It has not been long since we saw the first WiMax implementation. And even as we are getting a feel of it Wimax 2 has been announced. A consortium WCI has been announced which will strive for meeting the standards set by WiMax 2. The WCI (WiMAX 2 Collaboration Initiative ) is an initiative lead by leading WiMAX™ silicon suppliers, equipment makers and research organizations to accelerate interoperability of WiMAX 2 based on the IEEE 802.16m standard.
What is WiMax 2?
WiMAX 2 is the next phase of WiMAX technology which is based on the IEEE 802.16m standard. This standard has been built upon the existing 802.16e standard by adding new capabilities while maintaining backward compatibility. Yes, WiMax 2 will be backward compatible to the existing WiMax standard. WiMAX 2 offers higher system capacity with peak rates of more than 300 Mbps, lower latency and increased VoIP capacity, meeting the International Telecommunications Union (ITU) requirements for 4G technology.WiMAX forum vice president Mohammad Shakouri says the goal is for the new WiMAX standard to deliver average downlink speeds of more than 100Mbps to users. 802.16m amendment will provide the basis for WiMAX System Release 2 and provide existing WiMAX operators a graceful migration path to gain performance enhancements and add new services. IEEE 802.16m specification is expected to be completed by end of the in the 3rd quarter of 2010.
Improvements
WiMax 2 is expected to offer improved performance in areas like
• Coverage and Spectral Efficiency
• Power Conservation
• Data Capacity and VoIP capabilities
• Lower Latency and QoS Enhancements
• Inter-working with other Wireless Networks
• Multi-carrier support
• GPS based services
• Self-Organizing network features
Future of WiMAX
According to WiMAX forum, nearly 45 companies have actively supported IEEE 802.16m as an IMT-Advanced technology alternative. It is widely expected that both LTE-Advanced and 802.16m will be included. The performance enhancements defined in IEEE 802.16m build on the capabilities established with IEEE 802.16e-2005, which has 4 years of worldwide, field-proven experience. This assures backwards compatibility, hence WiMAX System Release 2 will provide a graceful migration path for today’s WiMAX operators. This also provides them the confidence that they have selected a proven technology that is structured to meet current and future network demands. With this evolutionary growth path, the WiMAX technology is well-positioned to
meet the challenges and demands anticipated for the next generation of mobile networks.
Ref: www.wimaxforum.org
Showing posts with label mobile WiMAX. Show all posts
Showing posts with label mobile WiMAX. Show all posts
Tuesday, May 11, 2010
Wednesday, February 3, 2010
LTE is IMT advanced - 3GPP
In September 2009 the 3GPP Partners made a formal submission to the ITU proposing that LTE Release 10 and successors (called LTE-Advanced) be evaluated as a candidate for IMT-Advanced. This suggests that the next generation or truly 4G mobile WiMAX is likely to be a specification that is never implemented on a significant scale. This news may be confusing to those who thought that lot of operators have already deployed "4G" WiMAX networks. Since the backwards compatibility of 802.16m with current 802.16e is being emphasized, the hopes that somehow LTE and mobile WiMAX might be merged, or that the latter could become the TDD version of LTE has been put to rest. Operators now installing and committed to 802.16e should be very wary about the long term roadmap for mobile WiMAX technology. They should ensure that they do not lock themselves into this technology for very long, and should be preparing paths for migration to LTE. Intel has been a champion of WiMAX since its inception. But Intel’s future in mobile product markets is much more dependent upon its ability to carve out a substantial share for its low power processors in this business and to have its components incorporated into devices that will work on 3GPP networks, than it is upon the supply of chipsets for WiMAX wireless modems. LTE supports voice and efficient support of voice was one of the key considerations in designing LTE. The voice solution for LTE is IMS VoIP and it is fully specified.
Monday, December 21, 2009
OFDM - Accelerating data rates
Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system. Each signal travels within its own unique frequency range (carrier), which is modulated by the data. Orthogonal FDM (OFDM) spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality" in this technique which prevents the demodulators from seeing frequencies other than their own. It is identical to Coded FDM and the Discrete Multitone (DMT) modulation.
Orthogonality
In OFDM, the sub-carrier frequencies are chosen so that the sub-carriers are orthogonal to each other, meaning that cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and the receiver. A separate requirement for different filters is thus eliminated. This results in high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. But this also means high accuracies in synchronization between transmitter and receiver is required.
OFDM exhibits lower multi-path distortion (delay spread), since the sub-signals are sent at lower data rates. Because of the lower data rate transmissions, multi-path-based delays are not nearly as significant as they would be with a single-channel high-rate system. For example, a narrow band signal sent at a high rate over a single channel will likely experience greater negative effects from delay spread because the transmitted symbols are closer together. In fact, the information content of a narrow band signal can be completely lost at the receiver if the multi path distortion causes the frequency response to have a null at the transmission frequency. The use of the multi-carrier OFDM significantly reduces this problem.
