Showing posts with label WCDMA. Show all posts
Showing posts with label WCDMA. Show all posts

A crash course in GSM, GPRS, EDGE, UMTS, HSPA, LTE and WiMax


This is almost a crash course in fundamentals on mobile standards. It does not matter if you are just a common man trying to understand the jargon or a professional who is trying to get a grip of things. This article i hope will help you started off :-) Please leave a comment if you don't understand any topic. I am very happy to clarify.





To understand Timeslots and frequencies you can read here!!


GSM stands for Global System for Mobile Comm. This is the most popular 2G protocol standard in the world. It is by law the only system deployed in Europe and is used in many other locations around the world. As a digital standard, GSM can carry both voice and data, although the maximum data rate per channel is only 14kbps. North America, Korea, and pockets worldwide use another 2G standard based on CDMA technology; this protocol, CDMAOne, was developed by Qualcomm and is also known as IS-95 or, more commonly, CDMA. GSM is based on time-division multiple access (TDMA) technology, in which a single frequency is divided into eight time slots, with each caller using a particular slot. Most GSM networks operate in two frequency bands: 900MHz and 1,800MHz. In North America, however, the allocated frequency bands are 850MHz and 1,900MHz. Thus, to support global roaming, a handset must support all four GSM bands. The frequencies in each band are assigned to either the downlink direction (from the base station to the user) or the uplink direction (from the user to the base station). Each band supports 124 carrier frequencies in each direction (uplink and downlink).

GPRS stands for General Packet Radio Service. This is a 2.5G protocol standard which allows a single handset to use up to four slots for the downlink and four for the uplink, thus consuming the entire frequency. Using a more efficient encoding than GSM, GPRS can transmit 20kbps per slot for a maximum of 80kbps in each direction using four slots. A later enhancement, EDGE, increases the data rate to a theoretical maximum of 384kbps, although the most bandwidth supported by any chip vendor or carrier is 240kbps.

EDGE stands for Enhanced Data GSM Environment is a 2.75G protocol standard, which increases the bandwidth of each time slot to 48kbps. Baseband processors commonly support either Class 10 or Class 12, which allow a maximum of four slots (192kbps) on the downlink.

UMTS stands for Universal Mobile Telecommunications Service which is a 3G standard and is a follow-on to GSM, created by ITU. (Japanese carrier NTT DoCoMo uses a pre-standard version of UMTS known as FOMA.) UMTS uses new spectrum at 2GHz and new air interfaces that can carry more data, and therefore a greater number of digital voice calls, than can 2G technologies. UMTS delivers symmetric data rates as high as 384kbps for handsets. Unlike earlier standards, UMTS supports simultaneous voice and data services (dual-transfer mode). With tremendous growth in cell-phone usage during the 1990s, vendors sought to use new frequency bands and new technologies to increase capacity. The term 3G indicates the generational leap involved in this major change. The first 3G network was deployed by NTT DoCoMo in Tokyo in 2001. Today, 3G is broadly deployed by operators around the world. Most operators, however, have not upgraded their entire networks, so 3G devices must include 2G compatibility to have the widest service area.

Qualcomm has continued to develop its own CDMA2000 air interface, thus providing its operators with an upgrade path. The 3G version, known as EV-DO, was first deployed in Korea in 2002. Since then, it has been broadly deployed in North America and other locations. The initial version, called Revision 0 (zero), supports data rates up to 2.4Mbps. Approved by the ITU in 1999 and officially adopted by China in January 2006, TD-SCDMA is a 3G standard deployed primarily by China Mobile, starting in 2008. As the name implies, this air interface combines TDMA and CDMA techniques, but the general characteristics and data rates are similar to those of UMTS. The TDMA aspect of the standard enables use of the same spectrum for both the uplink and downlink, thus providing some flexibility. TD, as the TD-SCDMA standard is sometimes called, provides aggregate data rates of 2Mbps.

HSPA stands for High-Speed (Uplink) Packet Access which is a 3.75G standard. This combine both HSDPA and HSUPA as explained in the next oaragrapgh. As with 2.5G technologies, new technologies enhance the data rates of UMTS while maintaining radio compatibility. The first to ship was HSDPA, which was first deployed in late 2005. HSDPA reserves a portion of the UMTS spectrum and converts it into a new high-speed downlink band. This 14.4Mbps band is shared by all users that are actively downloading data; as with any shared medium, actual bandwidth depends on how many users are simultaneously sharing the downlink band. The amount of data that each handset can accept may be limited.

