Too often we fail to learn from lessons of the past. As an industry, we have over 20 years of experience in designing cellular handsets and deploying cellular networks. The past tells us precisely what is and what is not possible in terms of future technology deployment. This allows us to detect when reality gaps occur. Reality gaps are those between technical practicality and wishful thinking. They happen all the time and can be particularly painful when technically complex systems are being deployed. Almost all technologies start with a reality gap. The technology fails to deliver as well as expected. Some technologies never close the gap and become failed technologies. Some people can make money from failed technologies, but the majority doesn’t. Failed technologies ultimately fail because they do not deliver user value. We also tend to forget that user expectations and customer expectations change over time. A technology has to be capable of sufficient dynamic range to be able to continue to improve as the technology and user expectations mature. Failed technologies often fail because they cannot close the reality gap and cannot catch up with changing user expectations. One example of a failed technology is WiMax!
Successful technologies are that which deliver along the whole industry value chain—device vendors, handset manufacturers, network manufacturers (software and hardware vendors), network operators, and end users. I aim to show in this article how different generations of wireless technology has been evolving to become a successful proposition, both technically and commercially. I hope you enjoy reading this article and hope to get your feedback.
The cellular wireless communications industry witnessed tremendous growth in the past decade with over four billion wireless subscribers worldwide. The first generation (1G) analog cellular systems supported voice communication with limited roaming. The second generation (2G) digital systems promised higher capacity and better voice quality than did their analog counterparts. Moreover, roaming became more prevalent thanks to fewer standards and common spectrum allocations across countries particularly in Europe.
The two widely deployed second-generation (2G) cellular systems are GSM (global system for mobile communications) and CDMA (code division multiple access). As for the 1G analog systems, 2G systems were primarily designed to support voice communication. In later releases of these standards, capabilities were introduced to support data transmission.
However, the data rates were generally lower than that supported by dial-up connections. The ITU-R initiative on IMT-2000 (international mobile Telecommunications 2000) paved the way for evolution to 3G. A set of requirements such as a peak data rate of 2 Mb/s and support for vehicular mobility were published under IMT-2000 initiative. Both the GSM and CDMA camps formed their own separate 3G partnership projects (3GPP and 3GPP2, respectively) to develop IMT-2000 compliant standards based on the CDMA technology. The 3G standard in 3GPP is referred to as wideband CDMA(WCDMA) because it uses a larger 5MHz bandwidth relative to 1.25MHz bandwidth used in 3GPP2’s cdma2000 system. The 3GPP2 also developed a 5MHz version supporting three 1.25MHz subcarriers referred to as cdma2000-3x. In order to differentiate from the 5MHz cdma2000-3x standard, the 1.25MHz system is referred to as cdma2000-1x or simply 3G-1x.
The first release of the 3G standards did not fulfill its promise of high-speed data transmissions as the data rates supported in practice were much lower than that claimed in the standards. A serious effort was then made to enhance the 3G systems for efficient data support. The 3GPP2 first introduced the HRPD (high rate packet data) system that used various advanced techniques optimized for data traffic such as channel sensitive scheduling, fast link adaptation and hybrid ARQ, etc. The HRPD system required a separate 1.25MHz carrier and supported no voice service. This was the reason that HRPD was initially referred to as cdma2000-1xEVDO (evolution data only) system. The 3GPP followed a similar path and introduced HSPA (high speed packet access) enhancement to the WCDMA system. The HSPA standard reused many of the same data-optimized techniques as the HRPD system.
A difference relative to HRPD, however, is that both voice and data can be carried on the same 5MHz carrier in HSPA. The voice and data traffic are code multiplexed in the downlink. In parallel to HRPD, 3GPP2 also developed a joint voice data standard that was referred to as cdma2000-1xEVDV (evolution data voice). Like HSPA, the cdma2000-1xEVDV system supported both voice and data on the same carrier but it was never commercialized. In the later release of HRPD, VoIP (Voice over Internet Protocol) capabilities were introduced to provide both voice and data service on the same carrier. The two 3G standards namely HSPA and HRPD were finally able to fulfill the 3G promise and have been widely deployed in major cellular markets to provide wireless data access.
A quick summary of the different generations!
First generation (1G).
AMPS/ETACS handsets in the 1980s required low-cost microcontrollers to manage the allocation of multiple RF (radio frequency) channels (833 × 30 kHz channels for AMPS, 1000 × 25 kHz channels for ETACS) and low-cost RF components that could provide acceptable performance at 800/900 MHz.
Second generation (2G). GSM, TDMA, and CDMA handsets in the 1990s required low-cost digital signal processors (DSPs) for voice codecs and related baseband processing tasks, and low-cost RF components that could provide acceptable performance at 800/900 MHz, 1800 MHz, and 1900 MHz.
Third generation (3G). W-CDMAand CDMA2000 handsets require—in addition to low-cost microcontrollers and DSPs—low-cost, low power budget CMOS or CCD image sensors; low-cost, low power budget image and video encoders; low-cost, low power budget memory; low-cost RF components that can provide acceptable performance at 1900/2100 MHz; and high-density battery technologies.
Beyond 3G systems While HSPA and HRPD systems were being developed and deployed, IEEE 802 LMSC (LAN/MAN Standard Committee) introduced the IEEE 802.16e standard for mobile broadband wireless access. This standard was introduced as an enhancement to an earlier IEEE 802.16 standard for fixed broadband wireless access. The 802.16e standard employed a different access technology named OFDMA (orthogonal frequency division multiple access) and claimed better data rates and spectral efficiency than that provided by HSPA and HRPD.
