What is 4G? 

4G takes on a number of equally true definitions, depending on who you are talking to. In simplest terms, 4G is the next generation of wireless networks that will replace 3G networks sometimes in future. In another context, 4G is simply an initiative by academic R&D labs to move beyond the limitations and problems of 3G which is having trouble getting deployed and meeting its promised performance and throughput. In reality, as of first half of 2002, 4G is a conceptual framework for or a discussion point to address future needs of a universal high speed wireless network that will interface with wireline backbone network seamlessly. 4G is also represents the hope and ideas of a group of researchers in Motorola, Qualcomm, Nokia, Ericsson, Sun, HP, NTT DoCoMo and other infrastructure vendors who must respond to the needs of MMS, multimedia and video applications if 3G never materializes in its full glory.  

Motivation for 4G Research Before 3G Has Not Been Deployed?

3G performance may not be sufficient to meet needs of future high-performance applications like multi-media, full-motion video, wireless teleconferencing. We need a network technology that extends 3G capacity  by an order of magnitude. 

There are multiple standards for 3G making it difficult to roam and interoperate across networks. we need global mobility and service portability

3G is based on primarily a wide-area concept. We need hybrid networks that utilize both wireless LAN (hot spot) concept and cell or base-station wide area network design. 

We need wider bandwidth

Researchers have come up with spectrally more efficient modulation schemes that can not be retrofitted into 3G infrastructure

We need all digital packet network that utilizes IP in its fullest form with converged voice and data capability.

Comparing Key Parameters of 4G with 3G

 

  3G (including 2.5G, sub3G) 4G

Major Requirement Driving Architecture  Predominantly voice driven -

data was always add onConverged data and voice over IP

Network Architecture Wide area cell-basedHybrid - Integration of Wireless LAN (WiFi,

Bluetooth) and wide area

Speeds 384 Kbps to 2 Mbps20 to 100 Mbps in mobile

mode

Frequency BandDependent on country or

continent (1800-2400 MHz)Higher frequency bands (2-8

GHz)Bandwidth 5-20 MHz 100 MHz (or more)

Switching Design Basis

Circuit and PacketAll digital with packetized

voice

Access Technologies W-CDMA, 1xRTT, EdgeOFDM and MC-CDMA (Multi

Carrier CDMA)Forward Error

CorrectionConvolutional rate 1/2, 1/3 Concatenated coding scheme

Component DesignOptimized antenna design,

multi-band adapters 

Smarter Antennas, software multiband and wideband

radios

IP A number of air link protocols,

including IP 5.0 All IP (IP6.0)

What is needed to Build 4G Networks of Future?

A number of spectrum allocation decisions, spectrum standardization decisions, spectrum availability decisions, technology innovations, component development, signal processing and switching enhancements and inter-vendor cooperation have to take place before the vision of 4G will materialize. We think that 3G experiences - good or bad, technological or business - will be useful in guiding the industry in this effort. We are bringing to the attention of professionals in telecommunications industry following issues and problems that must be analyzed and resolved: 

Lower Price Points Only Slightly Higher than Alternatives - The business visionaries should do some economic modeling before they start 4G hype on the same lines as 3G hype. They should understand that 4G data applications like streaming video must compete with very low cost wireline applications. The users would pay only a delta premium (not a multiple) for most wireless applications.

More Coordination Among Spectrum Regulators Around the World - Spectrum regulation bodies must get involved in guiding the researchers by indicating which frequency band might be used for 4G. FCC in USA must cooperate more actively with International bodies like ITU and perhaps modify its hands-off policy in guiding the industry. When public interest, national security interest and economic interest (inter-industry a la TV versus Telecommunications) are at stake, leadership must come from regulators. At appropriate time, industry builds its own self-regulation mechanisms.

More Academic Research: Universities must spend more effort in solving fundamental problems in radio communications (especially multiband and wideband radios, intelligent antennas and signal processing.

Standardization of wireless networks in terms of modulation techniques, switching schemes and roaming is an absolute necessity for 4G.

A Voice-independent Business Justification Thinking: Business development and technology executives should not bias their business models by using voice channels as economic determinant for data applications. Voice has a built-in demand limit - data applications do not.

Integration Across Different Network Topologies: Network architects must base their architecture on hybrid network concepts that integrates wireless wide area networks, wireless LANS (IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.15 and IEEE 802.16, Bluetooth with fiber-based Internet backbone. Broadband wireless networks must be a part of this integrated network architecture.

Non-disruptive Implementation: 4G must allow us to move from 3G to 4G.

Industry Initiatives

WWRF (Wireless World Research Forum)- consisting of Alcatel, Ericsson, Nokia and Siemens have started a research forum for 4G

NTT DoCoMo has started conceptual (we mean paper) design of a 4G network. 

For More Information - Go to the following resources on this site and cached papers published elsewhere: 

Do a keyword search on our website using 4G Wireless as keywords. You will find more than 10 references.

