Abstract: The nomadic and mobile broadband wireless access will become an important future market demand for communications. WiMax (802.16d / e) is dedicated to the development of this demand, performance, high efficiency and low cost. The flexible system can be configured to meet the requirements of various application scenarios. The basic technology is mainly: Fast planning and scheduling, burst packet data to achieve shared wireless link consisting of multiple sub-channel; adaptive modulation and coding; fast automatic re. the further use of MIMO and other space time processing techniques to improve performance .3 G business needs in accordance with the design of voice-based, connection-oriented, to provide fixed-bandwidth channels for IP packet data burst efficiency is very low. In order to enter the broadband wireless access market, 3GPP development was referred to as 3.5G's HSPA (1xEV DO), can greatly improve the packet data transmission rate. In order to compete with WiMax in late 2004 decided to develop long-term evolution of 3GPP plans LTE, the indicators and with the WiMax technology is similar can be said the same thing. face competition on the LTE, WiMax broadband wireless access market in order to a place must have good frequency, the use of terrestrial television broadcasting frequencies to provide large area coverage and lower costs will greatly increase the competitiveness of WiMax.
Keywords WiMax ; 802.16d / e; 3G; HSDPA; HSUPA; OFDMA
1 Introduction
With the development of PDA and the popularity of notebook computers, users want to anytime, anywhere Internet access, a new market mm into the common core network, service support, and AAA systems. broadband wireless access rate required to achieve a few hundred kbit / s or even tens of Mbit / s, the terminal is mainly laptops and PDA.
current 2.5G/3G Mobile Phone data services and broadband wireless access are two different market segments. mobile data business is basically a private network, download speeds in the 100 kbit / s or less. smart phones can access the Internet, but the performance is not satisfactory without the formation of mainstream .3 G system can not effectively meet the needs of this market. At present 3G mobile communication is the 3.5G (HSDPA / EV-DO) evolution, began to enter the broadband wireless access market.
WiMax by IEEE 802.16d / e is fixed (nomadic ) / mobile broadband wireless metropolitan area network, the radio link layer of the physical layer and MAC has been specifically designed to meet the sudden type of packet data services, to adaptive wireless channel environment, and the core network is a standard IP network. IEEE 802.21 was developed 802 series to solve a variety of wired / wireless, fixed / mobile network (Wi-Fi,, WiMax and fixed Ethernet, etc.) and cellular mobile communication protocol between the IP-based mobile roaming and handover issues. this system meet the IP of the technology trends, with superior performance.
3G systems to support IP data services in the spectrum of low efficiency because of its connection-oriented structure of the fixed bandwidth, burst not meet the demand for IP data services. To this end , added in the 3GPP R5 High Speed Downlink Packet Access (HSDPA, known as 3.5G), the rate can be achieved under good 10Mbit / s or more. will increase further in the R6 High Speed Uplink Packet Access (HSUPA), All IP core network is also to network evolution. To be able to compete with WiMax, 3GPP in late 2004 decided to develop long-term evolution of plans LTE (referred to as 3.9G).
2 fixed (nomadic) / mobile broadband wireless access 802.16d / e
IEEE 802 working group in its 802.3 Ethernet working group within the parallel development of a series of fixed / mobile broadband wireless access technologies, including 802.11 wireless LANs, wireless personal area network 802.15, and 802.16 wireless metropolitan area network Wireless wide area network 802.20. their radio link layer of the physical layer and MAC has been specifically designed to meet the sudden type of packet data service, adaptive wireless channel environment, and shared core network is a standard IP network. IEEE 802.21 was developed to solve 802 series of the above, and fixed Ethernet access networks and cellular mobile communication network based on mobile IP protocol between the roaming and handover issues. This system was in compliance and IP based NGN technology trends, with superior performance. 802.16 wireless metropolitan area network to provide point to point first sight wireless high-speed links, Link will use to cook with 802.11a wireless access hotspots to connect to the Internet, but also links to companies and families to a wired backbone environment. operating frequency of 10 ~ 60GHz. for further development to-multipoint, non-sight broadband wireless access network, 802.16a, cable modem and DSL can be used as a supplement to provide fixed wireless broadband access, frequency reduced to 2 ~ 11GHz. was further improved to become 802.16 d, and then further developed into mobile applications to support 802.16e, frequency reduced to 2 ~ 6 GHz.