HSUPA addresses the uplink. This direction is of concern for handset users wishing to transmit high-resolution photos or video. HSUPA raises uplink speed as high as 5.76Mbps. Initial commercial deployments began in early 2007. By pushing peak data rates to several megabits per second, HSDPA and HSUPA (together called HSPA) can also be used to deliver cellular broadband services. The data bandwidth using these technologies is similar to what older DSL and cable modems deliver.


HSPA+ further boosts data rates using two approaches. One uses a higher-order modulation to pack more bits into the signal; the second adds MIMO (multiple input, multiple output) capability, which can double throughput by transmitting two streams at once. To do so, MIMO requires two antennas at the base station and two antennas on the handset. The two approaches can be used separately or can be combined to achieve 42Mbps.

The TD-SCDMA standard can be extended to support faster downlink and uplink speeds using the same techniques that are defined in HSPA. The enhanced protocols are referred to as TD-HSDPA and TD-HSPA. Advancing CDMA2000, Qualcomm developed EV-DO Revision A, which boosts data rates as high as 3.1Mbps on the downlink and 1.8Mbps on the uplink. The new EV-DO Revision B supports 14.7Mbps on the downlink and 5.4Mbps on the uplink; these data rates are similar to those of HSPA. Qualcomm sampled the first EV-DO Rev B chips in late 2008.

LTE - Long Term Evolution
The UMTS camp has developed a 4G technology called Long-Term Evolution (LTE). The specification was completed in January 2008. In December 2009, TeliaSonera deployed the first commercial LTE network in Norway and Sweden. LTE uses a new modulation technique, OFDM (orthogonal frequencydivision multiplexing), and wider (20MHz) channels to deliver a peak data rate of 100Mbps. Optional MIMO support raises the peak rate to 326Mbps in a four-antenna configuration. Because of the space required for multiple antennas, high-end handsets and data cards are likely to use one or two antennas, whereas fixed broadband modems may use four (assuming the carrier supports that mode at the base station). The peak uplink rate is 86Mbps.

As a result of these changes, LTE provides about three times the spectral efficiency of HSPA, meaning that an operator can triple the data rate (or the number of voice calls) using the same set of frequencies. Thus, LTE should eventually reduce the cost of data services significantly. Deploying new base stations and bringing down the cost of LTE modems and handsets will require several years, however.

Another 4G technology is WiMax. Originally developed by Intel for fixed wireless broadband, WiMax is being used by some mobile service providers. WiMax is defined by the IEEE as 801.16. An industry group, the WiMax Forum, promotes the standard and certifies products for interoperability. Originally conceived as a data standard, WiMax can be used for voice as well. Like LTE, WiMax uses OFDM with channels widths of up to 20MHz. WiMax also supports MIMO. WiMax has a theoretical maximum capacity of 75Mbps, but mobile users will receive no more than 25Mbps—a far lower rate than that provided by LTE. For fixed WiMax, the practical peak rate is 45Mbps. An important difference is that WiMax, unlike LTE, is not optimized for power consumption on the uplink, making it less power efficient for handheld devices. According to the ITU, 4G technologies must deliver data rates of at least 1Gbps. Neither the first generation of LTE nor the initial mobile WiMax deployments meet this criterion, but both are generally considered to be 4G technologies because they use OFDM. As a follow-on to LTE, LTE Advanced is expected to be the first cellular standard to meet the ITU’s 1Gbps goal.

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The wireless generation dance - 1G, 2G, 2Gt, 3G, 3Gt, 4G


The worldwide communication technology thirst and demands in bringing digital information to widespread end users have pushed innovation to extremes. Each successive generation of cellular technology has been based on a new enabling technology. By new, i mean the availability of an existing technology at low cost, or, for handset designers, the availability of a technology sufficiently power efficient to be used in a portable device.




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 a
ccess) 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.

1G
AMPS family - AMPS · TACS · ETACS
Other - NMT · Hicap · Mobitex · DataTAC

2G
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

3G (IMT-2000)
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

4G (IMT-Advanced)
3GPP family - LTE Advanced
IEEE family - IEEE 802.16m