A technical paper published in Communications Systems Design Magazine (a CMP publication) during July 2001 - Fundamental Changes Required in Modulation and Signal Processing for 4G  

All IP Wireless – All the Way - Sun's vision of Mobile IP for 4G

Wireless Platforms for the Future: Integrating B-to-C Data Transmission & 4G – Where will it take us? url= http://www.mitforum.com/wireless-forum.htm

4G Wireless Systems in Virtex-II by James A. Watson -- Manager, Applications Engineering, Xilinx, Inc. (7/1/01 -- Issue 40) jim.watson@xilinx.com

Advanced Networks Beyond 3G - Ultra Wideband  

Advanced Networks Beyond 3G - ArrayComm's I-Burst

Advanced Networks Beyond 3G - Flarion's Flash OFDM

Related Resources:>   Wireless Networks >   Wireless LANs >   How to choose Wireless Networks?

Fundamental Changes Required in Modulation and Signal Processing for 4G 

(Published in Communications Systems Design Magazine - a CMP publication during July 2001)

While 3G hasn't quite arrived, designers are already thinking about 4G technology. With it comes challenging RF and baseband design headaches.

Cellular service providers are slowly beginning to deploy third-generation (3G) cellular services. As access technology increases, voice, video, multimedia, and broadband data services are becoming integrated into the same network. The hope once envisioned for 3G as a true broadband service has all but dwindled away. It is apparent that 3G systems, while maintaining the possible 2-Mbps data rate in the standard, will realistically achieve 384-kbps rates. To achieve the goals of true broadband cellular service, the systems have to make the leap to a fourth-generation (4G) network.

This is not merely a numbers game. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services.

The goal is to have data rates up to 20 Mbps, even when used in such scenarios as a vehicle traveling 200 kilometers per hour. New design techniques, however, are needed to make this happen, in terms of achieving 4G performance at a desired target of one-tenth the cost of 3G.

The move to 4G is complicated by attempts to standardize on a single 3G protocol. Without a single standard on which to build, designers face significant additional challenges. Table 1 compares some of the key parameters of 3G and 4G (4G does not have any solid specification as of yet, so the parameters rely on general proposals). It is clear that some standardization is in order.

TABLE 1: Key Parameters of 3g and 4 G Systems

  3G

4G

Frequency band 1.8 - 2.5 GHz 2 - 8 GHz

Bandwidth 5 - 20 MHz 5 - 20 MHz

Data rate Up to 2 Mbps (384 kbps deployed) Up to 20 Mbps

Access W-CDMA MC-CDMA or OFDM (TDMA)

Forward error correction Convolutional rate 1/2, 1/3 Concatenated coding scheme

Switching Circuit/packet Packet

Mobile top speeds 200 km/h 200 km/h

Multicarrier modulation

To achieve a 4G standard, a new approach is needed to avoid the divisiveness we've seen in the 3G realm. One promising underlying technology to accomplish this is multicarrier modulation (MCM), a derivative of frequency-division multiplexing. MCM is not a new technology; forms of multicarrier systems are currently used in DSL modems, and digital audio/video broadcast (DAB/DVB). MCM is a baseband process that uses parallel equal bandwidth subchannels to transmit information. Normally implemented with Fast Fourier transform (FFT) techniques, MCM's advantages include better performance in the intersymbol interference (ISI) environment, and avoidance of single-frequency interferers. However, MCM increases the peak-to-average ratio (PAVR) of the signal, and to overcome ISI a cyclic extension or guard band must be added to the data.

Equation 1, describes peak to average adjustment - the difference of the PAVR between MCM and a single carrier system is a function of the number of subcarriers (N) as:

(1)

Any increase in PAVR requires an increase in the linearity of the system to reduce distortion. Proposed approaches to reduce PAVR have consequences, however. One such technique is clipping the signal; this results in more non-linearity. Linearization techniques can be used, but they increase the cost of the system, and amplifier backoff may still be required.

Cyclic extension works as follows: If N is the original length of a block, and the channel's response is of length M, the cyclically extended symbol has a new length of N + M - 1. The image presented by this sequence, to the convolution with the channel, looks as if it was convolved with a periodic sequence consisting of a repetition of the original block of N. Therefore, the new symbol of length N + M - 1 sampling periods has no ISI. The cost is an increase in energy and uncoded bits added to the data. At the MCM receiver, only N samples are processed, and M - 1 samples are discarded, resulting in a loss in signal-to-noise ratio (SNR) as shown in Equation 2.

(2)

Two different types of MCM are likely candidates for 4G as listed in Table 1. These include multicarrier code division multiple access (MC-CDMA) and orthogonal frequency division multiplexing (OFDM) using time division multiple access (TDMA). Note: MC-CDMA is actually OFDM with a CDMA overlay.