802.16d / e runtime environment with reference to 3GPP (ETSI TR 101 112) operating environment is defined:
1 ) indoor environment, indoor use of pico-cell base stations, coverage radius (r) <100 m;
2) outdoor to indoor and nomadic, the use of micro-cell, 100 m 3) and high antenna inside the vehicle, the use of macro-cell, coverage radius (r)> 1000 m;
4) mixed, macro-cell and micro-cell overlap.
802.16 There are several different physical layer options for cellular use, suitable for different applications, frequency plans and policies.
1) OFDM (WirelessMAN-OFDM air interface) 256-point FFT, using time division multiple access TDMA (TDD TDD / FDD Frequency Division Duplex ).
2) OFDMA (WirelessMAN-OFDMA air interface) 2048 point FFT, uses orthogonal frequency division multiple access OFDMA (TDD / FDD).
3) single-carrier frequency (WirelessMAN-SCa. air interface) TDMA (TDD / FDD) BPSK, QPSK, 4-QAM, 16-QAM, 64-QAM, 256-QAM. most manufacturers use the frequency domain equalizer compensation for multipath interference caused by frequency decline to address the problem of channel equalization.
Single carrier frequency of the transmission system is mainly used for point to point, does not meet the demand for broadband access.
present, most commercial systems use 256OFDM, multiple access with TDMA. This method is simple and easy to implement. However, due to the client terminal transmit power by the peak average power ratio (PAR) constraints, the radio link must use an outdoor antenna gain is not enough to provide gain over ten db (such as 3.5GHz fixed broadband wireless access), because of the need to use an outdoor antenna, in fact, such systems can not support nomadic laptop mobile broadband wireless access applications. As most of the WiMax equipment maker is from the original 3.5 GHz fixed wireless access equipment manufacturers turn to, so most of the current WiMax products in this category, can not support the nomadic laptop application.
for nomadic / mobile broadband wireless access systems require the application of orthogonal frequency division multiple access OFDMA.OFDMA combination of time division and frequency division multiple access technology. the client terminal in the uplink sub-set using only a few frequency, transmission power can be concentrated in these sub-carrier frequency, the increase more than ten dB SNR to meet the laptop needs 0dB antenna indoor reception. In fact 802.16d (2004) has been defined in this work, but the equipment Manufacturers focus on doing an outdoor antenna 256OFDM TDMA fixed access systems. but will leave such a system to solve 802.16e, WiMax delay the development process.
802.16a / d of the media access control layer MAC layer required to support OFDM / OFDMA, supports automatic retransmission ARQ. do not permit the use of dynamic frequency band can select (DFS). he could support additional advanced antenna systems, Advanced Antenna System (AAS) in order to provide higher performance, you can also support network Mesh Mode-like model to work to provide customers TDD direct communication between the client. This approach can only work in non-license band.
802.16d the smaller the cell radius, can provide higher capacity. in the outdoor nomad state, cellular radius of 2.5 km, each cell capacity can reach 4.31 bit / sec / Hz. bandwidth of 5 MHz, in order to 21.5 Mbit / s, is the WCDMA several times. through the use of multi-antenna MIMO space-time processing can further improve the rate of several times.
3 3G high-speed packet data services development efforts
3GPP and 3GPP2 are aware of their current systems used to provide limited Internet access business to try, within the framework of the original system, the first downlink packet access technology used, a substantial increase download and streaming IP data rate.
3GPP R5 after the system was introduced in HSDPA standards, and the introduction of HSUPA R6 standard. HSDPA using the 802.16d / e similar to the three technologies: adaptive modulation and coding (AMC), fast hybrid automatic retransmission (HARQ) and fast scheduling time division multiple access, to improve the downlink data rate of data to meet the requirements of packet data burst.
fast scheduling shared multi-user multiplexing downlink (uplink) high-speed shared data channel HS-PDSCH. every 2 ms using a short time frame scheduling the channel resources allocated to multiple users, type of packet data burst to adapt to provide high average throughput.
with 802.16d / e in the use of OFDMA different, HSDPA uses code division multiplexing, code division multiplexing by multiple sub-channel multiplexed together to form the downlink data channel. HS-DSCH sub-channel frame length is 2 ms , contains three time slots. subchannel will be mapped to HS-DSCH physical channel spread spectrum techniques used, expand the spectrum using a fixed number of SF = 16 are the physical sub-channel HS-PDSCH.15 a spread-spectrum sub-channel HS-PDSCH physical Through a combination of code division multiplexing constitute the total HS-DSCH. In this way, client station code division and time division based shared channel in two ways. HSDPA and 802.16d / e in the shared packet data channel is the same principle, are In the sub-channel and time slot on the planning and scheduling. but 802.16d/ed subchannels to be able to offer more, and more flexible scheduling.