Simple Implementation
The orthogonality allows for efficient modulator and demodulator implementation using the FFT algorithm on the receiver side, and inverse FFT on the sender side. Although the principles and some of the benefits have been known since the 1960s, OFDM is popular for wideband communications today by way of low-cost digital signal processing components that can efficiently calculate the FFT.
Elimination of intersymbol interference
One key principle of OFDM is that since low symbol rate modulation schemes i.e. where the symbols are relatively long compared to the channel time characteristics suffer less from inter symbol interference caused by multi path propagation, it is advantageous to transmit a number of low-rate streams in parallel instead of a single high-rate stream. Since the duration of each symbol is long, it is feasible to insert a guard interval between the OFDM symbols, thus eliminating the inter symbol interference. The cyclic prefix, which is transmitted during the guard interval, consists of the end of the OFDM symbol copied into the guard interval, and the guard interval is transmitted followed by the OFDM symbol. The reason that the guard interval consists of a copy of the end of the OFDM symbol is so that the receiver will integrate over an integer number of sinusoid cycles for each of the multi paths when it performs OFDM demodulation with the FFT.
Simplified equalization
The effects of frequency-selective channel conditions, for example fading caused by multipath propagation, can be considered as constant (flat) over an OFDM sub-channel if the sub-channel is sufficiently narrow-banded, i.e. if the number of sub-channels is sufficiently large. This makes equalization far simpler at the receiver in OFDM in comparison to conventional single-carrier modulation. The equalizer only has to multiply each detected sub-carrier (each Fourier coefficient) by a constant complex number, or a rarely changed value.
Importance of channel coding
Channel coding is used in most cases of digital communication and especially in case of mobile communication. Channel coding implies that each bit of information to be transmitted is spread over several, often very many, code bits. If these coded bits are then, via modulation symbols, mapped to a set of OFDM subcarriers that are well distributed over the overall transmission bandwidth of the OFDM signal, each information bit will experience frequency diversity in case of transmission over a radio channel that is frequency selective over the transmission bandwidth, despite the fact that the subcarriers, and thus also the code bits, will not experience any frequency diversity. Thus, in contrast to the transmission of a single wideband carrier, channel coding (combined with frequency interleaving) is an essential component in order for OFDM transmission to be able to benefit from frequency diversity on a frequency-selective channel.
OFDM for Access control
OFDM can also be used as a user-multiplexing or multiple-access scheme, allowing for simultaneous frequency-separated transmissions to/from multiple mobile terminals. In the downlink direction, OFDM as a user-multiplexing scheme implies that, in each OFDM symbol interval, different subsets of the overall set of available subcarriers are used for transmission to different mobile terminals. Similarly, in the uplink direction, OFDM as a user-multiplexing or multiple access scheme implies that, in each OFDM symbol interval, different subsets of the overall set of subcarriers are used for data transmission from different mobile terminals.
Issues
A drawback of OFDM modulation, as well as any kind of multi-carrier transmission, is the large variations in the instantaneous power of the transmitted signal. Such power variations imply a
reduced power-amplifier efficiency and higher power-amplifier cost. This is especially critical for the uplink, due to the high importance of low mobile-terminal power consumption and cost. Several methods have been proposed on how to reducethe large power variations of an OFDM signal. However, most of these methods have limitations in terms of to what extent the power variations can be reduced. Furthermore, most of the methods also imply a significant computational complexity and/or a reduced link performance.
Orthogonality
In OFDM, the sub-carrier frequencies are chosen so that the sub-carriers are orthogonal to each other, meaning that cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and the receiver. A separate requirement for different filters is thus eliminated. This results in high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. But this also means high accuracies in synchronization between transmitter and receiver is required.
OFDM exhibits lower multi-path distortion (delay spread), since the sub-signals are sent at lower data rates. Because of the lower data rate transmissions, multi-path-based delays are not nearly as significant as they would be with a single-channel high-rate system. For example, a narrow band signal sent at a high rate over a single channel will likely experience greater negative effects from delay spread because the transmitted symbols are closer together. In fact, the information content of a narrow band signal can be completely lost at the receiver if the multi path distortion causes the frequency response to have a null at the transmission frequency. The use of the multi-carrier OFDM significantly reduces this problem.
Simple Implementation
The orthogonality allows for efficient modulator and demodulator implementation using the FFT algorithm on the receiver side, and inverse FFT on the sender side. Although the principles and some of the benefits have been known since the 1960s, OFDM is popular for wideband communications today by way of low-cost digital signal processing components that can efficiently calculate the FFT.
Elimination of intersymbol interference
One key principle of OFDM is that since low symbol rate modulation schemes i.e. where the symbols are relatively long compared to the channel time characteristics suffer less from inter symbol interference caused by multi path propagation, it is advantageous to transmit a number of low-rate streams in parallel instead of a single high-rate stream. Since the duration of each symbol is long, it is feasible to insert a guard interval between the OFDM symbols, thus eliminating the inter symbol interference. The cyclic prefix, which is transmitted during the guard interval, consists of the end of the OFDM symbol copied into the guard interval, and the guard interval is transmitted followed by the OFDM symbol. The reason that the guard interval consists of a copy of the end of the OFDM symbol is so that the receiver will integrate over an integer number of sinusoid cycles for each of the multi paths when it performs OFDM demodulation with the FFT.