Similar to single-carrier CDMA systems, the users are multiplexed with orthogonal codes to distinguish users in MC-CDMA. However, in MC-CDMA, each user can be allocated several codes, where the data is spread in time or frequency. Either way, multiple users access the system simultaneously.

In OFDM with TDMA, the users are allocated time intervals to transmit and receive data. As with 3G systems, 4G systems have to deal with issues of multiple access interference and timing.

Differences between OFDM with TDMA and MC-CDMA can also be seen in the types of modulation used in each subcarrier. Typically, MC-CDMA uses quadrature phase-shift keying (QPSK), while OFDM with TDMA could use more high-level modulations (HLM), such as, multilevel quadrature amplitude modulation (M-QAM) (where M = 4 to 256). How-ever, to optimize overall system performance, adaptive modulation can be used; where the level of QAM for all subcarriers is chosen based on measured parameters.

Let's consider this at the component level. The structure of a 4G transceiver is similar to any other wideband wireless transceiver. Variances from a typical transceiver are mainly in the baseband processing. A multicarrier modulated signal appears to the RF/IF section of the transceiver as a broadband high PAVR signal. Base stations and mobiles are distinguished in that base stations transmit

and receive/ decode more than one mobile, while a mobile is for a single user. A mobile may be a cell phone, a computer, or other personal communication device.

The line between RF and baseband will be closer for a 4G system. Data will be converted from analog to digital or vice versa at high data rates to increase the flexibility of the system. Also, typical RF components such as power amplifiers and antennas will require sophisticated signal processing techniques to create the capabilities needed for broadband high data rate signals.

Figure 1 shows a typical RF/IF section for a transceiver. In the transmit path inphase and quadrature (I&Q) signals are upconverted to an IF, and then converted to RF and amplified for transmission. In the receive path the data is taken from the antenna at RF, filtered, amplified, and downconverted for baseband processing. The transceiver provides power control, timing and synchronization, and frequency information. When multicarrier modulation is used, frequency information is crucial. If the data is not synchronized properly the transceiver will not be able to decode it.

From a high level, the structure of the RF/IF portions of the mobile and base station are similar, however, there are significant differences in their architectures and performance requirements. Key drivers for both are performance and cost; mobiles also need to consider power consumption and size.

4G processing

Figure 2 shows a high-level block diagram of the transceiver baseband processing section. Given that 4G is based on a multicarrier technique, key baseband components for the transmitter and receiver are the FFT and its inverse (IFFT). In the transmit path the data is generated, coded, modulated, transformed, cyclically extended, and then passed to the RF/IF section. In the receive path the cyclic extension is removed, the data is transformed, detected, and decoded. If the data is voice, it goes to a vocoder. The baseband subsystem will be implemented with a number of ICs, including digital signal processors (DSPs), microcontrollers, and ASICs. Software, an important part of the transceiver, implements the different algorithms, coding, and overall state machine of the transceiver. The base station could have numerous DSPs. For example, if smart antennas are used, each user needs access to a DSP to perform the needed adjustments to the antenna beam.

Receiver section

4G will require an improved receiver section, compared to 3G, to achieve the desired performance in data rates and reliability of communication. As shown in Equation 3, Shannon's Theorem specifies the minimum required SNR for reliable communication:

(3)

where C is the channel capacity (which is the data rate), and BW is the bandwidth.

For 3G, using the 2-Mbps data rate in a 5-MHz bandwidth, the SNR is only 1.2 dB. In 4G, approximately 12-dB SNR is required for a 20-Mbps data rate in a 5-MHz bandwidth. This shows that for the increased data rates of 4G, the transceiver system must perform significantly better than 3G.

With any receiver, the main issues for efficiency and sensitivity are noise figure, gain, group delay, bandwidth, sensitivity, spurious rejection, and power consumption. 4G is no exception; the sensitivity can be determined as shown in Equation 4 :

(4)

where KTo is the thermal noise (for this equation it is -174 dBm), BW is the receiver bandwidth, NF is the receiver noise figure, and SNRavgMCM is the average SNR for a MCM system needed for an expected bit error rate.

For a 4G receiver using a 5-MHz RF bandwidth, 16 QAM modulation and NF of 3 dB, the receiver sensitivity is -87 dBm. For 3G, the receiver sensitivity needs to be -122 dBm; the difference is due to the

modulation and PAVR. This illustrates the need to reduce PAVR by clipping or coding. Also the gain is required to be linear, and the group delay must be flat over the bandwidth of the signal.

The receiver front end provides a signal path from the antenna to the baseband processor. It consists of a bandpass filter, a low-noise amplifier (LNA), and a downconverter. De-pending on the type of receiver there could be two downconversions (as in a super-hetrodyne receiver), where one downconversion converts the signal to an IF. The signal is then filtered and then downconverted to or near baseband to be sampled.

The other configuration has one downconversion, as in a homodyne (zero IF or ZIF) receiver, where the data is converted directly to baseband.The challenge in the receiver design is to achieve the required sensitivity, intermodulation, and spurious rejection, while operating at low power.