HSDPA also uses adaptive modulation and coding, once every 2ms channel quality measurement, According to the channel quality index (CQI), decided to adopt the modulation and coding methods. using different parameters, and QAM modulation QPSK. using a physical sub-channel QPSK modulation transfer rate of 480 kbit / s, using 64QAM modulation to 1440 kbit / s, increased threefold. and above 15 HS-PDSCH physical channel code division multiplexing rate equal to 15 times increase. Taken together, the increase rate of 45 times. This is just a rough estimate, explain why within the framework of the WCDMA, the use of fast scheduling and adaptive modulation and coding rate to provide the number of times. reach the 802.11d / e standard can be compared.
HSDPA Another key technique used is a fast hybrid automatic retransmission (HARQ). The main principle is : receiver in the case of decoding failure, save the received data and request retransmission of the data sender, the receiver will be retransmitted data and the data previously received before the decoding combinations. hybrid automatic retransmission technology can improve system performance, and flexibility to adjust the effective symbol rate, you can compensate for link adaptation brought about by error. In WCDMA R5 after the introduction of HSDPA technology, UTRAN part of the structure of essentially the same, by the Node B increase the card, added a MAC-hs block, and in the physical layer added three new physical channel: 15 high-speed physical downlink shared channel, a high-speed shared control channel and a group of high-speed dedicated physical control channel uplink .
HSDPA Another improvement is to move the scheduling base station by the base station controller, which can reduce the delay. Currently, 3GPP organization such as MIMO and higher order modulation technology in further research, hoping to further improve the downlink link data rate. HSDPA typical rate of actual use: macrocell is 1 ~ 1.5 Mbit / s, micro cellular 4 ~ 6 Mbit / s, slightly cellular> 8 Mbit / s.
will be in 3GPP R6 the introduction of HSUPA uplink packet to solve problems and improve upstream. and then further to the introduction of adaptive beamforming and MIMO antenna array processing techniques such as downlink peak rate will be increased to 30 Mbit / s or so.
HSDPA and HSUPA is called medium-term evolution of 3.5G technology is technology, greater restraint by the original system. performance is not ideal .3 GPP found in the deployment of HSDPA and the ITU have a gap between B3G, this is the goal of WiMax. In a period of time, in broadband wireless access market, competition will be at a disadvantage with WiMax. To improve the 3G broadband wireless access in the emerging competitive market, get rid of Qualcom's CDMA patent constraints, need to develop long-term evolution technology LTE (long term evolution), to fill this a gap. The basic idea is to use the past for the development of B3G or 4G technology to the development of LTE, using the 3G spectrum for broadband wireless access market share in December 2004 when Athens was decided 3GPP 3GPP RAN working group responsible for carrying out long-term evolution LTE radio interface of .2006 June completed in June 2007 LTE standard release. participate in the work, including 200 members of the 3GPP.
LTE radio will select a new air interface standards (OFDMA loud voice), the use of bandwidth from 1.25MHz to 20MHz, speed downlink capacity of 100 Mbit / s, upstream 50 Mbit / s.LTE will also develop a new network structure. Prior to the evolution of 3GPP is in the original programs, including HSPDA RAN and core network based on the gradual evolution of more restricted . LTE will be in the original 3G radio access network, the establishment of a new all-IP radio access network (RAN), and pure IP convergence with the fixed core network. to meet the needs of broadband wireless access. This move Communications will no longer be a system, but only to provide broadband mobile wireless access. truly converged fixed and mobile networks. Currently LTE working group is in full swing starting from the fully operational needs. As opinion within the 3GPP, and is not completely unified, do not want to let go of the original system from scratch is still very powerful forces that can achieve booking goals are still some problems.
LTE in our country and the corresponding program is called plan and B3G E3G.863 FUTURE plans are considered the corresponding for the development of E3G, in LTE development work. in 3GPP2 is being called the implementation of air interface similar to the evolution of AIE (air interface evolution) evolution program.
