Continuing From Last Week
As a quick recap, Part 1 of this thread covered the differences between traditional cellular handset needs compared to M2M needs:
- M2M Devices Are Different.
- M2M Applications Are Different.
- Network Coverage Needs Are Not The Same.
- Device Longevity.
Part 2 began the simplified history of cellular technologies:
- Early M2M Data Transmission Experiences.
- Introduction of Digital TDMA and CDMA.
- Digital Service Expanded And Changed.
- The AMPS Sunset Requirement.
This week, I will continue to cover the simplified history of cellular technologiesas related to M2M.
New Digital Data Transmission Methods
With the introduction of CDMA and GSM (and earlier, to a lesser degree, ANSI-136 TDMA) came the introduction of digital data transports that could also be used for M2M applications.
Introduction of Text Messaging Services
Digital cellular introduced Short Message Service (SMS) or what is also called Text Messaging. This service allows composing and sending brief messages (with a maximum of 140 to 160 characters or bytes) from one mobile handset to another, and rapidly became popular in European and other markets in GSM.
Delivery was not instantindeed, with congestion and later introduction of spam filters and queues, successful delivery (let alone timeliness) of SMS messages was not common. Furthermore, in early digital cellular deployments, it was often not possible to send SMS messages to handsets on other Carriers.
Over the years, this situation has improvedCustomers can send SMS messages to almost any other handset. However, since inter-Carrier SMS is often handled by gateway service providers, the success and timeliness of deliveryparticularly when roamingis still not very good.
For M2M applications, the successful and timely delivery of data using SMS was, and is, still a problem. Customers resorted to multiple attempt scenariossending three identical SMS messages in the hope of getting one throughto improve service.
It required the introduction of network optimizations like the Aeris SMSDirect system, which avoids the inter-Carrier gateway and spam filter/congestion problem to provide service reliability that can be relied on, particularly for M2M applications that need a higher quality of service.
Data Using Internet Protocols
GSM and ANSI-2000 CDMA also saw the introduction of Internet Protocol (IP) connections for the transmission of data in sessions. Consumers expected to use this data transport for browsing the Internet. M2M applications could consider using this data transport when sending data that could not be fitted into a few SMS messages.
In GSM, the General Packet Radio Service (GPRS) technology became popular and in CDMA, the 1X Radio Transmission Technology (1xRTT) became the common method for transmitting IP data from handsets and radios to web sites and servers on the Internet. (By this time, ANSI-136 TDMA had ceased to be a competitive factor, and IP digital data transport on TDMA were not considered for deployment.)
These were relatively low-speed data transmission technologies that served (and still serve) M2M data requirements very well, since the volume of data per session is generally not very large, but were not sufficient for consumers who were beginning to use Smart Phones and data cards attached to their notebooks.
It should be noted that the performance of GPRS and 1xRTT is different: in general, 1xRTT will outperform GPRS by a factor of three to ten in usable bandwidth and degrade less severely with increased usage in a market, due (among other reasons) to the spectrum and encoding protocols used by each.
Higher Speed IP Data
For wired Internet consumers, web sites were becoming more graphics oriented. With many more images and with new technologies such as Flash providing a richer media experience. Short video clipsdriven by the YouTube phenomenonbecame more common on corporate and personal web sites.
The increased band-width requirement of these uses meant that Carriers had to provide higher performance data transports.
Thus, GSM added Enhanced Data Rates for GSM Evolution (EDGE) and CDMA added 1x Evolution-Data Optimized (1xEV-DO, also called simply EV-DO).
Again, due to protocol and spectrum reasons, EDGE could not perform as well as EV-DO in bandwidth availability and usage. Efforts to improve EDGE performance were cut short when a critical change occurred.
Another Fundamental Technology Change
Some years ago, it became clear that the underlying protocol used in GSMnamely TDMA (remember: not ANSI-136 TDMA)simply could not provide the spectrum efficiency necessary to be competitive with CDMA technologies.
The major CDMA Carriers had continued to increase their performance with the introduction of new protocols that improved bandwidth to where GSM and TDMA simply could not go. The CDMA Carriers introduced EV-DO Rev. A in a fully compatible way with EV-DO (now named EV-DO Rev. 0) and 1xRTT, and were working on others (EV-DO Rev. B) that would have widened the gap further.
Thus, the 3rd Generation Partnership Project (3GPP) run by the ITU in Europe decided to embrace CDMA as a protocol. Unfortunately, due to licensing and intellectual property concerns, this was deliberately not compatible with ANSI-2000 CDMA as used by the CDMA Carriers in North America and elsewhere.
For example, where the ANSI-2000 CDMA system uses 1.25MHz channels, the new Universal Mobile Telephone System (UMTS) system designed by 3GPP uses 5MHz channels and a different encoding scheme! And the technology incompatibility gulf widened ...! Now, UMTS devices used a new CDMA protocol (called Wide-Band CDMA or W-CDMA to distinguish it from CDMA) as well as provide backward compatibility for the older TDMA data transports (i.e., for GPRS and EDGE).
As a result of the increased complexity for multiple protocol support, W-CDMA radio modules are generally more expensive than comparable EV-DO radio modules and this has had an impact on M2M deployments that need higher bandwidths.
Spectrum Needs Increased
More importantly, since W-CDMA is fundamentally different from GPRS (and EDGE) that uses TDMA, these technologies cannot co-exist in the same channels (unlike 1xRTT, EV-DO Rev. 0, and EV-DO Rev. A).
Yes, UMTS devices can operate in EDGE and GPRS markets and bands since they switch to TDMA mode of operation, but GPRS and EDGE devices cannot operate at the bands where W-CDMA service is deployed.
Thus, the Carrier deployments for GSM evolving to UMTS services become more difficult, unless additional spectrum is allocated and used to carefully manage services. In North American markets, this complicates matters for AT&T and the other GSM Carriers far more than the CDMA technology evolution for Verizon, Sprint and other CDMA Carriers.
GSM Radio Prices Drop
Along with the introduction of new cellular technologies, the world experienced a tremendous expansion in cellular service availability for voice phone service. In many countries, it became easier and cheaper to deploy cellular service rather than drag expensive copper wire to every household and home.
Naturally, with the increased volume service came price reductions.
GSM handset prices plummeted world-wide to allow poorer countries to offer low-cost service to its citizens who could not afford high-priced handsets.
Since GSM also used Subscriber Identity Modules (SIM) to record account information, this drove the use of pre-paid SIM cards for consumers who could not get the necessary credit for post-paid cellular service. Again, GSM could provide this more easily than CDMA from the start, although CDMA also could use a similar feature called a Removable User Identity Module (R-UIM).
The SIM also affected GSM handset quality control, since a failed handset could be discardedthe SIM was simply moved to another handset. Low-cost GSM handset manufacturers sprang up in many countriesoften selling handsets that do not meet the full 3GPP specifications, but suffice for the needs of the consumers.
Impact on M2M
The large deployment of GSM handsets led to chipset price reductionssince volume is a direct connection to costs in the chip industry. For M2M applications using GSM and GPRS, this was a major boon: GPRS radio modules dropped in price to where large-scale M2M deployments became possible.
Unfortunately, the expansion of M2M applications using GPRS comes with a hidden problem that will be evident in later posts in this thread.
To Be Continued
Next week, I will cover more cellular technology history that impacts the technology selection process for M2M applications.