The first line of defense

The receiver bandpass filter is the first line of defense to eliminate unwanted interference and noise. This filter must be able to achieve the cutoff needed for each bandwidth. In a 4G implementation, the bandwidth could be as low as 5 MHz and as high as 20 MHz. If the filter were to be only 5-MHz wide, it would not have the capabilities to use the 20-MHz bandwidth. However, if the filter is 20-MHz wide and the signal is only 5-MHz wide, the extra interference would increase the noise and reduce sensitivity. This means that a tunable filter is needed. One option would be a bank of filters with different bandwidths, where selection is made based on the need.

A typical LNA has a noise figure of approximately 1 dB and a gain of about 20 dB. A trade-off is made between gain and noise to provide the best solution. The LNA sets the noise figure of the overall receiver, since it is one of the first components of the receiver. Because of the high PAVR of the signal, the LNA will also have to be very linear to minimize any extra distortion.

The downconverter section of the receiver will have to achieve good linearity and noise figure while consuming minimal power. A measure of the linearity in the mixer section is the spurious free dynamic range (SFDR). This is directly related to the second and third order intermodulation products also known as IP2 and IP3.

The analog-to-digital converter (ADC) is the key component that can break the new system. System issues of the ADC concern whether or not to use undersampling, the PAVR of the signal, the bandwidth, and the sampling rate. For a 5-MHz bandwidth signal a typical sampling rate would be 20 MHz. If IF sampling is used, the aperture uncertainty or jitter must be low enough to prevent errors.

The next requirement is the dynamic range. For an MCM system using the theoretical PAVR for a 512-point IFFT, the dynamic range required would be 80 dB, which is equal to 13 bits. This relationship is demonstrated in Equation 5, which shows quantization noise,determined from the link budget as follows:

(5)

The desired quantization noise is determined by the average ratio of average signal power to average noise spectrum density measured in dB (Eb/No) for the subcarriers, the data rate (DR), and backoff (which is generally 15 dB). The constant 20 dB is added to the end to put the quantization noise 20 dB lower than the system noise. The number of bits can be calculated as shown in Equation 6.

(6)

In this equation, fs is the sampling rate. If the signal has interference or blocking, the ADC requires additional bits. The required dynamic range of the ADC could increase from 15 to 17 bits.

Baseband processing

The error correction coding of 4G has not yet been proposed, however, it is known that 4G will provide different levels of QoS, including data rates and bit error rates. It is likely that a form of concatenated coding will also be used, and this could be a turbo code as used in 3G, or a combination of a block code and a convolutional code. This increases the complexity of the baseband processing in the receive section.

4G baseband signal-processing components will include ASICs, DSPs, microcontrollers, and FPGAs. The receiver will take the data from the ADC, and then use it to detect the proper signals. Baseband processing techniques such as smart antennas and multi-user detection will be required to reduce interference.

MCM is a baseband process. The subcarriers are created using IFFT in the transmitter, and FFT is used in the receiver to recover the data. A fast DSP is needed for parsing and processing the data.

Different algorithms can be used to create a smart antenna; the goal is to improve the signal by adjusting the beam pattern of the antennas. The number of DSPs needed to implement an smart antenna depends on the type of algorithm used. The two basic types of smart antenna are switched-beam antennas and adaptive arrays. The former selects a beam pattern from a set of predetermined patterns, while the latter dynamically steers narrow beams toward multiple users. Generally speaking, SA is more likely be used in a base station than a mobile, due to size and power restrictions.

Multi-user detection (MUD) is used to eliminate the multiple access interference (MAI) present in CDMA systems. Based on the known spreading waveform for each user, MUD determines the signal from other users and can eliminate this from the desired signal. Mobile devices do not normally contain the spreading codes of the other users in the cell, so MUD will likely be implemented only in base stations, where it can improve the capacity of the reverse (mobile-to-base) link.

Transmitter section

The purpose of the transmitter is to generate and send information. As the data rate for 4G increases, the need for a clean signal also increases. One way to increase capacity is to increase frequency reuse. As the cell size gets smaller to accommodate more frequency reuse, smaller base stations are required. Smaller cell sizes need less transmit power to reach the edge of the cell, though better system engineering is required to reduce intra-cell interference.

One critical issue to consider is spurious noise. The regulatory agencies have stringent requirements on the amount of unwanted noise that can be sent out of the range of the spectrum allocated. In addition, excess noise in the system can seriously diminish the system's capacity.

With the wider bandwidth system and high PAVR associated with 4G, it will be difficult to achieve good performance without help of linearity techniques (for example, predistortion of the signal to the PA). To effectively accomplish this task, feedback between the RF and baseband is required. The algorithm to perform the feedback is done in the DSP, which is part of the baseband data processing.