Although the IEEE 802.16 family of standards is officially called WirelessMAN in IEEE, it has been dubbedWiMAX (worldwide interoperability for microwave access) by an industry group named theWiMAX Forum. The mission of theWiMAX Forum is to promote and certify the compatibility and interoperability of broadband wireless access products. The WiMAX system supporting mobility as in IEEE 802.16e standard is referred to as MobileWiMAX. In addition to the radio technology advantage, MobileWiMAX also employed a simpler network architecture based on IP protocols.
The introduction of Mobile WiMAX led both 3GPP and 3GPP2 to develop their own version of beyond 3G systems based on the OFDMA technology and network architecture similar to that in MobileWiMAX. The beyond 3G system in 3GPP is called evolved universal terrestrial radio access (evolved UTRA) and is also widely referred to as LTE (Long-Term Evolution) while 3GPP2’s version is called UMB (ultra mobile broadband). It should be noted that all three beyond 3G systems namely Mobile WiMAX, LTE and UMB meet IMT-2000 requirements and hence they are also part of IMT-2000 family of standards.
Long-Term Evolution (LTE) The goal of LTE is to provide a high-data-rate, low-latency and packet-optimized radioaccess technology supporting flexible bandwidth deployments. In parallel, new network architecture is designed with the goal to support packet-switched traffic with seamless mobility, quality of service and minimal latency. The air-interface related attributes of the LTE system are summarized in Table 1.1. The system supports flexible bandwidths thanks to OFDMA and SC-FDMA access schemes. In addition to FDD (frequency division duplexing) and TDD (time division duplexing), halfduplex FDD is allowed to support low cost UEs. Unlike FDD, in half-duplex FDD operation a UE is not required to transmit and receive at the same time. This avoids the need for a costly duplexer in the UE. The system is primarily optimized for low speeds up to 15 km/h. However, the system specifications allow mobility support in excess of 350 km/h with some performance degradation. The uplink access is based on single carrier frequency division multiple access (SC-FDMA) that promises increased uplink coverage due to low peak-to-average power ratio (PAPR) relative to OFDMA. The system supports downlink peak data rates of 326 Mb/s with 4 × 4 MIMO (multiple input multiple output) within 20MHz bandwidth. Since uplink MIMO is not employed in the first release of the LTE standard, the uplink peak data rates are limited to 86 Mb/s within 20MHz bandwidth. In addition to peak data rate improvements, the LTE system provides two to four times higher cell spectral efficiency relative to the Release 6 HSPA system. Similar improvements are observed in cell-edge throughput while maintaining same-site locations as deployed for HSPA. In terms of latency, the LTE radio-interface and network provides capabilities for less than 10 ms latency for the transmission of a packet from the network to the UE.
Evolution to 4G The radio-interface attributes for Mobile WiMAX and UMB are very similar to those of LTE given in Table 1.1. All three systems support flexible bandwidths, FDD/TDD duplexing, OFDMA in the downlink and MIMO schemes. There are a few differences such as uplink in LTE is based on SC-FDMA compared to OFDMA in Mobile WiMAX and UMB. The performance of the three systems is therefore expected to be similar with small differences. Similar to the IMT-2000 initiative, ITU-R Working Party 5D has stated requirements for IMT-advanced systems. Among others, these requirements include average downlink data rates of 100 Mbit/s in the wide area network, and up to 1 Gbit/s for local access or lowmobility scenarios. Also, at the World Radiocommunication Conference 2007 (WRC-2007), a maximum of a 428MHz new spectrum is identified for IMT systems that also include a 136MHz spectrum allocated on a global basis. Both 3GPPand IEEE 802LMSCare actively developing their own standards for submission to IMT-advanced. The goal for both LTE-advanced and IEEE 802.16m standards is to further enhance system spectral efficiency and data rates while supporting backward compatibility with their respective earlier releases. As part of the LTE-advanced and IEEE 802.16 standards developments, several enhancements including support for a larger than 20MHz bandwidth and higher-order MIMO are being discussed to meet the IMT-advanced requirements.
AMPS family - AMPS · TACS · ETACS
Other - NMT · Hicap · Mobitex · DataTAC
GSM/3GPP family - GSM · CSD
3GPP2 family - cdmaOne (IS-95)
AMPS family - D-AMPS (IS-54 and IS-136)
Other - CDPD · iDEN · PDC · PHS
2G transitional (2.5G, 2.75G)
GSM/3GPP family - HSCSD · GPRS · EDGE/EGPRS
3GPP2 family - CDMA2000 1xRTT (IS-2000)
Other - WiDEN
3GPP family - UMTS (UTRAN) · WCDMA-FDD · WCDMA-TDD · UTRA-TDD LCR (TD-SCDMA)
3GPP2 family - CDMA2000 1xEV-DO (IS-856)
3G transitional (3.5G, 3.75G, 3.9G)
3GPP family - HSPA · HSPA+ · LTE (E-UTRA)
3GPP2 family - EV-DO Rev. A · EV-DO Rev. B
IEEE family - Mobile WiMAX (IEEE 802.16e-2005) · Flash-OFDM · IEEE 802.20
3GPP family - LTE Advanced
IEEE family - IEEE 802.16m