4 future broadband wireless access market, the competitive situation
WiMax is intended for broadband wireless access market, 3G mobile communication is intended for cellular phone-based mobile communication system, generally speaking, is a complementary relationship between them. But when the 3GPP for the development of broadband wireless access market HSDPA, particularly after the emergence of LTE development of competition. From the above analysis we can see the face of WiMax and 3GPP LTE is the same market, the indicators are similar, the use of technology is similar can be said the same thing. < br> 3GPP LTE is a decision to develop a strategic decision for the future development of its far-reaching impact. Although LTE's ability to shake off the shackles of the original architecture, there are problems, but its members are the mainstream of current 3G operators , the force and frequency of use of a 3G license, even if the performance of their LTE development, worse, in the broadband wireless access market still has a strong competitive edge. and once they have LTE will no longer consider the use of WiMax and other competitive technology. In addition, LTE frequency of use of 3G, or even use the 2G frequency, better penetration, higher cost performance support system.
WiMax by the IT industry of broadband wireless access technology, in the absence of the original system of constraints, most broadband access market. Since the emergence of LTE, operators may use WIMax main fixed network operators and new operators to enter the competition. Intel and other IT equipment manufacturers the firm is WiMax, a strong supporter of, they want to enter through the WiMax broadband wireless access market. Intel to bundle in the future WiMax notebook promises enhanced the competitiveness of WiMax.
WiMax development of today's major problems plagued is the frequency of the problem. is already accepted is 3.4 ~ 3.8 GHz frequency license, and 5.725 ~ 5.85 GHz frequency license-free frequency. Many countries allow the use of higher frequencies, its license-exempt 5 GHz band as part of the purpose of for outdoor applications. because of their poor penetrating power, the use of these frequencies WiMax and LTE system can not compete. awaiting approval is 2.3 ~ 2.7 GHz frequency license, only South Korea will be 2.3 ~ 2.4 GHz frequency allocated to WiMax. International the main focus for 2.5 ~ 2.6 GHz frequency. these frequencies are still high, compared with the performance of 3G mobile communication frequencies less.
WiMax broadband wireless access to the development of the best and may choose to use television broadcast band (UHF .) penetration of the UHF channels can achieve a large area of good coverage, easy to reduce costs and improve competitiveness. many parts of the world began the fight for distribution of <1 GHz frequency bands for broadband wireless access efforts. in the United States is +-free license to use license for the band. has been sold to the channel 54,55,59 (710 ~ 722 MHz, 740 ~ 746 MHz), lower frequency of future auctions Channel (698 ~ 746 MHz) or higher frequency Channels (747 ~ 794 MHz). In China Radio Management Committee has 798 ~ 862 MHz frequency from SARFT to directly manage their own hands to recover.
consultations in the United States is lower than the 700 MHz license-free use of empty TV channels. U.S. FCC must make sense to use these radio frequencies to avoid interference. this IEEE established the IEEE 802.22 wireless local area network aware (WRAN) Standards Working Group (November 2004). Its purpose is the development of air interface (MAC and PHY ) in various geographical regions to provide broadband wireless access, including sparsely populated rural areas, with the interference protection mechanisms for users to use as a secondary TV 54 ~ 862 MHz frequency band. WiMax so one more competitor. as this, IEEE 802.16 Working Group has set up a IEEE802.16h, dedicated to improving media access control, such as strategies and other mechanisms to ensure enhanced IEEE 802.16-based license-free coexistence between systems, as well as a major user of the system coexistence between. IEEE 802.16h to WiMax to meet FCC requirements, as a secondary user with a blank terrestrial TV channels.
terrestrial TV frequency of use of blank WiMax systems will have excellent performance and extremely competitive. especially in rural and remote areas, will be to eliminate the Conclusion
nomadic and mobile broadband wireless access will become an important future market demand for communications. WiMax (802.16d / e) is dedicated to the development of this demand, performance, high efficiency and low cost. Through its flexible system configuration to meet the requirements of various application scenarios .3 G is based on the design of voice-based business needs, can not meet the demand for broadband wireless access. In order to enter the broadband wireless access market, 3GPP 3.5G development known as the HSPA (1xEV DO ) after the remains inadequate, in order to compete with WiMax plans 3GPP decided to develop long-term evolution of LTE, the indicators and with the WiMax technology is similar can be said the same thing. WiMax frequency allocation by the development of the constraints, can use the terrestrial television broadcast band on WiMax essential for the development.
(Author: Institute of Acoustics, Chinese Academy of Sciences Laboratory of High Performance Network)
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