Power control will also be important in 4G to help achieve the desired performance; this helps in controlling high PAVR - different services need different levels of power due to the different rates and QoS levels required. Therefore, power control needs to be a very tight, closed loop. Baseband processing is just as critical whether dealing with the receiver or transmitter sections. As we've seed, RF and baseband work in tandem to produce 4G signals. The baseband processing of a 4G transmitter will obviously be more complicated than in a 3G design. Let's consider the chain of command.

The digital-to-analog converter (DAC) is an important piece of the transmit chain. It requires a high slew rate to minimize distortion, especially with the high PAVR of the MCM signals. Generally, data is oversampled 2.5 to 4 times; by increasing the oversampling ratio of the DAC, the step size between samples decreases. This minimizes distortion.

In the baseband processing section of the transmit chain, the signal is encoded, modulated, transformed using an IFFT, and then a cyclic extension is added. Dynamic packet assignment or dynamic frequency selection are techniques which can increase the capacity of the system. Feedback from the mobile is needed to accomplish these techniques. The baseband processing will have to be fast to support the high data rates.

Even as 3G begins to roll out, system designers and services providers are looking forward to a true wireless broadband cellular system, or 4G. To achieve the goals of 4G, technology will need to improve significantly in order to handle the intensive algorithms in the baseband processing and the wide bandwidth of a high PAVR signal. Novel techniques will also have to be employed to help the system achieve the desired capacity and throughput. High-performance signal processing will have to be used for the antenna systems, power amplifier, and detection of the signal.

Michael LeFevre is a system engineer in broadband communications in Motorola's Wireless Infrastructure Systems Group Division. He holds a MSEE from Brigham Young University in Provo, Utah. He can be reached at michael.lefevre@motorola.com.

Peter Okrah received his Ph.D. in electrical engineering from Stanford University. He is the Manager of 4G systems technologies research of the Wireless Infrastructure Systems Division of the Motorola Semiconductor Products Sector, Tempe, Arizona. He can be reached at at peter.okrah@motorola.com

NewThis article is about the mobile phone standard. For other uses, see 4G (disambiguation).

4G (also known as Beyond 3G), an abbreviation for Fourth-Generation, is a term used to describe the next complete evolution in wireless communications. A 4G system will be able to provide a comprehensive IP solution where voice, data and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at higher data rates than previous generations.

As the second generation was a total replacement of the first generation networks and handsets; and the third generation was a total replacement of second generation networks and handsets; so too the fourth generation cannot be an incremental evolution of current 3G technologies, but rather the total replacement of the current 3G networks and handsets. The international telecommunications regulatory and standardization bodies are working for commercial deployment of 4G networks roughly in the 2012-2015 time scale. At that point it is predicted that even with current evolutions of third generation 3G networks, these will tend to be congested.

There is no formal definition for what 4G is; however, there are certain objectives that are projected for 4G. These objectives include: that 4G will be a fully IP-based integrated system. 4G will be capable of providing between 100 Mbit/s and 1 Gbit/s speeds both indoors and outdoors, with premium quality and high security. [1]

Many companies have taken self-serving definitions and distortions about 4G to suggest they have 4G already in existence today, such as several early trials and launches of WiMAX. Other companies have made prototype systems calling those 4G. While it is possible that some currently demonstrated technologies may become part of 4G, until the 4G standard or standards have been defined, it is impossible for any company currently to provide with any certainty wireless solutions that could be called 4G cellular networks that would conform to the eventual international standards for 4G. These confusing statements around "existing" 4G have served to confuse investors and analysts about the wireless industry.

Contents

[hide] 1 Objective and approach

o 1.1 Objectives o 1.2 Approaches

1.2.1 Consideration points

1.2.2 Principal technologies 2 Wireless System Evolution 3 Components

o 3.1 Access schemes o 3.2 IPv6 o 3.3 Advanced Antenna Systems o 3.4 Software-Defined Radio (SDR)

4 Developments 5 Applications 6 Pre-4G wireless standards 7 4G wireless standards 8 4G Technology Demonstrations 9 See also 10 References

o 10.1 Citations

o 10.2 Additional resources

[edit] Objective and approach

[edit] Objectives

4G is being developed to accommodate the quality of service (QoS) and rate requirements set by forthcoming applications like wireless broadband access, Multimedia Messaging Service (MMS), video chat, mobile TV, HDTV content, Digital Video Broadcasting (DVB), minimal service like voice and data, and other streaming services for "anytime-anywhere". The 4G working group has defined the following as objectives of the 4G wireless communication standard:

A spectrally efficient system (in bits/s/Hz and bits/s/Hz/site),[2] High network capacity: more simultaneous users per cell,[3] A nominal data rate of 100 Mbit/s while the client physically moves at high speeds

relative to the station, and 1 Gbit/s while client and station are in relatively fixed positions as defined by the ITU-R,[1]

A data rate of at least 100 Mbit/s between any two points in the world,[1] Smooth handoff across heterogeneous networks,[4] Seamless connectivity and global roaming across multiple networks,[5] High quality of service for next generation multimedia support (real time audio, high

speed data, HDTV video content, mobile TV, etc)[5] Interoperability with existing wireless standards,[6] and An all IP, packet switched network.[5]

In summary, the 4G system should dynamically share and utilise network resources to meet the minimal requirements of all the 4G enabled users.

