Wednesday, January 26, 2011

Mobile Network 101 Part 3

In the beginning, Mobiles networks acted just like the wired phone system however over the air. Yet because each base station had limited capacity, it is not practical to maintain dialup-esque uninterrupted data sessions over analogue lines as it uses frequencies badly needed by everybody else. 

Soon it is found that some bands reserved to control messages can be re-used to send small packets of data, namely 160 latin characters of text. By setting up separate facilities called Short Message Service Centre (SMSC) to route packets, the service could be put into use with little overhead to the network.

The design proved to be simple yet very efficient;similar protocols were developed for most rival standards such as D-AMPS and CDMA. However just as SMS went viral worldwide, US carriers were unwilling or uninterested in co-ordinating SMSCs that allow text messages to be transferred between different networks. Such handicap resulted in a persistent lack of reliable SMS service and consumer interest in north America, leading to third-party services such as BIS that works independently across all networks. Texting between carriers is no longer an issue in US(quirks do remain, such as non-latin messages routinely gets corrupted should they cross network barriers), SMS is often not a regular service for mobile services but a paid add-on.

For a while, SMS was the only method of data transmission over GSM networks. People even wrote protocols to control remote devices via SMS. Fortunately, it did not take long before someone realised that a packet-based layer would be placed alongside voice in the digitised radio. By the time GPRS standard has stablised, it is capable of 80kbps download and 20bps upload, faster than dial-up on copper wire. However to achieve this speed, five concurrent TDMA timeslots must be used, hogging up a large portion of scarce network capacity. To furthur increase bandwidth, the need for new technology could not be any more obvious.

Numerous submissions were made, and the winner turned out to be a surprise to everybody. NTT DoCoMo's W-CDMA, a hybrid protocol using a CDMA air interface for capacity, while preserving the GSM core network to minimise transition costs and allow handsets to move seamlessly between 2G to 3G. Bearing in mind that Japan never had any commercial GSM service, we could only assume that NTT designed W-CDMA (soon to be known as UMTS), to be a global standard.

Legacy support was proven in its value such as in case of Vodafone NZ, which operates both WCDMA and GSM network. The latter is available in case the former fails. Whereas Telecom runs to incompatible standards (XT and CDMA2000), disruptions in XT service turned out to be a major flop.

CDMA was designed to be data-compatible from ground up. It underwent its own evolution into CDMA2000, and became fully 3G with the EV-DO extension, which happened before any other standards were formed. While CDMA2000 uses a much smaller channel which means it hogs less frequency, the smaller bandwidth meant that there is little room for expansion, and voice call cannot exist simutaneously with an active data session. 

3G was, shortly before the millennium, touted as the greatest thing that was ever invented since the lightbulb and sliced bread to "change the way we live forever". National authorities put 3G frequencies for auction and netted billions of dollars. However, the .com bubble promptly went burst thereafter and the hype suddenly died away. For many years, 3G was considered nothing more than combination of gimmicks like video calling; nobody took it seriously. 

Some of the players like Nortel never recovered from the damage and went out of business in another bad cycle. With the rollout of 4G and 4G-ish networks imminent, most operators have so far failed to recover their cost from the entire 3G fiasco.

One of the main reason was that few handsets were truly taking the advantage of 3G before 2007. Yes, I am talking about the iPhone. Before that, most phones are optimised for GPRS: messages were text only and browsers only return stripped down WAP pages. We all dislike iPhone for many reasons, but it is truly the game changer as everybody realised that how much rich media they could provide on people's everyday carry.

The slow transition to 3G is accompanied by the decline of two 2G-era giants: RIM and Nokia. I will write more about them in another post.

If it was not for the recession, three independent standards would have played out for 4G: LTE for the GSM/UMTS camp, UMB for CDMA2000 and WiMAX as an extended 802.11 protocol. Qualcomm, reacting to not-so-favourable financial conditions, decided to ditch UMB and concentrate on allowing present CDMA2000 networks to migrate to LTE.

Right now, most 3G carriers are planning for LTE while brading their HSPA+ compatible networks as 4G in all advertising material to attract attention. WiMAX has been deployed in a few places, however it's future as a major standard remains unclear.