 2,300 MHz instead of 900 MHz), which need more towers at planned locations.
There is an urgent need to increase the number of the towers so as to cater to the demands of a growing subscriber base. All major cities in India have far fewer towers than are needed. Civic authorities across the country appear to be ill informed and not telecom-friendly or savvy. The Internet and mass media are full of ads about cell phone models, processor speed, software versions, and exotic apps, and services like 3G, 4G, and Jio but very little about the biological growth of cell towers on the urban landscape. The hype keeps the general public blissfully ignorant of what kind of signal they get or how many towers located where will give some working signal to the cellphones they carry in their pockets.
What really works very well is a wonderful system called “auto downgrade”. As the signal gets weaker and weaker, the available service automatically downgrades – from 4G to 3G to 2G to H to E, and the subscriber hangs on to a feeble and dying signal. So what if it the call drops. He can always redial after getting dropped.
What a pity. Till the basic last mile problems get resolved, calls will keep getting dropped and my friend will quietly walk to his balcony with his 4G enabled iPhone7 with Reliance Jio service for making and taking calls.