[edit] Approaches

As described in 4G consortia including WINNER, WINNER - Towards Ubiquitous Wireless Access, and WWRF, a key technology based approach is summarized as follows, where Wireless-World-Initiative-New-Radio (WINNER) is a consortium to enhance mobile communication systems.[7][8]

[edit] Consideration points

Coverage, radio environment, spectrum, services, business models and deployment types, users

[edit] Principal technologies

Baseband techniques[9] o OFDM : To exploit the frequency selective channel property o MIMO : To attain ultra high spectral efficiency o Turbo principle : To minimize the required SNR at the reception side

Adaptive radio interface Modulation , spatial processing including multi-antenna and multi-user MIMO Relaying, including fixed relay networks (FRNs), and the cooperative relaying concept,

known as multi-mode protocol

It introduces a single new ubiquitous radio access system concept, which will be flexible to a variety of beyond-3G wireless systems.

[edit] Wireless System Evolution

First generation: Almost all of the systems from this generation were analog systems where voice was considered to be the main traffic. These systems could often be listened to by third parties. Some of the standards are NMT, AMPS, Hicap, CDPD, Mobitex, DataTac, TACS and ETACS.

Second generation: All the standards belonging to this generation are commercial centric and they are digital in form. Around 60% of the current market is dominated by European standards. The second generation standards are GSM, iDEN, D-AMPS, IS-95, PDC, CSD, PHS, GPRS, HSCSD, and WiDEN.

Third generation: To meet the growing demands in network capacity, rates required for high speed data transfer and multimedia applications, 3G standards started evolving. The systems in this standard are essentially a linear enhancement of 2G systems. They are based on two parallel backbone infrastructures, one consisting of circuit switched nodes, and one of packet oriented nodes. The ITU defines a specific set of air interface technologies as third generation, as part of the IMT-2000 initiative. Currently, transition is happening from 2G to 3G systems. As a part of this transition, numerous technologies are being standardized.

2.75G: o EDGE /EGPRS o CDMA2000 (1xRTT)

3G: o UMTS (W-CDMA) o CDMA2000 (1xEV-DO/IS-856) o FOMA o TD-SCDMA o GAN /UMA o WiMax

3.5G: o UMTS (HSDPA) o UMTS (HSUPA)

o CDMA2000 (EV-DO Rev.A) 3.75G

o UMTS (HSPA+) o CDMA2000 (EV-DO Rev.B/3xRTT)

4G: o Flash-OFDM o 3GPP LTE

Fourth generation: According to the 4G working groups, the infrastructure and the terminals of 4G will have almost all the standards from 2G to 4G implemented. Although legacy systems are in place to adopt existing users, the infrastructure for 4G will be only packet-based (all-IP). Some proposals suggest having an open platform where the new innovations and evolutions can fit. The technologies which are being considered as pre-4G are the following: Flash-OFDM, WiMax, WiBro, iBurst, and 3GPP Long Term Evolution. One of the first technology really fulfilling the 4G requirements as set by the ITU-R will be LTE Advanced as currently standardized by 3GPP. LTE Advanced will be an evolution of the 3GPP Long Term Evolution. Higher data rates are for instance achieved by the aggregation of multiple LTE carriers that are currently limited to 20MHz bandwidth[10].

[edit] Components

[edit] Access schemes

As the wireless standards evolved, the access techniques used also exhibited increase in efficiency, capacity and scalability. The first generation wireless standards used plain TDMA and FDMA. In the wireless channels, TDMA proved to be less efficient in handling the high data rate channels as it requires large guard periods to alleviate the multipath impact. Similarly, FDMA consumed more bandwidth for guard to avoid inter carrier interference. So in second generation systems, one set of standard used the combination of FDMA and TDMA and the other set introduced a new access scheme called CDMA. Usage of CDMA increased the system capacity and also placed a soft limit on it rather than the hard limit. Data rate is also increased as this access scheme is efficient enough to handle the multipath channel. This enabled the third generation systems to used CDMA as the access scheme IS-2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA. The only issue with CDMA is that it suffers from poor spectrum flexibility and scalability.

Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved FDMA and Multi-carrier code division multiple access (MC-CDMA) are gaining more importance for the next generation systems. WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is being considered for the downlink. By contrast, IFDMA is being considered for the uplink since OFDMA contributes more to the PAPR related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus avoids amplifier issues. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved.

The other important advantage of the above mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently requires high complexity equalization at the receiver.