Simplified equalization
The effects of frequency-selective channel conditions, for example fading caused by multipath propagation, can be considered as constant (flat) over an OFDM sub-channel if the sub-channel is sufficiently narrow-banded, i.e. if the number of sub-channels is sufficiently large. This makes equalization far simpler at the receiver in OFDM in comparison to conventional single-carrier modulation. The equalizer only has to multiply each detected sub-carrier (each Fourier coefficient) by a constant complex number, or a rarely changed value.
Importance of channel coding
Channel coding is used in most cases of digital communication and especially in case of mobile communication. Channel coding implies that each bit of information to be transmitted is spread over several, often very many, code bits. If these coded bits are then, via modulation symbols, mapped to a set of OFDM subcarriers that are well distributed over the overall transmission bandwidth of the OFDM signal, each information bit will experience frequency diversity in case of transmission over a radio channel that is frequency selective over the transmission bandwidth, despite the fact that the subcarriers, and thus also the code bits, will not experience any frequency diversity. Thus, in contrast to the transmission of a single wideband carrier, channel coding (combined with frequency interleaving) is an essential component in order for OFDM transmission to be able to benefit from frequency diversity on a frequency-selective channel.
OFDM for Access control
OFDM can also be used as a user-multiplexing or multiple-access scheme, allowing for simultaneous frequency-separated transmissions to/from multiple mobile terminals. In the downlink direction, OFDM as a user-multiplexing scheme implies that, in each OFDM symbol interval, different subsets of the overall set of available subcarriers are used for transmission to different mobile terminals. Similarly, in the uplink direction, OFDM as a user-multiplexing or multiple access scheme implies that, in each OFDM symbol interval, different subsets of the overall set of subcarriers are used for data transmission from different mobile terminals.
Issues
A drawback of OFDM modulation, as well as any kind of multi-carrier transmission, is the large variations in the instantaneous power of the transmitted signal. Such power variations imply a
reduced power-amplifier efficiency and higher power-amplifier cost. This is especially critical for the uplink, due to the high importance of low mobile-terminal power consumption and cost. Several methods have been proposed on how to reducethe large power variations of an OFDM signal. However, most of these methods have limitations in terms of to what extent the power variations can be reduced. Furthermore, most of the methods also imply a significant computational complexity and/or a reduced link performance.
Sunday, September 6, 2009
Next generation Mobile WiMAX
WiMAX, meaning Worldwide Interoperability for Microwave Access, is a telecommunications technology that provides wireless transmission of data using a variety of transmission modes, from point-to-multi-point links to portable and fully mobile internet access. Mobile WiMAX enables the convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. The next-generation mobile WiMAX will be capable of data-transfer rates in excess of 1 Gbps. It is expected to support a wide range of high quality and high capacity IP-based services and applications while maintaining full backward compatibility with the existing mobile WiMAX systems.
Architecture features
IEEE 802.16m (new version of the 802.16) uses OFDMA as the multiple access scheme in the DownLink and UpLink. It supports both time-division duplex (TDD) and frequency-division duplex (FDD) schemes including the half-duplex FDD (HFDD) operation of the mobile stations in the FDD networks. The frame structure attributes and base-band processing are common for both duplex schemes. The modulation schemes supported include quadrature-phase shift-
keying (QPSK), 16-QAM, and 64-QAM.To overcome the issue of performance of adaptive modulation, a constellation rearrangement scheme is utilized. The next generation mobile Wimax suppports advanced multi-antenna techniques like single and multiuser MIMO, alongwith various transmit diversity schemes. The MAC features are an extension of the existing standard.
The next gen system is designed to provide state-of-the-art mobile broadband wireless access in the next decade and to satisfy the growing demand for advanced wireless multimedia applications and services.
Architecture features
IEEE 802.16m (new version of the 802.16) uses OFDMA as the multiple access scheme in the DownLink and UpLink. It supports both time-division duplex (TDD) and frequency-division duplex (FDD) schemes including the half-duplex FDD (HFDD) operation of the mobile stations in the FDD networks. The frame structure attributes and base-band processing are common for both duplex schemes. The modulation schemes supported include quadrature-phase shift-
keying (QPSK), 16-QAM, and 64-QAM.To overcome the issue of performance of adaptive modulation, a constellation rearrangement scheme is utilized. The next generation mobile Wimax suppports advanced multi-antenna techniques like single and multiuser MIMO, alongwith various transmit diversity schemes. The MAC features are an extension of the existing standard.
The next gen system is designed to provide state-of-the-art mobile broadband wireless access in the next decade and to satisfy the growing demand for advanced wireless multimedia applications and services.
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