In addition to improvements in these multiplexing systems, improved modulation techniques are being used. Whereas earlier standards largely used Phase-shift keying, more efficient systems such as 64QAM are being proposed for use with the 3GPP Long Term Evolution standards.

[edit] IPv6

Main articles: Network layer, Internet protocol, and IPv6

Unlike 3G, which is based on two parallel infrastructures consisting of circuit switched and packet switched network nodes respectively, 4G will be based on packet switching only. This will require low-latency data transmission.

By the time that 4G is deployed, the process of IPv4 address exhaustion is expected to be in its final stages. Therefore, in the context of 4G, IPv6 support is essential in order to support a large number of wireless-enabled devices. By increasing the number of IP addresses, IPv6 removes the need for Network Address Translation (NAT), a method of sharing a limited number of addresses among a larger group of devices.

In the context of 4G, IPv6 also enables a number of applications with better multicast, security, and route optimization capabilities. With the available address space and number of addressing bits in IPv6, many innovative coding schemes can be developed for 4G devices and applications that could aid deployment of 4G networks and services.

[edit] Advanced Antenna Systems

Main articles: MIMO and MU-MIMO

The performance of radio communications obviously depends on the advances of an antenna system, refer to smart or intelligent antenna. Recently, multiple antenna technologies are emerging to achieve the goal of 4G systems such as high rate, high reliability, and long range communications. In the early 90s, to cater the growing data rate needs of data communication, many transmission schemes were proposed. One technology, spatial multiplexing, gained importance for its bandwidth conservation and power efficiency. Spatial multiplexing involves deploying multiple antennas at the transmitter and at the receiver. Independent streams can then be transmitted simultaneously from all the antennas. This increases the data rate into multiple folds with the number equal to minimum of the number of transmit and receive antennas. This is called MIMO (as a branch of intelligent antenna). Apart from this, the reliability in transmitting high speed data in the fading channel can be improved by using more antennas at the transmitter or at the receiver. This is called transmit or receive diversity. Both transmit/receive diversity and transmit spatial multiplexing are categorized into the space-time coding techniques, which does not necessarily require the channel knowledge at the transmit. The other category is closed-loop multiple antenna technologies which use the channel knowledge at the transmitter.

[edit] Software-Defined Radio (SDR)

SDR is one form of open wireless architecture (OWA). Since 4G is a collection of wireless standards, the final form of a 4G device will constitute various standards. This can be efficiently realized using SDR technology, which is categorized to the area of the radio convergence.

[edit] Developments

The Japanese company NTT DoCoMo has been testing a 4G communication system prototype with 4x4 MIMO called VSF-OFCDM at 100 Mbit/s while moving, and 1 Gbit/s while stationary. NTT DoCoMo recently reached 5 Gbit/s with 12x12 MIMO while moving at 10 km/h,[11] and is planning on releasing the first commercial network in 2010.

Digiweb, an Irish fixed and wireless broadband company, has announced that they have received a mobile communications license from the Irish Telecoms regulator, ComReg. This service will be issued the mobile code 088 in Ireland and will be used for the provision of 4G Mobile communications.[12][13]. Digiweb launched a mobile broadband network using FLASH-OFDM technology at 872 MHz.

Pervasive networks are an amorphous and at present entirely hypothetical concept where the user can be simultaneously connected to several wireless access technologies and can seamlessly move between them (See handover, IEEE 802.21). These access technologies can be Wi-Fi, UMTS, EDGE, or any other future access technology. Included in this concept is also smart-radio (also known as cognitive radio technology) to efficiently manage spectrum use and transmission power as well as the use of mesh routing protocols to create a pervasive network.

Sprint plans to launch 4G services in trial markets by the end of 2007 with plans to deploy a network that reaches as many as 100 million people in 2008 and has also announced WiMax service called Xohm. Tested in Chicago, this speed was clocked at 100 Mbit/s.

Verizon Wireless announced on September 20, 2007 that it plans a joint effort with the Vodafone Group to transition its networks to the 4G standard LTE. The time of this transition has yet to be announced.

The German WiMAX operator Deutsche Breitband Dienste (DBD) has launched WiMAX services (DSLonair) in Magdeburg and Dessau. The subscribers are offered a tariff plan costing 9.95 euros per month offering 2 Mbit/s download / 300 kbit/s upload connection speeds and 1.5 GB monthly traffic. The subscribers are also charged a 16.99 euro one-time fee and 69.90 euro for the equipment and installation.[14] DBD received additional national licenses for WiMAX in December 2006 and have already launched the services in Berlin, Leipzig and Dresden.

American WiMAX services provider Clearwire made its debut on Nasdaq in New York on March 8, 2007. The IPO was underwritten by Merrill Lynch, Morgan Stanley and JP Morgan. Clearwire sold 24 million shares at a price of $25 per share. This adds $600 million in cash to Clearwire, and gives the company a market valuation of just over $3.9 billion.[15]

Canadian Wireless Provider TELUS announced that they will be cooperating with BELL CANADA to the next step in its evolution towards building a fourth generation (4G) wireless broadband network, the most advanced mobile broadband network in Canada. This new wireless network, based on the latest generation of High Speed Packet Access (HSPA) technology, will enable TELUS to easily transition to long term evolution (LTE) technology, the emerging worldwide LTE technology standard. The new network will 'futureproof' our technology and position TELUS for an easy transition to LTE/4G technology.

Building will begin immediately and is expected to be complete by early 2010. When up and running, it will be one of the leading networks in the world..[16]

[edit] Applications

At the present rates of 15-30 Mbit/s, 4G is capable of providing users with streaming high-definition television, but the typical cellphone's or smartphone's 2" to 3" screen is a far cry from

the big-screen televisions and video monitors that got high-definition resolutions first and which suffer from noticeable pixelation much more than the typical 2" to 3" screen. A cellphone may transmit video to a larger monitor, however. At rates of 100 Mbit/s, the content of a DVD-5 (for example a movie), can be downloaded within about 5 minutes for offline access.

However, how cellphone companies might market 4G as a killer application for most cellphone users is unknown. Existing 2.5G/3G/3.5G phone operator based services are often limited in application (see "walled garden"), and the majority of cellphone users in industrialized nations do not purchase even this slower-speed Internet access. However, 4G's improved bandwidths might provide opportunities for previously impossible products and services to be released, and higher bandwidth for a given cost should be achieved.

[edit] Pre-4G wireless standards

See also section 3G evolution (pre-4G) of the 3G article.

According to a Visant Strategies study there will be multiple competitors in this space:[17]

WiMAX - 7.5 million units by 2010 (May include fixed and mobile) Flash-OFDM - 13 million subscribers in 2010 (only Mobile) 3GPP Long Term Evolution of UMTS in 3GPP - valued at US$2 billion in 2010 (~30%

of the world population) UMB in 3GPP2 - abandoned by Qualcomm in November 2008, now supporting LTE

instead. IEEE 802.20

Fixed WiMax and Mobile WiMax are different systems, as of July 2007, all the deployed WiMax is "Fixed Wireless" and is thus not yet 4G (IMT-advanced) although it can be seen as one of the 4G standards being considered.

[edit] 4G wireless standards

3GPP is currently standardizing LTE Advanced as future 4G standard. A first set of 3GPP requiremens on LTE Advanced has been approved in June 2008[18]. The working groups are currently evaluating various proposals for standardization. LTE Advanced will be standardized as part of the Release 10 of the 3GPP specification.

[edit] 4G Technology Demonstrations

In February 2007 NTT DoCoMo announced the completion of a 4G trial where they achieved a maximum packet transmission rate of approximately 5Gbps in the downlink using 100MHz frequency bandwidth to a mobile station moving at 10km/h[19

New2

Excerpt: 3G and WiMAX Deployment

The wide-area wireless industry is divided into three major technology families: GSM, CDMA, and WiMAX. GSM and CDMA span 2G to 4G platforms, while WiMAX spans 3G to 4G platforms.

Though 4G technical requirements do not yet exist, and no specified wireless technology actually meets such

requirements, the industry refers to technologies as 4G platforms if they?re likely to be able to meet expected 4G requirements, namely extremely high throughput rates of up to 1 Gbps peak in very wide radio channels of up to 100 MHz.

The GSM family is most broadly deployed in the world. At the end of 2007, 3G Americas reported 2.7 billion subscribers, 263 EDGE networks, 193 UMTS networks, 152 HSDPA networks, and 400 UMTS/HSDPA devices. EDGE (Enhanced Data Rates for GSM Evolution) provides data capabilities for GSM networks, whereas HSDPA (High Speed Downlink Packet Access) supplies enhanced data service for UMTS (Universal Mobile Telecommunications System) networks.

UMTS/HSDPA is a 3G technology.The successor to UMTS is a technology called 3GPP LTE (Third-Generation Partnership Project Long-Term Evolution).The leading GSM/UMTS operators in the U.S. are AT&T (previously Cingular) and T-Mobile. GSM/EDGE provides the broadest coverage, whereas UMTS/HSDPA is available in most major metropolitan areas, and multimode devices can access either network. LTE won?t happen until next decade.

The CDMA2000 family also has a strong global presence, though nowhere near the scope of GSM/UMTS. At the end of 2007, the CDMA Developer Group reported 400 million CDMA2000 subscribers and 83 million EVDO subscribers, 241 1X networks, and 95 commercial EVDO networks.

1X provides voice and data service and has widespread coverage, while EVDO, a higherspeed 3G technology, is available in most metropolitan areas.The successor to CDMA is a technology called Ultra Mobile Broadband (UMB).The leading CDMA2000 operators in the U.S. are Verizon, Sprint, and Alltel. Like LTE, UMB won?t be available until next decade.